Showing papers on "Volumetric flow rate published in 2010"

Cubic law with aperture-length correlation: implications for network scale fluid flow

Abstract: Previous studies have computed and modeled fluid flow through fractured rock with the parallel plate approach where the volumetric flow per unit width normal to the direction of flow is proportional to the cubed aperture between the plates, referred to as the traditional cubic law. When combined with the square root relationship of displacement to length scaling of opening-mode fractures, total flow rates through natural opening-mode fractures are found to be proportional to apertures to the fifth power. This new relationship was explored by examining a suite of flow simulations through fracture networks using the discrete fracture network model (DFN). Flow was modeled through fracture networks with the same spatial distribution of fractures for both correlated and uncorrelated fracture length-to-aperture relationships. Results indicate that flow rates are significantly higher for correlated DFNs. Furthermore, the length-to-aperture relations lead to power-law distributions of network hydraulic conductivity which greatly influence equivalent permeability tensor values. These results confirm the importance of the correlated square root relationship of displacement to length scaling for total flow through natural opening-mode fractures and, hence, emphasize the role of these correlations for flow modeling.

Conversion of carbon dioxide to value-added chemicals in atmospheric pressure dielectric barrier discharges

Abstract: The aim of this work consists of the evaluation of atmospheric pressure dielectric barrier discharges for the conversion of greenhouse gases into useful compounds. Therefore, pure CO2 feed flows are administered to the discharge zone at varying discharge frequency, power input, gas temperature and feed flow rates, aiming at the formation of CO and O2. The discharge obtained in CO2 is characterized as a filamentary mode with a microdischarge zone in each half cycle of the applied voltage. It is shown that the most important parameter affecting the CO2-conversion levels is the gas flow rate. At low flow rates, both the conversion and the CO-yield are significantly higher. In addition, also an increase in the gas temperature and the power input give rise to higher conversion levels, although the effect on the CO-yield is limited. The optimum discharge frequency depends on the power input level and it cannot be unambiguously stated that higher frequencies give rise to increased conversion levels. A maximum CO2 conversion of 30% is achieved at a flow rate of 0.05Lmin −1 , a power density of 14.75Wcm −3 and a frequency of 60kHz. The most energy efficient conversions are achieved at a flow rate of 0.2Lmin −1 , a power density of 11Wcm −3 and a discharge frequency of 30kHz. (Some figures in this article are in colour only in the electronic version)

Flow regime transition at high capillary numbers in a microfluidic T-junction: Viscosity contrast and geometry effect

Abstract: Flow regimes obtained as a consequence of two immiscible fluids interacting at a T-junction are presented for transitional to high capillary numbers and different ratios of the continuous and dispersed phase flow rates and viscosities. Results are presented for the formation of micron-sized droplets using simulations performed based on a three-dimensional lattice Boltzmann method. The influence of viscosity and geometry of the device on the frequency and volume of droplets formed has been examined and the nondimensional drop size correlated with the capillary number and flow rate ratio. This work reveals two important and new physical features: (a) the transition zone separating droplet and jet flows narrows for high capillary numbers and (b) the critical flow rate ratio separating droplet and parallel flows increases as the dispersed to continuous channel width ratio increases, aspects which have been correlated using a simple relation for both transitions from the droplet-at-T-junction to droplet-in-cha...

Ionic wind generation by a wire-cylinder-plate corona discharge in air at atmospheric pressure

Abstract: A wire-cylinder-plate electrode configuration is presented to generate ionic wind with a dc corona discharge in air at atmospheric pressure. The objective of the work is to maximize the power supplied to the flow in order to increase acceleration while avoiding breakdown. Thus, the proposed experimental setup addresses the problem of decoupling the mechanism of ion generation from that of ion acceleration. Using a wire-plate configuration as a reference, we have focused on improving the topography of the electric field to (1) separate the ionization and acceleration zones in space, and (2) guide the trajectory of charged particles as parallel to the median axis as possible. In the proposed wire-cylinder-plate setup, a dc corona discharge is generated in the space between a wire and two cylinders. The ions produced by the corona then drift past the cylinders and into a channel between two plates, where they undergo acceleration. To maximize the ionic wind it is found that the geometric configuration must be as compact as possible and that the voltage applied must be right below breakdown. Experimentally, the optimized wire-plate reference setup provides a maximum flow velocity of 8 m s−1, a flow rate per unit electrode length of 0.034 m2 s−1, and a thrust per unit electrode length of 0.24 N m−1. The wire-cylinder-plate configuration provides a maximum flow velocity of 10 m s−1, a flow rate per unit electrode length of 0.041 m2 s−1, and a thrust per unit electrode length of 0.35 N m−1. This 46% increase in thrust is obtained by increasing the electric power per unit electrode length by only 16% (from 175 to 210 W m−1), which confirms the gain in efficiency obtained with the decoupled system. In comparison with a simple wire-wire corona configuration, the wire-cylinder-plate configuration increases the ionic wind velocity by up to a factor of 3, and the thrust by an order of magnitude.

Experimental and Numerical Investigations of Two-Phase (Liquid−Liquid) Flow Behavior in Rectangular Microchannels

Abstract: The interaction between kinetics and mass-transfer effects is determined by the flow regime in liquid−liquid multiphase microreactors. The operating conditions under which the various flow regimes such as slug flow and stratified flow occur in liquid−liquid systems has not been extensively studied and is not well-understood. The effect of operating conditions on slug length for instance is not well-known. The present study focuses on microreactors fabricated in Perspex (poly(methyl methaacrylate) (PMMA)), which are essentially microchannels with a rectangular cross-section. Experiments are carried out for a wide range of flow rates, channel sizes, and fluid systems with varying properties. Two different kinds of flow regimes, slug flow and stratified flow, are experimentally observed, and these are predicted using numerical simulations. We divide the space of operating conditions (the two liquid flow rates) into different regions such that in each region the flow regime is distinct. The dependence of slug...

Melt Pool Temperature Control for Laser Metal Deposition Processes—Part I: Online Temperature Control

Abstract: Melt pool temperature is of great importance to deposition quality in laser metal deposition processes. To control the melt pool temperature, an empirical process model describing the relationship between the temperature and process parameters (i.e., laser power, powder flow rate, and traverse speed) is established and verified experimentally. A general tracking controller using the internal model principle is then designed. To examine the controller performance, three sets of experiments tracking both constant and time-varying temperature references are conducted. The results show the melt pool temperature controller performs well in tracking both constant and time-varying temperature references even when process parameters vary significantly. However a multilayer deposition experiment illustrates that maintaining a constant melt pool temperature does not necessarily lead to uniform track morphology which is an important criteria for deposition quality. The reason is believed to be that different melt pool morphologies may have the same temperature depending on the dynamic balance of heat input and heat loss.

Effects of Melt Pool Variables and Process Parameters in Laser Direct Metal Deposition of Aerospace Alloys

Abstract: Despite considerable advances in of laser direct metal deposition (LDMD) process optimization, there is rather limited work reported on the effects of melt pool variables on the final deposit characteristics. This article considers the effects of process parameters and melt pool characteristics on the deposition of Inconel 718 powder on a Ti-6Al-4V thin wall. A 1.5kW diode laser and LDMD system is used to produce a series of deposits. Images of the process are captured using Cu-vapor laser illumination and a high speed camera with long range microscopy optics, and quantitative results are extracted via image analysis. Process parameters such as carrier gas flow rate, powder mass flow rate and laser operating mode (CW and pulsed) and in process variables such as quantified melt pool disturbance, and final part characteristics are correlated and discussed. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and energy dispersive X-ray spectroscopy (EDS) are used to analyze deposited clads in terms of elemental composition and flow characteristics in the deposition melt pool. Melt pool disturbance is found to be a vital parameter in determining the surface roughness of the final part. An inverse relation between the mean surface disturbance of the melt pool and the surface roughness of the part is observed, and carrier gas flow rate and powder mass flow rate both affect the overall melt pool size. The work has implications for the selection of process parameters for commercial laser deposition processes-the speed with which powder is delivered to the melt pool as well as the mass flow rate may need to be taken into account when calculating build rate and for a good surface finish requiring minimum post process finishing a stable melt pool may actually be the worst situation.

Developments in the soluble lead-acid flow battery

Abstract: The history of soluble lead flow batteries is concisely reviewed and recent developments are highlighted. The development of a practical, undivided cell is considered. An in-house, monopolar unit cell (geometrical electrode area 100 cm2) and an FM01-LC bipolar (2 × 64 cm2) flow cell are used. Porous, three-dimensional, reticulated vitreous carbon (RVC) and planar, carbon-HDPE composite electrodes have been used in laboratory flow cells. The performance of such cells under constant current density (10–160 mA cm−2) cycling is examined using a controlled flow rate (mean linear flow velocity <14 cm s-1) at a temperature of approximately 298 K. Voltage versus time and voltage versus current density relationships are considered. High charge (<90%), voltage (<80%) and energy (<70%) efficiencies are possible. Possible failure modes encountered during early scale-up from a small, laboratory flow cell to larger, pilot-scale cells are discussed.

Engineering study of continuous supercritical hydrothermal method using a T-shaped mixer: Experimental synthesis of NiO nanoparticles and CFD simulation

Abstract: In the synthesis of metal oxide fine particles by continuous supercritical hydrothermal method, rapid mixing of starting solution with supercritical water is a key factor for producing nanoparticles that have a narrow size distribution. In this paper, continuous hydrothermal synthesis of NiO nanoparticles from Ni(NO3)2 aqueous solution at 400 °C and 30 MPa was carried out with T-shaped mixers and the effect of inner diameter, flow rate, and mixing directions on the particle size was examined. The computational fluid dynamics (CFD) simulation of the mixers was performed to evaluate the heating rate of the starting solution. When the inner diameter of the T-shaped mixer was decreased from 2.3 to 0.3 mm and the flow rate was increased from 30 to 60 g/min, the produced NiO particle size decreased remarkably from 54.3 to 20.1 nm. This trend of the decrease in particle size could be described as a function of the heating rate. The experimental and CFD results showed the detail regions of local heating that correlated with the NiO nanoparticle size.

Evaluation of Landfill Gas Decay Constant for Municipal Solid Waste Landfills Operated as Bioreactors

Abstract: Prediction of the rate of gas production from bioreactor landfills is important for the optimization of energy recovery and for estimating greenhouse gas emissions. To improve the predictability of gas production, landfill gas (LFG) composition and flow rates were monitored for 4 yr from one conventional and two bioreactor landfill cells at the Outer Loop Landfill in Louisville, KY. The ultimate methane yield (L 0) was estimated from the biochemical methane (CH4) potential of freshly buried refuse and the decay rate constant (k) was estimated from measured CH4 collection. The site-specific L 0 was estimated to be 48.4 m3-CH4 wet Mg−1. The estimated decay rate in the conventional cell (0.06 yr−1) was comparable to the AP-42 default value of 0.04 yr−1, whereas estimates for the two bioreactor cells were substantially higher (˜0.11 yr−1). The data document the ability of the bioreactor operation to enhance landfill CH4 generation, although the estimated decay rate is sensitive to the selected L0. Th...