Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
22
3
2015
EFFECT OF ASPECT RATIO ON EVAPORATION HEAT TRANSFER AND PRESSURE DROP OF R-410A IN FLATTENED MICROFIN TUBES
177-197
10.1615/JEnhHeatTransf.2015014433
Nae-Hyun
Kim
Department of Mechanical Engineering, Incheon National University, Incheon 406-772, Republic of Korea
extended surface
internal microfins
two-phase flow
refrigerant evaporator
In this study, evaporation heat transfer coefficients and pressure drops of R-410A were obtained in flattened microfin tubes (AR = 2, 4) made from 7.0 mm O.D. round microfin tube. The test range covered mass flux from 200 to 400 kg/m2s. The heat flux and saturation temperature were fixed at 10 kW/m2 and 15° C. Both the evaporation heat transfer coefficient and the frictional pressure drop increased as quality or mass flux increased. They also increased as the tube aspect ratio increased. The heat transfer enhancement ratio ranged from 1.51 to 3.08, which increased as mass flux decreased. However, the pressure drop penalty factors were less than 1.0. Comparison with existing round microfin tube correlations was made.
MAXIMUM SURFACE HEAT FLUX DURING JET IMPINGEMENT QUENCHING OF VERTICAL HOT SURFACE
199-219
10.1615/JEnhHeatTransf.2015014094
C.
Agarwal
Department of Mechanical Engineering, College of Technology and Engineering, Maharana Pratap University of Agriculture and Technology, Udaipur, 313001, India
Ravi
Kumar
Department of Mechanical & Industrial Engineering, Indian Institute of
Technology, Roorkee-247667, India
Akhilesh
Gupta
Department of Mechanical & Industrial Engineering, Indian Institute of
Technology Roorkee-247667, India
Barun
Chatterjee
Reactor Safety Division, Bhabha Atomic Research Centre, Mumbai-400085, India
forced convection boiling
jet impingement
peak heat flux
two phase flow
transient cooling
The rapid quenching of a hot surface is desirable in several industrial applications, e.g., metal processing, nuclear power plants, electronics, etc. Therefore, an experimental investigation has been carried out on a hot vertical stainless steel surface of 0.25 mm thickness at 800 ± 10° C initial temperature. The surface has been quenched with the impingement of a round water jet in the range of 2.5−4.8 mm diameters. The maximum surface heat flux during quenching has been determined for jet Reynolds number in the range of Re = 5000−24,000. The observations are made from the stagnation point to the 24 mm downstream spatial locations, for both upside and downside directions of the test surface. It has been observed that the maximum surface heat flux increases with the rise in jet Reynolds number and jet diameter. The correlation proposed to determine the maximum surface heat flux predicts the experimental data within an error band of ±20%. The published correlation for the horizontal surface predicts the experimental data of maximum surface heat flux within the range of +40% to −20%.
THE EFFECT OF TRANSVERSE TUBE PITCH ON THE THERMAL-HYDRODYNAMIC PERFORMANCE OF A CIRCULAR TUBE-PLATE-FIN HEAT EXCHANGER WITH FIN-MOUNTED VORTEX GENERATORS
221-246
10.1615/JEnhHeatTransf.2015014211
Wan-Ling
Hu
School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou, 730070, China; Key Laboratory of Railway Vehicle Thermal Engineering (Lanzhou Jiaotong University), Ministry of Education of China, Lanzhou, 730070, China
Liang-Bi
Wang
School of Mechanical Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu 730070, PR China; Key Laboratory of Railway Vehicle Thermal Engineering of MOE, Lanzhou Jiaotong University, Lanzhou,
Gansu 730070, PR China
Yong
Guan
School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou, 730070, China
displaced enhancement devices
extended surface
single-phase flow
numerical analysis
compact heat exchanger
To increase the heat transfer performance of a tube-plate-fin heat exchanger and improve the convective heat transfer coefficient of the air side, winglet-type vortex generators can be punched on the fin surface of a circular tube-plate-fin heat exchanger. In real application, the transverse tube pitch has great influence on the heat transfer and flow resistance characteristics of the tube-plate-fin heat exchanger with vortex generators. Therefore, the effect of the transverse tube pitch on heat transfer performance of such heat exchanger should be considered. In this paper we numerically studied the effect of transverse tube pitch on heat transfer and the intensity of secondary flow performance. The results show that at the same front inlet velocity of a heat exchanger, with increasing the transverse tube pitch, the volume average intensity of secondary flow, overall average Nusselt number and pressure drop all decrease. To screen the optimal transverse tube pitch, an appropriate evaluation criterion has been developed. Under the same width, height, and length of the heat exchanger and the same front inlet velocity, the optimal transverse tube pitch is screened. As the front inlet velocity changes, the optimal transverse tube pitch also changes. When the front inlet velocity is less than 3.5 m/s, the larger the transverse tube pitch is, the better the comprehensive heat transfer performance is, and when the front inlet velocity is greater than 3.5 m/s, the optimal transverse tube pitch is about 2.3 times of the tube outside diameter.
NUCLEATE POOL BOILING HEAT TRANSFER FROM A FLAT-PLATE GROOVED SURFACE
247-265
10.1615/JEnhHeatTransf.2015014319
Alangar
Sathyabhama
Department of Mechanical Engineering, National Institute of Technology Karnataka, Surathkal,
Mangalore, India-575025
rough surface
two-phase convection
electronic cooling
experimental heat transfer
This paper presents the experimental investigation of pool boiling heat transfer performance of copper plain and grooved horizontal circular surfaces immersed in saturated water at atmospheric pressure. The effect of the geometric parameters of the groove on boiling heat transfer was studied. From the experimental results, it was observed that the enhanced surfaces have a positive effect on the heat dissipation and the effect is greater than in the case of a plain surface. It was found that the heat dissipation increases with increasing groove depth, decreasing groove angle, and decreasing channel width. The improved heat transfer is attributed to improved bubble dynamics, which are a function of the heat transfer area, bubble escape resistance, and capillary force. The dominance of any of these factors over the other depends on a particular specimen. The modified Rohsenow correlation predicts the present experimental data with an error of ±20%.