| Evaporation technology on horizontal tube falling film have a good energy conservation.This technology has the advantages of high heat efficiency,good water quality,product quality requirements of low heat and good operation stability,which make it become one of the most promising technology in thermal seawater desalination.Based on the research of horizontal tube falling film flow structure optimization and vibration heat transfer enhancement,the characteristics of flow and heat transfer enhancement are discussed,which can provide reference for the design of evaporatorand otherhorizontal tube falling film equipment.Through the observation of flow pattern,the flow pattern of the liquid film outside the horizontal tube is taken.The conductance probe study on film thickness distribution of horizontal tube,horizontal tube falling film thickness distribution of film flow outside the tube were measured and photographed,studied the spray density,tube spacing and diameter parameters influence onfilm thickness.According to the CFD model,the velocity distribution,pressure distribution,temperature distribution inside the liquid film and the change of the distribution of heat transfer were calculated and analyzed under different ratio between long and short axes.The results show that Compared with a circular tube,the liquid flow rate in the tube of the elliptical tube is faster.Wall pressure gradually decreased along the circumferential direction and rapid recovery near the X=0.9.With the increase of ratio between long and short axes,the position of the minimum value of the circumferential pressure is gradually increased.The local Nu in X=0.9 reaches the minimum value.The local Nu distribution is consistent with the pressure distribution on the trend.When e=1.65 is near,the heat transfer performance of ellipse is optimal.At last,the heat transfer modelofhorizontal tube is presented through the study and analysis ofthe tube shape.To study the influence of liquid discharge plate on the flow and heat transfer of the horizontal tube falling film,a physical model was for the flow and heat transfer model of the horizontal tube established.The results show that horizontal tube with drainage plate canalleviate "dry spot" phenomenon due to droplet dropping caused by intermittent and stable the liquid film;the liquid film distribution of horizontal tube with drainage plate is more uniform and thereby can affect the temperature distribution of liquid film.horizontal tube with drainage plate can restrain the collision and mixing at the bottom of tube;Increasing flow rate will lead to the formation of stagnation zone of the liquid film,and the heat transfer.Adding liquid discharging boardcan speedup the liquid film flow rate at the bottom ofhorizontaltube.Based on the VOF model and the dynamic mesh technique,a two-phase flow model of the falling film flow and heat transfer is established.The effects of frequency,amplitude and flux on the heat transfer of the falling film outside the tube were calculated and analyzed.The results show that the factors that affect the heat transfer of the falling film in the horizontal tube are from the large to the small: the flow frequency and the amplitude.The average convective heat transfer coefficient increases with the increase of frequency,and then tends to be gentle.The relative heat transfer intensity of the liquid filled transverse tube is much larger than that of the falling film vibration tube.The main reason is that the secondary flow caused by the full liquid transverse pipe vibration is more severe than that caused by the falling film transverse tube. |
