No abstract

A conjugate analysis via the finite volume approach is performed to study the effects of a thick plate on the excess (peak) temperature of an iso-heat flux heat source cooled by laminar forced convection flow. A thick plate of temperature-dependent thermal conductivity is placed between the heat sources and the cooling fluid. A cooling fluid flows over the thick plate and removes the heat by laminar forced convection. On account of the two-dimensional heat redistribution in the finite thick plate with one face subjected to iso-heat flux and the other face exposed to forced flow, the interface ceases to be an iso-heat flux and, consequently, reduces the excess temperature of the heat sources. In the numerical analysis, the thickness of the plate is relaxed one by one to search for the optimal thickness that minimizes the excess temperature. It is shown that the reduction in the excess temperature due to the insertion of the thick plate with optimal thickness depends upon the Reynolds number of the fluid flow and the fluid-to-solid thermal conductivity ratio.

Summary Depleting fossil fuels and the pollution resulting from their consumption indicate an urgent need for clean and dependable alternatives such as renewable energies. Biomass is a free and abundant source of renewable energy. Municipal solid waste (MSW) as one of the main categories of biomass has always been an issue for metropolitan cities. It has, however, a high potential for biogas production. In this study, the technical and economic aspects of generating electrical power through solid oxide fuel cells (SOFCs) powered by injecting biogas derived from Tehran's MSW, as a case study, are investigated. The main objectives of the current study are to identify the power generation capability of the process and find out if it can result in a competitive energy resource. The total amount of obtainable methane through anaerobic digestion of MSW and then the achievable power generation capacity by using the obtained biogas are computed using the electrochemical relations inside the SOFC. The economic calculations are carried out to estimate the final price of the generated electricity, taking into account the major capital and ongoing costs of the required equipment. The effect of variations of MSW composition on the power generation capability and final electricity price is also studied. Moreover, the application of a gas turbine (GT) with the SOFC as a hybrid SOFC–GT system to recover the produced heat by SOFC and its effect on the power generation capability and the final electricity price are investigated. Results indicate that around 997.3 tons day−1 biomethane can be generated using Tehran's MSW. By using the SOFC, the produced biogas can generate 300 MWAC electrical power with a final cost of $0.178 kWh−1. By using the hybrid SOFC–GT, the electrical power capacity is increased to 525 MWAC, and the final electricity cost drops to $0.11 kWh−1, which indicates its competitiveness with other common energy resources in the near future, especially by considering different governmental subsidy policies that support renewable energy resources. The considerable environmental benefits of the proposed procedure, from both MSW management and CO2 emission reduction points of view, make it a promising sustainable energy resource for the future. Copyright © 2016 John Wiley & Sons, Ltd.

Fundamental understanding of water confined in graphene is crucial to optimally design and operate sustainable energy, water desalination, and bio-medical systems. However, the current understanding predominantly remains in the static properties near the graphene surfaces. In this paper, a key water transport property, i.e., self-diffusivity, is examined under confinement by various graphene nanogap sizes (L z ¼ 0.7-4.17 nm), using molecular dynamics simulations with various graphene-water interatomic potentials (Simple Point Charge (SPC/E) and TIP3P water models). It is found that the water self-diffusivity nearly linearly decreases as the graphene-water interatomic potential energy increases at a given nanogap size. It also decreases as the graphene nanogap size decreases down to L z ¼ 1.34 nm; however, it shows the peak water self-diffusivity at L z ¼ 0.8 nm and then continues to decrease. The peak water self-diffusivity is related to the significant change of the overlapping surface force, and associated, nonlinear local water density distribution. The in-plane water selfdiffusivity is higher up to nearly an order of magnitude than that of the out-of-plane due to the geometrical confinement effect by the graphene nanogap. The obtained results provide a roadmap to fundamentally understand the water transport properties in the graphene geometries and surface interactions.

Optimization of a highly conductive insert embedded into a heated rectangular chip has been lately investigated. The role of the insert was to gather the heat current within the chip body and remove it to a minimum temperature heat sink. The central goal of this paper is to invoke several reconsiderations, which result in excessive reduction of the peak temperature in the heated chip in comparison with the lowest peak temperature existed in the archival literature. It is proved that for the configuration under study with its bottom surface receiving a heat flux, the branching patterns of the insert must be avoided, in case the appropriate revisions in the architecture (width, location and cross section area) of the simple branchless patterns are considered. An analytical solution for predicting the peak temperatures in the chip is also addressed. It is demonstrated that under the same volume fraction and thermal conductivity of the cooling insert, the peak temperature is reduced to 2.9℃, which is 94% below the lowest temperature existed in the archival literature, which was around 50℃.