• Energy Research

In this paper a high temperature thermal storage in a honeycomb solid matrix is numerically investigated and a parametric analysis is accomplished. In the formulation of the model it is assumed that the system geometry is cylindrical, the fluid and the solid thermophysical properties are temperature independent and radiative heat transfer is take into account whereas the effect of gravity are neglected. Air is employed as the working fluid and the solid material is cordierite. The evaluation of the fluid and thermal behaviors are accomplished assuming the honeycomb as a porous medium. The Brinkman-Forchheimer-extended Darcy model is used in the governing equations and the local thermal non equilibrium is assumed. The commercial CFD Fluent code is used to solve the governing equations in transient regime. Numerical simulations are carried out with storage medium at different mass flow rates of the working fluid and different porosity values. Results show the effects of storage medium, different porosity values, porosity effect and mass flow rate on stored thermal energy and storage time. Results in terms of temperature profiles and stored thermal energy as function of time are presented.

In recent years, the depletion of fossil fuel reserves, coupled with the European Union targets to increase the integration of renewable energy into the energy mix hasprompted both industries and the scientific community to shift their focus towards alternative systems driven by sustainable energy sources. The imperative forrenewable energies arises from the necessity to decrease dependency on fossil fuels, particularly to mitigate carbon dioxide emissions. The existing literatureextensively documents how integrating renewable energy into industrial processes can help reduce environmental impact. The novelty of this study lies in the lifecycle assessment (LCA) of ceramic sanitaryware production in Italy, specifically evaluating the use of thermal energy from a solar thermal system in the drying andfiring processes, thereby reducing fossil fuel consumption. To this end, an LCA was conducted to assess the environmental impacts of replacing natural gas in thedrying process with thermal energy from the SunDial solar thermal technology. The LCA methodology was applied to quantify the energy and environmental burdensof the system throughout its entire life cycle, including manufacturing, operation, and end-of-life stages. The functional unit is 1000 kg of sanitaryware production.Data was collected from the Ecoinvent database, and the assessment was performed using SimaPro software. The results indicate a 4 % reduction in global warmingpotential (GWP) due to the implementation of SunDial, which covers 20 % of the process’s energy demand. On a national scale, considering the entire Italiansanitaryware production, this translates into a savings of 180 tons of CO2 emissions.

This report provides information on energy demand profiles and commercial aspects relevant to the end-users involved in the ASTEP project.

Abstract A numerical study is accomplished to evaluate thermal and fluid-dynamic behaviours of a compact heat exchanger in aluminum foam. LTNE condition are assumed. The purpose of the investigation is to find the heat exchanger dimensions to evaluate a compromise between the heat transfer improvement and the increase in pressure drop. The results are showed in terms of heat and mechanical power ratio. It is found an optimal foam thickness in terms of tube diameter equal to 5. At the end, the Energy Performance Ratio (EPR) is evaluated to determine the efficiency of the metal foam and the best value is obtained for Re=800.

The effects of metal foams on Latent Heat Thermal Energy Storage System, LHTESS, based on a phase change material, PCM, is numerically investigated. The geometry of the system is a vertical shell and tube LHTESS made of two concentric tubes. A constant temperature above the melting temperature of the PCM on the internal surface of the hollow cylinder is assumed to simulate the heat transfer from a hot fluid. The external surfaces are adiabatic. The PCM is completely embedded in the volume between the two coaxial cylinders. An aluminum metal foam is chosen, and it partially fills the volume starting from the internal cylinder. The enthalpy-porosity theory and the Darcy-Brinkman-extended model are employed to simulate, respectively, the phase change of the PCM and the metal foam which is modelled in local thermal equilibrium. Ansys-Fluent code is adopted to solve the governing equations. The results are rendered in terms of melting time, liquid fraction, temperature, and stored thermal energy as a function of time and for different metal foam thickness values. The results indicate that the melting time reduces with increase in the thickness of the metal foam. The partially filled thermal storage system exhibits varying characteristics at the initiation and at the sustenance periods of the heating process. A scale analysis is performed to estimate the melting time and the values are in tandem with the numerical model evaluation. (C) 2022 Elsevier Ltd. All rights reserved.

Abstract A parametric analysis of natural convection in air, in a channel–chimney system, symmetrically heated at uniform heat flux, obtained by means of a numerical simulation, is carried out. The analyzed regime is two-dimensional, laminar and steady-state. Results are presented in terms of wall temperature profiles in order to show the more thermally convenient configurations which correspond to the channel–chimney system with the lowest maximum wall temperature. For the considered Rayleigh number, the difference between the highest and the lowest maximum wall temperatures increases with increasing the channel aspect ratio. The optimal expansion ratio values depend strongly on the Rayleigh number and extension ratio values and slightly on the channel aspect ratio. Correlations for dimensionless mass flow rate, maximum wall temperature and average Nusselt number, in terms of Rayleigh number and dimensionless geometric parameters are presented in the ranges: 5 ⩽ Ra ∗ ⩽ 2.0 × 10 4 , 1.5 ⩽ L / L h ⩽ 4.0 and 1.0 ⩽ B / b ⩽ 4.0 .

Abstract In this study, an analytical solution of a porous fin with natural convection and radiation heat transfer is carried out. For the first time, the analysis is accomplished in Local Thermal Non-Equilibrium (LTNE) model. The investigation is carried out on a porous fin with finite length and adiabatic tip. The Darcy model and Boussinesq approximation for buoyancy effects are used to evaluate the infiltration velocity in the porous medium. Two energy equations are solved using the Adomian Decomposition Method (ADM). The solution is validated with the numerical solution of the finite difference method, and with the asymptotic solution for the Local Thermal Equilibrium (LTE) model. The results are presented in terms of temperature profiles and total average Nusselt numbers. They pointed out the effects of internal and external radiation and convection heat transfer, as well as thermal conductivity ratio and dimensionless thickness. It was found that solid phase temperature profiles decrease as the Biot, Bi, and Rayleigh, Ra*, numbers decrease, whereas the difference between the solid phase and fluid phase temperatures, for assigned Bi, decreases for lower Ra. Thermal conductivity ratio and dimensionless thickness increase engender higher solid phase temperature for assigned Bi and Ra*. The total Nusselt number increases as Ra*, Bi and external radiation increase, whereas it decreases with the thermal conductivity ratio. Criteria to compare LTNE and LTE assumptions are proposed, and they highlight the fact that the minimum Biot number to accept the LTE assumption becomes lower as the Rayleigh number decreases.

Abstract In the present paper a two-dimensional convective heat transfer problem in a partially filled channel with metal foam is numerically solved in steady state regime. An external thermoelectric generators (TEG) component is placed on the top surface of the channel. The numerical analyses are accomplished assuming the local thermal equilibrium (LTE) model to simulate the presence of the aluminum foam. The working fluid is exhaust gas with properties equal to the air for fixed temperature of the upper surface of the thermo-electric generator (TEG). The thermophysical properties are assumed temperature independent and the TEG component is considered as a solid with an internal energy generation. The Ansys-Fluent code is applied in order to resolve the governing equations for gas, porous media and TEG. Several mass flow rates of exhaust gas on the inlet section of the channel are considered. Different thicknesses of aluminum foam are assumed into the duct. The foam is characterized by different porosity equal to 0.90, 0.95, 0.97. Moreover, the number of pores per inch also changes and assumes the following values of 5, 20, 40. Results are showed in terms of temperature distributions, pressure drop, thermoelectric efficiency for different exhaust gas flow rates and metal foam characteristics and thicknesses. The results highlight that the use of metal foams significantly increases the heat transfer between the surface of exhaust gas tube and hot gas. Consequently, the effectiveness improves, and it increases between three-ten times with respect to the one for tube without metal foams. It is shown that the pore density does not affect the effectiveness.