Numerical analysis of the vapor flow in an axially rotating heat pipe in drilling processes

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Two-phase flow modelling of liquid-feed direct methanol fuel cell

A two-phase flow model was developed for liquid-feed methanol fuel cells (DMFC) to evaluate the effects of various operating parameters on the DMFC performance. In this study, a general homogenous two-dimensional model is described in details for both porous layers and fluid channels. This two-dimensional general model accounts for fluid flow, electrochemical kinetics, current density distribution, hydrodynamics, multi-component transport, and methanol crossover. It starts from basic transport equations including mass conservation, momentum transport, energy balance, and species concentration conservation in different elements of the fuel cell sandwich, as well as the equations for the phase potential in the membrane and the catalyst layers. These governing equations are coupled with chemical reaction kinetics by introducing various source terms. It is found that all these equations are in a very similar form except the source terms. Based on this observation, all the governing equations can be solved using the same numerical formulation in the single domain without prescribing the boundary conditions at the various interfaces between the different elements of the fuel cell. The numerical simulation results, such as velocity field, local current density distribution, and species concentration variation along the flow channel, under various operation conditions are computed. The performance of the DMFC affected by various parameters such as temperature, pressure, and methanol concentration is investigated in this paper. The numerical results are further validated with available experimental data from the published literatures

Numerical analysis of the hydrodynamics of the flow in an axially rotating heat pipe

A numerical study is conducted on the vapor and liquid flow in a wick structure of an axially rotating heat pipe. For the vapor, the governing equations are the Navier-Stokes. For the liquid a space average of the Navier-Stokes equation is performed and a porous media model is introduced for the cross correlation that appears from the averaging process. A control volume approach on a staggered grid is used in the development of the computer program. Suction and blowing velocities are used as boundary conditions of the vapor and liquid, which are related to a local heat flux input in the evaporator section, and local heat flux output in the condenser section, respectively. The aim behind this study is the application of heat pipes in drilling applications. A triangular heat flux distribution is assumed in the evaporator due to the higher heat flux generated at the tip of the drill. A parametric study is conducted to analyze the effect of different parameters such as rotational speeds, saturation conditions, porosity, permeability and dimensions of the wick structure in the porous medium. These parameters significantly affect the pressure drop in the heat pipe and allow predicting failure conditions, which is critical in the design of heat pipes in drilling applications. The results of this study will be useful for the complete analysis of the heat pipe performance including the solution of the heat transfer on the solid wall as a conjugate problem

Turbulent heat transfer analysis of a three-dimensional array of perforated fins due to changes in perforation sizes

Turbulent heat transfer characteristics of three-dimensional and rectangular perforated fins, including perforation like channels along the length of the fins, are investigated. Both dimensions and numbers of perforations are changed at the highest porosity in the study of Shaeri and Yaghoubi [7] to determine the effects of perforation sizes on the heat transfer characteristics of the perforated fins. Results show that at a specific porosity, a fin with a higher number of perforations enhances the heat transfer rate more efficiently. Also, total drag is not only remarkably lower in perforated fins compared with a solid fin, but also becomes smaller by decreasing the number of perforations

Residual stress characterization from numerical analysis of the multi-particle impact behavior in cold spray

Abstract: In cold spray, bonding is created between a substrate and the particles and between particles through impact deformation at high strain rates. A prominent feature of the cold spray process is the compressive residual stress that arises during the deposition process. Compressive residual stress on the surface can be beneficial for fatigue resistance. As a post processing technique several applications require surface treatment processes that produce this state of stress on component surfaces such as shot peening, laser shock peening, ultrasonic impact treatment, low plasticity burnishing, etc. In all of these methods the compressive stress is produced through plastic deformation of the surface region. In a similar manner, the cold spray process induces compressive stress by high speed impact of the sprayed particles on the surface, causing a peening effect. The effects of these variations in the properties of the coatings are rarely reported. Moreover there are some applications which require minimal residual stresses in the components such as in optics. In this study, we have investigated the residual stress using numerical analysis of the multi-particle impact behavior in cold spray

Intermetallics Formation and Their Effect on Mechanical Properties of Al-Si-X Alloys

This study focuses on primary impurities, called intermetallics, in the microstructure of Al-Si-X alloys, their formation, effects and treatments to eliminate or ameliorate their deleterious effects. Intermetallic compounds are usually formed when alloying elements, such as Fe, Cu, Mn, Mg and Sr. are added to Al-Si based alloys. These elements are depicted by X in the alloys formation expression. The chapter noted that the most common intermetallics are iron (Fe) based, and several of these Fe-phases, including the most harmful Fe-phase, β-Al5SiFe, are listed and discussed. Fe-phase intermetallics are deleterious to the mechanical properties of Al-alloys; however, addition of <0.7% Fe helps prevent soldering in die casting mould. The effects of Fe-phase and other intermetallics formed by Cu, Mg and Mn were examined. Further, some techniques of eliminating or mitigating the negative influences of intermetallics were discussed

The effect of perforation sizes on laminar heat transfer characteristics of an array of perforated fins

Shaeri and Yaghoubi [25] reported the highest heat transfer rate in a laminar flow for a perforated fin with the most perforations (porosity), regardless of investigation on the effects of perforation sizes. In this study, the effects of size and number of perforations on laminar heat transfer characteristics of an array of perforated fins at the highest porosity of the study of Shaeri and Yaghoubi [25] have been numerically investigated. The Navier–Stokes and energy equations are solved by the finite volume procedure using the SIMPLE algorithm. Results show that at a specific porosity, the thermal entrance length of each perforation of a fin with a lower number of perforations is larger than that of each perforation of a fin with a higher number of perforations. Therefore, in a laminar flow and at a constant porosity, a fin with fewer perforations is more efficient to enhance the heat transfer rate compared with a fin with more perforations. Although perforated fins have higher friction drag and lower pressure drag with respect to solid fins, perforated fins do not affect total drag

Comparative study of Hydrogen yield from magnesium waste products in Acetic acid and Iron chloride solution

Abstract: Low-grade magnesium (Mg) waste from post-consumer products and production waste cannot be recycled efficiently and economically. This work addresses this challenge by converting this waste into hydrogen. Hydrogen (H2) offers a wide range of benefits and the greatest of them all is its ability and flexibility to be used as a green energy carrier. In this work Mg waste is re-melted, loaded on one side of a stainless steel and allowed to solidify at room temperature to form a galvanic Mg stainless steel couple. Mg reacts slowly with water and releases hydrogen at room temperature and this is followed by the formation of magnesium hydroxide on its surface. Stainless steel net is considered as a metallic catalyst and two acids as accelerators reacting with the couples separately. A set of couples were used to generate hydrogen in 3.5% by weight acetic acid (CH3COOH). The experimental results show that a mean accumulated H2 volume of 3.17 – 3.21 litres was produced in 3600 seconds. Another set of couples produced H2 in 1.5 wt. % of iron chloride (FeCl3). The results confirmed FeCl3 as an excellent hydrolysis reaction accelerator with stainless steel as an effective catalyst. On average, the reaction yielded 2700mL of H2 over 3600 seconds which appear to be substantially higher than the litres achieve when CH3COOH was considered as an accelerator

Casting and Applications of Functionally Graded Metal Matrix Composites

This chapter discusses the concepts, casting techniques and applications of functionally graded materials metal matrix composites (FGMMCs). Considerations were given to bulk functionally graded aluminium matrix composites (FGAACs) production processes. Liquid-metal forging processes of FGAACs fabrication, such as infiltration process, squeeze casting, friction casting or compocasting, stir, and centrifugal casting were discussed. The chapter provides basic concepts of the processes and overview of their processing parameters, such as mould rotational speed; reinforcement particles size and volume; degassing method; melting and pouring temperatures; pressure; and stirrer. The study notes that functionally graded materials (FGMs) are commonly used in automotive, aircraft, aviation, chemical, medical, engineering, renewable energy, nuclear energy, and optics electronics industries