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Title:Control of flash gas bypass mac system with emphasis on start-ups and transients
Author(s):Li, Yueming
Advisor(s):Hrnjak, Pega
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:M.S.
Genre:Thesis
Subject(s):Flash gas bypass
Control strategy
Transients
Air-conditioning system
Abstract:Flash Gas Bypass (FGB) approach has the benefits of eliminating refrigerant maldistribution and reducing refrigerant pressure drop across the evaporator. Most of the previous research on flash gas bypass focused on performance improvement in steady state and demonstrated that compared to direct expansion mode (DX), FGB mode have better performance. However, the control strategy of FGB system and dynamic behavior during start-ups and transients were not yet clearly defined and investigated. In this paper, a novel control strategy has been proposed for an automobile air conditioning system operating in flash gas bypass mode with R134a as the refrigerant. This research aims at understanding FGB system performance in dynamic and transient load conditions using Sporlan electronic flow controls. This research identified three important issues for FGB system start-up process: size of bypass valve, size of FGB tank and control strategy for system operation. Although the exact sizing of both valve and FGB tank would be different from system to system, this study gave a basic guideline and a practical example of choosing corresponding components. More importantly, an innovative control strategy was implemented to make sure FGB system could be well-functioned under different working conditions in both start-up and transient scenarios automatically. The proposed control strategy utilized an electronic expansion valve (EV) for the control of subcooling from condenser outlet and a bypass valve(BV) for superheat from compressor inlet. Both start-up and transient system behaviors were studied. Transients include changes in air mass flow rate on evaporator side, face velocity on condenser side and compressor speed. The experimental results showed that the proposed cycle control strategy was found to be able to provide reliable control to the system.
Issue Date:2016-12-08
Type:Thesis
URI:http://hdl.handle.net/2142/95409
Rights Information:Copyright 2016 Yueming Li
Date Available in IDEALS:2017-03-01
Date Deposited:2016-12


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