Numerical Study on the Heat Transfer of Carbon Dioxide in Horizontal Straight Tubes under Supercritical Pressure.

Mei Yang,Bing-Yang Cao

doi:10.1371/journal.pone.0159602

Abstract

Cooling heat transfer of supercritical CO2 in horizontal straight tubes with wall is numerically investigated by using FLUENT. The results show that almost all models are able to present the trend of heat transfer qualitatively, and the stand k−ε with enhanced wall treatment model shows the best agreement with the experimental data, followed by LB low Re turbulence model. Then further studies are discussed on velocity, temperature and turbulence distributions. The parameters which are defined as the criterion of buoyancy effect on convection heat transfer are introduced to judge the condition of the fluid. The relationships among the inlet temperature, outlet temperature, the mass flow rate, the heat flux and the diameter are discussed and the difference between the cooling and heating of CO2 are compared.

Highlights

CO2 has zero ozone depletion potential (ODP) and zero global warming potential (GWP).The critical temperature CO2 is relatively low and about 31.1°C
Using some turbulence models to simulate the heat transfer coefficient of supercritical CO2 in horizontal straight tube, they found that the LB low Re turbulence model was better in predicting heat transfer, followed by standard k−ε model with enhanced wall doi:10.1371/journal.pone.0159602.g003
In order to study the difference between heating and cooling of the CO2 in the straight tube, the change of heat transfer coefficient on heating under the same length, diameter, and the mass flow rate is compared and the results demonstrate that heat transfer coefficient on heating and cooling is not the same

Summary

Introduction

CO2 has zero ozone depletion potential (ODP) and zero global warming potential (GWP).The critical temperature CO2 is relatively low and about 31.1°C. It is close to the ambient temperature. The systems with CO2 operating at ambient temperature are likely to work close to the critical pressure of 7.38 MPa. Recently there are many studies about the heat transfer of heating and cooling of supercritical CO2 in the tube. Liao and Zhao[1] experimentally investigated the convective heat transfer of supercritical CO2 in horizontal and vertical tube. The diameter of the tube was 0.7mm, 1.4mm and 2.16mm, and they found that the buoyancy still had an important influence on convective heat transfer of supercritical CO2 Re had reached 105,

Methods

Results

Conclusion