Abstract
A transient three-dimensional volume of fluid (VOF) simulation on condensation of upward flow of wet steam inside a 12 mm i.d. vertical pipe is presented. The effect of gravity and surface tension are taken into account. A uniform wall temperature has been fixed as boundary conditions. The mass flux is 130~6400 kg m−2's−1and the turbulence inside the vapor phase and liquid phase have been handled by Reynolds stress model (RSM). The vapor quality of fluid is 0~0.4. The numerical simulation results show that, in all the simulation conditions, the bubbly flow, slug flow, churn flow, wispy annular flow, and annular flow are observed; in addition, the results of flow pattern are in good agreement with the regime map from Hewitt and Roberts. The typical velocity field characteristic of each flow pattern and the effect of velocity field on heat transfer of condensation are analyzed, indicating that the slug flow and churn flow have obvious local eddy. However, no obvious eddy is observed in other flow patterns and the streamlines are almost parallel to the flow direction. The simulation results of heat transfer coefficients and frictional pressure drop show good agreement with the correlations from existing literatures.
Highlights
Vertical pipes used in heat exchangers are very common
The characteristics of condensation heat transfer and pressure drop for refrigerant R-134a flowing in a horizontal small circular pipe which has an inside diameter (i.d.) of 2 mm and the effects of the heat flux, mass flux, vapor quality, and saturation temperature of R-134a on the measured condensation heat transfer and pressure drop have been reported in Yan and Lin [3]
In order to verify the accuracy of simulation results, Boyko-Kruzhilin’s correlation [20] is adopted to compare with the simulated heat transfer coefficients
Summary
Vertical pipes used in heat exchangers are very common. It is very important to calculate the heat transfer coefficient accurately for the design and optimization of heat exchangers, especially for the large-scale heat exchangers. Local heat transfer coefficients of Isceon 59, R407C, and R404A, obtained from the measurement within a single smooth horizontal circular 3/8 copper tube, have been compared with the existing correlations for condensation heat transfer to assess the validity of these models for refrigerant mixtures by Boissieux et al [1]. They found that the Dobson and Chato correlation [2] provided the best prediction for these refrigerant mixtures.
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