Thermal performance experiment for multiple clamber trough solar air collector with dual collector tubes for solar greenhouse

Abstract: Because of its simple structure, pipeline without cracking in winter and other advantages, solar air collectors are getting more and more applications in industry, agriculture and residence. However, air has the disadvantages of small specific heat and density, so how to increase the collector efficiency and heat collection of air collectors has become the focus of research on solar air collectors. In recent years, multi-surface condenser air collector has gradually developed, which has the advantages of small size, easy installation and maintenance management, and high outlet temperature. Our research team has put forward a multi-chamber trough solar air collector with single collector tube. However, it has the shortcomings of low air flow and low heat collection efficiency however. In order to improve solar greenhouse solar energy utilization, this study proposed a new type of multi-chamber trough solar air collector with dual collector tubes to improve the collector performance. This collector is combined with the heat storage ventilation wall of solar greenhouse with solar active-passive "triple" structural phase change to constitute the active solar thermal storage system, which is used in Urumqi solar greenhouse. Based on the theory of optics and heat transfer, the experiment was designed and carried out to investigate the influence discipline of different parameters on thermal performances and optical performances for multi-chamber trough solar air collector with dual collector tubes. The parameters include the structure size (the relative position and the length of double collector tubes), air velocity inside the collector, inlet air temperature, and solar radiation. The test instruments include air collector, temperature sensor, flowmeter and data collection system. The experiment results illustrate that the collector performance of the double-tube collector is better than that of the single tube collector. Compared with the single collector tube concentrator, the air flow of the dual increased by 100%, the heat collection per unit area of the dual increased by 16%, and the heat collection efficiency of the dual increased by 9% (the heat collection efficiency of the dual was 44%-52% without tracking in winter). The relative position of double collector tubes, air velocity inside the collector and inlet air temperature were discussed in the study. The relative position 1 of double collector tubes is the best and the best air flow rate in the tube is 1.8-2.0 m/s. The collector was also applied to the solar greenhouse in Urumqi, and the results illustrate that: From November 2015 to February 2016, when the collector length is 16 m and the air velocity inside the concentrator is 2.0 m/s, the heat collecting system can provide solar thermal energy of about 50-65 MJ/day for solar greenhouse on the condition of sunny days, 35-45 MJ/day on the condition of cloudy days and 20-25 MJ/day on the condition of overcast days which have weak solar radiation. The heat collecting system can provide solar thermal energy of about 5 325 MJ for solar greenhouse by active heat storage of the wall in whole winter. This study can provide the reference for the thermal performance optimization of the collector and the new technical support for the efficient use of solar energy in solar greenhouse.