Experimental Study On R245fa Condensation Heat Transfer In Horizontal Smooth Tube And Enhancement Tube

With the rapid development of the economy,most countries in the world are faced with the environmental damage and energy shortage.Therefore,looking for environmentally friendly refrigerants and development new energy and improve the performance of heat exchanger become a research focus.R245fa(five fluorine propane)is the international development of the fourth generation,it is an excellent high temperature refrigerant.At the same time in the low pressure water chillers,high temperature heat pump and the application of polyurethane foam industry has a good prospect.This paper mainly study the R245 fa in horizontal and enhanced tube condensing heat transfer characteristics and reconstructed the condensation heat transfer experimental bench.By parallel experimental tube section for comparison experiment with horizontal tube,and get the corresponding universal law.The range of condensation temperature,pure working medium R245 fa mass velocity,cooling water flow is 30-45°C,84-191kg/m2.s,732-1228kg/m2.s,respectively.The range of changes in dryness is 0-1.By research different refrigerant mass flow rate,different condensing temperature and different quality of cooling water flow,analysis condensation heat transfer coefficient with the change of dryness.And comparison of the difference between the horizontal pipe and the condensing heat transfer coefficient.Concluded as follow:1.The condensation heat transfer coefficient of R245 fa in horizontal enhanced tube is affected by condensing temperature,mass flow rate of refrigerant,cooling water flow rate and dryness.2.The condensing heat transfer coefficient increases with the mass flow rate and dry weight of the working fluid.The main influencing factors are latent heat and dynamic viscosity,and the condensation heat transfer coefficient linear growth in the horizontal and enhanced tube between the dryness range of 0.2-0.8.The condensation heat transfer coefficient decreases with the increase of condensation temperature from 30-45°C,the main reason is that the change of the condensing temperature will cause the physical properties of the working fluid(such as pressure,density,enthalpy,entropy).3.The condensation heat transfer coefficient increases slowly with the increase of the mass flow rate of cooling water.The main reason is that the cooling water as the carrier of energy exchange,which has little effect on the heat transfer of R245 fa in the horizontal tube.4.The heat transfer coefficient of the enhanced tube is 1.8-2.5 times higher than the horizontal pipe.The primary reason is that the internal thread pipe increases the heattransfer area in the tube.The presence of the helix angle and the toothed angle causes the fluid in the tube to produce a secondary flow that is different from the radial direction and enhanced turbulence intensity,thus make the thickness of the condensate heat transfer film become thinning.5.By summing up the experience of condensing heat transfer and comparing with the experimental value,inferred that the experimental value of Shah and cavallini correlation error is the smallest with horizontal and enhance tube,respectively.And the error is within20%.It provides a reference basis for the design and optimization of R245 fa condenser through horizontal and enhanced tube condensed heat transfer study.