Numerical Study Of The Characteristics Of Supercritical Carbon Dioxide Fluid Flow And Heat Transfer

A better knowledge and understanding of the characteristics of supercritical carbon dioxide fluid flow and heat transfer with better dynamics and heat transfer properties are important in a number of industrial applications ,such as power plants ,aerospace engineering and refrigeration engineering ,etc .The issue is on the background of the need to study further the characteristics of supercritical carbon dioxide fluid flow and heat transfer which do not reach a uniform cognition at present and discuss the reliability of the turbulence model in simulating the flowing and heat transfer of supercritical carbon dioxide in mini-tube . The detailed flow distribution with numerical simulation at the aim of deep understanding the observed phenomenon in the experiments by the theoretical analysis and numerical simulation of the flow and the temperature field are obtained. By analyzing and summarizing the performances of the characteristics of supercritical carbon dioxide fluid flow and heat transfer in the aspect of experiments and researching the flowing and heat transfer of supercritical carbon dioxide in mini- tube in the form of CFD, then comparing the results of the two methods, the mathematics expression: Nu_x = C·R_rxⁿP_rx^m·F is concluded.In the course of theoretical analysis on supercritical carbon dioxide fluid flow and heat transfer, major factors such as pressure, mass rate, flowing directions, tube diameter, heat flux and buoyancy etc are analyzed. By discussing the mechanism of heat transfer enhancement of supercritical carbon dioxide in tube, the causes that were responsible for the heat transfer enhancement, with the first contribution being the larger temperature gradient and the thinner thermal boundary layer near the tube wall; the second being the fluid viscosity of supercritical carbon dioxide decrease and specific heat capacity increase; and the third being that the velocity field or temperature field does not fully develop under the conditions.Numerical simulation is one effective means to study the flowing and heat transfer of supercritical carbon dioxide. The cloud atlas of the distribution of the velocity and the temperature field in different cross sections by simulating with CFD code FLUENT6 are obtained and the cognition of the flowing and heat transfer of supercritical carbon dioxide is deepened.Obtaining the law by which the temperatures on wall, the average heat transfer coefficient and the velocity on different cross sections in flow direction change with the bulk temperature by changing the operating pressure, the entrance temperature, mass rate, heat flux on wall in the course of simulating the flowing and heat transfer of supercritical carbon dioxide in mini-tube. The effects of the buoyancy because the properties change with the bulk temperature on the velocity and temperature field is very small, and can be ignore by the results of the theory calculations under simulating conditionsBy arranging,analyzing and checking the data of experiments, ultimately determining the expression:The study of the issue has achieved the anticipated goals, and proved that numeral simulation is a kind of efficient method to research the flowing and heat transfer of supercritical carbon dioxide, but it needs setting the boundary conditions reasonably, and the precision of numeral simulation needs to be enhanced further. However, the expression also has some engineering application value. At the same time, the research process and results also contribute to study the heat exchange structures with supercritical carbon dioxide as medium and the heat transfer characteristics further.