A Numerical Study on the Heat Transfer Enhancement Behavior of Water-Microparticles Suspension

The heat transfer enhancement characteristics of water with polystyrene particles are examined in the present numerical study. The numerical study is conducted in the hydrodynamically fully developed turbulent flows within a circular duct with the wall boundary condition of a constant heat flux. The thermal conductivity of the turbulent flow obtained by the Reynolds analogy is 1000 times as much as the thermal conductivity of water. On the contrary, the enhancement of thermal conductivity caused by water-microparticles suspension is relatively low. Slight enhancements of the local Nusselt number are obtained in the numerical calculations of Newtonian turbulent flows with the micro-convection effects, thus showing large deviations from the experimental data. The numerical results in non-Newtonian flows are in agreement with the experimental data. Thus, the main cause for the enhancement of the heat transfer of the suspension might be not due to the micro-convection effects but to the non-Newtonian effects     

Heat Transfer Enhancement—The Maturing of Second-Generation Heat Transfer Technology

This paper is basically the text of the Kern Lecture for 1991 (the 1990 Kern Award). The paper begins with some remarks about Dr. Kern. By way of introduction to heat transfer enhancement, historical notes and the evolution of literature in this area are presented. Comments are made about the increasing practical applications of enhancement technology. Developments in single-phase convection are presented, with particular emphasis on offset strip fins and twisted-tape inserts. Pool boiling and flow boiling (particularly microfin tubes) are then considered in some detail. It is concluded that enhancement represents a powerful technology to improve heat exchanger performance.     

Numerical Study of Heat Transfer Enhancement by Liquid Film on the Walls

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The Experimental Study on Regenerative Heat Transfer in High Temperature Air Combustion

For the purpose of decomposing the processing gases CF4 from semiconductor manufacturers, ceramic honeycomb regenerative burner system is suggested by using the principle of HTAC. A simulated high temperature air combustion furnace has been used to determine the features of HTAC flames and the results of the decomposition of CF4. The preheat air temperature of it is above 900℃. The exhaust gas released into the atmosphere is lower than 150℃. Moreover, the efficiency of recovery of waste heat is higher than 80%, the NOx level in exhaust gas is less than 198 mg/m3 and the distribution of temperature in the furnace is nearly uniform. The factors influencing on heat transfer, temperature profile in chamber and NOX emission were discussed. Also some CF4 can be decomposed in this system.     

Effect of Radiative Heat Transfer on Indoor—Fire

The importance of radiative heat transfer in the simulation of indoor-fire has been studied.Computer codeshave been developed based on four-flux model and discrete transfer model,respectively.Evaluation of the codesagainst exact analytic solution and experimental data shows that the discrete transfer model gives numericalresults with acceptable accuracy while the four-flux model underpredicts the heat fluxes although the gen-eral trend is reasonable.Numerical studies have been performed of two-dimensional,axisymmetric turbulent,buoyancy-controlled indoor fire.The computational results show that neglecting radiation in the simulationcan cause overprediction of 500K in the maximum temperature and less uniform velocity field compared to theprediction by discrete transfer model.The four-flux method has been found to produce less uniform velocityand temperature values than discrete transfer model,but is more economic in computation.     

On the Numerical Modeling of Impinging Jets Heat Transfer—A Practical Approach

This article compares steady-state and transient simulations in predicting impinging jet heat transfer. The configurations tested are H/D = 2 and 6, Re = 10,000, 20,000, 23,000, and 30,000. The variables considered are: turbulence model (LES, k-?, k-ω, V2F), discretization schemes, mesh density and topology, inlet velocity profile, and turbulence. The V2F model performs best for the steady state simulations. The inlet velocity profile plays an important role. Mesh topology and distribution is also important. The turbulence created in the shear layer plays a stronger role than the inlet turbulence. The LES model reproduces the turbulent structures with a useful degree of accuracy.     

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.     

Study on Characteristics of Steady Flow Condensation Heat Transfer in a Fube Under Zero—Gravitation

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Experimental Study on the Optimization of Heat and Mass Transfer of Industrial Drying of the TiO_2 Bulb by Infrared Radiation

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The Feasibility Study of the Waste Heat Air—Conditioning System for Automobile

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A CFD Study on the Effect of Shrinking Box Size on Cooling Airflows in Compact Electronic Equipment—The Case of Portable Projection Display Equipment

This work is concerned with the thermal design of portable projection display equipment (i.e., a portable projector). The portable projector is being made smaller and lighter to better serve the carrier, while its luminance is enhanced to benefit the viewer. The confluence of these demands increases the thermal loading on the projector. The design of cooling airflow path is becoming evermore important; however, the complex internal organization of the projector hampers an attempt to conduct flow and heat transfer analysis. A particularly important issue for the projector designer is to predict the effect of shrinking box size of the next generation product on cooling airflow. This paper describes a way to foresee the effects of reducing the key geometric dimensions of the projector on the distribution of airflow. The analysis is conducted using a computational fluid dynamics (CFD) code. CFD results are obtained on sampled points in the parameter domain and used to find the effects of various geometric parameters on the airflow rates. The sampling and screening of CFD results follows the Taguchi method (or the method of experimental design). The most influential parameters for the total airflow rate and the airflow rate over the electronics board are identified. This conclusion, however, is only an illustration of how the CFD analysis can assist the equipment designer in planning the next generation product. The methodology reported here can be applied in the plan and design of other electronic equipment that have similarly complex internal organizations in shrinking system boxes.     

Effects of Variable Jet Nozzle Angles on Cross-Flow Suppression and Heat Transfer Enhancement of Swirl Chamber

This paper investigated the effects of variable jetting nozzle angles on the cross-flow suppression and heat transfer enhancement of swirl cooling in gas turbine leading edge. The swirl chamber with vertical jet nozzles was set as the baseline, and its flow fields and heat transfer characteristics were analyzed by 3D steady state Reynolds-averaged numerical methods to reveal the mechanism of cross-flow weakening the downstream jets and heat transfer. On this basis, the flow structure on different cross sections and heat transfer characteristics of swirl chamber with variable jetting nozzle angels were compared with the baseline swirl chamber. The results indicated that for the baseline swirl chamber the circumferential velocity gradually decreased and the axial velocity gradually increased, and the cross-flow gradually formed. The cross-flow deflected the downstream jets and drawn them to the center of the chamber, thus weakening the heat transfer. For swirl chamber with variable jetting nozzle angles, the air axial velocity is axial upstream, opposite to the mainstream, so that the impact effects of cross-flow on the jets were reduced, and the heat transfer was enhanced. Furthermore, with the increase of axial velocity along the swirl chamber, the jetting nozzle angle also gradually increased, as well as the effect of cross-flow suppression, which formed a relative balance. For all swirl chambers with variable jet nozzle angles, the thermal performance factors were all larger than 1, which indicated the heat transfer was enhanced with less friction increment.     

CFD Modeling of Heat Transfer by 1.7 MHz Ultrasound Waves

This article reports the results of numerical study on the effect of high frequency ultrasounic waves on heat transfer rate. A cylindrical heater surrounded by water was exposed to a 1.7 MHz piezoelectric transducer, and its temperature was measured with and without employing the ultrasound vibrations. Heat transfer rate enhancement values at various inputted heat fluxes were found, and augmentations up to 100% were obtained during sonication. The CFD modeling of ultrasound wave propagation was carried out to predict the fluid flow pattern and heat transfer inside the water. The CFD predicted results were in good agreement with the observed results.     

Numerical Study of the Effects of the Face Velocity on Ceramic Filter

INTRODUCTIONTheproductsofcoalcombustionsuchasNOx,SOx,COb,andparticulatehavebeenstronglyregulatedtoreducepollutionintheearthenvironment.TherecentlydevelopedCleanCoalTechnologies(CCT)knownasPressurizedFluidizedBedCombustion(PFBC)[']andintegratedGasificationCombinedCycle(IGCC)I"']providetheimprovementofthermalefficiencywithsignificalltlyreducedenvironmelltalimpacts.ThusthePFBCandIGCChaveincreasingattentiontoachievestringentenvironmentalprotection.Advancingthetechnologyofthehotg…     

Analytical Study on Impingement Heat Transfer with Single—Phase Free—Surface Circular Liquid Jets

ＡｎａｌｙｔｉｃａｌＳｔｕｄｙｏｎＩｍｐｉｎｇｅｍｅｎｔＨｅａｔＴｒａｎｓｆｅｒｗｉｔｈＳｉｎｇｌｅ－ＰｈａｓｅＦｒｅｅ－ＳｕｒｆａｃｅＣｉｒｃｕｌａｒＬｉｑｕｉｄＪｅｔｓＡｎａｌｙｔｉｃａｌＳｔｕｄｙｏｎＩｍｐｉｎｇｅｍｅｎｔＨｅａｔＴｒａｎｓｆｅ...     

Experimental Study on Heat Transfer of Heated Falling Film Under Gas–Liquid Cross-Flow Condition

With the influence of the different gas Reynolds numbers and liquid Reynolds numbers on heated falling film heat transfer, an experiment was performed by noncontact thermal infrared imaging technology under the gas–liquid cross-flow condition. The results indicated that during the increase of liquid Reynolds number the thickness and thermal resistance of liquid film increased in the determined temperature of the heating water, which weakened the heat transfer of the liquid film. However, the increase of liquid Reynolds number strengthened liquid film turbulence and therefore enhanced heat transfer. Under the synergistic effect of these two factors, there should be an optimal liquid Reynolds number that minimizes thermal resistance and maximizes the heat transfer coefficient of the liquid film. Temperature plays an important role in heat transfer of laminar liquid film flow. However, the heat transfer of turbulent liquid film flow is not sensitive to liquid film inlet temperature.     

An Experimental Study of Condensation Heat Transfer in Sub-Millimeter Rectangular Tubes

The characteristics of local heat transfer and pressure drops were experimentally investigated using condensing R134a two-phase flow, in single rectangular tubes, with hydraulic diameter of 0.494, 0.658, and 0.972 mm. New experimental techniques were used to measure the in-tube condensation heat transfer coefficient especially for the low heat and mass flows. Tests were performed for a mass flux of 100, 200, 400, and 600 kg/m2s, a heat flux of 5 to 20 kW/m2, and a saturation temperature of 40℃. In this study, effect of heat flux, mass flux, vapor qualities, and hydraulic diameter on flow condensation were investigated and the experimental local condensation heat transfer coefficients and frictional pressure drop are shown. The experimental data of condensation Nusselt number are compared with previous correlations, most of which are proposed for the condensation of pure refrigerant in a relatively large inner diameter round tubes.     

Experimental Study on Heat Transfer and Pressure Drop Characteristics of Four Types of Plate Fin－and－TUbe Heat Exchanger Surfaces

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Study on the Effects of Flow in the Volute Casing on the Performance of a Sirocco Fan

The flow at the exit from the runner blade of a centrifugal fan with forward curved blades (a sirocco fan) sometimes separates and becomes unstable. We have conducted many researches on the impeller shape of a sirocco fan, proper inlet and exit blade angles were considered to obtain optimum performance. In this paper, the casing shape were decided by changing the circumferential angle, magnifying angle and the width, 21 sorts of casings were used. Performance tests, inner flow velocity and pressure distributions were measured as well. Computational fluid dynamic calculations were also made and compared with the experimental results. Finally, the most suitable casing shape for best performance is considered.     

Experimental Study of Melting Heat Transfer in an Enclosure with Three Discrete Protruding Heat Sources

INTRoDUCTIONTheremovalofheatfr0melectroniccomp0nelltisessentialtothereliableoperationofelectronicequiP-mellt.TurnerandFlarkl1],Kelleheretal.l2]andotherinvestigatorsreportedtheirexperimentalresultsonairnaturalc0nvecti0nheattransferinrectangularenclDesurewithconcentratedheatsources,simulatingtheliaturalcoolingofchipsmouned0nprintedcircuitboard.Theirresultsshownthatthecoolingcapac-ity0fairnaturalc0nvecti0nisqultelimited.UsingsolidniquldphasechangetocoolelectroniccompDenelltsmaybeaprondsinga…