温室双集热管多曲面槽式空气集热器模型构建与应用

Modeling of a multi-surface air collector with double-receiver tubes applied in solar greenhouse

为定量分析并预测复杂多变的室外工况对双集热管多曲面槽式空气集热器热工性能的影响,该研究针对双集热管多曲面槽式空气集热器结构及光学性能,结合能量守恒理论分析其传热过程,采用有限元及集总参数法建立其数学模型,并通过搭建双管集热器热性能测试平台和北京地区实际温室系统验证其有效性。结果表明:无论双管集热器反射槽体外是否贴附保温层,其数学模型的平均绝对误差为±0.9℃,平均相对误差为3.7%,误差分析指数IA(Indexof Agreement)可达0.994;对于北京地区实际工程中的16 m双集热管多曲面槽式空气集热器串联集热系统,其数学模型能够较为准确的给出不同室外工况及不同串联长度的集热系统出口空气温度,其平均绝对误差为±(1.3~2.7)℃,平均相对误差为5.4%~7.0%,误差分析指数IA为0.988~0.994。该模型为指导太阳能空气集热器在日光温室中的最优配置及其运行策略提供方法手段及技术参考。

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.