螺旋折流板换热器对流传热特点分析

Analysis and study of convective heat transfer characteristics of helical baffle heat exchanger

利用计算流体力学(CFD)软件对8°折流板倾角的螺旋折流板换热器进行了壳程对流传热的数值模拟,通过与传热研究公司的HTRI软件计算结果的对比验证发现相关结果具有一致性。基于数值模拟结果,发现壳程流动呈现距壳体轴心越远流速越低,且换热效果越差的特点。借鉴"流路分析"的基本思想对上述问题进行了初步探讨,认为这是由于壳程主体螺旋流使得流经外侧管束的流体经过更多换热管管排,流经外侧管束的流体必须降低速度以维持其相同的进出口压力降,故外侧管束换热较差。这可能是较大壳体直径的螺旋折流板换热器表现不佳,故其在工程上使用较少的原因。同时发现经过一个螺旋周期后流场具有周期相似性,而这可以作为利用周期性边界条件对螺旋折流板换热器进行简化计算的依据。

The convective heat transfer characteristics in shell side of helical baffle heat exchanger with 8 baffle inclination are numerically simulated by CFD software, and the consistence is found by the compari son with HTRI＇ s calculation results. Based on the results of numerical simulation, it is found that the shell side flow has the feature of lower velocity and lower heat flux in outer bundle tubes. The primary analysis has been made on the above problem on the basis of principle of ＂stream analysis＂. It is concluded that the fluid flows through more tube rows in outer bundle area under the effect of shell side helical flow, and the fluid flow through outer bundle area must reduce its velocity to maintain the same inlet-outlet pressure drop. Therefore, the heat transfer in outer tube bundles is poor. This maybe the cause of that the helical baffle heat exchanger of larger shell diameter has poor performance and is less applied in the project. It is also found that the flow field has periodic similarity after one period, which can be the basis for the simplified simulation by using peri-odic boundary conditions.