Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
3
4
1996
A Review of Flow Boiling Heat Transfer with Twisted Tape Inserts
233-257
10.1615/JEnhHeatTransf.v3.i4.10
D. P.
Shatto
Department of Mechanical Engineering Texas A&M University College Station, TX 77843, USA
G. P. "Bud"
Peterson
Woodruff School of Mechanical Engineering, Georgia Institute of Technology
Atlanta GA, USA; Associate Professor of Mechanical Engineering Texas A&M University College Station, Texas 77843
This report reviews experimental investigations of in-tube flow boiling enhancement using twisted tape inserts. Special aspects of the experimental methods used in these studies are described in detail, and the general trends observed in the results are presented. Methods of mathematically characterizing the geometric parameters associated with swirl flow are introduced, and the theoretical relationships between swirl flow and axial flow boiling are described. Previously proposed empirical and semi-empirical predictive methods are presented for heat transfer and pressure drop with twisted tape inserts in various convective boiling regimes. These existing correlations are compared, and recommendations are made regarding experimental methods, design practices, and the use of existing predictive methods.
A Study of the Deposition of Fine Particles in Compact Plate Fin Heat Exchangers
259-272
10.1615/JEnhHeatTransf.v3.i4.20
M. A.
Masri
Chemical Engineering & Fuel Technology, University of Sheffield, Mappin Street, Sheffield SI 3JD, UK
K. R.
Cliffe
Chemical Engineering & Fuel Technology, University of Sheffield, Mappin Street, Sheffield SI 3JD, UK
The main purpose of this study was to investigate the performance of plain fin heat exchangers (PFHE) under particulate fouling for a wider application potential. A simulated PFHE was subjected to accelerated fouling tests with aluminium oxide (6 μ;m) and ferric oxide (3 μ;m) particles suspended in water. Both plain fin and wavy fin corrugations were used. Experimental tests were performed under non-heating (30°C) and heating (105°C) conditions. In all tests, the deposition/time curves showed an asymptotic behaviour. Deposition rates were higher under heated conditions. Under isothermal conditions, the deposition appeared to be governed by mass transfer from the bulk suspension to the wall surfaces and the particle deposition was mainly due to the effect of Brownian diffusion. The theoretical predictions of mass transfer coefficients from a convective mass transfer correlation were in general in reasonable agreement with the mass transfer coefficients obtained from experimental data. The effect of surface temperature was to increase the bulk temperature, therefore the diffusivity of the depositing species. Increasing the bulk temperature from 8°C to 60°C also increased the deposition rate. The wavy fin heat exchanger showed higher deposit weights compared with the plain fin and the pressure drop was also higher. Increasing the fluid flow velocity (Re up to 2500), increased the deposit weight onto the plain fin geometry. For the wavy fin geometry, beyond Re > 1500, the deposit weight started to decrease.
Heat Transfer and Skin Friction Comparison of Dimpled Versus Protrusion Roughness
273-280
10.1615/JEnhHeatTransf.v3.i4.30
Mark E.
Kithcart
Mechanical Engineering Department North Carolina A&T State University Greensboro, NC 27411
David E.
Klett
Mechanical Engineering Department North Carolina A&T State University Greensboro, NC 27411
This paper presents results of skin friction and heat transfer measurements made on flat plates with closely-spaced, three-dimensional surface roughness elements (hemispherical dimples, hemispherical protrusions, and rectangular protrusions) in turbulent boundary-layer flow at velocities ranging from 18 to 40 m/s (roughness Reynold's nos. from 1500 to 4000). The roughness element densities for each plate were chosen using Simpson's sand-grain roughness correlation to study the effects of spacing on drag and heat transfer in the vicinity of the peak of the Simpson-Dvorak correlation curve. The data is presented in terms of the efficiency factor, n = (Str/Sts/(Cfr/Cfs), to provide a means of comparing the effects on skin friction and heat transfer collectively. Dimpled surfaces have the advantage of significantly increasing heat transfer at a lower penalty in increased drag compared to the protrusion roughness studied.
A Genetic Algorithm Optimization Technique for Compact High Intensity Cooler Design
281-290
10.1615/JEnhHeatTransf.v3.i4.40
Timothy S.
Schmit
Department of Mechanical Engineering, University of Wisconsin, Milwaukee, WI 53201
Anoop K.
Dhingra
Department of Mechanical Engineering, University of Wisconsin, Milwaukee, WI 53201
Fred
Landis
Department of Mechanical Engineering, University of Wisconsin, Milwaukee, WI 53201
Gunol
Kojasoy
Department of Mechanical Engineering, University of Wisconsin-Milwaukee P.O. Box 784, Milwaukee, Wisconsin 53201
This paper initially reviews the operation and design criteria for a compact high intensity cooler (CHIC) unit as used in avionic equipment. Here high heat loads are dissipated via multiple impinging jets fed sequentially through a series of fins connected with a bus bar to the heat source. The analytical basis for the heat transfer design, most of which has been published previously, is shown to predict the performance of CHIC units to a high degree of accuracy. This then permits optimizing the design. Most optimization techniques depend on continuous variables, while in the design of CHIC unit many of the critical geometrical variables must assume discrete values. A genetic algorithm, generally not well known in engineering circles, that looks for an optimum by simulating an evolutionary process was found to be satisfactory for this problem with its mixture of discrete and continuous variables. It is also shown that in an actual optimization problem, where the fluid pressure drop across the unit has to be balanced against a low overall thermal resistance, an optimum geometrical design can be determined. This design is an improvement over the empirical "best" design previously reported in the literature.
Enhancement of Forced Convection in an Asymmetrically Heated Duct Filled with High Thermal Conductivity Porous Media
291-299
10.1615/JEnhHeatTransf.v3.i4.50
R. F.
Bartlett
Heat Transfer Laboratory School of Mechanical Engineering Purdue University, West Lafayette, IN 47907, U.S.A
Raymond
Viskanta
Heat Transfer Laboratory, School of Mechanical Engineering, Purdue University, West Lafayette, USA
Forced convection of a fluid through a porous structure bounded by heated surfaces has been shown in a number of studies to enhance heat transfer from the heated surface over that of flow and heat transfer in an open duct. Heat transfer enhancement from a heated surface using porous structures has a potential application in electronics cooling. In this work closed form analytical solutions to the problem of thermally-developing forced convection through an asymmetrically heated duct filled with an isotropic high thermal conductivity porous medium is reported. The analytical solutions can be used as first approximation to the heat transfer problem and as a means for checking numerical codes. The results are compared against the available experimental data to validate the model. Results of parametric calculations are reported to illustrate the potential convective heat transfer enhancement using high thermal conductivity porous materials.
Boiling Heat Transfer Enhancement of R-134a in a Tube Bundle Utilizing The EHD Technique
301-309
10.1615/JEnhHeatTransf.v3.i4.60
K.
Cheung
Heat Transfer Enhancement Laboratory Center for Environmental Energy Engineering, Department of Mechanical Engineering University of Maryland College Park, Maryland 20742
Michael M.
Ohadi
Small and Smart Thermal Systems Laboratory, Center for Energy Environmental Engineering, Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, USA
Serguei V.
Dessiatoun
Department of Mechanical Engineering, University of Maryland, College Park, Maryland, USA
Compound enhancement of boiling heat transfer with R-l34a in a tube bundle was studied experimentally utilizing the electrohydrodynamics (EHD) technique. A laboratory-scale tube bundle utilizing commercially available forty fins per inch (40 fpi) tubes with R-134a as working fluid was used in the experiments. Two electrode configurations were tested (straight wire and wire mesh type). The results of the experiments suggest the applicability of the EHD technique for heat transfer enhancement in tube bundle while quantifying the role of various operating parameters. More than a four fold increase in the overall bundle heat transfer coefficient was obtained with wire mesh electrode. The corresponding enhancement with the straight wire electrode was two fold. The maximum EHD power consumption for the two electrode configurations were 5% and 1.2% of the bundle heat transfer rate, respectively. The experiments also addressed the effect of electric field polarity, which was found to have no pronounced effect on the enhancement mechanism for the bundle configuration at hand.