Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Citation - WoS: 120Citation - Scopus: 136Numerical Study on Latent Thermal Energy Storage Systems With Aluminum Foam in Local Thermal Equilibrium(Elsevier, 2019) Buonomo, Bernardo; Çelik, Hasan; Ercole, Davide; Manca, Oronzio; Mobedi, MoghtadaThe paper analyzes the behavior of a Latent Heat Thermal Energy Storage system (LHTES) with a Phase Change Material (PCM), with and without aluminum foam. A numerical investigation in a two-dimensional domain is accomplished to investigate on the system thermal evolution. The enthalpy-porosity method is used to describe the PCM melting. The open-celled aluminum foam is described as a porous medium by means of the Darcy-Forchheimer law. A hollow cylinder represents the considered thermal energy storage and it consists of the enclosure between two concentric shell tubes. The external surface of the internal tube is at assigned temperature with a value greater than the melting PCM temperature, while the other surfaces are adiabatic. Local thermal equilibrium (LTE) is numerically adopted for modelling the heat transfer between the PCM and the solid matrix in aluminum foam. In the case with metal foam, simulations for different porosities are performed. A comparison in term of liquid fraction, average temperature of the system, temperature fields, stream function and a performance parameter are made between the clean case and porous assisted case for the different porosities. A scale analysis is developed for evaluating the time and the melting zone in different regimes (i.e. conduction, mixed conduction-convective and convective) during the melting processes of the PCM in porous media. Numerical simulation shows that aluminum foam increases overall heat transfer by a magnitude of two, with respect to the clean case.Article Citation - WoS: 12Citation - Scopus: 13A General Expression for the Stagnant Thermal Conductivity of Stochastic and Periodic Structures(The American Society of Mechanical Engineers(ASME), 2018) Bai, X.; Çelik, Hasan; Mobedi, Moghtada; Nakayama, AkiraA general expression has been obtained to estimate thermal conductivities of both stochastic and periodic structures with high-solid thermal conductivity. An air layer partially occupied by slanted circular rods of high-thermal conductivity was considered to derive the general expression. The thermal conductivity based on this general expression was compared against that obtained from detailed three-dimensional numerical calculations. A good agreement between two sets of results substantiates the validity of the general expression for evaluating the stagnant thermal conductivity of the periodic structures. Subsequently, this expression was averaged over a hemispherical solid angle to estimate the stagnant thermal conductivity for stochastic structures such as a metal foam. The resulting expression was found identical to the one obtained by Hsu et al., Krishnan et al., and Yang and Nakayama. Thus, the general expression can be used for both stochastic and periodic structures.