Analysis Of Asymmetrical Flow In Vertical Parallel Tubes

The asymmetric distribution of two-phase flow in the vertical parallel heat exchangers has a great effect on the heat transfer performance and operation safety.In order to studied the distribution and flowing characteristics of two-phase flow in parallel vertical tube,the distribution experiment of two-phase flow in the parallel pipe was carried out with air-water as the medium of two-phase flow.The diameter of the parallel tubes was 0.01 m,and 36 experimental images were obtained when the flow rate of gas and liquid were 1.67×10(-5)m3/s,3.33×10(-5)m3/s,5 ×10(-5)m3/s,6.67×10(-5)m3/s,8.33×10(-5)m3/s,1×10(-4)m3/s.It was found that the distribution of the two-phase flow in the parallel pipe was not always evenly distributed,there was flow rate region where the distribution of the two-phase flow in the parallel tubes was asymmetric,and the fluid could not achieve uniformity by itself.What's more,compared with the high liquid flow rate,the asymmetric flow was more common when liquid flow rate was low.The drift flow model was used to calculate the asymmetric flow in the experiment.It was found that the gravity pressure drop would lead to the decrease of total pressure drop with the increase of fluid flow rate,which was the essential reasons of asymmetric two-phase flow.The distribution characteristics of two-phase flow of the experimental flow rates were predicted by using the minimum potential energy principle,and the simulation results were consistent with the experimental results.The results showed that the drift-flow model was good to simulate the slug flow.Finally,the flow and distribution characteristics of air-water two phase flow were simulated by Fluent.The liquid flow rates were 0.2 m/s and 0.6 m/s respectively,and the gas volume fraction was 0.6.The simulation results showed that when the liquid flow velocity was 0.2m/s,the flow in two parallel tubes was asymmetric and the two-phase fluid flows in the single tube,however,when the liquid flow velocity was 0.6m/s,the flow in two parallel tubes was asymmetric and the two-phase fluid flows in the two tubes.The flow and distribution characteristics of two-phase flow of simulation corresponds with the result of experiment.It showed that the flow velocity of the two-phase flow had a great influence on the distribution of the two-phase flow in the parallel pipe.,At the same time,the fluid counter current under low liquid flow velocity was verificated.