Numerical Study on the Gravity Effect on Heat Transfer of Supercritical CO 2 in a Vertical Tube

Xiaojing Zhu, Ruizeng Zhang, Xiao Yu, Maoguo Cao and Yongxiang Ren
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Xiaojing Zhu: Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, Dalian University of Technology, Dalian 116024, China
Ruizeng Zhang: Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, Dalian University of Technology, Dalian 116024, China
Xiao Yu: Shenyang Aeroengine Research Institute, Aero Engine Corporation of China, Shenyang 110015, China
Maoguo Cao: Shenyang Aeroengine Research Institute, Aero Engine Corporation of China, Shenyang 110015, China
Yongxiang Ren: Shenyang Aeroengine Research Institute, Aero Engine Corporation of China, Shenyang 110015, China

Energies, 2020, vol. 13, issue 13, 1-20

Abstract: The effects of gravity on the heat transfer performance of supercritical CO 2 flowing within a vertical tube with a diameter of 4.75 mm are numerically studied in this paper. The main objectives are to comprehensively investigate the action of gravity and buoyancy on the supercritical heat transfer. An effective numerical method, which employs a modified Shear Stress Transfer k - ω model (SST k - ω ), is applied at various gravity conditions. It is found that, for both upward and downward flows, the heat transfer of supercritical CO 2 is improved with increased gravity magnitude. The effect of gravity on heat transfer are more pronounced under a low mass flux condition than that under a high mass flux condition and it is closely related to the variations of thermal properties. For the upward flow, the increased gravity magnitude accelerates the near wall fluid and creates a classic “M-shaped” radial velocity distribution. For the downward flow, the increased gravity magnitude decelerates the near wall fluid and creates a parabola-like radial velocity distribution. On one hand, the turbulent kinetic energies of both the upward and downward flows are enhanced as the gravity magnitude increases, which benefits heat transfer dominated by turbulent eddy diffusion. On the other hand, high-density fluid with high thermal conductivity occupies the near wall region as the gravity magnitude increases, which benefits heat transfer dominated by molecular diffusion. The results might provide some instructive advice to improve the design and operation safety of heat exchanger at various gravity conditions.

Keywords: supercritical CO 2; convective heat transfer; vertical flow; gravity effect; numerical study (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2020
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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