Session: 10-01: Heat and Mass Transfer in Small Scale

Paper Number: 133587

133587 - Numerical Investigation of Heat Transfer Characteristics of Supercritical Co2 in a Microchannel 

Abstract: 

Advanced energy utilization technology can change the traditional energy structure and help achieve clean and efficient energy use, thereby enabling a rapid response to climate and environmental changes. Therefore, this technology has become a new trend in global energy development. As an advanced energy utilization technology, supercritical CO₂ power cycle configurations have the advantages of compact equipment, high thermal power conversion efficiency, simple system, and wide heat source adaptability. They have attracted increasing attention in many fields, such as nuclear reactors, solar thermal power generation, geothermal energy systems, and fuel cells. The thermos-physical properties of the supercritical fluid are significantly different from those of the subcritical state. The density, dynamic viscosity, specific heat, and thermal conductivity change dramatically around T_pc. The slopes of different parameters versus temperature become flatter with an increase in pressure. The drastic variations in thermos-physical properties exert additional buoyancy and inertial force on the flow, changing the flow structure and the strength of turbulence, resulting in heat transfer enhancement (HTE) or heat transfer deterioration (HTD). It is crucial to provide insights into the thermodynamic properties of supercritical CO₂ in the design scheme and safety analysis of the supercritical CO₂ power cycle. The flow and heat transfer characteristics of supercritical CO₂ in a vertical micro-circular tube are performed numerically. The most reliable numerical method is determined by the comparison of the agreement between the results of the numerical simulations of different turbulence models and the experimental results. The effects of pressure, mass flux, heat flux, inlet temperature, and flow direction are studied. The heat transfer of supercritical fluids in micro channels is different from regular dimensions. In micro-tubes, the buoyancy effect is insignificant even at relatively high heating rates. In these conditions, the heating-induced flow acceleration significantly impacts turbulence and reduces heat transfer at high heat fluxes. No heat transfer deterioration was observed in either flow direction over a relatively high Reynolds number range. The flow direction has a strong effect at low Reynolds numbers and an almost negligible effect at high Reynolds numbers. Moreover, analyses were conducted on the effects of mass flux and heat flux, respectively, on the wall temperature distribution. Detailed thermal physical characteristics and turbulence fields were captured, which helped to explain the variations in wall temperature at various heat fluxes and mass fluxes. The current study could provide important insights for a supercritical CO₂ heat exchanger's safe operation and design optimization.

Presenting Author: Qinggang Qiu Dalian University of Technology

Presenting Author Biography: Professor Qiu's research interests include supercritical fluid heat transfer, heat and mass transfer, and seawater desalination.

Authors:

Qinggang Qiu Dalian University of Technology
Ren Qianqian Dalian University of Technology