Abstract
Solar air heaters (SAHs) are widely used devices for solar energy utilization at low temperature. The low convective heat transfer performance limits the energy conversion efficiency. This paper was aimed at investigating the flow characteristics and heat transfer enhancement mechanism, thermal hydraulic performance, and energy conversion efficiency of the SAH fitted with novel inclined trapezoidal vortex generators (ITVGs). The heat transfer performance and flow characteristics of a simplified unit were obtained by numerical simulation. A pair of longitudinal swirls were found close to both sides of each ITVG and the shape of vortex was rectangular in the front view. In the range of this paper, the order of overall thermal hydraulic performance for four different arrangements was listed as: upwind aligned (A1) > mixed staggered (A4) > upwind staggered (A2) > downwind aligned (A3). Furthermore, the A1 arrangement was applied to study the thermal hydraulic performance by altering parameters b/pt, e/H, and pl/H with Reynolds number ranging from 6000 to 18,000. The range of Nu/Nu0, f/f0, EEC, and R3 were 1.24–3.71, 1.39–11.8, 0.26–0.98 and 1.11–1.89, respectively. On this basis, energy and exergy efficiency evaluations were carried out on the practical SAH integrated by sixteen basic units. The energy efficiency and exergy efficiency could be maximally enhanced by 24% and 31% compared with the smooth SAH, respectively.
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