Numerical Modeling And Optimization Of Thermofluid Systems: Heat Pumps, Turbocompressors, Porous Media

Abstract

In this dissertation, three types of thermofluid systems: an air Brayton cycle heat pump, a centrifugal compressor stage, and a porous media heat pipe, are investigated. In each of the investigations, numerical modeling is used as the basis that underpins the analyses. Furthermore, the goal of each investigation is to develop a framework for the design and optimization of practical engineering systems. The parameterization of each system is explored and defined. A thermodynamic model of a recuperated air cycle heat pump is developed and used to parametrically study the effects of component performance, operating environment, and design parameters. A numerical optimization is conducted to maximize the heating COP of the air cycle heat pump while maintaining robust performance across a wide operating envelope. Comparison is made to a conventional vapor compression cycle heat pump. It is found that a judicious choice of pressure ratio and maximization of component performance enables a recuperated air cycle heat pump to be comparable in COP to a vapor cycle heat pump for high temperature ratio duty. The recommended pressure ratio is determined to be 1.4. Such a heat pump requires high performance compressor, expander, and heat exchangers. A novel method of the flow path synthesis of a centrifugal compressor stage is revealed. A preliminary design procedure that enables fast and efficient candidate designs is reported. Computational fluid dynamics in conjunction with optimization algorithms, surrogate modeling, and machine learning is used to analyze the fundamental fluid mechanics and to automatically optimize the designs. A single stage performance improvement of over 4% points of isentropic efficiency gain is demonstrated using numerical methods. The microstructure of a flat porous media heat pipe consisting of layers of wire mesh is characterized using numerical techniques. The analysis encompasses the characterizations of the flow-induced pressure drop and interfacial heat transfer for liquid and vapor water phases in a 16-gauge and 200-gauge wire mesh porous domain.