| Summary: | 博士 === 國立交通大學 === 機械工程系所 === 107 === In this thesis, a constrains-free transcritical CO2 heat pump model for medium and large system applications and a transient heat pump for clothes drying applications are developed. On each model, the detailed geometric characteristics of the major component are taken into account and, unlike existing models existing in literature applicable for CO2 system, the developed models do not impose constraints upon simulation, such as fixed operating pressures and constant temperatures. Yet, pressure optimization is also addressed and heat rejection pressure is modulated through a recent sophisticated generalized dimensionless log-linear correlation of the Poisson type.
The models are tested against experimental data for a wide range of operating conditions and the results accurately reflected an actual system with a maximum error of 9.6% and 3.9% for the coefficient of performance and heating capacity, respectively. Moreover, the simulation results of both models are discussed and substantiated in the context of experimental results reported in literature. Yet, the generalized correlation employed for pressure optimization is also tested, validated and discussed thorough comparison to experimental data and other correlations available from literature. The correlation can accurately predict heat rejection pressure with an average error of 1.31% and a standard deviation of 4.26 bar, with a valid range of applicability for ambient temperatures from -18 to 50 °C, and within -7 to 15 °C and 10 to 50 °C for the evaporator and gas cooler outlet, respectively.
Once the transcritical heat pump model, pressure optimization method and heat pump dryer models are validated, a fully transient heat pump dryer model is developed and simulated using CO2 and then R-134a, for comparison purposes. A standard performance test is carried out and employed later as the reference case when investigating the influence of relevant parameters affecting the overall performance of the system for both refrigerants. Subsequently, comprehensive parametric studies are conducted to identify relevant parameters influencing system performance. In this regard, simulations for both systems (CO2 and R-134a) are conducted for comparison purposes. Additionally, guidelines and control strategies to optimize system performance and highlight the advantages of transcritical CO2 systems are provided.
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