Direct Pore-Scale Simulations of Fully Periodic Unit Cells of Different Regular Lattices

Open-cell metal foams are known for their superior heat dissipation capabilities. The morphological, pressure-drop and heat transfer characteristics of stochastic metal foams manufactured through traditional 'foaming' process are well established in the literature. Employment of stochastic metal foams in next generation heat exchangers, is however, challenged by the irregularity in the pore-and fiber-geometries, limited control on the pore-volume, and an inherent necessity of a bonding agent between foam and heat source. On the other hand, additive manufacturing is an emerging technology that is capable of printing complex user-defined unit cell topologies with customized fiber shapes directly on the heated substrates. Moreover, the user-defined regular lattices are capable of exhibiting better thermal and mechanical properties than stochastic metal foams. In this paper, we present a numerical investigation on fully periodic unit-cells of three different topologies, viz. Tetrakaidecahedron (TKD), Rhombic-dodecahedron (DDC), and Octet with air as the working fluid. Pressure gradient, interfacial heat transfer coefficient, friction factor, and Nusselt number are reported for each topology. Rhombic-dodecahedron yielded in the highest average interfacial heat transfer coefficient whereas Octet incurred the highest flow losses. Pore diameter, defined as the maximum diameter of a sphere passing through the polygonal openings of the structures, when used as the characteristics length scale for the presentation of Nusselt number and Reynolds number, resulted in a single trendline for all the three topologies.

Double-Layer Metal Foams for Further Heat Transfer Enhancement in a Channel: An Analytical Study

A local thermal non-equilibrium analysis of heat and fluid flow in a channel fully filled with aluminum foam is performed for three cases: (a) pore density of 5 PPI (pore per inch), (b) pore density of 40 PPI, and (c) two different layers of 5 and 40 PPI. The dimensionless forms of fully developed heat and fluid flow equations for the fluid phase and heat conduction equation for the solid phase are solved analytically. The effects of interfacial heat transfer coefficient and thermal dispersion conductivity are considered. Analytical expressions for temperature profile of solid and fluid phases, and also the channel Nusselt number (NuH) are obtained. The obtained results are discussed in terms of the channel-based Reynolds number (ReH) changing from 10 to 2000, and thickness ratio between the channel height and sublayers. The Nusselt number of the channel with 40 PPI is always greater than that of the 5 PPI channel. It is also greater than the channel with two-layer aluminum foams until a specific Reynolds number then the Nusselt number of the channel with two-layer aluminum foams becomes greater than the uniform channels due to the higher velocity in the outer region and considerable increase in thermal dispersion.

Cloud FEA of hot stamping processes using a software agnostic platform

Finite element analysis (FEA) of a hot stamping process demands the implementation of accurate material properties and boundary conditions to precisely predict and evaluate the post-form quality of a component. A software agnostic platform was developed to provide cloud FEA of a hot stamping process in three stages, namely, pre-FE modelling, FE simulation and post-FE evaluation. When the desired materials and process window were uploaded on the platform, the flow stress, material properties, interfacial heat transfer coefficient (IHTC) and friction coefficient were predicted by the model-driven functional modules and then generated in the form of compatible packages that could be implemented into the desired FE software. Subsequently, the FE simulation was performed either locally or remotely on the developed platform. When the simulated evolutionary thermomechanical characteristics of the formed component were uploaded, the formability, quenching efficiency and post-form strength could be predicted and then demonstrated on a dedicated visualiser on the developed platform. Cloud FEA of two different hot stamping technologies was conducted to demonstrate the function of the developed platform, showing an error of less than 10%.

Wetting layer evolution and interfacial heat transfer in water-air spray cooling process of hot metallic surface

Spray cooling experiments on the hot metallic surfaces with different initial temperatures were performed. This paper adopts a self-developing program which is based on the inverse heat transfer algorithm to solve the interfacial heat transfer coefficient and heat flux. The temperature-dependent interfacial heat transfer mechanism of water-air spray cooling is explored according to the wetting layer evolution taken by a high-speed camera and the surface cooling curves attained by the inverse heat transfer algorithm. Film boiling, transition boiling, and nucleate boiling stages can be noticed during spray cooling process of hot metallic surface. When the cooled surface?s temperature drops to approximately 369?C - 424?C; the cooling process transfers into the transition boiling stage from the film boiling stage. The wetting regime begins to appear on the cooled surface, the interfacial heat transfer coefficient and heat flux begin to increase significantly. When the cooled surface?s temperature drops to approximately 217?C - 280?C, the cooling process transfers into the nucleate boiling stage. The cooled surface was covered by a liquid film, and the heat flux begins to decrease significantly.

Experimental investigation on steam bubble interfacial heat transfer in large range Reynolds number and water subcooling

An experimental study on the heat transfer characteristics of the steam bubbles generated by steam injection was performed. The bubble Nusselt number and Reynolds number were calculated based on the visual observation. The steam bubble Reynolds number and water subcooling were 600–360,000 and 15–60 K, respectively. In the large range of steam bubble Reynolds number, it was found that the heat transfer correlation in previous literatures cannot accurately predict the heat transfer coefficient of steam bubble. Based on the experimental results, the steam bubble Reynolds range was divided into three sections, namely 600–3000, 3000–22,000 and 22,000–360,000, to analyze the bubble heat transfer coefficient. Three experimental correlation formulas were obtained to calculate the steam bubble interfacial heat transfer coefficient, with deviations within ±30%. By comparing these three correlations, it was found that with the increase of Re[Formula: see text], the exponential coefficient of Re[Formula: see text] term in the correlation of Nu[Formula: see text] increased, and the absolute value of Ja term exponential coefficient decreased. The results indicated that with the increase of Re[Formula: see text], the influence of Re[Formula: see text] on bubble heat transfer increased, and the influence of water subcooling on bubble heat transfer decreased.