Small Mass Flow Research Articles

A 3D Numerical Study of Fluid Flow and Heat Transfer in a Single Screw Extruder

Abstract A numerical study of three-dimensional fluid flow and heat transfer in the metering section of a single screw extruder has been performed. The screw channel was simplified by unwinding the channel and the coordinate system was fixed on the screw root in the present model. The pressure distribution over the inlet region was to be extrapolated from the solution of interior pressure. The prescribed mass flow rate was imposed on the outlet of the unwinding screw channel. The three-dimensional velocity fields, temperature, viscosity, and pressure profiles in the screw channel were calculated by using the commercial code, STAR-CD, based on the finite volume method. Some of the results of the present full 3D model were compared with the results from the marching-type 3D model. It is shown that the present work can capture the back flow by the pressure gradient near the screw root in the cases of small mass flow rates. There exist significant discrepancies in temperature between the marching-type 3D model and the present 3D model. The present work well describes the effects of heating-up through the circulation flow and viscous dissipation. The cross-section contours of velocities, temperature, viscosities and pressures along the down-channel direction are also shown in this study.

Influence of inlet pressure and mass flow rate on the temperature rise of superconducting strands in SSTF under the normal operating conditions [of KSTAR

In order to estimate the operating characteristics of the main coils, blip and compensating coils of SSTF (Samsung superconducting test facility) which will be operated under the pulsed field to simulate the operating scenarios of KSTAR (Korean Superconducting Tokamak Advanced Research), an analysis has been performed to study the influence of cryogenic parameters, such as inlet temperature, pressure and mass flow rate on the temperature margin for the main, blip and compensating coils. The temperature margin is studied under the given operating scenarios. The reduction of mass flow rate and peak temperature rise, which are strongly depending on the inlet pressure and inlet position of supercritical helium in the CICC are studied. It is noticed that the initial mass flow rate remarkably influences on the peak temperature of superconducting strands. The large mass flow rate can reduce the temperature rise when the helium inlet is installed at the high field region. On the other hand, the small initial mass flow rate results in the low peak temperature in strands when the helium inlet is located at the low field region, since the heat induced flow occurs to improve the cooling condition of the superconducting strands.

Evaluation of Flammable Gas Detector Networks Based on Experimental Simulations of Offshore, High Pressure Gas Releases

Data from detailed experimental measurements of the dispersion of natural gas following high pressure releases in a naturally ventilated, simulated offshore process module were used to examine how flammable gas detector networks would respond to the releases. A network of gas detectors was simulated, incorporating detector alarm levels and response times, based on current industry practice; the response of this network to the gas releases was evaluated using various criteria. The response times of the networks were also optimized by altering the number, location and type of gas detectors used. Infrared point detectors on a 5 m grid successfully detected all releases before a 5 m diameter explosive cloud formed; catalytic detectors failed to achieve this. Examination of infrared beam detector performance indicated that due to wider coverage and faster response time they could achieve shorter detection times with fewer detectors than infrared point detectors. While large mass flow rate releases were detected, the time available before formation of significant explosive clouds was very short. Small mass flow rate releases were hard to detect, even when the total amount released became large. Well-placed detectors can improve the performance of a detection system and emphasizes the need for understanding of gas dispersion, ventilation and knowledge of the processes being undertaken in a module and their layout when deciding detector placement.

Positive feedback stabilization of centrifugal compressor surge

Stable operation of axial and centrifugal compressors is limited towards low mass flows due to the occurrence of surge. The stable operating region can be enlarged by active control. In this study, we use a control valve which is fully closed in the desired operating point and only opens to stabilize the system around this point. As a result, only nonnegative control values are allowed, which complicates the controller design considerably. A novel positive feedback controller is proposed which is based on the pole placement technique. This controller has been successfully applied to a laboratory-scale gas turbine installation. Initial experiments show that the surge point mass flow can be reduced by at least 7%. Using this efficient control strategy, stable operation in the desired operating point is maintained with small average control valve mass flow.

AC losses and heat removal in three-dimensional winding pack of Samsung superconducting test facility under pulsed magnetic field operation

The Samsung superconducting test facility (SSTF) will be operated under the highly pulsed field to simulate the operating conditions of KSTAR. An analysis has been performed to study the transient heat removal characteristics and temperature margin for the main, blip and compensating coils in the SSTF. This method is based on a quasi-three-dimensional model, which the thermal coupling of turn-to-turn, pancake-to-pancake and channel-to-channel is taken into account, to simulate the conductor temperature rise and the thermal expansion of supercritical helium due to the high AC losses under the pulsed field. The local AC losses, which include coupling loss, eddy current loss and hysteresis loss in the cable-in-conduit conductor, are estimated. The temperature margin, mass flow rate, distribution of AC losses are studied under the given operating scenario. The mass flow reduction and peak temperature rise depending on the inlet pressure and inlet position of CICC are studied. It is shown that the initial mass flow rate remarkably influences on the peak temperature of superconducting strands. The large mass flow rate can reduce the temperature rise when the inlet of helium is located at the high field region. By contrast, because of heat induced flow to improve the cooling condition of the superconducting strands, the small initial mass flow rate results in the low peak temperature in strands when the inlet of helium is located at the low field region.

G211 極細管強制対流沸騰熱伝達に関する研究(オーガナイズドセッション11 : マイクロ熱流体システム)

The convective boiling in a micro tube of 0.3 mm ID was investigated with relatively small wall heat fluxes and mass flow rates. In this experiment, we have found some peculiar superheat phenomenon, which deteriorates the heat transfer coefficient and makes the pressure loss larger. The degree of the superheat is dependent upon fluids and influenced by the specified wall heat flux. Their relationship is given in the form of the flow map with two distinct zones.

Development of a transfer standard with sonic Venturi nozzles for small mass flow rates of gases

We have developed a transfer standard system with sonic Venturi nozzles for small mass flow rates of gases. The system is composed of a newly developed automatic pressure controller, two pressure sensors and one temperature sensor to measure the flow conditions in the upstream and downstream sides of a nozzle. The whole system is packed in a portable aluminum trunk. The data are sent to a laptop computer, and the results are displayed on the screen and are written to files. The system can calibrate a flow meter in the flow rate range from 10 mg/min to 100 g/min using ten different sonic Venturi nozzles with the expanded standard uncertainty ( k=2) being less than 0.2% for nitrogen. Examples of mass flow controller calibrations are given.

Heat and mass transfer processes in two phase He II/vapor

Modeling heat and mass transfer characteristics of two phase He II is discussed. The case considered assumes that the channel flow is one-dimensional and stratified, with mass exchange between the two phases. Two specific examples are considered in some detail. The first is the heat and mass transfer characteristics for small liquid flow rate. Use of several simplifying assumptions allows the problem to be reduced to solution of a one-dimensional ordinary differential equation. The result is a non-dimensional expression for the liquid level or void fraction along the channel. A set of dimensionless parameters are defined that establish the relative contributions of vapor mass transport and counterflow in the He II. The model also predicts the temperature profile and vapor mass flow rate. The second case concerns the flow of liquid under nearly isothermal conditions with relatively small vapor mass flow rate. Under these conditions, the flow may be modeled using classical hydrodynamics taking into consideration the unique characteristics of the He II. Results of these models are compared to experimental data for heat and mass transfer in a two phase He II/vapor flow.

SIZE SEGREGATION DURING MASS FLOW—EFFECT OF DEPOSITION METHOD AND BIN SIZE

ABSTRACT Size-Segregation of granulated sugar during discharge from hopper bins was studied, with respect to the effect of bin size and bin fill method. Particle size distributions (PSDs) were analyzed from large and small mass flow hopper bins, using three different fill methods. Spoon-by-spoon deposition was used as a control, whereas funnel fill and inverted cone deflector fill were used to model industrial fill methods. Samples were taken during the discharge of the bins and PSDs were analyzed. For all three bin fill methods and both bin sizes, the PSDs were within the 95% confidence interval of the original, in bag, sugar PSD. The worst case scenario occurred at the 250 μm sieve size, where the greatest percent difference from original PSD value was observed. At 50% discharge for the 250 μm sieve the small (large) bin showed a maximum percent difference for spoon-by-spoon, funnel and inverted cone deflector fill of 21(4), 10 (9) and 6 (28), respectively. For the small and large bins, the largest percent differences of 49 and 37, respectively, occurred at 40% and 20% material discharged, respectively. The bin fill method did not affect the PSD significantly based on 95% confidence interval.

Development of the Calibration Facility for Small Mass Flow Rates of Gases and the Sonic Venturi Nozzle Transfer Standard.

A calibration facility based on gravimetric method has been developed at NRLM for small mass flow rates of gas. This calibration facility establishes a primary gas flow rate measurement standard in Japan with an extended standard uncertainty of 0.12 percent at maximum, in mass flow rates from 0.01 g/min to 50 g/min for nitrogen. Five sonic Venturi nozzles were tested using this facility and the results showed that they can work well as a flow transfer standard for small mass flow rates. These sonic Venturi nozzles can be used to establish flow transfer standards within an extended standard uncertainty of 0.15 percent.

Development of the Calibration Facility for Small Mass Flow Rates of Gases and the Sonic Venturi Nozzle Transfer Standard.

A calibration facility based on the gravimetric method has been developed at NRLM for small mass flow rates of gases. This calibration facility establishes a primary gas flow measurement standard in Japan with an expanded maximum uncertainty of ±0.12 percent for small mass flow rates from 0.1 g / min to 50 g / min for nitrogen gas. Five sonic Venturi nozzles were tested using this facility and the results showed that they can work well as a flow transfer standard for small mass flow rates. These sonic Venturi nozzles can be used to establish flow transfer standards within an expanded uncertainty of ±0.15 percent.

International comparison of a NIST primary standard with an NRLM transfer standard for small mass flow rates of nitrogen gas

International comparisons of small gas flow measurements were carried out between the National Institute of Standards and Technology (NIST) in the United States of America and the National Research Laboratory of Metrology (NRLM) in Japan. An NRLM transfer standard package composed of sonic venturis, two pressure transducers, and two temperature sensors was calibrated using the NRLM primary standard for low gas flows (a gravimetric system) and was brought to the US in April 1996. The NRLM transfer standard was compared with the NIST Fluid Flow Group piston provers (a volumetric system) using mass flow rates of nitrogen between 0.4 g/min and 11.5 g/min. The mean differences between the NRLM transfer standard and the NIST Fluid Flow Group piston provers ranged from -0.09 % to +0.13 %.

Propellant Utilization in Hall Thrusters

Fuel optimal trajectories for electrically propelled spacecraft require a varying thrust acceleration. To achieve this requirement the electric thruster has to be operated with a variable thrust to power ratio at the maximum available input power. In order to implement this operating mode with a Hall thruster it is necessary to modify both the mass flow rate and the discharge voltage during the flight time. A crucial problem, associated with Hall thruster operation in a variable thrust mode, is the degradation of thruster performance under mass flow rate variations. Experiments with a laboratory Hall thruster have indicated that this degradation is mainly caused by a reduction of the propellant utilization at lower values of the mass flow rate. Modifying the channel geometry, namely, the channel length and channel profile, improvements in the behavior of the propellant utilization at small mass flow rate and consequently an improved thruster performance have been achieved. Results of experimental tests of a Hall thruster at various operating points and geometry are presented.

Development of a calibration facility for small mass flow rates of gas and the uncertainty of a sonic venturi transfer standard

A calibration facility based on the gravimetric method has been developed at NRLM for small mass flow rates of gas. This calibration facility establishes a primary gas flow measurement standard with a combined standard uncertainty of ±0.105% at maximum, for mass flow rates up to about 5 g/min. Two differently sized sonic venturis were tested using this facility and the results show that they can work well as a flow transfer standard for small mass flow rates. It is also shown that these sonic venturis can be used to establish flow transfer standards with a combined standard uncertainty of ±0.112% for the larger venturi and ±0.089% for the smaller venturi.

Application of pressure sensors to the measurement of small liquid mass flows

New Technologies applied to the manufacture of sensors permit us to obtain more sensitive devices of high linearity that, with suitable conditioner circuits, can be incorporated into digital control systems by means of a control and acquisition data board. In this paper a method is described based on pressure sensors which can measure small flows (in the range 0 - 10 ) such as those generated in transportation through membranes. This problem was treated previously by means of an automated flowmeter, using a programmable logic controller (Forte J et al 1990 Rev. Sci. Instrum. 61 1123 - 6). The main problem that we attempt to solve is that of on-line flow measurement, to know the flow at each moment and to take corresponding action in the experimental system. Another method was used before (Molina C et al 1995 Rev. Sci. Instrum. 65 2726 - 30) but, if we wanted to make measurements at different temperatures, we had to obtain another calibration curve.

Late Quaternary sediment, sediment mass flow processes and slope stability on the Scotian Slope, Canada

ABSTRACTThe study area, just to the west of the Verrill Canyon on the Scotian Slope, eastern Canada, exhibits both large and small scale sediment mass movement features. Study of high resolution seismic reflection and sidescan sonar data shows that a large portion (approximately 70%) of the near surface sediment (<20 m) in the area has undergone erosion, rotational slumping and internal deformation. Remoulded sediment observed in physical properties profiles of piston cores and sediment deformation structures are further evidence of slumping. Small scale mass flow events are recorded by abundant turbidites and debris flow deposits noted in piston cores. Sediment physical properties are highly dependent on sediment type (lithofacies). Frequent facies changes, both temporally and spatially, make correlation between cores difficult.Although the small scale mass movement events correlate with glacial recession on the continental shelf and lower relative sea levels, the triggering mechanisms for the large scale events are less obvious. Slope stability analyses indicate that, at present, the seabed is stable. The most plausible explanation for large scale slope failures in this region are ground accelerations related to earthquake shock. Our analyses demonstrate that it is unlikely that large magnitude, distant earthquakes, such as those previously proposed in the Laurentian Slope Seismic Zone (LSP) model, could initiate failure of sediment in the study region. Our data support the interpretation that more frequent, lower magnitude earthquakes, closer to the study region, as previously proposed in the Eastern Slope Experimental Source Zone (ESX) model, are the likely causes of large scale slope failures. Furthermore, excess pore pressures resulting from shallow gas and/or high sedimentation rates during deglaciation contribute to slope failure.

Mixed convection heat and Mass transfer in a vertical channel with film evaporation

AbstractNumerical results are presented for effects of latent heat transport associated with film vaporization on laminar mixed convection heat and mass transfer in a vertical channel with a half channel width b = 0.01 m. The influences of the inlet liquid mass flowrate and wall temperature on the film vaporization and the associated heat and mass transfer characteristics are examined for air‐water and air‐ethanol systems with gas Reynolds number Reg = 2000. Predicted results obtained by including transport in the liquid film are contrasted with those where liquid film transport is neglected, showing that the assumption of an extremely thin film made in Lin et al. (1988) and Yan and Lin (1989) is only valid for systems having small liquid mass flow rates. Additionally, it is found that the interfacial heat flux is predominantly determined by latent heat transfer connected with film evaporation.

Effects of film evaporation on laminar mixed convection heat and mass transfer in a vertical channel

A numerical study of finite liquid film evaporation on laminar mixed convection heat and mass transfer in a vertical parallel plate channel is presented. The influences of the inlet liquid mass flow rate and the imposed wall heat flux on the film vaporization and the associated heat and mass transfer characteristics were examined for air-water and air-ethanol systems. Predicted results obtained by including transport in the liquid film are contrasted with those where liquid film transport is neglected, showing that the assumption of an extremely thin film made by Tsay and Yan ( Wärme- und Stoffübertragung 26, 23–31 (1990)) is only valid for a system with a small liquid mass flow rate. Additionally, it is found that the heat transfer between the interface and gas stream is dominated by the transport of latent heat associated with film evaporation. The magnitude of the evaporative latent heat flux may be five times greater than that of sensible heat flux.

Vertical two-phase flow in porous media

New concepts are introduced to describe single-component two-phase flow under gravity. The phases can flow simultaneously in opposite directions (counterflow), but information travels either up or down, depending on the sign of the wavespeedC. Wavespeed, saturation and other quantities are defined on a two-sheeted surface over the mass-energy flow plane, the sheets overlapping in the counterflow region. A saturation shock is represented as an instantaneous displacement along a line of constant volume fluxJ Q in the flow plane. Most shocks are of the wetting type, that is, they leave the environment more saturated after their passage. When flow is horizontal all shocks are wetting, but it is a feature of vertical two-phase flow that for sufficiently small mass and energy flows there also exist drying shocks associated with lower final saturations.

Combined heat and mass transfer in natural convection between vertical parallel plates with film evaporation

A numerical analysis is carried out to investigate the effects of latent heat transfer, in association with the evaporation of a finite liquid film on the channel wall, on the natural convection heat and mass transfer. Results for heat and mass transfer rates are specifically presented for the systems with ethanol film evaporation and water film evaporation. The predicted results with the transport in the liquid film treated are contrasted with those with the transport in the liquid film untreated and show that the assumption of an extremely thin film is only valid for a system with small liquid mass flow rate. But for a system with a large liquid mass flow rate, the assumption becomes inappropriate.