Showing papers on "Mass flow published in 2002"

Experimental studies on particle behaviour and turbulence modification in horizontal channel flow with different wall roughness

Abstract: Detailed measurements in a developed particle-laden horizontal channel flow (length 6 m, height 35 mm, the length is about 170 channel heights) are presented using phase-Doppler anemometry for simultaneous determination of air and particle velocity. The particles were spherical glass beads with mean diameters in the range of 60 µm–1 mm. The conveying velocity could be varied between about 10 m/s and 25 m/s, and the particle mass loading could reach values of about 2 (the mass loading is defined as the ratio of particle to gas phase mass flow rates), depending on particle size. For the first time, the degree of wall roughness could be modified by exchanging the wall plates. The influence of these parameters and the effect of inter-particle collisions on the profiles of particle mean and fluctuating velocities and the normalised concentration in the developed flow were examined. It was shown that wall roughness decreases the particle mean velocity and enhances fluctuating velocities due to irregular wall bouncing and an increase in wall collision frequency, i.e. reduction in mean free path. Thereby, the larger particles are mainly more uniformly distributed across the channel, and gravitational settling is reduced. Both components of the particle velocity fluctuation were reduced with increasing mass loading due to inter-particle collisions and the momentum loss involved. Moreover, the effect of the particles on the air flow and the turbulent fluctuations was studied on the basis of profiles in the developed flow and turbulence spectra determined for the streamwise velocity component. In addition to the effect of particle size and mass loading on turbulence modulation, the influence of wall roughness was analysed. It was clearly shown that increasing wall roughness also results in a stronger turbulence dissipation due to two-way coupling.

Mass flow ratio system and method

Abstract: A system for dividing a single mass flow, including an inlet adapted to receive the single mass flow and at least two flow lines connected to the inlet. Each flow line includes a flow meter and a valve. The system also includes a controller programmed to receive a desired ratio of flow through a user interface, receive signals indicative of measured flow from the flow meters, calculate an actual ratio of flow through the flow lines based upon the measured flows, and compare the actual ratio to the desired ratio. The controller is also programmed to calculate the desired flow through at least one of the flow lines if the actual ratio is unequal to the desired ratio, and provide a signal indicative of the desired flow to at least one of the valves.

Subsonic gas flow in a straight and uniform microchannel

Abstract: A nonlinear equation based on the hydrodynamic equations is solved analytically using perturbation expansions to calculate the flow field of a steady isothermal, compressible and laminar gas flow in either a circular or a planar microchannel. The solution takes into account slip-flow effects explicitly by utilizing the classical velocity-slip boundary condition, assuming the gas properties are known. Consistent expansions provide not only the cross-stream but also the streamwise evolution of the various flow parameters of interest, such as pressure, density and Mach number. The slip-flow effect enters the solution explicitly as a zero-order correction comparable to, though smaller than, the compressible effect. The theoretical calculations are verified in an experimental study of pressure-driven gas flow in a long microchannel of sub-micron height. Standard micromachining techniques were utilized to fabricate the microchannel, with integral pressure microsensors based on the piezoresistivity principle of operation. The integrated microsystem allows accurate measurements of mass flow rates and pressure distributions along the microchannel. Nitrogen, helium and argon were used as the working fluids forced through the microchannel. The experimental results support the theoretical calculations in finding that acceleration and non-parabolic velocity profile effects were found to be negligible. A detailed error analysis is also carried out in an attempt to expose the challenges in conducting accurate measurements in microsystems.

Experimental investigation of the performance of R22, R407C and R410A in several capillary tubes for air-conditioners

Abstract: The objective of this study is to present test results and to develop a dimensionless correlation on the basis of the experimental data of adiabatic capillary tubes for R22 and its alternatives, R407C (R32/125/134a, 23/25/52 wt.%) and R410A (R32/125, 50/50 wt.%). Several capillary tubes with different length and inner diameter were selected as test sections. Mass flow rate through the capillary tube was measured for several condensing temperatures and various degrees of subcooling at the inlet of each capillary tube. Experimental conditions for the condensing temperatures were selected as 40, 45 and 50°C, and the degrees of subcooling were adjusted to 1.5, 5 and 10°C. Mass flow rates of R407C and R410A were compared with those of R22 for the same test conditions. The results for straight capillary tubes were also compared with those of coiled capillary tubes. A new correlation based on Buckingham π theorem to predict the mass flow rate through the capillary tubes was presented based on extensive experimental data for R22, R407C and R410A. Dimensionless parameters were chosen considering the effects of tube geometry, capillary tube inlet conditions, and refrigerant properties. Dimensionless correlation predicted experimental data within relative deviations ranging from −12% to +12% for every test condition for R22, R407C and R410A. The predictions by the developed correlation were in good agreement with the results in the open literature.

Two-temperature coronal flow above a thin disk

Abstract: We extended the disk corona model to the inner region of galactic nuclei by including different temperatures in ions and electrons as well as Compton cooling. We found that the mass evaporation rate, and hence the fraction of accretion energy released in the corona, depend strongly on the rate of incoming mass flow from the outer edge of the disk, a larger rate leading to more Compton cooling, less efficient evaporation, and a weaker corona. We also found a strong dependence on the viscosity, with higher viscosity leading to an enhanced mass flow in the corona and therefore more evaporation of gas from the disk below. If we take accretion rates in units of the Eddington rate, our results become independent of the mass of the central black hole. The model predicts weaker contributions to the hard X-rays for objects with higher accretion rate like narrow-line Seyfert 1 galaxies, in agreement with observations. For luminous active galactic nuclei, strong Compton cooling in the innermost corona is so efficient that a large amount of additional heating is required to maintain the corona above the thin disk.

Peristaltic transport of blood in small vessels: study of a mathematical model

Abstract: The peristaltic flow of blood in small vessels is investigated in the paper by developing a mathematical model in which blood has been treated as a two-layer fluid where the core region is described by Casson model and the peripheral region is taken to be Newtonian viscous. Wave frame steady solutions for channel flow as well as axisymmetric flow are presented. Due care has been taken to consider the conservation of mass separately in the two layers. It is found that the higher the viscosity of the peripheral layer, the greater is the flow rate. Moreover, a thinner peripheral layer enhances the flow rate, whereas the flow rate reduces when the yield stress increases. It is further observed that the flow-rate in the case of a single layer is more than the two layer flow-rate when the peripheral layer is more viscous than the core layer. Besides, the flow-rate in the case of axisymmetric flow is always found to be much greater than that of channel flow under identical conditions.

Gaseous mixture flow through a long tube at arbitrary Knudsen numbers

Abstract: The mass flow, heat flux, and diffusion flux of rarefied gas mixture through a tube caused by gradients of pressure, temperature, and concentration were calculated over a wide range of the Knudsen number on the basis of the kinetic equation. The thermodynamic fluxes are presented in the form that allows us to prove the Onsager relations and then to reduce the number of kinetic coefficients determining the solution down to six. The numerical values of the kinetic coefficients are tabulated and the velocity profiles are given in figures.

Backward Traveling Rotating Stall Waves in Centrifugal Compressors

Abstract: Rotating stall waves that travel against the direction of rotor rotation are reported for the first time and a new, low-order analytical approach to model centrifugal compressor stability is introduced. The model is capable of dealing with unsteady radially swirling flows and the dynamic effects of impeller-diffuser component interaction as it occurs in centrifugal compression systems. A simple coupling criterion is developed from first principles to explain the interaction mechanism important for system stability. The model findings together with experimental data explain the mechanism for first-ever observed backward traveling rotating stall in centrifugal compressors with vaned diffusers. Based on the low-order model predictions, an air injection scheme between the impeller and the vaned diffuser is designed for the NASA Glenn CC3 high-speed centrifugal compressor. The steady air injection experiments show an increase of 25% in surge-margin with an injection mass flow of 0.5% of the compressor mass flow. In addition, it is experimentally demonstrated that this injection scheme is robust to impeller tip-clearance effects and that a reduced number of injectors can be applied for similar gains in surge-margin. The results presented in this paper firmly establish the connection between the experimentally observed dynamic phenomena in the NASA CC3 centrifugal compressor and a first principles based coupling criterion. In addition, guidelines are given for the design of centrifugal compressors with enhanced stability.Copyright © 2002 by ASME

Self-Recirculating Casing Treatment Concept for Enhanced Compressor Performance

Abstract: A state-of-the-art CFD code (APNASA) was employed in a computationally based investigation of the impact of casing bleed and injection on the stability and performance of a moderate speed fan rotor wherein the stalling mass flow is controlled by tip flow field breakdown. The investigation was guided by observed trends in endwall flow characteristics (e.g., increasing endwall aerodynamic blockage) as stall is approached and based on the hypothesis that application of bleed or injection can mitigate these trends. The "best" bleed and injection configurations were then combined to yield a self-recirculating casing treatment concept. The results of this investigation yielded: 1) identification of the fluid mechanisms which precipitate stall of tip critical blade rows, and 2) an approach to recirculated casing treatment which results in increased compressor stall range with minimal or no loss in efficiency. Subsequent application of this approach to a high speed transonic rotor successfully yielded significant improvements in stall range with no loss in compressor efficiency.

Progress toward gas atomization processing with increased uniformity and control

Abstract: Many advanced technologies based on particulate materials demand the availability of fine spherical powders or spherical powders of a narrow particle size class. Generally, high-pressure gas atomization (HPGA) is a close-coupled discrete jet atomization method and is one of the most effective methods of producing such powders. Development of HPGA nozzles with discrete jets resembling convergent–divergent (C–D) rocket nozzle designs, instead of the previous cylindrical jets, was conducted to increase atomization efficiency and uniformity and to reduce the required gas supply pressures. Results of compressible gas flow measurements on both types of HPGA nozzles revealed a steadily increasing trend of gas mass flow with gas supply pressure and a positive deviation from isentropic behavior that increases for increasing supply pressure. This has been attributed to an insufficient volume in the atomization nozzle gas manifold that experiences enhanced expansion cooling at increasing pressures. In experiments on 316L stainless steel, the atomization efficiency of the HPGA nozzle with C–D jets was higher than that of the HPGA nozzle with cylindrical jets, reflecting a lower gas/metal mass flow ratio. In other words, while the powder size distributions were nearly the same for all of the HPGA experiments, the HPGA nozzle with C–D jets utilized atomization gas with a significantly reduced operating pressure and mass flow rate.

Spark model of pulsed discharge in water

Abstract: Underwater sparks have long been used in many fields, but up until now there are no widely accepted model for them. In this article we present a more practical model for them, taking into account the nature of the plasma of pulsed discharge in water, where the following corrections are included: (1) correction of the ionization potentials; (2) pressure caused by the effect of charge interaction on the bound state electrons; (3) line spectra; and (4) mass flow caused by evaporation, condensation, and bubble wall ablation. Using this model, the time-varying pressure, temperature, and density can be obtained for given circuit parameters. The simulation results are in good agreement with the experimental measurements. We also give a simulation with capacitance of 1.25 nF, initial voltage of 4×104 V, circuit inherent inductance of 20 nH, and circuit resistance of 15 mΩ; the maxima of the pressure, temperature, and electron density are about 5×104 K, 5×103 atm, and 4×1026 m−3, respectively.

Unsteady Ejector Performance:An Experimental Investigation Using a Pulsejet Driver

Abstract: An experimental investigation is described in which thrust augmentation and mass entrainment were measured for a variety of simple cylindrical ejectors driven by a gasoline-fueled pulsejet. The ejectors were of varying length, diameter, and inlet radius. Measurements were also taken to determine the effect on performance of the distance between pulsejet exit and ejector inlet. Limited tests were also conducted to determine the effect of driver cross-sectional shape. Optimal values were found for all three ejector parameters with respect to thrust augmentation. This was not the case with mass entrainment, which increased monotonically with ejector diameter. Thus, it was found that thrust augmentation is not necessarily directly related to mass entrainment, as is often supposed for ejectors. Peak thrust augmentation values of 1.8 were obtained. Peak mass entrainment values of 30 times the driver mass flow were also observed. Details of the experimental setup and results are presented. Preliminary analysis of the results indicates that the enhanced performance obtained with an unsteady jet (primary source) over comparably sized ejectors driven with steady jets is due primarily to the structure of the starting vortex-type flow associated with the former.

Fluidic thrust vectoring for low observable aircraft

Abstract: The work presented in this paper deals with the development of a coflow fluidic thrust vectoring system for use on a low observable unmanned air vehicle operating in the subsonic flight regime. Two approximately 1/10 th scale fluidic thrust vectoring demonstrator rigs were designed and built in order to investigate the effect of various geometric variables on thrust vectoring effectiveness. These included secondary gap height, dh, and Coanda surface diameter, ∅. Load measurements were obtained using a six component overhead balance. The thrust vector force, Fz,tv, was made non-dimensional using the thrust force of the nonvectored primary jet, F x , to give a thrust vector coefficient, Cz. Tests were carried out over the mass flow ratio range 0 � m s /m p < 0.13 which corresponded to a momentum flow ratio range of 0 � Ms/Mp < 0.4. A computational investigation for 2D flow was also undertaken primarily to aid in the design of the experimental demonstrator rigs and smoke flow visualisation techniques were used to further investigate the flow characteristics of a non-vectored and a vectored primary jet. The investigation shows that both the experimental and computational results obtained follow a similar trend line. A ‘dead zone’ appears at low mass flow ratios in which no control can be achieved. There then follows a control region in which continuous thrust vector control can be achieved followed by a hypothetical saturation region. The secondary jet blowing rate, the Coanda surface diameter and the primary nozzle to secondary nozzle height ratio are seen to determine whether effective and efficient fluidic thrust vectoring can be achieved. Nomenclature Ap Cross sectional area of primary jet m 2 As Cross sectional area of secondary jet m 2

Velocity profile characterization in sub-millimeter diameter tubes using molecular tagging velocimetry

Abstract: Fluid flow through microtubes is of interest to many industries and there exists a need for detailed measurements of the velocity field. Velocity profile data are critical for momentum, mass, and heat transport analysis, and thus the design of devices utilizing microgeometries. This paper outlines a measurement technique that has led to time-resolved measurements of velocity profiles in microtubes (less than 1,000 μm). The research program was experimental in nature and consisted of an extension of molecular tagging velocimetry to the microscale. Average velocity and rms profile data in the fully developed region, in addition to mass flow rate and pressure drop data, are presented for numerous Reynolds numbers ranging from 600 to 5,000 in a tube of diameter 705 μm.

Pressure loss in constriction microchannels

Abstract: Constriction devices contain elements inserted into the fluid stream, which change the local streamwise flow area. One such element is the orifice-like obstruction with sharp corners, a back-to-back abrupt contraction and expansion, which could trigger flow separation. A series of microchannels, 40 /spl mu/m /spl times/ 1 /spl mu/m /spl times/ 4000 /spl mu/m in nominal dimensions, with constriction elements at the centers of the channels has been fabricated using standard micromachining techniques. The channel widths at the constriction sections varied from 10 /spl mu/m to 34 /spl mu/m, with pressure sensors integrated in each channel. Nitrogen gas was passed through the microdevices under inlet pressure up to 50 psi. The mass flow rates were measured for all the devices as a function of the pressure drop. A monotonic decrease of the flow rate with decreasing constriction-gap width was observed. The pressure distribution along the microchannel with the smallest constriction gap showed a pressure drop across the constriction element. Both mass flow rate and pressure measurements indicate that flow separation from the constriction sharp corners could occur.

Surge instability on a cavitating propeller

Abstract: The present study details results from experiments investigating a surge instability on a cavitating propeller. Initially, the stable behavior of the propeller is explored, and the nature and extent of the cavitation is documented at various experimental conditions, including propeller yaw. The cavitation surge instability is first explored through visual observation of the cavitation on the propeller blades and in the tip vortices. Particular note is made of similarities between the behavior of the re-entrant jets and that noted by other investigators. It is also observed that the nature of the instability is closely related to the partial cavity instability observed on single, two-dimensional hydrofoils. The flow conditions that lead to instability are determined and it is shown that onset corresponds to a specific configuration of attached cavity lengths on an individual propeller blade. Pressure measurements are obtained from transducers within the experimental facility, and the acoustic signature of the instability is identified. The magnitude of the fluctuating pressures is very large, presumably capable of producing severe hull vibration. A simple model is developed based on cavity volume estimates obtained from high speed video footage, and the predictions of the model are compared with the experimentally obtained pressures. To assess the significance of the surrounding facility in initiating and sustaining the instability, a model is developed for the experimental facility dynamics. The predictions of this model are then compared with an experimentally determined facility response to a volumetric excitation imposed by an oscillating piston. To quantify the response of the cavitation to fluctuations in test section conditions, quasistatic estimates are obtained for the cavitation compliance and mass flow gain factor of the propeller. These parameters have previously been employed in developing system transfer functions for cavitating pumps. Finally, a model is developed for the complete system, incorporating both the cavitation and facility dynamics. The model predicts active system dynamics and therefore potentially unstable behavior for two distinct frequency ranges, and one such range is hypothesized to correspond to the observed instability. The ability of the model to predict the observed characteristics of the instability is then evaluated.

Cht3d: fensap-ice conjugate heat transfer computations with droplet impingement and runback effects

Abstract: A conjugate heat transfer procedure including droplet impingement and runback effects is presented and validated against experimental data in a mist-flow heat exchanger configuration and an engine nacelle geometry. Computations include the solution of the air flow field, the prediction of water droplets motion and the evaluation of the cooling effect of the water film on the solid surface. The entire analysis is carried out using FENSAP-ICE (Finite Element Navier-Stokes Analysis Package for Inflight icing), a simulation system developed by Newmerical Technologies for icing applications. The numerical model is described, including the Navier-Stokes solution, the water thin film computation, the droplet impingement prediction and the conjugate heat transfer procedure. The predictions are verified against experimental data for different droplet mass flow rates, showing satisfactory agreement and allowing a useful insight in the physical characteristics of the problem. NOMENCLATURE CD Air-droplet drag coefficient Cp Specific heat [kJ/kgK] D Tube diameter [m] d Droplet diameter [m] G Droplet mass flow rate [kg/mh] h Heat transfer coefficient [kW/m K] HQ Total enthalpy [kJ/kg] K Droplet inertia parameter k Thermal conductivity [kW/mK] L Reference length [m] raj Impinging mass flow [kg/s] t Associate Fellow. AIAA Copyright ©2002 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc., by permission mev Evaporating mass flow [kg/s] rrifin Incoming film mass flow [kg/s] M Molecular weight [kg/kmol] mev Evaporating mass flow [kg/s] N Finite element shape function p Static pressure [Pa] Pr Prandtl number q Specific heat flux [kW/m] Qa Conduction heat flux from the wall [kW] Qa Convective heat flux to the air [kW] Red Droplet Reynolds number Sc Schmidt number T Static temperature [K] Tf Film temperature [K] Tfin Incoming film temperature [K] Td Droplet temperature [K] Tr Kinetic heat contribution for droplets [K] UOQ Reference air velocity [m/s] v, Vi Air velocity vector and i-th component [m/s] v, v\ Droplet velocity vector and i-th component [m/s] X, Y Dimensional spatial coordinates [m] x, y Non-dimensional spatial coordinates a Liquid volume fraction /3 Collection efficiency 6ij Kronecker delta A Latent heat of evaporation [kJ/kg] ^ Dynamic viscosity [kg/ms] Q/, Q, Fluid and solid domain p Air density [kg/m] F Solid Fluid interface Tij Shear stress tensor component [N/m]