结冰工况下闭式地表水换热器换热性能研究

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

建立了闭式地表水换热器传热特性的数学模型,并对模型进行了验证,在非结冰工况下,模型计算值与试验值误差在±17.3%之内;基于该数学模型,研究了换热管在结冰工况下的冰层变化规律、传热热阻构成比例、换热管沿程传热系数以及换热管换热量。结果表明:换热管外冰层厚度沿流动方向呈下降趋势;冰层导热热阻约占总热阻的6.5%;沿载冷剂流动方向,换热管沿程传热系数呈先增加、后减小的趋势,其转折点在冰层消失处;在相同条件下,DN32换热管在结冰工况下的换热量衰减为未结冰工况下的93.07%。

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.