Airside Characteristics Of Evaporator & Refrigerant Distribution Of Air-Conditioner

Airside characteristics of evaporator and refrigerant distribution are two key problems of air-conditioner. During the system run process, dehumidifying phenomenon will happens when fin surface temperature of fin-and-tube heat exchanger is lower than incoming air dew temperature. The one purpose of this dissertation is to study airside heat/mass transfer and friction characteristic under wet conditions through experimental method.At the same time, the study of refrigerant distribution characteristic plays a very important role on improving the air conditioning performance and optimizing the control strategy. So the other purpose is to study the R410A refrigerant distribution under steady and dynamic conditions. Based on above purposes, this dissertation realized the following work:1) Build fin-and-tube heat exchanger airside characteristic test system. The dissertation designed a set of test rig based on the experiment conditions and objects. The test system not only has wide test range, high speed and stableness, also it has compact structure and is easy to tear down and transport. The test system has good reliability; deviation analysis shows that all parameter's errors are in the range of±15%, and test data are believable.2) Develop date analysis model for partial wet conditions. Extend current data analysis model from full wet conditions to partial wet conditions. Analysis how to deal with test data using Threlkeld method under partial wet conditions. Illuminate data reduction and develop wet fin efficiency calculation model under partial wet condition, the dissertation also explain the heat and mass transfer data reduction arithmetic in detail.3) Parameters influence analysis on airside characteristic of fin-and-tube heat exchanger with hydrophilic coating. A total of fourteen fin-and-tube heat exchangers with hydrophilic coating (seven wavy fin, four slit fin and three louver fin) were tested and examined. The effect of fin pitch, number of tube rows, and inlet relative humidity on airside heat/mass transfer, the ratio of between heat and mass transfer, and friction characteristic were analyzed.4) The effect analysis of hydrophilic coating on the airside performance under wet conditions. Six wavy fin-and-tube heat exchangers (three with hydrophilic coating and three without hydrophilic coating) and ten split fin-and-tube heat exchangers (five with hydrophilic coating and five without hydrophilic coating) were tested and examined. The effect of hydrophilic coating on airside performance under different fin pitch, frontal velocity, inlet relative humidity and inlet water temperature were analyzed. The heat transfer coefficient ratio and pressure drop ratio between coated heat exchanger and uncoated heat exchanger were correlated with multiple linear regression technique.5) Build airside heat/mass transfer and friction model of fin-and-tube heat exchanger under wet condition. For wavy fin and split fin-and-tube heat exchanger, the predictabilities of the state-of-the-art heat, mass and momentum transfer correlations to experimental data were verified, and it showed that the state-of-the-art correlations gave poor predictive ability to the experimental data. The new heat, mass, the ratios between heat and mass transfer and momentum transfer correlations were proposed to describe the present test results according to the multiple linear regression technique.6) For the refrigerant mass measurement of heat exchanger and compressor, a new measurement method-QOMM is put forward. For accumulator and receiver, a more simple and quick method-liquid level method (LLM) was put forward. Refrigerant mass measurement method in air-conditioning components was verified on a R410A inverter air-conditioning system. The results showed that the sum of measured refrigerant mass in all components has a max deviation 1.7% with system charge.7) The refrigerant distribution and migration under steady and dynamic condition were study through experimental method. The effects of compressor frequency and outdoor wind flux on the refrigerant distribution were analyzed. The refrigerant migration of air conditioning system under start-up and shut-down was also analyzed.8) The suitable void fraction model for R410A refrigerant was validated based on the test data. A new combined void fraction model was put forward, which is based on the Taitel-Dukler flow pattern map. This kind of void fraction model scheme can improve the accuracy of refrigerant charge further.At the end of this dissertation, the author explains the main shortcomings and the further research ideas in the field.