The effects of orientation of an inclined enclosure on laminar natural convection

Natural convective laminar flow is numerically investigated in a two-dimensional and square enclosure at various angles of inclination respect to horizontal. Two adjacent walls of the enclosure are insulated and the other two are kept at different temperatures. The influence of Rayleigh number representing the effects due to the differential heating of the enclosure walls as well as the effect of inclination angle on natural convection flow are studied. The flow field and isothermal lines show different patterns at high Rayleigh numbers. The average Nusselt number, maximum stream function and average temperature appear to be a little affected by the inclination angle at low Rayleigh numbers. However, as the Rayleigh numbers rises, these parameters behave differently at various inclination angles. In this study, the effects of inclination on the temperature along the centerline of the enclosure and the local Nusselt number along the cold wall are also examined. The results show negligible effects of inclination angle at low Rayleigh numbers and considerable effects at high Rayleigh numbers

Computational analysis of magnetohydrodynamic natural convection in a square cavity with a thin fin

A numerical study of laminar natural convection in a square cavity with a thin fin that is under the influence of a uniform magnetic field is presented. The side walls of the cavity are kept at different temperatures and the horizontal walls are thermally insulated. An Adaptive Network-based Fuzzy Inference System (ANFIS) approach and an Artificial Neural Network (ANN) approach are developed, trained and validated using the results of Computational Fluid Dynamics (CFD) analysis. The effects of pertinent parameters on fluid flow and heat transfer characteristics are studied. Among these parameters are the Rayleigh number (103≤≤;106), the Hartmann number (0≤&Ha;≤;100), the position of the thin fin (0.1≤ Y p≤) and the length of the thin fin (0≤Lp≤0.8). The results show that ANFIS and ANN can successfully predict the fluid flow and heat transfer behaviour within the cavity in less time without compromising accuracy. In most cases, ANFIS can predict the results more accurately than ANN

Improving the performance of the hardy cross algorithm for large ventilation models

The Hardy Cross algorithm offers a reliable method of solving network systems of fluid flow and has become widely used for solving water and ventilation flow networks. A limitation is that computational iterations and time to solve a network rises rapidly with the size of the model and modern detailed ventilation networks have typically grown to thousands of airways. Non-linear matrix solving methods can offer improved performance, however these are more complex and may be unstable if initial estimates are poor. This paper presents improvements that can be applied to the traditional Hardy Cross algorithm to greatly reduce iterations and solving time for large ventilation models

Recent developments in fibre optic shape sensing

This paper presents a comprehensive critical review of technologies used in the development of fibre optic shape sensors (FOSSs). Their operation is based on multi-dimensional bend measurements using a series of fibre optic sensors. Optical fibre sensors have experienced tremendous growth from simple bend sensors in 1980s to full three-dimensional FOSSs using multicore fibres in recent years. Following a short review of conventional contact-based shape sensor technologies, the evolution trend and sensing principles of FOSSs are presented. This paper identifies the major optical fibre technologies used for shape sensing and provides an account of the challenges and emerging applications of FOSSs in various industries such as medical robotics, industrial robotics, aerospace and mining industry

Numerical analysis of gas diffusion in drilled hollow–core photonic crystal fibres

Hollow-Core Photonic Crystal Fibres (HC-PCFs) have emerged as an area of interest for fibre-optic based distributed gas sensing. In order to allow the gas to enter the hollow core of the fibre, various techniques such as lateral drilled side holes have been investigated in the literature. However, it is essential to understand the mechanisms of gas flow in HC-PCFs with drilled side holes in order to determine the optimum design parameters of the sensor such as the size and spacing of drilled side holes. This study aims to analyse the gas flow behaviour and determine the response time of HC–PCFs with drilled side holes by developing and applying a numerical model based on gas diffusion in a microchannel. The model is validated against the results of two different experimental studies. The model is then applied to determine the response time is a function of the length, the number and spacing of side holes and the gas type (methane and acetylene). It is found that an inverse relationship exists between the effects of number and spacing of side holes on the response time and the optical loss, suggesting that an optimum design point exists

The effects of sample position and gas flow pattern on the sintering of a 7xxx aluminum alloy

The effects of sample position and gas flow pattern on the sintering of a 7xxx aluminum alloy Al-7Zn-2.5Mg-1Cu in flowing nitrogen have been investigated both experimentally and numerically. The near-surface pore distribution and sintered density of the samples show a strong dependency on the sample separation distance over the range from 2 mm to 40 mm. The open porosity in each sample increases with increasing separation distance while the closed porosity remains essentially unchanged. A two-dimensional computational fluid dynamics (CFD) model has been developed to analyze the gas flow behavior near the sample surfaces during isothermal sintering. The streamlines, velocity profile, and volume flow rate in the cavity between each two samples are presented as a function of the sample separation distance at a fixed nitrogen flow rate of 6 L/min. The CFD modeling results provide essential details for understanding the near-surface pore distribution and density of the sintered samples. It is proposed that the different gas flow patterns near the sample surfaces result in variations of the oxygen content from the incoming nitrogen flow in the local sintering atmosphere, which affects the self-gettering process of the aluminum compacts during sintering. This leads to the development of different near-surface pore distributions and sintered densities

Characterisation of creep in coal and its impact on permeability: An experimental study

Creep is a time-dependent deformation that affects coal permeability and should be considered in the prediction of Coalbed Methane (CBM) production. This study experimentally characterises and quantifies the impact of creep on coal permeability. The experiments were conducted on a bituminous coal sample, excavated from Bowen Basin, Australia, using a triaxial gas rig equipped with strain and displacement transducers. Two different types of gases (helium and methane) were injected into the sample under various stress and pore pressure conditions. It was found that for the experiments with helium, creep caused permanent partial closure of cleats and pathways under constant effective stress, and hence a reduction in permeability. Under hydrostatic stress only, a Residual Deformation Ratio (RDR) of 14.1% and a Permeability Loss Ratio (PLR) of 71% were found following the removal of the axial load. This can be due to the damage to coal microstructure along with closure of cleats. For the experiments with methane, coal experienced an instantaneous elastic deformation, at the onset of pore pressure depletion, followed by consolidation and matrix shrinkage. Then, creep occurred when gas desorption ceased. A total permeability loss of 26% was achieved due to an increase of 1.91 MPa in effective stress caused by gas desorption. In addition, the model previously developed by authors was validated against the experimental permeability data. A good agreement was found between the model-predicted permeability data and the experimental permeability data, particularly for higher pore pressure ranges