|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.