DEVELOPMENT OF ADVANCED NUMERICAL MODELS FOR VARIABLE GEOMETRY MICROCHANNEL HEAT EXCHANGERS

Abstract

Air-to-refrigerant microchannel heat exchangers (MCHXs) are now extensively used in the heating, ventilation, air-conditioning and refrigeration (HVAC&R) industry. Numerical models are favored in the research and development process due to the fast calculation speed and lower cost as opposed to prototype development and testing. More recently, the evolving simulation and manufacturing capabilities have given the engineers new opportunities in pursuing complex and cost-efficient novel heat exchanger designs. Advanced heat exchanger modeling tools are desired to explore geometries out of conventional boundaries of design.

The current research and development of MCHXs has reached a plateau, in that, the optimum designs cannot be further improved with the limited number of geometry related design variables currently used. Freeing up the current MCHX uniform geometry restriction would lead to novel designs that address various design and applications objectives, such as performance enhancement, material reduction and space constraints.

This thesis presents the research, development and comprehensive validation of advanced heat exchanger models for microchannel heat exchangers. These new models include unprecedented modeling capabilities, with extensive consideration of various underlying heat transfer and fluid flow phenomena. The proposed microchannel heat exchanger models are capable of simulating variable geometry microchannel heat exchangers with variable tubes, ports and fins while accounting for effects such as heat conduction, combined heat and mass transfer as well as air and refrigerant flow mal-distribution, thus distinguishing itself as the cutting edge modeling tool in the open literature.

The models are validated against 247 MCHX experimental data points obtained from open literature, in-house laboratories and industry partners. This is the most comprehensive validation of microchannel heat exchanger models in open literature, including eight different fluids and eighteen different geometries. The validated model is then coupled with a multi-objective genetic algorithm to optimize the variable geometry heat exchangers to minimize material and envelope volume. The optimization study shows up to 35 percent reduction in material and 43 percent savings in envelope volume for the same performance compared to a baseline conventional geometry design. This research will be help engineers to develop creative microchannel heat exchangers ultimately resulting in improved systems efficiency at lower costs.