Author ORCID Identifier
Date of Award
Doctor of Philosophy in Mechanical Engineering - (Ph.D.)
Mechanical and Industrial Engineering
Eon Soo Lee
This dissertation introduces a novel vacuum technology that leverages low-pressure saturated steam and cooling-controlled condensation, offering an efficient way to utilize low-grade thermal energy sources like waste heat, steam, or solar energy. At the heart of this technology is a unique duo-chamber vacuum pump system, featuring a reciprocating piston and a heat-conductive wall, designed to generate a vacuum through steam-condensation and cooling processes.
The core of this research lies in developing and validating mechanistic models for the steam-condensation depressurization process, a complex phenomenon involving phase change and transport mechanisms. Prior to this work, these mechanisms were not sufficiently modeled or understood, limiting the potential for quantitative assessment and optimization of the technology. This study addresses this gap by establishing comprehensive models that simulate the dynamic depressurization process, incorporating factors like transient cooling and non-uniform steam condensation. Dynamic depressurization characteristics, such as chamber pressure, condensation rate, and vapor temperature, have been investigated, along with parametric effects of key operation and system parameters, including initial vapor pressure/temperature, coolant flowrate and temperature, and system geometric dimensions and material selections.
Specifically, a parametric model of depressurization process is developed, which is based on a modified formulation of film condensation within an enclosed cylinder. This model, based on simplified lumped-heat capacity approximation of system components, can reasonably predict various parametric effects on the depressurization process, including the parametric effects of initial steam vapor pressure or temperature, coolant flow rate, and inlet temperature of coolant. These parametric analyses are vital to the optimized system design selections and operations.
To account for the transient and nonuniformity of heat and mass transfer with coolant-flow-influenced vapor condensation in a three-dimensional system, a more complicated numerical model and associated computational fluid dynamics (CFD) simulation is conducted. The depressurization-process CFD model of the condensing vapor-liquid two-phase flow is based on a Eulerian approach with the volume of fraction (VOF) method and space condensation modeling approximation. The CFD simulation reveals some strong three-dimensional non-uniform temperature distributions of both steam vapor and coolant flow. The steam condensation is also strongly non-uniformly distributed near the cooling wall of inner cylinders. However, the transient vapor pressure is nearly uniformly distributed within the chamber at any moment. The deviation between the non-uniform vapor temperature distribution and the uniform pressure distribution clearly suggests that there exists strong thermodynamic non-equilibrium in the vapor phase during the vapor condensation process, and the depressurization is mainly due to the vapor condensation rather than the cooling of vapor.
A lab-scale prototype of the vacuum pump system was constructed to provide the quantitative proof-of-concept assessment of the innovative vacuum generation technology. The experimental system is also used to provide important measurements on vacuum generation processes for the validation of the proposed parametric and CFD models. In addition, a preliminary design of the automatic operation of the dual-chamber steam-based reciprocating vacuum pump is proposed. All these results and preliminary studies not only demonstrate the practical viability of the proposed vacuum technology but also provide critical insights for its optimized design and automated operation, which also lay down some foundation for the follow-up research.
Deng, Hongling, "Depressurization characteristics of steam-based reciprocating vacuum pump" (2023). Dissertations. 1713.