The Simulation Of Heat Convection About Supercritical Carbon Dioxide In Single Pipe

As a natural and environmentally favorable fluid, the refrigerant carbon dioxide has been revived due to its good thermal properties recently. In recent years, lots of theoretical analysis and experimental studies have been proved that the transcritical carbon dioxide cycle has a widely future and the automobile air conditioning refrigeration and heat pump systems used CO₂ as working fluid at home and abroad, but also have some difficulties to conquer. Therefore the dissertation principally presents the heat convection of supercritical carbon dioxide flowing in horizontal and vertical single tube with downward and upward flowing cooled by wall. The major researches are summarized as follows:(1) In the dissertation, SC-CO₂ thermal properties and the related charts are systematically described firstly. The main effects SC-CO₂ heat convection are flow direction, mass flow, diameter and gravity force and so on, ultimately its physical parameters affected it, such as density, viscosity, thermal conduction and specific heat. Therefore Refprop7.0 used in the calculation of the carbon dioxide's parameters under the same pressure of 7.5 MPa.(2) The parameter values are curve fitting using Matlab, and then compiled function to UDF, added into CFD-Fluent. In the whole simulated process, main consideration is four kinds of influence factors on the supercritical carbon dioxide in the single-tube heat convection, including gravity, inlet fluid temperature, different single-tube diameters and different quality affected it, and using fixed-wall temperature (T=300k) as cooling condition.(3) Calculated mean Nu_m and local Nu_b, which at the same ratio of the length and diameter, of supercritical CO₂ flowing in single tube. Under the same conditions we can know the optimum inlet fluid temperature, the best single-tube's diameter and the prime mass flowing from comparing with Nu_m. We can also know the relation between heat convection intensity and distinction temperature. At the same time calculated Nu_b values compared to three correlations, it presents the correlation which is recommended by Tao-yubing is anastomosed best.(4) The intense of heat convection in horizontal single-pipe is best among vertical single-tube, and intense of heat convection in downward flow condition is better than upward flow condition.