A Study on Top Heat Loss of a Closed Loop Oscillating Heat Pipes Solar Collector

Abstract

In this study, a closed-loop oscillating heat pipes solar collector was constructed to investigate experimentally the effect of filling ratio of working fluid, flow rate of cooling water, and air gap thickness between absorber plate and glass cover on top heat loss and performance of the collector.

To absorb and transport thermal heat energy from heating to cooling section, closed-loop oscillating heat pipes was used combining with absorber plate/black chrome coating copper plate. The absorber plate was shined by solar simulator simulated by 12-300W halogen lamps. Top heat loss of the collector was determined basing on temperatures of absorber plate, glass cover, and ambient air that were measured and recorded by MV2000-Yokogawa recorder via K-type thermocouples.

Top heat loss of the collector were determined at the air gap thicknesses of 5mm, 15mm, 25mm and 35mm. Solar irradiation intensity was adjusted to 200W/m2, 400W/m2, 500W/m2, 600W/m2, 700W/m2 and 800W/m2. The results show that the optimal air gap thickness for minimum top heat loss of the collector is 15mm.

Working fluid for the heat pipes was tested at filling ratios of 30% to 80%. Irradiation intensity was set to 545W/m2, 645W/m2, 718W/m2 and 825W/m2. The results show that top loss of the collector decreases dramatically at filling ratios of 60%, 70% at solar irradiation intensities of 545W/m2, 645W/m2, and 718w/m2, 825w/m2, respectively. The collector operates more effectively at filling ratio of 80% than that at 50%, 40%, and 30%.

Flow rate of cooling water was also investigated in this study. It was adjusted to 0.15l/min, 0.30l/min and 0.45l/min. The results show that flow rates of cooling water of 0.15l/min and 0.30l/min give the collector better performance than that of 0.45l/min.