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Persistent URL http://purl.org/net/epubs/work/29528
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Record Id 29528
Title Numerical simulation of low Reynolds number slip flow past a confined microsphere
Abstract One of the major difficulties in simulating gas transport through micron-sized devices is caused by the fact that the continuum flow hypothesis implemented in the Navier-Stokes equations begins to break down when the dimensions of the flow domain are comparable to the mean free path of the molecules. Under such conditions the fluid can no longer be regarded as being in thermodynamic equilibrium and a variety of non-continuum or rarefaction effects are likely to be exhibited. Velocity profiles, boundary wall shear stresses, mass flow rates and hydrodynamic drag forces are all affected by the non-continuum regime and consequently microfluidic devices which are simply scaled down versions of macro-scale systems may not always function as intended. This study investigates the important problem of low Reynolds number rarefied gas flow past a confined microsphere within a circular pipe. The geometry of a confined sphere is utilised in conventional spinning-rotor vacuum gauges where the drag on an electro-magnetically suspended rotating sphere can be used to measure a number of important physical properties of a rarefied gas including pressure, viscosity or molecular weight. Similar principles have been envisaged for the measurement of flow rates and pressures in microfluidic devices. In the present investigation, the problem has been restricted to the estimation of the drag forces on a stationary (non-rotating) sphere. Numerical simulations are carried out over a range of Knudsen numbers covering the continuum and slip flow regimes (0 0.1). In addition, blockage effects are studied by varying the ratio between the diameter of the pipe and the diameter of the sphere, / H D. The results indicate that blockage effects are extremely important in the continuum flow regime and cause an amplification in the drag force on the sphere. However, blockage phenomena are found to be less significant as the Knudsen number is increased. At the upper limit of the slip flow regime ( 0.1 Kn ; ), blockage amplification is shown to be reduced by almost 50% for a pipe-sphere geometry of / H D = 2.
Organisation CCLRC , CSE , CSE-CEG
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Language English (EN)
Type Details URI(s) Local file(s) Year
Report DL Technical Reports DL-TR-2001-001. 2001. dltr-2001001.pdf 2001