425 / 2018-12-27 15:51:06

Study of improvements on flow maldistribution of double tube-passes shell-and-tube heat exchanger with rectangular header

flow maldistribution; improvement; rectangular header; shell-and-tube heat exchanger;

全体主题 > 数值模拟、建模与CFD

In the present paper, a simple and effective method was proposed to improve the flow maldistribution for the small and compact double tube-passes shell-and-tube heat exchanger (DTP-STHX) with rectangular header. Two inlet tubes with several holes were inserted into the inlet and outlet headers, respectively, to uniform the flow distribution. The approach of 3D whole modeling was adopted to conduct the numerical simulation calculations for the DTP-STHX with conventional and improved header configurations. Meanwhile, an experimental system was built up to verify the accuracy of the numerical simulation model. The flow distribution of double tube-passes was numerically investigated and discussed using three statistical parameters, namely, the absolute flow deviation Ei of each tube relative to the average flow, the standard flow deviation Es of all tubes, and the ratio Rv of the maximum velocity vmax to minimum vmin. Some conclusions have been drawn as follows.
(1) For the second tube-pass, the flow distribution of the conventional header configuration is uniform enough to use in practice. But for the first tube-pass, the flow distribution of the conventional header configuration is serious. The absolute flow deviation Ei of 40% tubes was greater than 10%. The standard flow deviation Es was 0.157 and the ratio Rv of maximum velocity to minimum was 2.21. Although the improved header configuration has improved the flow distribution a lot with Es=0.131 and Rv=1.63, the flow velocity in the first row is still larger than the average.
(2) Furthermore, two approaches were proposed to improve the flow field for the improved header. Firstly, the number of holes on the upper part of inlet tubes was reduced, which are defined as the configurations B, C and D, respectively. Secondly, the inclination hole was adopted alternatively to force the fluid flow downwards.
(3) After considering all cases with both different header configurations and degrees of inclination hole, the configuration B with θ = 50°was found to perform best. The statistical analysis demonstrated that the standard flow deviation Es was 0.068 and the ratio Rv of maximum velocity to minimum is 1.28. Meanwhile, the absolute flow deviation Ei of 27 tubes is less than 10%, which accounts for 90% of the total tubes in the first tube-pass. Compared to the conventional header configuration, the flow maldistribution in the first tube-pass has been greatly improved.