Airside Heat And Mass Transfer Characteristics Of Wavy Fin-And-Tube Heat Exchangers & Refrigerant Distribution Characteristics Of R410A Air-Conditioner

Whether or not the air-conditioners can run efficiently are dependent on many factors, including the airside heat, mass transfer and friction characteristics of fin-and-tube heat exchangers as well as the dynamic characteristics at start-up or shut-down and refrigerant distribution characteristics under steady conditions in the air-conditioners. In order to improve the performance of air-conditioner, the above two issues are studied in this dissertation.The wavy fin-and-tube heat exchanger is one of the most frequently used kinds of fin-and-tube heat exchangers. The airside heat, mass transfer and friction characteristics of 7 hydrophilic coated and 3 uncoated wavy fin-and-tube heat exchangers are studied under dehumidifying conditions experimentally. The airside heat, mass transfer and friction characteristics are presented in the form of Colburn heat transfer factor, Colburn mass transfer factor and Fanning friction factor, respectively. The main conclusions are as follows:(1) The effects of inlet air conditions and geometric parameters of heat exchanger on the airside characteristics of wavy fin with hydrophilic coating are evaluated. The airside heat transfer and friction correlations of wavy fin-and-tube heat exchangers with hydrophilic coating under dehumidifying conditions are proposed and the mean deviations are 6.5% and 9.1%, respectively. The correlations can be used when designing and evaluating the above kind of heat exchanger.(2) The effects of hydrophilic coating on the airside characteristics of wavy fin-and-tube heat exchangers under dehumidifying conditions are evaluated. It is found that the airside heat transfer performance of wavy fin with hydrophilic coating is slightly poorer than that of uncoated wavy fin. But the pressure drop of wavy fin with hydrophilic coating is pronouncedly lower than that of uncoated wavy fin and the degradation can be up to 44%.(3) The airside characteristics of wavy fin-and-tube heat exchangers under dry and wet conditions are compared. As for the wavy fin with hydrophilic coating, pressure drop under dehumidifying conditions is pronouncedly higher than that under dry conditions and the ratio of the former one to the latter one can reach as high as 2.2. When the inlet air velocity is larger than 2.0 m/s, heat transfer performance under dehumidifying conditions is better than that under dry conditions.(4) The airside mass transfer factor correlation and heat and mass transfer analogy correlation of hydrophilic coated wavy fin-and-tube heatexchangers under dehumidifying conditions are proposed and the mean deviations are 5.9% and 6.4%, respectively. It is convenient to calculate the airside mass transfer rate and latent heat transfer rate of wavy fin-and-tube heat exchangers when using the above correlations.In addition, the refrigerant migration characteristics at start-up and shut-down and distribution characteristics under steady conditions in a R410A air-conditioning system are studied through refrigerant weighing experiment. An online-liquid nitrogen measure method (QOMM) is proposed to weigh the refrigerants in the main components of the system. This method can save more refrigerants, protect the environment more easily and perform experiments more quickly than the tradition ones when assuring the measurement accuracy. According to the experimental results of refrigerant inventory in the evaporator and condenser under steady conditions, eleven classic void-fraction models are validated. The applicable void-fraction models for two-phase regions of R410A air-conditioner under cooling and heating mode are proposed respectively. Then it is very convenient to calculate two-phase region parameters of R410A system. Hughmark model is the best void-fraction model for R410A air-conditioner under cooling mode and Premoli model is the best one under heating mode.