Comparative analysis of heat loss performance of flat plate solar collectors at different altitudes.

• The heat transfer mathematical model of the collector was analyzed and obtained. • An outdoor experimental platform was built and verified the accuracy of the mathematical model. • The pattern of convection and radiation heat loss with altitude has been simulated and analyzed. • The correction coefficient of total heat loss of collector at different altitudes was obtained. Flat plate solar collectors (FPSC) are a vital component in the medium and low temperature utilization system of solar energy and are widely used at different altitudes throughout China. Changes in altitude can cause changes in outdoor meteorological conditions, which can affect radiation and convection heat transfer processes on the surface of FPSC. Research into the heat loss characteristics of FPSC, when used at different altitudes, is relatively inadequate. To analyze the comprehensive impact of the change in altitude on the heat loss performance of FPSC, a model for the calculation of heat losses of FPSC was developed in this study. The influence of air pressure on air convection and long-wave radiation heat transfer was considered, and the accuracy of the model was verified by experimental test data. The variation of convection heat loss (CHL) and radiation heat loss (RHL) caused by environmental conditions such as atmospheric pressure, air density, solar irradiance and water vapor partial pressure with changes in altitude is investigated using the numerical calculation method. The results show that with increasing altitude, CHL and RHL show opposite trends, with the former gradually decreasing and the latter gradually increasing. The maximum variation of CHL and RHLs as a percentage of total heat loss can exceed 50%. Two opposite processes of heat loss play a combined role in the variation of the total heat loss, resulting in a decreasing and then an increasing trend in the altitude of the total heat loss coefficient, with a maximum variation of 10%. [ABSTRACT FROM AUTHOR]