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Proceedings of eSim 2016: 9th Conference of IBPSA-Canada

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Dynamic performance of a forced convective direct storage system using water and PCMs for low temperature applications

HebatAllah Teamah, Marilyn Lightstone, James Cotton

Abstract: The paper presents the heat transfer characteristics of a shell and tube latent thermal energy storage system. A two dimensional computational fluid dynamics model based on enthalpy porosity was developed to investigate the charging and discharging of the system. Organic fatty acids were used as phase change materials in the tubes and water was used as heat transfer fluid in the shell. A variety of numerical investigations were carried out for both constant and variable inlet temperature profiles. The gains in energy storage for the studied system were compared to a sensible water-only system. The melting times were found to be reasonable (less than 12 hours) and a gain in stored energy from 132-376% can be obtained by increasing phase change volume fraction from 30% to 80% for a 7 ᵒC operating range of temperature. NOMENCLATURE Atₐnk Outer surface Area of the tank [m²] Cpl Liquid specific heat capacity [ J/kg K] Cps Solid specific heat capacity [ J/kg K] Dh Hydraulic diameter [m] E Energy stored [J] H Dimensionless specific enthalpy h Heat transfer coefficient [W/m²K] i Specific enthalpy [J/kg] K Thermal conductivity [W/mK] Lc Length of cylinder [m] M Number of axial nodes ṁ Mass flow rate inlet to the tank [kg/s] N Number of radial nodes Nc Number of cylinders in the tank Nuc Nusselt number based on cylinder outer radius T Temperature [ᵒC] Rc,inn Inner radius of phase change material cylinder [m] Rc,out Outer radius of phase change material cylinder [m] rs Latent heat [kJ/kg] Re Reynolds number Tst Initial (start) temperature of the tank [ᵒC] Uf,mₑₐn Mean fluid velocity [m/s] V Volume of control volume [m³] Vtₐnk Tank volume [m³] ΔFₒ Fourier number Δt Time step [seconds] ΔTm Transition melting range [ᵒC] Nup Nusselt number based on Dittis Botter correlation Abbreviations CFD Computational fluid dynamics HTF Heat transfer fluid LES Latent energy storage PCM Phase change material SDHW Solar domestic hot water SES Sensible energy storage TES Thermal energy storage Latin symbols 𝜀 Convergence criteria θ Dimensionless temperature μ Dynamic viscosity ρ Density ∑ Summation Superscripts it Current iteration level It-1 Previous iteration level Subscripts c,inn Inner surface of cylinder c,out Outer surface of cylinder conv Convective f Fluid f,m Mean for fluid In Inlet k Inner surface of control volume k-1 Outer surface of control volume l Liquid m Melting m₁ Lower melting m₂ Upper melting st Start t Transition ∞ Surrounding
Pages: 250 - 261
Paper:
esim2016_1-76