Research On Film Flow Characteristics Of Falling Film In Inclined Tube Under Forced Convection

Based on the double carbon target of CO 2 and CO 2,energy saving by technology innovation can enhance industrial and economic competitiveness.In the field of refrigeration,the development and research of evaporative condensers have received widespread attention.During the heat transfer process of evaporative condenser,the refrigerant steam inside the tube becomes liquid refrigerant after condensation,which is easy to lead to the accumulation of condensate inside the tube,affecting the heat transfer area and efficiency.Designing the heat exchange tube as an inclined falling film can effectively alleviate this phenomenon,and can speed up the flow rate of liquid film outside the tube,so it is valuable to study.For this reason,it is necessary to investigate the flow condition of falling film outside the tube of evaporative condenser,In this paper,the flow characteristics of falling film outside the inclined tube under the action of reverse airflow are analyzed in depth to provide theoretical guidance for the development of evaporative condensers and engineering applications.For the falling film flow process outside the inclined tube under the action of reverse airflow,the heat transfer process is complex under the combined action of refrigerant condensation and heat release inside the tube,air flow outside the tube and evaporation and heat transfer of spray circulating water.Therefore,this paper mainly combines theory with experiment to build an experimental platform for falling film in the inclined tube under the condition of hot reverse flow,and uses laser induced fluorescence technology to measure the liquid film coverage and thickness distribution outside the tube,Combined with programming and digital image processing,the film formation outside the tube was analyzed and studied under the conditions of different tube types,spray flow rates,tilt angles,countercurrent wind speeds and heat flow densities,and the influence rules of various factors on the falling film flow outside the tube were obtained.The experimental results show that:(1)The influence of pipe type on the liquid film flow outside the pipe: under the comprehensive consideration of the liquid film thickness and coverage,although the liquid film thickness of the semi elliptical pipe is smaller than that of the circular pipe,its liquid film spreading rate is inferior to that of the circular pipe due to its own structural problems.The selection of the optimal pipe type should be considered from a comprehensive perspective.We should not only pursue the ultra-thin liquid film thickness,but also ensure the liquid film coverage,Therefore,it is also necessary to consider the coverage rate to avoid "dry spot" and dry burning,and it is better to choose the round pipe under comprehensive consideration.(2)Effect of spray flow on liquid film flow outside the pipe: With the increase of flow rate,the liquid film coverage,the liquid film thickness in the stationary section and the maximum liquid film thickness all show an increasing trend,but the increment decreases with the maximum flow rate.It can be seen that with the continuous increase of flow rate,the liquid film coverage,the liquid film thickness in the stationary section and the maximum liquid film thickness tend to a stable value.When the stable value is reached,Continue to increase the spray flow rate is only a waste of resources,and there may be excessive thermal resistance to reduce the heat transfer efficiency of the condenser.(3)The effect of inclination angle on the flow of liquid film outside the tube:Although the thickness of the liquid film at 20 ° inclination is the smallest,and the axial fluid film of the entire pipe is more uniform,the liquid film thickness is relatively good,because the liquid film coverage will turn at an inclination of 15 °,the coverage will start to decrease at an inclination of 20 °,and the increase of inclination angle will increase the vertical height of the condenser,Considering the liquid film coverage rate,liquid film thickness and structure size,the inclination angle of 15 ° is more appropriate under this experimental condition.(4)The influence of countercurrent wind speed on the liquid film flow outside the pipe: the coverage and thickness of the liquid film outside the pipe increase first and then decrease with the increase of countercurrent wind speed,and there is a critical value of countercurrent wind speed,which increases with the increase of inclination angle and spray flow rate.For this experimental condition,the inclination angle of15 ° and spray flow rate of 0.097kg/(m * s)are optimal,and the critical value of countercurrent flow is 4.1m/s.(5)The influence of heat flow density on the liquid film flow outside the tube:there is a heat flow density effect in the practical application of evaporative condenser.The experimental study shows that the heat flow density has little influence on the liquid film coverage rate,and the liquid film coverage rate almost does not change with the increase of heat flow density at each counter current wind speed.With the increase of the heat flux,the thickness of the liquid film.The results of this paper can provide a theoretical reference for the following analysis and design of inclined falling film heat transfer under the condition of reverse flow.