Comparative Study on the Thermal Performance of Evacuated Solar Collectors with U-Tubes and Heat Pipes

Evacuated solar collectors with U-tubes (ESCU) and heat pipes (ESCHP) were designed and constructed to allow heat from solar radiation to be collected at a relatively high efficiency. A theoretical investigation of the overall performance of solar collectors under local weather conditions in Korea was carried out for two kinds of solar collectors: those with U-tubes and those with heat pipes. The results of the two models were then compared to those of the collector model to investigate their performance di fferences, which were affected by radiation, ambient temperature absorber areas, and structures. The comparisons showed high accordance between the simulation and experimental results for both types of solar collectors. The results obtained from the simplified model show that each type of collector had advantages. They had great efficiency disparities when the heat pipe-type had an 8% higher efficiency than the U-tube-type during the sunny day, while the U-tube-type showed steadier and better thermal performance when it was cloudy.