低温氦气在螺旋盘管换热器中对流换热的数值模拟

Numerical simulation of convective heat transfer of helium in a helical tube heat exchanger under constant wall temperature condition

针对大型氦低温系统液氮槽中的螺旋盘管换热器,建立三维仿真模型,模拟研究等壁温条件下低温氦气在盘管内部预冷过程中流动速度、温度及密度分布,分析盘管内氦气径向速度分布及换热系数沿螺旋角的变化特性。通过改变低温氦气的质量流量,研究流量变化对换热系数以及换热器出口温度的影响。结果表明低温氦气在螺旋盘管内流动受离心力影响,管内密度,温度及速度分布沿径向存在梯度,湍流在螺旋角>90°后进入完全发展阶段。在0.0034~0.005 kg/s范围内增大质量流量,Nu数增加,压降增大,出口温度几乎不变。

A three-dimensional model was made for analyzing the helical tube heat exchanger used in large-scale helium cryogenic system,the distribution of pressure,velocity and temperature in the helical tube during the process of cooling the low-temperature helium were studied.The radial velocity distribution of helium in the tube and the variation characteristics of the heat transfer coefficient along the helical angle were obtained and analyzed.The influence of mass flow on the heat transfer coefficient and outlet temperature of heat exchanger were studied by changing the mass flow of the helium.The results show that the flow of helium in the pipe is affected by centrifugal force which causes gradients in radial velocity,density and temperature distribution,and the turbulence enters the stage of complete development after the helix angle of 90°.Increasing the mass flow within a certain range during 0.0034~0.005 kg/s,the heat transfer enhances,the pressure drop increases,while the outlet temperature is almost constant.