Commenced in January 2007
Frequency: Monthly
Edition: International
Paper Count: 30172
Turbulent Mixing and its Effects on Thermal Fatigue in Nuclear Reactors

Authors: Eggertson, E.C. Kapulla, R, Fokken, J, Prasser, H.M.

Abstract:

The turbulent mixing of coolant streams of different temperature and density can cause severe temperature fluctuations in piping systems in nuclear reactors. In certain periodic contraction cycles these conditions lead to thermal fatigue. The resulting aging effect prompts investigation in how the mixing of flows over a sharp temperature/density interface evolves. To study the fundamental turbulent mixing phenomena in the presence of density gradients, isokinetic (shear-free) mixing experiments are performed in a square channel with Reynolds numbers ranging from 2-500 to 60-000. Sucrose is used to create the density difference. A Wire Mesh Sensor (WMS) is used to determine the concentration map of the flow in the cross section. The mean interface width as a function of velocity, density difference and distance from the mixing point are analyzed based on traditional methods chosen for the purposes of atmospheric/oceanic stratification analyses. A definition of the mixing layer thickness more appropriate to thermal fatigue and based on mixedness is devised. This definition shows that the thermal fatigue risk assessed using simple mixing layer growth can be misleading and why an approach that separates the effects of large scale (turbulent) and small scale (molecular) mixing is necessary.

Keywords: Concentration measurements, Mixedness, Stablystratified turbulent isokinetic mixing layer, Wire mesh sensor

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1060155

Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 1816

References:


[1] S. Chapuliot, C. Gourdin, T. Payen, J.P. Magnaud, and A. Monavaon, "Hydro-thermal-mechanical analysis of thermal fatigue in a mixing tee," in Nuclear Engineering and Design, vol. 235, 2005, pp. 575-596.
[2] K.J. Metzner and U. Wilke, "European THERFAT project - Thermal fatigue evaluation of piping system tee-connections," in Nuclear Engineering and Design, vol. 235, 2004, pp. 473-484.
[3] H.D. Kweon, J.S. Kim, and K.Y. Lee, "Fatigue Design of nuclear class 1 piping considering thermal stratification," in Nuclear Engineering and Design, vol. 238, 2008, pp. 1265-1274.
[4] R. Kapulla, C. Dyck, M. Witte, J. Fokken, A. Leder, "Optical flow and cross correlation techniques for velocity field calculation," in 2009 Conf. Proc. Lasermethoden in der strömungsmesstechnik, pp. 284-295.
[5] J. Fokken, R. Kapulla, S. Kuhn, C. Dyck, H.M. Prasser, "Stably stratified isokinetic turbulent mixing layers: Comparison of PIVmeasurements and numerical calculation," in 2009 Conf. Proc. Lasermethoden in der strömungsmesstechnik, pp. 296-303.
[6] C. Walker, M. Simiano, R. Zboray, and H.M. Prasser, "Investigations on mixing phenomena in single phase flow in a T-junction geometry," in Nuclear Engineering and Design, vol. 239, 2009, pp. 116-126.
[7] H. Rouse and J. Dodu, "Turbulent diffusion across a density discontinuity," in Houille Blanche, vol. 10, 1955, pp. 522-532.
[8] J.S. Turner, "The influence of molecular diffusivity on turbulent entrainment across a density interface," in Journal of Fluid Mechanics, vol. 33, 1968, pp. 639-656.
[9] J.S. Turner, "Buoyancy effects in fluids," Cambridge: University Press, 2nd ed., 1980, 368 pp.
[10] H.J.S. Fernando, "Turbulent mixing in stratified fluids," in Annual Review of Fluid Mechanics, vol. 23, 1991, pp. 455-493.
[11] P. Huq and R. Britter, "Mixing due to grid-generated turbulence of a two-layer scalar profile," in Journal of Fluid Mechanics, vol. 285, 1995, pp. 17-40.
[12] P. Huq and R. Britter, "Turbulence evolution and mixing in a two-layer stably stratified fluid," in Journal of Fluid Mechanics, vol. 285, 1995, pp. 41-67.
[13] E.C. Itsweire, K.N. Helland, and C.W. Van Atta, "Evolution of gridgenerated turbulence in a stably stratified fluid," in Journal of Fluid Mechanics, vol. 162, 1986, pp. 299-338.
[14] T.K. Barrett and C.W. Van Atta, "Experiments on the inhibition of mixing in stably stratified decaying turbulence using LDA and LIF," in Physics of Fluids, vol. 3, 1991, pp. 1321-1332.
[15] Jayesh and Z. Warhaft, "Probability distribution, conditional dissipation, and transport of passive temperature fluctuations in grid generated turbulence," in Physics of Fluids, vol. 4, 1992, pp. 292-307.
[16] Z. Bubnik, P. Kadlec, D. Urban, M. Bruhns, "Sugar Technologists Manual," Bartens pub co. Berlin, 1995, pp. 125-170.
[17] H.M. Prasser, A. Böttger, and J. Zschau, "A new electrode-mesh tomograph for gas-liquid flows," in Flow Measurement and Instrumentation, vol. 9, 1998, pp. 111-119.
[18] J. Fokken, et al, "LIF-measurements and self similarity considerations in a stably stratified isokinetic turbulent mixing layer," in 2010 Conf. Proc. Lasermethoden in der strömungsmesstechnik, pp. 12-19.
[19] J. Fokken, R. Kapulla, G. Galgani, O. Schib, H.M. Prasser, "Stably stratified isokinetic turbulent mixing layers: Investigation in a square flow channel," in 2010 Conf. Proc. International Youth Nuclear Congress, pp. 120.1-120.9.
[20] H. Tenekes, J.L. Lumley, "A first course in turbulence," MIT Press, 1972, 300 pp.
[21] C.G. Koop and F.K. Browand, "Instability and turbulence in a stratified fluid with shear," in Journal of Fluid Mechanics, vol. 93, 1979, pp. 135-159.
[22] Xuequan E. and E.J. Hopfinger, "On mixing across an interface in stably stratified fluid," in Journal of Fluid Mechanics, vol. 166, 1986, pp. 227-244.