Micro-scale turbopump blade cavitation

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001.Includes bibliographical references (p. 195-196).The possibility of a silicon micro-fabricated turbopump for the use in a micro-fabricated bipropellant liquid rocket engine is of interest. Such a pump might have airfoils on the order of 1mm chord and 0.2mm span and operate at a Reynolds number of 6000. Cavitation is a major technical issue in such a pump, but there is little work in the literature at this length scale. This work documents analytical and experimental investigations of cavitation on millimeter long pump blading. Cavitation inception and bubble growth are analyzed on a micro-scale and deviations from macro-scale theory are discussed. The analysis suggests that residence time, surface roughness, surface tension, and passage area constraints are significant factors in cavitation inception and growth. A non-rotating microfabricated cascade has been designed, fabricated, and tested to quantify the behavior of micro-scale cavitation. An experimental rig has been constructed, and 18 micro-cascades have been tested. Visual observations confirm the existence of cavitation, and illustrate the phenomena of hysteresis and time lag. Comparisons of test results with analysis indicate that cavitation inception is adequately modeled by macro-scale theory. Test repeatability is established and the experimental data is found to be in agreement with 3D numerical results. Performance impacts of cavitation on micro-scale bade rows are discussed and several useful correlations are included. No apparent surface damage has been observed in these experiments. The experimental and analytical results are compiled in the form of design criteria for micro-scale turbopumps, and are used to evaluate the performance impacts due to cavitation. It is estimated that for a micro-turbopump operating at the most severe expected cavitating conditions, the performance loss in terms of pressure recovery is not greater than 20%.by Sumita Pennathur.S.M

Hydronium-dominated ion transport in carbon-dioxide-saturated electrolytes at low salt concentrations in nanochannels

Nanochannel ion transport is known to be governed by surface charge at low ionic concentrations. In this paper, we show that this surface charge is typically dominated by hydronium ions arising from dissolution of ambient atmospheric carbon dioxide. Taking the hydronium ions into account, we model the nanochannel conductance at low salt concentrations and identify a conductance minimum before saturation at a value independent of salt concentration in the dilute limit. Via the Poisson-Boltzmann equation, our model self-consistently couples chemical-equilibrium dissociation models of the silica wall and of the electrolyte bulk, parametrized by the dissociation reaction constants. Experimental data with aqueous KCl solutions in 165-nm-high silica nanochannels are described well by our model, both with and without extra hydronium from added HCl

Energy Harvesting with a Liquid-Metal Microfluidic Influence Machine

We describe and demonstrate a new energy harvesting technology based on a microfluidic realization of a Wimshurst influence machine. The prototype device converts the mechanical energy of a pressure-driven flow into electrical energy, using a multiphase system composed of droplets of liquid mercury surrounded by insulating oil. Electrostatic induction between adjacent metal droplets drives charge through external electrode paths, resulting in continuous charge amplification and collection. We demonstrate a power output of 4 nW from the initial prototype and present calculations suggesting that straightforward device optimization could increase the power output by more than 3 orders of magnitude. At that level the power efficiency of this energy harvesting mechanism, limited by viscous dissipation, could exceed 90%. The microfluidic context enables straightforward scaling and parallelization, as well as hydraulic matching to a variety of ambient mechanical energy sources such as human locomotion.Comment: 7 pages, 7 figure

Multiphase flow in lab on chip devices: a real tool for the future?

Many applications for lab on a chip (LOC) devices require the use of two or more fluids that are either not chemically related (e.g. oil and water) or in different phases (e.g. liquid and gas). Utilizing multiphase flow in LOC devices allows for both the fundamental study of multiphase flow and the development of novel types of pumping, mixing, reaction, separation, and detection technologies. Current examples of multiphase LOC applications include inkjet printers, separation of biochemical samples, manipulation of biomolecules, bio-sensing, enhanced mixing for bio-sample reactions, biomolecule detection, microelectronic cooling, drug delivery devices, explosives detection, dairy analysis, bubble computing and analysis of emulsions, foams, and bubble coalescence. In this focus article, we will briefly review the basics of multiphase flow with reference to microfluidic systems, describe some of the most promising flow control methods for multiphase fluid systems, and discuss our thoughts about future directions of microfluidic multiphase flow

Optofluidics: field or technique?

Speculation on the future of optofluidics—part of a series of mini-reviews covering new trends in fundamental and applied research, and potential applications of miniaturised technologies

Energy conversion in microsystems: is there a role for micro/nanofluidics?

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