Experimental and numerical study of the freezing process of flat-plate solar collector

Flat-plate solar collector is vulnerable to the freezing-damage. But the study of the antifreeze performance of the flat-plate solar collector is rarely reported in the published literatures. This paper presents a model with high precision to simulate the cooling and freezing process of flat-plate solar collector exposed to cold ambient air and conducts a prototype experiment to validate the model. Based on the validated model, factors influencing the antifreeze performance of flat-plate solar collector are investigated. Besides, the antifreeze effect of introducing TIM transparent honeycomb (TIM: transparent insulation materials) in the flat-plate collector is studied numerically. Results show that narrowing the pipe space, increasing the pipe diameter or header diameter and reducing the emissivity of absorber and glass-cover are the effective ways of enhancing the antifreeze performance of flat-plate collector. Meanwhile, employing TIM transparent honeycomb can significantly improve the antifreeze performance of flat-plate collector and can put off the completely frozen time of the collector by 2.5 h.