Studies On Direct-contact Vaporization Between Coolant And Hot Viscous Liquid In Analogy Hele-Shaw Cell

This paper presents the theoretical and experimental study on the direct-contact heat transfer process and on the interfacial shape of a drobble formed as the volatile coolant injected into another hot viscous liquid.The change of a drobble during its rise in an hot immiscible viscous liquid is analyzed, on the basis of which the mathematical model about the process of the drobble's evaporation in the hot continuous phase is set up. The governing equations derived from the analysis above are solved simultaneously applying a numerical method (Runge-Kutta). The simulation results confirm that there is a little effect on heat transfer coefficient of entering velocity of drobble. The small size of drobble and low initial difference in temperature will make the heat transfer coefficient high.The direct-contact heat transfer experiment of sucrose solution as hot viscosity liquid are performed in a vertical analogous Hele-Shaw cell by using n-pentane (immiscible with the hot solution) and acetone (miscible with the hot solution) as volatile coolants, respectively. The effects of coolant flow rate, inlet temperature etc. on the temperature of sucrose solution and volumetric heat transfer rate are discussed with the analysis of the cooling curves of hot sucrose solution plotted with the experimental data. The following results were obtained: The volumetric heat transfer rate decreases if the time goes on or the flow rate of the coolant goes down, the results are in reasonable agreement with theoretical analysis. Also, the mechanism of this process has been analyzed with the concept of "interfacial vaporization heat sink".At the same time, the experimental study is performed on the interfacial shape of drobble in an analogous Hele-Shaw cell. By observing the photographs of the interfacial viscous fingering and dealing with the theory of fractal, the effects of macroscopical factors on the interfacial shape are analyzed. It is found that the fractal dimension of interfacial viscous fingering increases when the sucrose solution's concentration increases; There are different effects on the interfacial shape in different driving manners, the fractal dimension upward is the largest and downward is next. The fractal dimension of horizontal experiment is the smallest.