Steam Condensation from a Moving Steam-Gas Mixture

摘要

To date, heat exchange has been studied to the greatest extent for the case of the condensation of pure still and moving steam as well as for the case of condensation from a still steam-gas mixture. There are hardly any papers available wherein a moving steam-gas mixture with a substantial content of noncondensable gases is considered. To investigate this process, an experimental workbench of the working section has been developed, which makes it possible to determine the local values of the heat transfer coefficient from the steam-gas mixture to the walls of cooled heat-exchange tubes at different parameters and velocities of the gas-steam mixture. In the first four rows of tubes of the working section, there is no cooling, and their function consists in a hydraulic stabilization of the flow. In the fifth and the sixth row of tubes, the wall temperature of the cooled heat-exchange tubes is measured for determining the heat transfer coefficients from the moving steam to the tube walls. The seventh row of tubes is also not under cooling. Measuring tubes with temperature sensors have been manufactured that make it possible to obtain the wall temperature for determining the heat transfer coefficient. The adopted scheme of steam motion and the measurement system make it possible to obtain correct results of the heat and mass transfer investigation in the course of steam condensation from a gas-steam mixture with a significant content of noncondensing gases. The studies on steam condensation from a moving steam-gas mixture have been carried out in the range of parameter ρ w _(2)= 9.5 − 66 Pa and at a volume concentration of air in the steam amounting up to ν~(air)= 0.18. Convective heat transfer coefficient α values for the heat transfer from a moving steam-gas mixture to the wall of a cooling tube were obtained. At small values of parameter ρ w _(2)= 9.5 Pa and the volume fraction of the air content ν~(air)= 0.06 in the steam, the average heat transfer coefficient exhibits a decrease by a factor of two as compared with that inherent in the condensation of almost pure steam. At the values of parameter ρ w _(2)= 66 Pa and at ν~(air)= 0.06, the average heat transfer coefficient decreases by 1.3 times. The studies on almost pure steam are in good agreement with Berman’s dependence.