螺旋折流板换热器的熵产分析

Entropy generation of heat exchanger with helical baffles

通过CFD数值方法,从热力学第二定律的熵产数NS出发,对比研究折面折流板换热器与原始扇形折流板换热器的性能。以分析改进型换热器能量转换数量和质量的优化程度。研究结果发现:折面折流板换热器封闭了扇形折流板相邻直边之间的三角泄漏区,使换热器不仅保持了壳程流体较好的螺旋状流动,而且流动形成了更加明显的径向速度梯度。折面折流板换热器总传热系数增加30.4%—36.3%,壳程压降增加36.0%—36.5%。螺旋折流板换热器熵产数NS随着传热单元数NTU增加而减小。在相同的入口流量下,折面折流板换热器传热单元数NTU均大于扇形折流板换热器,而熵产数NS均小于扇形折流板换热器,减小了24.4%—28.4%。折面折流板换热器不仅在提高换热器能量转换数量方面具有明显的优势,而且在能量的转换质量,即热力完善程度,也有显著的提高。文中的研究结果对于进一步了解螺旋折流板换热器流动换热的机理、指导换热器优化设计具有重要的意义。

A comparative study on the performance of fold helical baffle heat exchanger with the original sectorshaped helical baffle heat exchanger was carry out based on the entropy generation number of second law of thermodynamics with CFD numerical methods for analyzing the optimized degree of energy conversion quantity and quality of the improved heat exchanger. The result shows that the fold helical baffle heat exchanger can close the outer triangle leakage zone at the straight edge of the sector-shaped baffles,which makes the heat exchanger not only maintain a better plunger flow in the shell-side,but also form a more significant radial velocity gradient. The overall heat transfer coefficient of fold helical baffle heat exchanger increases by 30. 4%-36. 3% and the shell-side pressure drop increases by 36. 0%-36. 5%. The entropy generation number of helical baffle heat exchanger decreases with an increase in heat transfer unit number. Under different entrance flow rates,the heat transfer unit numbers of fold helical baffle heat exchanger are all greater than those of sector-shaped helical baffle heat exchanger,but entropy production numbers are less,reduced by 24. 4%-28. 4%. The fold helical baffle heat exchanger not only has obvious advantages in the quantity of energy conversion,but also has a significantly improvement in the quality energy conversion,that is,the degree of perfection of thermodynamic. The results are of important significance to further understand the flow and heat transfer mechanism of helical baffle heat exchanger and to guide the optimization design of helical baffle heat exchanger.