Applied Mechanics and Materials Vol. 819

Abstract: Slug flow regime in two and multi-phase flow in pipes is a complicated flow phenomena representing challenge in the design of the piping system. In the present work, water/air two phase flow was modeled and simulated as 3 dimensional, transient, and incompressible flow using Volume of Fluid technique in STAR-CCM+ software. The simulation was conducted to predict and evaluate the air-water slug flow in a horizontal pipe with 0.16 m diameter and 7 m long. The superficial velocities for both phases were extracted from Baker chart slug zone. The results were validated against experimental bench marking referenced in Baker chart and the proposed VOF technique shows a good capability in simulating the development of the slug flow regime. This model could be utilized for simulation of various two phase flow regimes.

Abstract: Impedance pump is a type of valveless pumping device, in which it utilizes a bio-inspired mechanism for pumping of fluid based on resonant wave interactions along a flexible media. By inducing a periodic asymmetrical compression on the flexible media will produce a unidirectional flow within the system. The impedance pump has many beneficial characteristics which make it an effective driving mechanism, especially for micro-fluidic systems. In addition, the wave-based mechanism through which pumping occurs infers many benefits in terms of simplicity of design and manufacturing. Adjustment of simple parameters such as the excitation frequency or compression location will reverse the direction of flow, providing a very versatile range of flow outputs. This paper describes the experimental analysis of such impedance-driven flow with emphasis on dynamical study of the reverse flow in open-loop environment. In this study, tapered section with converging steps is introduced at both ends of the flexible media to amplify the reverse flow. Study conducted shows that the reverse peak flow is rather significant with estimate of 23% lower than the forward peak flow. The flow dynamics on the other hand has shown to exhibit different characteristics as per the forward peak flow.

Abstract: Substantial research has been completed with more on-going on the flow pattern and heat transfer associated with two-phase flows. Discrepancies reported may have been as much as agreements, due to the different models, approaches, flow regimes, correlations, and new working fluids being utilized. This paper reports the outcome of a study to look at the effects of applying two different friction factor correlations on the simultaneous minimization of the pressure drop and Martinelli parameter under optimized flow rate and vapor quality, using genetic algorithm. The homogeneous model is assumed with ammonia as the working fluid, the coolant being environmentally friendly and having recently discovered as a potential replacement for the current refrigerants in micro and mini-channels. Results show that significant differences in the frictional pressure drop and Martinelli parameter arise due to the different correlations used, and this is only the outcome from two different correlations currently being considered by researchers in pressure drop analysis for two-phase flows in mini-channels. Thus, absolute agreement is indeed not possible between theoretical, experimental, and numerical work in view of the many different available correlations being utilized today with differences between 10 to 100 percent that has already been established.

Abstract: Research in two-phase flow in heat exchanging devices plays an important part in today’s applications in miniaturization of engineering systems. The phase change process factors in the flow conditions and heat transfer in evaporators and condensers. Numerous studies in the past have looked at the predicted and measured frictional pressure drop of coolants as the vapor quality increases. This paper reports a preliminary attempt at modeling of the relationship between the frictional pressure drop and vapor quality in an ammonia-cooled and R22-cooled mini-channel of 1.5 mm diameter under optimized conditions using multi-objective genetic algorithm. R22 is a being phased-out due to its ozone-depleting characteristic and ammonia is being considered as its potential replacement. The properties of ammonia and R22 used have been obtained experimentally at the saturation temperature of 5°C and 10°C respectively. Modeling of the minimized pressure drop per unit tube length together with the Lockhart-Martinelli parameter was completed under optimized flow rate and vapor quality.The outcomes obtained are similar to those that have been reported experimentally with other coolants, increasing pressure drop with increasing vapor quality.

Abstract: It is well-known that when slug flow occurs in pipes it may result in damaging the pipe line. Therefore it is important to predict the slug occurrence and its effect. Slug flow regime is unsteady in nature and the pipelines conveying it are indeed susceptible to significant cyclic stresses. In this work, a numerical study has been conducted to investigate the interaction between the slug flow and solid pipe. Fluid Structure Interaction (FSI) coupling between 3-D Computational Fluid Dynamic (CFD) and 3-D pipeline model code has been developed to assess the stresses on the pipe due to slug flow. Time – dependent stresses results has been analyzed together with the slug characteristic along the pipe. Results revealed that the dynamic behavior of the pipelines is strongly affected by slug parameters. The FSI simulation results show that the maximum stresses occurred close to the pipe supports due to slug flow, where the pipe response to the exerted slug forces is extremely high. These stresses will subsequently cause fatigue damage which is likely reduce the total lifetime of the pipeline. Therefore a careful attention should be made during the design stage of the pipeline to account for these stresses. The system has been investigated under multiple water velocities and constant air velocity, the maximum stress was obtained at the water velocity of 0.505 m/s. Moreover, when the water velocity is increased from 0.502 to 1.003 m/s the maximum stress magnitude is decreased by 1.2% and when it is increased to 1.505 m/s the maximum stress is diminished by 3.6%.

Abstract: A new particle method, namely the Moving Particle Pressure Mesh (MPPM) method is developed to compute incompressible single- and multi-fluid flows. Unlike the conventional particle method (such as SPH and MPS) whereby the pressure variable is associated with individual moving particle, the pressure is treated as a field (or Eulerian) variable due to the fact that there is no transport equation of pressure can be expressed for an incompressible moving fluid particle. A more accurate method can then be easily devised to evaluate the pressure gradient, which is important in governing the subsequent motion of individual fluid particle. The method is applied to compute several incompressible flow cases and the numerical results agree considerably well with the reference solutions.

Abstract: The turbulent flow in orifice plate was investigated and solved numerically using 3-D Navier-Stockes (N-S) equations by employing commercial CFD code ANSYS. The N-S equations were solved for unsteady flow of an orifice plate at different values of Reynolds number, Re=ρVDμ, and different aspect ratios, β=dorificedpipe. Physical parameters such as velocity, differential pressure, and vorticity and mechanical properties such as stress, strain, and total deformation were examined for Reynolds numbers of 10000, 20000, and 30000 and at aspect ratios β of 0.2, 0.4, and 0.6. It was found that as Reynolds number increases, the velocity increases while the differential pressure shows very steep jump across the orifice. As aspect ratio increases, the maximum pressure declines. The vorticity patterns show that images of very condensed lines. At certain aspect ratio, the differential pressure increases as Reynolds number increases.

Abstract: Multipurpose Amphibious Vehicles (MAV) and other blunt shaped floating vehicles encounter the problem of a large bow wave forming and hydrodynamic resistance at high speeds. This wave formation is accompanied by higher resistance and at a critical speed results in bow submerging or swamping. Three new shapes of hull bow design for the multipurpose amphibious vehicle were conducted at several speeds to investigate the hydrodynamic phenomena using Computational Fluid Dynamics (CFD, RANS code), which is applied by Ansys-CFX14.0 and Maxsurf. The vehicle’s hydrodynamic bow shapes were able to break up induced waves and avoid swamping. Comparative results with the vehicle fitted with U-shape, V-shape and Flat-shape of hull bow, showed that the U-shape of the hull bow has reduced the total resistance to 20.3% and 13.6% compared with the V-shape and flat shape respectively. Though, the U-shape of hull bow is capable to increase the amphibious operating life and speed of vehicle. Also it has ability to reduce the vehicle’s required power, fossil fuel consumption and wetted hull surface. On the other hand, the use of air cushions to support marine vehicles, heavy floating structures and in other operation is well known. The main problem in Multi-purpose Amphibious Vehicles (MAV) is the amount of power needed in order to overcome the hydrodynamic resistance acting on the hull which is included the frictional and pressure resistances. Therefore, more power is needed to move the MAV forward. In this respect, more fuel will be required to operate the amphibious vehicles. This problem could be effectively reduced by the introduction of the air cushion concept. With the air being drawn from top of craft to the cavity below the hull will produce some cushioning effect and also help to reduce skin friction drag. In this paper, air cushion effect will be studied in rigid surface cavity instead of using flexible skirts. This would avoid the problem of high maintenance due to replacement of damaged skirts. Finally, the MAV will be supported using air cavity and bubbles generated by an air pump (compressor and air pressure vessel) to pushes the hull of multi-purpose amphibious vehicle up and reduce the frictional resistance due to draft and wetted surface reduction and layer of air between hull surface and water. This research would be done via CFD (ANSYS-CFX 14.0) and analyzed the hydrodynamic resistance

Abstract: Nanotechnology is a novel approach in thermal engineering science to enhance the overall thermal performance of compact heat exchangers by the homogeneous dispersion of solid nanoparticles of higher thermal conductivity in conventional base fluid like water, oil, ethylene glycol etc. The heat transfer rate is substantially intensified by the addition of nanosized solid particles which provide superior thermo-physical properties in comparison with base fluid. In the present study, a numerical simulation is performed to investigate the turbulent convective heat transfer characteristics of Al₂O₃-water nanofluid of volume fractions (1%, 3% and 5%) through a rough circular tube subjected to constant heat flux for a range of Reynolds number 10,000 to 30,000. The finite volume method is employed for solving the governing equations and k-ω SST turbulent model for single phase analysis is considered. At a Reynolds number of 25000, application of nanofluid combined with rough tube enhances the Nusselt number by 13.10%, 21.86% and 63.03% in case of relative roughness of the wall of 0.001, 0.005 and 0.01 respectively.

Abstract: In this paper the wind speed is predicted by the use of data provided from the Mehrabad meteorological station located in Tehran, Iran, Collected between 2003 and 2008. A comprehensive analogy study is presented on Comparison of various Back Propagation neural networks methods in wind velocity forecasting. Four types of activation functions, namely, BFGS quasi-Newton, Bayesian regularized, Levenberg-Marquardt, and conjugate gradient algorithm, werestudied. The data was investigated by correlation coefficient and characterizing the amount of dependency between the wind speed and other input data. The meteorological parameters (pressure, direction, temperature and humidity) were used as input data, while the wind velocity is used as the output of the network.The results demonstrate that for the similar wind dataset, Bayesian Regularized algorithm can accurately predict compared with other method. In addition, choosing the type of activation function is dependent on the amount of input data, which should be acceptably large.