Run-Fu Shi

Experimental and Numerical Investigation of Convection Heat Transfer of CO2 at Super-Critical Pressures in a Vertical Mini Tube

Convection heat transfer of CO2 at supercritical pressures in a 0.27mm diameter vertical mini tube was investigated experimentally and numerically. The tests investigated the effects of inlet temperature, pressure, mass flow rate, heat flux, buoyancy and flow direction on the convection heat transfer. The experimental results indicate that for inlet Reynolds numbers exceeding 4000, the flow direction and buoyancy force have little influence on the local wall temperature, with no deterioration of the convection heat transfer observed in either flow direction. The convection heat transfer coefficient initially increases with increasing heat flux and then decreases with further increases in the heat flux for both upward and downward flows. These effects are due to the variation of the thermophysical properties, especially cp . For inlet Reynolds numbers less than 2900, the local wall temperature varies nonlinearly for both flow directions. The numerical results correspond well with the experimental data for inlet Reynolds numbers exceeding 4000 using several turbulence models, especially the Realizable k-e turbulence model. However, for inlet Reynolds numbers less than 2900, none of the turbulence models could properly simulate the convection heat transfer at super-critical pressures with high heat fluxes.Copyright

A Computational Study of Convection Heat Transfer to CO2 at Supercritical Pressures in a Vertical Mini Tube

Computational simulations of experiments on turbulent convection heat transfer of carbon dioxide at supercritical pressures in a vertical tube of diameter 0.948 mm have been carried out using low-Reynolds number eddy viscosity turbulence models. The simulations were able to reproduce the general features exhibited in the experiments. The modelling study has provided valuable information on the detailed flow and turbulence fields. It has been shown that for mini tubes such as the one used in the current study, the buoyancy effect is generally insignificant. Heat transfer can be significantly impaired when the heating is strong. This is due to the reduced turbulence production, induced by the flow acceleration which is in turn caused by strong heating.Copyright

Convection heat transfer of CO{sub 2} at supercritical pressures in a vertical mini tube at relatively low reynolds numbers

Convection heat transfer of CO{sub 2} at supercritical pressures in a 0.27 mm diameter vertical mini tube was investigated experimentally and numerically for upward and downward flows at relatively low inlet Reynolds numbers (2900 and 1900). The effects of inlet temperature, pressure, mass flow rate, heat flux, flow direction, buoyancy and flow acceleration on the convection heat transfer were investigated. For inlet Reynolds numbers less than 2.9 x 10{sup 3}, the local wall temperature varies non-linearly for both flow directions at high heat fluxes (113 kW/m{sup 2}). For the mini tube used in the current study, the buoyancy effect is normally low even when the heating is relatively strong, while the flow acceleration due to heating can strongly influence the turbulence and reduce the heat transfer for high heat fluxes. For relatively low Reynolds numbers (Re{sub in} {<=} 2.9 x 10{sup 3}) and the low heat flux (30.0 kW/m{sup 2}) the predicted values using the LB low Reynolds number correspond well with the measured data. However, for the high heat flux (113 kW/m{sup 2}), the predicted values do not correspond well with the measured data due to the influence of the flow acceleration on the turbulence. (author)

Experimental and Numerical Investigation of Convection Heat Transfer of CO2 at Supercritical Pressures in a Vertical Mini Tube

Convection heat transfer of CO2 at supercritical pressures in a vertical mini tube with a diameter of 0.948 mm was investigated experimentally and numerically. The local heat transfer coefficients, bulk fluid temperatures and wall temperatures were measured and presented. The effects of inlet fluid temperature, fluid pressure, mass flow rate, heat flux and wall thickness on the convection heat transfer in the mini tube were investigated. The experimental results were compared with calculated results using well-known correlations and numerical simulations. The results showed that the variable thermophysical properties of supercritical CO2 significantly influenced the convection heat transfer in the vertical mini tube and that for the studied conditions the influence of the wall thickness on the convection heat transfer in the mini tube was not great. For bulk fluid temperatures higher than the pseudo-critical temperature, the simulation results and the correlation results for the convection heat transfer coefficients in the mini tube corresponded well to the experimentally measured results.Copyright