Experimental Study On Flow Characteristics Of Liquid Film On Nonplanar Walls

The liquid film fluid refers to a phenomenon in which the thickness is small and flows under the action of gravity or shear force,and has the characteristics of small flow rate,small temperature difference,high heat and mass transfer coefficient,and high heat flow density.The liquid film flow parameters and the vortex characteristics in the wall structure have a significant influence on the flow stability of the liquid film.In this paper,the experimental method is used to study the liquid film flow characteristics on non-flat wal s.The liquid film flow test bench is built,which mainly includes the experimental plate,the water circuit circulation system,the optical imaging system,the data acquisition and processing system.The liquid film is formed by the combination of overflow and narrow slit method,spray method,and the wall structure is formed by triangle and rectangle.The liquid film thickness,the sonic wave velocity and the frequency are statistical y analyzed by changing the wall tilt angle,the Reynolds number,the path distance and the wall structure.The law of variation of eddy characteristics.The results show that the liquid film can be formed by the combination of overflow and narrow slit method and spray method.As the Reynolds number and the distance along the path increase,the thickness of the liquid film increases continuously,and the sonic wave velocity increases.The solitary wave is generated at a distance of 20 cm along the path,and the frequency is relatively small at 30 cm and 40 cm;however,the effect of the Reynolds number on the solitary wave frequency is not obvious,and the frequency fluctuates within the range of 4-11 Hz.Gravity has a great influence on the development of liquid film.At a temperature of ?=75°,the development speed of the liquid film is faster,and the sonic wave velocity is larger,but the thickness of the liquid film is thinner than when the wall surface is gentle.The degree of influence of Reynolds number and gravity on the surface fluctuation of liquid film is closely related to the type of non-flat wall structure.At Re=137 and Re=219,no vortex appears in the triangular structure,and a vortex appears in the rectangular wall structure.As the Reynolds number increases,vortices appear in the triangular wall structure,and the size increases and the shape becomes irregular.By changing the influence of the wall structure type and the Reynolds number,it is known that the vortex is generated in two ways: by the wall structure and by the hydrodynamic effect.The Reynolds number and the angle of inclination of the wall have an important influence on the vortex structure,which is reflected in the change in position,size and shape.The surface wave velocity on the rectangular and triangular wal s is higher than the surface wave velocity on the plate.The difference between the wave velocity and the Reynolds number and the wall structure type is closely related.