Modelling and Optimization Methods for a Microchannel Heat Exchanger

Abstract

Microchannel heat exchangers are being considered for use in the Generation IV nuclear reactors for their ability to provide increased thermal efficiency in a small volume relative to other types of heat exchangers via an extremely high surface area-to-volume ratio. Three distinct analysis methods that may be used to evaluate the technology are presented in this work: finite element method modelling, application of smoothed particle hydrodynamics, and Kriging-based optimization. The finite element method model generated for a single pair of channels for the hot and cold working fluids yields results that agree with those produced using the effectiveness-number of transfer units method, and is a suitable base for the optimization performed. More complex free surface flows are effectively modelled using smoothed particle hydrodynamics in a number of demonstrative cases, including boiling flow through a heated channel. The results generated with this method qualitatively simulate the observed physics and match analytical solutions in problems where one exists, although further evaluation of the VrSuite solvers must occur once additional data extraction capabilities are introduced. An initial optimization of a microchannel heat exchanger is performed using the effectiveness-number of transfer units method once more, determining an optimal design with an objective function value of 0.081 that is obtained through a combination of a 3.29 m long channel, 0.023 m channel width, a 0.0001 m wall thickness between channels, and hot and cold inlet flow velocity of 3.91 m/s. A preliminary optimization using finite element methods is also performed. I would first like to express the most sincere gratitude to my supervisors, Dr. John Goldak and Dr. Tarik Kaya of Carleton University, for their excellent guidance and seemingly endless patience throughout this process. Furthermore, I owe a debt of gratitude to the Goldak Technologies Inc c staff, which has included Dan Downey, Stanislav Tchernov, and Jianguo Zhou, for their technical support throughout my endeavours with the VrSuite software. Their assistance has been tremendous. I offer thanks to my colleagues Graeme Schmidt, Hossein Nimrouzi, Komeil Kazemi, and Alex Zakharchenko for their time and support. I would also like to thank Anne Wice for her companionship, for always being there to keep me balanced and focused, and for providing motivation when it was most needed. I could not have done this without you.