This paper describes a novel pumping device without mechanical moving parts based on the periodic generation and collapse of a single vapour bubble in a channel. The channel shape is such that it creates an asymmetry in the surface tension forces, which results in a pumping effect. The principle can be implemented over a broad range of channel sizes and repetition frequencies. For illustration purposes, a particular implementation is described here where the working fluid is a salt solution in water, the channel diameters are of the order of 1 mm and the repetition frequency is between 1-10 Hz. In these conditions, the device develops a head of a few centimetres of water with typical flow rates in the range of 100 µl per minute. It appears possible to increase both head and flow rate by adjusting geometrical parameters and operating conditions. A simple modification of the design would render the same principle also applicable to the pumping of non-conducting liquids.

https://iopscience.iop.org/article/10.1088/0960-1317/11/3/317/pdf

Bubble-based micropump for electrically conducting liquids

We investigate the control of flow direction around a water vapor bubble using the thermoplasmonic effect of a gold nanoisland film (GNF) under laser irradiation with multiple spots. By focusing a laser spot on the GNF immersed in degassed water, a water vapor bubble with a diameter of ~10 μm is generated. Simultaneously, a sub laser spot was focused next to the bubble to yield a temperature gradient in the direction parallel to the GNF surface. Consequently, rapid flow was generated around the bubble, whose flow direction was dependent on the power of the sub laser spot. The observed flow was well-described using a stokeslet; the latter contained components normal and parallel to the GNF surface and was set to 10 μm above the GNF. This technique allows us to apply a significant force on the microfluid at the vicinity of the wall in the direction parallel to the wall surface, where the flow speed is generally suppressed by viscosity. It is expected to be useful for microfluidic pumping and microfluidic thermal management.

/pdf/direction-control-of-quasi-stokeslet-induced-by-4j08rxcg2k.pdf

Direction control of quasi-stokeslet induced by thermoplasmonic heating of a water vapor microbubble

We have experimentally investigated the control of Marangoni flow around a micro bubble using photothermal conversion. Using a focused laser spot acting as a highly localized heat source on Au nanoparticles/dielectric/Ag mirror thin film enables us to create a micro bubble and to control the temperature gradient around the bubble at a micrometer scale. When we irradiate the laser next to the bubble, a strong main flow towards the bubble and two symmetric rotation flows on either side of it develop. The shape of this rotation flow shows a significant transformation depending on the relative position of the bubble and the laser spot. Using this controllable rotation flow, we have demonstrated sorting of the polystyrene spheres with diameters of 2 μm and 0.75 μm according to their size.

/pdf/photothermally-controlled-marangoni-flow-around-a-micro-ah1667b82l.pdf

Photothermally controlled Marangoni flow around a micro bubble

Seed bubbles stabilize flow and heat transfer in parallel microchannels

Rapid Marangoni flows around a water vapor microbubble (WVMB) is investigated using the thermoplasmonic effect of a gold nanoisland film (GNF). By focusing a laser onto the GNF, a stable WVMB with a diameter of ~10 μm is generated in degassed water, while an air bubble generated in non-degassed water is larger than 40 μm. Under continuous heating, the WVMB involves significantly rapid Marangoni flow. This flow is well-described by a stokeslet sat ~10 μm above the surface of GNF, from which the maximum flow speed around the WVMB is estimated to exceed 1 m/s. This rapid flow generation is attributed to the small bubble size, over which the temperature is graded, and the superheat at the bubble surface in contact with the GNF. It is expected to be useful not only for microfluidic mixing but also for fundamental research on viscous flow induced by a single stokeslet.

/pdf/quasi-stokeslet-induced-by-thermoplasmonic-marangoni-effect-3m8nxtuf1c.pdf

Quasi-stokeslet induced by thermoplasmonic Marangoni effect around a water vapor microbubble

This work explores the application of the Marangoni effect in micro systems involving small gas or vapor bubbles in a liquid environment subjected to a temperature gradient. The Marangoni effect characterizes the variation of surface tension along the bubble surface resulting from the temperature gradient around the bubble, thus driving the bubble toward the higher temperature region. This phenomenon is more pronounced as the bubble becomes smaller and the temperature gradient becomes steeper, both of which can be achieved in microbubble systems. Potential applications based on the Marangoni effect include linear bubble actuators, dynamic microvalves, and hot-spot locators. The optimum bubble size for these applications is expected to be of the order of 10 mu m. A smaller bubble may be difficult to introduce into the working system and maintain its size. Presented for illustration is a feasibility analysis for both a noncondensable gas bubble and a vapor bubble situated above a microheater. The analysis y...

Chang Lin Tien

Papers

Marangoni effect in microbubble systems