Seminars 2019-2020
Numerical study of a multiple-segment metal foam-PCM latent heat storage unit: Effect of porosity, pore density and location of heat source
Hayder I. Mohammed, ../../2019
Abstract:
This study numerically investigates the performance of the melting process for a PCM based heat storage system under the effect of different variables in a vertical container with a copper metal foam. Different cases were studied and compared including the effects of variable porosities and pore densities, nonequilibrium porous medium model, a multiple-segment metal foam case and different heater locations in the system on the liquid fraction and temperature as presented by contour plots and diagrams. The results show high performance for the copper foam-PCM unit compared with on its own PCM, for reducing the melting time by almost 85%. By changing the location of constant temperature heater from the bottom to the side and top surface, the melting time decreases by 70.5% and 4.7%, respectively. By using a multiple-segment porous system, the melting time reduces by 3.5% compared with the case of uniform porosity. Furthermore, the more accurate non-equilibrium numerical model shows a 7.4% difference in the melting time compared with the equilibrium model. This study optimises the design to improve practical application performance and to reduce waste energy.
Multiphase flow and boiling heat transfer modelling of nanofluids in horizontal tubes embedded in a metal foam
Hayder I. Mohammed, ../../2019
Abstract:
The aim of this numerical study is to evaluate the boiling process of nanofluid in horizontal tubes in the presence of a metal foam as porous medium and represent the experimental work of Zhao et al. in a numerical aspect with a different range of dependent variables. High conductive metal foams are employed to increase the rate of heat transfer and enhance the boiling performance in the domain. Two-phase mixture model is used to simulate the characteristics of nanofluid and solve the governing equations in a two-phase flow and boiling heat transfer problem. R134a and ZnO are considered as the base-fluid and nanoparticles, respectively. The characteristics of metal foam including the porosity and pore density as well as operating conditions including the fluid flow including the velocity, induced heat flux and concentration of nanoparticles on the pressure drop, vapour volume fraction and heat transfer coefficient are examined. The results show the positive effect of the metal foam on vapour production and overall heat transfer coefficient of the nanofluid in the pipe outlet; however, due to the flow resistance as a result of porous medium addition, a higher pressure drop is achieved. For the heat flux of 19 kW/m2 and inlet velocity of 0.05 m/s, by using a metal foam with the porosity of 70% and pore density of 20PPI, the vapour volume fraction, heat transfer coefficient and pressure drop enhances by 7.1%, 9.4% and 82.7%, respectively, compared with the case of without metal foam. However, by using the porosity of 90%, the vapour volume fraction, heat transfer coefficient and pressure drop enhances by 1.6%, 3.5%, and 7.0%, respectively. Consequently, according to the developed results in this paper, a system with a moderate to low porosity with a high to moderate pore density is recommended which is finally determined based on the required vapour production and allowed pressure drop.