OPEN ACCESS
The design and optimisation of a latent heat thermal storage system require knowledge of flow, heat and mass transfer during the melting (charging) and solidification (discharging) processes of high-temperature phase change materials (PCMs). Using fluent, numerical modeling was performed to study the impact of natural convection and turbulence in the melting process of a high- temperature PCM in a latent heat storage system with Ra = 1012. Numerical calculation was conducted, considering a two dimensional symmetric grid of a dual-tube element in a parallel flow shell and tube configuration where the heat transfer fluid passes through the tube and PCM fills the shell. Three melting processes of PCM were considered; pure conduction, conduction and natural convection, and finally the latter with turbulence. The first study showed a one dimensional melt front, evolving parallel to the tube, which results in lower peak temperatures and temperature gradients, higher heat transfer area for a longer period of time, however lower heat transfer rate due to natural convection being ignored. The second study presented a two dimensional melt front which evolves mainly perpendicular to the tube, shrinking downward, resulting in the loss of heat transfer area and higher peak temperatures and temperature gradient, however, the higher rate of heat transfer rate due to the creation of convection cells which facilitate mass and heat transfer. Including turbulence led to a higher mixing effect due to the higher velocity of convection cells, resulting in a more uniform process with lower peak temperature and temperature gradients and higher heat transfer rate. In a melting process with Ra>1011, including convection and turbulence impact provides more realistic data of flow, mass and heat transfer.
convection heat transfer, latent heat storage, melting, numerical modeling, PCM, shell and tube, turbulence
[1] Kuravi, S., Trahan, J., Goswami, D.Y., Rahman, M.M. & Stefanakos, E.K., Thermal energy storage technologies and systems for concentrating solar power plants. Progress in Energy and Combustion Science, 39(4), pp. 285–319, 2013. http://dx.doi.org/10.1016/j.pecs.2013.02.001
[2] Wang, S., Faghri, A. & Bergman, T.L., A comparison study of sensible and latent thermal energy storage systems for concentrating solar power applications. Numerical Heat Transfer, Part A: Applications, 61(11), pp. 860–871, 2012.
[3] Kenisarin, M.M., High-temperature phase change materials for thermal energy storage. Renewable and Sustainable Energy Reviews, 14(3), pp. 955–970, 2010. http://dx.doi.org/10.1016/j.rser.2009.11.011
[4] Bejan, A., Transition to turbulence. In Convection Heat Transfer, John Wiley & Sons, Inc. pp. 295–319, 2013. http://dx.doi.org/10.1002/9781118671627.ch6
[5] Verdier, D., Ferriere, A., Falcoz, Q., Siros, F. & Couturier, R., Experimentation of a high temperature thermal energy storage prototype using phase change materials for the thermal protection of a pressurized air solar receiver. Energy Procedia, 49, pp. 1044–1053, 2013. http://dx.doi.org/10.1016/j.egypro.2014.03.112
[6] Markatos, N.C. & Pericleous, K.A., Laminar and turbulent natural convection in an enclosed cavity. International Journal of Heat and Mass Transfer, 27(5), pp. 755–772, 1984. http://dx.doi.org/10.1016/0017-9310(84)90145-5
[7] Basal, B. & Ünal, A., Numerical evaluation of a triple concentric-tube latent heat thermal energy storage. Solar Energy, 92, pp. 196–205, 2013. http://dx.doi.org/10.1016/j.solener.2013.02.032
[8] Belusko, M., Tay, N.H.S., Liu, M. & Bruno, F., Effective tube-in-tank PCM thermal storage for CSP applications, Part 1: Impact of tube configuration on discharging effectiveness. Solar Energy, 2015. http://dx.doi.org/10.1016/j.solener.2015.09.042
[9] Lakeh, R.B., Lavine, A.S., Kavehpour, H.P. & Wirz, R.E., Study of turbulent natural convection in vertical storage tubes for supercritical thermal energy storage. Numerical Heat Transfer, Part A: Applications, 67(2), pp. 119–139, 2014. http://dx.doi.org/10.1080/10407782.2014.923224
[10] Lan, C.W. & Yang, D.T., Dynamic simulation of the vertical zone-melting crystal growth. International Journal of Heat and Mass Transfer, 41(24), pp. 4351–4373, 1998. http://dx.doi.org/10.1016/S0017-9310(98)00119-7
[11] ANSYS Fluent Users Guide, Release 15.0, ANSYS, 2015.
[12] Riahi, S., Saman, W.Y., Bruno, F. & Tay, N.H.S., Numerical modeling of inward and outward melting of high temperature PCM in a vertical cylinder. SOLARPACES 2015: International Conference on Concentrating Solar Power and Chemical Energy Systems, AIP Publishing, 1734, 2016. http://dx.doi.org/10.1063/1.4949137
[13] Modest, M.F., Radiation combined with conduction and convection. In Radiative Heat Transfer, 3rd edn., Academic Press: Boston, pp. 724–778, 2013. http://dx.doi.org/10.1016/B978-0-12-386944-9.50022-4
[14] Voller, V.R., Brent, A. & Prakash, C., The modelling of heat, mass and solute transport in solidification systems. International Journal of Heat and Mass Transfer, 32(9), pp. 1719–1731, 1989. http://dx.doi.org/10.1016/0017-9310(89)90054-9
[15] Jones, B.J., Sun, D., Krishnan, S. & Garimella, S.V., Experimental and numerical study of melting in a cylinder. International Journal of Heat and Mass Transfer, 49(15), pp. 2724–2738, 2006. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2006.01.006