Decrease In Volume Flow Rate Research Articles

Methane pyrolysis: Kinetic studies and mechanical removal of carbon deposits in reactors of different materials

CO 2 -free hydrogen can be produced by pyrolysis of methane using renewable energy. In a simple tubular reactor, however, carbon formation leads to clogging. The aim of this work is to deliberately coke reactors of different materials in order to investigate and characterize the mechanical removal of carbon. A design of experiments is used to study the influence of temperature, volumetric flow rate and methane mole fraction on the rate of reaction, which was followed by a kinetic fit of the methane pyrolysis process. The investigations show an increase in conversion with an increase in temperature and a decrease in volume flow rate, while methane mole fraction shows no significant influence. Fitting of collision factor, activation energy and reaction order results in deviations <10% between experiment and model. The force required for mechanical carbon removal can be decreased significantly by internally coating the reactor with calcium oxide. Using a simple plunger device, more than 90% of the agglomerated carbon can be removed easily from the reactors. • Design of Experiments and kinetic studies for four different reactor materials. • Kinetic modeling to describe carbon production and deposition. • Determination of force needed to remove carbon from simple tubular reactors. • Internally coating reactor with calcium oxide simplifies carbon removal.

Induced magnetic field effect on MHD free convection flow in nonconducting and conducting vertical microchannel walls

AbstractThe current examination employs a numerical analysis to ascertain the effect of the Eckert number along with the Prandtl number on a magnetohydrodynamic natural convection flow of an incompressible viscous fluid in which it is electrically conducting, passing through a perpendicular microchannel. Conduction along with non‐conducting immeasurable perpendicular walls within the existence of temperature and velocity slip at the microchannel is analyzed. The induced magnetic field (IMF) generated by the motion of an electrically conducting fluid in the presence of a transverse magnetic field is considered. The momentum and induction equations are coupled in the presence of an induced magnetic field. A set of similar variables are used to convert the governing set of equations to nonlinear‐coupled ordinary differential equations. With the aid of MATLAB in built solver is carried out to get the numerical solutions. The influences of Hartman number, Prandtl number, and Eckert number along with some physical parameters are explained through graphs. The results indicate that increasing the Hartmann and magnetic Prandtl numbers results in a significant decrease in volume flow rate.

Impact of roof geometry on cross-ventilation in vaulted buildings: a CFD study

The roof geometry is an important parameter in determining the natural cross-ventilation in buildings. Although many studies have been performed on natural ventilation, the impact of the large set of vaulted roofs on the building cross-ventilation remains to be addressed. In this paper, high-fidelity computational fluid dynamics (CFD) simulations, validated with experimental data, are performed on five naturally ventilated buildings with two opposing windows, each with a specific type of vaulted roof and otherwise identical, in 0° incident flow angle, to assess the impact of vaulted roof geometry on the building cross-ventilation performance. The following vault geometries are investigated and compared against a flat-roof building with the same specifications: (i) segmental, (ii) low-rise pointed, (iii) mid-rise catenary (iv) high-rise pointed and (v) high-rise catenary. The results show that compared to the flat-roof building, the vaulted roofs cause a <5% decrease in volume flow rate and 16-29% increase in the average mean velocity magnitude at the occupants’ level. In vaulted buildings, the low-velocity regions of the flow are moved further away from the occupied zone towards the ceiling, thus providing a fresher air to the occupants. The results clarify the high potential of vaulted roofs for natural ventilation and sustainable design.

Numerical modeling of annular flow with phase change in a microchannel

Phase change phenomena in microchannels have been projected as an effective option for thermal management of various microscale systems. However, for the design of heat sinks which utilize these phenomena, a clear understanding of the physical mechanisms involved, in the microscale domain, is required. In the present study, a numerical simulation is carried out to predict the characteristics of two phase flow with liquid to vapor phase change, in rectangular microchannels for a range of hydraulic diameters. The annular flow pattern, reported to be the most common in microchannel, has been investigated, with water as the flowing medium. The analysis considers, among other parameters, the effect of surface tension on the flow dynamics, which could be significant in microchannels. The mathematical model is numerically solved using a quasi-three dimensional approach, incorporating the variations in the cross-sectional areas of both the phases along the flow direction. Since it is expected that the continuum approximation may be insufficient in the vapor domain in channels of very small dimensions, an analysis incorporating slip flow at the liquid vapor interface analysis has been performed, where the channel dimensions produce Knudsen number values in the range 0.001–0.1, as suggested in the literature. The liquid film thickness along the flow direction is determined utilizing mass conservation, and the velocity distributions at different locations along the flow direction are obtained by solving the governing differential equations numerically. The two phase pressure drop is calculated for cases demanding slip and no slip conditions. A comparison has been made of the fluid flow characteristics, between the slip and no slip cases for the cases where slip flow is expected. The effects of the imposed heat flux, volume flow rate and channel geometry on the velocity distribution and pressure drop are examined. The predicted pressure drop values are found to increase with increasing heat flux, and decrease with an increase in the flow rate and the channel height. The two phase heat transfer coefficient and the wall temperature of the channel are also determined. The two phase heat transfer coefficient is found to increase with an increase in the vapor quality. It is also noticed that the wall temperature decreases along the length of the channel and the wall temperature at the exit of the channel decreases with decrease in volume flow rate, within the range of parameters used, which is in accordance with observations reported in the literature. The results are found to be in good agreement with the experimental and theoretical results available in the literature.

Correlation of cine MR velocity measurements in the internal carotid artery with collateral flow in the circle of Willis: preliminary study.

The velocity-phase relationship intrinsic to phase-contrast magnetic resonance (MR) angiography permits the quantitative and qualitative assessment of blood flow. The ability to measure velocity and vessel cross-sectional area allows noninvasive assessment of volume flow rate (VFR) in the internal carotid artery (ICA). Phase-contrast techniques also demonstrate flow direction. Using two-dimensional cine phase-contrast angiography, the authors evaluated VFR in the ICA and collateral flow about the circle of Willis in 15 patients with ischemic neurologic symptoms. The VFR in each carotid artery was correlated with the degree of stenosis and presence or absence of abnormal circle of Willis collateral flow. There was a correlation between a decrease in VFR and abnormal circle of Willis collateral flow. In addition, a correlation between severe stenosis and a decrease in VFR was found. In patients with ischemic neurologic symptoms without severe stenosis (< 70% diameter stenosis), no decrease in VFR was seen. It is hoped that flow quantification and directional flow imaging with phase-contrast angiography will help further characterize carotid artery occlusive disease by enabling assessment of VFR changes associated with ischemic neurologic symptoms. This study also supports the hypothesis that two mechanisms--hemodynamic and embolic--play a role in ischemic neurologic symptoms.

Regional blood flow in the cat retina

Linear and relative volume flow rates in arterioles of different calibre in different parts of the retina were studied in 12 cat eyes using high-speed cine fluorescein angiographic technique. The flow rates were correlated with areas of supply which were measured on photographs of the Indian ink injected retinas. A rapid and highly significant decrease in volume flow rate per unit area of retina was found from the disc to the periphery. This was due to decreasing linear flow rate per arteriolar calibre and increasing area of supply per arterioles of comparable calibre towards the periphery. The effects of different branching patterns on the vessel width and linear flow rate were compared.