Solar energy is the most abundant renewable energy that has the capability to meet the world’s growing demand. However, it requires good solar concentrators to increase the trap efficiency. The efficient mean to utilize solar energy is to convert solar energy into heat stored in water by solar thermal collectors. Techniques such as high efficiency heat transfer absorber and solar radiation concentration are the main methods to improve the performance of solar thermal collector.
Pulsating heat pipe is one of the highly efficient absorber with simple stricture and low cost. The pulsating heat pipe has three working states namely: start-up, steady state and dry-out as the heat input increases. Altogether, the pulsating heat pipe exhibits an excellent potential for application as heat collector credit due to its high heat transfer capacity. However, the heat flux of the of the evaporation section of pulsating heat pipe should be sufficiently high to meet the demand of its steady and high-efficiency work, which has a significant effect on the thermal performance of pulsating heat pipe. Therefore, a solar concentrator is necessary in order to increase the heat flux of the pulsating heat pipe absorber to ensure that efficient heat transfer capacity of pulsating heat pipe can be fully utilized.
Researchers led by Professor Rong Ji Xu from Beijing University of Civil Engineering and Architecture and in collaboration with Dr. Hua Sheng Wang at Queen Mary University of London proposed a study on a novel solar collector that integrates a closed-end pulsating heat pipe and a compound parabolic concentrator. Their main objective was to test the operating characteristics and thermal performance of the detailed designed collector, under different weather conditions. Their work is now published in the research journal, Energy Conversion and Management.
Briefly, the research team initiated their empirical procedure by developing a prototype of the solar collector. Secondly, they analyzed the operating characteristics of the pulsating heat pipe absorber. The team then assessed the thermal efficiency of the solar collector under different weather conditions.
The authors observed that the collector showed start-up, operational and shutdown stages at the starting and ending temperatures of 75 0C. More so, they noted that the solar collector operated stably even in cloudy days. Additionally, the thermal resistance of the pulsating heat pipe absorber was seen to decrease with the increase in ambient temperature, solar intensity, and evaporation temperature which was found to be the main factor that affects the thermal efficiency of the collector.
Rong Ji Xu and colleagues successfully presented a novel solar collector that integrates a closed-end pulsating heat pipe and a compound parabolic concentrator. In their study, they have assessed the effects of operating parameters on the operating characteristics of the pulsating heat pipe and the performance of the solar collector under varying weather conditions. The experimental results suggest that the heat flux of the pulsating heat pipe absorber’s evaporation section concentrated by compound parabolic concentrator with a concentration ratio of 3.4 is appropriate and the use of compound parabolic concentrator is reasonable. Their proposed design offers a promising efficiency of 50% when compared with conventional solar collectors and pulsating heat pipe solar collectors.
According to Rong Ji Xu, the mathematical model of the solar collector has been built. The effects of the solar density, ambient temperature, weed speed, glass thickness and collecting temperature on the thermal performance were simulated. A theoretical efficiency of 70% can be realized which is more promising than experimental results.
Rong Ji Xu, Xiao Hui Zhang, Rui Xiang Wang, Shu Hui Xu, Hua Sheng Wang. Experimental investigation of a solar collector integrated with a pulsating heat pipe and a compound parabolic concentrator. Energy Conversion and Management 148 (2017) 68–77
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