Several applications such as liquid-liquid extraction in micro-fluidic devices are concerned with the flow of two immiscible liquid phases. The commonly observed flow regimes in these systems are slug-flow and stratif...Several applications such as liquid-liquid extraction in micro-fluidic devices are concerned with the flow of two immiscible liquid phases. The commonly observed flow regimes in these systems are slug-flow and stratified flow. The latter regime in micro-channels has the inherent advantage that separation of the two liquids at the exit is efficient. Recently extraction in a stratified counter-current flow has been studied experimentally and it has been shown to be more efficient than co-current flow. An analytical as well as a numerical method to determine the steady-state solution of the corresponding convection-diffusion equation for the two flow-fields is presented. It is shown that the counter-current process is superior to the co-current process for the same set of parameters and operating conditions. A simplified model is proposed to analyse the process when diffusion in the transverse direction is not rate limiting. Different approaches to determining mass transfer coefficient are compared. The concept of log mean temperature difference used in design of heat exchangers is extended to describe mass transfer in the system.展开更多
In this work, two novel approaches were developed for miniaturized liquid-liquid(L-L) extraction on microfluidic chips, based on a stopped-flow extraction technique. In the first approach, trapped droplets extraction ...In this work, two novel approaches were developed for miniaturized liquid-liquid(L-L) extraction on microfluidic chips, based on a stopped-flow extraction technique. In the first approach, trapped droplets extraction mode, organic solvent droplets of a few hundred 10 -12 L were trapped within micro recesses fabricated in the channel walls of microfluidic chips, and analytes in aqueous streams flowing over the droplets were transferred into them, affecting a preconcentration. In the second approach, a stable interface between stationary organic phase and continuously flowed aqueous phase was formed by stopping the flow of organic phase. Analytes were transferred from the aqueous phase into the organic phase on the interface. Enrichment factors exceeding 1 000 and 300 were achieved with a preconcentration period of 20 min with sample consumption lower than 10 μL for trapped droplets and stopped-flow microextraction. In situ laser induced fluorescence detection of the concentrated analyte was performed following the preconcentration.展开更多
文摘Several applications such as liquid-liquid extraction in micro-fluidic devices are concerned with the flow of two immiscible liquid phases. The commonly observed flow regimes in these systems are slug-flow and stratified flow. The latter regime in micro-channels has the inherent advantage that separation of the two liquids at the exit is efficient. Recently extraction in a stratified counter-current flow has been studied experimentally and it has been shown to be more efficient than co-current flow. An analytical as well as a numerical method to determine the steady-state solution of the corresponding convection-diffusion equation for the two flow-fields is presented. It is shown that the counter-current process is superior to the co-current process for the same set of parameters and operating conditions. A simplified model is proposed to analyse the process when diffusion in the transverse direction is not rate limiting. Different approaches to determining mass transfer coefficient are compared. The concept of log mean temperature difference used in design of heat exchangers is extended to describe mass transfer in the system.
文摘In this work, two novel approaches were developed for miniaturized liquid-liquid(L-L) extraction on microfluidic chips, based on a stopped-flow extraction technique. In the first approach, trapped droplets extraction mode, organic solvent droplets of a few hundred 10 -12 L were trapped within micro recesses fabricated in the channel walls of microfluidic chips, and analytes in aqueous streams flowing over the droplets were transferred into them, affecting a preconcentration. In the second approach, a stable interface between stationary organic phase and continuously flowed aqueous phase was formed by stopping the flow of organic phase. Analytes were transferred from the aqueous phase into the organic phase on the interface. Enrichment factors exceeding 1 000 and 300 were achieved with a preconcentration period of 20 min with sample consumption lower than 10 μL for trapped droplets and stopped-flow microextraction. In situ laser induced fluorescence detection of the concentrated analyte was performed following the preconcentration.
