System-level two-phase ejector modeling and integration for enhanced cop in heat pump systems
Subramaniyan, Sarath
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Permalink
https://hdl.handle.net/2142/124557
Description
Title
System-level two-phase ejector modeling and integration for enhanced cop in heat pump systems
Author(s)
Subramaniyan, Sarath
Issue Date
2024-04-29
Director of Research (if dissertation) or Advisor (if thesis)
Miljkovic, Nenad
Department of Study
Mechanical Sci & Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
Ejector
Heat pump
Abstract
The optimization of the coefficient of performance (COP) in heat pump systems during winter heating operations is crucial for reducing energy consumption and operational costs. Additional modular components aimed to enhance overall system performance during these conditions are undergoing widespread development. This research focuses on integrating ejectors into the high-side pressure control of heat pump cycles to maximize system performance. Leveraging the Kornhauser model, a two-phase ejector model in Simulink-MATLAB was developed and validated with experimental results available. However, this constant pressure mixing model approach is highly sensitive to the type of fluid used. With the help of relevant data and correlations from previous work, we modified the existing model to suit majorly three different working fluids- R1234yf, CO2, and R290 (Propane). The initial assumptions on efficiencies of different sections of the ejector, initial mixing pressures, and mass entrainment ratio were carefully selected according to available experimental data and theoretical correlations. Individual fluid-ejector model is simulated to understand variations of core efficiency parameters such as the pressure ratio and mass entrainment ratio of the ejector with respect to external parameters such as high side pressure, low side pressure, flow rates at such nozzle section, and efficiencies of each nozzle section. Once the ejector performance is analyzed on a component level for different working fluids, we shifted focus to a major application to injector this system-level model. The study primarily focuses on the incorporation of ejectors into Electric vehicle indoor winter heating operations including assessing the feasibility and trade-offs of integrating the ejector model into existing heat pump models. Simulation blocks in Simulink are modified to incorporate dynamic changes in motive nozzle and suction nozzle mass flow rates, ultimately affecting system COP. Transient effects due to dynamic mass changes in the ejector system are successfully incorporated into the system-level heat pump model. This enables the analysis of ejector efficiency, COP of the combined system, and condenser heat transfer rate through a comparison with the baseline heat pump model. Using R1234yf as the main fluid for analysis, a maximum COP increase of approximately 2.8% is observed at a condenser high-side pressure of 1000 kPa and low-side pressure of 220 kPa at an ejector working efficiency of 11.5%. This research highlights the potential of ejector integration to significantly enhance the performance of heat pump systems in winter heating operations.
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