【作者】 曲宏伟；

【导师】 李敏霞； 张云宪；

【作者基本信息】 天津大学 ， 动力工程， 2012， 硕士

【摘要】 CO₂是环境友好型制冷剂,在制冷剂替代过程中具有非常大的应用潜力。本文以提高CO₂跨临界循环系统性能为分析重点,对CO₂跨临界循环系统不同的循环形式和满液式蒸发器进行了计算和数值模拟,为提高系统效率提供参考。本文从热力学循环角度出发,对CO₂跨临界循环系统不同的循环形式建立了计算模型并分别进行计算,分析比较了单级循环形式和双级循环形式的优化配置方案,通过比较分析发现,在CO₂双级压缩循环中配置回热器和膨胀机对系统性能的改善效果最好,从而为CO₂跨临界循环系统性能的提高提供理论支持。对单管池沸腾换热关联式进行了整理分析,结合实验数据,对应用在CO₂的换热关联式进行了比较发现,各个关联式得到的数据与实验数据相差较大;通过实验数据,拟合CO₂单管池沸腾换热系数与热流密度和对比压力的经验公式。以实验室CO₂热泵热水器实验台为基准,结合实际工况及要求,建立CO₂用的管束式满液式蒸发器进行了设计计算、校核计算模型;在此基础上,分析比较了满液式蒸发器中管束池沸腾换热系数随管外径、管间距等的变化特点,从传热学分析角度为CO₂满液式蒸发器的设计优化形式提供参考。以设计的满液式蒸发器为研究对象,通过计算机数值模拟软件对管侧水的流动进行了模拟计算,分析其温度场、压力场、速度场的变化特点,对设计的满液式蒸发器进行理论分析,为今后CO₂满液式蒸发器的优化设计奠定基础。更多还原

【Abstract】 The natural refrigerant CO₂ is an environmentally friendly refrigerant, and possesses a good application prospect in the refrigeration substitution. This study mainly focused on the improvement of CO₂ trans-critical system, combining theoretical analysis on different styles of CO₂ trans-critical system and computational numerical simulation on flooded evaporator, to provide references to improve the system efficiency.This study made theoretical analysis on CO₂ trans-critical systems by establishing calculation models of different styles of CO₂ system from thermodynamic prospective, and analyzed the optimal application of single-stage cycles and two-stage cycles. After comparing them, it was found that the system with the regenerator and expander had the highest efficiency.On the basis of the experimental data, several heat transfer correlations were analyzed, and an empirical correlation was proposed to show the relationship between the heat transfer coefficients with heat flux and reduced pressure. According to the experimental system of CO₂ heat pump water heater, the flooded evaporator applied in CO₂ trans-critical system was designed, and analysis of heat transfer coefficients of tube bundle pool boiling was presented.In this study, the temperature field, pressure field and velocity field of water in tube side of the flooded evaporator were analyzed by CFD software to lay the foundation for optimization of flooded evaporator used in CO₂ trans-critical system.更多还原