Experimental Study On Flow And Heat Transfer Of Falling Film On Inclined Wall

The falling film flow and heat transfer on the wall are widely used in industry and life,for example,low-temperature multi-effect seawater desalination,nuclear power plant containment cooling,rocket combustion chamber cooling,large-scale integrated circuits and heat pipe radiators,liquid radiators,and new solar integrated cooling.Therefore,it is very important for the study of falling film flow,fluctuation,rupture,and heat and mass transfer.It lays a good theoretical foundation for the application of falling film flow in seawater desalination.In this paper,a falling film flow and heat transfer test bench was built to carry out the falling film flow experiment on the inclined copper plate surface.The liquid film flow on the copper plate was photographed by image method.The effects of the tilt angle of the liquid film and the Reynolds number on the flow state of the liquid film were analyzed,and the distribution law of the ripple on the copper plate was obtained.The result shows that as the Reynolds number and the inclination angle increase,the ripples break and merge with each other.The instability of the liquid film becomes larger,and the fluctuation becomes more severe.When the volatility increases to a certain level,the liquid film flow tends to be disordered.As the heat flux density increases,the width of the bottom of the liquid film gradually narrows,and the decrease speed increases first and then decreases.As the Reynolds number increases,the width of the bottom gradually becomes larger,and the growth rate of the width of the bottom also gradually decreases.When the heat flux density increases,the number of bubbles generated on the wall increases.The shape of the ripple is randomly distributed with the change of the flow distance,and as the angle of inclination increases,the horseshoe-shaped ripples become steeper.The ripple wavelength gradually decreases with increasing flow distance.As the Reynolds number and tilt angle increase,the wavelength gradually decreases,and the effect of the liquid film tilt angle on the ripple wavelength is more significant than the Reynolds number.In this paper,the heat transfer laws of liquid film flow on inclined walls are studied,and the changes of local heat transfer coefficient and average heat transfer coefficient of falling film flow are summarized.The effects of cloth liquid density,heat flux density,tilt angle,initial temperature,temperature difference and salinity on local heat transfer coefficient and average heat transfer coefficient are analyzed.The results show: with different liquid density,heat flux density,tilt angle,initial temperature,temperature difference and salinity,the local heat transfer of the liquid film gradually increases along the flow direction of the inclined plate.As the flow density increases,the local heat transfer coefficients gradually increase.As the heat flux density increases,the local heat transfer coefficient of the liquid film increases.The local heat transfer coefficient increases as the tilt angle increases.Local heat transfer coefficient increases with initial temperature increases.When the temperature difference increases,the local heat transfer coefficient decreases.When the working medium is pure water,the local heat transfer coefficient is greater than when the working medium is seawater.The average heat transfer coefficient increases with increasing flow density,heat flux density,and liquid film tilt angle.