Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
18
4
2011
IN MEMORIAM: PROFESSOR RALPH L. WEBB (1934−2011)
2
10.1615/JEnhHeatTransf.v18.i4.10
Raj M.
Manglik
Thermal-Fluids and Thermal Processing Laboratory, Mechanical and Materials Engineering, University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45220, 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
Mark
Kedzierski
NIST
Thomas M.
Rudy
Essex Consulting Group, Meadow Brook Farm LLC, Warrenton, Virginia 20186, USA
PORE SCALE SIMULATION OF LAMINAR FLOWAND HEAT TRANSFER IN POROUS MEDIA USING THE LATTICE BOLTZMANN METHOD
273-279
10.1615/JEnhHeatTransf.v18.i4.20
S. S.
Hosseini
1Department of Mechanical Engineering, Faculty of Engineering, University of Tehran, Tehran, Iran
Sh. Farhadi
Nia
Institute of Petroleum Engineering, Faculty of Engineering, University of Tehran, Tehran, Iran
Mohammad Hassan
Rahimian
Department of Mechanical Engineering, Faculty of Engineering, University of Tehran, Tehran, Iran
lattice Boltzmann method
porous media
pore-scale simulation
convective heat transfer
In the present work, fluid flow and heat transfer in porous media were simulated at the pore scale using the lattice Boltzmann method. The method is based on random distribution of solid bars to generate the porous media in the desired region. To simulate the temperature field, a simplified thermal lattice BGK model with doubled population method was employed. The physical configuration is a parallel-plate channel with adiabatic walls filled with porous media. Comparing average Nusselt numbers in the present work with previous works, a reasonable agreement was observed.
THERMOHYDRAULICS OF TURBULENT FLOW THROUGH SQUARE AND RECTANGULAR DUCTS WITH TRANSVERSE RIBS AND TWISTED TAPES WITH AND WITHOUT OBLIQUE TEETH
281-293
10.1615/JEnhHeatTransf.v18.i4.30
Sujoy
Saha
Department of Mechanical Engineering, Indian Maritime University, Kolkata Campus, Kolkata- 700088, ( A central University, Govt. of India)
turbulent swirl flow
forced convection
transverse ribs
twisted tape
square and rectangular ducts
oblique teeth
Thermal and friction characteristics of turbulent flow through square and rectangular ducts with periodic transverse ribs and different types of twisted tapes with and without oblique teeth have been studied experimentally. Circular ducts have also been used. Correlations for predicting the friction factor and the Nusselt number have been developed and performance has been evaluated. Although both the friction factor and the Nusselt number are higher for all types of twisted tapes with oblique teeth in combination with transverse ribs, the performance evaluation has shown that the ducts with transverse ribs and regularly spaced twisted-tape elements with oblique teeth are better than those in the case without oblique teeth and this is recommended. Also, since the pressure drop in a heat exchanger is a small fraction of the total system pressure drop, the heat transfer being higher, full-length and short-length twisted tapes with oblique teeth in combination with transverse ribs can be recommended since the heat exchanging surface area requirement will be less.
HEAT TRANSFER ENHANCEMENT IN A HORIZONTAL PIPE: THE EFFECTS OF FLOWRATE, PULSATION FREQUENCY AND AMPLITUDE
295-309
10.1615/JEnhHeatTransf.v18.i4.40
Nurin Wahidah Mohd
Zulkifli
Department of Mechanical and Aerospace Engineering, Monash University, Clayton, Victoria 3800, Australia
Mir-Akbar
Hessami
Department of Mechanical and Aerospace Engineering, Monash University, Australia
flow pulsation
heat transfer enhancement
pulsation frequency
pulsatile flow
pulsating flow
oscillating flow
empirical equations
error analysis
The effects of flow pulsation on heat transfer in a heated horizontal pipe were investigated experimentally for 7000 < Re < 70,000 and for 0.025 Hz < f < 1.0 Hz (2 < Wo < 20) and various pulsation amplitudes. Dimensional analysis of the governing equations showed that for such applications Nu can be described in terms of Re, Wo, Pr, and A*; the effects of Pr are not investigated in this study. The results showed that heat transfer enhancement (defined in terms of Nu of a pulsating flow compared to that of a steady flow) was achieved for 3 < Wo < 17 (0.05 < f < 0.7), with a maximum enhancement of 200% when f = 0.3 Hz at Re ј 8000. For this range of f, Nu increased with increasing f up to 0.3 Hz after which it decreased with increasing f until f = 0.7 Hz. For f < 0.05 Hz and f > 0.7 Hz, Nu for a pulsating flow was lower than that for a steady flow. Similarly, Nu increased with increasing A as well as with increasing Re. However, heat transfer enhancement decreased with increasing Re. A number of empirical correlations were developed for Nu = f (Re) for various values of f, and for Nu = f (Wo) for various values of Re. A single correlation was also developed for Nu = f (Re, Pr, Wo) for the range of parameters studied in this project. The experimental error in the heat transfer results of this study was estimated to be less than 20%. Results of this study can be used to improve heat transfer efficiency of industrial heat exchangers in order to reduce the demand for electrical energy with a consequential reduction of greenhouse gas emissions to the environment.
EXPERIMENTAL STUDY OF POOL BOILING ON PIN-FINNED AND STRAIGHT-FINNED SURFACES ON AN INCLINED PLATE IN FC-72
311-324
10.1615/JEnhHeatTransf.v18.i4.50
Shu-Che
Lee
Department of Energy and Refrigerating Air-conditioning Engineering, National Taipei University of Technology, Taipei, 10608, Taiwan
Liang-Han
Chien
National Taipei University of Technology
boiling
dielectric fluid
pin fin
straight fin
inclination angle
Pool boiling experiments were conducted on copper surfaces in a saturated dielectric fluid, FC-72, at three orientations at a saturation temperature of 50°C. A plain surface, four types of straight-finned surfaces, and six types of pin-finned surfaces were tested to investigate the effects of fin dimensions. Fins were 0.1−0.4 mm thick and the fin lengths varied from 0.1 to 1.6 mm. For the plain surface, the heat transfer coefficient increased as the inclination angle increased at low heat fluxes for the increasing heat flux tests. No marked effect on CHF and heat transfer coefficient during the decreasing heat flux tests was observed for all surfaces in the present tests. The pin fins made by wire cutting yield higher boiling performance than the wet-etched surfaces because of the advantage of larger surface roughness and sharper fin base corners. The heat transfer coefficient increased with increasing fin height/width ratio. The best surface was the pin-finned surface having a fin width of 0.4 mm, a fin height of 1.6 mm, and a fin pitch of 0.8 mm. It enhanced the boiling heat transfer coefficient about eightfold. For the same fin height and width, the straight fins and the pin fins yield similar performance at q" < CHF (critical heat flux). However, the CHF of the pin fins was greater than that of the straight fins because the opening area on the top of the pin fins was greater than that of the straight fins. For both straight fins and pin fins, the boiling heat transfer efficiency was mainly enhanced by increasing the total surface area at q" < CHF. A CHF correlation of the finned surfaces has been proposed. It predicts the CHF data of FC-72 from four sources with an rms deviation of 14.95%.
MARANGONI CONDENSATION HEAT TRANSFER OF WATER-ETHANOL MIXTURE VAPOR
325-343
10.1615/JEnhHeatTransf.v18.i4.60
Junjie
Yan
State Key Laboratory of Multiphase Flow in Power Engineering, School of Energy & Power Engineering, Xi'an Jiaotong University, Xi'an, 710049, P. R. of China
Jinshi
Wang
Xi’an Jiaotong University
Shenhua
Hu
State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Daotong
Chong
State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Jiping
Liu
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, Xi'an Jiaotong University, Xi'an 710049, China
condensation
heat transfer coefficient
temperature gradient
plate
The heat transfer characteristics for condensation onto three plates (flat, taper fin, and flat fin) of water-ethanol vapor have been systematically investigated. A comparison of the three condensation heat transfer characteristics was made, and the effect of temperature gradients on the Marangoni condensation heat transfer was investigated. The results showed that the condensation modes on the surfaces with temperature gradients were usually a mixture of several different modes, while a single mode usually occurred on the condensing surface of the plat plate. The change of condensation modes on plates with fins was less marked and frequent than that on the flat plate. The mean heat transfer coefficients for the flat-fin plate, which had larger temperature gradients on the condensing surface, were greater than those on the surfaces with smaller temperature gradients. However, the degree of promotion of heat transfer by the temperature gradients depended on their values. Temperature gradients on the condensing surface made the vapor-to-surface temperature difference region, responsible for enhancing heat transfer, move to the lower region, and larger temperature gradients produced more significant movement. Moreover, the positive effect of both vapor velocity and pressure on the heat transfer was weakened by temperature gradients. The enhancement effect of vapor velocity and pressure on heat transfer was weaker when the temperature gradients on the condensing surface were larger.
EXPERIMENTAL AND NUMERICAL STUDY ON NATURAL AIR COOLING OF A REMOTE RADIO UNIT
345-359
10.1615/JEnhHeatTransf.v18.i4.70
P.
Chu
State Key Laboratory of Multiphase Flow in Power Engineering, School of Energy & Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
Ya-Ling
He
Key Laboratory of Thermo-Fluid Science and Engineering, Ministry of Education, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
R. J.
Xu
MOE Key Laboratory of Thermo-Fluid Science and Engineering, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaan xi 710049, China
H.
Han
MOE Key Laboratory of Thermo-Fluid Science and Engineering, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaan xi 710049, China
cooling design
natural convection
heat spot problem
heat transfer performance
With the rapid increase of heat dissipation level in modern electronic equipments, the thermal management of electronic equipments becomes increasingly important. The remote radio unit (RRU) has been widely used in the third-generation mobile communication technology, and the cooling design is important to maintain the reliability and functionality of an RRU. The heat transfer and flow characteristics of an RRU are experimentally and numerically investigated under a natural convection condition. The experimental results are in good agreement with numerical results. The effects of fin density, vapor chamber, pin-fin heat sink, and surface emissivity on the heat transfer performance of the RRU are numerically investigated. The results indicate that the optimal fin number for the RRU with the given dimensions is around 25. The vapor chamber alleviates the heat spot problem on the heat sink base and improves the average heat transfer coefficient by 16.6%. The pin-fin heat sink increases the average heat transfer coefficient by 11.2%, while it decreases the heat transfer surface area by 38.6%. The augmentation of surface emissivity slightly improves the heat transfer performance of the RRU.