| Steam direct contact condensation(SDCC)is widely used in various industrial production fields due to large contact area,low driving energy coconsumption,efficient heat and mass transfer.However,the non-condensable gas is usually involved during the process of SDCC in industrial applications,which induces thermal parameters oscillation and largely deteriorates heat transfer.Hence,many scholars have focused on SDCC with non-condensable gas recently.In this paper,experimental research and numerical simulation are both used to clarify the oscillation characteristics,based on observation and analysis,the mechanism of heat and mass transfer in SDCC,as well as depression effect of condensation oscillation by non-condensable gas in process of SDCC have been revealed.The main research contents of this paper are as follows:Firstly,an optical experimental platform of SDCC in a pipe with non-condensable gas was built,which carried out the visualization,temperature and pressure data measurement experiments.Based on the spatial distribution and movement of gas-liquid interface captured in visualization,the phenomenon of SDCC with non-condensation gas in a pipe are observed and analyzed.Four typical condensation flow patterns are observed under this experimental conditions:chugging condensation,oscillating bubble flow,slug flow and stratified flow.The influence of non-condensable gas content,mass flux of mixture gas,Reynolds number and temperature of subcooled water on condensation flow patterns is analyzed.Two-dimensional and three-dimensional condensation flow pattern diagrams are constructed to visually show the relationship between condensation flow pattern and various influencing factors.Secondly,based on the temperature and pressure measurement experiments,the influence laws of non-condensable gas content,mass flux of mixed gas,Reynolds number and temperature of subcooled water on the oscillation characteristics of SDCC with non-condensable gas in a pipe are analyzed and summarized.Using the data of condensation temperature and pressure oscillation at the monitoring point obtained from the experimental measurement,the condensation oscillation characteristics of four typical condensation flow pattern are analyzed and the induction mechanism of condensation pressure oscillation is elaborated.The influence of non-condensable gas content,mass flux of mixture gas,Reynolds number and temperature of subcooled water on oscillation characteristics of condensation temperature and pressure oscillation form,temperature and pressure oscillation intensity,frequency spectrum and domain frequency of pressure oscillation are analyzed.The weakening mechanism of non-condensable gas on condensation pressure oscillation is explained.Finally,a mathematical model of SDCC with non-condensable gas is established.The effects of non-condensable gas on multi-phase flow and heat and mass transfer of SDCC is predicted numerically.Compared with the experimental results,the numerical results have certain reliability.Based on the numerical results,the gas-liquid interface movement characteristics,pressure and temperature oscillation characteristics,non-condensable gas component distribution and interfacial pressure characteristics during the process of SDCC with non-condensable gas in a pipe were obtained.The internal relationship between gas-liquid interface motion pattern and condensation temperature and pressure oscillation was analyzed.Flow and phase transition mechanism of SDCC with non-condensable gas in a pipe,generation of condensation pressure oscillation and the restraint mechanism of non-condensable gas on its oscillation peak were revealed.The above research further promotes the recognition of SDCC with non-condensable gas in a pipe,clarifies the influence of gas-water parameters on oscillation characteristics of SDCC with non-condensable gas in a pipe,and elaborates the generation mechanism of condensation pressure oscillation and the action mechanism of non-condensable gas on its suppression.The expected research results can provide technical means and theoretical guidance for engineering application of steam direct contact condensation and pressure oscillation suppression. |
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