Dissertations / Theses on the topic 'Heat source models'

Finite element models of friction welding can be used to estimate internal conditions of welds which are useful for weld analysis and developing experimental welding procedures. Many modeling techniques are used to accomplish these goals, each with relative strengths and weaknesses. A comparative analysis of friction welding models using different heat generation methods is presented. The three different heat generation methods examined were viscoplastic friction, constant steady-state generation, and experimentally measured power data. The models were compared against each other using three output measurements: temperature, axial force, and upset. The friction model predicted temperatures within 40 degrees C. Temperature accuracy improved at a higher upset rate and higher spindle speed, when weld samples heated up faster. The model was excellent at predicting upset, with accuracy within 1.5%. Maximum force was predicted within 9-18%. The constant heat generation model typically predicted temperatures within 30 degrees C. Upset was estimated within 7%. Maximum force was predicted within 12% at high feed rates, but accuracy dropped to 28% when feed rate was reduced. The motor power model was the most accurate model at estimating temperature, with a typical accuracy within 25 degrees C. Axial upset was predicted within 5%. Maximum force was predicted within 1-8%, with greater accuracy occurring at higher feed rates.

Fire spread between objects within a compartment is primarily due to the impingement of thermal radiation from the fire source. In order to estimate if or when a remote object from the fire will ignite, one must be able to quantify the radiative heat flux being received by the target. There are a variety of methods presented in the literature that attempt to calculate the thermal radiation to a target; each one based on assumptions about the fire. The performance of six of these methods, of varying complexity, is investigated in this research. This includes the common point source model, three different cylindrical models, a basic correlation and a planar model. In order to determine the performance of each method, the predictions made by the models were compared with actual measurements of radiant heat flux. This involved taking heat flux readings at numerous locations surrounding a propane gas burner. Different fire scenarios were represented by varying the burner geometry and heat release rate. Video recordings of the experiments were used to determine the mean flame heights using video image analysis software. After comparing the measured data with predictions made by the theoretical radiation methods, the point source model was found to be the best performing method on average. This was unexpected given the relative simplicity of the model in comparison to some of its counterparts. Additionally, the point source model proved to be the most robust of the six methods investigated, being least affected by the experimental variables. The Dayan and Tien method, one of the cylindrical models, was the second most accurate over the range of conditions tested in this work. Based on these findings, recommendations are made as to the most appropriate method for use in a radiation sub-model within an existing zone model software. The accuracy shown by the point source model, coupled with its ease of implementation, means that it should be suitable for such a use.

Laser welding is an advanced joining technique with the capability to form deep, narrow, and precise welds. Numerical models are used to simulate the process in attempts of predicting distortions and stresses in the material. This is done to reduce physical testing, optimize processes and enable integrated product- and process development. The Virtual Manufacturing Process research group at University of Skövde wishes to increase their knowledge on modeling options of thermomechanical simulations to grant local industries these benefits. A numerical model for the laser welding process was developed in ABAQUS. This was done by examining the macrograph structure of a simple weld and applied to a stainless-steel T-joint welding application. The macrograph data was used to calibrate a mathematical heat source model. User subroutine DFLUX was used to enable movement of the heat source and element activation was used to simulate the fusion of the two parts. A T-joint welding experiment was carried out to measure deflection and the result was compared to numerical simulations. Different combinations of heat source models, coupling type and element activation was compared in relation to predicting the deflection. Computational time and modeling complexity for the techniques was also considered.The results showed that a 3D Gaussian heat source model will imitate the keyhole weld achieved superior to the compared 2D model. The 3D model provides greater flexibility since it enables combinations of any geometrical bodies. It was shown that element activation has a significant contribution on part stiffness and thus resulting distortions. To implement element activation a fully coupled analysis is required. The deflection of the fully coupled 3D simulation with element activation showed a 9% deviance in deflection compared with experiments.

The purpose of a heat pump is to control the temperature of an enclosed space. This is done by using heat exchange with a heat source, for example water, air, or ground. In the air source heat pump that has been studied during this master thesis, a refrigerant exchanges heat with the outdoor air and with a water distribution system. The heat pump is controlled through the circuit containing the refrigerant and it is therefore crucial that this circuit is functional. To ensure this, a diagnosis system has been created, to be able to detect and isolate sensor errors. The diagnosis system is based on mathematical models of the refrigerant circuit with its main components: a compressor, an expansion valve, a plate heat exchanger, an air heat exchanger, and a four-way valve. Data has been collected from temperature- and pressure sensors on an air source heat pump. The data has then been divided into data for model estimation and data for model validation. The models are used to create test quantities, which in turn are used by a diagnosis algorithm to determine whether an error has occurred or not. There are nine temperature sensors and two pressure sensors on the studied air source heat pump. Four fault modes have been investigated for each sensor: Stuck, Offset, Short circuit and Open circuit. The designed diagnosis system is able to detect all of the investigated error modes and isolate 40 out of 44 single errors. However, there is room for improvement by constructing more test quantities to detect errors and decouple more fault modes. To further develop the diagnosis system, the existing models can be improved and new models can be created.

Building heating is one of the most important sources of energy consumption. GroundSource Heat Pumps (GSHP) are efficient heating systems, particularly popular in the Nordiccountries. However, the GSHPs available for the consumer market today typically only utilizebasic control schemes that are relatively inflexible. More advanced strategies such as ModelPredictive Control (MPC) appear as a promising approach to improve comfort while reducingconsumption. The present thesis considers a typical user case of a single family house heatedby a ground source heat pump willing to reduce its environmental impact. We design a MPCcontroller to be used on top of the existing heat pump system and with almost no additionalhardware needed. Specific attention is dedicated to the system’s efficiency in order to reflectthe real working performances of a ground source heat pump. The controller is evaluated insimulation on different scenarios using an identified model of a single family house. The resultsshow the MPC strategy becomes most beneficial when including time varying prices or reducedcomfort during certain hours of the day. When both are conjugated the economic savings areup to 8% despite the loss of efficiency of the heat pump. The controller was implemented andtested on a real system with promising results.
Uppvärmning av byggnader är en av samhällets största energiförbrukare. I Norden användsofta bergvärmepumpar som ett effektivt alternativ för uppvärmning. De flesta bergvärmepumparstyrs av väldigt enkla algoritmer. Model Predictive Control (MPC) är en lovande metodför att ta hänsyn till både inomhustemperatur och energiförbrukning, speciellt om man hartillgång till en väderprognos. Denna rapport studerar hur ett typiskt enfamiljshus kan minskasin energiåtgång och miljöpåverkan. Ansatsen är att lägga till ett yttre reglersystem till bergvärmepumpen.Speciell vikt läggs vid modellering av bergvärmepumpens effektivitet. Olikascenarion jämförs, bland annat att ta hänsyn till elprisets variation över dygnet med hjälpav ekonomisk MPC. Simuleringar visar att användning av MPC är mest fördelaktig i det fallbåde elpriset och krav på innetemperatur varierar över dygnet. I sådana fall kan energikostnadenminska med upp till 8%, trots att bergvärmepumpen stundtals arbetar i ett ogynnsamtdriftläge. Ett verkligt system har använts för systemidentifiering och experiment med en MPCregulator.

Electro-Magnetic Source Imaging (EMSI) is the estimation of the position, orientation and strength of active electrical sources within the brain from electrical and magnetic measurements. For an accurate source localization, the head model must correctly represent the electrical and geometrical properties of the head. To solve the forward problem using realistic head models numerical techniques must be used. This work uses the Boundary Element Method (BEM) for solving the forward problem. The accuracy of the existing BEM formulation is improved by using second order elements, recursive integration and the isolated problem approach (IPA). Two new formulations are developed to improve the solution speed by computing transfer matrices for EEG and MEG solutions. The IPA formulation is generalized and integrated into the accelerated BEM algorithm. Once the transfer matrices are computed, the forward solutions take about 300 ms for a 256 sensor EEG and MEG system. The head model used in the BEM solutions is constructed by segmenting three dimensional multimodal magnetic resonance images. For segmentation, a semi-automatic hybrid algorithm is developed that makes use of snakes, morphological operations, thresholding and region growing. The mesh generation algorithm allows intersecting tissue compartments. For the inverse problem solution genetic algorithm (GA) is used to search for a given number of dipoles. Source localization with simulated data show that the localization error is within 1.1 mm for EEG and 1.2 mm for MEG when SNR is 10 on a realistic model with 7 compartments. When a single-dipole source in a realistic model is explored using a best-fit spherical model, the localization errors increase up to 8.5 mm for EEG and 7 mm for MEG. Similar tests are also performed with multiple dipoles. It was observed that realistic models provide definitely more accurate results compared to spherical models. The EMSI approach is also tested using experimental EEG data to localize the sources of auditory evoked potentials. The reconstructed source locations are correctly found in the Heschl'
s gyrus. In conclusion, this thesis presents a complete source localization framework for future brain research using the EMSI.

With global warming on the rise and the urge for conserving our natural resources, it becomes very important that proper steps are taken to protect our natural resources and utilize them efficiently. Forest fires are one of the many issues on the charts towards protection of natural resources. The catastrophic aftermaths caused by forest fires are known to all. The causes for these fires could be known/unknown natural causes or human intervention. Remote sensing techniques use the electromagnetic radiation in the RF/Microwave region, emitted from an object. The amount of energy emitted from an object depends on its present conditions, primarily its temperature and its emissivity. The sensing devices used in such measurements are classified into active and passive sensors. Herein, passive radiometry is used to investigate a model for the propagation of subsurface radiation from underground forest fires through upper ground layers of soil till the land-air interface. Passive radiometry involves capturing the radiation incident on a radiometer antenna aperture directly or deflected from several objects. The energy emitted from sources above 0K is collected and is compared with the calibration standards to estimate the physical quantity under test. Detecting forest fires is one of the potential applications of passive radiometry investigated here.

The thesis has been conducted at Bosch Thermoteknik AB and its aim is to develop a Model Predictive Control (MPC) controller for a ground source heat pump which minimizes the power consumption while being able to keep the inside air temperature and Domestic Hot Water (DHW) temperature within certain comfortintervals. First a model of the system is derived, since the system consists of both continuous and binary states a hybrid model is used. The MPC controller utilizes the model to predict the future states of the system, and by formulating an optimizationproblem an optimal control is achieved. The MPC controller is evaluated and compared to a conventional controller using simulations. After some tuning the MPC controller is capable of maintaining the inside air and DHW temperature at their reference levels without oscillating too much. The MPC controller’s general performance is quite similar to the conventional controller, but with a power consumption which is 1-3 % lower. A simulation using an inside air temperature reference which is lowered during the night is also conducted, it achieved a power consumption which was 7.5 % lower compared to a conventional controller.

The transient temperature fields induced by welding processes largely determine the size of the fusion and heat-affected zones, the microstructures, residual stresses and distortion both in the vicinity of the weld and in the final component as a whole. An accurate prediction of these fields relies heavily on the representation of the welding heat source, both in space and in time. The double-ellipsoidal heat source model proposed by Goldak and co-workers has been widely used to simulate the heat transferred from an electric arc to a component and to compute the induced transient temperature fields. This double-ellipsoidal distribution has worked well for many welding applications, but it is less appropriate when representing the heat transfer at the base of a groove whose width is narrow in relation to its depth. Similarly the conical heat source models used to represent the electron beam welding process, when applied in keyhole mode, are less appropriate when the keyhole terminates within the component, such as in the case of a partial penetration weld. In this work, the double-ellipsoidal heat source model is extended, and alternatives presented, to account for a wider set of welding scenarios, including narrow weld groove geometries and keyhole welding scenarios. A series of mathematically robust novel heat source models is presented and the models are validated against experimental data obtained during the application of various welding processes to an important grade of pressure vessel steel, namely SA508 Grade 3 class 1 steel. The calculation of the transient temperature fields during welding is extremely computationally expensive using numerical methods. Where available, and appropriate, analytical solutions are presented for these novel welding heat source models, coupled with analytical methods for accounting for time dependent heat input rates, to not only reduce computational cost but also to achieve precise predictions of the temperature fields. This, in turn, has the potential to contribute to improvements in safety assessments on critical welded infrastructure through improved predictions for the evolution of microstructure, mechanical properties and the levels of residual stress and distortion in welded joints.

Friction stir welding (FSW) has been studied extensively for the past two decades. Thermal modeling has been of particular interest, as the quality of the weld is dependent upon the temperature history of the work piece during the process. Since direct temperature measurements of the welded zone are not possible, an analytical model was developed to predict the temperature in this area. This model requires parameters that cannot be easily experimentally determined, so a best fit for these parameters was acquired via regression analysis by comparing the model to experimental data acquired outside of the weld zone. The model was then validated by comparing it to additional temperature data, not including the data used for regression analysis.

Energy demand for the twenty first century is expected to increase many fold along with corresponding diversification of energy sources and generation methods. Of the many energy sources available, use of Ground Source Heat Pump (GSHP) system is the focus of the analysis in this research. This work is carried out to identify the key parameters which affect the performance of the GSHP system. A mathematical model has been developed to understand the complex operation of the heat pump under typical working conditions. Individual sub-systems, such as Ground Heat Exchanger (GHE), evaporator, condenser, compressor and radiator are modelled in MathCAD and coupled together and solved simultaneously. The performance of the system is predicted while varying air temperature, power input to the compressor and the ground temperature beneath the earth's surface. In addition a special sub-model was developed for the single vertical U-tube GHE in FLUENT, a Computational Fluid Dynamics (CFD) software, to calculate the overall heat transfer coefficient for varying outer surface temperature of the borehole. The overall system results are validated against the published results with the system operating range of 18°C to 33°C with around 10 percent deviations. It is determined that the COP of the system increases with surface area and overall heat transfer coefficient (OHTC) of the heat exchanger. An increase in up to 500 m2 surface area, steep raise of COP from 10.05 to 10.3 is observed. Similarly increase of 10 W/m2K of OHTC has steep COP rise from 10.05 to 10.28. The temperature gradient across the system also has influence on its operating performance, where a 15°C increase in the ground temperature for cooling mode reduces the COP by around 5%. Finally the degree of refrigerant sub-cooling has a positive effect, for every 5°C temperature drop the COP improves by 0.5 similarly for degree of super-heating, COP improves by 0.25. Scope for performance enhancement for GSHP is investigated by tuning operating conditions. The effect of operating variables to the sensitivity of performance of heat pump is also determined.

Thermal diffusivity in an important thermophysical property that quantifies the ratio of the rate at which heat is conducted through a material to the amount of energy stored in a material. The pulsed laser diffusion (PLD) method is a widely used technique for measuring thermal diffusivities of materials. This technique is based on the fact that the diffusivity of a sample may be inferred from measurement of the time-dependent temperature profile at a point on the surface of a sample that has been exposed to a pulse of radiant energy from a laser or flash lamp. An accepted standard approach for the PLD method is based on a simple model of a PLD measurement system. However, the standard approach is based on idealizations that are difficult to achieve in practice. Therefore, models that treat a PLD measurement system with greater fidelity are desired. The objective of this research is to develop and test a higher fidelity model that more accurately represents the spatial and temporal variations in the input power. This higher fidelity model is referred to as Distributed Source Finite Absorption (DSFA) model. The cost of the increased fidelity associated with the DSFA model is an increase in the complexity of inferring values of the thermal diffusivity. A new method of extracting values from time dependent temperature measurements based on a genetic algorithm and on reduced order modeling was developed. The primary contribution of this thesis is a detailed discussion of the development and numerical verification of this proposed new method for measuring the thermal diffusivity of various materials. Verification of the proposed new method was conducted using numerical experiments. A detailed model of a PLD system was created using advanced engineering software, and detailed simulations, including conjugate heat transfer and solution of the full Navier-Stokes equations, were used to generate multiple numerical data sets. These numerical data sets were then used to infer the thermal diffusivity and other properties of the sample using the proposed new method. These numerical data sets were also used as inputs to the standard approach. The results of this verification study show that the proposed new method is able to infer the thermal diffusivity of samples to within 4.93%, the absorption coefficient to within 10.57 % and the heat capacity of the samples to within 5.37 %. Application of the standard approach to these same data sets gave much poorer estimates of the thermal diffusivity, particularly when the absorption coefficient of the material was relatively low.

Heat transfer systems contain many sources of nonlinearity including temperature dependent material properties, radiation boundary conditions, and internal source terms. Despite progress in numerical simulations, producing accurate models that can predict these complex behaviors are still encumbered by lengthy processing times. Accurate models can be produced quickly by utilizing projection Reduced Order Modeling (ROM) techniques. For discretized systems, the Singular Value Decomposition technique is the preferred approach but has had limited success on treating nonlinearities. In this research, the treatment of nonlinear temperature dependent material properties was incorporated into a ROM. Additional sources of nonlinearities such as radiation boundary conditions, temperature dependent source heating terms, and complex geometry were also integrated. From the results, low conductivity, highly nonlinear material properties were predicted by the ROM within 1% of full order models, and additional nonlinearities were predicted within 8%. A study was then done to identify initial snapshots for use in developing a ROM that can accurately predict results across a wide range of inputs. From this, a step function was identified as being the most accurate and computationally efficient. The ROM was further investigated by a discretization study to assess computational gains in both 1D and 3D models as a function of mesh density. The lower mesh densities in the 1D and 3D ROMs resulted in moderate computational times (up to 40 times faster). However, highly discretized systems such as 5000 nodes in 1D and 125000 nodes in 3D resulted in computational gains on the order of 2000 to 3000 times faster than the full order model.
Ph. D.

[ES] La energía geotérmica de baja entalpía es una alternativa eficiente y renovable a los sistemas convencionales para proporcionar calefacción, refrigeración y producir agua caliente sanitaria (ACS) de forma sostenible. El proyecto GEOTeCH plantea el desarrollo de sistemas con bomba de calor geotérmica más eficientes y con un coste menor en comparación con el mercado. Para ello, se ha desarrollado un nuevo tipo de intercambiador enterrado coaxial con flujo helicoidal en el tubo externo que presenta una mayor eficiencia y permite reducir la longitud de intercambiador a instalar, así como una bomba de calor dual con compresor de velocidad variable, capaz de trabajar con el terreno o el aire como fuente/sumidero, seleccionando la que proporcione un mejor rendimiento del sistema. El principal objetivo es desarrollar un sistema eficiente y replicable para proporcionar calefacción, refrigeración y producir ACS en el sector de mercado de pequeños edificios con un tamaño menor en el campo de intercambiadores enterrados y un aumento de la eficiencia. Para demostrar la aplicabilidad de estos sistemas, se han construido tres instalaciones demostración en tres países europeos. En esta tesis doctoral se ha desarrollado un modelo dinámico completo del sistema en el software TRNSYS, capaz de reproducir el comportamiento de los diferentes componentes y del sistema en general. Este modelo constituye una herramienta útil para el desarrollo y análisis de diferentes estrategias de control sin la necesidad de implementarlas en instalaciones reales, así como analizar el comportamiento del sistema funcionando bajo condiciones diferentes. Para este propósito, es necesario desarrollar modelos detallados de los nuevos componentes desarrollados en el proyecto: el intercambiador enterrado coaxial helicoidal y la bomba de calor dual; para poder acoplarlos al resto de componentes en el modelo completo del sistema. Por ello, se ha desarrollado un modelo dinámico del nuevo intercambiador, capaz de reproducir con precisión el comportamiento a corto plazo del intercambiador, enfocado a la evolución de la temperatura del fluido, y se ha validado con datos experimentales en diferentes condiciones de operación. Para poder reproducir no solo el comportamiento dinámico del intercambiador enterrado, sino también la respuesta a largo plazo del terreno y la interacción entre intercambiadores en un campo, se ha desarrollado otro modelo en TRNSYS que realiza esta función. De esta manera, al acoplar ambos modelos es posible reproducir el comportamiento a corto plazo del intercambiador enterrado a la vez que la respuesta a largo plazo del terreno. Por otro lado, se ha implementado en TRNSYS un modelo de la bomba de calor dual desarrollado. Con este modelo es posible calcular la capacidad de la bomba de calor dependiendo del modo de operación en que esté funcionando, de la frecuencia del compresor y otras variables y condiciones de operación. El modelo del sistema dual en TRNSYS se ha utilizado para hacer un análisis de su comportamiento funcionando en diferentes climas, para ello se han seleccionado tres ciudades en España y en Europa con diferentes climas y se han realizado simulaciones del sistema funcionando en cada ciudad. Por otro lado, también se ha modelado en TRNSYS una de las instalaciones demostración del proyecto GEOTeCH, incluyendo el edificio climatizado y el acoplamiento con los fan coils. Con este modelo se estudia una nueva estrategia para controlar la frecuencia del compresor en base a la temperatura de las habitaciones, en lugar de controlarla en base a la temperatura de suministro, con el objetivo de reducir el consumo del compresor cuando ya se haya conseguido el confort. Además, otras estrategias de optimización se han analizado con el modelo.Por tanto, los modelos desarrollados constituyen herramientas útiles para ayudar en el diseño del sistema y los diferentes componentes, el análisis de su comportamiento y el d
[CAT] L'energia geotèrmica de baixa entalpia es planteja com una alternativa eficient i renovable als sistemes convencionals per proporcionar calefacció, refrigeració i produir aigua calenta sanitària (ACS) de forma sostenible. El projecte GEOTeCH planteja el desenvolupament de sistemes amb bomba de calor geotèrmica més eficients i amb un cost menor en comparació amb el mercat. Per a això, s'ha desenvolupat un nou tipus d'intercanviador enterrat coaxial amb flux helicoïdal en el tub extern que presenta una major eficiència i permet reduir la longitud a instal·lar, així com una bomba de calor dual amb compressor de velocitat variable, capaç de treballar amb el terreny o l'aire com a font, seleccionant la que proporcione un millor rendiment. Aquests components s'utilitzen en el nou sistema amb bomba de calor dual. El principal objectiu és desenvolupar un sistema eficient i replicable per proporcionar calefacció, refrigeració i produir ACS en edificis xicotets amb una grandària menor d'intercanviadors soterrats i un augment de l'eficiència. Per demostrar l'aplicabilitat d'aquests sistemes, s'han construït tres instal·lacions demostració en Itàlia, Països Baixos i Regne Unit. En aquesta tesi s'ha desenvolupat un model dinàmic complet del sistema en TRNSYS, capaç de reproduir el comportament dels components i del sistema en general. Aquest model constitueix una eina útil per al desenvolupament i anàlisi de diferents estratègies de control sense la necessitat d'implementar-les en instal·lacions reals, així com analitzar el comportament del sistema funcionant en condicions diferents. Per a això, cal desenvolupar models detallats dels nous components desenvolupats en el projecte: l'intercanviador enterrat i la bomba de calor dual; per poder acoblar-los a la resta de components. Per això, s'ha desenvolupat un model dinàmic del nou intercanviador enterrat, capaç de reproduir amb precisió el comportament a curt termini de l'intercanviador, enfocat a l'evolució de la temperatura del fluid, i s'ha validat amb dades experimentals en diferents condicions d'operació. Per a poder reproduir no només el comportament dinàmic de l'intercanviador soterrat, sinó també la resposta a llarg termini del terreny i la interacció entre intercanviadors en un camp, s'ha desenvolupat un altre model en TRNSYS que realitza aquesta funció. D'aquesta manera, en acoblar els dos models és possible reproduir el comportament a curt termini de l'intercanviador enterrat, al mateix temps que la resposta a llarg termini del terreny. D'altra banda, s'ha implementat en TRNSYS un model de la bomba de calor. Amb aquest model és possible calcular la capacitat de la bomba de calor depenent del mode d'operació en què estiga funcionant, de la freqüència del compressor i altres variables i condicions d'operació. El model del sistema dual en TRNSYS s'ha utilitzat per a fer una anàlisi del seu comportament funcionant en diferents climes, per a això s'han seleccionat tres ciutats a Espanya i tres a Europa amb diferents climes i s'han realitzat simulacions del sistema funcionant en cada ciutat durant un any. S'ha analitzat l'eficiència del sistema en cada ciutat, així com l'ús de cadascuna de les fonts (aire / terreny). D'altra banda, també s'ha modelat en TRNSYS una de les instal·lacions demostració del projecte GEOTeCH, incloent l'edifici d'oficines climatitzat i l'acoblament amb els fan coils. Amb aquest model es pretén estudiar una nova estratègia per a controlar la freqüència del compressor d'acord amb la temperatura de les habitacions, en lloc de controlar-la en base a la temperatura de subministrament, amb l'objectiu de reduir el consum del compressor quan les habitacions ja es troben en condicions de confort. A més, altres estratègies d'optimització s'han analitzat amb el model. Per tant, els models desenvolupats constitueixen eines útils per ajudar en el disseny del sistema i els diferents components, l'anàlisi del
[EN] Low enthalpy geothermal energy is considered as an efficient and renewable alternative to conventional systems to provide heating, cooling and Domestic Hot Water (DHW) production in a sustainable way. In this context, the GEOTeCH project proposes the development of more efficient geothermal heat pump systems with a lower cost compared to the market. To this end, a new type of coaxial Borehole Heat Exchanger (BHE) with helical flow through the outer tube has been developed, which presents a higher efficiency and allows to reduce the length of the heat exchanger to be installed, as well as a Dual Source Heat Pump (DSHP) with variable speed compressor, capable of working with the ground or air as a source / sink, selecting the one that provides the best performance of the system. These components are used in the new DSHP system developed. The main objective is to develop efficient and replicable systems to provide heating, cooling and DHW in the market sector of small buildings with a smaller size of the BHE field and an increase in the efficiency. To demonstrate the applicability of these systems, three demonstration facilities have been installed in Italy, the Netherlands and the UK. In this thesis, a complete dynamic model of the system has been developed in the TRNSYS software, capable of reproducing the behavior of the different components and the system in general. This model is a useful tool for the development and analysis of different control strategies without the need to implement them in real installations, as well as analyses the behavior of the system operating under different conditions. For this purpose, it is necessary to develop detailed models of the new components developed in the project: the BHE and the DSHP; to couple them to the rest of the components of the system. For this reason, a dynamic model of the new BHE was developed, able to accurately reproduce its short-term behavior, focused on the evolution of the fluid temperature, and validated with experimental data in different operating conditions. In order to reproduce not only the dynamic behavior of the BHE, but also the long-term response of the ground and the interaction between BHEs in a field, another model was developed in TRNSYS. In this way, by coupling both models, it is possible to reproduce the short-term behavior of the BHE as well as the long-term response of the ground. On the other hand, a model of the DSHP was implemented in TRNSYS. With this model, it is possible to calculate the capacity of the heat pump depending on the operating mode in which it is operating, the frequency of the compressor and other variables and operating conditions. The model of the hybrid system in TRNSYS has been used to make an analysis of its behavior working in different climatic conditions, for which three cities have been selected in Spain and three in Europe, with different climates. So, different simulations of the system have been carried out in each city for one year. The efficiency of the system in each city has been analyzed, as well as the use of each of the sources (air / ground). On the other hand, one of the demo-sites of the GEOTeCH project, including the conditioned office building and the coupling with the fan coils, has also been modelled in TRNSYS. With this model, it is studied a new strategy to control the frequency of the compressor based on the temperature of the rooms, instead of controlling it based on the supply temperature, with the aim of reducing the consumption of the compressor when the rooms are already in comfort conditions. In addition, other optimization strategies have been analyzed with the model. Therefore, the models developed, both for the BHE and the system, are able to reproduce their operation and can be used as virtual installations, constituting useful tools to help in the design of the system and the different components, the analysis of their behavior and the development of optimization strategies.
I would like to acknowledge the financial support that has made this PhD thesis possible. The present work has been supported by the European Community Horizon 2020 Program for European Research and Technological Development (2014-2020) inside the framework of the project 656889 – GEOTeCH (Geothermal Technology for Economic Cooling and Heating), also by the Generalitat Valenciana inside the program “Ayudas para la contratación de personal investigador en formación de carácter predoctoral (ACIF/2016/131)” and by the Institute for Energy Engineering of the Universitat Politècnica de València.
Cazorla Marín, A. (2019). MODELLING AND EXPERIMENTAL VALIDATION OF AN INNOVATIVE COAXIAL HELICAL BOREHOLE HEAT EXCHANGER FOR A DUAL SOURCE HEAT PUMP SYSTEM [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/125696
TESIS

Ground Source Heat Pumps (GHSPs) is a relevant application and around 3 million installations are setting up at the beginning of 2010 (IEA ECES Annex 21). The improvements in GSHPs are currently focused on the optimization of the system and the reduction of costs installations. The thermal conductivity of the ground and thermal resistance of the Borehole Heat Exchanger (BHE) are important design parameters for Borehole Thermal Energy Storage (BTES) systems. The Thermal Response Test (TRT), which has been used up to now in the GHE design, only allows estimating mean values for thermal conductivity of the surrounding ground and borehole resistance. However, the ground thermal conductivity and borehole thermal resistance may present local variation along the borehole depth. For improving conventional TRT, the optical fiber technology is applied to collect information about the temperature profiles in the borehole. Thermal Response Test (TRT) logs the inlet and outlet fluid temperatures; meanwhile, the Distributed Thermal Response Test (DTRT) carries out a profile of the temperature along the borehole depth, in this case with fiber optic cables. This Master of Science Thesis focuses on the comparison and analysis of DTRT measurements in a U-pipe borehole in order to estimate the thermal conductivity and the borehole thermal resistance along the borehole. The comparison and the analysis are carried out by: •Comparing the differences of TRT results depending on the heat power rate considered – constant and by steps-. •Comparing the results from two different resolution Distributed Test Sensing (DTS) equipments: Halo and Sentinel DTS. •Comparing the differences of TRT results as depending on the analytical procedure based on the line source theory: line source model and line source approximation.

Sudden cardiac death following cardiac arrest is a major killer in the industrialised world. The leading cause of sudden cardiac death are disturbances in the normal electrical activation of cardiac tissue, known as cardiac arrhythmia, which severely compromise the ability of the heart to fulfill the body's demand of oxygen. Ventricular fibrillation (VF) is the most deadly form of cardiac arrhythmia. Furthermore, electrical defibrillation through the application of strong electric shocks to the heart is the only effective therapy against VF. Over the past decades, a large body of research has dealt with the study of the mechanisms underpinning the success or failure of defibrillation shocks. The main mechanism of shock failure involves shocks terminating VF but leaving the appropriate electrical substrate for new VF episodes to rapidly follow (i.e. shock-induced arrhythmogenesis). A large number of models have been developed for the in silico study of shock-induced arrhythmogenesis, ranging from single cell models to three-dimensional ventricular models of small mammalian species. However, no extrapolation of the results obtained in the aforementioned studies has been done in human models of ventricular electrophysiology. The main reason is the large computational requirements associated with the solution of the bidomain equations of cardiac electrophysiology over large anatomically-accurate geometrical models including representation of fibre orientation and transmembrane kinetics. In this Thesis we develop simulation technology for the study of cardiac defibrillation in the human heart in the framework of the open source simulation environment Chaste. The advances include the development of novel computational and numerical techniques for the solution of the bidomain equations in large-scale high performance computing resources. More specifically, we have considered the implementation of effective domain decomposition, the development of new numerical techniques for the reduction of communication in Chaste's finite element method (FEM) solver, and the development of mesh-independent preconditioners for the solution of the linear system arising from the FEM discretisation of the bidomain equations. The developments presented in this Thesis have brought Chaste to the level of performance and functionality required to perform bidomain simulations with large three-dimensional cardiac geometries made of tens of millions of nodes and including accurate representation of fibre orientation and membrane kinetics. This advances have enabled the in silico study of shock-induced arrhythmogenesis for the first time in the human heart, therefore bridging an important gap in the field of cardiac defibrillation research.

The Swedish government has set a target of a 100% renewable electricity system by 2040. To reach this goal, many actions have to be undertaken. Electrification of buildings is one action to be undertaken as the residential sector accounts for a large share of greenhouse gas emissions, where the most energy efficient method is to use heat pumps. Ground Source Heat Pumps typically have the highest efficiency out of the different heat pumps. These types of heat pumps are most commonly used in single family houses, as multi-family houses often are located in highly densely areas. However, when adding hybrid PV/thermal collectors to ground source heat pump systems, studies have shown that the borehole drilling area can be reduced, which increases the potential for combined PV/thermal collectors and ground source heat pump systems in multi-family areas.  In this project, a time-efficient, flexible and user- friendly model was developed to increase the potential for designing combined PV/thermal collectors and ground source heat pump systems. The model is based on the research model by Sommerfeldt and Madani (2019), where the flexibility and time step of the model was investigated and adjusted. The finished model was verified to the model by Sommerfelt and Madani (2019). Overall, the results show that the new model gives similar results to the original model, despite all adjustments. The heaviest adjustments were made in the heat pump where the quantitative results show a mean bias error of -0.51 kWh and a total yearly difference of -5.18% for the compressor power. The corresponding values for the condenser heating rate are -1.05 kWh and -2.86%. The user is able to change boundary conditions such as location, PVT array, building size, and borehole field size. The model takes approximately 2 minutes to run for a 20 years simulation on a business grade desktop computer, which is a five-hour twenty minute reduction from the original research model and assumed to be an acceptable time range for a commercial applications.
Regeringen har satt ett mål om att nå ett 100% förnybart energisystem till 2040. För att nå målet måste många insatser göras. Bostadssektorn står för höga halter av växthusgasutsläpp och elektrifiering av sektorn är en lovande väg att gå. Värmepumpar tillhör de mer energieffektiva tillvägagångssätten, av vilka bergvärmepumpar oftast erhåller den högsta effektiviteten. Bergvärmepumpar är idag mestadels installerat i enfamiljshus där det finns utrymme för att borra borrhål. Flerfamiljshus finns ofta i tätbebyggda områden där ytan tillgänglig för borrhål är begränsad. Emellertid har studier har visat att kombinerade PVT och bergvärmesystem kan minska borrhålsytorna, vilket ökar möjligheten för dessa typ av system även till flerfamiljshus.  Detta projekt syftar till att utveckla en kommersiell modell för design av PVT och bergvärmesystem för att underlätta design av dessa system. Att modellen är kommersiell antyder på att den är användarvänlig, flexibel och tidseffektiv. Modellen är baserad på en forskningsmodell av Sommerfeldt och Madani (2019) men justerades för att möta kraven för en kommersiell modell. Den färdiga modellen jämfördes och verifierades med modellen av Sommerfeldt och Madani (2019). Övergripande visades resultat som är jämförbara med forskningsmodellen, trots alla justeringar. De största justeringarna gjordes i värmepumpen där de kvantitativa resultaten visar ett mean bias error på -0.51 kWh och en årlig skillnad på -5.18% för elbehovet i kompressorn. Motsvarande värden för värmeutbytet i kondensorn är -1.05 kWh och -2.86%. Användaren har möjlighet att ändra gränsvillkor så som geografisk plats, PVT system, byggnadsstorlek och storleken på borrhålsfältet. Den färdiga modellen tar cirka två minuter att köra för en 20-års simulering på en typisk arbetsdator, vilket motsvarar en minskning på 5 timmar och 20 minuter jämfört med originalmodellen. Detta kan anses vara inom tidsramen för kommersiella appliceringar.

Predložen je i testiran model za energetsko vrednovanje kogenerativnih postrojenja pri čemu se proračun koeficijenta gubitka električne snage obavlja pomoću postupka koji je posebno naveden i predložen.Sam model može i treba da predstavlja snažan alat prilikom kreiranja energetske politike, u delu koji se odnosi na kogeneraciju, s obzirom na to da pruža mogućnost jasnog energetskog vrednovanja postrojenja u smislu efikasnosti i uštede primarne energije kao i definisanja koji deo i koliko kogeneracija treba da bude stimulisana, odnosno potencijalno zastupljena u okviru nekog energetskog sistema.Predloženi model je testiran na složenom kogenerativnom postrojenju snage 150 MW.
A model for energy evaluation of a cogeneration plant is proposedand tested with the calculation of electric power loss done by meansof a procedure which is particularly specified and proposed.The model itself can and should be used as a powerful tool for thecreation of energy policies in the part regarding cogeneration since itgives opportunities for a clear energy evaluation of a plant in terms ofefficiency and primary energy saving, as well as for defining whichpart and to what extent cogeneration should be stimulated, that is,potentially represented within a specified energy system.The proposed model has been tested on a cogeneration plant withthe capacity of 150 MW.

The UK domestic sector accounts for more than a quarter of total energy use. This energy use can be reduced through more efficient building operations. The energy efficiency can be improved through better control of heating in houses, which account for a large portion of total energy consumption. The energy consumption can be lowered by using renewable energy systems, which will also help the UK government to meet its targets towards reduction in carbon emissions and generation of clean energy. Building control has gained considerable interest from researchers and much improved ways of control strategies for heating and hot water systems have been investigated. This intensified research is because heating systems represent a significant share of our primary energy consumption to meet thermal comfort and indoor air quality criteria. Advances in computing control and research in advanced control theory have made it possible to implement advanced controllers in building control applications. Heating control system is a difficult problem because of the non-linearities in the system and the wide range of operating conditions under which the system must function. A model of a two zone building was developed in this research to assess the performance of different control strategies. Two conventional (On-Off and proportional integral controllers) and one advanced control strategies (model predictive controller) were applied to a solar heating system combined with a heat pump. The building was modelled by using a lumped approach and different methods were deployed to obtain a suitable model for an air source heat pump. The control objectives were to reduce electricity costs by optimizing the operation of the heat pump, integrating the available solar energy, shifting electricity consumption to the cheaper night-time tariff and providing better thermal comfort to the occupants. Different climatic conditions were simulated to test the mentioned controllers. Both on-off and PI controllers were able to maintain the tank and room temperatures to the desired set-point temperatures however they did not make use of night-time electricity. PI controller and Model Predictive Controller (MPC) based on thermal comfort are developed in this thesis. Predicted mean vote (PMV) was used for controlling purposes and it was modelled by using room air and radiant temperatures as the varying parameters while assuming other parameters as constants. The MPC dealt well with the disturbances and occupancy patterns. Heat energy was also stored into the fabric by using lower night-time electricity tariffs. This research also investigated the issue of model mismatch and its effect on the prediction results of MPC. MPC performed well when there was no mismatch in the MPC model and simulation model but it struggled when there was a mismatch. A genetic algorithm (GA) known as a non-dominated sorting genetic algorithm (NSGA II) was used to solve two different objective functions, and the mixed objective from the application domain led to slightly superior results. Overall results showed that the MPC performed best by providing better thermal comfort, consuming less electric energy and making better use of cheap night-time electricity by load shifting and storing heat energy in the heating tank. The energy cost was reduced after using the model predictive controller.

Temperature is a very important process parameter in Friction Stir Welding (FSW), but until lately active control of temperature has not been practiced. Recently, temperature control via a PID controller has proven to be effective. Model Predictive Control (MPC) is a control method that holds promise, but has not been attempted in FSW before. Two different model forms are developed for MPC and are evaluated. The first is a simple first-order plus dead time (FOPDT) model. The second is the Hybrid Heat Source model and is more complex; it combines the heat source method and a 1D discretized thermal model of the FSW tool. Model parameters were determined by fitting model predictions to actual weld data. The models were evaluated for their performance in modeled and unmodeled disturbances once the process was already at a quasi steady state condition and also were evaluated for control immediately after plunge. The FOPDT based MPC controller has very good performance and was comparable in performance to previously proven and well-tuned PID controllers. For small modeled disturbances the FOPDT controller settled within 1°C of the setpoint in 10s with almost no oscillations and only 2°C of overshoot. For large unmodeled disturbances, the FOPDT controller settled within 1°C of the setpoint in 30s with no oscillations and 16°C of overshoot. For the same disturbances, the PID servo controller settled in 30s with no oscillations and 9°C of overshoot, and the PID regulator controller settled in 15s but had almost a full oscillation and 13°C of overshoot.The Hybrid Heat Source MPC controller and the PID regulator controller were also able to control temperature within 5°C of the setpoint immediately after the plunge during the highly transient portion of the weld, which previously had been assumed to be too difficult to control. The PID regulator controller had a high degree of variability between the two runs (a settling time of 10s and 30s, and .5 and 4.5 oscillations before settling), but settled quickly and once settled was able to hold the temperature within 2°C of the setpoint. The HHS MPC controller on the other hand had far fewer oscillations (0 and 1 oscillation) before settling, but could only hold the temperature within 5°C of the setpoint. Both of these controllers performed far better than the FOPDT MPC and PID servo controllers.

Increasing the efficiency of conventional power plants is a crucial aspect in the quest of reducing the energy consumption of the world and to having sustainable energy systems in the future. Thus, within the scope of this thesis the possible efficiency improvements for the Wärtsilä 18V50DF model gas engine based combine power generation options are investigated by recovering waste heat of the engine via Organic Rankine cycle (ORC).  In order to this, four different ORC models are simulated via Aspen Plus software and these models are optimized for different objective functions; power output and price per unit of electricity generation. These ORC models are: regenerative Organic Rankine cycle (RORC), cascaded Organic Rankine cycle with an economizer (CORCE), cascaded Organic Rankine cycle with two heat sources (CORC2) and cascaded Organic Rankine cycle with three heat sources (CORC3). In the cascaded cycle models there are two loops which are coupled with a common heat exchanger that works as a condenser for the high temperature (HT) loop and as a preheater for the low temperature (LT) loop. By using this common heat exchanger, the latent heat of condensation of the HT loop is utilized. The engine’s hot exhaust gases are used as main heat source in all the ORC models. The engine’s jacket water is utilized in the CORC2 models as an additional heat source to preheat the LT working fluid. In the CORC3 models engine’s lubrication oil together with the jacket water are used as additional sources for preheating the LT loop working fluid. Thus, the suitability of utilizing these two waste heat sources is examined. Moreover, thermodynamic and economic analyses are performed for each model and the results are compared to each other. The effect of different working fluids, condenser cooling water temperatures, superheating on cycles performance is also evaluated. The results show that with the same amount of fuel the power output of the engine would be increased 2200 kW in average and this increases the efficiency of the engine by 6.3 %. The highest power outputs are obtained in CORC3 models (around 2750 kW) whereas the lowest are in the RORC models (around 1800 kW). In contrast to the power output results, energetic efficiencies of the RORC models (around 30 %) are the highest and CORC3 models (around 22 %) are the lowest. In terms of exergetic efficiency, the highest efficiencies are obtained in CORC2 (around 64.5 %) models whereas the lowest in the RORC models (around 63 %). All the models are found economically feasible since thermodynamically optimized models pay the investment costs back in average of 2 years whereas the economically optimized ones in 1.7. The selection of the working fluid slightly affects the thermodynamic performance of the system since in all the ORC configurations Octamethyltrisiloxane (MDM) working fluid cycles achieve better thermodynamic performances than Decamethyltetrasiloxane (MD2M) working fluid cycles. However, the choice of working fluid doesn’t affect the costs of the system since both working fluid cycles have similar price per unit of electricity generation. The CORC2 models obtain the shortest payback times whereas the CORC3 models obtain the longest Thus the configuration of the ORC does affect the economic performance. It is observed from the results that increasing the condenser cooling water temperature have negative impact on both thermodynamic and economic performances. Also, thermodynamic performances of the cycles are getting reduced with the increasing degree of superheating thus superheating negatively affects the cycle’s performances. The engine’s jacket water and lubrication oil are found to be sufficient waste heat sources to use in the ORC models.

Em projetos de oleodutos e gasodutos utilizam-se aços de alta resistência e baixa liga (ARBL), como o aço API 5L X80. Na soldagem multipasse destas tubulações, a zona afetada pelo calor (ZAC) do passe de raiz é submetida a um novo ciclo térmico pelos passes de soldagem subsequentes. Isto resulta em alterações nos valores das propriedades físicas. Nos aços ARBL, a ZAC de grãos grosseiros reaquecida intercriticamente (IC-ZACGG) pode se tornar uma zona frágil localizada, isto é, uma zona com maior dureza. Consequentemente, falhas estruturais podem ocorrer, ocasionando paradas não desejadas no transporte de fluidos. O objetivo deste trabalho é desenvolver uma metodologia baseada no modelo de fontes de calor distribuídas de Mhyr e Gröng, para avaliar o fluxo de calor na soldagem considerando as propriedades físicas dependentes da temperatura. Estender a aplicação desta ferramenta em soldagens multipasses para identificar sub-regiões da ZAC de um passe anterior sendo afetada pela ZAC de passes subsequentes. As isotermas simuladas foram validadas através de medições realizadas em macrografias de juntas soldadas. Os ciclos térmicos simulados foram validados através das temperaturas máximas atingidas e pelos tempos de resfriamento de 800 a 500 ºC (?t8-5) dos ciclos térmicos experimentais. Ao aplicar a metodologia proposta, foi possível delimitar com acurácia as regiões reaquecidas da ZAC e analisar os efeitos dos passes subsequentes em cada uma das sub-regiões da ZAC do passe de raiz. A IC-ZACGG na região do passe de raiz foi localizada, mas não se comportou como zona frágil devido à boa soldabilidade do aço API 5L X80 comprovada pelos ensaios de dureza e de tenacidade ao impacto Charpy-V.
In pipelines projects, the high strength low alloy (HSLA) steels are used, such as the API 5L X80 steel. During the multipass welding of these pipes, the heat affected zone (HAZ) of the root pass is subjected to a new thermal cycle by the subsequent welding passes. This results in changes in the values of the physical properties. In the HSLA steels, the intercritical reheated coarse-grained heat-affected zone (IR-CGHAZ) can become a local brittle zone, that is, a region with greater hardness. Consequently, structural failures could happen, causing undesired shutdowns in fluid transportation. The objective of this work is to develop a methodology based on the distributed heat sources model of Mhyr and Gröng, to evaluate the heat flux in the welding considering the temperature-dependent physical properties. Extend the application of this tool in multipass welds to identify HAZ subregions of a previous pass being affected by the HAZ of subsequent passes. The simulated isotherms were validated through measurements made on macrographs of welded joints. The simulated thermal cycles were validated through the maximum temperatures reached and the cooling times from 800 °C to 500 ºC (?t8-5) of the experimental thermal cycles. By applying the proposed methodology, it was possible to accurately delimit reheated HAZ regions and analyze the effects of subsequent passes in each of the root pass HAZ subregions. The IRCGHAZ in the root pass region was localized, but it did not behave as a brittle zone due to the good weldability of the API 5L X80 steel as proven by the hardness and Charpy-V impact tests.

In diesem Beitrag wird über die erzielten Ergebnisse der durchgeführten simulativ-experimentellen Untersuchungen für additive Fertigung von komplexen Bauteilgeometrieflächen mittels 3D – Plasma-Auftragschweißen berichtet. Hierbei wurde mittels des 3D – Plasma-Pulver-Auftragschweißenes von komplexen Konturflächen für ein Werkzeugmodell und ähnliche Bauteilgeometrien aus reinem Schweißgut in Mehrlagentechnik beanspruchungsgerecht hergestellt. Infolge der Besonderheiten des 3D – Plasma-Auftragschweißenes mit großer Schweißgutvolumina wie stark abweichende Eigenschaften zwischen Grund-/ Auftragswerkstoff und asymmetrischer Wärmeeintrag sind die entstehenden Schrumpfungen, Verformungen/ Eigenspannungen besonders kritisch. Diese führen demzufolge zu Maß- und Formabweichungen sowie Bildung von Bauteilrissen, welche die Qualität der additiv plasma-auftraggeschweißten Bauteilstrukturen negativ beeinflussen können. Mittels des aufgebauten thermo-elastisch-plastischen Simulationsmodells wurden die auftretenden Temperaturfeldverteilung, Verformungen und Eigenspannungen während des additiven 3D – Plasma-Auftragschweißenes von Werkzeugkonturflächen vorausbestimmt und analysiert. Anhand des aufgebauten Ellipsoid-Wärmequellenmodells für Plasma-Pendelschweißprozess wurden die Temperaturfeldverteilung und deren Gradienten ermittelt. Darauf aufbauend wurden eine gekoppelte thermisch-elastisch-plastische struktur-mechanische Analyse durchgeführt. Mittels der Durchführung von werkstofflich-fertigungstechnischen Maßnahmen wie Verwendung von zähen Werkstofflegierungen, Grundköpervorwärmen und -festeinspannen wurden die damit entstehenden Bauteilverformung und -eigenspannungen simulativ kompensiert bzw. minimiert. Demzufolge wurden die damit erreichten Ergebnisse für die Herstellung endkonturnaher Werkzeugkonturflächen mit vordefinierten Schichteigenschaften praxisnah genutzt. Die dabei erreichten Simulationsergebnisse der Temperaturfeldverteilung und des Verformungs- und Eigenspannungszustandes präsentierten eine gute Übereinstimmung mit den Experimentresultaten.

No presente trabalho é apresentado um estudo do efeito da diluição com inertes sobre as características da transferência de calor por radiação em chamas laminares não pré-misturadas de metano. O trabalho também apresenta um estudo sobre a modelagem do fluxo radiativo proveniente de chamas turbulentas visando à obtenção de fatores de ponderação para o modelo das múltiplas fontes pontuais. Em ambos os estudos, a distribuição do fluxo radiante é obtida através de medições ao longo do eixo da chama e os valores de fração radiante são calculados a partir da integração dessa distribuição. É mostrado qualitativamente que a adição de gás inerte ao combustível propicia a inibição da formação de fuligem. É mostrado quantitativamente que a adição de gás inerte pode reduzir ou ampliar a fração radiante da chama, dependendo do tipo de gás, dos níveis de diluição e do tempo de residência característico da chama. São reportados valores para os fatores de ponderação utilizados no modelo de múltiplas fontes pontuais obtidos experimentalmente a partir de medições nas chamas. O formato da curva formada pelos fatores de ponderação é semelhante para os diferentes níveis de diluição com gás carbônico. A utilização desses fatores de ponderação no modelo de múltiplas fontes pontuais apresenta resultados satisfatórios em comparação com a distribuição dos fluxos radiativos medidos ao longo do eixo da chama.
In this work it is presented a study of the effect of fuel dilution with inerts on the radiative heat transfer characteristics of laminar non premixed methane flames. A study on the radiative flux distribution from turbulent flames is conducted in order to obtain weighting factors for the model of multiple point sources. The distribution of radiative heat flux is obtained by measuring the fluxes along the axis of the flame and the radiant fraction is calculated by the integration of such distribution. It is qualitatively shown that the addition of inert gas in the fuel leads to the inhibition of soot formation. It is quantitatively shown that the addition of inert may decrease or increase the radiant fraction depending on gas type, dilution levels and characteristic residence times of the flame. It is also reported values for the weighting factors used in the model of multiple point sources experimentally obtained from measurements. The shapes of the curves formed by the weighting factors are similar for the different dilution levels of carbon dioxide. The use of these weighting factors in the multi-point source model shows satisfactory results in comparison to the distribution of radiative fluxes measured along the flame axis.

Due to changes in UK and Scottish policy and NHS directives, there have been many changes and improvements in the way information is provided to patients affected by cancer and their families over the last decade. The information provided should be accurate, detailed and tailored to the individual’s needs across the whole of their cancer trajectory. People affected by laryngeal cancer could be classed as a “Cinderella” group as there is a lack of research with this group of patients and their families, in comparison to other types of cancer, even though the impact of treatment can have a profound and debilitating effect on the individual and their family’s quality of life. How this group of patients and their families use and source information to help them make sense of their experiences across their trajectory is unknown, therefore this study explored the role of information based on the experiences of people affected by laryngeal cancer across their cancer trajectory. The study adopted an interpretive prospective longitudinal approach, using two in-depth qualitative interviews with twenty patients and eighteen carers from across the main treatment pathways associated with this type of cancer. The data were analysed using Framework Analysis and influenced by Dingwall’s Illness Action Model. Four broad thematic headings were developed to explain the role of information: “Search for Normality”, “Illusion of Certainty”, “Reality of Uncertainty” and “Culture of Caring”. Relationships were identified between these headings at four key stages across the cancer trajectory. The ii broad theme “Search for Normality” overarched the whole of the cancer trajectory explaining how information was sourced and used to help this group understand their experience of symptoms. The main findings from the study show that two broad categories of information are used: information from health professionals and experiential information from one’s own and others’ experiential knowledge of health and illness. Both categories of information are sourced and used in different ways at different stages over the course of the trajectory and become inextricably linked over time. The study shows that information is not an entity that can be studied on its own but needs to be studied and explained in the ways it is situated, used and experienced within the context of the complex needs and experiences of this group of patients and their families. This study is the first longitudinal study to provide an explanation of the role of information with people affected by laryngeal cancer across their cancer trajectory. The findings show how the different types of information used from the various sources influence how people affected by laryngeal cancer perceive and understand their diagnosis, treatment and the outcome of treatment. The study findings suggest that health professionals need to situate information in the context of the individual’s understanding and prior knowledge of health and illness to ensure that it does not set unrealistic expectations, with a clear need for continuity and supportive care identified in the post-treatment and follow-up phases.

Le perçage de l’os est couramment pratiqué dans de nombreux types de chirurgie comme lors de la pose de vis d’ostéosynthèse et d’implants dentaires et cochléaires. Lors de l'opération de perçage, le chargement thermomécanique dû à l'interaction outil-os peut endommager les tissus osseux au voisinage de la zone de perçage. Ainsi, une augmentation significative de la température peut provoquer une ostéonécrose thermique. Il est donc important d'optimiser les conditions opératoires (vitesses de rotation et d'avance, géométrie du foret, stratégie de perçage...) afin de réduire les risques d'endommagement de l'os. Pour ce faire, il faut analyser et comprendre les effets des conditions de coupe sur les mécanismes contrôlant l'interaction foret-os. Les travaux de cette thèse ont pour objectif de contribuer à la compréhension de ces mécanismes en combinant une approche expérimentale avec de la modélisation numérique et analytique. L'étude expérimentale porte sur l’effet de la vitesse de coupe, de l’avance du foret et de la microstructure de la zone percée sur l’évolution des efforts de coupe (l'effort d'avance et le moment axial) et de l’augmentation de la température pendant le perçage d’un échantillon d’os porcin et de matériaux de tests biomécaniques (Sawbones). Ces derniers présentent l'avantage d'une microstructure uniforme par échantillon donné contrairement à l'os. Les modèles numériques de la coupe orthogonale et du perçage de l’os cortical sont développés en utilisant le code Eléments Finis ABAQUS/Explicit. L’objectif est d'analyser l’influence des lois de comportement et d’endommagement sur les prédictions du modèle (mécanisme de coupe, température et efforts de coupe). Afin de proposer une approche simplifiée, une modélisation analytique basée sur la théorie de la source mobile a également été proposée. La validation expérimentale a montré la pertinence des approches proposées ainsi que leurs limites
Bone drilling is commonly practised in various surgical operations for orthosynthesis screws insertion or placement of dental and cochlear implants. During bone drilling procedure, the thermomechanical constraints resulting from the tool-bone interaction can damage the bone tissues in the vicinity of the drilling area. Thus, a significant increase in temperature can cause thermal osteonecrosis. It is therefore important to optimize the operating conditions (spindle speed and feed rate, geometry of the drill, drilling operation strategy ...) in order to reduce the risk of damage to bone tissues. To do this, it is necessary to analyse and understand the effects of cutting conditions on the mechanisms controlling the drill-bone interaction. The present work aims to contribute to the understanding of these mechanisms by combining an experimental approach with numerical and analytical modelling. The experimental study investigates the effect of the cutting speed, feed rate of the drill and the microstructure of the drilled area on the resulting cutting forces (thrust force and axial torque) and temperature rise during the drilling of porcine bone specimens and biomechanical test materials (Sawbones). These materials have the advantage of a uniform microstructure per given sample unlike bone. Numerical models of orthogonal cutting and bone drilling are implemented using the Finite Element code ABAQUS / Explicit. The purpose of this development is to analyse the influence of bone constitutive and damage laws on the model predictions (cutting mechanism, temperature and cutting forces). In order to propose a simplified approach, an analytical modelling based on moving heat source theory is developed for predicting bone thermal response. The relevance and limits of the approach proposed is shown through experimental validation

La thermographie infrarouge est une méthode largement employée pour la caractérisation des propriétés thermophysiques des matériaux. L’avènement des diodes laser pratiques, peu onéreuses et aux multiples caractéristiques, étendent les possibilités métrologiques des caméras infrarouges et mettent à disposition un ensemble de nouveaux outils puissants pour la caractérisation thermique et le contrôle non desturctif. Cependant, un lot de nouvelles difficultés doit être surmonté, comme le traitement d’une grande quantité de données bruitées et la faible sensibilité de ces données aux paramètres recherchés. Cela oblige de revisiter les méthodes de traitement du signal existantes, d’adopter de nouveaux outils mathématiques sophistiqués pour la compression de données et le traitement d’informations pertinentes. Les nouvelles stratégies consistent à utiliser des transformations orthogonales du signal comme outils de compression préalable de données, de réduction et maîtrise du bruit de mesure. L’analyse de sensibilité, basée sur l’étude locale des corrélations entre les dérivées partielles du signal expérimental, complète ces nouvelles approches. L'analogie avec la théorie dans l'espace de Fourier a permis d'apporter de nouveaux éléments de réponse pour mieux cerner la «physique» des approches modales.La réponse au point source impulsionnel a été revisitée de manière numérique et expérimentale. En utilisant la séparabilité des champs de température nous avons proposé une nouvelle méthode d'inversion basée sur une double décomposition en valeurs singulières du signal expérimental. Cette méthode par rapport aux précédentes, permet de tenir compte de la diffusion bi ou tridimensionnelle et offre ainsi une meilleure exploitation du contenu spatial des images infrarouges. Des exemples numériques et expérimentaux nous ont permis de valider dans une première approche cette nouvelle méthode d'estimation pour la caractérisation de diffusivités thermiques longitudinales. Des applications dans le domaine du contrôle non destructif des matériaux sont également proposées. Une ancienne problématique qui consiste à retrouver les champs de température initiaux à partir de données bruitées a été abordée sous un nouveau jour. La nécessité de connaitre les diffusivités thermiques du matériau orthotrope et la prise en compte des transferts souvent tridimensionnels sont complexes à gérer. L'application de la double décomposition en valeurs singulières a permis d'obtenir des résultats intéressants compte tenu de la simplicité de la méthode. En effet, les méthodes modales sont basées sur des approches statistiques de traitement d'une grande quantité de données, censément plus robustes quant au bruit de mesure, comme cela a pu être observé
Infrared thermography is a widely used method for characterization of thermophysical properties of materials. The advent of the laser diodes, which are handy, inexpensive, with a broad spectrum of characteristics, extend metrological possibilities of infrared cameras and provide a combination of new powerful tools for thermal characterization and non destructive evaluation. However, this new dynamic has also brought numerous difficulties that must be overcome, such as high volume noisy data processing and low sensitivity to estimated parameters of such data. This requires revisiting the existing methods of signal processing, adopting new sophisticated mathematical tools for data compression and processing of relevant information.New strategies consist in using orthogonal transforms of the signal as a prior data compression tools, which allow noise reduction and control over it. Correlation analysis, based on the local cerrelation study between partial derivatives of the experimental signal, completes these new strategies. A theoretical analogy in Fourier space has been performed in order to better understand the «physical» meaning of modal approaches.The response to the instantaneous point source of heat, has been revisited both numerically and experimentally. By using separable temperature fields, a new inversion technique based on a double singular value decomposition of experimental signal has been introduced. In comparison with previous methods, it takes into account two or three-dimensional heat diffusion and therefore offers a better exploitation of the spatial content of infrared images. Numerical and experimental examples have allowed us to validate in the first approach our new estimation method of longitudinal thermal diffusivities. Non destructive testing applications based on the new technique have also been introduced.An old issue, which consists in determining the initial temperature field from noisy data, has been approached in a new light. The necessity to know the thermal diffusivities of an orthotropic medium and the need to take into account often three-dimensional heat transfer, are complicated issues. The implementation of the double singular value decomposition allowed us to achieve interesting results according to its ease of use. Indeed, modal approaches are statistical methods based on high volume data processing, supposedly robust as to the measurement noise

Reach defined analysis concentrated on the water temperature change that occurred in a stream/river segment over the course of one full diurnal cycle. Digital thermistors, data loggers and computer model development were utilized in reach analysis to link parameters of the stream system to a specific temperature change. The methodology employed was relatively simple and fast, and many successive stream segments were analyzed simultaneously. Reach analysis of stream temperature change identified the existing components of the stream system that caused increased water temperature and predicted the effectiveness of managed improvements to the stream system. Stream and river temperature regulation has focused on system and basin wide management. Often, the source of increased water temperature originates in only a part of the stream system. Reach defined analysis identified the portions of the stream system in which most water temperature change occurred, offered an explanation for the temperature response and provided specific information about the alternate strategies that may ameliorate undesired water temperatures. The development of the computer model Heat Source included physically based mathematical descriptions of stream energy and hydrologic processes. An implicit finite difference numerical method was implemented for simultaneous solution. The methodology presented in Heat Source is portable and applicable to all streams, rivers and open channels.
Graduation date: 1997

Vertical ground source heat pumps are established and still growing on the global market. The modelling of these systems is important for system design and optimization. This is an active field of research, and many models are often built into system simulation software such as TRNSYS. With the intention of having a better sensibility for existing TRNSYS tools, three different cases are simulated with several TRNSYS tools, so called Types. A Thermal Response Test, a large borehole field of an IKEA building complex in Sweden, as well as the Marine Corps Logistic Base in Albany, USA. The vertical ground heat exchanger types 203, 244, 243, 246, 451, 55a and 557b are used. Most of the simulations are investigated and evaluated by comparing them to measured data. The result shows that, for these specific cases, the DTS types 557a and 557b can underestimate the heat transfer early on due to a poor consideration of the thermal capacity inside the borehole. Depending on how the thermal resistance is calculated by a module, the fluid mean temperature simulation is affected by a constant throughout the simulation time. The simulation results indicate that the type 557b, where the borehole resistance is pre-set as an input and known from experimental data, is the most accurate of the types for groundwater filled boreholes. On short term, type 451 provides a good coherence with the measured data, with a relative deviation of 10.3 %. The borehole models that consider the borehole thermal capacity overestimate the short term heat transfer rate, whereas those that neglect the borehole capacity underestimate the short term thermal heat transfer on short term. Existing Types describe successfully the long term behaviour of large borehole fields. Serial versus parallel coupled BHE fields show relatively small differences in performance when simulated with type 557b for a specific study case.

博士
國立中正大學
機械工程學系暨研究所
102
Abstract This study proposed a tailored laser heat source model for the finite element analysis of the laser cladding process. The beam characteristics, including wavelength, beam radius, TEM mode and focusing conditions, were comprehensively considered in the heat source model. The model was integrated in a SYSWELD package to predict the temperature distribution and clad bead profile during laser cladding of preplaced powder layer or coaxial powder feeding on a steel substrate. Cladding process parameters were evaluated by varying the TEM mode, focusing conditions, wavelength and scanning speed. Single mode and tailored multi-mode TEMmixed laser beams were established for simulation. Validation of the heat source model was explored with laser cladding experiments at different beam powers and scanning speeds for both Nd:YAG and CO2 laser having a TEMmixed beam mode. As a comparison, the evolution of the melt pool isotherms and the clad bead profiles during laser cladding were simulated under identical laser parameter range as well as the materials and boundary conditions in the experiments. The threshold power for the clad bead formation and the feasible process parameter range for a successful laser cladding were verified. This work also presented an theoretical energy transfer model for laser cladding of preplaced powder layer. The energy transfer during laser cladding process was analyzed in the following consecutive steps: energy absorption by the preplaced layer, heat transfer from preplaced layer into base metal, melting of powder and base metal. To accomplish a successful cladding, two energy threshold values were proposed. The first threshold is necessary for melting of preplaced powder; the second threshold is required for melting of base metal and mixing of powder into a weld pool. The powder layer may be blown away without clad layer formation if the energy does not exceed threshold value. Feasible thickness range of the preplaced powder layer can be predicted with this model. The numerical results were verified by laser cladding experiment. The theoretical energy model shows good agreement with the clad layer thickness obtained from experiment.

Closed-loop ground source heat pumps (GSHPs) are used to transfer thermal energy between the subsurface and conditioned spaces for heating and cooling applications. A basic GSHP is composed of a ground heat exchanger (GHX), which is a closed loop of pipe buried in the shallow subsurface circulating a heat exchange fluid, connected to a heat pump. These systems offer an energy efficient alternative to conventional heating and cooling systems; however, installation costs are higher due to the additional cost associated with the GHX. By further developing our understanding of how these ground loops interact with the subsurface, it may possible to design them more intelligently, efficiently, and economically. To gain insight into the physical processes occurring between the GHX and the subsurface and to identify efficiencies and inefficiencies in GSHP design and operation, two main research goals were defined: comprehensive monitoring of a fully functioning GSHP and intensive simulation of these systems using computer models. A 6-ton GSHP was installed at a residence in Elora, ON. An array of 64 temperature sensors was installed on and surrounding the GHX and power consumption and temperature sensors were installed on the system inside the residence. The data collected were used to help characterize and understand the function of the system, provide motivation for further investigations, and assess the impact of the time of use billing scheme on GSHP operation costs. To simulate GSHPs, two computer models were utilized. A 3D finite element model was employed to analyse the effects of pipe configuration and pipe spacing on system performance. A unique, transient 1D finite difference heat conduction model was developed to simulate a single pipe in a U-tube shape with inter-pipe interactions and was benchmarked against a tested analytical solution. The model was used to compare quasi-steady state and transient simulation of GSHPs, identify system performance efficiencies through pump schedule optimization, and investigate the effect of pipe length on system performance. A comprehensive comparison of steady state and pulsed simulation concludes that it is possible to simulate transient operation using a steady state assumption for some cases. Optimal pipe configurations are identified for a range of soil thermal properties. Optimized pump schedules are identified and analysed for a specific heat pump and fluid circulation pump. Finally, the effect of pipe spacing and length on system performance is characterized. It was found that there are few design inefficiencies that could be easily addressed to improve general design practice.

Ground source heat pumps (GSHPs) offer an efficient method for cooling and heating buildings, reducing energy usage and operating cost. In hot, arid regions such as Texas and the southwest United States, building load imbalance towards cooling causes design and performance challenges to GSHP systems in residential and commercial building applications. An integrated building load and GSHP model is developed in this thesis to test approaches to reduce GSHP cost, to properly size ground heat exchanger (GHEX) installations and to offer methods to improve GSHP performance in commercial buildings. The integrated model is comprised of a three-story office building, heat pumps, air handling system and a GHEX. These component models were integrated in the Matlab® Simulink® modeling environment, which allows for easy model modification and expansion. The building-load model was developed in HAMBASE, which simulates the thermal and hygric response of each zone in the building to external weather and internal loads. The building-load model was validated using the ASHRAE 140-2007 Standard Method of Test and with results from EnergyPlus. The heat pump model was developed as a performance map, based on data commonly provided by heat pump manufacturers. This approach allows for easy expansion of the number and type of heat pump models supported. The GHEX model was developed at Oklahoma State University and is based on Eskilson’s g-function model of vertical borehole operation. The GHEX model accurately represents the interaction between boreholes and the ground temperature response over short and long time-intervals. The GHEX model uses GLHEPRO files for parameter inputs. Long time-interval simulations of the integrated model are provided to assess the sensitivity of the GSHP system to various model parameters. These studies show that: small changes in the total GHEX length reduce system cost with minimal impact on performance; increased borehole spacing improves system performance with no additional cost; supplemental heat rejection reduces installation costs and improves system performance; industry-recommended design cutoff temperatures properly size the GHEX system; and, while cooling is the greatest contributor to operating cost in the southwest and southcentral United States, heating is the limiting design case for GHEX sizing.
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The high population growth rate and rapid urbanization that the world is experiencing today has aggravated the competition for the already scarce resource ¡V water ¡V between the agricultural sector and the other economic sectors. Moreover, within the agricultural sector, water is increasingly being used for commercial plantations as opposed to growing food crops, threatening food security. Therefore, it is very important that this scarce resource is managed in an efficient and sustainable manner, for now and future use. This requires understanding the process of evaporation for accurate determination of water-use from agricultural lands. In the past, direct measurements of evaporation have proven difficult because of the cost and complexity of the available equipments, and level of expertise involved. This justifies a quest for relatively simple, accurate and inexpensive methods of determining evaporation for routine field applications. Estimation of sensible heat flux (H) from high frequency air temperature measurements and then calculating latent energy flux (ƒÜE) and hence evaporation as a residual of the shortened surface energy balance equation, assuming that closure is met, is appealing in this sense. Concurrent net irradiance (Rn) and soil heat flux (G) measurements can be conducted with relative ease for use in the energy balance equation. Alternately, evaporation can also be mathematically modelled, using single- or multi-layer models depending on vegetation cover, from less expensive routine meteorological observations. Therefore, the ultimate objective of this study is to estimate and model H and ƒÜE, and thereby evaporation, accurately over sparsely vegetated agricultural lands at low cost and effort. Temperature-variance (TV) and surface renewal (SR) methods, which use high-frequency (typically 2 to 10 Hz) air temperature measurements, are employed for estimation of H. The TV method is based on the Monin and Obukhov Similarity Theory (MOST) and uses statistical measures of the high frequency air temperature to estimate H, including adjustments for stability. The SR method is based on the principle that an air parcel near the surface is renewed by an air parcel from above and, to determine H, it uses higher order air temperature differences between two consecutive sample measurements lagged by a certain time interval. Single- and double-layer models that are based on energy and resistance combination theory were also used to estimate evaporation and H from sparse vegetation. Single- and double-layer models that were extended to include inputs of radiometric temperature in order to estimate H were also used. The transmission of solar irradiance to the soil beneath in sparse canopies is variable and depends on the vegetation density, cover and apparent position of the sun. A three-dimensional radiation interception model was developed to estimate this transmission of solar irradiance and was used as a sub-module in the double-layer models. Estimations of H from the TV (HTV), SR (HSR) and double-layer models were compared against H obtained from eddy covariance (HEC), and the modelled ƒÜE (single- and double-layer) were compared with that obtained from the shortened energy balance involving HEC. Besides, long-term ƒÜE calculated from the shortened energy balance using HTV and HSR were compared with those calculated using HEC. Unshielded and naturally-ventilated fine-wire chromel-constantan thermocouples (TCs), 75 ƒÝm in diameter, at different heights above the ground over sparse Jatropha curcas trees, mixed grassland community and bare fallow land were used to measure air temperature. A three-dimensional sonic anemometer mounted at a certain height above the ground surface was also used to measure virtual temperature and wind speed at all three sites. All measurements were done differentially at 10-Hz frequency. Additional measurements of Rn, G and soil water content (upper 60 mm) were also made. The Jatropha trees were planted in a 3-m plant and inter-row spacing in a 50 m ¡Ñ 60 m plot with the surrounding plots planted to a mixture of Jatropha trees and Kikuyu grass. Average tree height and leaf area index measurements were taken on monthly and bimonthly basis respectively. An automatic weather station about 10 m away from the edge of the Jatropha plot was also used to obtain solar irradiance, air temperature and relative humidity, wind speed and direction and precipitation data. Soil water content was measured to a depth of 1000 mm from the surface at 200 mm intervals. Soil and foliage surface temperatures were measured using two nadir-looking infrared thermometers with one mounted directly above bare soil and the other above the trees. The three-dimensional solar irradiance interception model was validated using measurements conducted on different trees and planting patterns. Solar irradiance above and below tree canopies was measured using LI-200 pyranometer and tube solarimeters respectively. Leaf area density (LAD) was estimated from LAI, canopy shape and volume measurements. It was also determined by scanning leaves using either destructive sampling or tracing method. The performance of the TV method over sparse vegetation of J. curcas, mixed grassland community and fallow land was evaluated against HEC. Atmospheric stability conditions were identified using (i) sensor height (z) and Obukhov length (L) obtained from EC and (ii) air temperature difference between two thermocouple measurement heights. The HTV estimations, adjusted and not adjusted for skewness (actual and estimated) of air temperature (sk), for unstable conditions only and for all stability conditions were used. An improved agreement in terms of slope, coefficient of determination (r2) and root mean square error (RMSE), almost over all surfaces, was obtained when the temperature difference rather than the z/L means of identifying stability conditions was used. The agreement between the HTV and HEC was improved for estimations adjusted for actual sk than not adjusted for sk. Improved agreement was also noted when HTV was adjusted using estimated sk compared to not adjusting for sk over J. curcas. The TV method could be used to estimate H for surfaces with varying homogeneity with reasonable accuracy. Long-term water-use of a fetch-limited sparse vegetation of J. curcas was determined as a residual of the shortened surface energy balance involving HTV and HSR and compared with those estimated using HEC. Concurrent measurements of Rn and G were also performed. The long-term water-use of J. curcas trees calculated from the shortened surface energy balance involving HTV and HSR agreed very well when compared with those obtained from HEC. The seasonal HTV and HSR also agreed very well when compared with HEC. Changes in structure of the canopy and environmental conditions appeared to influence partitioning of the available energy into H and ƒÜE. The seasonal total evaporation for the EC, TV and SR methods amounted to 626, 640 and 674 mm respectively with a total rainfall of 690 mm. Footprint analysis also revealed that greater than 80% of the measured flux during the day originates from within the surface of interest. The TV and SR methods, therefore, offer a relatively low-cost means for long-term estimation of H, and ƒÜE, hence the total evaporation, using the shortened surface energy balance along with measurements of Rn and G. Evaporation and biomass production estimations from tree crops requires accurate representation of solar irradiance transmission through the canopy. A relatively simple three-dimensional, hourly time-step tree-canopy radiation interception model was developed and validated using measurements conducted on isolated trees, hedgerows and tree canopies arranged in tramline mode. Measurements were obtained using tube solarimeters placed 0.5 m from each other starting from the base of a tree trunk in four directions, along and perpendicular to the row up to mid-way between trees and rows. Model-simulations of hourly radiant transmittance were in good agreement with measurements with an overall r2 of 0.91; Willmott.s index of agreement of 0.96; and general absolute standard deviation of 17.66%. Agreement between model-estimations and measurements, however, was influenced by distance and direction of the node from the tree trunk, sky conditions, symmetry of the canopy, and uniformity of the stand and leaf distribution of the canopy. The model could be useful in planning and management applications for a wide range of tree crops. Penman-Monteith (PM) equation and the Shuttleworth and Wallace (SW) model, representing single- and dual-source models respectively, were used to determine the total evaporation over a sparse vegetation of J. curcas from routine automatic weather station observations, resistance parameters and vegetation indices. The three-dimensional solar irradiance interception model was used as a sub-module in the SW model. The total evaporation from the sparse vegetation was also determined as a residual of the shortened surface energy balance using measurements of Rn, G and HEC. The PM equation failed to reproduce the .measured. daily total evaporation during periods of low LAI, with improved agreement with increased LAI. The SW model, however, produced total evaporation estimates that agreed very well with the .measured. with a slope of 0.96, r2 of 0.91 and RMSE of 0.45 mm for a LAI ranging from 0 (no leaves) to 1.83 m2 m-2. The SW model also estimated soil evaporation and plant transpiration separately, and about 66 % of the cumulative evaporation was attributed to soil evaporation. These findings suggest that the PM equation should be replaced by the SW model for surfaces that assume a range of LAI values during the growing season. The H was estimated using (i) SW model that was further developed to include surface radiometric temperature measurements; (ii) one-layer model, but linked with a two-layer model for estimation of excess resistance, that uses surface radiometric temperature; and (iii) the SW model (unmodified). The agreement between modelled and measured H, using 10-min data, was in general reasonably good with RMSE (W m-2) of 45.11, 43.77 and 39.86 for the three models respectively. The comparative results that were achieved from (iii) were not translated into the daily data as all models appeared to have a tendency to underestimate H. The resulting RMSEs for the daily H data for the three models were (MJ m-2) 1.16, 1.17 and 1.18 respectively. It appears that similar or better agreement between measured and estimated H can be forged without the need for surface radiometric temperature measurements. The study showed, in general, that high frequency air temperature measurements can be used to estimate H with reasonable accuracy using the simple and relatively low-cost TV and SR methods. Moreover, these methods can be used to calculate ƒÜE, hence ET, as a residual of the shortened surface energy balance equation along with measurements of Rn and G assuming that energy balance closure is met. The simple and low-cost nature of these methods makes replication of measurements easier and their robust nature allows long-term measurements of energy fluxes. The study also showed that H and ƒÜE can be modeled using energy and resistance combination equations with reasonable accuracy. It also reiterated that the SW-type models, which treat the plant canopy and soil components separately, are more appropriate for estimation of H and ƒÜE over sparse vegetation as opposed to the PM-type models.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Ground source heat pumps (GSHP) have the ability to significantly reduce the energy required to heat and cool buildings. Historically, deployment of GSHP's in the cooling-dominated Texas and Southwest region has been significantly less than in other regions of the United States. The long term technical and economic viability of GSHPs in arid regions such as Texas has been questioned due to failures of ground loop heat pump systems by early adopters. A proposed solution is to include a supplemental heat rejection (SHR) device to help offset the unbalanced ground loads. An integrated building load-ground source heat pump model is developed in this thesis and is designed to be a test bed for potential SHR devices. The model consists of discrete component models that can be mixed and matched to represent various types of buildings and ground source heat pumps. One of the unique features of the integrated model is the use of the Simulink/Matlab environment. This environment allows the user to develop component models that take advantage of the built-in functionality of Matlab and Simulink. Another unique feature is the full coupling of the building load, heat pump, and ground loop at every time step. The building load, heat pump, and ground loop models were chosen to allow for short time step simulations, which allows for a range of dynamic response times to be modeled and for different heat pump/SHR control methods to be explored. The integrated model can be used on any computer that has the Matlab and Simulink software. The building load model used, called HAMBASE, can model both residential and commercial buildings. HAMBASE was validated using the ASHRAE 140-2007 standard. The heat pump model uses readily available data provided by GSHP manufacturers to accurately model operation across a wide range of input conditions. The vertical borehole ground loop model, developed at Oklahoma State University, is based on Eskillson's g-function model, but included a one-dimensional numerical model to calculate the short term thermal response of the borehole and ground. The ground loop model utilizes GLHEPRO, a ground loop sizing and simulation tool, to create the required parameter files. Using the integrated building load-ground source heat pump model, a model of a single family house with a ground source heat pump was developed. The house model was validated by the results from eQuest and GELHPRO. A series of sensitivity studies were completed to determine dominant factors affecting the use of GSHPs in Texas and the Southwest regions of the United States. The results show that the life of a vertical borehole can be significantly extended/cut short if the ground parameters are properly/not properly designed prior to ground loop sizing.
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To uilize the shallow geothermal energy, heat pumps are often coupled with borehole heat exchangers (BHE) for heating and cooling buildings. In cold regions, soil freezing around the BHE is a potential problem which can seriously influence the underground soil temperature distribution, inlet and outlet fluid temperature of the BHE, and thus the efficiency of the whole GSHP system. The influence of the freezing process on the overall system performance is investigated by comparing different BHE configuration with and without latent heat effect from the frozen groundwater. The coefficient of performance (COP) of the heat pump will alter when freezing process in taken into account and lead to various electricity consumption. Except for the efficiency aspect, the freezing behavior can also lead to the redistribution of pore pressure and fluid flow, and in some extreme cases can even result in frost damage to the BHEs. A fully coupled thermohydro-mechanical model is required for advanced system design and scenario analyses. Based on the framework of the Theory of Porous Media, a triphasic freezing model is derived and solved with the finite element method. Ice formation in the porous medium results from a coupled heat and mass transfer problem with phase transition and is accompanied by volume expansion. The model is able to capture various coupled physical phenomena through the freezing process including the latent heat effect, groundwater flow with porosity change and mechanical deformation. With this kind of THM freezing model, we are also able to solve different kinds of engineering problem, e.g. geotechnics, construction engineering and material engineering.

碩士
逢甲大學
通訊工程所
100
A 3D multiple sound source system with the low computational complexity and the low storage capacity are constructed by combining with the presented binaural synthesis structure and the method proposed in this essay. The basis vectors and the weight vector set, extracted from head-related transfer function (HRTF) dataset by using the linear decomposition, are a prototype of the synthesis system. The low computational complexity comes from the low order modeling for basis vectors using IIR filters with common set of poles. The low storage capacity requirement can be obtained by reducing the quantity of weight vector dataset. This essay proposed a method to achieve the reduction of weight vector dataset. By means of performance analysis, we find that the quantities of the sound source increase more, and this system has prominently high computational efficiency. We propose the method based on a low quantity of data comparing with the related reference, and the results reveal that our method is better than the reference in the same simulation environment and the error criterion situations.

This thesis presents two interrelated studies that consider nutrient management and seasonal changes in recharge on agricultural lands within the context of source water protection. The research focuses first on the management of the risk to groundwater quality through the implementation of various nutrient management practices and secondly considers the dynamic nature of the transport pathway to the groundwater system associated with seasonal changes in climate and hydrology. The combined results provide insight into several of the key factors influencing the protection of groundwater sources within the agricultural landscape. Field work was completed between 2009 and 2010 on an agricultural field near the City of Woodstock, Ontario. The site is located within a source water protection area; the two-year travel time zone of the Thornton Well Field which represents the primary water supply for the City of Woodstock and which has experienced chronic increases in nitrate concentrations over the last few decades. The wells are completed in glacial overburden consisting of intermingling sand and gravel till aquifers which overly a limestone bedrock aquifer. Agricultural best or beneficial management practices (BMPs) field have been implemented and monitored since 2004. The BMPs were adopted in order to reduce nitrogen losses to the aquifer, and consisted of a reduction in nitrogen fertilizer application rates over a series of agricultural fields located near the well The first study is a one year experiment designed to compare alternative nutrient management practices for corn. Combinations of fertilizer treatments with or without a legume cover crop (red clover) were assessed. The fertilizer treatments studied were: a polymer coated urea (slow-release fertilizer) applied at planting, a conventional urea applied at planting, side-dress treatment of a solution of urea and ammonium nitrate in water containing 28% nitrogen with two different application rates applied in the early summer, and a control. The legume cover crop was incorporated in the soil in the previous fall, and acts as a slow release fertilizer as nitrogen is made available to the following crop as the plants decompose. Treatments were compared based on crop yield, overall economic return, and the potential for nitrate leaching. The potential for nitrate leaching was evaluated with bi-weekly shallow soil core during the growing season, and deep soil cores taken before planting, after harvest and the following spring. The deep cores allowed changes in nitrate storage below the rooting zone to be assessed. The results of this study highlight the importance of timing of fertilizer applications and rate of fertilizer applications. Treatments which provide a delay in the release or application of fertilizer, the polymer-coated urea, the calculator-rate side-dress and the clover cover crop, were found to be advantageous. The polymer-coated urea treatments and side-dress treatments were found to reduce leaching compared to the conventional urea treatment. Treatments with the clover cover crops were not found to reduce crop yields or increase leaching potential, and lower fertilizer costs associated to this practice were found to have a positive economic effect. Plots treated with the high-rate side-dress fertilizer application lost more nitrate to the subsurface compared to the other treatment options, and an economic disadvantage was observed as yields did not compensate for higher fertilizer costs. The study highlights the advantages of the different treatments under study, which may be used to inform policy makers and farmers in the selection of economically and environmentally sustainable nutrient management BMP options. Groundwater monitoring at the site over the years has indentified interesting recharge dynamics, particularly in the vicinity of an ephemeral stream which develops annually during spring and winter melt events in a low lying area of the study site. It was hypothesized that rapid recharge could occur beneath the stream allowing for surface water to quickly reach groundwater, posing a threat to municipal water wells. The current framework of source water protection does not take into account the potential risk posed by this type recharge event. At this field site, rapid infiltration associated with this type of event may pose a risk to drinking water quality due to the proximity of the stream to the pumping wells and the nature of the aquifer. The second study examines rapid groundwater recharge processes beneath the ephemeral stream during the course of a spring melt in 2010. The goals of the study were to quantify recharge at one location beneath the stream and to assess whether temperature variations above the water table can be used as a tracer to reasonably estimate recharge during a short live recharge event. A novel housing for the temperature sensors was designed in order to deploy and position them into gravelly materials within the vadose zone, which reduced the potential for the formation of preferential pathways and permitted the retrieval of the sensors at a later date. Field data were collected during the course of the spring melt period from a network of groundwater monitoring wells and subsurface temperature sensors. Spatial and temporal changes in groundwater geochemistry, hydraulic head and temperature were were used to characterize recharge dynamics at the field site. Recharge beneath a segment of the ephemeral stream was quantified through the numerical analysis of the field data using Hydrus 1-D, a one-dimensional numerical model designed to simulate soil water flow and heat transport in variably saturated porous media. Site specific data were used to create the model domain, provide estimates of physical parameters, and to define initial and time variable boundary conditions. Model parameters were first calibrated by simulating periods where it was expected that soils would be gravity drained with minimal soil water flow, and then further refined by simulating the period when the ephemeral stream was present. A final set of parameters was determined, and the initial gravity drained conditions were re-simulated. The model was able to reproduce field observations under different flow scenarios using the final set of parameters, suggesting that the conceptual model and final model domain representative of the actual field conditions. The successful simulation of the field data sets under the different flow scenarios also increases confidence in the uniqueness of the model results. The model estimated that 0.15 m of recharge occurred beneath the instrumented site during the period between March 9th and March 22nd of 2010 when the ephemeral stream was present. This represents approximately a third of the expected total annual recharge for this location. Regional changes in hydraulic head, groundwater temperature and groundwater chemistry provided additional insight into the dynamic nature of the recharge process during the spring meld period and further illustrated the spatial variability of the aquifers’ response to the stream. The study found that the use of temperature as a tracer provided useful and quantifiable insight into recharge phenomena. The results of this study suggest that high rates of rapid recharge occur beneath the ephemeral stream, and are spatially variable. This type of focused infiltration that occurs during the spring melt may represent a risk to municipal water quality if the infiltrating waters are carrying contaminants.

碩士
國立臺灣科技大學
營建工程系
96
The interior spaces of most architectures are usually equipped with air-conditioning systems because of poor ventilation designs, but the air-conditioning system in modern buildings is a major energy-consumer. The purpose of this paper is to study the natural ventilation system in an indoor environment. Since most of activities of occupants happen in the lower layer of the space, the control of natural ventilation will focus on the temperature regulation of the lower space. This study discusses the relationship between different heat source heights and the indoor flow fields. Theoretical analysis based on the plume theory is derived to investigate the relationship between positions of point heat sources and indoor ventilation. Using a reduced-scale rectangular acrylic box and placing this acrylic model in an environment tank to simulate an indoor space in a constant environment. I change the vertical height of the heat source, and observe the corresponding indoor flow and temperature. In the experiments, I could estimate the indoor temperature, and determine the interface height when steady state attains. This study shows that the higher of the heat source position, the higher of the upper space temperature. The higher of the heat source position causes the lower exchange volume flux of the indoor space.