Heat and Mass Transport in Proton Exchange Membrane Fuel Cells—A Review

This review brings out those aspects of the development of proton exchange membrane (PEM) fuel cells over the last two to three decades that are of interest to the heat and mass transfer community. Because the heat transport and mass transport in proton exchange membrane fuel cells are very important from the efficiency point of view, an emphasis is given here to these transports and their influence on operating cell parameters. The works are classified as models with either isothermal or non-isothermal conditions of various assumed dimensionality and with either single-phase or two-phase flow. Along with modeling, a few experimental studies available are also reported here. Researchers in the area of PEM fuel cells are involved in activities such as development of new and low-cost materials, modeling the relevant physical processes, and electrochemical experimentation. These collective efforts may lead to making this technology viable to meet world needs for clean and cheap energy. This review brings out the fact that computational fluid dynamics (CFD) has become an inevitable tool in fuel cell analysis, as the detailed interactions between the flow structure geometry, fluid dynamics, multiphase flow, heat transfer, mass transfer, and electrochemical reaction can be modeled simultaneously, given the present state of the art in CFD. Through the predictive capability of CFD, it will be possible for fuel cell designers to better optimize the design and operating parameters of fuel cells before testing them in laboratory.     

Local Heat and Mass Transfer for Gas—Solid Two Phase Flow in CFB

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Experimental and Numerical Investigation of Enhancement of Heat and Mass Transfer in Adsorbent Beds

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Two-Phase Flow and Heat Transfer across Horizontal Tube Bundles‐A Review

This paper presents a state-of-the-art review of two-phase flow and flow boiling across horizontal tube bundles. The review covers studies related to the dynamic aspects of two-phase flow on the shell side of staggered and in-line tube bundles for upward, downward, and side-to-side flows (i.e. the evaluation of void fraction, two-phase flow behaviors and pressure drops). Heat transfer experimental work and heat transfer prediction methods on tube bundles in cross-flow for plain, low-fin, and enhanced boiling tubes are also covered. The proposed flow pattern maps and semi-empirical correlations for predicting void fraction and frictional pressure drop are critically described. These prediction methods are generally based on experimental results for adiabatic air-water flows, and noticeable discrepancies are revealed in the results provided by them. This study reveals that before now, there were no heat transfer prediction methods that can be recommended as a general design tool. Finally, this study suggests further research focusing on the development of representative databanks and prediction methods.     

Simulating Experimental Investigation on the Safety of Nuclear Heating Reactor in Loss—of —Coolant Accidents

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Undergraduate Education in Heat Transfer—A Point of View

During the past three decades, many new technologies have enhanced the application of heat transfer, while other technologies (computational and measurement) have strongly influenced its practice. These developments present the heat transfer instructor with many options, and compromises must be made in deciding what balance should be reached in presenting heat transfer principles, establishing their relationship to thermal system behavior, and introducing modern tools of heat transfer analysis and measurement. In this paper, reasonable goals of a first course in heat transfer are identified and prioritized. Highest priority is assigned to those goals which enhance the student's understanding of basic principles and the skill to apply these principles in thermal system design and evaluation.     

Convective Heat and Mass Transfer in Water at Super—Critical Pressures under Heating or Cooling Conditions in Vertical Tubes

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Heat Transfer and hydrodynamics in Annular Chromatography：CFD—Simulation and Experiments

IntrotctiouAImular chrDmatography Provides the POssibility ofseparating multicomponent fixtures continuously inone single unit. The rotating annulus of thechromatotw can be filled with arbitw stationalsPhases depending on the existing separation Problem.The feed is introduced at a fixed and stationary sechonat the top of the unit, while the eluent is distributedeverywhere else around the upper circumference. At thebottom the separated Products can be collected atcendn stationals exit angle…     

Influence of Lubricant on the Nucleate Boiling Heat Transfer Performance of Refrigerant—A Review

This review provides an overview of the lubricant on the heat transfer performance pertaining to nucleate boiling. It appears that the effect of individual parameter on the heat transfer coefficient may be different from study to study. This is associated with the complex nature of lubricant and some compound effects accompanying the heat transport process. Some important effects such as oil concentration, heat flux, geometric configuration, saturation temperature, thermodynamic and transport properties, miscibility, foaming, and additional surface active agent are reported and discussed. In general, the heat transfer coefficient is impaired provided the oil concentration is sufficient high (e.g., >7%), and this is applicable to smooth and structured tubes. But normally structured tubes tend to suffer more from lubricant, yet this is especially conspicuous when the size of the reentrant channel is small. On the other hand, foaming and partial miscibility seem to benefit the heat transfer coefficient.     

Heat Transfer,Fluid Mechanics,and Thermodynamics in Our Environment—HEFAT2012

This editorial provides an overview of a special issue dedicated to the 9th International Conference on Heat Transfer, Fluid Mechanics, and Thermodynamics—HEFAT2012—hosted on Malta. All papers for this conference were peer reviewed and 270 papers were accepted. Of these, 10 of the best papers were selected for this issue and peer reviewed for a second time according to journal standards. The 10 papers focus on the characteristics of oxyfuel and air-fuel combustion in an industrial water tube boiler, numerical and optical analysis of a weather-adaptable solar reactor, the mitigation of crystallization fouling using projectiles in tubular heat exchangers, the mitigation of crystallization fouling in a single heated tube using projectiles of different sizes and hardness, a framework for the analysis of thermal losses in reciprocating compressors and expanders, an annular impinging jet controlled by radial synthetic jets, multi-effect plants and ionic liquids for improved absorption chillers, the effect of climatic parameters on the heat transfer mechanisms in a solar distillation still, empirical correlations for slightly decaying grid turbulence, and pool boiling on modified surfaces using R-123. The current issue of Heat Transfer Engineering is the ninth special journal issue dedicated to selected papers from the HEFAT conferences.     

Natural Convective Heat and Mass Transfer of Water with Corrosion Products at Super—Critical Pressures under Cooling COnditions

A numerical study is reported of laminar natural convective heat and mass transfer on a vertical cooled plate for water containing metal corrosion products at super-critical pressures. The influence of variable properties at super-critical pressures on natural convection has been analyzed. The difference between heat and mass transfer under cooling or heating conditions is also discussed and some correlations for heat and mass transfer under cooling conditions are recommended.     

Flow Pattern and Heat Transfer Behavior of Boiling Two—Phase flow in Inclined Pipes

Movable Electrical Conducting Probe (MECP), a kind of simple and reliable measuring transducer, used for predicting full-flow-path flow pattern in a boiling vapor/liquid two-phase flow is introduced in this paper. When the test pipe is set at different inclination angles, several kinds of flow patterns, such as bubble, slug, churn, intermittent, and annular flows, may be observed in accordance with the locations of MECP. By means of flow pattern analysis, flow field numerical calculations have been carried out, and heat transfer coefficient correlations along full-flow-path derived. The results show that heat transfer performance of boiling two-phase flow could be significantly augmented as expected in some flow pattern zones.The results of the investigation, measuring techniques and conclusions contained in this paper would be a useful reference in foundational research for prediction of flow pattern and heat transfer behavior in boiling two-phase flow, as well as for turbine vane liquid-cooling design.     

Analysis of Entropy Generation of Combined Heat and Mass Transfer in Internal and External Flows with the Assumption of Local Thermodynamic Equilibrium

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Critical Heat Flux in Flow Boiling—Review of the Current Understanding and Experimental Approaches

ABSTRACT

A comprehensive review of current literature on subcooled flow boiling with a focus on the mechanistic modeling of the departure from nucleate boiling is presented. This review covers parametric trends, other reviews on the topic, previous modeling approaches, applicable measurement techniques for two-phase flow, and an extensive literature review on mechanistic models for the prediction of critical heat flux (CHF). The models have been carefully deconstructed to give an overview about differences and similarities in the respective modeling approaches. Drawing on previously successful application of measurement techniques for two-phase flow, recommendations for future experimental investigation regarding specific parameters of the respective models are given for the refinement of the current modeling approaches of CHF phenomena.     

Mixed Thermocapillary and Forced Convection Heat Transfer Around a Hemispherical Bubble in a Miniature Channel—A 3D Numerical Study

It has been established that for certain conditions, such as microgravity boiling, thermocapillary Marangoni flow has associated with it a significant enhancement of heat transfer. Typically, this phenomenon was investigated for the idealized case of an isolated and stationary bubble resting atop a heated solid that is immersed in a semi-infinite quiescent fluid or within a two-dimensional cavity. This article presents a three-dimensional numerical study that investigates the influence of thermal Marangoni convection on the fluid dynamics and heat transfer around a bubble during laminar flow of water in a minichannel. This mixed thermocapillary and forced convection problem is investigated for channel liquid inlet velocity of 0.01 m/s to 0.03 m/s and Marangoni numbers in the range of 10 to 300 under microgravity conditions. Three-dimensional effects become particularly important on the side and rear regions of the bubble. The thermocapillary forces accelerate the flow along almost the entire bubble interface. The hot core fluid from the heated bottom wall region is forced inward and propelled upward into the thermocapillary jet above the bubble. It can be quantified that the influence of thermocapillary flow on heat transfer enhancement shows an average increase by 40% at the downstream of the bubble and by 60% at the front and rear regions. This heat transfer enhancement depends mainly on the temperature differential as the driving potential for thermocapillary flow and bulk liquid velocity.     

Modeling Heat Transfer and Skin Friction Frequency Responses of a Cylinder in Cross-Flow—a Unifying Perspective

The dynamic behavior of skin friction and heat transfer of a cylinder in pulsating cross-flow is investigated. Existing analytical solutions are presented as transfer functions versus frequency, known from control theory. New results for Reynolds number ranges where no appropriate model exists until now are derived. These results are obtained by the combination of computational fluid dynamics and system identification (CFD/SI). In the CFD/SI approach, time series for fluctuations of skin friction and the rate of heat transfer are generated by imposing broad-band inlet velocity fluctuations in a CFD simulation of laminar flow across a cylinder. Direct numerical simulations are conducted for mean flow Reynolds numbers between 0.1 and 40, solving the incompressible Navier–Stokes equations in a two-dimensional domain using a finite volume approach. The SI framework allows to estimate transfer functions for the response of skin friction and heat transfer to velocity fluctuations from time series data. Available analytical models for the dynamic behavior of skin friction and heat transfer usually match the simulated data up to a point, but do not give any dependence on Reynolds number. This shortcoming is addressed in this work. The identified models especially excel at Reynolds numbers of order 10.     

Selected Papers From the Seventh HEFAT Conference—Heat Transfer,Fluid Mechanics,and Thermodynamics in Society

This editorial provides an overview of a special issue dedicated to the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, HEFAT2010, which took place July 19–21, 2010, in Antalya, Turkey. All papers for this conference were peer reviewed and almost 150 papers were accepted. Of these papers, eight were selected for this issue and were peer reviewed for a second time according to journal standards. The eight articles focus on recent developments of heat transfer and include the acidity and method of preparation of nanofluids on nucleate pool boiling, industrial boiler circulation, spray cooling of electronic components, freezing in a horizontal plate freezer with CO₂ as refrigerant in a cascade refrigeration system, thermal simulation of a pulsing heat pipe, condensation of R22 retrofits, vertically downward-blowing single-jet air curtains in cold rooms, and a gravity-assisted heat pipe air-to-air cooler. This issue of Heat Transfer Engineering is the seventh special journal issue dedicated to selected papers from the HEFAT conferences.     

Experimental Research on Heat Transfer and Pressure Drop of Two Configurations of Pin Finned—Tubes in an In—line Array

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Logarithmic Mean Pressure Difference—A New Concept in the Analysis of the Flow Distribution in Parallel Channels of Plate Heat Exchangers

This paper deals with a new concept of logarithmic mean pressure difference (LMPD) to find an accurate mean or true friction coefficient for variable flow in parallel flow channels of the plate heat exchangers while considering the first and the last channel pressure drops. This is analogous to the log mean temperature difference (LMTD) used for the computation of heat transfer in heat exchangers. A method has been suggested to improve the computation of mean or a newly defined “true friction factor” and the mean velocity for considerable flow variations in the channels. A comparative study has been made between the conventional average friction factor and the true mean friction factor for large parallel channels. The results have also been compared between the mean channel pressure drop and LMPD for different sizes of the channels. The analysis shows that the mean channel pressure drop of parallel channels can be predicted accurately by using the so-called true mean friction factor rather than the average friction factor. Using the LMPD method, one can find the last channel pressure drop by knowing the first channel pressure drop of the plate package. Hence, the nature of flow distribution in parallel channels can be predicted easily.     

Effect of the Inclination Angle and Eccentricity on Free Convection Heat Transfer in Elliptical–Triangular Annuli: A Lattice Boltzmann Approach

In this study, a Lattice Boltzmann method is used to simulation steady-state, laminar, free convection in two-dimensional annuli between a heated triangular inner cylinder and elliptical outer cylinder. The gap is filled with air as the working fluid. A constant temperature boundary condition is imposed on both the inner and outer surfaces. The study is performed for different inclination angles of inner triangular and outer elliptical cylinders at Ra = 10⁴. The inclination angle is varied from 0° to 120° for the triangular cylinder and from 0° to 90° for the elliptical cylinder. Furthermore, the vertical and horizontal eccentricity of the inner cylinder is investigated. The results for the inner and outer cylinders are presented in the form of isotherms, streamlines, and local and average Nusselt numbers. The results indicated that overall average Nusselt number has a type of nonlinear polynomial function with the triangular inclination angles and an approximately linear relation with the elliptical inclination angles. Also, the overall average Nusselt number decreases with the inclination of the outer elliptical cylinder. In addition, the results show that maximum heat transfer rate is reached when the inner cylinder is located at the center of the elliptical cylinder and at the lowest possible location vertically.