Modeling of heat transfer of supercritical water in helical finned double pipe

Abstract

Supercritical water (SCW) is a promising fluid for achieving high thermal efficiency. In the present work, the SST k-ω turbulence model is employed to numerically simulate flow and heat transfer behavior of supercritical water in horizontal double pipe with helical fins. Grid independence test was firstly carried out and then model was validated with experimental data. Different combinations of width, height and pitch in helical double pipe numerical model, width varying from 2 mm to 4 mm, height ranging from 2 mm to 6 mm and pitch available from 15 mm to 25 mm, were examined. In addition, effects of buoyancy force, hot fluid temperature and mass flux on the heat transfer performance were investigated. Buoyancy disturbs the flow field by inducing secondary flow. The flow field is symmetrically distributed on the tube-side. In contrast, the presence of the fins in shell-side breaks the symmetrical distribution and generates a swirling flow at the top of the fins. The results indicated that the peak tube-side and overall heat transfer coefficients emerged at hot fluid slightly greater than the pseudo-critical point temperature. Moreover, the overall heat transfer coefficient improved as mass flux on both the tube-side and the shell-side. However, the shell-side would induce a greater magnitude. Also, the shell-side pressure drop closely related to the shape factor and increased with it. The performance evaluation criterion for case 8 and case 9 were 2.08 and 1.88, respectively. Nevertheless, the pressure drop of case 8 was more than twice case 9. Consequently, case 9 may be an optimal configuration simultaneously considering the coupling effect of heat transfer and pressure drop.