The Research On Condensation Of Pure Refrigerants Inside Horizontal Tubes

With the aggravating of environmental pollution and energy shortage, the heat transfer enhencement technology is a hot spot of the research for refrigeration and air conditioning industry. For the condensation enhancement technology, it is considered to be the most suitable technique for the condenser optimizing design that discharges liquid at a particular position,for it’s small influence on the flow resistance.In this paper, based on this idea, it is analysed the heat transfer characteristics of horizontal tube by simulation and experimental methods.The main contents of this paper are as follows:(1)To meet the requirement of the simulation, a mathematical model is proposed in this paper, based on MH81 model, and can be applied to the sub-cooling area and the overheating area. In overheating area, the value of p,v,T can be calculated using only a few parameters at one state point. In sub-cooling area, the formulae keep constant and the corresponding coefficient can be obtained by east-squares refinement. Simulation of the sub-cooling keep the precision with the overheating condition on the basis of uniform formation, which make the programming more easier.(2)Based on the two-phase flow pattern, the heat transfer correlation of condensation heat transfer in tube is constructed by using the combination of Dobson,Thome,and kim formulas. By comparing the calculated values with the experimental data, the results show that the kim formula is the most suitable for the simulation of 4.38 mm diameter in this experiment,while Thome is suitable for the calculation of the normal diameter of 8mm. The average error of the three formulas is about 30%.(3)The visualization experiment system of R245 fa is built to measure the condensation characteristics along the horizontal tube. The experimental system is made of three parts,which is called the cooling water cycle section, the steam cycle section and the test tube section. The test tube section is used for the study of the heat transfer coefficients and flow pattern of the two phase fluid in the horizontal tube with parallel arrangement of a copper tube and a quartz tube. The steam cycle section make use of the cooling coil and electrical heating device to cool the residual gas and control the flow quality of refrigerant before the inlet of the tube. And the cooling water section consist of a cooling tower, which will cool the water with high temperature, guarantees the mass flow rate of cooling water to achieve the ideal cooling effect.(4)Investigation of condensing heat transfer is conducted for the vapor in horizontal tubes by analyzing heat transfer coefficient, void fraction, liquid film thickness, liquid pool cooling degree and other parameters. What’s more, theoretical calculation models are established. Aiming at solving the condensing heat transfer of the pure working fluid, simulation process are designed to obtain the changing curves of parameters, such as flow quality and void fraction, through the combination of various models and iterative solution.