Begell House Inc.
Heat Transfer Research
HTR
1064-2285
46
12
2015
EXPERIMENTAL RESEARCH ON COUPLED HEAT TRANSFER OF A HEAT SOURCE ENCAPSULATED INTO A SUBATMOSPHERIC HYPOBARIC CHAMBER
1065-1079
Han
Wang
Harbin Institute of Technology, College of Energy, Nanjing University of Technology, Nanjing, People's Republic of China
Chuang
Sun
School of Energy Science and Engineering, Harbin Institute of Technology,
Harbin, Heilongjiang, 150001, People's Republic of China
Xin-Lin
Xia
School of Energy Science and Engineering, Harbin Institute of Technology, 92, West Dazhi Street, Harbin 150001, P.R. China
In this work, an experimental setup was built to measure the coupled heat transfer mechanism of natural convection and radiation in a low-pressure enclosure with a heating cubic element, in which the pressure varied from 90 kPa to 0.1 kPa. The cubic element was heated by six attached electrical heating plates. An infrared thermography was used to measure the wall emissivities, based on which the net heat radiation flux between the component and hypobaric chamber was calculated by the Monte Carlo method. Eventually, the relative magnitude of natural convection and surface radiation can be estimated in the form of heat flux ratio, which was useful for better understanding the heat exchanger process in the low pressure environment. Experimental results provided the temperature distribution on the surface of the element, and heat dissipation was demonstrated. Considering the variable density of air at a low pressure, the average Nusselt numbers in the above pressure range could be correlated well with the Rayleigh number into three correlations, providing valuable reference for the engineering design calculations and thermal analysis.
FLOW OVER A POROUS STRUCTURE IN A SQUARE CAVITY: EFFECTS OF THE POROUS STRUCTURE SIZE AND POROSITY ON THE HEAT TRANSFER PERFORMANCE AND FLUID PRESSURE LOSS
1081-1099
S. Z.
Shuja
Mechanical Engineering Department, KFUPM Box 1913, Dhahran 31261, Saudi Arabia
Bekir S.
Yilbas
Mechanical Engineering Department, KFUPM Box 1913, Dhahran 31261, Saudi Arabia
S. M. A.
Khan
Mechanical Engineering Department, KFUPM Box 1913, Dhahran 31261, Saudi Arabia
A porous structure around a heat generating body improves the heat transfer rates and increases the flow resistance in the forced-convection regime. Consequently, investigation into the heat transfer performance and the fluid pressure loss in the flow system employing a porous structure becomes essential. In the present study, the flow subjected to a porous structure around a heat generating body situated in a square cavity is considered. The effects of porosity and of the size of the porous structure on the heat transfer performance and flow resistance are examined. Air is used as a working fluid in the cavity and the heat generation in the solid body is kept the same for all the cases simulated. A numerical scheme is introduced to solve the governing equilibrium equations for the flow and heat transfer. It is found that increasing porosity and size of the porous structure enhance the heat transfer performance parameter and the flow resistance coefficient in the cavity. However, the increase in the heat transfer performance parameter is larger than in the flow resistance coefficient for a large area porous structure at high porosity.
HEAT TRANSFER ENHANCEMENT OF MHD FLOW BY A ROW OF MAGNETIC OBSTACLES
1101-1121
Xidong
Zhang
Academy of Frontier Science, Nanjing University of Aeronautics and Astronautics, 29 Yudao St., Nanjing, Jiangsu 210016, P.R.China
Hulin
Huang
College of Astronautics, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, China
The appearance of vortex-shedding phenomena in electrically conducting viscous fluid flow past a magnetic obstacle is similar to the flow behind solid obstacles. This feature can be used for efficient enhancement of the wall-heat transfer, for better mixing of passive scalars or for the flow control of electrically conductive fluid. In the present work, the fluid flow and heat transfer characteristics around a row of magnetic obstacles are investigated numerically. The heat transfer behaviors, flow resistance, and vortex structures of the magnetic obstacles are presented, and the influence of dimensionless parameters, such as Reynolds numbers and interaction parameters, are also discussed. It is shown that the downstream cross-stream mixing induced by the magnetic obstacle wakes can enhance the wall heat transfer, so that the maximum value of percentage heat transfer increment (HI) is equal to about 69.5%. Moreover, the global thermal performance factor is increasingly dependent on the interaction parameter for a constant Reynolds number.
THE EFFECT OF BLOCKAGE RATIO ON HEAT TRANSFER AND ENTROPY GENERATION IN PULSATING FLOW THROUGH PARALLEL BLUFF PLATES
1123-1145
M.
Rahimi
Department of Mechanical Engineering, Golestan University, POB 155, Gorgan, Iran
Ali Akbar
Ranjbar
School of Mechanical Engineering, Babol University of Technology, P.O. Box 484, Babol, Iran
M. J.
Hosseini
Department of Mechanical Engineering, Golestan University, POB 155, Gorgan, Iran
The effects of frequency and amplitude on the flow field, heat transfer, and entropy generation in pulsating flow through parallel bluff plates at two different blockage ratios are studied numerically using a finite volume approach on a nonuniform staggered grid domain. Diffusion and convection terms are discretized by using a central difference scheme. The semi-fractional step method [revised step method of Kim and Moin (1985)] is used to solve the Navierâˆ’Stokes equations. The results show that for a smaller blockage ratio at a low amplitude, the peak value of the mean surface pressure coefficient moves upstream and the local Nusselt number increases with the frequency. This phenomenon occurs also for a low frequency and an increased amplitude.
SQUEEZING FLOW WITH SECOND-ORDER VELOCITY AND THERMAL SLIP CONDITIONS
1147-1166
Tasawar
Hayat
Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000, Pakistan; Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Faculty of Science,
King Abdulaziz University, P.O. Box 80257, Jeddah 21589, Saudi Arabia
A.
Qayyum
Department of Mathematical Science, Urdu University of Art, Science, and Technology, Islamabad, Pakistan
Ahmed
Alsaedi
Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, P. O. Box. 80257,
Jeddah 21589, Saudi Arabia
Effects of second-order velocity and thermal slip conditions in flow between two squeezing disks are considered, as well as thermal and concentration slips. The effect of chemical reaction is present. The fluid is taken to be incompressible and electrically conducting. The system of governing partial differential equations for the flow with heat and mass transfer are reduced to the system of nonlinear ordinary differential equations using appropriate transformations. Convergent series solutions are constructed. Values of skin friction coefficient and local Nusselt number are computed and analyzed. The developed series solutions are also compared with a numerical solution in a limiting case. Excellent agreement is achieved.
VOLUME 46 CONTENTS
1167-1175