Miniaturization of conventional energy sources has so far proven to be a cumbersome process. A recently developed concept of thermopower waves has shown tremendous potential to reduce the dimensions of power sources while maintaining their energy generation capabilities. We demonstrate a tremendous improvement in the output for these thermopower wave-based energy generation devices by implementing manganese dioxide (MnO 2 ) as the core thermoelectric material. In this work, the thermoelectric MnO 2 layer is used as a pathway for the propagation of thermopower waves that are generated as a result of an exothermic chemical reaction of a solid fuel (nitrocellulose). Such selfpropagating thermopower waves result in exceptionally high voltage output on the order of 1.8 V and a specific power (power-tomass ratio) on the order of 1.0 kW•kg −1 . The output voltage is at least 300% higher than any other thermopower wave system reported so far.
Increasing the thermal conductivity of PDMS (polydimethylsiloxane) based microfluidics is an important issue for the thermal management of hot spots produced by embedding electronic circuits in such systems. This paper presents a solution for enhancing the thermal conductivity of such PDMS based microfluidics by introducing thermally conductive alumina (Al2O3) nanoparticles, forming PDMS/Al2O3 nanocomposites. The materials are fully characterized for different concentrations of Al2O3 in PDMS for experiments which are conducted at different flow rates. Our results suggest that incorporation of Al2O3 nanoparticles at 10% w/w in the PDMS based nanocomposite significantly enhances the heat conduction from hot spots by enhancing the thermal conductivity, while maintaining the flexibility and decreasing the specific heat capacity of the developed materials. This proof-of-concept study offers potential for a practical solution for the cooling of future embedded electronic systems.
Recently, the bubble-based systems have offered a new paradigm in microfluidics. Gas bubbles are highly flexible, controllable and barely mix with liquids, and thus can be used for the creation of reconfigurable microfluidic systems. In this work, a hydrodynamically actuated bubble-based microfluidic system is introduced. This system enables the precise movement of air bubbles via axillary feeder channels to alter the geometry of the main channel and consequently the flow characteristics of the system. Mixing of neighbouring streams is demonstrated by oscillating the bubble at desired displacements and frequencies. Flow control is achieved by pushing the bubble to partially or fully close the main channel. Patterning of suspended particles is also demonstrated by creating a large bubble along the sidewalls. Rigorous analytical and numerical calculations are presented to describe the operation of the system. The examples presented in this paper highlight the versatility of the developed bubble-based actuator for a variety of applications; thus providing a vision that can be expanded for future highly reconfigurable microfluidics.
We present the thermal analysis of liquid containing Al(2)O(3) nanoparticles in a microfluidic platform using an infrared camera. The small dimensions of the microchannel along with the low flow rates (less than 120 μl min(-1)) provide very low Reynolds numbers of less than 17.5, reflecting practical parameters for a microfluidic cooling platform. The heat analysis of nanofluids has never been investigated in such a regime, due to the deficiencies of conventional thermal measurement systems. The infrared camera allows non-contact, three dimensional and high resolution capability for temperature profiling. The system was studied at different w/w concentrations of thermally conductive Al(2)O(3) nanoparticles and the experiments were in excellent agreement with the computational fluid dynamics (CFD) simulations.
Budding yeast cells are quick and easy to grow and represent a versatile model of eukaryotic cells for a variety of cellular studies, largely because their genome has been widely studied and links can be drawn with higher eukaryotes. Therefore, the efficient separation, immobilization, and conversion of budding yeasts into spheroplast or protoplast can provide valuable insight for many fundamentals investigations in cell biology at a single cell level. Dielectrophoresis, the induced motion of particles in non-uniform electric fields, possesses a great versatility for manipulation of cells in microfluidic platforms. Despite this, dielectrophoresis has been largely utilized for studying of non-budding yeast cells and has rarely been used for manipulation of budding cells. Here, we utilize dielectrophoresis for studying the dynamic response of budding cells to different concentrations of Lyticase. This involves separation of the budding yeasts from a background of non-budding cells and their subsequent immobilization onto the microelectrodes at desired densities down to single cell level. The immobilized yeasts are then stimulated with Lyticase to remove the cell wall and convert them into spheroplasts, in a highly dynamic process that depends on the concentration of Lyticase. We also introduce a novel method for immobilization of the cell organelles released from the lysed cells by patterning multi-walled carbon nanotubes (MWCNTs) between the microelectrodes.
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