CFD Simulations Of Liquid-liquid Taylor Flow In Microchannels

Microchannel heat exchanger has been widely used in aerospace,modern medical,chemical and biological engineering and many other fields.Study on its hydrodynamics and heat transfer behavior can provide guidance for optimizing the operation of existing reactors and developing a novel reactor with high performance.Based on the computational fluid dynamics software Fluent16.2,the hydrodynamics and heat transfer of the liquid-liquid two-phase Taylor flow in the microchannel were simulated.The main contents included the following aspects:The two-dimensional physical model of toluene-water two-phase flow in a microchannel was established to study the hydrodynamics and heat transfer characteristics of Taylor flow.The hydrodynamics and heat transfer characteristics of the completely developed Taylor flow showed a stable periodic distribution trend.The wall shear stress and interface vorticity had certain effect on the fluctuating changes of wall and interface temperature,and had a certain time lag.The wall Nusselt number of toluene-water two-phase Taylor flow was much greater than that of gas-liquid two-phase flow.The average Nusselt number of a liquid slug unit was 1.3 times of single-phase flow under the same conditions.Via changing the disperse phase system,fluid feed rate and wall heat flux,the effects on the heat transfer of Taylor flow were investigated.The choice of the dispersed phase with higher thermal conductivity and the increase of the feed rate of the dispersed phase would accelerate the heat transfer rate of the two-phase flow in microchannels.However,the feed rate of two-phase Taylor flow also had a certain limit.When it exceeded this limit,the liquid-liquid two-phase flow would form parallel flow in the microchannel,which made it difficult for the fluid at the center of the microchannel to achieve heat transfer.When the wall heat flux was increased,the wall temperature near the head and tail increased fasted.The physical models of the microchannels with diameter-expansion or reduction zones were established to study the deformation and heat transfer law of the Taylor flow in the diameter-variation zone.The geometrical dimension of the diameter-variation zone had a certain limit.When it was greater than this limit,the structure of flow film through here would be damaged,the liquid slug would contact the microchannel wall directly,and the wall and center fluid temperature would change significantly.When it was less than the limit,the slug could be restored to the original shape as the resistance effect was not strong enough.The loss of the liquid film depended on whether the Taylor flow slug passed through the diameter-variation zone before the liquid film which was blocked by the wall.