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ACRC Technical Report 159PDF


Title:Regulation of the Liquid-Mass-Fraction of the Refrigerant Exiting an Evaporator
Author(s):Solberg, J.R.
Contributor(s):Miller, N.R.
Subject(s):mobile air conditioning systems
Abstract:As the digital age engulfs our society, more and more devices surrender to the inevitable fate of digital control. Routinely, digital electronics replace traditional mechanical systems usually yielding an improvement in cost, size, weight, durability, performance, repeatability, and power consumption. As of the date of this document, no commercially available automobile is equipped with a digitally controlled throttling device for their air conditioning system. A primary reason for this is economics. Automotive manufactures cannot justify the additional costs associated with a microcontroller and an electronically controlled throttling device, even if they significantly improve performance and durability. As electronics become smaller, cheaper, "smarter", and faster, electronic alternatives to traditional systems become increasingly prevalent. Most techniques of actively controlling the performance of vapor-compression air conditioning system use evaporator superheat as the feedback parameter. Unfortunately, any amount of superheat causes the evaporator to operate at reduced capacity due to dramatically lower heat transfer coefficients in the superheated region. This document presents and defends a system that allows a vapor-compression air conditioning system to be stably controlled in a regime where liquid and vapor refrigerant are exiting the evaporator. The uniqueness of this system is attributed to the feedback transducer. The transducer is able to deliver a signal to the controller that is a function of the amount (by mass) of liquid droplets impinging on the transducer. By placing the transducer in the stream of refrigerant exiting the evaporator, a refrigerant throttling device can be manipulated to regulate the amount of liquid refrigerant that impinges the feedback transducer. With the signal from this transducer as the feedback in a control scheme, a controller can be constructed that essentially regulates system performance, and is able to control the system in regimes where superheat feedback is unable to operate.
Issue Date:2000-01
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center TR-158
Genre:Technical Report
Sponsor:Air Conditioning and Refrigeration Project 78
Date Available in IDEALS:2009-05-26
Identifier in Online Catalog:4287908

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