Simulation And Experimental Study Of Actively Adjusting Vapor-liquid In The Evaporator

Improving energy conversion efficiency has become a significant energy conservation and emission reduction issue with the increase in global energy consumption.Flow boiling is an efficient way of energy transfer,which is widely used in the fields of microelectronic cooling,HVAC,and thermal power generation.At present,the common means of heat transfer enhancement are mainly passive enhancement technologies such as extended surface or turbulence devices.These enhanced heat transfer technologies improve the heat transfer coefficient through the increase of fluid disturbance and bring an increase in flow resistance,leading to an increase in system power consumption.Therefore,it is urgent to develop new enhanced heat transfer technologies.Based on the flow boiling characteristics of the working medium,the active adjusting vapor-liquid technology-enhanced heat transfer realizes the reallocation of the vapor quality and mass flow rate of the working medium through gas-liquid distribution and makes full use of the efficient heat transfer zone.It is expected to improve the flow boiling heat transfer coefficient,reduce the flow pressure drop and effectively improve the thermal performance of the evaporator.Therefore,the research and optimization design of the thermal performance of the active adjusting vapor-liquid evaporator has important engineering value and scientific significance.Firstly,the principle of active adjusting vapor-liquid flow boiling heat transfer enhancement is introduced and revealed its feasibility.Then,the structure of the active adjusting vapor-liquid evaporator is introduced.The mathematical moth of the active adjusting vapor-liquid evaporator model is established by using the finite element calculation.The average heat transfer coefficient and pressure drop data of the ordinary evaporator and the active adjusting vapor-liquid evaporator under different working conditions are obtained through experiments to verify the model.The results show that the model’s average heat transfer coefficient error is less than 35% and the pressure drop error is less than 30%.Then,the enhanced heat transfer mechanism and the relationship between various parameters of the active adjusting vapor-liquid evaporator are deeply analyzed by using this mathematical model.Mainly discussed the overall and local variation laws of the thermodynamic performance parameters of the evaporator under different liquid separation efficiency.It is found that under different inlet vapor quality,the heat transfer coefficient first decreases and then increases with the increase of separation efficiency,reaches the peak value,and then decreases sharply,which is up to 4% higher than that of an ordinary evaporator.Compared with the heat transfer coefficient,the pressure drop improvement of the active adjusting vapor-liquid evaporator is more obvious.The pressure drop of the active liquid distribution evaporator is lower than that of the ordinary evaporator,and becomes more obvious with the increase of flow,with a maximum decrease of 37.7%.Therefore,the pressure drop reduction effect of the active adjusting vapor-liquid evaporator is more significant.Comparing the local performance of the two evaporators,it is found that the high-efficiency heat transfer zone of the active adjusting vapor-liquid evaporator appears in advance,and the area is larger than that of the ordinary evaporator,which is the main reason for the improvement of its heat transfer performance.Finally,the multi-objective optimization algorithm is used to optimize the design of the active adjusting vapor-liquid evaporator,and five optimal schemes are obtained.Among them,the 2-4-5-6-7 tube pass and the liquid separation efficiency are 46% and 41%respectively have the best comprehensive performance,which is 15.3% higher than that of the ordinary evaporator.The study of the optimized design of these two evaporators found that the active adjusting vapor-liquid evaporator improves the pressure drop performance most significantly,and the increased heating capacity is mainly concentrated in the rear passes.The adaptability of this evaporator under variable working conditions is studied.Although the heating capacity fluctuates after the flow exceeds 25 g/s,it is still higher than the ordinary evaporator in a large flow range which means it has good adaptability.It is proven that the active liquid distribution evaporator has excellent comprehensive performance and great application potential.