Journal
INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER
Volume 39, Issue 7, Pages 945-952Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.icheatmasstransfer.2012.05.016
Keywords
Heat transfer; Turbulent channel flow; Baffle; Vortex generator; Nusselt number
Categories
Funding
- Commission on Higher Education (CHE) under the CHE-PhD-THA scholarship program
- National Metal and Materials Technology Center, (MTEC), Thailand
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The influence of baffle turbulators on heat transfer augmentation in a rectangular channel has been investigated experimentally and numerically. In the experiment, the baffles are placed in a zigzag shape (Z-shaped baffle) aligned in series on the isothermal-fluxed top wall, similar to the absorber plate of a solar air heater channel. The aim at using the Z-baffles is to create co-rotating vortex flows having a significant influence on the flow turbulence intensity leading to higher heat transfer enhancement in the tested channel. Effects of the Z-baffle height and pitch spacing length are examined to find the optimum thermal performance for the Reynolds number from 4400 to 20,400. The Z-baffles inclined to 45 degrees relative to the main flow direction are characterized at three baffle- to channel-height ratios (e/H = 0.1, 0.2 and 0.3) and baffle pitch ratios (P/H = 1.5, 2 and 3). The experimental results show a significant effect of the presence of the Z-baffle on the heat transfer rate and friction loss over the smooth channel with no baffle. The Nusselt number, friction factor and thermal performance enhancement factor for the in-phase 45 degrees Z-baffles are found to be considerably higher than those for the out-phase 45 degrees Z-baffle at a similar operating condition. The in-phase 45 degrees Z-baffle with larger e/H provides higher heat transfer and friction loss than the one with smaller e/H while the shorter pitch length yields the higher Nu, f and TEF than the larger one. The numerical work is also conducted to investigate the flow friction and heat transfer behaviors in the channel mounted with the 45 degrees Z-baffles, and the numerical results are found in good agreement with experimental data. (C) 2012 Elsevier Ltd. All rights reserved.
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