Experimental Pressure Profiles Research Articles

Analysis of Fluid Flow Under a Grinding Wheel

Fluid flow under a grinding wheel is modeled using a perturbation scheme. In this initial effort to understand the flow characteristics, we concentrate on the case of a smooth wheel with slight clearance between the wheel and workpiece. The solution at lowest order is that given by standard lubrication theory. Higher-order terms correct for inertial and two-dimensional effects. Experimental and analytical pressure profiles are compared to test the validity of the model. Lubrication theory provides good agreement with low Reynolds number flows; the perturbation scheme provides reasonable agreement with moderate Reynolds number flows but fails at high Reynolds numbers. Results from experiments demonstrate that the ignored upstream and downstream conditions significantly affect the flow characteristics, implying that only a model based on the fully two- (or three-) dimensional Navier-Stokes equations will accurately predict the flow. We make one comparison between an experiment with a grinding wheel and the model incorporating a one-dimensional sinusoidal roughness term. For this case, lubrication theory surprisingly provides good agreement with experiment.

An axisymmetric model for fluid flow in the annulus of a spout-fluid bed

The axisymmetric model previously developed for spouted beds is adapted to describe fluid flow in the annulus of a spout-fluid bed at the minimum spout-fluid flow rate. Experimental axial pressure profiles provide the boundary condition at the spout-annulus interface. The fluid streamlines, residence time distribution, average residence time, average axial fluid velocity in the annulus and the fluid flow rate entering the annulus from the spout are all calculated. The fluid streamlines in spout-fluid beds are shown to be very different from those of spouted beds in the lower part of the annulus. Although the residence time distribution of the fluid percolating through the annulus of a spout-fluid bed is more uniform than that of a spouted bed, the average residence time does not vary significantly with the inlet fluid flow to the annulus.

Ballooning stability of JET discharges

Conditions under which ballooning modes are expected to be excited have recently been obtained in two different types of discharges in JET. In the first type, extremely large pressure gradients have been produced in the plasma core through pellet injection in the current rise phase followed by strong additional heating. In the second type, the total pressure of the discharge is approaching the Troyon limit (1988). The stability of these discharges with respect to the ideal MHD ballooning modes has been studied with the stability code HBT. The equilibria are reconstructed with the IDENTC code using the external magnetic measurements and the experimental pressure profile. The results show that the evaluated high beta discharge is unstable in the central region of the plasma. This instability is related to the low shear and not to a large pressure gradient, as expected at the Troyon limit. In the pellet discharges the regions with the large pressure gradients are unstable to ballooning modes at the time of the beta decay, which ends the period of enhanced performance. The maximum pressure gradient in these discharges is limited by the boundary of the first region of stability. The observed phenomena at the beta decay are similar to those observed at the beta limit in DIII-D and TFTR.

A study of injection molding. (4th Report, Analysis of pressure build-up during the packing and the cooling stage in the injection molding).

The fluid motion within the mold cavity during the packing and the cooling stages is studied. To evaluate the pressure history in the postfilling process of injection molding, an analytical approach is chosen. The fluid is considered as Newtonian, and its compressibility is explained by the Spencer-Gilmore equation. Also, the cooking effect during the whole process is considered. The results of the analysis are compared with the experimental pressure profile in the model die. The analytical pressure profile is in fairly good agreement with the experiment for different mold thickness parameters. The pressure drop by the cooling effect is also explained quantitatively.

Temperature, pressure and film thickness measurements for an offset half bearing

A fluid film journal bearing test rig with a shaft, 70 mm in diameter, was developed and an offset half journal bearing was tested at five vertical loads and two rotational speeds. The bearing had a length-to-diameter ratio of 1.00, a pre-load factor of 0.51 and an offset factor of 1.0. Loads from 0 to 4450 N and speeds of 2250 and 1650 rev min −1 were tested. On-rotor instrumentation and amplification are used to measure continuous fluid film pressures around the bearing, film thicknesses and journal temperatures. Slip ring telemetry is used to transmit the data to a real time data collection system. External instrumentation is used to measure film pressures and temperatures in discrete locations on the bearing surface, thus, allowing comparison with the on-shaft measurements. The eccentricity ratio and attitude angle are pressure measurements obtained indicate agreement within 5% between the results recorded by the on-shaft and the external pressure transducers. The experimental film thickness, temperature and pressure profiles and journal eccentricity agree with the expected behavior for this bearing type and are presented for Sommerfeld numbers from 0.41 to 2.2.

Pressure distribution in a two-roll mill.

An asymmetric pressure distribution in a pair of rolls rotating at equal and unequal speed for Newtonian fluid was obtained by lubrication model analysis and was compared with experimental values. The work was carried out with a pair of rolls of radius R = 8.2cin in the range of fluid viscosity μ = 1.5-15 Pa•s, half of minimum nip clearance h0 = 35-390μ/m, mean roll speed um = 0.26-1.56 m/s and roll speed ratio Nr = 0.5-7. The experimental pressure profiles and force separating rolls are well represented by the calculated values in the region of N''ca (= μuf(R/h0)2/γ)7, where γ is liquid surface tension. In the range of N''ca>2.5 × 107, the absolute values of the minimum pressure decrease with increasing N''ca. The theoretical pressure distribution can be well corrected by considering that the liquid film separating point predicted by the theory comes near to the minimum nip.

A two-phase flow model for geothermal wells in the presence of non-condensable gas

Quantitative information on the phenomena occuring during the upward flow of a geothermal fluid in water-dominated wells is a requisite for designing the wellhead system and optimizing resource exploitation. The geothermal fluid consists, for the most part, of a two-phase mixture of water containing dissolved salts, steam and non-condensable gases. Various, closely interrelated effects must therefore be taken into consideration: pressure drop of the rising fluid; heat and mass transfer between the phases (due to evaporation and desorption); heat exchange with rock formations. Simultaneous application of the mass, energy and momentum equations results in a rather complex model that can be solved by a numerical computer program. The model described here accounts for the effects of: the presence of salts, when computing all the thermodynamic properties of the fluids, especially enthalpy, density, vapour pressure of the brine and superheated steam enthalpy; the presence of non-condensable gases, considering their deviations from ideal behaviour and their contribution to density; the heat exchange with the surrounding rock formations; variation in salt concentration along the flow-path; possible variation in pipe diameter and surface roughness with height. The simplified hypotheses adopted are: fluid flow is stationary; thermodynamic equilibrium conditions exist between the phases in each point along the well; the non-condensable gases are assumed to be CO 2; Henry's law is assumed valid and the quantity dissolved chemically is assumed negligible; the salts are assumed to be NaCl; the activity coefficients are unitary; liquid surface tension and viscosity values are assumed equal to those of pure water. Comparison of the results of the computer program and the experimental pressure and temperature profiles shows that these are in satisfactory agreement within a rather wide range of operative conditions. The noncondensable gases, even in very low concentrations, were shown to be of importance to these calculations. Once the experimental temperature and pressure profiles are known, the model will also permit calculation of the concentration of non-condensable gases. The most efficient of the two correlations used to compute pressure drop in two-phase regimes seems to be that devised by CISE ‡ ‡ Centro Italiano Studi ed Esperienze, Milan, Italy. , which is based on global parameters not correlated to the different flow regimes.

Effects of diffraction on stress pulse propagation

Investigations have been made of the effect of diffraction on the propagation of acoustic impulses in water. Gaussian shape pressure pulses were obtained by applying 0.2-μs-wide voltage pulses to thick piezoelectric plates that act as piston sources. Acoustic probe techniques were used to examine in detail the resulting pressure profiles. These are strongly affected by diffraction phenomena, and because of the transient nature of the process, special care must be taken in interpreting the observed data. Comparisons between experimental and theoretical time and space pressure profiles are presented.

Effects of diffraction on pressure impulse propagation

Investigations are being made of the effect of diffraction on the propagation of acoustic impulses in water. Gaussian-shaped pressure pulses are obtained by applying 0.1 μsec wide voltage pulses to thick piezoelectric plates that act as piston sources. Acoustic probe techniques are being used to examine in detail the resulting pressure pulses. These are strongly affected by diffraction phenomena and, because of the transient nature of the process, special care must be taken in interpreting the observed data. Comparisons between experimental and theoretical time and space pressure profiles are presented. [Supported in part by the Office of Naval Research.]

Verification of a One-Dimensional Two-Phase Flow Model of the Frontal Gap in Electrochemical Machining

A set of six equations, which are based on the ECM model developed by Thorpe and Zerkle, can be solved numerically to yield the one-dimensional distributions of pressure, temperature, gas density, gap thickness, void fraction, and electrolyte velocity in the rectilinear ECM frontal gap under equilibrium conditions. The validity of the model, which also applies to radial flow geometries, is confirmed by comparing experimental pressure and gap profiles with theoretical predictions. It is shown that for a given set of operating parameters there is a minimum supply pressure below which no machining is possible. When machining steel with an aqueous NaCl electrolyte the deposition of a black smut (Fe(OH)2) occurs beyond a certain smut-free entrance length, which was experimentally found to be proportional to the inlet gap thickness.

An Analytical and Experimental Investigation of Turbulent Flow in Bearing Films Including Convective Fluid Inertia Forces

A means of handling both fluid film turbulence and the effects of fluid convective inertia in bearing films has been developed. The analysis employs a number of simplifying assumptions but has proved quite successful in the prediction of experimentally measured pressures. In this analysis turbulence is treated by means of turbulent viscosity correction factors. Convective inertia is accounted for by convective derivatives of mean fluid velocities averaged over the bearing film. Direct numerical solution of simultaneous equations representing conservation of momentum and fluid continuity is employed. The analysis developed is applied to pad bearings of arbitrary surface geometry, and has been incorporated in a computer program to calculate the film pressures developed in such bearings. Results from this program are compared with experimental pressure profile measurements made on a 12-in. dia, four pad, shrouded step journal bearing with silicone fluids as test lubricants. Good agreement is obtained for both concentric and eccentric operation.

Development of a Sonic Boom Simulator with Detonable Gases

A sonic boom pressure profile was simulated in the far-field by detonation of a methane-oxygen mixture contained in a slender, shaped Mylar envelope. Ideal N-waves were synthesized with peak overpressures from two to five psf and durations of 30 to 75 milliseconds. The detonation of the gas mixture was initiated by a single Primacord strand running the length of balloon. The N-wave producing balloon was synthesized as a composite structure, utilizing experimental pressure profiles obtained from the detonations of slender, axisymmetric balloons with elementary, non-cylindrical shapes.

Some Experiments at Low Speed on Compressor Cascades

Some results of recent work on low-speed cascade tunnels are described. Preliminary investigations, directed toward the analysis and improvement of the airflow and testing techniques, revealed that, when porous sidewall suction was employed, almost all change in axial velocity occurred within the blade row. Variation of axial velocity ratio, aspect ratio, Reynolds number, and turbulence level for one particular cascade facilitated an explanation of differences between the results of early British and American cascade tests. More recently, work has involved cascade tests on an analytically derived cascade. Good agreement was obtained between theoretical and experimental pressure distributions and profile boundary layers.