Mathematical model for heat transfer during laser material processing.

The article presents development of a new heat transfer model for calculating temperature distribution in porous and non-porous materials during laser cutting. The novelty of this model lies in incorporating melting and vaporisation progression of porous media during laser interaction. The modelling has been implemented through a transient finite difference scheme and the results have been validated against experimental data of cutting various materials by laser including rock and metals

Numerical analysis of a horizontal pressure differential wave energy converter.

CFD modeling of an innovative wave energy device has been carried out in this study. OpenFoam wave modeling solver interFoam has been employed in order to investigate the energy extraction capability of the wave energy device. The innovative concept is based on utilizing the pressure differential under the crest and trough of a wave to drive flow through a pipe. The simulated surface elevation of a wave has been validated against the reported wave tank experimental data in order to provide confidence in the modeling outcome. Further, simulations have been carried out with the device placed near to the bottom of the numerical wave tank in order establish the energy extraction potential. The simulation results confirm that effective power can be generated from the wave energy device. The efficiency of the device decreases with the increase in wave height, although it increases with the wave period. Higher power-take off (PTO) damping is also beneficial in extracting increased energy from waves

Modeling aerosol cloud aerodynamics during human coughing, talking, and breathing actions.

In this paper, we investigate the aerosol cloud flow physics during three respiratory actions by humans (such as coughing, talking, and breathing). With given variables (i.e., velocity, duration, particle size and number of particles, and ambient conditions), the standoff safe distance during coughing, talking, and breathing should be the distance where virus-laden droplets and aerosols do not have significant transmission to another person. However, at a critical distance, the aerosol cloud flux can still be extremely high, which can immediately raise the transmission in a localized area to another person during a static condition. In this study, computational fluid dynamics analysis of selective respiratory actions has been carried out to investigate the effect of the standoff distance and assess the importance of social distancing in indoor places. The prediction of the aerosol transport due to flow generated from coughing, talking, and breathing was obtained by applying the Eulerian-Lagrangian approach. From the simulation results, it can be concluded that the aerosols released due to continuous talking travel a similar distance to that released due to sudden coughing. On the other hand, aerosols exhaled from breathing do not travel a long distance but float in air for a long time

Numerical study of bluff-body non-premixed flame structures using laminar flamelet model

A laminar flamelet model is applied for bluff-body stabilized flames to study the flow field, mixing pattern, and the flame structure at two different velocities. The k 1 turbulence model is applied for accounting the turbulence fluctuations. It is found that the recirculation zone dominates the near field, while the far field structure is similar to the jet flow. The intermediate neck zone is the intense mixing region. The computation shows that the fuel jet velocity has significant effect on the structure of the flow field, which in turn has significant effect on the combustion characteristics. The laminar flamelet model is found to be adequate for simulating the temperature and the flame composition inside the recirculation zone. The flamelet model has, however, failed to account for the local extinction in the neck zone. Possible limitation of the laminar flamelet model to predict the local extinction is discussed

Effect of fracture roughness on the hydrodynamics of proppant transport in hydraulic fractures.

The effect of fracture roughness is investigated on proppant transport in hydraulic fractures using Joint Roughness Coefficient and a three-dimensional multiphase modelling approach. The equations governing the proppant transport physics in the fracturing fluid is solved using the hybrid computational fluid dynamics model. The reported proppant transport models in the literature are limited to the assumption of a smooth fracture domain with no fluid leak-off or fluid flow from fracture to rock matrix interface. In this paper, a proppant transport model is proposed that accounts for the proppant distribution in rough fracture geometry with fluid leak-off effect to surrounding porous rock. The hydrodynamic and mechanical behaviour of proppant transport was found directly related to the fracture roughness and flow regime especially under the influence of low viscosity fracturing fluid typically used in shale gas reservoirs. For the proppant transport in smooth fractures, the fracture walls employ mechanical retardation effects and reduce the proppant horizontal velocity resulting in more significant proppant deposition. On the contrary, for the proppant transport in rough fractures, the inter-proppant and proppant wall interactions become dominant that adds turbulence to the flow. It results in mechanical interaction flow effects becoming dominant and consequently higher proppants suspended in the slurry and greater horizontal transport velocity. Furthermore, the mechanical interaction flow effects were found to be principally dependant on the proppant transport regime and become significant at higher proppant Reynolds number

Proppant transport in dynamically propagating hydraulic fractures using CFD-XFEM approach.

Numerically modelling the fluid flow with proppant transport and fracture propagation together are one of the significant technical challenges in hydraulic fracturing of unconventional hydrocarbon reservoirs. The existing models either model the proppant transport physics in static predefined fracture geometry or account for the analytical models for defining the fracture propagation. Furthermore, the fluid leak-off effects are usually neglected in the hydrodynamics of proppant transport in the existing models. In the present paper, a dynamic and integrated numerical model is determined that uses computational fluid dynamics (CFD) technique to model the fluid flow with proppant transport and Extended finite element method (XFEM) to model the fracture propagation. The results of fracture propagation were validated with the real field results and analytical models, and the results of proppant transport are validated with the experimental results. The integrated model is then used to comprehensively investigate the hydrodynamical properties that directly affect the near-wellbore stress and proppant distribution inside the fracture. The model can accurately model the proppant physics and also propose a solution to a frequent challenge faced in the petroleum industry of fracture tip screen out. Thus, using the current model allows the petroleum engineers to design the hydraulic fracturing operation successfully, model simultaneously fracture propagation and fluid flow with proppant transport and gain confidence by tracking the distribution of proppants inside the fracture accurately

Computational fluid dynamics modelling of multiphase flows in double elbow geometries.

This study investigates the effects of elbow on the transition and development of multiphase flow using computational fluid dynamics modelling techniques. The Eulerian - Multifluid VOF model coupled with an Interfacial Area Transport Equation has been employed to simulate air-water two-phase flow in a pipe with two standard 90 degree elbows mounted in series. Turbulence effects were accounted for by the RNG k-ε model. The effects of separation distance on two-phase flow development have been studied for initial slug and churn flow regimes. Computational fluid dynamics simulation results of phase distribution and time series of void fraction fluctuations were obtained and they showed good agreement with available experimental data. The results show that for initial slug flow regime, there is no flow regime transformation upstream and downstream of the two elbows. While at initial churn flow regime, flow regime transformation occurs at different sections of the flow domain before and after the two elbows. It was noticed that irrespective of the flow regime, the amplitudes and frequencies of void fraction fluctuation become smaller as the fluid flows along the pipe. Changes in the separation distance between the two elbows have larger effects on the flow at churn flow regime

Numerical study of the effect of effective diffusivity and permeability of the gas diffusion layer on fuel cell performance.

A three-dimensional, single-phase, isothermal, explicit electrochemistry polymer electrolyte membrane fuel cell model has been developed and the developed computational model has been used to compare various effective diffusivity models of the gas diffusion layer. The Bruggeman model has traditionally been used to represent the diffusion of species in the porous gas diffusion layer. In this study, the Bruggeman model has been compared against models based on particle porous media, multi-length scale particles and the percolation-type correlation. The effects of isotropic and anisotropic permeability on flow dynamics and fuel cell performance have also been investigated. This study shows that the modelling of the effective diffusivity has significant effects on the fuel cell performance prediction. The percolation-based anisotropic model provides better accuracy for the fuel cell performance prediction. The effects of permeability have been found to be negligible and the specification of any realistic value for permeability has been found to be sufficient for polymer electrolyte membrane fuel cell modelling

Developing a capacity sizing and energy management model for a hybrid photovoltaic-hydrogen grid-connected building scenario.

In June 2019, the parliament passed a new legislation requiring the UK to bring down all greenhouse gas emissions (GHG) by 100% by 2050, compared to 1990 levels. The energy supply sector has been the second largest contributor to GHG emissions in 2020 after transport sector, constituting 21% of total GHG emissions. The admission of renewable energy systems into the grid is subject to significant variability due to their intermittency, requiring central generations to cover any transient variation between renewable power input and consumer demand. The proposed system will be based on PV and H2 Storage systems. During hours of high PV production, the excess energy from PV will be used to generate Green H2 by electrolyser, then the green H2 generated will be stored and discharged during the hours of off-peak generation and peak-load demand through a FC facility, to cover the shortage in PV production. The grid import will only take place to cover the deficit from both PV and H2 fuel cell

A new CFD approach for proppant transport in unconventional hydraulic fractures.

For hydraulic fracturing design in unconventional reservoirs, the existing proppant transport models ignore the fluid leak-off effect from the fracture side wall and the effect of fracture roughness. In this paper, a model is proposed using three-dimensional computational fluid dynamics approach with fluid leak-off rate defined along the fracture length and considering the effect of fracture roughness on proppant distribution. Based on the simulation results, it is recommended that neglecting the fracture roughness in the proppant transport model can result in over predicting the proppant bed length and underpredicting the proppant suspension layer by 10–15%. Furthermore, neglecting the fluid leak-off effect can result in under predicting the proppant bed height by 10–50% and over predicting the proppant suspension layer by 10–50%. This study has enhanced the understanding of the proppant-fracturing fluid interaction phenomenon by accounting detailed physics to optimise the hydraulic fracturing design