Heat transfer properties of closed-loop surface water heat exchanger under freezing condition

Establishes a mathematical model of closed-loop surface water heat exchanger and verifies this model with experimental data. Indicates the proposed model data compliant with a ±17.3% error margin between calculated and test values under unfreezing condition. Based on the model, analyses the ice layer thickness variation, heat transfer resistance, frictional heat transfer coefficient and heat transfer rate under freezing condition.  The results show that the thickness of ice layer outside the heat exchange tube decreases along the flow direction; resistance of  ice layer heat conduction is about 6.5% of the total heat resistance; frictional heat transfer coefficient increases firstly and then decreases along the secondary refrigerant flow direction where the obvious turning point is at the ice disappeared. Under the same condition, heat transfer rate of DN32 heat exchange tube under freezing condition is lowered to 93.05% of that under unfreezing condition.