Nanofluids are considered to offer important advantages over conventional heat transfer fluids. Over a decade ago, researchers focused on measuring and modeling the effective thermal conductivity and ...viscosity of nanofluids. Recently important theoretical and experimental research works on convective heat transfer appeared in the open literatures on the enhancement of heat transfer using suspensions of nanometer-sized solid particle materials, metallic or nonmetallic in base heat transfer fluids. The purpose of this review article is to summarize the important published articles on the enhancement of the forced convection heat transfer with nanofluids.
Transportation sector is the important sector and consumed the most fossil fuel in the world. Since COVID-19 started in 2019, this sector had become the world connector because every country relies ...on logistics. The transportation sector does not only deal with the human transportation but also relates to logistics. Research in every country has searched for alternative transportation to replace internal combustion engines using fossil fuel, one of the most prominent choices is fuel cells. Fuel cells can use hydrogen as fuel. Hydrogen can be fed to the fuel cells to provide electric power to drive vehicles, no greenhouse gas emission and no direct combustion required. The fuel cells have been developed widely as the 21st century energy-conservation devices for mobile, stationary, and especially vehicles. The fuel cell electric vehicles using hydrogen as fuel were also called hydrogen fuel cell vehicles or hydrogen electric vehicles. The fuel cells were misconceived by several people that they were batteries, but the fuel cells could provide electric power continuously if their fuel was provided continuously. The batteries could provide electric power as their only capacities, when all ions are released, no power could be provided. Because the fuel cell vehicles play important roles for our future transportation, the overall review for these vehicles is significantly interesting. This overall review can provide general and technical information, variety of readers; vehicle users, manufacturers, and scientists, can perceive and understand the fuel cell vehicles within this review. The readers can realize how important the fuel cell technologies are and support research around the world to drive the fuel cell vehicles to be the leading vehicles in our sustainable developing world.
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•Fuel cells use hydrogen as fuel to provide electric power.•Fuel cells do not emit greenhouse gas and do not require direct combustion.•The fuel cell electric vehicles (FCEVs) are one of the zero emission vehicles.•Fuel cell technology has been developed for many types of vehicles.•Hydrogen production, transportation, storage and usage links play roles on FCEVs.
The solid oxide fuel cell (SOFC) is one of the most promising fuel cells for direct conversion of chemical energy to electrical energy with the possibility of its use in co-generation systems because ...of the high temperature waste heat. Various mathematical models have been developed for three geometric configurations (tubular, planar, and monolithic) to solve transport equations coupled with electrochemical processes to describe the reaction kinetics including internal reforming chemistry in SOFCs. In recent years, considerable progress has been made in modeling to improve the design and performance of this type of fuel cells. The numbers of the contributions on this important type of fuels have been increasing rapidly. The objective of this paper is to summarize the present status of the SOFC modeling efforts so that unresolved problems can be identified by the researchers.
Nanofluids have shown their advantages and potentials in improving heat transfer rates when the nanofluids are applied as working fluids in thermal systems. Researcher groups concentrating on the ...nanofluids have increased continuously and focused deeply into various fields; theoretically, experimentally and numerically. This review summarized the important published works on nanofluid preparations, properties, experimental and numerical heat transfer behaviors. In the simulations, two main categories were discussed in detail as the single-phase modeling which the combination of nanoparticle and base fluid is considered as a single-phase mixture with steady properties and the two-phase modeling which the nanoparticle properties and behaviors are considered separately from the base fluid properties and behaviors.
The transient behaviour of conjugated heat transfer in laminar microchannel flow is investigated, taking into account the axial diffusion effects, which are often of relevance in microchannels, and ...including pre-heating or pre-cooling of the region upstream of the heat exchange section. The solution methodology is based on the Generalized Integral Transform Technique (GITT), as applied to a single domain formulation proposed for modelling the heat transfer phenomena at both the fluid stream and the channel wall regions. By making use of coefficients represented as space dependent functions with abrupt transitions occurring at the fluid–wall interfaces, the mathematical model carries the information concerning the transition of the two domains, unifying the model into a single domain formulation with variable coefficients. The proposed approach is illustrated for microchannels with polymeric walls of different thicknesses. The accuracy of approximate internal wall temperature estimates deduced from measurements of the external wall temperatures, accounting only for the thermal resistance across the wall thickness, is also analyzed.
•Transient behaviour of conjugated heat transfer in laminar microchannel flow is investigated.•The analysis includes pre-heating or pre-cooling of the region upstream of the heat exchange section.•A hybrid numerical-analytical solution based on integral transforms is advanced to tackle the problem.•The present solution is critically compared to a finite element solution from a commercial code with excellent agreement.•The accuracy of approximate internal wall temperatures obtained from measurements of the external temperatures is analyzed.
A 2‐D mathematical model for the entire sandwich of a proton‐exchange membrane fuel cell including the gas channels was developed. The self‐consistent model for porous media was used for the ...equations describing transport phenomena in the membrane, catalyst layers, and gas diffusers, while standard equations of Navier‐Stokes, energy transport, continuity, and species concentrations are solved in the gas channels. A special handling of the transport equations enabled us to use the same numerical method in the unified domain consisting of the gas channels, gas diffusers, catalyst layers and membrane. It also eliminated the need to prescribe arbitrary or approximate boundary conditions at the interfaces between different parts of the fuel cell sandwich. By solving transport equations, as well as the equations for electrochemical reactions and current density with the membrane phase potential, polarization curves under various operating conditions were obtained. Modeling results compare very well with experimental results from the literature. Oxygen and water vapor mole fraction distributions in the coupled cathode gas channel‐gas diffuser were studied for various operating current densities. Liquid water velocity distributions in the membrane and influences of various parameters on the cell performance were also obtained.
In this work, a mathematical transport model for a planar solid oxide fuel cell has been developed and the analysis has been performed by the use of an in-house program which can help developers to ...understand the effects of various parameters on the performance of the fuel cell. In the model, electrochemical kinetics, gas dynamics and transport of energy and species are coupled. The model predicts polarization curve, velocity and temperature fields, species concentration and current distribution in the cell depending on fuel cell temperatures and electrolyte materials used in the components, such as yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (CGO). SOFC operating temperatures at 500, 600, 800, and
1000
∘
C
are considered and the modified Nernst equation is used to obtain a reversible cell voltage. It is shown that the anode-supported solid oxide fuel cells with YSZ electrolyte can be used to obtain a high power density in the higher current density range than the YSZ electrolyte-supported solid oxide fuel cells when they are operated at
800
∘
C
. Performance comparisons between two electrolyte materials, YSZ and CGO are made. The YSZ-electrolyte solid oxide fuel cell in this work shows higher power density than the CGO-electrolyte solid oxide fuel cell at the higher temperatures than
750
∘
C
.
In this paper, we establish a numerical model for simulating an indirect internal reforming section in a solid oxide fuel cell to demonstrate the effect of the electrochemical promotion and coupling ...between selective anode catalysts and selective cathode catalysts in the catalyst pack. The model employs a simplified geometrical model of an indirect internal reforming section in the anode chamber of a solid oxide fuel cell. However, the model includes very complicated combination of conventional reforming processes, electrochemical promotion and coupling. The results predict that the electrochemical promotion and coupling in a microscopic scale can enable a significant reforming and production of hydrogen at a relatively low temperature (500
°C).
This study is an extension of the Graetz problem to include the rarefaction effect, viscous dissipation term and axial conduction with constant-wall-heat-flux thermal boundary condition. The energy ...equation is solved analytically by using general eigenfunction expansion. The temperature distribution and the local Nusselt number are determined in terms of confluent hypergeometric functions. The effects of the rarefaction, axial conduction and viscous dissipation on the local Nusselt number are discussed in terms of dimensionless parameters such as the Knudsen number, Peclet number and Brinkman number.
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