Numerical analysis of solidification of PCM in a closed vertical cylinder for thermal energy storage applications
- PDF / 2,832,039 Bytes
- 14 Pages / 595.276 x 790.866 pts Page_size
- 57 Downloads / 226 Views
ORIGINAL
Numerical analysis of solidification of PCM in a closed vertical cylinder for thermal energy storage applications Burak Izgi 1 & Mevlut Arslan 1 Received: 2 March 2020 / Accepted: 30 June 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The solidification dynamics of cylindrical encapsulated PCM have been analyzed under convective boundary conditions that relate to thermal energy storage systems. A three dimensional, transient CFD model has been solved for examinations. Besides the widely used conduction model of solidification, in this study, the effect of natural convection within the liquid layer has been considered in the numerical model. The effects of parameters such as the initial superheating temperature, the encapsulation size, and the heat transfer coefficient at the outer surface of the capsule have been examined in terms of solidification dynamics and extracted energy during the phase change process. It was found that while the diameter of encapsulation significantly affects the solidification and the energy extraction times, the effect of encapsulation height on the solidification and the energy extraction times are not notable. Keywords Phase change materials . Solidification . Thermal energy storage . CFD
Nomenclature A mushy zone constant Bi Biot number Cp specific heat of the PCM [J/(kg K)] D inner diameter of the tube [m] E energy [J] Gr Grashof number (Gr = gβ(T0-Ts)H3/ ν2) g gravity [m/s2] H height of the tube [m] h enthalpy [J/kg h∞ external heat transfer coefficient [W/m2K] k thermal conductivity [W/(m K)]] L latent heat of fusion [J/kg] m mass [kg] n shell thickness [m] P pressure [Pa] Q heat transfer rate [W] q˙ heat flux [W/m2] SteL liquid phase Stefan number (Ste = Cp(T0-Ts)/L) T temperature [K]
t time [min] Tb bulk temperature [oC] T∞ free stream temperature [oC] Tm melting temperature [oC] Ts solidification temperature [oC] T0 initial temperature [oC] V velocity [m/s] Greek symbols β thermal expansion coefficient [1/K] ρ density [kg/m3] μ dynamic viscosity [kg/(m s)] ν kinematic viscosity [m2/s] φ liquid fraction Subscripts and superscripts l latent r radial direction s sensible w wall θ angular direction z axial direction
* Burak Izgi [email protected]
1 Introduction
1
Department of Mechanical Engineering, Yozgat Bozok University, 66200 Yozgat, Turkey
The phase change materials (PCMs) for thermal energy storage (TES) applications have significant research attention due to the
Heat Mass Transfer
necessity of improving the reliability of thermal energy from renewable sources for sustainable green energy systems [1, 2]. Due to the favorable proportion of the volume to the surface area, cylindrical and spherical encapsulated PCMs are preferred systems for TES applications [3, 4]. Plenty of studies have been conducted for a better understanding of the phase change process inside encapsulated PCMs to obtain an accurate thermal design of TES [5–9]. However, the majority of the studies have focused on only the melting process [10–14]. Whereas
