The effect of the choice of shape and dimensions of the air flow passages in plate-type, air-heating solar collectors is assessed. Particularly examined is their effect on the overall heat transfer coefficient Upf between the air stream and the plate, which has an important effect on collector efficiency. It is emphasized in this study that in comparing various designs of flow passage, they should be compared for the same pressure drop Δp suffered by the air in passing through the collector, and for the same mass flow rate m per unit of collector area. On the basis of this type of comparison, two main conclusions are drawn. First, when the length of the air flow passage L is made less than about 1 m, Upf increases dramatically with decreasing values of L. Second, outside the transition regime, the value of Upf for a V-corrugated absorber plate is from 47 to 300 percent higher than that for a flat absorber plate, depending on whether the flow is laminar or turbulent, and on whether the V-corrugated plate is thermally bonded to the back plate. The first conclusion has led to a proposal for a novel air-heating solar collector design, called the “short-path” design.
Performance of Cylindrical Plastic Solar Collectors for Air Heating (Dept.M)