Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
24
1-6
2017
COMPACT HEAT EXCHANGERS: VORTEX GENERATORS
1-28
10.1615/JEnhHeatTransf.v24.i1-6.10
Martin
Fiebig
Institut fur Thermo- & Fluiddynamik, Ruhr-Universitat Bochum, Postfach 1021 48, 4630 Bochum 1, GERMANY
Compact heat exchangers
Manufacturability
Vortex generators
Heat transfer
Pressure loss
Compact heat exchangers are characterized by high heat duties per unit volume and high heat transfer coefficients. This implies small hydraulic diameters, low Reynolds numbers and fins. Emphasis is placed on wing-type vortex generators (WVG). They can be used as fins or to modify fins and are easily incorporated into heat exchangers. Different WVGs are evaluated experimentally and numerically with regard to heat transfer enhancement and pressure loss. Detailed data are presented for flow structure, local and global heat transfer and pressure losses. The high potential of WVGs for compact heat exchangers is shown. Comparison of WVG-fins with offset-strip fins and louvered fins shows the advantages of WVGs. Examples of fin-tube heat exchanger elements indicate the large saving potential inherent in WVGs. Because of the many geometrical parameters of WVGs, many possibilities for improvements and incorporation into heat exchangers exist. Examples of fin-tube and fin-plate heat exchanger elements with and without WVGs are given.
FLOW BOILING HEAT TRANSFER WITH TWISTED TAPE INSERTS
29-60
10.1615/JEnhHeatTransf.v24.i1-6.20
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
Flow boiling
convective boiling
boiling
heat transfer
twisted tape inserts
vaporization
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.
ENHANCED HEAT TRANSFER IN NUCLEATE POOL BOILING OF AQUEOUS SURFACTANT AND POLYMERIC SOLUTIONS
61-81
10.1615/JEnhHeatTransf.v24.i1-6.30
Vivek M.
Wasekar
Department of Mechanical, Industrial and Nuclear Engineering, University of Cincinnati, Cincinnati, OH 45221-0072, USA
Raj M.
Manglik
Thermal-Fluids and Thermal Processing Laboratory, Mechanical and Materials Engineering, University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45220, USA
Enhancement
pool boiling
liquid additives
thermal processing
The presence of surfactant or polymer additives at low concentrations in water has been found to enhance the nucleate boiling heat transfer coefficient significantly. Traces of these additives cause no significant change in thermo-physical properties of the solvent except for surface tension and/or apparent viscosity. However, the boiling behavior of the solution is changed appreciably, and the extent of enhancement has been found to be dependent on additive concentration, its type and chemistry, wall heat flux, and the heater geometry. Several mechanisms have been proposed to explain the observed enhancement, that include, among others, effects of dynamic surface tension, Marangoni convection resulting from the variation of the surface tension along the vapor-liquid interface, increased number of active nucleation sites, and change in kinetics of vapor formation. With surface-active or surface-tension decreasing agents in water, nucleate boiling is generally characterized by the formation of smaller-size bubbles with increased departure frequencies, and a decreased tendency to coalesce that causes considerable foaming. This paper discusses these and several other issues, as well as presents new experimental findings in reviewing the current status of pool boiling research with surfactant/polymer additives in water.
EXPERIMENTAL RESULTS OF FLOW CONDENSATION IN SMOOTH AND MICRO-FIN TUBES WITH HCFC-22, HFC-134A AND HFC-410A REFRIGERANTS
83-106
10.1615/JEnhHeatTransf.v24.i1-6.40
Liangyou
Tang
Outokumpu Copper Franklin, Inc., 4720 Bowling Green Road, Franklin, KY 42134
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
Arthur T.
Johnson
Department of Biological Resources Engineering, University of Maryland, College Park, MD 20742
Alternative refrigerant
single-phase
flow condensation
micro-fin tube
heat transfer enhancement
tube
A study of single-phase convection and flow condensation heat transfer in horizontal copper tubes (8.81 mm inside diameter) was conducted using three refrigerants (HCFC-22, HFC-134a and HFC-410A). A smooth tube and three micro-fin tubes (axial, helical and Crosshatch enhancement) were examined. Local-mean flow condensation data were experimentally obtained. Experimental conditions were selected to reflect typical operating conditions encountered in refrigeration and air-conditioning applications. All micro-fin tubes illustrated significant enhancement in single-phase convection and flow condensation. The cross-hatch enhancement performed particularly better in both single-phase convection and flow condensation. For the three refrigerants investigated, the refrigerant type seemed to have little influence on the enhancement mechanism of the micro-fin tubes examined. The experimental results are presented in Part I. Development of design equations is presented in Part II.
DESIGN EQUATIONS OF FLOW CONDENSATION IN SMOOTH AND MICRO-FIN TUBES WITH HCFC-22, HFC-134A AND HFC-410 REFRIGERANTS
107-122
10.1615/JEnhHeatTransf.v24.i1-6.50
Liangyou
Tang
Outokumpu Copper Franklin, Inc., 4720 Bowling Green Road, Franklin, KY 42134
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
Arthur T.
Johnson
Department of Biological Resources Engineering, University of Maryland, College Park, MD 20742
Alternative refrigerant
single-phase
flow condensation
micro-fin tube
heat transfer enhancement
correlation
An empirical study of single-phase convection and flow condensation heat transfer in horizontal tubes was conducted. Three refrigerants (HCFC-22, HFC-134a and HFC-410A), a smooth tube, and three micro-fin tubes (axial, helical and Crosshatch enhancement) were examined. Commonly cited correlations were evaluated, utilizing the experimental data obtained in Part I of this study. Although these correlations had fairly good agreement with HCFC-22 and HFC-134 results, all of them failed to predict HFC-410A performance. A modified Shah equation was developed for smooth tube annular flow condensation, which overcomes the shortcomings of the existing correlations. Furthermore, design equations were developed for single-phase heat transfer and two-phase condensation with all three micro-fin tubes investigated, and covering all three refrigerants tested.
HEAT TRANSFER IN SQUARE CHANNELS WITH WEDGE-SHAPED AND DELTA-SHAPED TURBULENCE PROMOTERS
123-140
10.1615/JEnhHeatTransf.v24.i1-6.60
Je-Chin
Han
Turbine Heat Transfer Laboratory, Department of Mechanical Engineering, Texas A&M University College Sation, TX 77843-3123, USA
J. Joy
Huang
Department of Mechanical Engineering, Texas A & M University, College Station, Texas 77843-3123
Ching-Pang
Lee
General Electric Company, Cincinnati, Ohio 45215, U.S.A.
Heat transfer augmentation
Wedge-shaped turbulator
Delta-shaped turbulator
Blade cooling
The effect of rib configuration on local heat transfer coefficients and pressure drop in a square channel with two opposite in-line ribbed walls was investigated at Reynolds numbers from 15,000 to 80,000. Two types of rib configurations were studied. The first group is a wedge-shaped rib with the rib height-to-hydraulic diameter ratio of 0.125 and the rib pitch-to-height ratio of 5 or 10. Both full length and broken ribs are studied. The second group is a delta-shaped rib with the rib height-to-hydraulic diameter ratio of 0.125 and the rib pitch-to-height ratio of 5. Both aligned and offset arrangements are studied for a forward and backward direction relative to the mainstream flow. Results show that, for the delta-shaped rib, the backward flow direction has higher heat transfer than the forward flow direction, and the aligned arrangement is better than the offset arrangement. The broken configuration for the wedge-shaped rib performs better than the full length one. In general, the delta-shaped rib performs better than the wedge-shaped rib. The backward delta-shaped aligned rib configuration produces the highest heat transfer augmentation (3-4 times), while the backward delta-shaped offset rib creates the smallest pressure drop penalty (5-6 times). Results also show that the surface heat flux ratio has significant effect on the smooth-side heat transfer augmentation, while the effect on the ribbed-side is relatively small.
PERFORMANCE OF THREE-DIMENSIONAL HELICALLY DIMPLED TUBES INFLUENCED BY ROUGHNESS SHAPE AND SPACING
141-158
10.1615/JEnhHeatTransf.v24.i1-6.70
Thomas J.
Rabas
Energy Systems Division, Argonne National Laboratory, Argonne, IL USA 60439-4815; Consultant, 1015 Claremont Drive. Downers Grove, IL 60516
Ralph L.
Webb
Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802, USA
Petur
Thors
Wolverine Tube, Inc., 2100 Market Street N.E., Decatur, Alabama 35602, USA
N.-K.
Kim
Kum-Oh National Institute of Technology, Kumi-City Kyungbuk-Korea
Enhanced cubes; Three-dimensional roughness; Helically dimpled; Roughness shape; Efficiency index
A comparison of measured and predicted heat-transfer and friction-factor values is first presented for two newly developed doubly enhanced tubes. The internal enhancement consists of three-dimensional roughness elements that are essentially spherical segments and are formed by externally dimpling the outside surface. Very good agreement was obtained with these experimental data and the heat-transfer and friction-factor values obtained with prediction methods developed by Taylor and Hodge (1992a, 1992b) for three-dimensional roughened tubes. These prediction methods were then used to determine the variations of the inside heat-transfer enhancement level and the efficiency index (heat-transfer enhancement divided by the friction-factor increase) for different spherical shapes and spacings. This analysis revealed the following: significant performance improvements are possible with a greater roughness curvature and closer roughness spacings. The maximum enhancement level and efficiency-index value of 3.5 and 1.7, respectively, were obtained for water with touching half-spheres. These predicted values exceed all previously published values for passive enhancement geometries. However, these values are obtained for roughness geometries that are very different from those used for validation of the prediction algorithms developed by Taylor and Hodge (1992a, 1992b).
PLATE HEAT EXCHANGERS: RESEARCH AND DEVELOPMENTS
159-167
10.1615/JEnhHeatTransf.v24.i1-6.80
Bernard
Thonon
GRETh/CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble, Cedex 9, France
R.
Vidil
GRETh CEN Grenoble BP, 85 x 38041, Grenoble Cedex, France
Ch.
Marvillet
GRETh CEN Grenoble BP, 85 x 38041, Grenoble Cedex, France
Plate Heat Exchanger
Single phase flow
Evaporation
Condensation
Pressure Drop
Flow Pattern
This paper deals with the design of plate heat exchangers for processes in single-phase, evaporation and condensation. Some results are given for the thermal and hydraulic performance of corrugated channels in single phase flow. The flow pattern is analysed to give some local information on the heat transfer and the velocity field.
In two phase flows, the heat transfer coefficient and the pressure drop are correlated with models originally developed for smooth tubes. Some recommendations are proposed for future research.
HEAT TRANSFER AND PRESSURE DROP IN MULTILOUVERED FINS
169-180
10.1615/JEnhHeatTransf.v24.i1-6.90
Kazuhiko
Suga
Department of Mechanical Engineering, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku,
Sakai, Osaka 599-8531, Japan; Osaka Metropolitan University, Sakai, Osaka, 599-8531, Japan
Hiroshi
Aoki
Heat Transfer Lab., Mechanical Engineering Division I, TOYOTA CENTRAL R&D LABS., Inc., 41-1 Aza Yoicomichi, Oaza Nagakute, Nagakute-cho, Aichi-gun, Aichi, 480-11, Japan
Numerical study
Heat transfer
Pressure drop
Multilouvered fin
Optimization
Overlaid grids
To determine the optimum combinations among geometrical parameters of multilouvered fins, a numerical study was performed with a two-dimensional finite difference code. The code was developed by the authors using an overlaid grids method. The numerical results showed that the existence of the optimum ratio of fin-pitch/louver-pitch for each louver angle. The effects of thermal wakes on the heat transfer characteristics were discussed from the numerical results to understand the correlation between the fin geometries and heat transfer characteristics. This discussion concluded that the control of the thermal wakes after louvers was a key point for the optimization of multilouvered fins. A simple numerical expression was proposed to estimate the optimum relation among the fin parameters. The numerical expression was evaluated through the discussion about the effects of the fin parameters and performance of heat exchangers composed of multilouvered fins. Also, it was obtained that a heat exchanger with smaller louver angle (θ) had superior performance in the range of 20° θ < 30°.
BRAZED ALUMINUM HEAT EXCHANGERS AND THEIR AIR SIDE PERFORMANCE
181-200
10.1615/JEnhHeatTransf.v24.i1-6.100
Yu-Juei
Chang
Energy and Resources Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan
Chi-Chuan
Wang
Nantional Yang Ming Chiao Tung Univ
Louver Fin
Brazed Aluminum Heat Exchanger
Flat or round tube
Extensive experiments on the heat transfer and pressure drop characteristics of brazed aluminum heat exchangers were carried out. In the present study, 27 samples of louvered fin heat exchangers with different geometrical parameters, including tube width, louver length, louver pitch, fin height, and fin pitch were tested in an induced draft open wind tunnel. Results are presented as plots of friction factor, f, and Colburn j factor against Reynolds number based on louver pitch in the range of 100 to 1000. Comparisons between the Sahnoun and Webb model and the present test data are reported and good agreements were found. By introducing “area ratio” parameters, a simpler correlation of the Colburn j factor and friction factor f were obtained. It is shown that 85% of the experimental data of heat transfer and friction data were correlated within ± 10%.
CRITICAL REVIEW ON HEAT FLUX AND PRESSURE DROP OF SUBCOOLED FLOW BOILING IN SMALL-DIAMETER TUBES WITH TWISTED-TAPE INSERTS
201-222
10.1615/JEnhHeatTransf.v24.i1-6.110
W.
Tong
Department of Mechanical Engineering, Aeronautical Engineering & Mechanics, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
Arthur E.
Bergles
Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA; University of Maryland, College Park, MD, USA; Massachusetts Institute of Technology, Cambridge, MA, USA
Michael K.
Jensen
Center for Multiphase Flow, Rensselaer Polytechnic Institute, Troy, NY, USA; University of Wisconsin-Milwaukee, Mechanical Engineering Department Milwaukee, Wisconsin 53201
Critical heat flux
Pressure drop
Subcooled flow boiling
Twisted-tape insert
Critical heat flux (CHF) and pressure drop of small diameter tubes with twisted-tape inserts in subcooled flow boiling have been investigated experimentally. The influences of twisted-tape and test-section geometries (twist ratio, tube diameter and length) and fluid thermal-hydraulic conditions (mass flux, exit pressure, and inlet temperature) on both CHF and pressure drop have been analyzed and presented. Experiments were performed using stainless steel tubes with diameters ranging from 2.44 to 6.54 mm and aluminum twisted tapes (δ = 0.42 mm) with twist ratios from 1.9 to
∞. The gap between the twisted-tape edge and the tube wall was between 0.05–0.1 mm. The experimental results show significant enhancement of stable CHF by using twisted tapes with small twist ratios. Under high-mass-flux conditions, swirl-flow CHF is shown to be inversely proportional to twjst ratio, tube diameter, inlet temperature, and length-to-diameter ratio, but directly proportional to mass flux and exit pressure. Based upon the experimental data, an empirical subcooled swirl-flow CHF correlation, covering all six parameters, is proposed for a wide range of parametric values.
Pressure drop is strongly coupled to the conditions of CHF. The studies have revealed that the heat transfer enhancement achieved by means of twisted-tape inserts is generally accompanied by an increase in pressure drop. In this study, the influences of the above six parameters and heat flux on pressure drop have been addressed. The principal parameters affecting both single- and two-phase pressure drop are twist ratio, tube diameter, length-to-diameter ratio, and mass flux.
HEAT TRANSFER ENHANCEMENT IN LATENT HEAT THERMAL ENERGY STORAGE SYSTEM
223-238
10.1615/JEnhHeatTransf.v24.i1-6.120
Yuwen
Zhang
University of Missouri, Columbia, MO 65201, USA
Amir
Faghri
College of Engineering, Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Rd., Unit 3139, Storrs CT 06269-3139, USA; Department of Mechanical and Materials Engineering Wright State University Dayton, OH 45435
Thermal energy storage
Finned tube
The heat transfer enhancement in the latent heat thermal energy storage system by using an externally finned tube is presented in this paper. The melting in the phase change materials and heat conduction in the tube wall and fins are described by a temperature transforming model coupled to the heat transfer from transfer fluid. The forced convection inside the tube was solved by an analytical method. The results show that the local Nusselt number inside the tube cannot be simply given by the Graetz solution. The effects of the tube wall and initial subcooling on the heat transfer performance are also studied.
MORPHOLOGY: TWO-TEMPERATURE STATEMENTS FOR CONVECTIVE TRANSPORT IN POROUS MEDIA
239-269
10.1615/JEnhHeatTransf.v24.i1-6.130
L. J.
Gratton
Mechanical, Aerospace and Nuclear Engineering Department, University of California, Los Angeles, CA 90024-1597
V. S.
Travkin
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, California 90024-1597
Ivan
Catton
Morin, Martinelli, Gier Memorial Heat Transfer Laboratory, Department of Mechanical and Aerospace Engineering, School of Engineering and Applied Science, University of California, Los Angeles, USA
Highly porous media
Convective heat transfer
Two-temperature energy eq'uation
Transport coefficients
Solid medium morphology
Transport models for forced, single phase fluid convection are reviewed for non-uniformly and randomly structured highly porous media. Special attention is given to the evaluation of a two-temperature energy model. For means of comparison, a one-temperature, effective thermal diffusivity model is developed, emphasizing local solid phase morphology using analytic techniques. Random characteristics of the porous medium are simulated by the use of regular and unspecified, pre-assigned solid phase morphologies. An overall coefficient of drag resistance is determined by implementing a multiple-regime superposition approach. Coefficient models are evaluated using the governing averaged transport equations set and solved numerically. Variability of the morphology descriptors is shown to potentially govern large fluctuations in transport parameter values and distributions. Results generally compare favorably among work by Koch and Brady; Fand and Thinakaran; Adnani, Raffray, Abdou, and Catton; and Watanabe.
COMPACT HIGH INTENSITY COOLER DESIGN: A GENETIC ALGORITHM OPTIMIZATION TECHNIQUE
271-285
10.1615/JEnhHeatTransf.v24.i1-6.140
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
High heat flux
Jet impingement
fins
avionics
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.
DESIGN OF ABSORPTION-HEAT-PUMP HEAT EXCHANGERS
287-311
10.1615/JEnhHeatTransf.v24.i1-6.150
Srinivas
Garimella
Sustainable Thermal Systems Laboratory, The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
J. W.
Coleman
Department of Mechanical and Aeronautical Engineering Western Michigan University, Kalamazoo, MI 49008
A.
Wicht
Universität-GH-Paderborn Fachbereich Verfahrenstechnik Paderborn, Germany
Heat Exchanger
finned surfaces
The present study investigates the possibility of using highly compact, flat-tube/multilouver fin heat exchangers as replacements for conventional round-tube hydronic fluid-to-air heat exchangers used in space-conditioning applications. The advantages of these novel heat exchangers such as smaller frontal obstruction to air flow compared to round tubes (drag and fan power reduction), larger heat transfer coefficients due to the interrupted multilouver fins, and larger surface areas per unit volume can benefit absorption space-conditioning systems.
A comparison of the performance of this new geometry versus conventional round-tube heat exchangers was performed through the quantification of the decrease in heat exchanger mass for equivalent heat duties. Within the limitations of the available heat transfer and friction factor correlations, round-tube heat exchangers with flat, wavy, louvered and annular fins, and flat-tube heat exchangers with multilouver fins were designed to meet typical absorption cycle design conditions. The effect of design variables such as parallel/serpentine flow arrangements of tubes, fin densities, core depth, and other parameters on heat transfer performance and tube- and air-side pressure drops was investigated. It was shown that flat-tube heat exchangers can transfer equivalent heat duties while meeting pressure drop constraints with a significant reduction in the overall mass and size.
FLOW BOILING HEAT TRANSFER OF REFRIGERANTS IN MICROFIN TUBES
313-326
10.1615/JEnhHeatTransf.v24.i1-6.160
Satish G.
Kandlikar
Mechanical Engineering Department, Rochester Institute of Technology, Rochester, New York 14623, USA
Taavo
Raykoff
Mechanical Engineering Department, Rochester Institute of Technology, Rochester, NY 14623
Enhanced flow boiling
flow boiling augmentation
microfin tube
evaporation
flow boiling correlation
Microfin tubes are used in evaporators and condensers of refrigeration systems. The performance of different microfin tubes has been experimentally determined by a number of investigators, and the data are available in literature. In order to use this information in the design of equipment, it is necessary to correlate this data into a readily usable form. It is desirable that the correlation not only fit the available data well, but also reflect the parametric trends correctly.
Kandlikar (1991a) presented a correlation scheme to correlate flow boiling data for augmented tubes and compact evaporators. This correlation was based on the original correlation by Kandlikar (1990) for smooth tubes which accurately represented various trends in heat transfer coefficient with important system parameters. In the present work, the Kandlikar (1991a) correlation is modified to correctly account for the Reynolds number exponent in the single-phase flow. Also the missing (k/D) ratio is introduced in the single-phase heat transfer correlation. The augmented tube correlation scheme is applied to five sets of microfin tube flow boiling data available in literature. A single set of constants is found to correlate different refrigerant data sets obtained with the same microfin tube geometry. Parametric trends in heat transfer coefficient for microfin tubes obtained from the correlation are presented. It has been found that the enhancements in the nucleate boiling and the convective boiling contributions in the microfin tubes are influenced by the microfin geometry. To further improve the correlation capability for microfin tubes, it is recommended that single-phase heat transfer data should be obtained for that tube over a wide range of Reynolds number.
TURBULENT FLOW IN CIRCULAR TUBES WITH TWISTED-TAPE INSERTS AND AXIAL INTERRUPTED RIBS
327-342
10.1615/JEnhHeatTransf.v24.i1-6.170
Y. M.
Zhang
Turbine Heat Transfer Laboratory, Department of Mechanical Engineering, Texas A & M University, College Station, TX 77843-3123
Je-Chin
Han
Turbine Heat Transfer Laboratory, Department of Mechanical Engineering, Texas A&M University College Sation, TX 77843-3123, USA
Ching-Pang
Lee
General Electric Company, Cincinnati, Ohio 45215, U.S.A.
Twisted tapes
turbulent flow
axial interrupted ribs
Local heat transfer distributions and pressure drop in smooth circular tubes with twisted-tape inserts and axial interrupted ribs were investigated. Experimental data for isothermal friction factors and regionally averaged Nusselt numbers are presented for turbulent air flows for Reynolds numbers ranging from 17,000 to 82,000. The circular tube is composed of ten isolated copper sections with a tube length-to-diameter ratio (L/D) of 15. Three different 360° twisted-tape ratios are studied: H/D = 6(2.5 turns), 7.5 (2 turns), and 10 (1.5 turns). Three axial interrupted rib configurations attached to the inner wall of three test tubes with twisted-tape inserts are investigated: e/D = 0.0625 in-line rib, e/D = 0.0625 staggered rib, and e/D = 0.125 staggered rib.
The results show that the heat transfer and pressure drop in the tube with twisted-tape inserts increase by increasing the number of twisted-tape turns. The tube with twisted-tape inserts provide 1.5−2.0 times the heat transfer augmentation with 3-4 times the pressure drop penalty. The tube with twisted-tape inserts and staggered ribs produce higher heat transfer and pressure drop than that with twisted-tape inserts and in-line ribs, and significantly higher than without ribs. The tube with twisted-tape inserts (H/D = 7.5) and e/D = 0.125 staggered ribs provides 1.8−2.8 times the heat transfer enhancement with about 9−10 times the pressure drop penalty. The tube with twisted-tape inserts (H/D = 6) and with staggered ribs (e/D = 0.125) gains 2.2−3.2 times the heat transfer while paying 13−14 times the pressure drop. The best heat transfer performance in the tube with twisted-tape insert and staggered ribs (e/D = 0.125) is about 25−40% higher than that with the twisted-tape only for different H/D for a constant pumping power.
FIN-AND-TUBE HEAT EXCHANGERS: RECENT PATENTS
343-359
10.1615/JEnhHeatTransf.v24.i1-6.180
Chi-Chuan
Wang
Nantional Yang Ming Chiao Tung Univ
Fin-and-tube heat exchangers
This study presents updated information about patents of the fin-and-tube heat exchangers during 1981 ∼ 1999. A total of 51 patents were examined and compared. Fin patterns like convex-louver, enhanced wavy, enhanced slit, enhanced louver, vortex generators, and several special fin patterns are reported in the present report. It is recommended that further detailed examinations via numerical simulation or experimental investigation be carried out in the future to gain further insight of these fin designs.
BOILING HEAT TRANSFER FROM A SILICON CHIP IMMERSED IN DEGASSED AND GAS-DISSOLVED FC-72: EFFECTED BY SIZE AND NUMBER DENSITY OF MICRO-REENTRANT CAVITIES
361-372
10.1615/JEnhHeatTransf.v24.i1-6.190
H.
Kubo
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
Hiroshi
Takamatsu
Department of Mechanical Engineering, Kyushu University, Fukuoka 819-0395, Japan
Hiroshi
Honda
Institute of Advanced Material Study, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
Immersion cooling
silicon chip
micro-reentrant cavity
cavity mouth size
cavity number density
FC-72
Boiling heat transfer of FC-72 from newly developed treated surfaces with micro-reentrant cavities was studied experimentally. The surface structure was fabricated on a silicon chip by use of microelectronic fabrication techniques. Four kinds of treated surfaces with the combinations of two cavity mouth diameters (about 1.6 μ;m and 3.1 μ;m) and two number densities of the micro-reentrant cavities (81 l/cm2 and 96 × 103 l/cm2) were tested along with a smooth surface. Experiments were conducted at the liquid subcoolings of 3 K and 25 K with degassed and gas-dissolved FC-72. While the wall superheat at boiling incipience was strongly dependent on the dissolved gas content; it was little affected by the cavity mouth diameter and the liquid subcooling. The heat transfer performance of the treated surface was considerably higher than that of the smooth surface. The highest performance was obtained with a treated surface with a larger cavity mouth diameter and a larger cavity number density. The results were compared with those for previously developed treated surfaces.
MEASUREMENT OF CONDENSATE FILM THICKNESS FOR SOLUTAL MARANGONI CONDENSATION
373-385
10.1615/JEnhHeatTransf.v24.i1-6.200
Yoshio
Utaka
Yokohama National University, Department of Mechanical Engineering, Tokyo Institute of Technology 2-12-1 0-okayama, Meguro-ku Tokyo 152 JAPAN; School of Mechanical Engineering, Tianjin University, 135 Ya Guan Rd. Tianjin Haihe Education Park, Jinnan District, Tianjin300350, China; Key Laboratory of Efficient Utilization of Low and Medium Grade Energy (Tianjin University), Ministry of
Education, China
Tetsuji
Nishikawa
Air Liquide Japan
condensation heat transfer
solutal Marangoni condensation
water and etha-nol mixture
condensate thickness
laser extinction method
During solutal Marangoni dropwise condensation of a water–ethanol vapor mixture, condensation was observed by a high-speed camera while condensate film thickness was measured by the laser light extinction method. Good correspondence was observed between the film thickness data and the observed condensate behaviors. Minimum condensate film thickness occurred immediately after a departing drop swept by and decreased with increasing initial drop distance in the steep increase region of the condensation characteristic curve. In the region of higher cooling intensity, both initial drop distance and minimum condensate thickness increased with cooling intensity. The smallest thickness of the condensate film was less than 1 μ;m. A close relationship was confirmed to exist among condensate film thickness, initial drop distance, and heat transfer characteristics.
DETERMINING LOG MEAN TEMPERATURE DIFFERENCE CORRECTION FACTOR AND NUMBER OF SHELLS OF SHELL AND TUBE HEAT EXCHANGERS
387-402
10.1615/JEnhHeatTransf.v24.i1-6.210
Ahmad
Fakheri
Department of Mechanical Engineering Bradley University, 1501 W Bradley Ave, Peoria, IL 61625, USA
The challenge of enhancing or optimizing the rate of heat transfer from heat exchangers is compounded by the lack of a simple and generally applicable approach for its analysis. Because the expressions for the log mean temperature difference (LMTD) correction factor, F, or those for heat exchanger effectiveness, e, are difficult to evaluate, the traditional analysis methods rely on heat exchanger specific charts. In addition to being applicable only to a particular heat exchanger, these charts are highly nonlinear and strongly dependent on the traditional parameters used for their evaluation. Expressed in terms of the nondimensional parameters P and R, the LMTD correction factor F charts are particularly difficult to read in the steep regions. These shortcomings also make the assessment of different heat transfer enhancement strategies tedious. In this study, an alternative approach for determining F in terms of two new nondimensional parameters, r and f, is presented. This new approach results in a single general algebraic equation for determining the LMTD correction factor of multipass shell and tube heat exchangers with any number of shell passes and an even number of tube passes per shell. This single expression can be used to devise and compare different enhancement strategies for shell and tube heat exchanger networks, including their arrangement, to optimize their rate of heat transfer. It is shown that the approach presented results in a novel expression for the determination of the number of shells needed to meet a predefined overall correction factor for multishell and tube heat exchangers.
POROUS COUNTERFLOW HEAT EXCHANGER MODEL: EXPERIMENTAL AND NUMERICAL INVESTIGATION
403-420
10.1615/JEnhHeatTransf.v24.i1-6.220
Jose C. F.
Pereira
IDMEC, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal
Mário
Costa
IDMEC, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
Isabel
Malico
Department of Physics, University of Évora, R, Romão Ramalho, 59, 7000-671, Évora, Portugal ; IDMEC/IST, Department of Mechanical Engineering, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
Inverse method
Experiments
Heat transfer
Ceramic foams
Numerical simulations
Thermophysical properties
An experimental and numerical investigation was performed in order to evaluate the performance of several heat transfer sub-models for conduction, convection and radiation in the prediction of flow and heat transfer through 10 ppi Al2O3 foams with Peclet number based on the pore size o(102). These sub-models comprise either effective conductivity models or two phase (gas and solid) models, corresponding to thermodynamic equilibrium or non-equilibrium assumptions, respectively. Experiments were conducted in a counterflow coaxial heat exchanger, where the hot outer air, flowing at a maximum temperature of 800°C, heats the counter cold inner pipe water flow. Temperature measurements were obtained at several locations inside the porous media, pipe walls and inlet/outlet ports. Two-dimensional finite volume calculations of the coupled phenomena in the full geometrical configuration of the heat exchanger were performed.
This study shows that the effective conductivity sub-models derived for packed beds of spheres and arrays of cylinders do not provide satisfactory solutions when applied to ceramic foams. An inverse method was used to estimate the effective conductivity and contact resistance between the porous media and the inner pipe as a function of the reference temperature. Two phase flow models were scrutinised in order to discuss the influence of the relevant heat transfer parameters.
DESIGN, EXPERIMENT AND MATHEMATICAL MODEL OF VORTEX HEAT EXCHANGER
421-430
10.1615/JEnhHeatTransf.v24.i1-6.230
B.
Krasovitski
Department of Agricultural Engineering, Technion, Technion City, Haifa 32000, Israel
L.
Tunkel
Universal Vortex Inc. P.O. Box 338, New Jersey 08555-0338 USA
Vortex tube
Heat transfer
Heat exchanger
Gas
Cooling
The paper presents an investigation of a vortex tube (VT), operating with closed "hot" valve. A set of experiments conducted showed a substantial decrease of the outlet gas stagnation temperature and rise of the VT wall temperature. For this objective, a VT based heat exchanger was designed and built. The design was named as Vortex Heat Exchanger (VHE). The outlet gas temperature decreased as much as 27°C, depending on the cooling mode. The temperature may fall much lower than the cooling agent temperature. A model of the VHE, developed on the basis of the experimental data, permits prediction of the outlet flow temperature at various regimes.
ENDLESS FRONTIER, OR MATURE AND ROUTINE OF ENHANCED HEAT TRANSFER
431-443
10.1615/JEnhHeatTransf.v24.i1-6.240
Arthur E.
Bergles
Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA; University of Maryland, College Park, MD, USA; Massachusetts Institute of Technology, Cambridge, MA, USA
Enhancement of heat transfer
augmentation of heat transfer
intensification of heat transfer
passive enhancement techniques
active enhancement techniques
This paper considers the many techniques that have been developed to enhance convective heat transfer. They are presented according to the mode of heat transfer. The current advanced enhancement represents 3rd generation heat transfer technology. The many contributions of Prof. Ralph Webb are integral to this development. It is felt that this field has a bright future.
REVIEW ON LAMINAR FLOW AND HEAT TRANSFER IN INTERNALLY FINNED TUBES
445-468
10.1615/JEnhHeatTransf.v24.i1-6.250
Biswadip
Shome
Global Technology and Engineering Center, Offices No. 501 & No. 502, D Block, Weikfield IT Citi Info Park, Pune-Nagar Road, Pune, India 411014; TATA Technologies Limited, 25 Rajiv Gandhi Infotech Park, Hinjewadi, Pune 411057, India
Michael K.
Jensen
Center for Multiphase Flow, Rensselaer Polytechnic Institute, Troy, NY, USA; University of Wisconsin-Milwaukee, Mechanical Engineering Department Milwaukee, Wisconsin 53201
Finned tubes
heat transfer
enhancement
experimental
laminar flow
An experimental investigation of laminar flow and heat transfer in internally finned tubes was performed. Length-averaged measurements of heat transfer and pressure drop for thermally developing flow were conducted for both heating and cooling situations as well as for low and high heat flux cases using ethylene glycol as the test fluid. The heat transfer tests were performed with fluid-to-fluid heating or cooling which closely approximates constant wall temperature boundary conditions. Isothermal friction factors, diabatic friction factors, and Nusselt numbers were measured for fin geometry ranges of 8 ≤ N ≤ 54, 0.015 ≤ H ≤ 0.17, and 0 ≤ γ ≤ 45 degrees and operating condition ranges of 150 < Re < 2.000, 50 < Pr < 185, 0.3 < μb/μw < 3.6, and 3 × 105 < Ra < 8 × 104. The length-to-inside tube diameter ratios for the tubes tested were around 120. The maximum heat transfer enhancement relative to a smooth tube was obtained for tubes with fewer number of tall fins with strong free convection effects and was around 75% at the expense of 50% increase in pressure drop penalty over the smooth tube value. Overall, the micro-finned tubes and the tubes with fewer number of tall fins were found to be ineffective in laminar flow with small to moderate free convection effects as little or no heat transfer enhancement was obtained at the expense of a fairly large pressure drop penalty. The results also indicated that the fin geometry has little effect on the heat transfer, particularly for micro-finned tubes. The effect of free convection on the pressure drop was marginal but its influence on the heat transfer was found to be substantial.
A REVIEW OF FULLY-DEVELOPED NUSSELT NUMBERS AND FRICTION FACTORS IN PIPES WITH 3-DIMENSIONAL ROUGHNESS
469-488
10.1615/JEnhHeatTransf.v24.i1-6.260
Robert P.
Taylor
Mechanical Engineering Department, Mississippi State University, Mississippi State, MS, USA 39762
B. K.
Hodge
Mechanical Engineering Department, Mississippi State University, Mississippi State, MS, USA 39762
Roughness
Fully developed
Friction factor
Nusselt number
Discrete element
Turbulent flow
A computer program based on the discrete element method has been developed and validated to compute friction factors and Nusselt numbers for thermally fully-developed turbulent flow in pipes with 3-dimensional roughness elements. Validation is achieved by comparing the computational results with accepted experimental data cited in the heat transfer literature. The predictions are in general in very good agreement with the experimental data and tend to confirm the predictive validity of the approach.
A REVIEW ON EFFECT OF PARTICLE SIZE AND SIZE DISTRIBUTION ON PARTICULATE FOULING IN ENHANCED TUBES
489-506
10.1615/JEnhHeatTransf.v24.i1-6.270
L. M.
Chamra
Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802 USA
Ralph L.
Webb
Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802, USA
Fouling
Particulate fouling
Enhanced tubes
This paper describes the results of accelerated particulate fouling tests performed on different enhanced tubes and a plain tube. The key purpose of the tests was to investigate particulate fouling in practical heat exchanger systems where a mixture of particles exists in a flowing water stream. The applications considered are electric utility steam condensers on the Mississippi and Ohio rivers. These condensers operate with foulant materials consisting of silt and clay, having a distribution of particle sizes. Fouling data were taken for a wide range of particle concentrations, particle size, and velocity. The concentration was varied between 800 and 2,000 ppm for the particle sizes of 2,4 and 16 μm. In addition, the Reynolds number was varied between 24,000 and 65,000 for a constant concentration of 1,500 ppm.
The experimental results show that the enhanced tubes foul faster than the plain tube. However, at very low concentration the enhanced and plain tubes foul at the same rate. The asymptotic fouling resistance increases as the concentration increases and it decreases as the particle diameter and velocity increase.
A REVIEW ON SATURATED POOL BOILING ENHANCEMENT BY MEANS OF AN ELECTRIC FIELD
507-530
10.1615/JEnhHeatTransf.v24.i1-6.280
Paolo
Di Marco
Department of Energy, Systems, Constructions and Territory Engineering, University of Pisa, largo Lucio Lazzarino 1, Pisa 56122, Italy
Walter
Grassi
Lo.Th.A.R. (Low gravity and Thermal Advanced Research Laboratory), DESTEC (Department of Energy, Systems, Territory and Constructions Engineering), University of Pisa−Largo Lucio Lazzarino, 56122 Pisa, Italy
Boiling
Electric field
Enhanced heat transfer
The effect exerted by an externally imposed electrostatic field on regime transitions in saturated pool boiling is treated in the paper. After introducing the equations governing the influence of the electric field on boiling, the EHD effect on bubble dynamics and interface stability in a two-phase fluid is briefly illustrated. The nucleate boiling region, the peak and minimum film boiling heat flux conditions and stable film boiling are separately dealt with, in order to better emphasize the influence of the electric field on the different features of the pool boiling process. The main theoretical and experimental results obtained by the different researchers and available in the open literature are critically reviewed, attempting to stress the more significant findings as well as the aspects still needing further research work.
A REVIEW ON CONDENSATION AND EVAPORATION IN MICRO-FIN TUBES AT EQUAL SATURATION TEMPERATURES
531-548
10.1615/JEnhHeatTransf.v24.i1-6.290
L. M.
Chamra
Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802 USA
Ralph L.
Webb
Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802, USA
Condensation
Evaporation
Inside tubes
Micro-fin
Data were taken for condensation and evaporation in a micro-fin tube at the same saturation temperature to examine similarities and differences of condensation and evaporation in micro-fin tubes. The condensation and evaporation data were taken in the same tube at 24.4°C saturation temperature, for a range of mass velocities (150−327 kg/m2-s), and vapor qualities (0.1−0.9). If the heat transfer mechanism is "convection dominated", one would expect that the condensation and evaporation coefficients should be nearly equal. The present data show that this behavior was verified, except for a possible nucleate boiling contribution at low vapor quality. Both vaporization and condensation show a small effect of heat flux in the high vapor quality regions. These data provide insight of the heat transfer mechanisms, and suggest a basis for developing heat transfer correlations that may apply to both condensation and evaporation.
A REVIEW ON HEAT TRANSFER COEFFICIENT AND AERODYNAMIC RESISTANCE ON A SURFACE WITH A SINGLE DIMPLE
549-568
10.1615/JEnhHeatTransf.v24.i1-6.300
Viktor I.
Terekhov
Kutateladze Institute of Thermophysics, Laboratory of Thermal and Gas Dynamics, Russian Academy of Sciences, Siberian Branch, 630090,1, Acad. Lavrent'ev Avenue, Novosibirsk, Russia; Novosibirsk State Technical University, K. Markx av., 20, Novosibirsk, 630073, Russia
S. V.
Kalinina
Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Yu. M.
Mshvidobadze
S. S. Kutateladze Institute of Thermal Physics, Russian Academy of Sciences, Novosibirsk, Russia
Heat transfer enhancement
channel
cavity
vortex structure
hole
Recent attention in the field of enhanced heat transfer has focused on heat transfer coefficients and aerodynamic resistance on surfaces of various physical constructions. Experimental investigations have shown that a favorable relationship exists on a concave surface where the dimples are defined as holes with rounded off edges. On such surfaces, dimples may be established which increase the heat transfer coefficient greater than they increase aerodynamic resistance, leading to an overall increase in the rate of heat transfer for an established set of extraneous conditions. The heat transfer coefficient increases at a rate greater than can be attributed to the increasing surface area. This appears due to auto oscillations generated by the cavity under turbulent flow regime. The regime of these auto oscillations is characterized by large scale, non-periodic transverse current oscillations and asymmetrical vortexes within the cavity. The parameters of this regime are dependent upon the depth and radius of the dimple. This study investigates the relationship of these characteristics to the heat transfer coefficient and the aerodynamic resistance on the surface.
A REVIEW ON SHELL-AND-TUBE HEAT EXCHANGERS FOR THE CHEMICAL PROCESSING INDUSTRY: HEAT TRANSFER AUGMENTATION
569-586
10.1615/JEnhHeatTransf.v24.i1-6.310
John R.
Thome
Laboratory of Heat and Mass Transfer (LTCM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 9, CH-1015 Lausanne, Switzerland
Shell-and-tube heat exchangers
laminar flows
evaporation
condensation
practical considerations
new enhancements
costs
Numerous tubular heat transfer augmentations are commercially available for application to the shell-and-tube types of heat exchangers favored by the chemical processing industries. In appropriate applications, these augmentations are able to reduce heat exchanger tubing linear footage by 25−75% relative to conventional plain tube units, yet they are utilized in only a fraction of these opportunities. Thermal design guidelines together with practical technical and cost considerations for enhanced shell-and-tube heat exchangers are provided here to facilitate their use in process intensification.
A REVIEW ON ENHANCED HEAT TRANSFER CHARACTERISTICS OF SINGLE-PHASE FLOWS IN A PLATE HEAT EXCHANGER
587-607
10.1615/JEnhHeatTransf.v24.i1-6.320
Arun
Muley
Department of Mechanical, Industrial and Nuclear Engineering University of Cincinnati, Cincinnati, OH 45221-0072
Raj M.
Manglik
Thermal-Fluids and Thermal Processing Laboratory, Mechanical and Materials Engineering, University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45220, USA
Enhancement
single-phase flow
plate heat exchanger
mixed chevron plates
Wilson plot
The enhanced thermal-hydraulic performance of single-phase flows in a plate heat exchanger with mixed chevron plates is investigated experimentally. The mixed arrangement consists of plates with chevron angle β = 30° and 60°, alternatingly stacked in a single-pass, U-type, counterflow configuration. Vegetable oil (130 < Pr < 220) and water (2.4 < Pr < 4.5) are used as test fluids, with flow rates in the laminar, transition, and turbulent flow regimes (2 < Re < 6000). Results for isothermal friction factor and heat transfer under cooling conditions, along with respective correlations for laminar (2 < Re < 400) and fully developed turbulent (Re ≥ 1000) flows are presented; transition is observed to set in when Re ∼ 500. The heat transfer data are obtained from controlled experiments, employing an extension of the Wilson Plot technique. A comparison of the data with previously reported results and predictive equations for Nu and / highlights the latter’s lack of general applicability, and the need for a larger database. The relative impact of using mixed chevron plate arrangement is discussed, and their enhanced performance, in comparison with parallel-plate channels, is evaluated.
A REVIEW ON HEAT TRANSFER AND PRESSURE DROP DURING EVAPORATION AND CONDENSATION OF R22 INSIDE 9.52-MM O.D. MICROFIN TUBES OF DIFFERENT GEOMETRIES
609-626
10.1615/JEnhHeatTransf.v24.i1-6.330
Adriano
Muzzio
Dipartimento di Energetica - Politecnico di Milano, Milan, Italy
Alfonso
Niro
Department of Energy, Politecnico di Milano, Via Lambruschini 4, Milano IT−20156, Italy
S.
Arosio
Dipartimento di Ingegneria Energetica, Universita di Genova, Politecnico di Milano piazza Leonardo da Vinci 32, 20133 Milano, Italy
Heat transfer
enhanced flow boiling
convective condensation
microfin tubes
Saturated flow boiling and convective condensation experiments for oil-free Refriger-ant-22 have been carried out with a microfin tube with a new cross-section profile, as well as with two traditional microfin tubes and with a smooth one. All tubes have the same outer diameter. Data are for mass fluxes ranging from about 90 to 400 kg/m2·s. In boiling tests, the nominal saturation temperature is 5°C, with inlet quality varying from 0.2 to 0.6 and the quality variation along the test section ranging from 0.1 to 0.5. In condensation, results are for saturation temperature equal to 35°C, with inlet and outlet qualities of 0.8 and 0.2, respectively. The new microfin tube shows the best thermal performances among the microfin tubes tested, especially in evaporation. For this case, the enhancement factor comes up to 4. Experimental results for microfin tubes are compared with predictions of a correlation scheme recently proposed; these predictions correlate well only with data for the microfin tube with a geometry much similar to one accounted by the scheme.
A REVIEW ON MICRO/MINIATURE HEAT PIPES
627-642
10.1615/JEnhHeatTransf.v24.i1-6.340
Yiding
Cao
Department of Mechanical and Materials Engineering, Florida International University,
Miami, Florida 33174; Department of Mechanical and Materials Engineering Wright State University Dayton, OH 45435
Amir
Faghri
College of Engineering, Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Rd., Unit 3139, Storrs CT 06269-3139, USA; Department of Mechanical and Materials Engineering Wright State University Dayton, OH 45435
Miniature and micro heat pipes
Longitudinal groove design
Vapor continuum limitation
A literature review related to miniature and micro heat pipes is given. It is found that longitudinal groove designs are crucial to increase the heat transport capacity of miniature heat pipes. In addition to the operational limitations of conventional heat pipes, micro heat pipes may be subject to the vapor continuum limitation, which may prevent micro heat pipes from operating under lower working temperatures. An analysis of the capillary limit reveals that the disjoining pressure may play a role in heat transfer for the micro heat pipe and may increase its heat transfer capacity.
A REVIEW ON FALLING FILM EVAPORATION
643-659
10.1615/JEnhHeatTransf.v24.i1-6.350
John R.
Thome
Laboratory of Heat and Mass Transfer (LTCM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 9, CH-1015 Lausanne, Switzerland
Evaporation
falling film
enhancement
A state-of-the-art review of falling film evaporation on single tubes and tube bundles is presented. Emphasis is placed on recent work and, in particular, on studies on the new alternative refrigerants and ammonia. Both plain and enhanced tubes are addressed in the survey plus the effects of oil on heat transfer. The enhanced tubes provide a very high level of heat transfer augmentation for falling film evaporation on horizontal bundles, sharply reducing the required refrigerant charge compared to flooded evaporator designs.
A REVIEW ON HORIZONTAL CONVECTIVE CONDENSATION OF REFRIGERANTS WITHIN A MICRO-FIN TUBE
661-683
10.1615/JEnhHeatTransf.v24.i1-6.360
Mark
Kedzierski
NIST
J. M.
Goncalves
NIST Guest Researcher from Escola Tecnica Federal de Santa Catarina - UnED/SJ, R. Jose Lino Kretzer, 608, Praia Comprida, Sao Jose, S.C., 88.103-902, Brazil
Enhanced heat transfer
micro-fin
refrigerant mixtures
fluid heating
condensation
pressure drop
This paper presents local convective-condensation measurements for four refrigerants: R134a, R410A (R32/R125, 50/50% mass), R125, and R32 in a micro-fin tube. Both heat transfer and pressure drop measurements are provided. The heat transfer degradation associated with R410A was shown to be relatively small and believed to be mostly due to nonlinear property effects. The measured convective-condensation Nusselt numbers for all of the test refrigerants were correlated to a single expression consisting of a product of dimensionless properties. The correlation was shown to predict some existing data from the literature within acceptable limits. The correlation poorly predicted the heat transfer performance of cross-grooved, micro-fin tubes. The pressure drop measurements for the micro-fin tube were predicted satisfactorily by an existing correlation for flow-boiling pressure drop in a smooth tube. Correlation of the pressure drop measurements suggested that the heat transfer enhancement was due to the fins behaving as a surface roughness.
A REVIEW ON HEAT TRANSFER ENHANCEMENT IN A CONVECTIVE FIELD BY APPLYING IONIC WIND
685-705
10.1615/JEnhHeatTransf.v24.i1-6.370
Y.
Tada
Department of Human and Mechanical Systems Engineering, Kanazawa University, Kanazawa, Japan
Akira
Takimoto
Department of Human and Mechanical Systems Engineering, Kanazawa University, 2-40-20 Kodatsuno, Kanazawa 920-8667, JAPAN
Yujiro
Hayashi
Department of Mechanical Systems Engineering, Kanazawa University, Ishikawa 060, Kanazawa, Japan
Forced convection
heat transfer enhancement
electro-hydrodynamics
ionic wind
channel flow
heat exchanger
This study has been conducted to pursue the enhancement of forced-convection heat transfer by applying an electric field. Experiments were performed in an air channel flow where a series of wire-electrodes were installed in parallel with the primary flow direction, or installed at right angle to the primary flow direction. By applying the electric field, secondary flow was electro-hydrodynamically induced by the Coulomb force. The visualization of flow patters and measurement of heat transfer coefficient and consuming power were carried out. The theoretical analysis on electric, flow and temperature field was also performed taking account of momentum transfer between ions and neutral fluid molecules. On the basis of these results, fundamental characteristics of the EHD combined flow and the heat transfer were clarified in conjunction with applied voltage, primary velocity and wire-electrode arrangement. And, the possibility of the practical applications of the ionic wind are discussed.