Survey on measurement of tangential momentum accommodation coefficient

Abstract

The value of tangential momentum accommodation coefficient (TMAC) is required while prescribing the boundary condition for flow of gases in the slip and transition flow regimes. The precise determination of its value is important for several other applications as well. This article reviews the experimental techniques employed by researchers over the decades to measure this coefficient and the values reported in the literature, with relevance to calculation of the slip velocity. The review shows that the value of TMAC is dependent on a number of parameters including nature of the gas, pressure of the gas, material of the surface, surface cleanliness and roughness, and surface temperature. For monatomic gases, the TMAC at about 0.93 is almost constant with respect to the Knudsen number, and this value can be employed for most commonly available surface materials. However, for nonmonatomic gases, TMAC decreases with an increase in Knudsen number; a correlation of TMAC with Knudsen number for this class of gases, is proposed based on the available data. It is also revealed that TMAC depends strongly on the surface cleanliness and roughness, while temperature has an influence although it may not be very important for values greater than the room temperature.

Experimental measurement on tangential momentum accommodation coefficient in a single microtube

“…However, the flow in a tube is a two-dimensional problem, which is much simpler than that in a rectangular channel or a bundle of tubes where the problem could be a three-dimensional problem. It is also worth noting that the reported TMACs are still few (Agrawal and Prabhu 2008;Verma et al 2009) compared to EAC (Saxena and Joshi 1988), which is known to have a certain amount of variation among data in many cases. Therefore, the measurement of TMAC itself is important and valuable.…”

“…TMAC is known to vary depending on gas species, surface materials, surface temperature, surface conditions such as roughness and contaminant. TMAC has been measured by various approaches in a variety of gas-surface combinations and conditions (Agrawal and Prabhu 2008). Recently, TMAC was measured by the slip flow through microchannels fabricated by the semiconductor processing technique on silicon and related materials, which is often used for microdevices (Arkilic et al 2001;Maurer et al 2003;Colin et al 2004;Ewart et al 2006;Jang and Werely 2006;Ewart et al 2007a, b;Pitakarnnop et al 2010).…”

Study of subsonic–supersonic gas flow through micro/nanoscale nozzles using unstructured DSMC solver

“…We consider both of these coefficients unity in studying diatomic nitrogen gas flow. Meanwhile, Agrawal and Prabhu (2008) have shown that the value of tangential momentum accommodation coefficient would be 0.926 for monatomic gas studies. Alexeenko et al (2002) showed that the dependency of nozzle flow solution to the accommodation coefficient is quite weak if this coefficient increases from 0.8 to 1.…”

Gaseous slip flow of a rectangular microchannel with non-uniform slip boundary conditions

“…The gas flow model can be used to find the TMAC of a gas on the surface of a microchannel by fitting mass flow measurements with the flow model (Agrawal and Prabhu 2008), which is now referred to as the microchannel flow method. The TMAC is an important parameter that is required to prescribe the boundary conditions in the gaseous slip or transition flow regimes, and it depends on wall material, gas flowing through the microchannels, and wall roughness.…”