Heat Transfer And Pressure Drop Characteristics Of R410A-Oil Mixture Flow Condensation Inside 5mm Horizontal Enhanced Tube

R410A is one kind of the environmentally-friendly refrigerant, and it is an ideal substitute refrigerant for R22 due to its small temperature glide and good heat transfer and flow characteristics. It is an important way to utilize small diameter tubes to reduce the cost and improve efficiency of condenser. Recently, tubes with outside diameter of 5 mm have been used widely in condensers of R410A air-conditioners, while small tubes with outside diameter less than 5mm will be used into condensers in the near future. The presence of oil increases the complexity of R410A flow condensation heat transfer inside such small scale tubes. How to predict the heat transfer and pressure drop characteristics of R410A-oil mixture flow condensation inside such small scale tubes? How to quantitatively estimate the influence of oil on performance of condenser? To give the reply to these issues is important for promoting practical application of small-scale tubes in compact condenser design and promoting the substitute of R22 by R410A.Employing the method of combination of experimental and theoretical approach, this paper analyzes the heat transfer and the frictional pressure drop characteristics of R410A-oil mixture flow condensation inside 5 mm enhanced tube. Based on experimental research, a new correlation to predict the local heat transfer and a new correlation to predict the frictional pressure drop of R410A-oil mixture flow condensation inside 5mm enhanced tube are developed. Furthermore, the effect of fin height on the heat exchanger performance is analyzed by using the existing heat transfer and frictional pressure drop correlations of R410A-oil mixture flow condensation and boiling inside 5mm enhanced tube. The main work and the conclusions are as follows:(1) The experimental rig which is used for testing the heat transfer and the frictional pressure drop characteristics of R410A-oil mixture flow condensation is build by reconstructing the existing experimental rig for testing the heat transfer and the frictional pressure drop characteristics of R410A-oil mixture flow boiling.(2) Experimental study for the heat transfer characteristics of R410A-oil mixture flow condensation inside 5mm enhanced tube is performed. The test results show that the heat transfer coefficient of R410A-oil mixture flow condensation inside 5mm enhanced tube increases with the increase of mass flux; differing with the mass flux, the heat transfer coefficient of pure R410A decreases with the decrease of vapor quality, while the heat transfer coefficient of R410A-oil mixture increases with the increase of vapor quality and reaches maximum at 0.7 vapor quality, then decreases with the increase of vapor quality. The heat transfer coefficients curve of R410A-oil mixtures with 0% and 1% oil concentration are very close to each other. Therefore, at small oil concentration of 1%, the lubricant influence is negligible. However, for the condition of 3%, 5% oil concentration, oil decreases the heat transfer seriously and heat transfer coefficient decreases by 9.3%～36.5%. A new correlation to predict the local heat transfer coefficient of R410A-oil mixture flow condensation inside 5mm enhanced tube is developed based on the properties of R410A-oil mixture, and it agrees with 92% of the experimental data within the deviation of±20% and mean deviation of 6.7%. The new correlation can provide satisfying predictions to the heat transfer characteristics of R410A-oil mixture flow condensation inside 5mm enhanced tube.(3) Experimental study for the pressure drop characteristics of R410A-oil mixture flow condensation inside 5mm enhanced tube is performed. The test results show that the frictional pressure drop of R410A-oil mixture flow condensation inside 5mm enhanced tube increases with the increase of mass flux and vapor quality; for R410A-oil mixture, the effect of oil on the frictional pressure drop has a strong association with vapor quality, at low and intermediate vapor qualities, the presence of oil reduces the frictional pressure drop, while at high vapor qualities, on the contrary, the presence of oil increases the frictional pressure drop. At low and intermediate vapor qualities, the frictional pressure drop of R410A-oil mixture decrease by 29% in maximum when mean oil concentration increases from 0% to 5%; at high vapor qualities, the frictional pressure drop of R410A-oil mixture can increase by up to 8% when mean oil concentration increases from 0% to 5%. A new correlation to predict the frictional pressure drop of R410A-oil mixture flow condensation inside 5mm enhanced tube is developed based on the properties of R410A-oil mixture, and it agrees with 91% of the experimental data within the deviation of±20% and mean deviation of -1.86%. The new correlation can provide satisfying predictions to the frictional pressure drop characteristics of R410A-oil mixture flow condensation inside 5mm enhanced tube.(4) The effect of fin height on refrigeration system characteristics is analyzed, and the recommended value of fin height in 5 mm enhanced tube is given in this paper.