摘要
为了揭示二氧化碳逆循环气体冷却器中的传热窄点分布特征,探明二氧化碳和换热流体间温差的沿程变化规律,以及如何防止传热窄点的产生进行相应的理论分析。建立二氧化碳的冷却换热模型,明确冷却过程中传热窄点产生的条件,并利用状态方程得到不同压力下二氧化碳温度与焓值的对应关系,分段计算焓随温度的变化率进而得到多种压力下发生传热窄点现象的机率。根据换热器的最小传热温差,确定不同压力下进出气体冷却器的换热流体的物性参数和窄点分布规律。在气体冷却过程中,传热窄点的位置随压力的增加而逐步向换热后程移动;换热流体在气体冷却器出口的温度随二氧化碳压力的升高呈现先降低再升高的趋势。此外,还给出6种压力下避免发生传热窄点现象的换热流体温差控制范围,为合理选择二氧化碳逆循环工况提供理论依据。
In order to reveal distribution characters of heat transfer pinch point of gas cooler in CO2 inverse-cycle, and explore the change rule of temperature difference between CO2 and heat-transfer fluid, and how to avoid the occurrence of pinch point inside heat exchangers, corresponding theoretical analysis are carried out. A cooling model of CO2 is built, so the occurrence condition of pinch point is obtained, also the situation equation of CO2 is used to compute some relationship between temperature and enthalpy, gradient of （dH/dt）p and probability of occurring pinch point under different pressures. According to the minimum temperature difference at pinch point in the CO2 gas cooler, heat-transfer fluid parameters at inlet and outlet of the cooler and position of pinch point are obtained under different pressures. During the gas cooling process, the position of pinch point moves gradually to back of the cooler with pressure increasing, at the same time, temperature of heat transfer fluids at outlet of the gas cooler reduces flrstiy and then increases. Increasing limit of temperature heat-transfer fluid in the gas cooler is presented in order to avoid pinch point occurring in 6 kinds of pressures. These may be helpful to rationally selecting CO2 invcrse-cycle operation in air-conditioner or heat pump units.
出处
《机械工程学报》
EI
CAS
CSCD
北大核心
2009年第9期307-311,共5页
Journal of Mechanical Engineering
基金
新世纪优秀人才支持计划资助项目(NCET-07-0609)
