A numerical analysis aiming to investigate the influence of numerous parameters on the energy storage systems has been conducted. The system performance working with phase change materials (PCMs) is evaluated in terms of complete melting time and metal foam radial distance in annulus. A comprehensive transient analysis is presented to monitor the melting behavior of the integrated PCM in the presence of porous metal foam sleeves under constant volume at various locations as thermal conductivity enhancers (TCEs). Aluminum alloy T-6201 is used for the porous metallic foam, while paraffin is introduced as PCM. The porosity, pore size (PPI), various PCM materials, and porous distance from the heat sources were investigated. Results show that porous TCEs radial distance from the applied heat sources has a substantial effect and can lead to an improved rate of melting depending on the sleeve location. In addition, high thermal conductivity near the heat source suppresses the porous resistance to liquid PCM flow and thus natural convection. Results revealed that case B provides a uniform liquid PCM profile and heat distribution while case D has the highest melting during the initial stage and lower one at the final stages of melting. Pure PCM case imposed the least resistance but has the slowest melting time while a turning point in melting rate is noticed from case C. Eventually, results show that higher PPI materials have a similar melting pattern as a result of high thermal conductivity.

Thermal transport of nanofluid natural convection in a wavy porous enclosure exposed to an external and uniform magnetic source is investigated numerically. Numerous pertinent factors in terms of Darcy (Da = 10−4–10−2), Hartmann (Ha = 0–40), Rayleigh (Ra = 104–107), Prandtl (Pr = 0.71–7) and undulation (n = 3) numbers, in addition to wave amplitudes (A = 0.025–0.1) and particle volume concentration ( $$\phi$$  = 0, 2 and 4%) have been investigated. The Brinkmann–Forchheimer extended Darcy model is utilized, and the governing equations are solved by employing our own finite difference ADI-based program. Code accuracy was successfully validated with the open literature. The results revealed that for Ra > 105 and Da < 10−3, the magnetic field does not play a substantial role in the convective thermal energy, while at high Ha and low Ra, the intensity of conduction increases. The surface waviness and Darcy number both have significant effects on the heat transfer suppression if insulation is desired. Furthermore, a critical value of Ra = 105 is observed whereby the mean Nusselt number decreases despite particle volume concentration, particularly at high Hartmann values.

Author(s): Albojamal, Ahmed | Advisor(s): Vafai, Kambiz | Abstract: Two different models were analyzed: single phase (homogenous and dispersion) and two-phase (Lagrangian-Eulerian model or discrete phase model and the mixture) with both constant and temperature dependent properties to further investigate and clarify the differences and evaluate the assumption of the single-phase model. The obtained results were subjected to an intensive comparison with the available experimental data and numerical works in the literature. The influence of some important parameters such as, source and sink terms, injected particle mass flow rate, particle diameter, particle type, slip velocity, particle forces, Reynolds and Peclet numbers, wave amplitude, constant or temperature dependent properties and particle concentration on the heat transfer and flow characteristics of nanofluids were determined and discussed in detail. It was observed that the two phase Lagrangian-Eulerian model (DPM) overestimated the heat transfer coefficient values and the results from the mixture model displayed an unrealistic increase in heat transfer particularly for high particle volume fraction. The proposed single-phase approach revealed a very good agreement with the experimental data and the maximum difference in the average heat transfer coefficient between the single-phase and DPM was found to be 5.9%. Particle deposition through porous media was analyzed utilizing the discrete particle model (DPM). The Brinkman-Forchheimer extended Darcy model was used for the flow inside a saturated porous matrix. The effect of porous permeability (Da=10-8-10-4), Reynolds number (Re=500-2000), volume concentration (0%, 0.3% and 3%) and different particle forces on the deposition rate have been documented. The particle adhesion/detachment was solved with respect to the force balance considering drag, Saffman lift, Brownian, thermophoresis, gravity and Van Der Waals. Our results reveal that the mass deposition rate can be omitted when there is no porous media inside the channel. It is found that, the porous permeability has a substantial role on nanoparticle mobility and a critical Reynolds number (500≤Re≤1000) exists where the entrapment rate is maximized. The impact of different pertinent forces on the deposition was also considered, and our results establish that Brownian motion had the most dominant effect on the deposition rate in the presence of a porous medium.

A single or an array of metallic porous structures of various geometries are introduced on the inside surface of a partially heated wall of a channel with air or water flow. Forced convective heat transfer rate from the heated wall to the fluid, as well as the average pressure drop along the channel are numerically studied. Effects of the aluminum porous block's structural parameters such as porosity (ϵ), Darcy number (Da) and Forchheimer coefficient (F) are taken into account. The optimum geometrical conditions of the system is extensively explored considering parameters such as blocks' height, width and spacing between them. Our results demonstrate great potential for metal foams to perform as heat sinks and pave the way for their further implementation in applications such as solar thermal collectors and electronic cooling.

Laminar forced convection of heat transfer and pressure drop of Al2O3 and CuO/water nanofluids flow through a horizontal tube and wavy channel under constant wall temperature boundary condition is numerically investigated. Two different models were employed in our study: single phase (homogenous and dispersion) and two phase (Lagrangian-Eulerian model or discrete-phase model (DPM) and the mixture). The effects of various parameters, such as particle concentration, particle diameter, particle type, constant or temperature-dependent properties, wave amplitude, Reynolds number and Peclet number on the thermal, and flow field of the Nanofluids are analyzed. Our results revealed that variable properties assumption play a dominant role in horizontal tubes and provide better predictions for the heat transfer enhancement. The difference between constant and variable properties becomes insignificant and can be ignored in wavy channel due to the high mixing and generated recirculation zones, whereas the difference between the DPM and the single-phase variable properties diminish as Peclet number and volume fraction increases. However, dispersion model shows an excellent agreement with the experimental data; the absence of the reference values for the adjustable factor C-d in the open literature put it in a questionable position. Therefore, DPM and homogenous single-phase model with well-chosen thermal conductivity and viscosity correlations can be considered as an accurate way and more dependable in nanofluid simulations especially the homogenous single-phase model because it requires less time, CPU, and memory usage. As expected, it is found that the heat transfer increases as the Reynolds number and particle volume fraction increases, but it is accompanied by a higher pressure drop. The obtained results have been successfully validated and compared with the experimental and numerical data available in the literature.

A numerical investigation of developing forced convective heat transfer and pressure drop of nanofluid flow inside a tube subject to a constant wall heat flux boundary condition is presented. The single-phase homogenous and two different two-phase models: Lagrangian-Eulerian model or (discrete phase model) and mixture model are utilized with both constant and temperature dependent properties to further investigate and clarify the differences and evaluate the assumption of the single-phase model. The obtained results were subjected to an intensive comparison with the available experimental data and numerical works in the literature. The influence of some important parameters such as, source and sink terms, injected particle mass flow rate, slip velocity, particle forces, Reynolds number, constant or temperature dependent properties and particle concentration on the heat transfer and flow characteristics of nanofluids were determined and discussed in detail. It was observed that the two phase Lagrangian-Eulerian model (DPM) overestimated the heat transfer coefficient values and the results from the mixture model displayed an unrealistic increase in heat transfer particularly for high particle volume fraction. The proposed single phase approach revealed a very good agreement with the experimental data and the maximum difference in the average heat transfer coefficient between the single-phase and DPM was found to be 5.9% considering variable properties. The results also revealed that increasing the injected particle mass flow rate does not have a significant effect on the heat transfer coefficient values and that the particles move with the same velocity of the fluid. Furthermore, the heat transfer coefficient increases as the particle volume fraction and Reynolds number increases, but it is accompanied by a higher pressure drop and wall shear stress values. DPM model provides a reasonable prediction for the thermal behavior of the nanofluids transport, the single-phase approach with temperature dependent viscosity and thermal conductivity is an accurate way to analyze the transport of nanofluids while requiring less CPU usage and memory for predicting the enhancement in nanofluids convective heat transfer. (C) 2017 Elsevier Ltd. All rights reserved.

A numerical investigation of nanoparticle deposition for flow through a partially filled channel subject to a constant heat flux boundary condition is presented. The discrete particle model (DPM) is utilized for the simulations. The Brinkman-Forchheimer extended Darcy model is used for the flow inside a saturated porous matrix. The effect of porous permeability (Da = 10(-8)-10(-4)), Reynolds number (Re = 5002000), volume concentration (0%, 0.3% and 3%) and different particle forces on the deposition rate have been documented. The particle adhesion/detachment is solved with respect to the force balance considering drag, Saffman lift, Brownian, thermophoresis, gravity and Van Der Waals. Our results reveal that the mass deposition rate can be omitted when there is no porous media inside the channel. In addition, no heat transfer enhancement is noticed for low particle loading <1% of nanofluid compared to water for Da <= 10(-5). It is found that, the porous permeability has a substantial role on nanoparticle mobility and a critical Reynolds number (500 <= Re <= 1000) exists where the entrapment rate is maximized. On the other hand, the particle velocities and mass deposition rates are high for volume concentration of 3% while accompanied by an increased rate of heat transfer and pressure drop, particularly for Da >= 10(-5) when compared to 0.3% volume fraction. It was observed that increasing porous permeability to Da >= 10(-4) decreases the deposition rate. The impact of different pertinent forces on the deposition was also considered, and our results establish that Brownian motion had the most dominant effect on the deposition rate in the presence of a porous medium. (C) 2020 Elsevier Ltd. All rights reserved.

Forced convective heat transfer in a solar water collector channel with three metal-foam blocks attached on the inside wall, is studied numerically. Darcy equation with the Brinkman and Forchheimer terms is used to analyze the flow in the porous section; and Local thermal equilibrium (LTE) is considered between the working fluid and the porous region. The fluid flow in the channel and the thermal behavior of the system are analyzed considering various parameters such as Darcy number, thermal conductivity ratio, porosity and Reynolds number. The results prevail that the generated recirculation zones between blocks will significantly improve the heat transfer rate from the heated surface; and metallic porous material can perform as effective heat exchangers in thermal applications such as electronic cooling and solar heat collectors