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Electro-hydrodynamics

Traditionally, fluid pumping techniques have been mainly based on using mechanical pumps that have different types and operation principles. Due to increased development in MEMs and Lap-on-chip (LOC) devices, there is a need to develop small-scale, reliable, and low-cost pump. One of the most promising pumping techniques is to use the electro-hydrodynamic (EHD) fluid pumping principle. This pumping technique is based on the fact that when an aqueous solution is brought into contact with a surface such as a channel wall, the surface will acquire a negative charge. The positively-charged ions in the solution will be attracted to the surface leading to a higher concentration of positive ions in its vicinity. The concentration of positive ions in the fluid bulk will be lower. When an electric field is applied between two points in the fluid, a bulk motion of the fluid occurs. This is known as electro-osmotic flow (EOF).

EOF has a unique feature that can suitable for LOC applications. EOF has a plug flow profile that can reduce sample dispersion. Also, for heat transfer in micro-channels, plug profile increases the amount of heat transfer due to the increase in the heat transfer coefficient.

I. Sample transport and micro-reactions control:  Research investigated controlled sample transport to micro-reactors where pinching and switching techniques were implemented. The research was conducted experimentally and was verified using numerical calculations. Nano-liter discrete samples were transported to a micro-reactor using EOF. The samples were allowed to react for a specific amount of time while their concentrations were monitored in the reactor. Sample pinching process is shown in Fig. 2. The lab is in the process of developing diagnostic devices for immunoassays that help detect biomolecules, cells, and pathogens in throughput screening. One such method of immunoassay is magnetophoretic separation that uses magnetic microbeads conjugated with antibodies against specific cell surface epitopes (antigens) and are used to tag cells of interest.

II. Heat transfer in micro-channels using EOF:  Heat transfer in micro-channels using EOF, as a flow pumping technique, is currently being studied. Experimental studies are being conducted as well as numerical calculations for verification. Silicon-based micro-channels were fabricated and a micro-scale heat exchanger device was assembled using various components. Micro-channels used in one of our micro-scale heat exchanger are shown in Fig. 2. Flow and heat transfer data were gathered and analyzed to assess the performance of the device.
Additionally, studies are being performed on hybrid micro-channels heat exchangers using combinations of different materials. Also, the use of different cooling liquids is being evaluated for optimal heat transfer characteristics.

eos flow-figure 1

Fig. 1. Numerical and experimental results of sample pinching process at different times

eos flow-figure 2

Fig. 2. SEM photograph of micro-channels used in the fabrication of micro-scale heat exchangers

by zopeown last modified 2015-05-06 11:21