深冷人工地层冻结醇-盐水基冷媒热物性及对流换热特征

Thermophysical properties and convective heat transfer characteristic of alcohol-salt aqueous refrigerant in deep cryogenic artificial ground freezing

  • 摘要: 针对常规低温人工地层冻结CaCl2盐水(> -30 ℃)载冷量低,冻结速率慢且冻结效果差的问题,研制了可实现-50 ~ -60℃深冷制冷的新型醇-盐水基冷媒。冷媒冻结点低至-65.8 ℃,当冷媒温度达-60 ℃,冷媒黏度、导热系数和比热容分别为206.8 mPa·s、1.359 kJ/(m·h·C)和2.584 kJ/(kg·℃)。通过单管冻结冷媒对流换热数值分析发现,冷媒流速控制在0.5 m/s时,采用-60 ℃醇-盐水基冷媒作为冷源冻结效率较使用-30 ℃CaCl2盐水显著提高。冻结12h土体平均温度降低8.5 ℃,冻土平均半径扩大66.9%。此外,提高冷媒流速可以增强冻结管的换热能力,流速由0.5m/s提升至1.5m/s,冻结管出口处热边界层厚度降低36.3%,对流换热系数提高50.0%。本文研制的醇-盐水基冷媒冷量输送稳定,为解决富水地层冻结难题提供了新型冷媒材料和深冷冻结新路径。

     

    Abstract: To address the low cooling capacity, slow freezing rate, and poor freezing effect of CaCl2 brine (> -30 ℃) used in conventional artificial ground freezing, an alcohol-salt aqueous refrigerant capable of achieving deep refrigeration in the range of -50 ~ -60 ℃ was developed. The refrigerant exhibited a freezing point as low as -65.8 ℃. When the refrigerant temperature reached -65 ℃, its viscosity, thermal conductivity, and specific heat capacity were 206.8 mPa·s, 1.359 kJ/(m·h·C), and 2.584 kJ/(kg·℃), respectively. Numerical analysis indicated that, at a flow velocity of 0.5 m/s, the freezing efficiency of -60 ℃ alcohol-salt aqueous refrigerant significantly outperforms -30 ℃ CaCl2 brine. After 12 h, the average soil temperature decreased by 8.5 ℃, and the frozen radius increased by 66.9%. Additionally, increasing the refrigerant flow velocity enhanced the heat transfer performance of the freezing pipe. As the velocity rose from 0.5 m/s to 1.5 m/s, the thickness of the thermal boundary layer decreased by 36.3%, and the convective heat transfer coefficient increased by 50.0%. The refrigerant developed in this study exhibits stable cooling transport capacity, providing a novel refrigerant material and a new pathway for deep cryogenic artificial ground freezing in water-rich strata.

     

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