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Research on the Flow Field Characteristics in Duct System of Indoor Air Conditioner

Author: LiuQi
Tutor: ChenHuanXin
School: Huazhong University of Science and Technology
Course: Refrigeration and Cryogenic Engineering
Keywords: Indoor Air Conditioner Duct System Heat-exchanger Cross-flow Fan
CLC: TB657.5
Type: Master's thesis
Year: 2011
Downloads: 74
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Abstract

Air flow field characteristics in duct system of indoor air conditioners have great influence on comfort and noise of the air conditioners. Comfort of the existing air conditioners is difficult to meet people’s requirements, By studying the structural characteristics and flow field parameters, a theoretical basis can be provided for optimizing the design of duct system, increasing the energy efficiency factor of air conditioners, reducing noise and improving the quality.In this paper, the physical models of duct system of indoor air conditioners are established on the theoretical basis of computational fluid dynamics. And producing three-dimensional mathematical model of air turbulence flowing isothermally in the duct system by Gambit. Then simulating the flow field of duct system with Fluent software respectively as air return inlet、heat exchanger and the structure and parameters of cross-flow fan changing.Firstly,A comparison study on the difference of flow field between air duct system with down return inlet and up return inlet, we can know that both with down return inlet and up return inlet, the poor quality of flow field of duct system is inevitable.Secondly,The results of simulating four air duct systems with different layout of heat-exchanger show that the layout of heat-exchanger have influence on the supply air volume directly. Then the air duct system with the second kind of heat-exchanger is chosen as the basic model of simulation. As the heat exchangers have same structure and layout and work under the same conditions, we conclude with the resistance of heat exchanger increases as follows: (1) the effective intake area of cross-flow fan reduces, the uniform of air flow at the intake of cross-flow fan becomes poor, the rotation of air around the cross-flow fan enhances; (2) turbulence intensity of air supply increases, but the comfort decreases and the performance of cross-flow fan becomes inferior; (3) the supply air reduces obviously.Finally, just change the rotate speed of the cross-flow fan and simulate with the same model of air duct system with the second kind of heat-exchanger. After the calculation and analysis,we get: (1) the static pressure changes significantly with the rotate speed of cross-flow fan increases, but the location of the eccentric vortex core does not move with the speed varies; (2) the distribution of the airflow flowing through refrigerant flow tubes of the heat exchanger has no reference to the speed of cross-flow fan but determined by the structure of heat exchanger; (3) the air supply capacity of indoor air conditioner is up to the speed of cross-flow fan. And it has no connection with the eccentric vortex and other factors but varying linearly with the speed of cross-flow fan approximately.

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