Gas Flow in Microchannel / Rarefied Gas Flow

Microscale passages are an intricate part of any microfluidic device. These devices have potentially large applications in health-care, defense, electronic and agriculture industries. Gas flow behavior at small scales is governed by an additional non-dimensional parameter – the Knudsen number. The flow physics at high Knudsen number is however not well understood. Studies have shown that new effects such as: velocity and temperature jump at the solid-fluid interface and compressibility effect at low Mach numbers, are present at micro-scale involving gas flow.

Flow of low pressure gas through a passage involving sudden expansion. The experimental result clearly shows absence of flow separation at the junction(left), Simulation result for flow in bend at Re = 2.14 showing an early onset of flow separation in the corner(right)

We have performed detailed experiments and numerical simulations which help elucidate the non-intuitive flow behaviour when the passage is complex. We consider passages involving a sudden change in cross-sectional area or a bend. Unlike conventional flow, the absence of flow separation is noted at the junction in a passage involving a sudden change in the cross sectional area (see figure). In contrast, flow separation is noted even at very low Reynolds numbers in the presence of a bend. The experiments in our lab have shown that the Nusselt number is anomalously low with gas flow, and that the available theoretical analyses are unable to correctly predict its value.

References

  1. Hemadri, V., Varade, V., Agrawal, A., and Bhandarkar, U.V., "Rarefied Gas Flow in Converging Microchannel in Slip and Early Transition Regimes," Physics of Fluids, (under review).

  2. Hemadri, V., Varade, V., Agrawal, A., and Bhandarkar, U.V., "Investigation of rarefied gas flow in microchannels of non-uniform cross section," Physics of Fluids, Vol. 28, 022007 (10 pp), 2016.

  3. Varade, V., Agrawal, A., Prabhu, S.V., Pradeep, A.M., "Early onset of flow separation with rarefied gas flowing in a 90o bend tube," Experimental Thermal and Fluid Science, Vol. 66, 221-234, 2015.

  4. Varade, V., Agrawal, A., Pradeep, A.M., "Slip flow through converging microchannel: Experiments and three-dimensional simulations," Journal of Micromechanics and Microengineering, Vol. 25 025015 (23 pp), 2015.

  5. Varade, V., Agrawal, A., Prabhu, S.V., Pradeep, A.M., "Velocity measurement of low Reynolds and low Mach number slip flow through a tube," Experimental Thermal and Fluid Science, Vol. 60, pp. 284-289, 2015.

  6. Varade, V., Agrawal, A., Pradeep, A.M., "Behavior of rarefied gas flow near junction of a suddenly expanding tube," Journal of Fluid Mechanics, Vol. 739, pp. 363-391, 2014.

  7. Varade, V., Agrawal, A., Pradeep, A.M., "Experimental study of rarefied gas flow near sudden contraction junction of a tube," Physics of Fluids, Vol. 26, 062002 (1-21), 2014.

  8. Demsis, A., Prabhu, S.V., and Agrawal, A., "Influence of wall conditions on friction factor for flow of gases under slip condition," Experimental Thermal and Fluid Science, Vol. 34, pp. 1448-1455, 2010.

  9. Demsis, A., Verma, B., Prabhu, S.V., and Agrawal, A., "Heat transfer coefficient of gas flowing in a circular tube under rarefied condition," International Journal of Thermal Sciences, Vol. 49, pp. 1994-1999, 2010.

  10. Demsis, A., Verma, B., Prabhu, S.V., and Agrawal, A., "Experimental determination of heat transfer coefficient in the slip regime and its anomalously low value," Physical Review E, Vol. 80 (016311), pp. 1-8, 2009.

  11. Verma, B., Demsis, A., Agrawal, A., and Prabhu, S.V., "Semi-empirical correlation for friction factor with gas flow through smooth microtube," Journal of Vacuum Science and Technology A, Vol. 27 (3), pp. 584-590, 2009.