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•Internal circulation in a rising drop resolved through coupled calculations.•Heat transfer characteristics elicited through transient simulations.•Heat transfer found to be governed by a convective phase sandwich between diffusive phases.•Convective enhancement of heat transfer elicited.•Correlation proposed for convective enhancement.

Machined monolithic components provide the foundation for modern aircraft structures requiring high performance designs in terms of weight, strength, and fatigue properties. Part distortions arising from machining-induced stresses and tool deflection resulting from high dynamic cutting forces frustrate manufacturing and assembly processes, necessitating expensive in-process and post-machining corrective measures aimed at eliminating their effects. Component weight and cost requirements are often compromised by adding thicker component section designs or off-machine part flipping processes as a distortion control mechanism. Similarly, small depths of cut are taken to minimize cutting forces and tool deflection. Additional spring passes are also taken to eliminate any undercut errors introduced by unanticipated deflection and distortion problems. The ability to accurately predict and minimize tool deflections and part distortion via simulations can significantly reduce manufacturing and assembly costs. This paper presents physics-based models for predicting tool deflection and part distortions by considering the appropriate physics for each problem. Dynamic cutting forces predicted by physics-based machining models, and tool compliance properties are incorporated into a detailed linear elastic deflection model in order to predict in-process deflections along a computer numerical control (CNC) machining toolpath. Similarly, bulk stress state and machining-induced stresses for large, monolithic part machining are taken into account for predicting part distortions. Sources of stresses may include heat treatment, quenching, forging, and machining operations. Bulk stress data from heat treatment predictive models can also be imported and mapped onto the workpiece finite element model. CNC part programs, along with stresses arising from corresponding tooling, are processed and analyzed. Results of a validation study for workpiece distortion predictions are presented for a number of monolithic, thin-walled components. Predictions for tool deflection are also compared against experimental measurements for multiple cutting configurations and tool diameters. Good correlation is found between predictions and measurements of deflection.

Machining is a pervasive manufacturing process used in industries such as automotive, aerospace, medical implants and oil and gas. Analysis of processes via physics-based modeling enables new and innovative designs for cutting tools, provides confidence of machined workpiece quality characteristics and allows reduction in machining cycle times and tooling costs. Progressively sophisticated analyses of machining processes have evolved with the inclusion of effects of full three-dimensional analysis of cutting tools and complex tool/workpiece kinematics. Detailed-level analysis of machined workpiece surfaces based on finite element method (FEM) allows prediction of residual stresses, work hardened layer depths and heat flow. However, with the increase in model sophistication has come with computational burden. This paper details a high performance computing (HPC) environment for finite element models used for machining analysis. First, the FEM model is reviewed and its extension to high core-count shared memory environments is described. Scaled performance improvements for up to forty cores are demonstrated and performance improvements documented. Next, an HPC cluster is designed and a specialized batch queuing software is implemented that allows submission, monitoring and management of large scale machining simulations. Finally, an infrastructure for delivering the HPC capability to customers through Software as a Service (SaaS) is introduced.

Proper water management is critical for near-ambient temperature operation of a fuel cell. A simplified water balance model has been developed to predict when incipient flooding/dehydration may take place. The present model is based on multicomponent diffusion in the electrodes and molar balance in the flow channels. The overall model is in the form of a closed-form expression for the critical or threshold or balance current density at which the water production rate and the water vapor evacuation rate are exactly balanced. The model incorporates the influence of the operating conditions, properties of electrodes, and flow and geometric parameters in the gas channels on the balance current density. Predictions from the model of the state—incipient flooding or dehydration—of operation of the fuel cell agree well with the available experimental data. Using the model, a parametric study has been conducted over a range of parameters.

Proper water management is critical for near-ambient temperature operation of a fuel cell. A simplified water balance model has been developed to predict when incipient flooding/dehydration may take place. The present model is based on multicomponent diffusion in the electrodes and molar balance in the flow channels. The overall model is in the form of a closed-form expression for the critical or threshold or balance current density at which the water production rate and the water vapor evacuation rate are exactly balanced. The model incorporates the influence of the operating conditions, properties of electrodes, and flow and geometric parameters in the gas channels on the balance current density. Predictions from the model of the state—incipient flooding or dehydration—of operation of the fuel cell agree well with the available experimental data. Using the model, a parametric study has been conducted over a range of parameters.

Proper water management is critical for near-ambient temperature operation of a fuel cell. A simplified water balance model has been developed to predict when incipient flooding/dehydration may take place. The present model is based on multicomponent diffusion in the electrodes and molar balance in the flow channels. The overall model is in the form of a closed-form expression for the critical or threshold or balance current density at which the water production rate and the water vapor evacuation rate are exactly balanced. The model incorporates the influence of the operating conditions, properties of electrodes, and flow and geometric parameters in the gas channels on the balance current density. Predictions from the model of the state—incipient flooding or dehydration—of operation of the fuel cell agree well with the available experimental data. Using the model, a parametric study has been conducted over a range of parameters.

Helical ribbon impellers are widely used in chemical and process industries for the mixing of pseudoplastic fluids of high viscosity. The design of such impellers is based on an assumed linear relation between shear rate and the rotation speed of the impeller. A number of computational fluid dynamics (CFD) simulations of the flow field have been carried to verify this hypothesis. It is shown that while the shear rate varies greatly within the mixing vessel, there does exist a linear relationship between the impeller speed and the local shear rate near the tip of the impeller. The proportionality constant Ks associated with this linear relation is found to be dependent on the geometric parameters of the system, but is largely independent of the flow behavior index. Based on these results, a new correlation, applicable to both Newtonian and power‐law fluids for power consumption, is proposed.

In 1957 Metzner and Otto proposed a simplified way of calculating the power consumption in impeller‐driven systems for power‐law type of fluids. Assuming a proportionality between the shear rate and rotational speed of the impeller, they reported that the proportionality constant was independent of the geometric and fluid properties of the mixing system. This was later contested by a number of researchers, and different correlations have been given to evaluate the proportionality constant. An in‐depth investigation of the Metzner–Otto concept is discussed with the help of computational fluid dynamics (CFD) techniques to calculate the flow field created by an anchor impeller. Fundamentally, both of the assumptions are broadly valid for typical operating parameters used in anchor‐driven impeller systems. A new correlation, based on the Metzner–Otto concept and making use of the present CFD simulations, was developed to calculate power consumption in anchor‐driven mixing systems.

Systematic experiments were conducted to study the postflooding situation in air–water countercurrent flow in a tube of 0.025 m internal diameter with smooth inlet and outlet conditions for the two phases. The downflow rate of water and the pressure gradient were measured over a range of flow rates for test‐section lengths of 0.6, 1.2 and 2.0 m. Additional experiments were conducted with increasing and decreasing water flow rates at a constant air flow rate. The length of the test section or the way the flooding point was approached did not significantly affect the onset of flooding. The data show that, as the gas flow rate is increased, the pressure gradient can fall significantly in the postflooding situation due to depleting the downflow rate of liquid. Dimensionless correlations are proposed to calculate the downflow rate and the pressure gradient given for overall flow parameters.

1-Aryl-2, 5-dithiohydrazodicarbonamide (aryl=ethoxyphenyl-(I) and chlorophenyl-(II)) forms 1:1 complexes of the type M(epthc) wherein M=Co(II), Ni(II), Cu(II) and Zn(II) and epthc=p-ethoxyphenyl dithiohydrazodicarbonamide; M(cpthc) M=Co(II), Cu(II) and Zn(II) and M(cpthc). 2H2O (M=Ni(H)) and cpthc=p-chlorophenyldithiohydrazodicarbonamide. Magnetic and electronic spectral studies suggest tetrahedral geometry for Co(epthc) and Co(cpthc) while a square-planar geometry is indicated for Ni(epthc), Cu(epthc) and Cu(cpthc); Ni(cpthc). 2H2O is shown to possess an octahedral geometry. Infrared spectra ascertain a binegative tetradentate behaviour of the ligands and the bonding sites are both hydrazidic nitrogens and the thiolo-sulphur. The Co(II), Ni(II) and Cu(II) complexes and ligands (I, II) have been found to exhibit pronounced antifungal activity against H. oryzae and A. flavus. The antibacterial properties of all the metal complexes and the ligands towards Bacillus-subtilis, Proteus microbilis and E. coli have been evaluated.

The hydrodynamics and heat transfer of thin film flow with a wavy interface has been studied using computational fluid dynamics techniques. The velocity and temperature fields are obtained for periodic laminar flow with an assumed interface shape. The effect of sinusoidal and solitary waves on the heat transfer across the film is investigated. It is shown that the overall heat transfer coefficient is determined mainly by conduction through the film, rather than by the recirculation, if any, under the waves. However, the presence of interfacial waves still enhances the heat transfer coefficient due, mainly, to the effective thinning of the film. Copyright © 1996 Elsevier Science Ltd.

The heat transfer characteristics of a coiled steam generating tube are very different from those of a straight tube. For example, the critical heat flux (CHF) in coiled tubes is less than that in straight tubes for subcooled boiling and significantly higher at higher qualities. In this paper, predictive methods are developed for the determination of the point of onset of nucleate boiling, the point of net vapour generation and the critical heat flux condition in curved ducts. The methods are based on the assumption that these phenomena are governed by the local hydro- and thermodynamic conditions which can be predicted using computational fluid dynamics techniques. Good agreement has been obtained with available experimental data.

AbstractThe response of turbulent pipe flow to sudden changes in wall roughness and flow cross-sectional area has been studied experimentally and numerically. Changes typical of those encountered by the gas phase in annular gas-liquid flow have been considered. The results show that the flow field and the pressure field can be significantly distorted at these transitions. Good agreement has been obtained between the measured results and those calculated using the Harwell-FLOW3D computational fluid dynamics (CFD) code.

In this paper, we present experimental studies of electrochemical performance of an all-vanadium redox flow battery cell employing an active area of 103 cm2, activated carbon felt, and a novel flow field, which ensures good electrolyte circulation at low pressure drops. Extended testing over 151 consecutive charge/discharge cycles has shown steady performance with an energy efficiency of 84% and capacity fade of only 0.26% per cycle. Peak power density of 193 mW cm−2 has been obtained at an electrolyte circulation rate of 114 ml min−1, which corresponds to stoichiometric factor of 4.6. The present configuration of the cell shows 20% improved in peak power and 30% reduction in pressure drop when compared to a similar cell with a different electrode and a serpentine flow field.