Experimental Study On Flow Boiling And Condensation Heat Transfer In Annulus Of Horizontal Enhanced Tube

In recent decades,enhanced heat transfer technology has developed to a new stage,which plays an important role in reducing energy consumption and improving energy utilization.In this paper,the characteristics of heat transfer and pressure drop of refrigerant R410A while flow boiling and condensation in annulus of horizontal enhanced tube are studied.The effects of surface structure,vapor quality,mass flow rate,saturation temperature and the other factors were investigated to evaluate the comprehensive heat transfer capacity under various operating conditions.Combined with the empirical correlation target parameters were predicted,which enriches the database of flow boiling and condensation heat transfer outside tubes,and provides a technical perspective and ideas for enhanced heat transfer research.The saturation temperature of single-phase experiment is 311K,and the mass flow rate of refrigerant between 40kg/(m~2·s)and 110 kg/(m~2·s).The experimental results show that the single-phase heat transfer coefficient and pressure drop of the four heat exchange tubes increase with the increase of the mass flow rate.The single-phase comprehensive heat transfer capacity of CEHT tube is the best.The relative errors between the predicted heat transfer coefficient of Dittus-Boelter correlation and Gnielinski correlation and the experimental values are within±10%.The saturation temperature of flow boiling experiment in the annulus is 279K.The entrance vapor quality is 0.2,and the export vapor quality ranges from 0.3 to 0.8.The mass flow rate of refrigerant between 40 kg/(m~2·s)to 80 kg/(m~2·s),and the heat flux density ranges from 1.90kW/m2 to 21.54kW/m2.The experimental results show that LEHT tube exhibits the best integrated heat transfer capacity of flow boiling.Under the conditions of vapor quality in inlet of 0.2 and outlet vapor quality of 0.8,the Gungor-Winterton correlation can predict 80%of the experimental data with a deviation of-15%,so it has been proved to have good accuracy.The effects of mass flow rate,vapor quality and other factors on heat transfer coefficient and pressure drop were further studied.The saturation temperature of condensing flow in the annulus is 308k,313k and318k,respectively.The mass flow rate of refrigerant between 45kg/(m~2·s)to110kg/(m~2·s).The entrance vapor quality and export vapor quality is 0.8 and 0.2.The experimental results show that the heat transfer performance of the four heat transfer tubes increases with the increase of mass flow rate and decreases with the increase of saturation temperature.CEHT tube has the best condensation heat transfer performance.Based on the thermal resistance analysis,the influence of saturation temperature,mass flow rate and other factors on the heat transfer coefficient and pressure drop was further studied,and Nusselt analysis theory was used to predict the heat transfer performance of smooth tube.