OPEN ACCESS
A steel plate is one of the critical components of a scroll expander system that can experience cavitation micro-pitting while in service. The content of the present paper consists of two distinct but interrelated parts. The first part aims to highlight that the use of computational fluid dynamics (CFD) simulations can constitute a potential tool for the prediction of cavitation erosion areas in scroll expander systems. For this purpose, a three-dimensional CFD, steady-state numerical simulation of the refrigerant working fluid is employed. Numerical results revealed the critical areas where cavitation bubbles are formed. These numerical critical areas are in direct qualitative agreement with the actual eroded regions by cavitation, which were found by microscopic observations across the steel plate on an after use, scroll expander system. The second part of the paper aims to further investigate the behaviour and the durability of the steel plate of the studied scroll expander system subjected to cavitation erosion by using an ultrasonic experimental test rig. Scanning electron microscopy and optical interferometer micrographs of the damaged surfaces were observed, showing the nature of the cavitation erosion mechanism and the morphological alterations of the steel plate samples. Experimental results are explained in terms of the cavitation erosion rates, roughness profile, accumulated strain energy, and hardness of the matrix. The experimental study can serve as a valuable input for future development of a CFD numerical model that predicts both cavitation bubbles formation as well as cavitation damage induced by the bubbles that implode on the steels plates.
CFD, multiphase flow, ultrasonic cavitation, erosion, refrigerant, steel
[1] Andriotis, A., Gavaises, M. & Arcoumanis, C., Vortex flow and cavitation in diesel. Journal of Fluid Mechanics, 610, pp. 195–215, 2008. doi: http://dx.doi.org/10.1017/S0022112008002668
[2] Nemdili, A., Experimental study of the infl uence of geometrical parameters on the cavitation of a small centrifugal pump. WIT Transactions on Engineering Sciences, 84, pp. 89–97, 2005.
[3] Tzanakis, I., Hadfi eld, M. & Khan, Z., Durability of domestic scroll compressor systems. WIT Transactions on Engineering Sciences, 62, pp. 229–240, 2009. doi: http://dx.doi.org/10.2495/SECM090211
[4] Tzanakis, I., Eskin, D.G., Georgoulas, A. & Fytanides, D.K., Incubation pit analysis and calculation of the hydrodynamic impact pressure from the implosion of an acoustic cavitation bubble. Ultrasonics Sonochemistry, 21, pp. 866–878, 2014 . doi: http://dx.doi.org/10.1016/j.ultsonch.2013.10.003
[5] Tong, R.P., Schiffers, W.P., Shaw, S.J., Blake, J.R. & Emmony, D.C., The role of ‘splashing’in the collapse of a laser-generated cavity near a rigid boundary. Journal of Fluid Mechanics, 380, p. 339, 1999. doi: http://dx.doi.org/10.1017/S0022112098003589
[6] Brujan, E.A., Ikeda, T. & Matsumoto, Y., Shock wave emission from a cloud of bubbles. Soft Matter, 21, pp. 5777–5783, 2012. doi: http://dx.doi.org/10.1039/c2sm25379h
[7] Krella, A. & Czyzniewski, A., Infl uence of the substrate hardness on the cavitation erosion resistance of TiN coating. Wear, 263, pp. 395–401, 2007. doi: http://dx.doi.org/10.1016/j.wear.2007.02.003
[8] Williams, P.R., Williams, P.M. & Brown, S.W.J., A technique for studying liquid jets by cavitation bubble collapse under shockwaves, near a free surface. Journal of Non-Newtonian Fluid Mechanics, 72, pp. 101–110, 1997. doi: http://dx.doi.org/10.1016/S0377-0257(97)00020-7
[9] Mann, B.S., High-energy particle impact wear resistance of hard coatings and their application in hydroturbines. Wear, 237, pp. 140–146, 2000. doi: http://dx.doi.org/10.1016/S0043-1648(99)00310-5
[10] Tzanakis, I., Hadfi eld, M., Thomas, B., Noya, S.M., Austen, S. & Henshaw, I., Future perspectives of sustainable tribology. Renewable and Sustainable Energy Reviews, 16(6), pp. 4126–4140, 2012. doi: http://dx.doi.org/10.1016/j.rser.2012.02.064
[11] Tzanakis, I., Hadfi eld, M., Georgoulas, A. & Kotsovinos, N., Cavitation damage observations within scroll expander lubrication systems. WIT Transactions on Engineering Sciences, 66, pp. 261–272, 2010. doi: http://dx.doi.org/10.2495/TD100221
[12] Tzanakis, I. & Eskin, D.G., Cavitation erosion behaviour of martensitic steels with different carbon content using ultrasonic methodology. Materials Science and Engineering: A (Submitted).
[13] Tzanakis, I., Hadfi eld, M. & Henshaw, I., Observations of acoustically generated cavitation bubbles within typical fl uids applied to a scroll expander lubrication system. Experimental Thermal and Fluid Science, 35(8), pp. 1544–1554, 2011. doi: http://dx.doi.org/10.1016/j.expthermfl usci.2011.07.005
[14] Tzanakis, I., Garland, N. & Hadfi eld, M., Cavitation damage incubation with typical fluids applied to a scroll expander system. Tribology International, 44(12), pp. 1668–1678, 2011. doi: http://dx.doi.org/10.1016/j.triboint.2011.06.013
[15] ANSYS Fluent 14.5 ANSYS, Inc. Release 14.5, October 2012.
[16] Tzanakis, I., Sustainable design and durability of domestic micro combined heat and power scroll expander systems. Ph.D. Thesis, Bournemouth University, 2010.
[17] Karunamurthy, B., Hadfi eld, M., Vieillard, C. & Morales G., Cavitation erosion in silicon nitride: experimental investigations on the mechanism of material degradation. Tribology International, 43, pp. 2251–2257, 2010. doi: http://dx.doi.org/10.1016/j.triboint.2010.06.012
[18] Asi, O., Failure of a diesel engine injector nozzle by cavitation damage. Engineering Failure Analysis, 13, pp. 1126–1133, 2006. doi: http://dx.doi.org/10.1016/j.engfailanal.2005.07.021