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Annals of the Assembly for International Heat Transfer Conference 13

ISBN 1-56700-225-0 / CD 1-56700-226-9

Volumes per year:

various

Year 2006

DOI: 10.1615/IHTC13.p5

CONVECTION HEAT TRANSFER OF CO₂ AT SUPERCRITICAL PRESSURES IN VERTICAL POROUS TUBES

Pei-Xue Jiang
Key Laboratory for Thermal Science and Power Engineering, Department of Thermal Engineering, Tsinghua University, Beijing 100084, China

Rui-Feng Shi
Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China

Y. J. Xu
Tsinghua University, Beijing, China

J. D. Jackson
School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester M1 3 9PL, UK

S. He
School of Engineering and Physical Sciences, University of Aberdeen, Aberdeen AB24 3UE, UK

ABSTRACT

Convection heat transfer of CO₂ at supercritical pressures in vertical sintered porous tubes with particle diameters of 0.2 ∼ 0.28 mm and 0.1 ∼ 0.12 mm was investigated experimentally and numerically. The influence of the inlet fluid temperature, mass flow rate, pressure, particle diameter, heat flux and flow direction on convection heat transfer in porous tubes was investigated. The experimental and numerical results for the friction factor of CO₂ at supercritical pressures flowing in sintered porous tubes at constant temperature (without heating) corresponded very well with the known correlation. The measured results for the friction factor of CO₂ at supercritical pressures flowing in the sintered porous tube with heating are larger than those predicted using known correlations both for upward and downward flows. The results show that the inlet temperature, pressure, mass flow rate, particle diameter and heat flux all strongly influence the convection heat transfer at supercritical pressures. When the inlet temperature is much larger than the pseudocritical temperature (T_pc), the local heat transfer coefficients in porous tubes are much less than those when the inlet temperature is less than T_pc. For T₀ < T_pc and wall temperatures not much larger than T_pc, the local heat transfer coefficients have a maximum for both upward flow and downward flow along the porous tube when the fluid bulk temperatures are near T_pc. Buoyancy caused the different variations in the local heat transfer coefficients along the porous tube for upward and downward flows. The results also show that the heat transfer coefficients increased as the particle diameter decreased. The numerical simulations were performed using the local thermal equilibrium model with consideration of the effect of variable porosity, thermal dispersion and area-of-contact stagnant effective thermal conductivity. The numerical results corresponded well with the measured wall temperatures.