CO2水合物蓄冷空调系统的热力学分析

    Thermodynamic Analysis of a CO2 Hydrate-based Refrigeration System With Cold Energy Storage

    • 摘要: 为了转移建筑峰值负荷, 提出一种CO2水合物蓄冷空调系统, 该系统以CO2为循环工质, 以CO2水合物为蓄冷介质, 采用直接接触式蓄冷方式, 可有效减少传热热阻, 提高系统性能。基于热力学循环分析方法, 对CO2水合物蓄冷系统循环建立数学模型, 进行理论分析, 结果表明: 当CO2消耗量增加到制冷剂质量流量的20%时, 系统的性能系数增加到原来的1.25倍。根据温度降低CO2水合物更容易生成的特性, 随着蒸发温度的升高, 潜热蓄冷量减少, 总瞬时蓄冷量和压缩机功耗降低, 系统性能系数增大。升高蒸发温度和降低气冷器出口温度有助于提升蓄冷系统的性能。气冷器出口温度对系统的最优排气压力影响较大, 而蒸发温度的变化对系统最优排气压力影响较小。当蒸发温度从2 ℃升高到8 ℃时, 系统的最优排气压力值均维持在8.6 MPa左右。当气冷器出口温度从35 ℃升高到45 ℃时, 最优排气压力的平均上升幅度约为0.24 MPa/℃。

       

      Abstract: A novel CO2 hydrate-based refrigeration system with cold energy storage is proposed to shift the peak load of buildings. The refrigerant utilized in the system cycle is CO2, and CO2 hydrate is used as the cold storage medium. The direct contact heat exchange method is applied to the system, which can greatly improve the performance of the unit. A mathematical model of the system was developed based on the thermodynamic analysis method and theoretical analysis was conducted. Results show that when the consumption of CO2 increases to 20% of the refrigerant mass flow rate, the coefficient of performance of the system is improved by 1.25 times compared to the original coefficient of performance. Based on the property that CO2 hydrates are more likely to be generated at lower temperatures, the latent heat storage capacity decreases as the evaporation temperature increases. Additionally, the total storage capacity and compressor power consumption decrease and the coefficient of performance increases as the evaporation temperature increases. The improvement of system performance can be achieved by increasing the evaporation temperature and reducing the gas cooler outlet temperature. The gas cooler outlet temperature has a greater effect on the optimal discharge pressure of the system, while the change in evaporation temperature has a lesser effect on the optimal discharge pressure of the system. When the evaporation temperature increases from 2 ℃ to 8 ℃, the optimal discharge pressure of the system remains at about 8.6 MPa. When the gas cooler outlet temperature increases from 35 ℃ to 45 ℃, the average increase of the optimal discharge pressure is about 0.24 MPa/℃.

       

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