Biomass energy is becoming a promising option to reduce CO2 emissions, due to its renewability and carbon neutrality. Normally, biomass has high moisture and volatile contents, and thus its combustion behaviour is significantly different from that of coal, resulting in difficulties for large percentage biomass co-firing in coal-fired boilers. The biomass combustion behaviour at high temperatures and high heating rates is evaluated based on an updated single particle combustion model, considering the particle size changes and temperature gradients inside particle. And also the apparent kinetics determined by high temperature and high heating rate tests is employed to predict accurate biomass devolatilization and combustion performances. The time-scales of heating up, drying, devolatilization, and char oxidation at varying temperatures, oxygen concentrations, and particle sizes are studied. In addition, the uncertainties of swelling coefficient and heat fractions of volatile combustion absorbed by solid on the devolatilization time and total combustion time are discussed. And the characterised devolatilization time and total combustion time are finally employed to predict the biomass combustion behaviour. At the last, a biomass combustion/co-firing approach is recommended to achieve a better combustion performance towards large biomass substitution ratios in existing coal-fired boilers

12 13 For hydraulic fracturing design in unconventional reservoirs, the existing proppant transport 14 models ignore the fluid leak-off effect from the fracture side wall and the effect of fracture 15 roughness. In this paper, a model is proposed using three-dimensional computational fluid 16 dynamics approach with fluid leak-off rate defined along the fracture length and considering 17 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. Keywords Proppant transport; Hydraulic fracturing; Computational Fluid Dynamics; Discrete Element Method; Fluid Leak-off; Fracture Roughness Highlights-• Proppant transport in rough fractures with fluid leak-off from fracture wall • Parametric study of proppant properties, fluid properties, and fracture properties • Effect of using foam (Non-Newtonian) fracturing fluid Graphical Abstract-1. The advancements in the multistage hydraulic fracturing technology have resulted in the considerable progress in the hydrocarbon production in the last decade (Lange et al., 2013; Li et al., 2015; Yuan et al., 2018). Hydraulic fracturing is a technique in which fractures are initiated and propagated due to the injection of highly pressurised fluid at sufficiently high rates in the subsurface reservoir (Donaldson et al., 2014). When the fracture is estimated to be sufficiently long and wide, sand or other suitable material called proppants are injected with the additional fluid, to keep the fractures open against the rock pressure (Yew and Weng, 2014). The hydraulic fracturing in unconventional reservoirs is significantly different from the conventional reservoirs mainly because of the two reasons. Firstly, in conventional reservoirs, the focus of the hydraulic fracture design is to have a large fracture width, whereas, in the low permeability unconventional reservoir, greater fracture length is the prime factor to optimise (Belyadi et al., 2016). Secondly, slick water is commonly used as a fracturing fluid in the unconventional reservoir and due to the low viscosity of slick water and negligible chemical additive, tendency to suspend the proppant significantly decreases (Sahai et al., 2014). This results in early proppant deposition compared with conventional fracturing fluids (Alotaibi and Miskimins, 2015). Therefore, both of these attributes for the unconventional reservoirs, i.e. focus is on creating a longer fracture and early deposition of the proppants, result in closing of the unpropped section of the fr...

Biomass co-firing is becoming a promising solution to reduce CO2 emissions, due to its renewability and carbon neutrality. Biomass normally has high moisture and volatile contents, complicating its combustion behavior, which is significantly different from that of coal. A computational fluid dynamics (CFD) combustion model of a single biomass particle is employed to study high-temperature rapid biomass combustion. The two-competing-rate model and kinetics/diffusion model are used to model biomass devolatilization reaction and char burnout process, respectively, in which the apparent kinetics used for those two models were from high temperatures and high heating rates tests. The particle size changes during the devolatilization and char burnout are also considered. The mass loss properties and temperature profile during the biomass devolatilization and combustion processes are predicted; and the timescales of particle heating up, drying, devolatilization, and char burnout are compared and discussed. Finally, the results shed light on the effects of particle size on the combustion behavior of biomass particle

Numerical simulations of two-phase flow induced fluctuating forces at a pipe bend have been carried out to study the characteristics of multiphase flow induced vibration (FIV). The multiphase flow patterns and turbulence were modelled using the volume of fluid (VOF) method and the − turbulence model respectively. Simulations of seventeen cases of slug and churn flows have been carried out showing the effects of superficial gas and superficial liquid velocities. The simulations results show good agreement of the volume fraction fluctuation frequencies of slug and churn flows with the reported experiment. In addition, the vibration characteristics of the excitation force have been accurately captured. The simulation results show that the predominant frequency of fluctuations of force decreases and the RMS of force fluctuation increases with the increase of superficial gas velocity. On the other hand, both predominant frequency and the RMS of force fluctuations increases with the increase of superficial liquid velocity. Increase of gas fraction narrows the range of frequency ranges, while increasing the liquid expands the frequency ranges of force fluctuations.

CopyrightItems in 'OpenAIR@RGU', Robert Gordon University Open Access Institutional Repository, are protected by copyright and intellectual property law. If you believe that any material held in 'OpenAIR@RGU' infringes copyright, please contact openair-help@rgu.ac.uk with details. The item will be removed from the repository while the claim is investigated."NOTICE: this is the author's version of a work that was accepted for publication in Renewable Energy. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Renewable Energy, [VOL 50 (2013) AbstractThe present study focuses on the investigation of water dynamics inside a polymer electrolyte membrane fuel cell using two different modelling approaches: Eulerian two-phase mixture and volume of fluid interface tracking models. The Eulerian twophase mixture model has provided overall information of species distribution inside a fuel cell and identified that the liquid water usually accumulates under the land area.