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Статті в журналах з теми "Thermo-diffusion system"
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Krehel, Oleh, Toyohiko Aiki, and Adrian Muntean. "Homogenization of a thermo-diffusion system with Smoluchowski interactions." Networks & Heterogeneous Media 9, no. 4 (2014): 739–62. http://dx.doi.org/10.3934/nhm.2014.9.739.
Повний текст джерела
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Sohail, Muhammad, Umair Ali, Fatema Tuz Zohra, Wael Al-Kouz, Yu-Ming Chu, and Phatiphat Thounthong. "Utilization of updated version of heat flux model for the radiative flow of a non-Newtonian material under Joule heating: OHAM application." Open Physics 19, no. 1 (January 1, 2021): 100–110. http://dx.doi.org/10.1515/phys-2021-0010.
Повний текст джерелаАнотація:
Abstract This study reports the thermal analysis and species transport to manifest non-Newtonian materials flowing over linear stretch sheets. The heat transfer phenomenon is presented by the Cattaneo–Christov definition of heat flux. Mass transportation is modeled using traditional Fick’s second law. In addition, the contribution of Joule heating and radiation to thermal transmission is also considered. Thermo-diffusion and diffusion-thermo are significant contributions involved in thermal transmission and species. The physical depiction of the scenario under consideration is modeled through the boundary layer approach. Similar analysis has been made to convert the PDE model system into the respective ODE. Then, the transformed physical expressions are calculated for momentum, thermal, and species transport within the boundary layer. The reported study is a novel contribution due to the combined comportment of thermal relaxation time, radiation, Joule heating, and thermo-diffusion, which are not yet explored. Several engineering systems are based on their applications and utilization.
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Hamid, R. A., W. M. K. A. Wan Zaimi, N. M. Arifin, N. A. A. Bakar, and B. Bidin. "Thermal Diffusion and Diffusion Thermo Effects on MHD Thermosolutal Marangoni Convection Boundary Layer Flow over a Permeable Surface." Journal of Applied Mathematics 2012 (2012): 1–14. http://dx.doi.org/10.1155/2012/750939.
Повний текст джерелаАнотація:
The problem of thermal diffusion and diffusion thermo effects on thermosolutal Marangoni convection flow of an electrically conducting fluid over a permeable surface is investigated. Using appropriate similarity transformations, the governing system of partial differential equation is transformed to a set of nonlinear ordinary differential equations, then solved numerically using the Runge-Kutta-Fehlberg method. The effects of thermal diffusion and diffusion thermo, magnetic field parameter, thermosolutal surface tension ratio, and suction/injection parameter on the flow field, heat transfer characteristic, and concentration are thoroughly examined. Numerical results are obtained for temperature and concentration profiles as well as the local Nusselt and Sherwood numbers are presented graphically and analyzed. It is found that these governing parameters affect the variations of the temperature and concentration and also the local Nusselt and Sherwood numbers.
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Martuzans, B., and Yu Skryl. "Numerical Simulation of Charge Transfer in Shocked Silicon at low Pressure." Latvian Journal of Physics and Technical Sciences 45, no. 4 (January 1, 2008): 33–46. http://dx.doi.org/10.2478/v10047-008-0018-2.
Повний текст джерелаАнотація:
Numerical Simulation of Charge Transfer in Shocked Silicon at low PressureA numerical method for simulation of electron and hole diffusion in silicon in the temperature gradient created by the shock load is developed. To analyze the transfer process, a complete system of electro-thermo-diffusion equations for charge carriers was solved based on the Poisson equation. The numerical solution was obtained using the difference methods developed for semiconductor devices. The comparison of the experimental results with the numerical calculation shows a good correlation, which means that the thermo-diffusion of charge carriers in the shock wave front is the main factor responsible for polarization in the shocked silicon.
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Khan, Sohail A., and Tasawar Hayat. "Entropy Analysis for Hydromagnetic Darcy–Forchheimer Flow Subject to Soret and Dufour Effects." Mathematical and Computational Applications 27, no. 5 (September 19, 2022): 80. http://dx.doi.org/10.3390/mca27050080.
Повний текст джерелаАнотація:
Here, our main aim is to examine the impacts of Dufour and Soret in a radiative Darcy–Forchheimer flow. Ohmic heating and the dissipative features are outlined. The characteristics of the thermo-diffusion and diffusion-thermo effects are addressed. A binary chemical reaction is deliberated. To examine the thermodynamical system performance, we discuss entropy generation. A non-linear differential system is computed by the finite difference technique. Variations in the velocity, concentration, thermal field and entropy rate for the emerging parameters are scrutinized. A decay in velocity is observed for the Forchheimer number. Higher estimation of the magnetic number has the opposite influence for the velocity and temperature. The velocity, concentration and thermal field have a similar effect on the suction variable. The temperature against the Dufour number is augmented. A decay in the concentration is found against the Soret number. A similar trend holds for the entropy rate through the radiation and diffusion variables. An augmentation in the entropy rate is observed for the diffusion variable.
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KHAN, SHEIKH IRFANULLAH, SYED TAUSEEF MOHYUD-DIN, and BANDAR BIN-MOHSIN. "THERMO-DIFFUSION AND DIFFUSO-THERMO EFFECTS ON MHD SQUEEZING FLOW BETWEEN PARALLEL DISKS." Surface Review and Letters 24, no. 02 (January 30, 2017): 1750022. http://dx.doi.org/10.1142/s0218625x17500226.
Повний текст джерелаАнотація:
In this article, Magnetohydrodynamic (MHD) squeezing flow between two parallel disks is considered. The upper disk is taken to be solid and the lower one is permeable. Soret and Dufour effects are measured to explore the thermal-diffusion and diffusion-thermo effects. Governing PDEs are converted into system of ODEs with the support of suitable similarity transforms. Homotopy analysis method (HAM) has been employed to obtain the expressions for velocity, temperature and concentration profiles. Effects of different emerging parameters such as squeezing number [Formula: see text], Hartman number [Formula: see text], Prandtl number Pr, Eckert number Ec, dimensionless length [Formula: see text] and Schmidt number Sc on the flow are also discussed with the help of graphs for velocity, temperature and concentration. The local Nusselt and Sherwood numbers along with convergence of the series solutions are presented with the help of graphs. From the results obtained, we observed that the physical quantities like skin friction coefficient increases with increasing value of Hartmann number [Formula: see text] in the blowing case [Formula: see text] whereas a fall is observed in the suction case [Formula: see text]. However, the rate of heat transfer at upper wall increases with increasing values of Dufour number Du and Soret number Sr for both the suction [Formula: see text] and blowing flow [Formula: see text], whereas, for the larger values of Dufour number Du and smaller values of Soret number Sr, a rapid fall is observed in Sherwood number Sh for both the suction [Formula: see text] and blowing [Formula: see text] cases. A numerical solution is obtained by employing Runge–Kutta method of order four (RK-4) to check the validity and reliability of the developed algorithm. A well agreement is found between both the solutions.
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Pochiraju, K. V., and G. P. Tandon. "Modeling Thermo-Oxidative Layer Growth in High-Temperature Resins." Journal of Engineering Materials and Technology 128, no. 1 (August 1, 2005): 107–16. http://dx.doi.org/10.1115/1.2128427.
Повний текст джерелаАнотація:
This paper describes modeling of degradation behavior of high-temperature polymers under thermo-oxidative aging conditions. Thermo-oxidative aging is simulated with a diffusion-reaction model in which temperature, oxygen concentration, and weight-loss effects are considered. A parametric reaction model based on a mechanistic view of the reaction is used for simulating reaction-rate dependence on the oxygen availability in the polymer. Macroscopic weight-loss measurements are used to determine the reaction and polymer consumption parameters. The diffusion-reaction partial differential equation system is solved using Runge-Kutta methods. Simulations illustrating oxidative layer growth in a high-temperature PMR-15 polyimide resin system under isothermal conditions are presented and correlated with experimental observations of oxidation layer growth. Finally, parametric studies are conducted to examine the sensitivity of material parameters in predicting oxidation development.
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Aouadi, Moncef, and Alberto Castejón. "Properties of global and exponential attractors for nonlinear thermo-diffusion Timoshenko system." Journal of Mathematical Physics 60, no. 8 (August 2019): 081503. http://dx.doi.org/10.1063/1.5066224.
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Khan, Najeeb Alam, Shahnila Aziz, and Saif Ullah. "Entropy Generation on MHD Flow of Powell-Eyring Fluid Between Radially Stretching Rotating Disk with Diffusion-Thermo and Thermo-Diffusion Effects." Acta Mechanica et Automatica 11, no. 1 (March 1, 2017): 20–32. http://dx.doi.org/10.1515/ama-2017-0004.
Повний текст джерелаАнотація:
Abstract An investigation is performed for an alyzing the effect of entropy generation on the steady, laminar, axisymmetric flow of an incompressible Powell-Eyring fluid. The flow is considered in the presence of vertically applied magnetic field between radially stretching rotating disks. The Energy and concentration equation is taking into account to investigate the heat dissipation, Soret, Dufour and Joule heating effects. To describe the considered flow non-dimensionalized equations, an exact similarity function is used to reduce a set of the partial differential equation into a system of non-linear coupled ordinary differential equation with the associated boundary conditions. Using homotopy analysis method (HAM), an analytic solution for velocity, temperature and concentration profiles are obtained over the entire range of the imperative parameters. The velocity components, concentration and temperature field are used to determine the entropy generation. Plots illustrate important results on the effect of physical flow parameters. Results obtained by means of HAM are then compared with the results obtained by using optimized homotopy analysis method (OHAM). They are in very good agreement.
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Sheri, Siva Reddy, Chamkha Ali. J., and Anjan Kumar Suram. "Thermal-diffusion and diffusion-thermo effects on MHD natural convective flow through porous medium in a rotating system with ramped temperature." International Journal of Numerical Methods for Heat & Fluid Flow 27, no. 11 (November 6, 2017): 2451–80. http://dx.doi.org/10.1108/hff-09-2016-0349.
Повний текст джерелаАнотація:
Purpose The purpose of this paper is to analyze the thermal-diffusion and diffusion-thermo effects on magnetohydrodynamics (MHD) natural convective flow through porous medium in a rotating system with ramped temperature. Design/methodology/approach Using the non-dimensional variables, the flow governing equations along with corresponding initial and boundary conditions have been transformed into non-dimensional form. These non-dimensional partial differential equations are solved by using finite element method. This method is powerful and stable. It provides excellent convergence and flexibility in providing solutions. Findings The effects of Soret number, Dufour number, rotation parameter, magnetic parameter, Hall current parameter, permeability parameter, thermal Grashof number, solutal Grashof number, Prandtl number, thermal radiation parameter, heat absorption parameter, Schmidt number, chemical reaction parameter and time on the fluid velocities, temperature and concentration are represented graphically in a significant way and the influence of pertinent flow governing parameters on the skin frictions and Nusselt number are presented in tabular form. On the other hand, a comparison for validation of the numerical code with previously published work is performed, and an excellent agreement is observed for the limited case existing literature. Practical implications A very useful source of information for researchers on the subject of MHD flow through porous medium in a rotating system with ramped temperature. Originality/value The problem is moderately original, as it contains many effects like thermal-diffusion (Soret) and diffusion-thermo (Dufour) effects and chemical reaction.
Дисертації з теми "Thermo-diffusion system"
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VO, ANK KHOA. "Corrector homogenization estimates for PDE Systems with coupled fluxes posed in media with periodic microstructures." Doctoral thesis, Gran Sasso Science Institute, 2018. http://hdl.handle.net/20.500.12571/9693.
Повний текст джерелаАнотація:
The purpose of this thesis is the derivation of corrector estimates justifying the upscaling
of systems of partial differential equations (PDEs) with coupled fluxes posed in media with
microstructures (like porous media). Such models play an important role in the understanding of, for example, drug-delivery mechanisms, where the involved chemical species
diffusing inside the domain are assumed to obey perhaps other transport mechanisms and
certain non-dissipative nonlinear processes within the pore space and at the boundaries of
the perforated media (e.g. interaction, chemical reaction, aggregation, deposition). In this
thesis, our corrector estimates provide a quantitative analysis in terms of convergence rates
in suitable norms, i.e. as the small homogenization parameter tends to zero, the differences
between the micro- and macro-concentrations and between the corresponding micro- and
macro-concentration gradients are controlled in terms of the small parameter. As preparation, we are first concerned with the weak solvability of the microscopic models as well as
with the fundamental asymptotic homogenization procedures that are behind the derivation
of the corresponding upscaled models. We report results on three connected mathematical
problems:
1. Asymptotic analysis of microscopic semi-linear elliptic equations/systems. We explore the
asymptotic analysis of a prototype model including the interplay between stationary diffusion and both surface and volume chemical reactions in porous media. Our interest
lies in deriving homogenization limits (upscaling) for alike systems, and particularly, in
justifying rigorously the obtained averaged descriptions. We prove the well-posedness
of the microscopic problem ensuring also the positivity and boundedness of the involved concentrations. Then we use the structure of the two-scale expansions to derive
corrector estimates delimitating quantitatively the convergence rate of the asymptotic
approximates to the macroscopic limit concentrations and their gradients. High-order
corrector estimates are also obtained. The semi-linear auxiliary problems are tackled
by a fixed-point homogenization argument. Our techniques include also Moser-like iteration techniques, a variational formulation, two-scale asymptotic expansions as well
as suitable energy estimates.
2. Corrector estimates for a Smoluchowski-Soret-Dufour model. We consider a thermodiffusion system, which is a coupled system of PDEs and ODEs that account for the
heat-driven diffusion dynamics of hot colloids in periodic heterogeneous media. This
model describes the joint evolution of temperature and colloidal concentrations in a
saturated porous tissue where the Smoluchowski interactions for aggregation process
and a linear deposition process take place. By a fixed-point argument, we prove the
local existence and uniqueness results for the upscaled system. To obtain the corrector
estimates, we exploit the concept of macroscopic reconstructions as well as suitable
integral estimates to control boundary interactions.
3. Corrector estimates for a non-stationary Stokes-Nernst-Planck-Poisson system. We investigate a non-stationary Stokes-Nernst-Planck-Poisson system posed in a perforated domain as originally proposed by Knabner and his co-authors (see e.g. [98] and [99]).
Starting off with the setting from [99], we complete the results by proving corrector estimates for the homogenization procedure. Main difficulties are connected to the choice
of boundary conditions for the Poisson part of the system as well as with the scaling of
the Stokes part of the system.
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Řezníček, Michal. "Optimalizovaný termodynamický senzor na bilančním principu." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-217235.
Повний текст джерелаЧастини книг з теми "Thermo-diffusion system"
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De Pascalis, Lorenzo, Giuseppe Starace, and Federica Carluccio. "The Diffusion Absorption Refrigerator Operation and Performance." In Handbook of Research on Advances and Applications in Refrigeration Systems and Technologies, 36–84. IGI Global, 2015. http://dx.doi.org/10.4018/978-1-4666-8398-3.ch002.
Повний текст джерелаАнотація:
This chapter focuses on the Diffusion Absorption Refrigerator (DAR) cycle and describes a new advanced thermodynamic model which allows good predictions of the chiller performance in terms of efficiency and cooling capacity, starting from a precise evaluation of the thermo-physical properties of the working mixture at each point of the circuit. A steady state thermodynamic analytical model of the thermal pump driving the DAR is also included. In addition, the experimental validation of the model, performed on a prototype built coupling a domestic 750 W-magnetron with a small purposely modified commercial DAR to activate the thermal pump, is here included: a maximum mismatch of 2.32% in the weak mixture mass flow rate and lower than 5% in COP between the predicted and measured data were found.
Тези доповідей конференцій з теми "Thermo-diffusion system"
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Geng, Wenguang, Baoming Chen, Maocheng Tian, and Fang Liu. "Numerical Study of Heat and Mass Transfer by Laminar and Turbulent Natural Convection With Cross Diffusion Effects in Square Cavity." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-68678.
Повний текст джерелаАнотація:
Laminar and turbulent natural convection flow in a two-dimensional square cavity filled two component system with compensating horizontal thermal and solute concentration gradients is investigated in this paper. The temperature gradient and volatile organic compounds (VOCs) concentration gradient are kept uniform in horizontal direction, while horizontal surfaces are kept adiabatic and impermeable within a square cavity. According to the principle of irreversible thermodynamics, with thermal-diffusion (Soret) effect and diffusion-thermo (Dufour) effect, a commercial computational fluid dynamics (Fluent) code is used to simulate heat and mass transfer numerically in present work. After validation of the method with available measurements, the range of the cross diffusion coefficients are analyzed firstly. Furthermore, the thermal field and solute concentration fields are presented for various conditions. Finally, the average Nusselt number and Sherwood number at the vertical wall are presented graphically. The numerical results show that the present work would help to know about the convective diffusion and distribution of VOCs indoor environment accurately. Also, it gives the more accurate characteristics of heat and mass transfer in multi-component system with cross diffusion effects.
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Magri, Luca, and Matthew P. Juniper. "A Novel Theoretical Approach to Passive Control of Thermo-Acoustic Oscillations: Application to Ducted Heat Sources." In ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-94344.
Повний текст джерелаАнотація:
In this paper, we develop a linear technique that predicts how the stability of a thermo-acoustic system changes due to the action of a generic passive feedback device or a generic change in the base state. From this, one can calculate the passive device or base state change that most stabilizes the system. This theoretical framework, based on adjoint equations, is applied to two types of Rijke tube. The first contains an electrically-heated hot wire and the second contains a diffusion flame. Both heat sources are assumed to be compact so that the acoustic and heat release models can be decoupled. We find that the most effective passive control device is an adiabatic mesh placed at the downstream end of the Rijke tube. We also investigate the effects of a second hot wire and a local variation of the cross-sectional area but find that both affect the frequency more than the growth rate. This application of adjoint sensitivity analysis opens up new possibilities for the passive control of thermo-acoustic oscillations. For example, the influence of base state changes can be combined with other constraints, such as that the total heat release rate remains constant, in order to show how an unstable thermo-acoustic system should be changed in order to make it stable.
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Graham, Owen, Nicholas Magina, A. J. Wickersham, Fei Han, Sebastiano Sorato, and Sven Bethke. "Thermo-Acoustic Analysis of a Realistic Liquid-Fueled GT Combustor." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91547.
Повний текст джерелаАнотація:
Abstract Thermo-acoustic instabilities are an important consideration in the design of modern power generation gas turbine combustors. While the design process must consider many competing requirements, such as temperature profiles, emissions, robustness to auto-ignition and flameholding, thermoacoustics is one of the most challenging to predict, and therefore design for. This is particularly true in the case of liquid-fueled systems, where the phenomenon results from a complex system of coupled multi-physics phenomena: fuel atomization and transport, mixing, reactive kinetics and acoustics. Nevertheless, emissions-compliant liquid fuel capability is becoming increasingly important to GT operators, thus it is critical to be able to predict the thermoacoustic instabilities of these combustors. In this work we present an approach to model the thermoacoustic feedback loop for a realistic liquid fuel nozzle in a single burner configuration. The approach is based on an analytical liquid-fuel diffusion flame model to provide the fluctuating heat release response to inflow perturbations. This is coupled with a 3D FEM description of the acoustic response of the single burner rig through a time-domain Green’s function model to predict the growth and saturation of pressure oscillations. The necessary flame model parameters are calibrated based on a range of test data obtained from the single burner rig with a tunable combustor length. The results are shown to compare well with test data across a range of operating conditions, and for two different nozzle geometries.
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Clark, J. W. G., D. G. McCartney, H. Saghafifar, and P. H. Shipway. "Modelling Chemical and Microstructural Evolution Across Dissimilar Interfaces in Power Plants." In ASME 2014 Power Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/power2014-32242.
Повний текст джерелаАнотація:
Dissimilar metal welds between different grades of ferritic steels or between ferritic steel and austenitic nickel alloys are used extensively in power plants. When such weldments are exposed to high temperature conditions, as might be found in service in a thermal power plant, local microstructural evolution will occur. This is due to diffusion, driven by chemical potential gradients, of solute atoms. Such diffusion can cause major changes in hardness and mechanical properties of joints and can lead to the formation of embrittling phases and/or softened zones. This can potentially lead to premature component failure by, for example, high temperature creep. Whilst finite element modelling of mechanical behavior and damage evolution is well established this is not the case for chemical diffusion and microstructural evolution at weld interfaces. In the present study, the general purpose linked thermodynamic and kinetic software packages Thermo-Calc and DICTRA have been applied to simulate chemical diffusion and precipitation/dissolution (i.e. phase fraction evolution) in dissimilar weld joints using commercially available thermodynamic databases TCFE7 and TTNI6. Two approaches for modelling multiphase, multicomponent systems using this software will be presented and discussed and their implementation will be illustrated. The paper will present results on modelling a range of dissimilar metal interfaces of both the ferritic-ferritic type and the ferritic-austenitic type (for example, grade 22 to grade 91 steel and grade 22 to Inconel 625). Ferritic-ferritic case studies will compare model predictions with a number of previously published experimental studies and it will be shown that the current approach can give good quantitative agreement in terms of carbon composition profiles and carbide depleted/carbide enriched zones. The results obtained from modelling a grade 22 steel-Inconel 625 system where the crystal structure of the matrix is different on either side of the weld will be compared with experimental observations on a weld overlaid tube component. The experimental results will include scanning and transmission electron microscopy studies of the weld interface regions and it will be shown that the predictions of diffusion and precipitate formation compare well with observations made experimentally following exposure at 650 °C. Also discussed are the options for further refining the computational model based on empirically observed phenomena, such as the unmixed zone of a weld.
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Fyrigos, Iosif-Angelos, Theodoros Panagiotis Chatzinikolaou, Vasileios Ntinas, Stavros Kitsios, Panagiotis Bousoulas, Michail-Antisthenis Tsompanas, Dimitris Tsoukalas, Andrew Adamatzky, Antonio Rubio, and Georgios Ch Sirakoulis. "Compact Thermo-Diffusion based Physical Memristor Model." In 2022 IEEE International Symposium on Circuits and Systems (ISCAS). IEEE, 2022. http://dx.doi.org/10.1109/iscas48785.2022.9937925.
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Kruizenga, Alan, Mark Anderson, Roma Fatima, Michael Corradini, Aaron Towne, and Devesh Ranjan. "Heat Transfer of Supercritical Carbon Dioxide in Printed Circuit Heat Exchanger Geometries." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22880.
Повний текст джерелаАнотація:
The increasing importance of improving efficiency and reducing capital costs has lead to significant work studying advanced Brayton cycles for high temperature energy conversion. Using compact, highly efficient, diffusion-bonded heat exchangers for the recuperators, has been a noteworthy improvement in the design of advanced carbon dioxide Brayton Cycles. These heat exchangers will operate near the pseudocritical point of carbon dioxide, making use of the drastic variation of the thermo-physical properties. This paper focuses on the experimental measurements of heat transfer under cooling conditions, as well as pressure drop characteristics within a prototypic printed circuit heat exchanger. Studies utilize type-316 stainless steel, nine channel, semi-circular test section, and supercritical carbon dioxide serves as the working fluid throughout all experiments. The test section channels have a hydraulic diameter of 1.16mm and a length of 0.5m. The mini-channels are fabricated using current chemical etching technology, emulating techniques used in current diffusion bonded printed circuit heat exchanger manufacturing. Local heat transfer values were determined using measured wall temperatures and heat fluxes over a large set of experimental parameters that varied system pressure, inlet temperature, and mass flux. Experimentally determined heat transfer coefficients and pressure drop data are compared to correlations and earlier data available in literature. Modeling predictions using the CFD package FLUENT are included to supplement experimental data. All nine channels were modeled using known inlet conditions and measured wall temperatures as boundary conditions. The FLUENT results show excellent agreement in total power removal for the near pseudocritical region, as well as regions where carbon dioxide is a high or low density fluid.
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Som, Abhijit. "Generalized Reynolds Analogy: An Engineering Prospective of Thermo-Fluid Physics for Heat Exchanger Design." In ASME 2021 Power Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/power2021-65820.
Повний текст джерелаАнотація:
Abstract In practical interest of Reynolds analogy for power and process industries, in a unified system approach an engineering prospective of thermo-fluid physics has been proposed by developing a theory of basic heat exchanger design and analysis. Needless to mention of excellent books on heat exchangers, this paper focuses on the novelty of heat exchanger, which in author’s view depends upon the possibility of energy exchange between two fluid streams at different temperatures. Since operation cannot be random, the principal act of design is to engineer a product such that it operates in specified manner to perform its desired function of de-energizing one stream by virtue of energizing the other. With law of the integral as the guiding principle of physics, it shall be made clear that energy exchange in the form of heat must be accompanied by energy transfer such that heat exchanger must operate due to simultaneous process of cooling and heating of the fluid streams with an intervening medium. To unlock the secret of steady operation a fundamental postulate concerning thermodynamic behavior of the system has been made by invoking zeroth law of thermodynamics. Remarkably, it lends itself a necessary and sufficient condition concerning proportionality between heat-flux and required temperature difference to yield fluids unique thermal response in relation to the heat transfer surface temperature. Consequently, far-reaching physical implications of the constant of proportionality on system design can be clearly exposed of with due consideration to Eulerian descriptions of conservation principles according to Newton’s mechanical theory. Consistently enough, because of thermal non-equilibrium, effectiveness of system design and off design performance warrants a fundamental theorem like one suggested by Reynolds concerning augmentation of thermal diffusion due to fluid motion. Accordingly, flow rates become critical operating parameters for thermal performance and pressure drop requirements. Furthermore, and most importantly, in support of the theorem an order magnitude analysis appears to be in order, to show the dependence of flow resistance and hence, system thermal response on fluid flow behavior in terms of non-dimensional parameters. As a result, it is made clear that development of design correlations for friction factor and non-dimensional heat transfer coefficient in terms of both Reynolds number and Prandtl number is an integral part of heat exchanger design process by gathering experimental data. Finally, generalized mathematical statement of Reynolds analogy has been obtained relating Stanton number with friction factor, which reduces to our familiar expression for Prandtl number of unity.
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Wang, Fuliang, Junhui Li, Lei Han, and Jue Zhong. "Atom diffusion mechanism of thermo-sonic flip chip bonding interface." In 2007 International Conference on Thermal, Mechanical and Multi-Physics Simulation Experiments in Microelectronics and Micro-Systems. EuroSime 2007. IEEE, 2007. http://dx.doi.org/10.1109/esime.2007.359927.
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Danov, Stanislav N., and Ashwani K. Gupta. "Understanding of Diesel Engine Combustion Process via Mathematical Modeling: Part 2 — Results." In ASME 1997 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/detc97/cie-4431.
Повний текст джерелаАнотація:
Abstract In the companion Part 1 of this two part series paper a mathematical model of combustion process in a diesel engine was presented having both premixed and diffusion flame. The combustion of fuel vaporized during the self-ignition delay period is modeled according to the conditions of premixed flame. A kinetic differential equation has been created for modeling this kind of combustion. The combustion of fuel during the injection process is modeled according to the theory of diffusion flames. This process is strongly influenced by processes of fuel injection, vaporization and diffusion. The atomization process is taken into account by means of the Sauter mean diameter (SMD) of fuel droplets. The instantaneous vaporization rate is defined by the current value of temperature, pressure, concentration of fuel vapors and the mean fuel droplet size in terms of the SMD. The mathematical model includes differential equations describing the processes of fuel injection, vaporization, heat transfer and combustion in both premixed and diffusion flame that occurs in the engine cylinder. The above equations are solved together with the differential equation of the first law of thermodynamics expressing the energy conversion process in the cylinder of diesel engine. The fourth-order Runge-Kutta method is applied for obtaining numerical solution of the system of differential equations. The model is calibrated and validated for two different turbocharged diesel engines — 8DKRN 74/160 and Sulzer-6RLB-66. The analysis is performed on a PC using FORTRAN 90. The comparison between the experimental data and numerical results shows very good agreement. Numerical experiments have been carried out for examining the combustion behavior in the cylinder of a marine DI diesel engine Sulzer 6RLB-66 having a cylinder diameter of 0.66 m bore and stroke of 1.4 m. The influence of the quality of fuel atomization process, estimated via the SMD, on the fuel vaporization rate and overall combustion rate has been evaluated. This influence is quantified and the results show very strong influence of SMD on the vaporization and combustion process, both with respect to the maximum rates and the duration of the processes. In addition numerical experiments have been carried out for determining the effect of duration of fuel injection and the beginning of fuel injection (degrees of crank angle rotation before TDC) on subsequent combustion parameters and integral indicator parameters of the engine. These results show that ratio: “amount of fuel burnt under the premixed flame conditions / amount of fuel burnt under diffusion flame conditions” for one cycle varies significantly with the change in fuel injection duration. The model provides both the instantaneous values of engine parameters in the cylinder (i.e., temperature, pressure, current air-gas mixture composition, heat transfer rate, thermo-physical properties of the air-gas mixture, etc.) and integral indicator engine parameters (mean indicated pressure, specific fuel consumption, efficiency, etc.). A comparison between experimental and modeling data show gratifying results.
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Seiler, P., J. Rösler, D. Mukherji, and T. Kopka. "Thermal Barrier Coatings on Novel High Temperature Cobalt Rhenium Substrates." In ITSC2011, edited by B. R. Marple, A. Agarwal, M. M. Hyland, Y. C. Lau, C. J. Li, R. S. Lima, and A. McDonald. DVS Media GmbH, 2011. http://dx.doi.org/10.31399/asm.cp.itsc2011p0926.
Повний текст джерелаАнотація:
Abstract Presently, highly stressed components in gas turbines are mainly made of single crystal nickel based alloys and the maximum application temperature (without coatings) is typically limited to 1100°C. Superalloys are now reaching limits posed by their melting temperatures. Increasing the substrate temperature beyond 1200°C will increase the efficiency of the turbine significantly. A new generation high temperature Co-Re alloys are aimed for use at +100°C above present single crystal nickel-superalloys. The substrates will be protected against the higher gas temperatures by thermal barrier coatings. For Co-Re alloy substrates CoReCrSi is a promising bond-coat material. CoReCrSi is thermo-chemically compatible to Co-Re due to the very similar mechanical and chemical properties. The oxide formation and the adhesion of the top coat are being investigated by studying a simplified coating system. The coating system consists of a CoReCrSi bond coat bulk material, and an yttria-stabilised zirconia top coat. The system was tested under cyclic conditions at 1200°C. This study provides a first insight into the TGO growth, the basic failure mechanism of the top coat, and the diffusion processes at the top coat/bond coat interface. It is shown that CoReCrSi with 2 at.% silicon promotes a good adhesion of the top coat by forming a dense chromium oxide layer. The critical TGO thickness beyond which the TGO fails by spallation was determined to be 25 microns and is roughly 2.5 times the critical thickness in MCrAlY based system in nickel-alloys.