Experimental Study Of Heat Transfer Of Supercritical Carbon Dioxide In Closed Upright Tubule

Extensive efforts have been made to investigate into heat transfer properties of supercritical media. However, accurate heat transfer film coefficients have not been obtained and applied in practical designs up to now. For different operating conditions, even initial pressure and heating strength have little difference, convection heat transfer is different for complex heat transfer mechanisms of supercritical fluids.The main work and conclusions are as follows:(1) Experimental apparatus about heat transfer of supercritical carbon dioxide in closed upright tubules are designed. The system, which includes of subsystems such as transfer, filtering, heating, test and data acquisition, etc., can be applied to experimental investigation in the range of higher parameter. Carbon dioxide enters into system through filter, and pressure is controlled by stop valve. Experimental segment is heated by heat band, and corresponding data about heat transfer properties of natural convection after balance are transmitted by data acquisition modules and handled by computer.(2) Heat transfer properties of supercritical carbon dioxide, as well as effects of initial pressure and heating strength on heat transfer film coefficient and Nusselt number, are investigated experimentally. The results show that, initial pressure and heating strength have striking influence on convection heat transfer under supercritical conditions. Under the condition of higher initial pressure and lower heating strength, variations of heat transfer film coefficient and Nusselt number are little, while variations of heat transfer film coefficient and Nusselt number are great with lower initial pressure and higher heating strength. Heat transfer film coefficient and Nusselt number increase greatly with increasing fluid temperature firstly, then decrease after reaching peak values. Heat transfer film coefficient and Nusselt number are the maximum at critical temperature. In experiments, as temperature and heating power are 31 ℃ and 50.91w, namely, heat flux density is 4.05kw/m2, heat transfer film coefficient can reach 6421.3w/(m2.K).(3) Quick cooling experiments of carbon dioxide are carried out by ice compress under supercritical conditions. The results show that, temperature at every measuring point of heating segment and cooling segment decreases at cooling instant. In addition, temperature reaches theminimum point at the same time. Variations of temperature at every measuring point are similar.