Dynamic heat transfer model of flat plate solar water collectors with consideration of variable flow rate.

• The model is developed with consideration of flow rate variations. • Matrix derivation is applied to obtain an analytical solution. • The model could present the temperature variations of each component. • The dynamic model is validated by the on-site test in the cold region. The dynamic thermal model of the collector could serve as a useful tool for the thermal prediction. Normally, collectors' thermal prediction models are developed based on the dynamic thermal process, and then the thermal output or the mean temperature of the fluid would be obtained from the mathematical derivation. The critical parameters in the equations are fitted from the test data. In which, the heat loss coefficient F ′ U L has a close relationship with the flow rate, and thus the fitting formula could only be used for a given flow rate. In this paper, a dynamic heat transfer model of the normal flat plate solar collector is introduced, with consideration of the mass flow rate variations. Matrix is employed for solving the heat transfer equations. The analytical solution of the model indicates that the temperatures at time τ are determined by the initial value and the accumulated effect of the ambient environment. The model is validated by the on-site experiment carried out in Zhangjiakou, Hebei Province, in the north part of China. The main trend of the simulation and measurement was in accordance continually in the initialization, operation, and halt phase for around 24 h. While, the thermal mass of the duct connected to the collector is not included in the model, leading to the accuracy reduction of the model prediction. The modification with consideration of the pipeline's thermal mass will be conducted in future work. [ABSTRACT FROM AUTHOR]