Begell House Inc.
Heat Transfer Research
HTR
1064-2285
40
6
2009
Effects of Fluctuating Surface Temperature and Concentration on Unsteady Convection Flow Past an Infinite Vertical Plate with Constant Suction
505-519
10.1615/HeatTransRes.v40.i6.10
Bhupendra K.
Sharma
Department of Mathematics, Birla Institute of Technology & Science, Pilani, Rajasthan, India
Pawan Kumar
Sharma
Department of Applied Mathematics Amity School of Engineering and Technology, 580 Delhi-Palam Vihar Road, U&I Building, Beijwasan, New Delhi, India
Rama C.
Chaudhary
The University of Rajasthan, Department of Mathematics, Jaipur, India
convection; heat transfer; mass transfer; suction
Combined heat and mass transfer along an infinite vertical porous plate have been investigated when the temperature and concentration are assumed to oscillate in time about a constant mean. Assuming constant suction at the plate, approximate solutions are calculated by the perturbation method for transient velocity, temperature and concentration. The effects of various parameters on transient velocity, temperature, concentration, skin-friction, and rate of heat transfer have been discussed with the help of graphs and tables.
Effect of the Heater Location on Heat Transfer and Entropy Generation in the Cavity Using the Lattice Boltzmann Method
521-536
10.1615/HeatTransRes.v40.i6.20
Mojtaba Aghajani
Delavar
Faculty of Mechanical Engineering, Babol Noshirvani University of Technology, Babol, Iran
Mousa
Farhadi
Faculty of Mechanical Engineering, Noshirvani University of Technology, Babol, Islamic Republic of Iran
Kurosh
Sedighi
Babol University of Technology, Faculty of Mechanical Engineering, Babol, Iran
natural convection; cavity; entropy generation; lattice Boltzmanm method
In this study, a lattice Boltzmann method (LBM) was employed to numerically investigate the effect of the heater location on entropy generation, flow pattern, and heat transfer in a cavity. The study was carried out for a heater of length 0.4H which is located at the lower wall of the cavity. The simulations were performed for Rayleigh numbers from 103 to 106 at Pr = 0.71. The results show that the location of the heater has a great effect on the flow pattern and temperature fields in the enclosure and subsequently on entropy generation. With increasing the distance between the heater and a cold wall the entropy generation decreases. On the other hand, a maximum Nusselt number is observed over the left cold wall when the heater is located near the cold wall. The slope variation (gradient) of the Nusselt number increases over the heater and the left wall of the cavity at a higher Rayleigh number for a fixed location of the heater. The dimensionless entropy generation decreases at a high Rayleigh number and is independent of the heater position.
Effect of Inclination Angle on Free Convection from an Elliptic Tube Confined between Walls
537-553
10.1615/HeatTransRes.v40.i6.30
Tooraj
Yousefi
Mechanical Engineering Department, Razi University, Kermanshah, Iran
Mehdi
Ashjaee
Department of Mechanical Engineering, University of Tehran, Tehran, Iran
Sajjad
Yazdani
School of Energy, Kermanshah University of Technology, Kermanshah, Iran
H.
Mahmoodi
School of Mechanical Engineering, University of Tehran, Tehran 11365-4563, Iran
free convection; inclination angle; elliptic tube; adiabatic walls
Laminar free-convection heat transfer from an inclined isothermal horizontal elliptic tube located in an infinite medium and between two adiabatic walls has been investigated experimentally by the Mach-Zender interferometry technique. The axis ratio of the elliptic tube is 0.67. The present paper focuses on the effect of an inclination angle of the tube with the horizon, wall spacing, and the Rayleigh number variation on the local and average free-convection heat transfer from the tube surface. To study the effect of axial inclination on free-convection heat transfer the tube has been inclined at five different angles (γ = 0°, 20°, 45°, 7°, 90°). The local and average Nusselt numbers are determined for Rayleigh numbers ranging from 103 to 2.5 × 103 . Also the ratio of the wall spacing to the tube projected length is changed from 1.25 to infinity. An optimum wall spacing distance for each inclination angle and Rayleigh number has been observed in which the Nusselt number is maximum.
The Overall Heat Transfer Characteristics of a Double-Pipe Heat Exchanger
555-570
10.1615/HeatTransRes.v40.i6.40
Amir Reza Ansari
Dezfoli
Department of Mechanical Engineering, Shahid Bahonar University of Kerman, P. O. Box 76175-133, Kerman, Iran
Mozaffar Ali
Mehrabian
Department of Mechanical Engineering, Shahid Bahonar University of Kerman, P. O. Box 76175-133, Kerman, Iran
double-pipe heat exchanger; temperature distribution; parallel flow; counter flow; two-dimensional flow
Heat exchangers are used in industrial processes to recover heat between two process fluids. The purpose of this paper is to develop analytical solutions using mathematical techniques to work out the two-dimensional (2D) temperature changes of flow in the passages of a double-pipe heat exchanger in parallel flow arrangement. Although the necessary equations for heat transfer in a double-pipe heat exchanger are available, using these equations the optimization of the system cost is laborious. Also, the solution of the problem yields the heat-transfer coefficient in inner and outer flows of double-pipe heat exchangers. The results are then compared with the experimental data available in other literature.
A Comparative Study on Flow Boiling Heat-Transfer Coefficient of R-134a and R-134a/R-290/R-600a Refrigerant Mixture
571-588
10.1615/HeatTransRes.v40.i6.50
Balakrishnan
Raja
IIITD&M Kancheepuram
Palanisamy
Balachander
R&AC Division, Department of Mechanical Engineering, College of Engineering, Guindy, Anna University, Chennai − 600 025, India
Dhasan Mohan
Lal
R&AC Division, Department of Mechanical Engineering, College of Engineering, Guindy, Anna University, Chennai − 600 025, India
Rajagopal
Saravanan
R&AC Division, Department of Mechanical Engineering, College of Engineering, Guindy, Anna University, Chennai-600 025, India
flow boiling; refrigerant mixture; heat-transfer coefficient; stratified flow; varied heat flux
The flow boiling heat-transfer coefficients of R-134a and R-134a/R-290/R-600a zeotropic refrigerant mixture were experimentally measured in a smooth horizontal tube of a 9.52-mm diameter. The values were compared for similar working pressure, reduced pressure, and liquid entry saturation temperature. The tests were conducted under varied heat flux conditions for stratified flow patterns; the conditions are found in evaporators of refrigerators and deep freezers. The varied heat flux conditions were imposed on the test fluids using a coaxial counter-current heat exchanger test section. The heat-transfer coefficients of the R-134a/R-290/R-600a refrigerant mixture were found to be better than those of R-134a under the same pressure and reduced pressure. However, under the same liquid entry temperature, the values of R-134a were found to be higher at low vapor qualities and lower at higher vapor qualities.
Boiling in a Stratified Two-Phase Flow: A Review
589-612
10.1615/HeatTransRes.v40.i6.60
Balakrishnan
Raja
IIITD&M Kancheepuram
Dhasan Mohan
Lal
R&AC Division, Department of Mechanical Engineering, College of Engineering, Guindy, Anna University, Chennai − 600 025, India
Rajagopal
Saravanan
R&AC Division, Department of Mechanical Engineering, College of Engineering, Guindy, Anna University, Chennai-600 025, India
flow boiling; flow patterns; stratified flow; heat-transfer coefficient; varied heat flux; nucleate boiling; convective vaporization
This article reviews the studies of flow boiling heat transfer of refrigerants with a stratified flow pattern in smooth horizontal tubes. The paper addresses the mechanisms of flow boiling and highlights the importance of nucleate boiling in a stratified two-phase flow. Further, the article addresses some of the familiar correlations used to predict the heat-transfer coefficient and their inconsistency for stratified flow conditions, conditions that prevail in horizontal evaporators of deep freezers and commercial refrigerators.