换热器内随温度变化的黏度对两流体[火积]的影响

Effect of temperature-dependent viscosity on the entransy of both fluids in heat exchangers

以橄榄油为例来研究黏度固定和黏度为温度函数的情况下黏性热效应对顺流换热器内两流体(火积)的影响.当黏度固定值大于黏度为温度函数的平均值时,在相同条件下黏度固定时得到的传热(火积)损耗率小于黏度为温度函数时得到的传热(火积)损耗率.而当黏度固定值小于黏度为温度函数时的平均值时会得到相反的结论.在黏度为温度函数的情况下,当较小热容流率的流体为热流体时换热器具有较小的无量纲传热(火积)损耗率.当冷流体的入口温度增加时,黏度固定条件下无量纲(火积)损耗率比黏度为温度函数条件下的无量纲(火积)损耗率具有较大的减小幅度.

In the present work, the olive oil is taken as the working fluid to demonstrate the effects of fixed viscosity and temperature-dependent viscosity on the entransy dissipation in the parallel flow heat exchangers. When the fixed value of the viscosity is larger than the average value of the temperature-dependent viscosity, the entransy dissipation with fixed viscosity is smaller than that with temperature-dependent viscosity. However, the opposite conclusion may be obtained when the fixed value of viscosity is smaller than the average value of the temperature-dependent viscosity. Under temperature-dependent viscosity condition, the smaller entransy dissipation is obtained when the hot fluid has the smaller heat capacity flow rate. The decreasing range of the entransy dissipation under fixed viscosity condition is larger than that under temperature-dependent viscosity condition as the inlet temperature of cold fluid increases.