Open Access

ARTICLE

MODELING OF THE HEAT TRANSFER IN A SUPERCRITICAL CO₂/DME MIXTURE FLOWING IN COOLED HELICALLY COILED TUBES

Yan Chen^a , Qingxin Ba^b,*, Xuefang Li^b

a School of Energy and Power Engineering, Shandong University, Jinan 250061, China
b Institute of Thermal Science and Technology, Shandong University, Jinan 250061, China
* Corresponding author. Email: qingxin90113@126.com

Frontiers in Heat and Mass Transfer 2021, 16, 1-9. https://doi.org/10.5098/hmt.16.18

Abstract

The heat transfer of supercritical CO₂/DME mixtures was modeled in this study for a mass ratio of 95/5 for cooling in horizontal helically coiled tubes. The CO₂/DME heat transfer coefficient was higher in the high-temperature zone than with pure CO₂. The heat transfer of CO₂/DME (95/5) was predicted for various mass fluxes, heat fluxes and pressures. The CO₂/DME heat transfer coefficient increased with the mass flux due to the increased turbulent diffusion, and first increased but then decreased with the heat flux. The peak heat transfer coefficient of CO₂/DME shifted toward the high-temperature region as the operating pressure increased. The effects of buoyancy and the centrifugal force were also analyzed to better understand the heat transfer mechanisms in helically coiled tubes. The gravitational buoyancy effect on the heat transfer decreased with mass flux while increased with heat flux. Higher heat fluxes strengthened the centrifugal buoyancy effect on the heat transfer at the beginning of the cooling process but weakened the centrifugal buoyancy effect later in the cooling process. The present study gives insight into the flow and heat transfer processes in helically coiled tubes which is useful for heat exchanger designs and refrigerant selection.

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