Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Abstract
This report details the efforts to exploit micro-electrical-mechanical-systems (MEMS)
and micro device technologies to improve control of multi-channel evaporators by
reducing maldistribution among channels, and increase capacity and efficiency of
current vapor-compression refrigeration chillers and heat-pumps. Besides
summarizing the market potential of MEMS technology for use in evaporators and
micro-heat-pumps, the report describes the accomplishments of an experimental
investigation of refrigerant-side maldistribution in multi-channel plate heat exchangers
(PHE's). A special test facility designed for the purpose of studying the
maldistribution of refrigerant in evaporators is described in the report. The facility
allows maldistribution caused by either normal superheat temperature control, or
induced by the user in controlled amounts, to be measured and quantified. Four
different techniques were used to detect the presence of liquid droplets in the stream of
superheated vapor at the evaporator exit, an indication of maldistributed flow. They
are: Helium-Neon laser, beaded thermocouple, static mixer and newly designed heated
MEMS sensor. Comparison of the four techniques shows that the MEMS sensor
designed and fabricated in this project has the highest potential for indicating
maldistribution, manifested by entrained liquid droplets, in multi-channel evaporators.
A complete set of test results in the time and frequency domain is show in graphical
form in the appendices. The design, fabrication, calibration, and testing of the MEMS
serpentine resistance sensor is also reported, along with a control scheme and strategy
for implementing the MEMS sensor in multi-channel evaporator systems
