螺旋格栅纽带开发及其综合换热性能分析

Analysis on Comprehensive Heat Transfer Characteristics and Development of the Spiral Grid Twisted Tape

针对燃气真空锅炉中较大直径的换热管,开发了一种新型管内插入物——螺旋格栅纽带,用于强化管内对流换热.分别建立了管内插入螺旋格栅纽带及相同结构参数普通纽带的三维几何模型,在相同工况下用FLUENT软件模拟了管内综合换热性能,根据模拟结果分析了螺旋格栅纽带强化管内对流换热的3种机理,即流通截面当量直径减小、螺旋流速度增大、离心力引发二次流等.结果表明:相同工况下,螺旋格栅纽带的对流换热系数比普通纽带减小了8.6%,同时单位长度螺旋格栅纽带的压降比普通纽带减小了32%,而综合评价因子J值大于1,表明螺旋格栅纽带具有良好的综合换热性能.

In order to enhance convective heat transfer of the heat transfer tubes with bigger diameter, a new kind of tube insert, spiral grid twisted tape, was developed for the gas-fired vacuum boiler. 3D geometric models of the spiral grid twisted tape and the classic twisted tape with the same twist ratio inserted the tubes were set up repectively. The comprehensive heat transfer characteristics in the tube was simulated using the FLUENT software under the same conditions. The mechanisms of heat transfer enhancement, such as de- creasement of hydraulic diameter of flow section, increasement of spiral flow speed, the secondary flow caused centrifugal force etc. are analyzed. The results show that the convective heat transfer coefficient of the spiral grid twisted tape decreases 8.6% than that of the classic twisted tapes and pressure drop decreases 32.0% , and comprehensive evaluation factor J is greater than 1. It shows that the spiral grid twisted tape has a good comprehensive heat transter perfermance.