【作者】 张帆；

【导师】 张东伟； 秦翔；

【作者基本信息】 郑州大学 ， 热能工程， 2021， 硕士

【摘要】 跨临界CO₂热泵因为出水温度高,低温性能好,对环境友好等特点,成为了近年来相关行业的研究热点。然而由于存在跨临界过程,这对热泵设备的设计,制造以及运行控制提出较高的要求。目前为止,在我国跨临界CO₂热泵的商业化进程发展较为缓慢。提高跨临界CO₂热泵系统COP有助于促进CO₂热泵的发展,推动我国的制冷剂替代工作以及满足我国人民清洁供暖的需求。本文从CO₂循环参数和运行工况两个方面,使用模拟与实验相结合的方法,研究了跨临界CO2热泵最优排气压力和峰值COP的影响因素,提出了排气压力的控制方法并给出了未来强化设备性能的注意事项。主要研究内容如下:1、建立了最优排气压力理论分析模型,使用多元ANOVA（方差分析）方法定量的研究了过热度,回热器效率,等熵效率,蒸发温度和气冷器出口温度对最优排气压力的影响。发现气冷器出口温度,蒸发温度和等熵效率是最优排气压力和峰值COP的主要影响因素。2、建立了压缩机热力学模型和基于多目标优化的气冷器分布式传热模型,结合最优排气压力模型提出了排气压力自寻优仿真计算程序。仿真结果显示系统的最优排气压力随着压缩机频率,蒸发温度和进水温度的增加而增加,随着过热度的增加而减小。而峰值COP随压缩机频率和进水温度的增加而减小,随蒸发温度的增加先增加后减小,随过热度的增加而增加。在实际中应该提高气冷器的传热性能,以降低气冷器出口温度。过热度和蒸发温度与理论分析模型产生区别的原因在于,过热度和蒸发温度会改变设备运行时CO₂的质量流量。在设计回热器时需要保证引入之后过热度增加。而设计喷射器时需要考虑质量流量对气冷器传热的影响,防止性能恶化。3、实验研究了压缩机频率,进水温度和进水流量对最优排气压力和峰值COP的影响,验证了模拟的结论。并根据最优排气压力计算模型提出了基于压力偏离度的最优排气压力确定方法,并验证了9种不同工况下的准确性。发现最优排气压力预测值平均误差是0.56%,造成的COP损失是0.54%。更多还原

【Abstract】 CO₂as a refrigerant have come back into people’s vision and become a hotspot research in recent years because of its high-temperature water heating capacity,good low temperature performance and environmentally friendly.However,due to the transcritical cycle,the requirements for the design,manufacture and operation control of heat pump equipment are more stringent.So far,the commercialization of transcritical CO₂heat pumps has developed slowly in China.Therefore,improving performance of transcritical CO₂heat pump system is helpful to promote the development of CO₂heat pump,accelerate refrigerant replacement work in China and meet the needs of clean heating of Chinese people.In this paper,based on the detailed and comprehensive research,the influencing factors of transcritical CO₂heat pump were studied from two aspects of CO₂cycle parameters and operating conditions,the control method of discharge pressure was put forward,and the matters needing attention in strengthening equipment performance in the future were given.The main research contents are as follows:1.The theoretical analysis model of optimal discharge pressure was established,and the effects of superheat,IHX efficiency,isentropic efficiency,evaporation temperature and gas cooler outlet temperature on optimal discharge pressure were quantitatively studied by using multivariate ANOVA（analysis of variance）method.The results show that the gas cooler outlet temperature,evaporation temperature and isentropic efficiency are the main factors affecting the optimal discharge pressure and peak COP.2.The thermodynamic model of compressor and the distributed heat transfer model of gas cooler based on multi-objective optimization were presented.Combined with the optimal discharge pressure model,the self-optimization simulation calculation program of discharge pressure was proposed.The simulation results show that the optimal discharge pressure increases with the increase of compressor frequency,evaporation temperature and inlet water temperature,and decreases with the increase of superheat.The peak COP decreases with the increase of compressor frequency and inlet water temperature,increases first and then decreases with the increase of evaporation temperature,and increases with the increase of superheat.In practice,the heat transfer performance of the gas cooler should be improved to reduce the gas cooler outlet temperature.The reason why the superheat and evaporation temperature differ from the theoretical analysis model is that the superheat and evaporation temperature change the mass flow of CO₂during the operation of theequipment.3.The influence of compressor frequency,inlet water temperature and inlet water flow rate on the optimal discharge pressure and peak COP is experimentally studied,and the simulation conclusion is verified.According to the calculation model of the optimal discharge pressure,a method to determine the optimal discharge pressure based on the discharge pressure deviation was developed,and the accuracy under nine different working conditions were verified.It is found that the average error of the predicted value of the optimal discharge pressure is 0.56%,and the COP loss is 0.54%.更多还原