Ahmad Ali Rabienataj Darzi, Mousa Farhadi, Mahmoud Jourabian and Yousef Vazifeshenas
The aim of this study is to apply an enthalpy-based lattice Boltzmann method with multi distribution function model, to investigate melting process with natural convection inside…
Abstract
Purpose
The aim of this study is to apply an enthalpy-based lattice Boltzmann method with multi distribution function model, to investigate melting process with natural convection inside a cavity with an obstacle. The cavity is filled with water (ice)-based nanofluid containing copper nanoparticles.
Design/methodology/approach
This methodology eliminates the requirement of satisfying conditions at the phase change front. The combination of lattice D2Q9 and D2Q5 models is implemented to determine the density, velocity and temperature fields. The simulations are carried out for Rayleigh number of 105, various volume fractions of the nanoparticles and various positions of the cubic obstacle.
Findings
The predicated results demonstrate that the use of nanoparticles leads to enhancement of thermal conductivity of nano-enhanced phase change materials in comparison with conventional PCMs. When the position of the obstacle changes from the top to the bottom of the cavity the melting rate increases 75 percent. The numerical study indicates that by increasing the solid concentration from 0 to 0.04, the heat release enhances 52.7, 41.2 and 30 percent when the obstacle is located on the top, middle and bottom sections of the cavity, respectively. It is also observed that, the employment of nanoparticles is more effective when the heat conduction dominates.
Originality/value
The main unacceptable property of most PCMs is their low thermal conductivity, and hence, heat transfer enhancement using nanofluid will be useful for thermal energy storage applications.
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Sana Ben Salah and Mohamed Bechir Ben Hamida
The purpose of this paper is to optimize the configuration of a heat sink with phase change material for improving the cooling performance of light emitting diodes (LED).
Abstract
Purpose
The purpose of this paper is to optimize the configuration of a heat sink with phase change material for improving the cooling performance of light emitting diodes (LED).
Design/methodology/approach
A numerical three-dimensional time-dependent model is developed with COMSOL Multiphysics to simulate the phase change material melting process during both the charging and discharging period.
Findings
The model is validated with previously published works. It found a good agreement. The difference between filled cavities with phase change materials (PCM) and alternate cavities air-PCM is discussed. The last-mentioned showed a good ability for reducing the junction temperature during the melting time. Three cases of this configuration having the same total volume of PCM but a different number of cavities are compared. The case of ten fins with five PCM cavities is preferred because it permit a reduction of 21 per cent of the junction temperature with an enhancement ratio of 2:4. The performance of this case under different power input is verified.
Originality/value
The use of alternate air-PCM cavities of the heat sink. The use of PCM in LED to delay the peak temperature in the case of thermal shock (for example, damage of fan) An amount of energy is stored in the LED and it is evacuated to the ambient of the accommodation by the cycle of charging and discharging established (1,765 Joule stored and released each 13 min with 1 LED chip of 5 W).