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Thermal characteristics in solar air duct with V-shaped flapped-baffles and chamfered-grooves
Author(s)
Skullong, Sompol
Date Issued
June 1, 2021
Type
Article
Abstract
The article deals with augmenting the thermohydraulic performance of a solar heat exchanger duct with combined V-shaped baffle-and-groove vortex generators (VGs). Heat transfer behaviors from the combined VGs mounted in the duct absorber were investigated experimentally. Two VGs mounted on the absorber plate, the V-shaped flapped-baffle and chamfered-groove with a similar attack angle, α = 45°, were arranged by two arrays: V-apex pointing upstream (VU) and pointing downstream (VD). The vital purpose of using the flapped-wing mounted on the baffle (called “flapped baffle”) is to decline the pressure loss from the baffle without deterioration of the main vortices behind. The present experiment was carried out to encompass Reynolds number (Re) in a range of 5290 to 22,600, using air as a working fluid. The pertinent parameters of grooves were three groove pitch ratios (PR = 1.0, 1.5 and 2.0) while the baffle characteristics included four flap angles of the flap mounted on the baffle central area (β = 30°, 45°, 60° and 90°), three relative baffle pitches (PR = 1.0, 1.5 and 2.0) at one baffle height. Effects of the baffle and groove parameters as stated above on Nusselt number (Nu), friction factor (f) and thermal enhancement factor (TEF) were examined. The experimental results have revealed that the use of flapped-baffle and groove VG devices at PR =1.0 and β = 30° gives the largest f and Nu, especially for the VU case owing to strongly impinging jets issuing from the flap opening on the absorber surface area behind the baffle. Specifically, the maximum TEF is found to be 2.68 for the combined VU devices with PR=1.5, β = 45° and Re=5290. With these measured data, the Nu and f correlations are also determined.
Citation
International Journal of Heat and Mass Transfer, 172, 2021