Simultaneous Water and Air Heating in a Corrugated‐Tube Flat Plate Solar Collector: An Experimental Comprehensive Thermal, and Exergy Investigation

ABSTRACT

Concurrent extraction of hot water and warm air by a single flat plate solar collector (FPSC) is thermodynamically more advantageous as a strategy to utilize solar energy in heating buildings, but the combined impact of the helically corrugated riser tube geometry and the dual‐fluid (water‐air) operation on the overall thermal‐hydraulic and exegetic behavior of these systems has not been experimentally studied. A systematic experimental study of a dual‐fluid FPSC (DFPSC) with five helically corrugated copper riser tubes (e/D = 0.052, p/D = 0.580, D _i  = 17.25 mm, A _collactor  = 0.9 m ² ) in comparison to smooth tubes as a control under Baghdad winter conditions (33.40643° N, 44.36964° E). They tested seven cases in water with a Reynolds number of Re = 4000–8000 and an air inlet velocity of V _ain  = 3.0–5.0 m/s, which was measured in the outlet velocity V _aout  = 1.5–2.5 m/s measured using a analysis of the optimal air inlet velocity was determined as 4.0 m/s (V _aout  = 2.0 m/s) as to reference condition to further Re parametric tests. The ratios of the Nusselt number enhancement of 2.09–2.68 at PEC = 1.351–1.673 with corrugated tubes were always above unity. At Re = 7000 and V _ain  = 4.0 m/s, the peak efficiency of 90.86% was determined to be the highest reported in non‐concentrating, non‐PCM, non‐dual‐fluid FPSCs. The highest outlet water temperature of 59.40°C at Re = 8000 was recorded and the highest outlet air temperature of about 49.7°C at Re = 8000 was recorded and the maximum COP = 2.175 at Re = 7000 (within 2.1% of the maximum COP = 2.222 at Re = 6000) and exergy efficiency η _ex .