This study aims to develop a solar multi-surface air collector with double-receiver tubes for an active-passive ventilation wall with phase change materials (PCM), in order to reduce the dependence on fossil energy for the overwintering production in the solar greenhouse, thereby to improve the utilization rate of solar energy resources. A mathematical model was proposed to quantitatively analyze the influence of complex outdoor conditions on the heat transfer performance of the developed device. An evaluation of heating and configuration requirements was made when the device was used as a heating system component in the early stage, particularly on modifying the problem for the separate evaluation of the thermal performance of collectors in previous most studies. According to the characteristics of optical structure in the collectors, LightTools optical software was selected to analyze the change rule of sunbeams convergence rate of the collector with the receiving angle. The results showed that the total sunbeams convergence coefficient of collector was between 0.74 and 1, with the average value of 0.90, without a sun-tracking device, when the solar radiation incidence angles in the range from 0-±20°. In addition, the ratio of solar energy received by each receiver tubes in the collector can be vary with the change of receiving angle. A mathematical model was finally established with seven reasonable simplified conditions in the heat transfer process using the energy conservation theory, according to the optical structure characteristics. Prior to the mathematical model, two conditions needed to be considered: without or a certain thickness thermal insulation layer attached to the outside surface of reflector. The reason was that the thermal insulation layer was often necessary on the outside surface of reflector, in order to reduce the emission of solar energy to the external environment via the reflector in the cold area of north China. A thermal performance test and engineering application were conducted to verify the proposed model for the solar multi-surface air collector with double-receiver tubes. The test results revealed that, no matter whether the outside of reflector was attached to the insulation layer or not, the average absolute error was ± 0.9℃, the average relative error was 3.7%, and the error analysis index reached 0.994. The average absolute error along the length of collector was ±(1.3-2.7)℃, verified by the actual engineering application of 16m solar multi-surface air collectors with double-receiver tubes, where the average relative error was 5.4%-7.0%, and the error analysis index was 0.988-0.994. Therefore, the results demonstrated that the mathematical model of collector can have a high prediction effect under different outdoor meteorological parameters, series length, inlet air temperature, and air flow rate. The findings can guide the optimal configuration of collector system, and thereby to optimize the air speed of collector, according to the changeable outdoor meteorological conditions, particularly in the cold area: of solar greenhouse.
|Translated title of the contribution||Modeling of a multi-surface air collector with double-receiver tubes applied in solar greenhouse|
|Original language||Chinese (Traditional)|
|Number of pages||9|
|Journal||Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering|
|Publication status||Published - 15 Jul 2020|