Heat transfer augmentation in a solar air heater channel with combined winglets and wavy grooves on absorber plate

An investigation on heat transfer characteristics in a solar air heater channel using wavy grooves incorporated with pairs of trapezoidal-winglets (TW) placed on the absorber plate has been experimentally conducted. Air as the test fluid entered the test section having a constant heat-flux on the absorber plate while the Reynolds numbers obtained by controlling the airflow rate is in a range of 4500-22,000. The TW characteristics include three relative winglet-pitches (P-R) and five relative winglet height or blockage ratios (B-R) at a single attack angle of 45 whereas the wavy rectangular-groove parameters are three relative groove-pitch lengths (P-R) similar to the TW case but at a fixed width and height. The investigation shows that the TW together with the groove provides the substantial increase in heat transfer over the smooth channel. The TW alone gives much higher heat transfer but the groove yields considerably lower pressure drop. The combined groove and TW devices at a given B-R, perform the highest heat transfer and friction factor at smaller PR and also provides considerably higher thermal performance than the single device acting alone. At P-R = 1, the compound device with B-R = 0.28 offers the highest heat transfer and friction factor while the one with B-R = 0.24 gives the maximum thermal performance. (C) 2017 Elsevier Ltd. All rights reserved.