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Showing papers on "Heat transfer published in 1995"


Book
28 Nov 1995
TL;DR: In this article, the authors present an overview of thermal system design using thermodynamics, modeling, and design analysis, including exergy analysis, energy analysis, and economic analysis.
Abstract: Introduction to Thermal System Design Thermodynamics, Modeling, and Design Analysis Exergy Analysis Heat Transfer, Modeling, and Design Analysis Applications with Heat and Fluid Flow Applications with Thermodynamics and Heat and Fluid Flow Economic Analysis Thermoeconomic Analysis and Evaluation Thermoeconomic Optimization Appendices Index

3,050 citations


Journal ArticleDOI
TL;DR: In this paper, the authors developed a jump condition based on the non-local form of the volume averaged momentum equation, which produces a jump in the stress but not in the velocity, and this has important consequences for heat transfer processes.

841 citations


Journal ArticleDOI
TL;DR: In this paper, the Kolmogorov velocity scale was introduced to account for the near-wall and low-Reynolds-number effects in both attached and detached flows.

724 citations


Book
20 Oct 1995
TL;DR: In this paper, the three-part structure of Heat Exchanger Irreversibility has been studied in the context of solar-thermal power generation, showing that the three parts of the structure of a two-phase-flow heat exchanger can be used to estimate the entropy generation rate.
Abstract: List of Symbols Thermodynamics Concepts and Laws Definitions Closed Systems Open Systems The Momentum Theorem Useful Steps in Problem Solving The Temperature-Energy Interaction Diagram, and the Entropy Interaction-Energy Interaction Diagram Problems Entropy Generation and Exergy Destruction The Gouy-Stodola Theorem Systems Communicating with More than One Heat Reservoir Adiabatic Systems Exergy Analysis of Steady Flow Processes Exergy Analysis of Non-Flow Processes Characteristic Features of Irreversible Systems and Processes Problems Entropy Generation in Fluid Flow Relationship between Entropy Generation and Viscous Dissipation Laminar Flow Turbulent Flow The Transition Buckling Theory of Turbulent Flow Entropy Generation in "Isothermal" Turbulent Flow The Bernoulli Equation Entropy Generation in Heat Transfer The Local Rate of Entropy Generation in Convective Heat Transfer Fluid Friction vs. Heat Transfer Irreversibility Internal Flows External Flows Conduction Heat Transfer Convective Mass Transfer General Heat Exchanger Passage Heat Transfer Augmentation Techniques Problems Heat Exchangers Counterflow Heat Exchangers Heat Exchangers with Negligible Pressure Drop Irreversibility The Three-Part Structure of Heat Exchanger Irreversibility Two-Phase-Flow Heat Exchangers Other Heat Exchanger Entropy Generation Studies Distribution of Heat Exchanger Area on the Absolute Temperature Scale Distribution of Heat Transfer Area in Counterflow Heat Exchangers Problems Insulation Systems Power Plants and Refrigeration Plants as Insulation Systems The Generation of Entropy in an Insulation with Fixed Geometry Optimum Continuous Cooling Regime Counterflow Heat Exchangers as One-Dimensional Insulations Parallel Insulations Intermediate Cooling or Heating of Insulation Systems for Power and Refrigeration Plants Problems Storage Systems Sensible Heat Storage Optimum Heating and Cooling Processes Subject to Time Constraint Hot Storage vs. Cold Storage Latent Heat Storage Power Generation Model with Bypass Heat Leak and Two Finite-Size Heat Exchangers Power Plant Viewed as an Insulation Between Heat Source and Ambient Combined-Cycle Power Plant Optimal Combustion Chamber Temperature Other Power Plant Optimization Studies Why Maximum Power Means Minimum Entropy Generation Rate Maximum Power from Fluid Flow Problems Solar-Thermal Power Generation Models with Collector Heat Loss to the Ambient Collector-Ambient Heat Loss and Collector-Engine Heat Exchanger Collector-Ambient Heat Loss and Engine-Ambient Heat Exchanger Storage by Melting Extraterrestrial Solar Power Plant Nonisothermal Collectors Time-Varying Conditions Other Areas of Solar Power Conversion Study Problems Refrigeration Refrigeration Plant Model with Heat Transfer Irreversibilities Model with Heat Leak in Parallel with Reversible Compartment Model with Cold End Heat Exchanger and Room Temperature Heat Exchanger Minimization of the Heat-Leak Entropy Generation Problems Time-Dependent Operation Defrosting Refrigerators Cleaning the Heat Exchanger of a Power Plant Power Plants Driven by Heating from a Bed of Hot Dry Rock Maximum Rate of Ice Production Problems Appendices Local Entropy Generation Rate Variational Calculus Author Index Subject Index

665 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that most of hot, optically thin accretion disk models which ignore advective cooling are not self-consistent, and they find new types of Optically thin disk solutions where cooling is dominated by radial advection of heat.
Abstract: We show that most of hot, optically thin accretion disk models which ignore advective cooling are not self-consistent. We have found new types of optically thin disk solutions where cooling is dominated by radial advection of heat. These new solutions are thermally and viscously stable.

639 citations


Journal ArticleDOI
TL;DR: In this article, the authors present experimental evidence of the wave nature of heat propagation in processed bologna meat and demonstrate that the hyperbolic heat conduction model is an accurate representation, on a macroscopic level, of the Heat conduction process in such biological material.
Abstract: The objective of this paper is to present experimental evidence of the wave nature of heat propagation in processed meat and to demonstrate that the hyperbolic heat conduction model is an accurate representation, on a macroscopic level, of the heat conduction process in such biological material. The value of the characteristic thermal time of a specific material, processed bologna meat, is determined experimentally. As a part of the work different thermophysical properties are also measured. The measured temperature distributions in the samples are compared with the Fourier results and significant deviation between the two is observed, especially during the initial stages of the transient conduction process. The measured values are found to match the theoretical non-Fourier hyperbolic predictions very well. The superposition of waves occurring inside the meat sample due to the hyperbolic nature of heat conduction is also proved experimentally. 14 refs., 7 figs., 2 tabs.

581 citations


Book
01 Dec 1995
TL;DR: In this paper, the dynamique des : fluides, transfert de chaleur, turbomachines, aerodynamique, thermodynamique Reference Record created on 2005-11-18, modified on 2016-08-08
Abstract: Keywords: dynamique des : fluides ; transfert de chaleur ; turbomachines ; aerodynamique ; thermodynamique Reference Record created on 2005-11-18, modified on 2016-08-08

528 citations


Journal ArticleDOI
TL;DR: In this paper, a conceptual framework for analysing the energy of density-stratified Boussinesq fluid flows is discussed, where the concept of gravitational available potential energy is used to formulate an energy budget in which the evolution of the background potential energy can be explicitly examined.
Abstract: A conceptual framework for analysing the energetics of density-stratified Boussinesq fluid flows is discussed. The concept of gravitational available potential energy is used to formulate an energy budget in which the evolution of the background potential energy, i.e. the minimum potential energy attainable through adiabatic motions, can be explicitly examined. For closed systems, the background potential energy can change only due to diabatic processes. The rate of change of background potential energy is proportional to the molecular diffusivity. Changes in the background potential energy provide a direct measure of the potential energy changes due to irreversible diapycnal mixing. For open systems, background potential energy can also change due to boundary fluxes, which can be explicitly measured. The analysis is particularly appropriate for evaluation of diabatic mixing rates in numerical simulations of turbulent flows. The energetics of a shear driven mixing layer is used to illustrate the analysis.

511 citations


Journal ArticleDOI
TL;DR: In this paper, the development of thermal-hydraulic design tools for rectangular offset strip fin compact heat exchangers and the associated convection process are delineated, and existing empirical f and j data for actual cores are reanalyzed.

480 citations


Journal ArticleDOI
TL;DR: A review of vortex-induced heat transfer enhancement can be found in this article, where the theoretical basis for the method is discussed and both active and passive implementations are reviewed, and the aim of this survey is to critically review recent progress and to identify research needs in the area of vortexinduced heat exchanger enhancement.

435 citations


Book ChapterDOI
TL;DR: In this article, the authors summarized the available analytical and experimental work in the area with the objective of correlating the research findings and suggested that there is considerable need for further research in liquid jet array applications, both in submerged and free-surface jet configurations.
Abstract: Publisher Summary Impinging liquid jets have been demonstrated to be an effective means of providing high heat or mass transfer rates in industrial transport processes. This chapter summarizes the available analytical and experimental work in the area with the objective of correlating the research findings. Significant progress has been made in understanding the fundamentals of heat, mass, and momentum transport in these systems. This chapter suggests that, there is considerable need for further research in liquid jet array applications, both in submerged and free-surface jet configurations. Cross-flow effects in these systems, which have been quite well characterized for submerged jets, have received only superficial treatment for free-surface jets. The physical phenomena are highly complex, requiring careful experimental investigation.

Journal ArticleDOI
TL;DR: The ideal refrigeration or heat pump cycle for a given purpose is defined by the boundary conditions of the application and is completely independent of the refrigerant used as mentioned in this paper, and the real cycle should approach the theoretical ideal as closely as practically possible.
Abstract: The ideal refrigeration or heat pump cycle for a given purpose is defined by the boundary conditions of the application and is completely independent of the refrigerant used. The real cycle should approach the theoretical ideal as closely as practically possible. The thermodynamic and heat transfer properties of the refrigerant are important in this respect. Natural substances such as ammonia, propane and carbon dioxide are often better than the present halocarbons in this regard. By using simple methods of safety it is possible to use these three natural fluids for practically all conventional refrigeration and heat pump systems.

Journal ArticleDOI
TL;DR: The naphthalene sublimation method can be used to study mass and heat transfer with confidence for a variety of applications, but with certain restrictions as discussed by the authors, such as high-velocity flows.

Journal ArticleDOI
TL;DR: In this article, the authors studied the rate of heat transfer for flow through a periodic array of wavy passages with an accurate numerical scheme, and observed that self-sustained oscillations lead to the destabilization of laminar thermal boundary layers, replenish the nearwall fluid with the fluid in the core region, and thus provide a natural mechanism of heat and mass transfer enhancement.

Journal ArticleDOI
TL;DR: In this article, two models are presented to predict the thermal behavior of the lithium/polymer battery, based on the model of Doyle et al. with the addition of an energy balance in the form given by Bernardi et al., which can be used to simulate a wide rang of polymeric separator materials, lithium salts, and composite insertion electrodes.
Abstract: Two models are presented to predict the thermal behavior of the lithium/polymer battery. Part 1 presents the one-cell model, a one-dimensional model for predicting the thermal behavior of the lithium negative electrode/solid polymer separator/insertion positive electrode cell. Part 2 presents the cell/stack model, a one-dimensional model that uses variable heat-generation rates calculated by the one-cell mode to predict temperature profiles in cell stacks. The one-cell model, presented in Part 1, is based on the model of Doyle et al. with the addition of an energy balance in the form given by Bernardi et al. Physical properties are allowed to vary with temperature. The model is general and can be used to simulate a wide rang of polymeric separator materials, lithium salts, and composite insertion electrodes. Simulation results for the Li/PEO{sub 15}-LiCF{sub 3}SO{sub 3}{vert_bar}TiS{sub 2} system are presented for isothermal operation at several temperatures and adiabatic operation at several discharge rates. Heat transfer to the surroundings is considered by defining a position-dependent heat-transfer coefficient for various cells in a cell stack.

Journal ArticleDOI
TL;DR: In this paper, a parabolic solver for steady-state equations in r−z two dimensions, a k−ϵ model for turbulence and a steam table library for physical properties of supercritical water cooling in a vertical pipe is numerically analyzed.

Journal ArticleDOI
TL;DR: In this paper, the authors use Eulerian and Lagrangian models and a simple analytical model to study the processes important in spray dispersion and evaporation within the droplet eva-oration layer (DEL).
Abstract: The part that sea spray plays in the air-sea transfer of heat and moisture has been a controversial question for the last two decades. With general circulation models (GCMs) suggesting that perturbations in the Earth's surface heat budget of only a few W m−2 can initiate major climatic variations, it is crucial that we identify and quantify all the terms in that heat budget. Thus, here we review recent work on how sea spray contributes to the sea surface heat and moisture budgets. In the presence of spray, the near-surface atmosphere is characterized by a droplet evaporation layer (DEL) with a height that scales with the significant-wave amplitude. The majority of spray transfer processes occur within this layer. As a result, the DEL is cooler and more moist than the atmospheric surface layer would be under identical conditions but without the spray. Also, because the spray in the DEL provides elevated sources and sinks for heat and moisture, the vertical heat fluxes are no longer constant with height. We use Eulerian and Lagrangian models and a simple analytical model to study the processes important in spray droplet dispersion and evaporation within this DEL. These models all point to the conclusion that, in high winds (above about 15 m/s), sea spray begins to contribute significantly to the air-sea fluxes of heat and moisture. For example, we estimate that, in a 20-m/s wind, with an air temperature of 20°C, a sea surface temperature of 22°C, and a relative humidity of 80%, the latent and sensible heat fluxes resulting from the spray alone will have magnitudes of order 150 and 15 W/m2, respectively, in the DEL. Finally, we speculate on what fraction of these fluxes rise out of the DEL and, thus, become available to the entire marine boundary layer.

Journal ArticleDOI
TL;DR: In this article, the local heat transfer from a small heat source to a normally impinging, axisymmetric, and submerged liquid jet, in confined and unconfined configurations, was experimentally investigated.
Abstract: The local heat transfer from a small heat source to a normally impinging, axisymmetric, and submerged liquid jet, in confined and unconfined configurations, was experimentally investigated. A single jet of FC-77 issuing from a round nozzle impinged onto a square foil heater, which dissipated a constant heat flux. The nozzle and the heat source were both mounted in large round plates to ensure axisymmetric radial outflow of the spent fluid. The local surface temperature of the heat source was measured at different radial locations (r/d) from the center of the jet in fine increments. Results for the local heat transfer coefficient distribution at the heat source are presented as functions of nozzle diameter (0.79 ≤ d ≤ 6.35 mm), Reynolds number (4000 to 23,000), and nozzle-to-heat source spacing (1 ≤ Z/d ≤ 14). Secondary peaks in the local heat transfer observed at r/d 2 were more pronounced at the smaller (confined) spacings and larger nozzle diameters for a given Reynolds number, and shifted radially outward from the stagnation point as the spacing increased. The secondary-peak magnitude increased with Reynolds number, and was higher than the stagnation value in some instances.

Journal ArticleDOI
TL;DR: In this article, a class of wing-type vortex generators, which can easily be incorporated into heat transfer surfaces, is considered in fully developed and developing channel flows with respect to heat transfer enhancement and pressure loss penalty.


Journal ArticleDOI
TL;DR: Reduction of the blood flow through thermally significant vessels was found to be the most effective way of reducing localized cooling.
Abstract: Large blood vessels can produce steep temperature gradients in heated tissues leading to inadequate tissue temperatures during hyperthermia This paper utilizes a finite difference scheme to solve the basic equations of heat transfer and fluid flow to model blood vessel cooling Unlike previous formulations, heat transfer coefficients were not used to calculate heat transfer to large blood vessels Instead, the conservation form of the finite difference equations implicitly modelled this process Temperature profiles of heated tissues near thermally significant vessels were calculated Microvascular heat transfer was modelled either as an effective conductivity or a heat sink An increase in perfusion in both microvascular models results in a reduction of the cooling effects of large vessels For equivalent perfusion values, the effective conductivity model predicted more effective heating of the blood and adjacent tissue Furthermore, it was found that optimal vessel heating strategies depend on the microvascular heat transfer model adopted; localized deposition of heat near vessels could produce higher temperature profiles when microvascular heat transfer was modelled according to the bioheat transfer equation (BHTE) but not the effective thermal conductivity equation (ETCE) Reduction of the blood flow through thermally significant vessels was found to be the most effective way of reducing localized cooling

Journal ArticleDOI
TL;DR: In this article, an experimental investigation was conducted to determine the heat transfer characteristics and cooling performance of rectangular-shaped microgrooves machined into stainless steel plates, using methanol as the cooling fluid, with different aspect ratios and a variety of center-to-center spacings.

Journal ArticleDOI
TL;DR: In this paper, a mathematical model and solution procedure for predicting the thermal performance of single-pass solar air collectors is presented, where the surface temperatures of the walls surrounding the air streams were assumed uniform whereas the air temperatures were assumed to vary linearly along the collector.

Journal ArticleDOI
TL;DR: In this article, a numerical atmospheric boundary layer model based on higher-order turbulence closure assumptions is developed and used to simulate the local advection of momentum, heat, and moisture during the melt of patchy snow covers over a 10-km horizontal domain.
Abstract: A numerical atmospheric boundary layer model, based on higher-order turbulence closure assumptions, is developed and used to simulate the local advection of momentum, heat, and moisture during the melt of patchy snow covers over a 10-km horizontal domain. The coupled model includes solution of the mass continuity equation, the horizontal and vertical momentum equations, an E−ϵ turbulence model, an energy equation, and a water vapor conservation equation. Atmospheric buoyancy is accounted for, and a land surface energy balance model is implemented at the lower boundary. Model integrations indicate that advective processes occurring at local scales produce nonlinear horizontal variations in surface fluxes. Under conditions of the numerical experiments, the energy available to melt snow-covered regions has been found to increase by as much as 30% as the area of exposed vegetation increases upwind of the snow cover. The melt increase is found to vary in a largely linear fashion with decreasing snow-c...

Journal ArticleDOI
TL;DR: In this paper, experimental data on the heat transfer performance of a periodically baffled tube subject to both steady (net) flow and oscillatory flow was reported. But the authors did not consider the effect of the superposition of fluid oscillations.

Journal ArticleDOI
TL;DR: In this article, a numerical simulation of forced convective incompressible flow through porous beds was performed in terms of non-dimensional parameters that successfully cast together all the pertinent influencing effects.
Abstract: The present work centers around the numerical simulation of forced convective incompressible flow through porous beds. Inertial as well as viscous effects are considered in the momentum equation. The mathematical model for energy transport was based on the two-phase equation model, which does not employ local thermal equilibrium assumption between the fluid and the solid phases. The transport processes for two different types of boundary conditions are studied. The analysis was performed in terms of nondimensional parameters that successfully cast together all the pertinent influencing effects. Comparisons were made between our numerical findings and experimental results. Overall, the comparisons that were made for the constant wall heat flux boundary condition display good agreement.

Journal ArticleDOI
TL;DR: In this article, a mathematical model of simultaneous heat and moisture transfer is proposed for the prediction of moisture and temperature distributions during drying in a slab-shaped solid, taking into account the effect of moisture-solid interaction at the drying surface by means of sorption isotherms of food.


Journal ArticleDOI
TL;DR: In this paper, a new theoretical formulation for the analysis of coupled heat, moisture and air transfer is presented, which is applicable to a deformable unsaturated soil, and three isothermal test problems are then considered to model the behaviour of unsaturated soils under varying stress and suction conditions.
Abstract: A new theoretical formulation for the analysis of coupled heat, moisture and air transfer is presented, which is applicable to a deformable unsaturated soil. The approach proposed extends previous analyses of the coupled transport of heat, pore water and pore air to take account of the deformation behaviour of partially saturated soil. A numerical solution of the governing differential equations is achieved by the use of the finite element method as a spatial discretization technique coupled with a finite difference recurrence relationship to describe transient behaviour. Three isothermal test problems are then considered to model the behaviour of unsaturated soil under varying stress and suction conditions. Both heave and collapse due to wetting are simulated. The model is applied to experimental work performed by others for the case of heating of an unsaturated montmorillonite clay and is shown to be capable of producing quantitatively physically correct results. These indicate that strong interactions ...

Journal ArticleDOI
TL;DR: In this article, the constraints that must be satisfied in order that the principle of local thermal equilibrium be valid are presented. But these constraints are not applicable to the case of transient heat conduction in two-phase systems.