Дисертації з теми "Textile heat flux sensor"

Les enfants souffrants de la paralysie cérébrale éprouvent un stress psychologique important lors de la rééducation. Ceci est lié à de nombreux facteurs psychologiques comme la peur, l'anxiété et les phobies, et d'autres physiques tels que le poids des appareils de rééducation, leurs frottements sur le corps, et les douleurs liées aux problèmes de motricité. Dans l'état de l'art, il a été montré que les chercheurs ont suivi une approche utilisant les paramètres physiologiques comme bioindicateurs de stress. Ils utilisent principalement des biosignaux tels que la température cutanée, l'électrocardiographie (ECG), l'activité électrodermale (EDA), l'électromyographie (EMG), la respiration, le diamètre de la pupille, l'électroencéphalographie (EEG) pour l'évaluation du stress. Etant donné que les échanges thermiques et hydriques sont fonction de l'évolution de la température, ils peuvent également faire l'objet d'un indicateur de stress, d'autant plus qu'ils représentent un indicateur d'inconfort thermique. Pour cela, dans ce travail, un fluxmètre thermique textile, qui possède des caractéristiques de perméabilité, souplesse et conformité à être utilisé sur la peau, a été développé, analysé et caractérisé. Un dispositif expérimental a été mis en place afin d'établir un système de calibration de fluxmètre. Ensuite le comportement thermo-hydrique des fluxmètres a été analysé dans des conditions de laboratoire. Les fluxmètres thermiques textiles développés ont montré des sensibilités dans le même ordre de grandeur que le capteur étalon. De plus, l'étude des performances de fluxmètre a montré un comportement similaire à celle du capteur étalon. Par conséquent, des tests de stress ont été menés sur 20 volontaires adultes en bonne santé, de différentes tranches d'âges, et différents gendres, femmes et hommes, et sur deux enfants, de 7 ans et 12 ans, également en bonne santé. Trois différents types d'activité ont été réalisés pour provoquer le stress, à savoir, des activités mathématiques, des jeux de réalité virtuelle et une activité sportive. Cela a été dans l'objectif de stimuler différents types de stress, i.e. le stress positif (eustress), le stress négatif et le stress physique, respectivement. Les résultats des tests montrent un comportement similaire entre les deux fluxmètres (textile et étalon), et une corrélation positive entre le comportement de l'électrocardiogramme et celui du fluxmètre. Un lien a été établi dans la majorité des cas entre le retour des volontaires concernant le stress ressenti, et leurs réponse thermo-hydrique relevée par le fluxmètre thermique textile
Children with cerebral palsy experience significant psychological stress during rehabilitation. This is related to many psychological factors such as fear, anxiety and phobias, and physical factors such as the weight of the rehabilitation devices, their friction on the body, and the pain related to motor problems. In the state of art, it has been shown that researchers have followed an approach using physiological parameters as biomarkers of stress. They mainly use biosignals such as skin temperature (ST), electrocardiography (ECG), electrodermal activity (EDA), electromyography (EMG), respiration, pupil diameter, electroencephalography (EEG) for stress assessment. Since thermal and hydric exchanges are a function of temperature evolution, they can also be an indicator of stress, especially since they represent an indicator of thermal discomfort. For this purpose, in this work, a textile heat fluxmeter, which has characteristics of permeability, flexibility and suitability for use on the skin, has been developed, analyzed and characterized. An experimental device was set up in order to establish a calibration system of the fluxmeter. Then the thermo-hydric behavior of the fluxmeters was analyzed under laboratory conditions. The developed textile heat fluxmeter showed similar sensitivities as the gold standard sensor. Moreover, the study of the fluxmeter performance showed a similar behavior to that of the standard sensor. Therefore, stress tests were conducted on 20 healthy adult volunteers of different ages and genders, women and men, and on two children, 7 and 12 years old, also healthy. Three different types of activities were performed to induce stress, namely, mathematical activities, virtual reality games and a sports activity. This was with the objective of stimulating different types of stress, i.e. positive stress (eustress), negative stress and physical stress, respectively. The results of the tests show a similar behavior between the two fluxmeters (textile and standard), and a positive correlation between the behavior of the electrocardiogram and the fluxmeter. A relation was established in the majority of cases between the volunteers' feedback on the stress they felt and their thermo-hydric response measured by the textile heat fluxmeter

A novel method for measuring heat flux of boiling water is designed and built to study critical heat flux (CHF) and observe the response of a heat flux sensor when CHF occurs. A high temperature heat flux sensor is embedded in the wall of a pipe to get a direct measurement of the surface heat flux and sensor temperature. By submerging the pipe in water and applying a controlled heat flux to the inside diameter over the area where the sensor is located, boiling is created on the outer surface while measuring the heat flux. The heat flux is gradually increased up to CHF and the heat flux response is observed to determine if the heat flux sensor could sense CHF when it occurred. The heat flux sensor is able to consistently measure the value for CHF, which is approximately 510 kW/m" for this system. It is also observed during the experiments that the heat flux response undergoes an inflection of the heat transfer coefficient at a consistent temperature just before reaching CHF. This observed inflection caused the heat flux response to deviate from its cubic relationship with the temperature and drastically increase for a very small change in temperature. This inflection response can be used as an indication for approaching CHF and can also be used to approximate its value without prior knowledge of when it occurs.
Master of Science

The purpose of this study is to quantify the effects of heat flux sensor design and interaction with both test article material choice and geometry on heat flux measurements. It is the public domain component of a larger study documenting issues inherent in heat flux measurement. Direct and indirect heat flux measurement techniques were tested in three thermally diverse model materials at the same Mach 6 test condition, with a total pressure of 1200 psi and total temperature of 1188° R, and compared to the steady analytic Fay-Riddell solution for the stagnation heat flux on a hemisphere. A 1/8 in. fast response Schmidt-Boelter gage and a 1/16 in. Coaxial thermocouple mounted in ¾ in. diameter stainless steel, MACOR, and Graphite hemispheres were chosen as the test articles for this study. An inverse heat flux calculation was performed using the coaxial thermocouple temperature data for comparison with the Schmidt-Boelter gage. Before wind tunnel testing, the model/sensor combinations were tested in a radiative heat flux calibration rig at known static and dynamic heat fluxes from 1 to 20 BTU/ft2/s. During wind tunnel testing, the chosen conditions yielded stagnation point convective heat flux of 15-60 BTU/ft2/s, depending on the stagnation point wall temperature of the model. A computational fluid dynamic study with conjugate heat transfer was also undertaken to further study the complex mechanisms at work. The overall study yielded complex results that prove classic methodology for inverse heat flux calculation and direct heat flux measurement require more knowledge of the thermal environment than a simple match of material properties. Internal and external model geometry, spatial and temporal variations of the heat flux, and the level of thermal contact between the sensor and the test article can all result in a calculated or measured heat flux that is not correct even with a thermally matched sensor. The results of this study supported the conclusions of many previous studies but also examined the complex physics involved across heat flux measurement techniques using new tools, and some general guidance for heat flux sensor design and use, and suggestions for further research are provided.
Ph. D.

This effort is focused on the design, calibration, and implementation of a high temperature heat flux sensor for thermal systems research and testing. The High Temperature Heat Flux Sensor (HTHFS) was designed to survive in the harsh thermal environments typically encountered in hypersonic flight, combustion and propulsion research, and large-scale fire testing. The sensor is capable of continuous use at temperatures up to 1000 â ¦C. Two methods for steady-state calibration of the HTHFS at elevated temperatures have been developed as a result of this research. The first method employs a water-cooled heat flux sensor as a reference standard for the calibration. The second method utilizes a blackbody radiant source and a NIST calibrated optical pyrometer as the calibration standard. The HTHFS calibration results obtained from both methods compare favorably with the theoretical sensitivity versus temperature model. Implementation of the HTHFS in several types of transient thermal testing scenarios is also demonstrated herein. A new data processing technique is used to interpret the measurements made by the HTHFS. The Hybrid Heat Flux (HHF) method accounts for the heat flow through the sensor and the heat storage in the sensor, and thus renders the HTHFS virtually insensitive to the material on which it is mounted. The calibrated output of the HTHFS versus temperature ensures accuracy in the measurements made by the sensor at high operating temperatures.
Ph. D.

Heat flux gages are important in applications where measurement of the transfer of energy is more important than measurement of the temperature itself. There is a need for a heat flux sensor that can perform reliably for long periods of time in high temperature and high heat flux environment. The primary objective is to design and build a heat flux sensor that is capable of operating for extended periods of time in a high heat flux and high temperature environment. A High Temperature Heat Flux Sensor (HTHFS) was made by connecting 10 brass and steel thermocouple junctions in a thermopile circuit. This gage does not have a separate thermal resistance layer making it easier to fabricate. The HTHFS was calibrated in a custom-made convection calibration facility using a commercial Heat Flux Microsensor (HFM) as the calibration standard. The measured sensitivity of the HTHFS was 20.4 ±2.0ìV/(W/cm2). The measured sensitivity value matched with the theoretically calculated value of 20.5 ìV/(W/cm2). The average sensitivity of the HTHFS prototype was one-fifth of the sensitivity of a commercially available HFM. Better ways of mounting the HTHFS in the calibration stand have been recommended for future tests on the HTHFS for better testing. The HTHFS has the potential to be made into a microsensor with thousands of junctions added together in a thermopile circuit. This could lead to a heat flux sensor that could generate large signals (~few mV) and also be capable of operating in high heat flux and high temperature conditions.
Master of Science

Doutoramento em Engenharia Mecânica
The development of a new instrument for the measurement of convective and radiative is proposed, based on the transient operation of a transpiration radiometer. Current transpiration radiometers rely on steady state temperature measurements in a porous element crossed by a know gas mass flow. As a consequence of the porous sensing element’s intrinsically high thermal inertia, the instrument’s time constant is in the order of several seconds. The proposed instrument preserves established advantages of transpiration radiometers while incorporating additional features that broaden its applicability range. The most important developments are a significant reduction of the instrument’s response time and the possibility of separating and measuring the convective and radiative components of the heat flux. These objectives are achieved through the analysis of the instrument’s transient response, a pulsed gas flow being used to induce the transient behavior.
Propõe-se o desenvolvimento de um novo instrumento para medição de fluxos de calor convectivos e radiativos, baseado na operação de um radiómetro de transpiração em regime transitório. Os radiómetros de transpiração atuais baseiam-se em medições de temperatura em regime estacionário num elemento poroso atravessado por um caudal mássico gasoso conhecido. Como consequência da inércia térmica intrinsecamente elevada do elemento sensível poroso, a constante de tempo do instrumento é da ordem dos segundos. O instrumento proposto preservará as vantagens estabelecidas dos radiómetros de transpiração incorporando características adicionais que alargarão a gama de aplicabilidade. As novas características mais importantes serão uma redução significativa do tempo de resposta do instrumento e a possibilidade de medir separadamente as componentes radiativa e convectiva do fluxo de calor. Estes objetivos serão conseguidos através da análise da resposta transitória do instrumento, utilizando-se um caudal pulsado de gás para induzir o comportamento transitório.

In this study the flux attenuation due to sensor displacement has been investigated over sea using an extensive set of data from the "Ocean Horizontal Array Turbulence Study". All previous investigations of the flux attenuation have been performed over land.

A function developed for correcting fluxes in the homogenous surface layer was compared to measured flux attenuation. This investigation revealed the possibility to find new functions describing the flux attenuation when measurements are carried out over sea. From the measured flux attenuation studied here a change in the form of correction functions was required to improve the estimated flux loss. The most significant difference found in this report compared to the previous landbased study Horst (2006) is for stable conditions, where significantly less flux loss is found over sea. Two new functions describing the attenuation due to sensor displacement over sea have been constructed.

One of these expressions has a discontinuity at z/L = 0. This is supported by measured flux attenuation. A reasonable interpretation is; however, that this discontinuity is caused by two separate turbulence regimes near neutrality on the stable and unstable side respectively. The discontinuity is thus not believed to be an effect merely of stability. A second correction function which is continuous over all stabilities has therefore also been constructed. These two functions and the correction function from Horst (2006) have been compared to measured flux loss. Based on this comparison the continuous correction function is recommended for correcting scalar fluxes measured over sea. It should be noted, however, that this expression only describes the mean attenuation and has been constructed from measurements at 5 and 5.5 m above mean sea level.

The theoretical basis used in the development of the function for flux attenuation over land allows for a direct link between a spectral shape and the attenuation expression. This link has been preserved for the new expressions presented in this report. The spectral shape corresponding to the continuous correction function has been compared to measured mean cospectra and also to the cospectra from Horst (2006) corresponding to crosswind displacements.

At a height of 10 m and a sensor displacement of 0.2 m the mean flux attenuation is about 1.3-4% in the stability interval −1 < z/L < 1.5 when using the new correction functions presented in this report.

Technical challenges for developing micro sensors for Ultra High Temperature and turbine applications lie in that the sensors have to survive extremely harsh working conditions that exist when converting fuel to energy. These conditions include high temperatures (500-1500°C), elevated pressures (200-400 psi), pressure oscillations, corrosive environments (oxidizing conditions, gaseous alkali, and water vapors), surface coating or fouling, and high particulate loading. Several technologies are currently underdeveloped for measuring these parameters in turbine engines. One of them is an optical-based non-contact technology. However, these nondirective measuring technologies lack the necessary accuracy, at least at present state. An alternative way to measure these parameters without disturbing the working environments is using MEMS type sensors. Currently, the techniques under development for such harsh environment applications are silicon carbide (SiC) and silicon nitrite (Si3N4) –based ceramic MEMS sensors. But those technologies present some limitation such as narrow processing method, high cost (materials and processing cost), and limited using temperatures (typically < 800 C). In this research we propose to develop two sensors based on recently developed polymer-derived ceramics (PDCs): Constant Temperature Hot wire Anemometer, temperature/heat-flux sensor for turbine applications. PDC is a new class of high temperature ceramics. As we shall describe below, many unique features of PDCs make them particularly suitable for the proposed sensors, including: excellent thermo-mechanical properties at high temperatures, enable high temperature operation of the devices; various well-developed processing technologies, such as injection molding,photolithography, embossing, DRIE etching and precise machining, can be used for the fabrication of the devices; and tunable electric conductivity, enable the proposed sensors fabricated from similar materials, thus reliability considerations associated with thermal mismatch, which is a big concern when using MEMS-based sensors at elevated temperatures, will be minimized.
M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering

The mechanism by which convective heat transfer is augmented by freestream turbulence in the stagnation region was studied experimentally. Previous work has suggested that the primary mechanism for the observed augmentation is the amplification of vorticity into strong vortices which dominate the flow field near the surface. Therefore, two separate experimental investigations were performed to further study this phenomenon. In the first, the spatiotemporal convection from a heated surface was measured during the normal collision of a vortex ring. The convection was observed to increase dramatically in areas where vortices forced outer fluid through the natural convection boundary layer to the surface. Regions where fluid was swept along the surface experienced much smaller increases in convection. These observations led to the development of a mechanistic model which predicted the heat transfer based on the amount of time that fluid remained within the thermal boundary layer prior to reaching the surface. In subsequent testing, the model was able to accurately predict the time-resolved convection based solely on the transient properties of the vortex present. In the second investigation, the model was applied to the vortices which form in a stagnating turbulent flow. Three turbulence conditions were tested which changed the properties of the vortices produced. Again, the model was successful in predicting the time-resolved convection over much of the experimental measurement time. The work of designing and calibrating the heat flux sensor used is also reported. A new sensor was developed specifically for the convection research performed herein as no existing sensor possessed the required spatiotemporal resolution and underwater capabilities. Utilizing spot-welded foils of thermoelectric alloys resulted in a very robust and sensitive sensing array which was thoroughly analyzed and calibrated. In the final section, the hybrid heat flux (HHF) method is presented which significantly increases the performance of existing heat flux sensors. It is shown (both numerically and experimentally) that by combining the spatial and temporal temperature measurements from a standard sensor, the time response increases by up to a factor of 28. Also, this method causes the sensor to be insensitive to the material to which it is mounted.
Ph. D.

The experimental work involves calculation of radial distribution of heat transfer coefficient at the surface of a flat Aluminium plate being impinged by a turbulent flame jet. Heat transfer coefficient distribution at the surface is computed from the measured heat flux and temperature data using a reference method and a slope method. The heat transfer coefficient (h) has a nearly bell shaped radial distribution at the plate surface for H/d =3.3. The value of h drops by 37 % from r/d =0 to r/d= 2. Upon increasing the axial distance to H/d = 5, the stagnation point h decreased by 15%. Adiabatic surface temperature (AST) distribution at the plate surface was computed from the measured heat flux and temperature. AST values were found to be lower than the measured gas temperature values at the stagnation point. Radial distribution of gas temperature at the surface was estimated by least squares linear curve fitting through the convection dominated region of net heat flux data and was validated by experimental measurements with an aspirated thermocouple. For low axial distances (H/d =3.3), the gas temperature dropped by only 15 % from r/d = 0 to r/d = 2. Total heat flux distribution is separated into radiative and convective components with the use of calculated heat transfer coefficient and estimated gas temperatures. At H/d = 3.3, the radiation was found to be less than 25 % of the net heat flux for r/d ≤ 2.
Master of Science

La paramétrisation du transfert de chaleur par télédétection, basée sur le schéma SEBS, s'est déjà avérée très adaptée pour l'estimation de l'évapotranspiration (ET) sur des surfaces naturelles homogènes. Cependant, l'utilisation d'une telle méthode pour des paysages hétérogènes (e.g. régions semi-arides ou surfaces agricoles) est plus délicate, puisque le principe de la théorie de la similarité est compromis par la présence de différentes sources de chaleur et de hauteurs variées. Dans un premier temps, cette thèse a pour objectif de proposer et d'évaluer différents modèles basés sur la géométrie de la végétation qui permettent d'estimer la longueur de rugosité pour le transfert de quantité de mouvement à la surface (z0m), cette dernière étant un paramètre clé dans la caractérisation du transfert de chaleur. En revanche, une telle investigation ne peut être menée qu'à une petite échelle et à l'aide de données de télédétection très haute résolution permettant ainsi une description très détaillée de la surface. Ensuite, le second aspect de ce travail est de caractériser le transfert de chaleur dans le cas d'études régionales. Puis, la capacité de SEBS à estimer les flux de chaleur turbulents à de grandes échelles spatiales et temporelles sera évaluée. Pour ce faire, l’approche multi-échelle de SEBS (MSSEBS) a été implémentée afin de traiter une zone de 2,4 millions km2, incluant le Plateau du Tibet et l’amont des principaux fleuves d’Asie du sud-est. La combinaison de données horaires de température de surface FY-2 avec un rayonnement net journalier et des paramètres de surface avancés, permet de produire une série temporelle d’ET sur le Plateau du Tibet pour la période 2008-2010, et à une fréquence journalière
The parameterization of heat transfer by remote sensing, and based on SEBS scheme for turbulent heat fluxes retrieval, already proved to be very convenient for estimating evapotranspiration (ET) over homogeneous land surfaces. However, the use of such a method over heterogeneous landscapes (e.g. semi-arid regions or agricultural land) becomes more difficult, since the principle of similarity theory is compromised by the presence of different heat sources with various heights. This thesis aims at first to propose and evaluate some models based on vegetation geometry for retrieving the surface roughness length for momentum transfer (z0m), which is a key parameter in the characterization of heat transfer. Such an investigation can only be led at a small scale with very-high resolution remote sensing data, for a precise description of the land surface. Therefore, the second aspect of this work is to determine how to address the characterization of heat transfer for regional studies. Then, the reliability of SEBS for estimating turbulent heat fluxes at large spatial and temporal scales has been evaluated. To do so, the Multi-Scale SEBS approach (MSSEBS) has been implemented for a 2.4 million km2 area including the Tibetan Plateau and the headwaters of the major rivers of East and South Asia. The addition of gap-filled hourly FY-2 LST data to advanced daily averaged net radiation and land surface parameters, allows to compute time-series of land surface ET over the Tibetan Plateau during the period 2008-2010, and on a daily basis

Study of liquid film dynamics is of significant importance to the understanding and control of various industrial processes that involve spray cooling (condensation), heating (boiling), coating, cleaning and lubrication. For instance, the critical heat flux (CHF) of boiling heat transfer is one of the key parameters ensuring the efficiency and safety of nuclear power plants under both operational and accident conditions, which occurs as the liquid layers (microlayer and macrolayer) near the heater wall lose their integrity. However, an experimental quantification of thin liquid film dynamics is not straightforward, since the measurement at micro-scale is a challenge, and further complicated by the chaotic nature of boiling process. The object of present study is to develop experimental methods for the diagnosis of liquid film dynamics, and to obtain data for the film instability under various conditions. A dedicated test facility was designed and constructed where micro conductive probes and confocal optical sensors were used to measure the thickness and dynamic characteristics of a thin liquid film on various heater surfaces, while a high speed camera was used to get visual observation. Extensive tests were performed to calibrate and verify the two thickness measuring systems. The micro conductive measuring system was proven to have a high reliability and repeatability with maximum system error less than 5µm, while the optical measuring system is capable of recording the film dynamics with spatial resolution of less than 1 mm. The simultaneous measurement on the same liquid film shows that the two techniques are in a good agreement with respect to accuracy, but the optical sensors have a much higher acquisition rate up to 30 kHz, which are more suitable for rapid process. The confocal optical sensors were therefore employed to measure the dynamic thickness of liquid films (ethanol, hexane and water) evaporating on various horizontal heater surfaces (aluminum, copper, silicon, stainless steel and titanium) to investigate the influences of heat flux, the surface and liquid properties on the film instability and the critical thickness. The critical thickness of water film evaporating on various surfaces was measured in the range of 60-150 mm, increasing with the increased contact angle or increased heat flux (evaporating rate) and also with the decreased thermal conductivity of the heater material. The data suggest the conjugate heat transfer nature of the evaporating liquid film dynamics at higher heat fluxes of interest to boiling and burnout. In the case of hexane on the aged titanium surface with contact angle of ~3o, the liquid film is found resilient to rupture, with film oscillations at relatively large amplitude ensuing as the averaged film thickness decreases below 15 µm. To interpret our experimental findings on liquid film evolution and its critical thickness at rupture, a theoretical analysis is also performed to analyze the dynamics of liquid films evaporating on heater surfaces. While the influences of liquid properties, heat flux, and thermal conductivity of heater surface are captured by the simulation of the lubrication theory, influence of the wettability is considered via a minimum free energy criterion. The thinning processes of the liquid films are generally captured by the simulation of the lubrication theory. For the case with ideally uniform heat flux over the heater surface, the instability of the liquid film occurs at the thickness level of tens micro meters, while for the case of non-uniform heating, the critical thicknesses for the film rupture are closer to  the experimental data but still underestimated by the lubrication theory simulation. By introducing the minimum free energy criterion to considering the influence of surface wettability, the obtained critical thicknesses have a good agreement with the experimental ones for both titanium and copper surfaces, with a maximum deviation less than ±10%. The simulations also explain why the critical thickness on a copper surface is thinner than that on a titanium surface. It is because the good thermal conductivity of copper surface leads to uniform temperature distribution on the heat surface, which is responsible for the resilience of the liquid film to rupture. A silicon wafer with an artificial cavity fabricated by Micro Electronic Mechanical System (MEMS) technology was used as a heater to investigate the dynamics of a single bubble in both a thick and thin liquid layer under low heat flux (<60 kW/m2). The maximum departure diameter of an isolated bubble in a thick liquid film was measured to be 3.2 mm which is well predicted by the Fritz equation. However, in a thin liquid layer with its thickness less than the bubble departure diameter, the bubble was stuck on the heater surface with a dry spot beneath. A threshold thickness of the liquid film which enables the dry spot rewettable was obtained, and its value linearly increases with increasing heat flux. In addition, another test section was designed to achieve a constant liquid film flow on a titanium nano-heater surface which helps to successfully carry boiling in the liquid film from low heat flux until CHF. Again, the confocal optical sensor was employed to measure the dynamics of the liquid film on the heater surface under varied heat flux conditions.  A statistical analysis of the measured thickness signals that emerge in a certain period indicates three distinct liquid film thickness ranges: 0~50 µm as microlayer, 50~500 µm as macrolayer, 500~2500 µm as bulk layer. With increasing heat flux, the bulk layer disappears, and then the macrolayer gradually decreases to ~105 µm, beyond which instability of the liquid film may lose its integrity and CHF occurs. In addition, the high-speed camera was applied to directly visualize and record the bubbles dynamics and liquid film evolution. Dry spots were observed under some bubbles occasionally from 313 kW/m2 until CHF with the maximum occupation fraction within 5%.  A dry spot was rewetted either by liquid receding after the rupture of a bubble or by the liquid spreading from bubbles’ growth in the vicinity. This implies that the bubbles’ behavior (growth and rupture) and their interactions in particular are of paramount importance to the integrity of liquid film under nucleate boiling regime.
QC 20111205
VR-2005-5729, MSWI

En vue d'applications futures dans le domaine de la récupération d'énergie à basse température à partir de microsystèmes, la connaissance des transferts thermiques aux parois est d'une grande importance. Ces mesures sont réalisées à l'aide de capteurs spécifiques qui permettent de connaître le flux thermique total échangé entre la paroi sur laquelle ils sont installés et le milieu environnant. Cette étude se situe dans le cadre du développement de fluxmètres thermiques a gradient répondant aux contraintes liées aux machines thermiques de type micro-moteur Stirling. Six types de fluxmètres thermiques à sondes à résistance ont été développés à partir de différents matériaux, géométries et formes de capteurs. Une étude électrothermique, prenant en compte l'effet d'auto-échauffement, a été menée et validée expérimentalement. Les techniques de fabrication et de caractérisation, opérés majoritairement en salle blanche, ont permis de réaliser de nombreux capteurs à couches minces. Des supports spécifiques pour ces capteurs ont été développés. Ces capteurs de flux thermique, dont les résistances ont été étalonnées par rapport à une sonde de référence de haute précision, permettent également la mesure de la température. Pour mesurer la densité de flux thermique, deux méthodes ont été testées. La première méthode est indirecte : elle consiste à mesurer le gradient de température à l'aide de deux sondes à résistance en platine. La deuxième méthode est directe : elle repose sur un étalonnage en flux. Enfin, l'influence de l'intrusion des capteurs sur le répartition des flux thermiques dans la pièce à mesurer, avec ou sans support spécifique, a été étudiée
For future applications in the field of low-temperature energy have sting in microsystems, knowledge of wall heat transfer is of great importance. These measurements are carried out using specific sensors which makes possible to know the total heat flux exchanged between walls and the surrounding environment. This study concerns the development of a gradient heat flux sensor compliant with their requirements associated with thermal machines such as micrometric Stirling engines. Six types of heat flux sensor with resistance temperature detector have been developed from different materials, with various geometries and shapes of sensing elements. An electro thermal study, taking into account the self-heating effect, was carried out and experimentally validated. The fabrication and characterization techniques, mainly carried out in clean rooms, allowed to produce numerous thin-film sensors. Specific housings for these sensors have been developed. These heat flux sensors, whose resistances have been calibrated with a highly accurate reference probe, also allow measuring the temperature. To measure the heat flux density, two methods were tested. The first method is indirect : it consists in measuring the temperature gradient using two platinum resistance probes. The second method is direct : it is based on heat flux calibration. The calibration and measurement benches have been modeled. Then, the experimental and numerical results have been compared. Finally, the influence of the sensor intrusion on the thermal fluxes distribution in the investigated sample, with or without a specific housing, has been studied

Current methods for measuring energy flow rate in a pipe use a variety of invasive sensors, including temperature sensors, turbine flow meters, and vortex shedding devices. These systems are costly to buy and install. A new approach that uses non-invasive sensors that are easy to install and less expensive has been developed. A thermal interrogation method using heat flux and temperature measurements is used. A transient thermal model, lumped capacitance method LCM, before and during activation of an external heater provides estimates of the fluid heat transfer coefficient h and fluid temperature. The major components of the system are a thin-foil thermocouple, a heat flux sensor (PHFS), and a heater. To minimize the thermal contact resistance R" between the thermocouple thickness and the pipe surface, two thermocouples, welded and parallel, were tested together in the same set-up. Values of heat transfer coefficient h, thermal contact resistance R", time constant �[BULLET], and the water temperature �[BULLET][BULLET], were determined by using a parameter estimation code which depends on the minimum root mean square RMS error between the analytical and experimental sensor temperature values. The time for processing data to get the parameter estimation values is from three to four minutes. The experiments were done over a range of flow rates (1.5 gallon/minute to 14.5 gallon/minute). A correlation between the heat transfer coefficient h and the flow rate Q was done for both the parallel and the welded thermocouples. Overall, the parallel thermocouple is better than the welded thermocouple. The parallel thermocouple gives small average thermal contact resistance average R"=0.00001 (m2.�[BULLET][BULLET]/W), and consistence values of water temperature and heat transfer coefficient h, with good repeatability and sensitivity. Consequently, a non-invasive energy flow rate meter or (BTU) meter can be used to estimate the flow rate and the fluid temperature in real life.
MS

An ash monitoring system prototype that consists of a “clean” heat flux sensor and a “dirty” heat flux sensor was developed in this study. The “clean” heat flux sensor was studied numerically and experimentally while the “dirty” heat flux sensor was tested in the experiment. Two different measurement methods were applied on the “clean” sensor, one from the original study and one proposed in the present work. The new method required additional data processing procedures to be able to work in an on-line basis. Among the three data processing procedures developed in this study the central temperature difference procedure was found to be the most reliable one. Numerical results provided valuable information about the heat transfer pattern at the sensing element and also the performance of the sensor at high radiation heat flux levels. A rough calibration of both “clean” and “dirty” heat flux sensors was conducted experimentally. Nevertheless, the experimental results still served as a primary assessment for both sensors. Observed disagreements between the original study and the present one were probably caused by the modification of the sensor structure made in the present study. Sensitivity variation at high heat flux levels did not appear in the numerical results of either measurement method. Low overall sensor temperature change was believed to be the main reason as it meant less change in thermal properties of the sensing disc. Although the results of the study suggested that the proposed oscillation method was less attractive than the original one, it increased the possibility of resolving the surface characteristic variation problem that was considered crucial for the performances of the “clean” heat flux sensor regardless of the measurement method used.
Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-09-03 16:38:26.48

This work seeks to apply the novel heat flux sensor called as the Atomic Layer Thermopile to measure high frequency heat flux in high speed and high temperature flows found in Gas Turbine combustors. To achieve this the sensor must be able to survive the harsh environment of high temperature and high pressure. To have any confidence in our measurement, it is also imperative that there are tools available for precise estimation of the measurement uncertainty. This works strives to achieve these objectives by developing calibration techniques for uncertainty estimation using both exposure to radiation and in convective environments by calibrating against power input in steady state flow and transient heat flux calculated using wall temperature measurement. The response of the sensor is then investigated in high speed flows by measuring the heat flux inside a supersonic nozzle when exposed to shock waves. The shock waves are generated using a fast throttle valve located at the entrance of the supersonic nozzle by generating sudden rise in pressure. Lastly a numerical study is carried out to design a cooling system that will allow the sensor to survive in high temperature conditions of 1000°C while the sensor film is maintained at 50°C. A one-dimensional model is used to provide initial design parameters and then a two-dimensional axisymmetric conjugate CFD analysis is carried out to obtain the desired geometry that can meet the design conditions. A static structural analysis is also carried out on this geometry to ensure that it will be able to survive and avoid distortion under the operational pressure required for providing the desired coolant mass flow.

Atmospheric convection is sensitive to the nature of the surface and its temperature. Both dry (without cloud) and moist (with cloud) convections depend on the surface temperature. Surface temperature is of critical importance in several practical applications like human comfort and crop cultivation. In the climate change scenario too, variations in the surface temperature take the center stage. Therefore, prediction of surface temperature is important. The evolution of the temperature is governed by the energy equation and the surface temperature by the surface energy balance. Important components of the surface energy balance are radiation (incoming solar radiation, reflected solar radiation, incoming and outgoing longwave radiation), sensible and latent heat fluxes and heat flux into the ground (called ground heat flux). A large number of individual and collective observations have been carried out in the past to understand the atmospheric boundary layer and the surface energy budgets. However a major share of the observations is from mid-latitudes. There have been few experiments carried out in India, for example, MONTBLEX, LASPEX, etc. One common drawback among these experiments is that the data time series is discontinuous and continuous measurements covering an entire season are lacking. Moreover these measurements were not comprehensive and hence did not allowed to calculate complete surface energy balance – in some cases radiation data is not available while in some humidity data. Therefore, continuous time series of sufficient duration and covering all variables needed to look at the seasonal energy balance based on measurements alone is missing in the Indian context. New programmes with the main objective of predicting convection are being planned in India. For example, PROWNAM (Prediction of Regional Weather with Observational Meso-Network and Atmospheric Modeling) is aimed at predicting the short term weather at SHAR and STORM (Severe Thunderstorms – Observations and Regional Modeling) aims to predict the occurrence of severe thunderstorms in the northeastern India. In both these programmes, measurement of all components of surface energy balance is one of the main objectives. However, the minimum configuration and data accuracy requirements for the flux towers, sensitivity of computed fluxes on data accuracy have not been carefully evaluated. This thesis is aimed at filling this gap. As a part of my work, a 10 m high micrometeorological tower was installed in an open area within the Indian Institute of Science (IISc) Air Field. Temperature, relative humidity and wind speed and direction instruments were mounted at two levels, 2 m and 8 m. All components of radiation were measured. Data, sampled every 5 s and averaged for 2 minutes were continuously stored, starting May 2006 onwards. Soil temperature was measured at 4 depths, 5 cm, 10 cm, 15 cm and 20 cm. In addition, a sonic anemometer capable of measuring 3 components of velocity and air temperature was installed at 2 m height, and data was collected for more than a month to enable the calculation of momentum and buoyancy fluxes using the Eddy correlation method (ECM). The present work evaluated the sensitivity of the fluxes for small calibration errors and quantified the minimum data accuracies and configuration needed for flux measurement with the Profile method (PM). After applying corrections, the comparison of fluxes from PM and ECM are in good agreement. The complete long-term surface energy balances is calculated in terms of source and sink. One aspect that emerges from the observation is that the seasonal variation in the sink term is relatively small (150-170 Wm-2) whereas the source term shows much larger variation from 180-250 Wm-2. A method has been implemented by which the ground surface temperature can be estimated by using the subsurface temperature timeseries by the method of Fourier decomposition and using the Fourier heat conduction equation. In addition we can compute the thermal diffusivity of the soil by using the amplitude and phase information of the sub-surface soil time series. The estimated temperatures from this method and one that estimated from radiation method are in good agreement with the maximum difference being less than 0º C.

Atmospheric convection is sensitive to the nature of the surface and its temperature. Both dry (without cloud) and moist (with cloud) convections depend on the surface temperature. Surface temperature is of critical importance in several practical applications like human comfort and crop cultivation. In the climate change scenario too, variations in the surface temperature take the center stage. Therefore, prediction of surface temperature is important. The evolution of the temperature is governed by the energy equation and the surface temperature by the surface energy balance. Important components of the surface energy balance are radiation (incoming solar radiation, reflected solar radiation, incoming and outgoing longwave radiation), sensible and latent heat fluxes and heat flux into the ground (called ground heat flux). A large number of individual and collective observations have been carried out in the past to understand the atmospheric boundary layer and the surface energy budgets. However a major share of the observations is from mid-latitudes. There have been few experiments carried out in India, for example, MONTBLEX, LASPEX, etc. One common drawback among these experiments is that the data time series is discontinuous and continuous measurements covering an entire season are lacking. Moreover these measurements were not comprehensive and hence did not allowed to calculate complete surface energy balance – in some cases radiation data is not available while in some humidity data. Therefore, continuous time series of sufficient duration and covering all variables needed to look at the seasonal energy balance based on measurements alone is missing in the Indian context. New programmes with the main objective of predicting convection are being planned in India. For example, PROWNAM (Prediction of Regional Weather with Observational Meso-Network and Atmospheric Modeling) is aimed at predicting the short term weather at SHAR and STORM (Severe Thunderstorms – Observations and Regional Modeling) aims to predict the occurrence of severe thunderstorms in the northeastern India. In both these programmes, measurement of all components of surface energy balance is one of the main objectives. However, the minimum configuration and data accuracy requirements for the flux towers, sensitivity of computed fluxes on data accuracy have not been carefully evaluated. This thesis is aimed at filling this gap. As a part of my work, a 10 m high micrometeorological tower was installed in an open area within the Indian Institute of Science (IISc) Air Field. Temperature, relative humidity and wind speed and direction instruments were mounted at two levels, 2 m and 8 m. All components of radiation were measured. Data, sampled every 5 s and averaged for 2 minutes were continuously stored, starting May 2006 onwards. Soil temperature was measured at 4 depths, 5 cm, 10 cm, 15 cm and 20 cm. In addition, a sonic anemometer capable of measuring 3 components of velocity and air temperature was installed at 2 m height, and data was collected for more than a month to enable the calculation of momentum and buoyancy fluxes using the Eddy correlation method (ECM). The present work evaluated the sensitivity of the fluxes for small calibration errors and quantified the minimum data accuracies and configuration needed for flux measurement with the Profile method (PM). After applying corrections, the comparison of fluxes from PM and ECM are in good agreement. The complete long-term surface energy balances is calculated in terms of source and sink. One aspect that emerges from the observation is that the seasonal variation in the sink term is relatively small (150-170 Wm-2) whereas the source term shows much larger variation from 180-250 Wm-2. A method has been implemented by which the ground surface temperature can be estimated by using the subsurface temperature timeseries by the method of Fourier decomposition and using the Fourier heat conduction equation. In addition we can compute the thermal diffusivity of the soil by using the amplitude and phase information of the sub-surface soil time series. The estimated temperatures from this method and one that estimated from radiation method are in good agreement with the maximum difference being less than 0º C.