A Quantitative Measurement of Wall Shear Stress Using Electric Capacity Sensing of Nematic Liquid Crystal Coating
Tribology Letters - 2013
Tóm tắt
The measurement of wall shear stress (WSS) still remains a challenge in many fields such as fluid hydrodynamics, microfluidics, or biomechanics. The nematic liquid crystal coating (LCC) is a prospective technique to measure WSS due to its global measurement capability, high resolution, and non-intrusive nature. But its current application based on the optical observation is severely limited by the requirement for a complex system. In this paper, we invented a novel WSS-measuring technique based on the anisotropic permittivity and the Freedericksz transition of nematic LCC under shear stress. First, a quantitative model was built to describe the reorientation responses of nematic liquid crystal molecules under shear stress, and the corresponding variation in dielectric property of LCC was derived. Thus, the quantitative relationship between WSS and the electric capacity output of LCC was obtained. Then, an LCC sensor was fabricated using spin coating and microlithography to verify the engineering feasibility in WSS measurement. The experimental results of capacity variation are in good agreement with the theoretical molecular model of LCC under shear stress. The mechanism and advantages of the capacity-sensing LCC technique were discussed in view of quantitative and wide-ranged WSS measurement: easy and reversible initialization, as well as potential on-site applications.
Từ khóa
Tài liệu tham khảo
Ireland, P.T., Jones, T.V.: Liquid crystal measurements of heat transfer and surface shear stress. Meas. Sci. Technol. 11, 969–986 (2000)
Martel, J., Bruno, B.A.: Shear stress measurement in microfluidic systems: liquid crystal technique. In: IMECE 2008: heat transfer, fluid flows, and thermal systems 10, 2009–2018 (2009)
Spikes, H.A., Anghel, V., Glovnea, R.: Measurement of the rheology of lubricant films within elastohydrodynamic contacts. Tribol. Lett. 17, 593–605 (2004)
Guo, F., Wong, P.L., Geng, M., Kaneta, M.: Occurrence of wall slip in elastohydrodynamic lubrication contacts. Tribol. Lett. 34, 103–111 (2009)
Li, X.M., Guo, F., Wong, P.L.: Study of boundary slippage using movement of a post-impact EHL dimple under conditions of pure sliding and zero entrainment velocity. Tribol. Lett. 44, 159–165 (2011)
Savio, D., Fillot, N., Vergne, P., Zaccheddu, M.: A model for wall slip prediction of confined n-alkanes: effect of wall-fluid interaction versus fluid resistance. Tribol. Lett. 46, 11–22 (2012)
Dabiri, D.: Digital particle image thermometry/velocimetry: a review. Exp. Fluids 46, 191–241 (2009)
Naughton, J.W., Sheplak, M.: Modern developments in shear-stress measurement. Prog. Aerospace Sci. 38, 515–570 (2002)
Tu, H., Li, J., Ming, X., Hu, C., Jiang, W.: Direct measurement technique of wall shear stress using MEMS sensors in a high-speed wind tunnel. J. Exp. Fluid Mech. 22, 94–98 (2008)
Jiang, F.: A flexible MEMS technology and its first application to shear stress sensor skin. In: Proceedings IEEE the tenth annual international workshop on micro electro mechanical systems (1997). doi:10.1109/MEMSYS.1997.581894
Lofdahl, L., Gad-el-Hak, M.: MEMS-based pressure and shear stress sensors for turbulent flows. Meas. Sci. Technol. 10, 665–686 (1999)
Tanner, L.H., Blows, L.G.: Study of motion of oil films on surfaces in air-flow, with application to measurement of skin friction. J. Phys. E. Sci. Instrum. 9, 194–202 (1976)
Buttsworth, D.R., Elston, S.J., Jones, T.V.: Direct full surface skin friction measurement using nematic liquid crystal techniques. J. Turbomach 120, 847–853 (1998)
Buttsworth, D.R., Elston, S.J., Jones, T.V.: Directional sensitivity of skin friction measurements using nematic liquid crystal. Meas. Sci. Technol. 9, 1856–1865 (1998)
Reda, D.C.: New methodology for the measurement of surface shear stress vector distributions. Aiaa. J. 35, 608–614 (1997)
Fujisawa, N., Oguma, Y., Nakano, T.: Measurements of wall-shear-stress distribution on an NACA0018 airfoil by liquid-crystal coating and near-wall particle image velocimetry (PIV). Meas. Sci. Technol. (2009). doi:10.1088/0957-0233/20/6/065403
Fujisawa, N., Aoyama, A., Kosaka, S.: Measurement of shear-stress distribution over a surface by liquid-crystal coating. Meas. Sci. Technol. 14, 1655–1661 (2003)
Ważyńska, B., Okowiak, J.A.: Tribological properties of nematic and smectic liquid crystalline mixtures used as lubricants. Tribol. Lett. 24, 1–5 (2006)
Nakano, K.: Scaling law on molecular orientation and effective viscosity of liquid-crystalline boundary films. Tribol. Lett. 14, 17–24 (2003)
Leslie, F.M.: Continuum theory for nematic liquid-crystals. Continuum Mech. Thermodyn. 4, 167–175 (1992)
Gestblom, B.O., Wrobel, S.: A thin cell dielectric-spectroscopy method for liquid-crystals. Liq. Cryst. 18, 31–35 (1995)
Rozanski, S.A.: Dielectric properties of the nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl in porous membranes. Liq. Cryst. 20, 59–66 (1996)
Hikmet, R.A.M., Zwerver, B.H.: Dielectric-relaxation of liquid-crystal molecules in anisotropic confinements. Liq. Cryst. 10, 835–847 (1991)
Panarin, Y.P., Kalinovskaya, O., Vij, J.K.: The investigation of the relaxation processes in antiferroelectric liquid crystals by broad band dielectric and electro-optic spectroscopy. Liq. Cryst. 25, 241–252 (1998)
Schad, H., Osman, M.A.: Elastic-constants and molecular association of cyano-substituted nematic liquid-crystals. J. Chem. Phys. 75, 880–885 (1981)
Zhang, S., Zhang, X., Meng, Y., Tian, Y.: A quantitative model and experimental investigations of wall shear stress between solid and gaseous fluid using liquid crystal coating. Acta. Phys. Sin (2012). doi:10.7498/aps.61.234702