基于螺旋片强化的套管换热器性能

基于RNG k-ε模型对螺旋片强化的套管换热器的传热进行模拟，通过模拟结果与文献中的实验结果进行对比来验证模拟的可行性；分析了Reynolds数为2362～16860范围内的螺旋升角α变化对Nusselt数和摩擦阻力系数f的影响；并考察了等泵功率下的综合传热性能PEC值的变化规律。结果表明：Nu和f的平均误差分别为7.1%和1.3%，证明所采用的研究方法是可行的；α在15°～75°范围内，Nu和f均随着α的减小而增大，特别地，当α小于35°时，f随α的减小剧烈增大；在等泵功率下，PEC值为0.84～1.93；α在15°～45°时，α为35°具有较好的综合传热性能，α为55°、65°和75°时，虽然其PEC值比35°时略高，但其Nu与35°时相比要小很多，实际应用中考虑到传热速率的问题，选择35°的螺旋升角较为合适，此时，PEC值为1.26～1.62。另外，为减小f，提出倾斜螺旋片强化的方法；螺旋升角α为35°、螺旋片倾斜角β为10°时，与普通螺旋片相比，Nu基本一致，甚至略大，而f减小了12.5%～14.5%，此时，PEC值为1.38～1.71；场协同理论也很好地验证了这一结果。

Performance of double-pipe heat exchanger enhanced by helical fins

In this paper, RNG k-ε model is used to simulate the heat transfer of a double-pipe heat exchanger enhanced by helical fins. The simulation results are verified with experimental results. With the Reynolds number from 2362 to 16860, the effect of helix angle α on the Nusselt number and frictional resistance coefficient f are analyzed. The change of performance evaluation criteria(PEC) value and the comprehensive heat transfer performance at the same pump power are examined. The average error of Nu and f are 7.1% and 1.3%, respectively, indicating that the method used is appropriate. For α from 15° to 75°, both Nu and f increase as α decreases. In particular, for α values less than 35°, f increases dramatically as α decreases. With the same pump power, the value of PEC varies from 0.84 to 1.93. In the α range from 15° to 45°, the comprehensive heat transfer performance is better with 35°. Although the PEC values with α of 55°, 65° and 75° are slightly higher than that of 35°, Nu is much smaller. Considering the rate of heat transfer in applications, helix angle of 35° is more appropriate, with PEC of 1.26—1.62. Besides, it is proposed to use oblique helical fins to reduce the value of f. Compared with double-pipe heat exchanger enhanced by common helical fins, the Nu value of that enhanced by oblique helical fins with α of 35° and β of 10° is a little higher, f is reduced by 12.5%—14.5%, and PEC varies from 1.38—1.71. The field synergy principle also verifies the result.