Experimental Study On Boiling Phenomenon Of One Liquid On The Surface Of Another Immiscible Liquid

Boiling phenomenon is widely used in industry production because of bubble disturbance,high heat transfer coefficient and high heat flux density.When liquids are heated on a solid surface,bubbles are most likely to be generated in the uneven places such as pits,crevices,and cracks of the solid surface.When the liquid is in direct contact with another immiscible liquid,there are no gaps,pits between the liquid-liquid interface,which is most likely to become the uneven place of the vaporization core.In this paper,the boiling phenomenon on the immiscible liquid interface was experimentally investigated,and the nucleation temperature and bubble shape at the liquid-liquid interface were studied,which compared with the nucleation temperature and bubble shape of liquid heated on the solid surface.In the aspect of experiment,a visualized experimental system of direct contact heat transfer between immiscible liquids was established.Firstly,n-pentane and HFE7100 were used as working fluids to be heated on copper surface to obtain the nucleation temperatures and bubble behaviors.The experimental results showed that the nucleation temperature of n-pentane heated on the copper surface was 38℃,that is,the degree of superheat was 1.9℃.While the nucleation temperature of HFE7100 heated on the copper surface was 63.4℃,that is,the degree of superheat was 2.4℃.During the boiling experiment of n-pentane and HFE7100 on the copper surface,the bubble behavior was similar.The experimental phenomenon was that isolated bubbles were generated near the center of the copper wall at the beginning of boiling.With the increase of the wall superheat,the number of bubbles increased and the intensity of boiling phenomenon increased.In addition,according to the experimental data,the relationship between superheat and heat flux density was obtained and compared with the literature.Secondly,the direct heat transfer experiments of n-pentane on the surface of ethylene glycol,n-pentane heated on the surface of deionized water and HFE7100 heated on the surface of liquid metal gallium were carried out.The experimental results showed that in the boiling experiment of n-pentane vaporizing on the surface of ethylene glycol and n-pentane vaporizing on the surface of deionized water,the liquid-liquid interface fluctuated because of the natural convection inside the working fluids and the base liquids,so the experimental phenomenon was that continuous bubbles were generated at a certain position of the liquid-liquid interface.And the bubble departure frequency was obviously faster than that on the solid suface,the bubble formed a string of gas columns.With the increase of wall temperature,the boiling phenomenon at the liquid-liquid interface became more and more severe,which was manifested in increase of the number of gas columns and accompanied by the phenomenon of gas column movement.In the experiment of HFE7100 heated on the liquid metal gallium surface,the bubble behavior of boiling was similar to that of HFE7100 boiling on the copper surface,and it showed the generation,growth and rise of isolated bubbles.As the wall temperature increased,the number of bubbles increased and boiling became severe.Because the thermocouple measurement would cause disturbance at the liquid-liquid interface,the temperature of the liquid-liquid interface generated bubbles was not obtained in the experiment.In order to obtain the nucleation temperature of the liquid-liquid interface,COMSOL simulation software was used to analyze the temperature field of the experimental system.According to calculation results,the nucleation temperature of n-pentane on the surface of ethylene glycol was 63℃,that is,the superheat was 26.9℃;the nucleation temperature of n-pentane on the surface of deionized water was 78.4℃,that is,the superheat was 42.3℃;the nucleation temperature of HFE7100 on the surface of liquid gallium was71℃,that is,the superheat was 10℃.The reason why the interfacial superheat of HFE7100 on liquid gallium was lower was that an oxide film formed on the liquid gallium surface,which was more likely to produce vaporized core..