极地船换热器中海水-冰晶两相流的流动及传热特性的数值研究

Numerical study on flow and heat transfer characteristics of seawater-ice crystals two-phase flow in heat exchanger of polar ship

为改善极地船舶在北极航行时换热器的换热以及解决管程的冰堵问题,保障船舶海水冷却系统的运行与控制,基于CFD数值模拟方法,使用欧拉-欧拉双流体模型耦合相间传热传质模型,对海水-冰晶在壳管式换热器入口直管中的流动和传热进行数值模拟,研究入口含冰率和速度对冰晶流动和传热特性的影响.结果表明,冰晶在流动过程中由于融化发生分层现象,增加入口IPF或降低速度,会出现更显著的分层现象且顶部近壁处的冰晶体积分数随之增大.此外,与单相海水传热特性相比,当速度为1.0 m/s时,冰晶会增强传热;当速度为1.5 m/s、IPF小于6%或者速度为2.0 m/s、IPF小于10%时,冰晶对海水-冰晶两相流的传热具有减弱的作用,而且这种影响随入口速度的增加而增大;IPF为20%时,传热系数达到最大值.

In order to improve the heat transfer in heat exchanger of polar ship during it sails in the Arctic and to solve the ice blockage in the pipelines so as to ensure the operation and control of the seawater cooling system of the ship,based on the CFD numerical simulation method,the flow and heat transfer characteristics of seawater-ice crystals in entrance straight pipe of shell-and-tube heat exchanger were numerically simulated by using Eulerian-Eulerian two-fluid model coupled with the interphase heat and mass transfer model. The influences of inlet ice packing factor（ IPF） and velocity on the flow and heat transfer characteristics of ice crystals were investigated. Results show that ice crystals are stratified due to melting during flow process,and when the inlet IPF increases or the velocity reduces,the more significant stratification occurs and the volume fraction of ice crystals near the top of the wall increases. In addition,compared with the heat transfer characteristics of single-phase seawater,when the velocity is 1. 0 m/s,the ice crystals will enhance heat transfer and when the velocity is 1. 5 m/s and the IPF is less than 6% or the velocity is 2. 0 m/s and the IPF is less than 10%,the ice crystals have a weakening effect on the heat transfer of the seawater-ice crystals two-phase flow,and this effect enhances with the increase of the inlet velocity. When the IPF is 20%,the heat transfer coefficient reaches its maximum value.