Experimental Study On Mass Transfer Of Single Bubbles In A Chamber With Viscous Fluids Under Elevated Temperature

Gas-liquid mass transfer process under elevated temperature and viscous systems is very common in chemical production process.The saturated vapor pressure of liquid at high temperature contains a large proportion of vapor pressure which cannot be neglected.In the gas-liquid equipment,the gas is distributed in the liquid in the form of bubbles.The increase of liquid viscosity will affect the diffusion rate of solute molecules and the size of phase interface,thus affecting the mass transfer.At present,the research on gas-liquid mass transfer process under high temperature viscous system is not enough.Therefore,it is of great significance to study the gas-liquid mass transfer in viscous fluids under high temperature.The particle image velocimetry technology is used to measure the turbulent flow field of liquid phase with different temperatures and viscosities in the chamber.The increase of temperature will cause the increase of liquid velocity:when the temperature increased from 25°C to 85°C,the average liquid velocity in the range of bubble motion region of the system with viscosity of 4.50±0.1m Pa·s increases by up to 21.6%.The average liquid velocity of the system with viscosity of 8.50±0.1 m Pa·s increases by up to 52.0%.It indicates that the increase of temperature can promote mass transfer is the result of the acceleration of chemical reaction rate and the intensification of liquid turbulence.However,the increase of liquid viscosity will cause the decrease of liquid velocity:when the viscosity increases from 1.03 m Pa·s to 8.50 m Pa·s,the average velocity of liquid phase in the range of bubble motion decreases from0.46 m/s to 0.14 m/s,with a decrease of up to 69.6%.The decrease of liquid pulsation velocity is not conducive to the mass transfer process.The oxygen-sodium sulfite system was selected as the materials in the experiment of single bubble mass transfer and the syrup solution was used to increase the viscosity of fluids.The liquid phase temperature was raised to 85°C,and the gas-liquid mass transfer under very high temperature conditions was studied.The effect of liquid viscosity on bubble motion behavior and mass transfer process was studied.The mass transfer coefficient of bubbles is in the order of 10^-5～10^-4 m/s.The increase of liquid temperature enhances the mass transfer:when the temperature increases from 25°C to 85°C,the mass transfer coefficient of the system with viscosity of 4.50±0.1 m Pa·s increases up to 33.0%under different flow conditions.The mass transfer coefficient of the system with viscosity of 8.50±0.1 m Pa·s increases by up to 118.3%.However,the increase of liquid viscosity weakens the mass transfer process:the viscosity increases from 1.03 m Pa·s to 8.50 m Pa·s,and the mass transfer coefficient decreases by71.7%under different flow conditions.With the increase of liquid flow rate,the negative effects of liquid viscosity on mass transfer is reduced.In addition,the mass transfer coefficients obtained from mass transfer experiments and the calculated values of three classical mass transfer models were analyzed.The experimental Sh is in good agreement with the predicted results of Fr?ssling model.