Michael John Kempiak

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

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

Development of a Hybrid Empirical-Analytical Method to Predict Adiabatic Flow Properties in Capillary Tubes

Capillary tubes have been used in household refrigerators and other cooling systems for several decades. Complicated geometry, inevitable manufacturing variations, and complex two-phase phenomena have been major prohibitory factors in the development of reliable and efficient modeling tools to analyze the flow properties inside capillary tubes. Friction factor correlations as are available in the open literature (as examined by the authors) unanimously fail to give accurate analysis of the refrigerant flow. The delicate operation of a capillary tube makes experimentation cumbersome, time and cost intensive, and prone to errors. The present study introduces a method to utilize the data from a standard Nitrogen flow test for a given capillary tube to develop a model specific to that tube which can predict the refrigerant flow properties through the tube at any desired spatial resolution, inlet state, and flow rate. Thereby, exploratory studies and capillary tube modifications for the purpose of system optimization can be greatly simplified.Copyright