Transient Heat Transfer Characteristics of Supercritical Fluid during Rapid Depressurization Process

• Published in: Applied thermal engineering 2018-12, Vol.145, p.435-443
• Main Authors: Zhang, Qiaoling, Cao, Jiahao, Bi, Qincheng, Yang, Zhendong, Yan, Jianguo
• Format: Article
• Language: English
• Subjects: Computer simulation; Critical point; Depressurization; Equilibrium; Evaporation; Evaporation rate; Flash evaporation; Heat transfer; Heat transfer characteristics; Initial conditions; Initial pressure; Nucleate boiling; Numerical simulation; Phase change; Pressure drop; Pressure effects; Pressure reduction; Simulation; Supercritical fluid; Supercritical fluids; Transient heat transfer
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2018.08.098

•A visualization study on rapid evaporation of supercritical liquid is performed.•Transient heat transfer is studied during rapid depressurization process.•The temperature and NEF are discussed from both experimental and numerical methods. A combination of experimental studies and numerical simulations is employed to probe into the transient heat transfer phenomenon during rapid depressurization of supercritical fluid in a cylindrical vessel connected to atmosphere via a sudden valve on the top. The effects of initial conditions on heat transfer characteristics are studied, and the morphological characteristics of supercritical fluid are analyzed. Results show: (i) there is a strong re-circulation inside the supercritical fluid with a sudden pressure drop. The heat transfer process is divided into four stages: the initial depressurization stage, the rapid evaporation stage, the nucleate boiling stage and the surface evaporation stage; (ii) under the subcritical state, a higher temperature contributes to a faster temperature drop rate and a shorter fast evaporation time. Moreover, a higher initial pressure leads to a lower equilibrium temperature and a shorter time it takes to reach the equilibrium temperature; (iii) differences are presented in terms of the effect of initial pressure in subcritical and supercritical zones on temperature drop rate with a turn near the critical point. A higher initial pressure gives rise to a higher equilibrium temperature, a slower temperature drop rate and the gradual increasing fast evaporation time; (iv) the experimental data are in good agreement with the calculated results, with a maximum error of 10%.