Keith Wesley Wait

Fast, High-Fidelity Simulation of Dynamic Thermo-Fluid States in Refrigeration Systems

A dynamic model of a heat exchanger containing a phase-changing refrigerant is presented. Due to fundamental characteristics of phase-changing fluids, the model is computationally inefficient. Remedies to this inefficiency, such as hastened computation of fluid properties, realistic heat transfer coefficient blending, and active control of oscillations in the thermodynamic state of the system are presented. These remedies are shown to minimally impact the output of the model while allowing it to execute much more quickly than real-time.Copyright

Adaptive temperature control of a class of home refrigerators

A simplified dynamic model of a household refrigerator incorporating a single evaporator, variable position air damper, and variable speed evaporator fan is constructed. It is shown that, with proper parametric values, the model can accurately recreate data measured from such a refrigerator. Using the model, a model reference adaptive controller is derived and executed on a physical plant. The new controller improves upon the temperature tracking accuracy of stock controllers and is shown to adapt to changing unit types, environmental conditions, and loading cases.

A Sealed System and Compressor Model for Optimal Control of Household Refrigerators

Increasingly stringent industry standards have posed significant challenges on manufacturers to enhance the design and performance of household refrigerators. One of the least expensive and most effective means of improving the system is optimizing the control strategy. Some of the most promising control systems, such as adaptive and optimal control methods, require an accurate model of the system to guide the control effort. However, the complexity and interconnectedness of thermal and refrigerant flow phenomena make developing modern control systems a particularly challenging aspect of designing refrigerators, in spite of many decades of research and development. There exist models to correlate the desired compartments’ temperatures to that of the evaporator coil. However, there is a lack of a general approach to translate the required evaporator temperature to a compressor speed that provides it in an energy efficient manner. This work introduces a method to make that connection. The technique developed in this work can be adjusted for implementation on various refrigerator sizes and platforms to help modulate and control the compressor speed in real time.© 2012 ASME