Showing papers on "Pressure drop published in 1986"

A simple friction pressure drop correlation for two-phase flow in pipes

Abstract: A new correlation for the prediction of frictional pressure drop for two-phase flow in pipes is suggested which is simple and more convenient to use than other methods. To determine their reliabilities, this correlation and fourteen correlations from the literature were checked against a data bank containing 9300 measurements of frictional pressure drop for a variety of fluids and flow conditions. It was found that the best agreement between predicted and measured values was obtained using the correlation suggested by Bandel. Somewhat less but still reasonable accuracy of pressure drop prediction is provided by a group of identified correlations, which includes the correlation described in this paper.

Drop breakup in turbulent stirred‐tank contactors. Part I: Effect of dispersed‐phase viscosity

Abstract: The extent to which dispersed-phase viscosity influences equilibrium mean drop size and drop size distribution at constant interfacial tension is determined for dilute suspensions by dispersing silicone oils of various viscosity grades in water. A mechanistic model for mean drop size is developed which predicts the moderate-viscosity data and whose parameters correlate the high-viscosity results. Trends in the mean size data coincide with those for the drop size distribution, which broadens considerably as viscosity increases and suggests a dependency on breakage mechanism.

Impingement cooled transition duct

Abstract: A transition duct in an advanced heavy duty gas turbine engine is cooled by impingement jets formed by apertures in a sleeve spaced a distance from the surface to be cooled. The sleeve is configured so as to duct spent impingement air towards the combustor, where it can be subsequently used for mixing with, and combustion of, the fuel, or for cooling of the combustor. The distance between the impingement sleeve and the transition duct surface is varied to control the velocity of air crossflow from spent impingement air in order to minimize the pressure loss due to crossflow. The cross-sectional areas of the apertures are varied to project impingement jets over the various distances and crossflow velocities. Generally, larger aperture areas are used with larger distances. The distance between the impingement sleeve and the transition duct systematically increases towards the combustor as the quantity of spent impingement air increases to a maximum value at the intersection of the combustor and the transition duct. The combination of variations in distance, aperture size, and inter-aperture spacing is utilized to vary the impingement cooling intensity to compensate for the variable internal heat load and also to produce the desired temperature distribution over the surface of the transition duct according to design requirements. The aforementioned variations are optimized to minimize the air flow pressure drop ahead of the combustion system which achieving the required cooling intensity according to design requirements.

Distillation Tray Fundamentals

Abstract: Preface Acknowledgements Nomenclature 1. Some general considerations 2. Bubbles, froth, spray and foam 3. Clear liquid height, dispersion height and density 4. Pressure drop 5. Maximum capacity 6. Weeping 7. Tray efficiency 8. Point efficiency 9. relationship between point efficiency and tray efficiency 10. Prediction on efficiency for multicomponent mixtures Appendix A. Horizontal momentum balance over the exit calming zone Appendix B. Apparent Murphree vapour-phase tray efficiency in the presence of entrainment and weeping References Index.

The hydrodynamics of trickling flow in packed beds. Part II: Experimental observations

Abstract: The liquid holdup and the pressure drop for two-phase trickling flow in a packed bed were measured experimentally. Different values of those parameters were obtained as the liquid flow rate was increased and then decreased, indicating a multiplicity in hydrodynamic states. This behavior was observed even when the gas flow rate was zero in the bed. It was determined that the hysteresis exhibited by the process is due to imperfect wetting of the packing and to the difference between advancing and receding contact angles at the gas-liquid-solid contact lines. The reduced wetting conditions are also the cause of the increase in liquid holdup observed when the surface tension of the liquid is decreased. In this case, the amount of liquid retained in the bed is controlled by the extension of the wetted regions due to the more favorable contact angles as the surface tension decreases. The transition from the trickling to the pulsing flow regime was also dependent on the history of the process. A new correlation for predicting liquid holdups and pressure drops for trickling flow in packed beds is proposed for the decreasing liquid flow rate operating mode. This correlation is based on the experimental determination of the liquid phase relative permeability as a function of the the liquid phase reduced saturation and the determination of the gas phase relative permeability as a function of the gas phase saturation and the gas phase Reynolds number. The new data are analyzed in the light of the theory developed in the first part of this paper.

Laminar compressible flow in a tube

Abstract: A two-dimensional solution for the velocity and pressure distributions in steady, laminar, isothermal flow of an ideal gas in a long tube is obtained as a double perturbation expension in β, the radius to length ratio, and e, the relative pressure drop. It is found that simple approximations estimate the exact flow rate-pressure drop relationship accurately.

Optimal structure for microgrooved cooling fin for high-power LSI devices

Abstract: We have evaluated the relationship between the cooling capability and the channel width with a constant pressure drop for microgrooved cooling fins, and found that there are optimal channel widths which give rise to the maximum allowable power density. There are also optimal microgrooved cooling fin structures in which enlarged channel widths are sufficient to cool high-power-consumption wafer-scale integrated chips with a pressure drop of only 200 kg/m2.

Determination of Proppant and Fluid Schedules From Fracturing-Pressure Decline

Abstract: A procedure is presented for designing a fracture treatment when little or no information is available. This procedure is based on fluid efficiency, which is defined as the fracture volume divided by the injected fluid volume. The fluid efficiency for a treatment was found to determine the pad size and optimum proppant schedule completely without any assumption of the appropriate fracture-geometry model or associated parameters. The efficiency was also found to determine the fluid's exposure time to temperature. This determination requires an assumption for the portion of the fracture face that is cooled during a treatment. The exposure is important for defining the fluid additives of relatively large and high-temperature treatments. The fluid efficiency can be determined from a pressure-decline analysis for a calibration treatment performed before the actual stimulation treatment. In addition, if the appropriate geometry model is assumed, the decline analysis of the calibration treatment provides inferred values of fluid-loss coefficient and fracture width and penetration. Also, for the case when the calibration treatment is smaller than the actual stimulation, analyses are presented for predicting the relative change in efficiency, width, and penetration for the treatments.

Theoretical and experimental studies on vortex chamber flows

Abstract: Analytical and experimental studies to investigate selected fluid parameters in vortex chambers are presented. From the analytical model, the dimensionless quantities of the core size, static pressure drop across the chamber, and radial static pressure distribution are shown to be functions of the chamber geometry only. Experimental results confirm all of the findings.

Supercritical fluid fractionation of petroleum- and coal-derived mixtures

Abstract: A supercritical fluid chromatographic system was constructed to provide separations and fraction collection on a semipreparative scale. Columns packed with silica materials of intermediate particle size (30-70 ..mu..m) were used to allow dynamic pressure programming with minimum pressure drop of the CO/sub 2/ mobile phase along the length of the column. A variety of complex coal- and petroleum-derived polycyclic aromatic compound mixtures were fractionated according to the number of aromatic rings using columns packed with an NH/sub 2/-modified stationary phase bonded on silica particles. The CO/sub 2/ mobile phase was programmed with an alternating series of linear pressure ramps and isobaric intervals to effect even peak spacing and near base line resolution of compounds of differing ring number in a coal tar. A solvent refined coal heavy distillate and a crude oil were similarly fractionated. Effluents were monitored with an ultraviolet spectrophotometer at 254 nm and a flame ionization detector while fractions were collected in pressurized vessels for subsequent analysis by capillary gas chromatography. Sample capacities of up to 20 mg were possible with this system.

Flow distribution in the fiber lumen side of a hollow-fiber module

Abstract: Little attention has been paid to the flow distribution among many thousands of fibers in the hollow-fiber modules of artificial kidney, ultrafiltration, and reverse osmosis devices despite its potential importance in the efficiency of the module. Numerical study by a finite-difference method, as well as experiment by direct sampling from individual fibers and high-speed photography of a color tracer, has shown that there exists a significant degree of nonuniformity in the flow distribution, which depends on the manifold design, the Reynolds number, and the pressure drop along the fibers.

A general design equation for air lift pumps operating in slug flow

Abstract: Air lift pumps are finding increasing use where pump reliability and low maintenance are required, and where corrosive, abrasive, or radioactive fluids must be handled. Although air lifts are used in nuclear fuel reprocessing plants, no general, theoretically sound equation has been proposed in the literature for tall air lift design. Such an equation is developed from two-phase flow theory to predict the height to which an air lift pump operating in the slug flow regime can lift a given volumetric flow rate of liquid, given the air flow rate and pressure at the point of gas introduction. The widely used drift-flux model for the prediction of holdup is combined with an approximate relationship to predict pressure loss, and is substituted into the total pressure differential. Integration of the resulting equation provides an explicit formula for the calculation of lift. Experimental work using a variety of liquids in a 38 mm dia. air lift test installation supports the new design equation and demonstrates its flexibility.

Method and system for enriching oxygen content of water

Abstract: A method and a system for enriching the oxygen content of a body water having a relatively low oxygen content are disclosed. The method contemplates providing, in a pipeline communicating with the body of water, a pressurized, flowing aqueous liquid stream that is at a pressure greater than ambient and supersaturated with respective to the dissolved oxygen concentration thereof. The liquid stream is maintained substantially free of bubbles which grow in size under conditions existing in the body of water. The flow rate of the oxygen-enriched aqueous liquid stream is modulated so as to maintain a dimensionless number, defined as: ##EQU1## wherein ρ=density of the pressurized aqueous liquid within the pipeline, D=internal diameter of the pipeline, V=mean liquid velocity of the pressurized aqueous liquid stream within the pipeline, g c =gravitational constant, ΔP=pressure drop of the aqueous liquid stream flowing through the pipeline, L=length of the pipeline, and t=mean transit time required by the aqueous liquid stream to flow through the pipeline, at a value in the range of about 1×10 -10 to about 5×10 -7 until the stream is commingled with the body of water, the oxygen concentration of which is to be enriched.

Excess air control with dual pressure switches

Abstract: A method and apparatus for maintaining the desired level of excess air in a two stage gas furnace system. Low and high pressure switches are placed across the heat exchanger and are successively closed, as the inducer motor accelerates during purging, when the pressure drop reaches the respective theoretically desired low and high firing pressure drop levels. As the switches are closed, the inducer motor speeds are sensed and recorded, with a ratio of the two then being calculated. After firing, the ratio is then directly applied to a desired high firing motor speed to obtain the desired low firing motor speed.

Aircraft engine bleed air flow balancing technique

Abstract: A bleed flow modulator is used in conjunction with pressure regulating valves regulating bleed air pressure from each engine to a common manifold. The bleed flow modulator monitors the pressure drop across a heat exchanger, which pressure drop is proportional to flow rate of bleed air through the heat exchanger. By providing a limited authority negative feedback signal to the pressure regulating valve from the bleed flow modulator, flow rate of bleed air from each engine to the common manifold is kept near a desired uniform value, thereby achieving balanced flow extraction of bleed air from the aircraft engines.

Method and apparatus for measuring the relative density of gases

Abstract: Gas is vented through a very small orifice or pore with substantially stable pressures before and after the orifice. The orifice is designed so that the expansion through it is similar to a Joule-Thompson expansion of the gas. With ideal gas, this occurs isothermally. The flow through this orifice is determined for a selected pressure drop across it and the square of this flow is inversely proportional to the relative density. With real gases there is a slight error introduced due to a supercompressibility of the gas, but this is offset by an error in the opposite direction believed to be due to the Joule-Thompson cooling of the gas as it passes through the orifice. Substantially exact error cancellation is obtained within a preferred operating range of the pressure drop across the orifice for a given orifice diameter.

Pressure drop of polymeric melts in conical converging flow: Experiments and predictions

Abstract: It is of importance to estimate the pressure drop of polymeric materials in a converging die with an abrupt change in geometry for many polymer processes. In the present study, experiments have been conducted with an extruder and conical dies of four different converging angles for two different polymeric melts under various processing conditions. As part of the analysis, numerical calculations have been carried out using a finite element method (FEM) for a power-law fluid model, A simple formula for estimating pressure drops has also been derived based on a power-law fluid model with normal-stress effects incorporated. In particular, the formula with the normal-stress term excluded underpredicts pressure drops systematically at high flow rates, giving very similar results to those by the FEM calculation. When the normal-stress term is included, the formula is in bettor agreement with the experimental data, confirming that the normal stress effect is important at high flow rates. Other formulae in the literature have been also compared with the present experimental data.

Internal Flow Effects in Prefilming Airblast Atomizers: Mechanisms of Atomization and Droplet Spectra

Abstract: Fuel atomization with prefilming airblast nozzles has been investigated. The present analysis is directed toward a detailed investigation of the atomization processes and the clarification of the fundamental phenomena. Two-dimensional models were utilized. High-speed films, showing the deterioration of the liquid film close to the atomizing edge, reveal the dynamics of the liquid’s deterioration and show the motion of the film during the drop formation. The liquid separation is shown to be a periodic process with the drop formation caused by momentum transfer. The frequency spectrum of the liquid separation is determined by means of an optical technique. It is seen that the main frequencies depend only on the air velocity. They are always lower than the corresponding wave frequencies. The droplet size measurements obtained by a light scattering technique emphasize the dominant role of the air velocity at the atomizing edge. A decrease in the surface tension provides an improvement in atomization quality. Other parameters such as liquid flow rate, liquid viscosity, gap height, and length of the prefilming surface within the nozzle were found not to affect directly the droplet size distribution produced, if the air velocity in each of the two ducts of the nozzle is kept constant. The pressure drop of the air, however, rises. It is shown that the droplet size distribution can be easily determined, if the arithmetic mean value of the air velocity in both ducts is known, e.g., from a calculation of the internal flow. Due to the high liquid mass flow rates of airblast nozzles, the wavy film is partly atomized within the nozzle before the liquid separates at the atomizing edge. The measurements show that the portion of the liquid mass flow atomized remains relatively small and that the droplet sizes are equivalent to those produced at the atomizing edge.

Pneumatic Conveying Calculations

Abstract: An empirical model to calculate the pipe line pressure loss for a pneumatic conveying system is described. The model was originally proposed for lean phase conveying and is modified to use solids friction proposed by Weber (1982). The calculated pressure loss for a given pipe diameter, pipe length, air mass flow rate and material mass flow rate is compared to recent experimental results of a number of authors. Generally the model predicts the pipe pressure loss to be better than a factor of 2, and this, surprisingly, for a range of product to air mass flow ratios in the range 2 to 530. The model performance was observed to decrease as pipe length increases, for L greater than 500m the model is not applicable. However defining the particle Froude number as Weber (1981) allows successful pressure loss predictions for all pipe lengths considered. The factor of 2 pressure loss estimate will allow a preliminary optimization and economic assessment of possible pneumatic conveying systems. The method may be used to investigate optimal positioning of expansions in pipe diameters, introduced to reduce pressure loss, along a longer pipe line. Conveying tests are necessary to prove the feasibility of economically attractive options and to confirm that products can be conveyed at the selected mass flow ratios and air velocities.

Vapor flow analysis in a double-walled concentric heat pipe

Abstract: The equation of fluid motion for the steady flow in a double-walled concentric heat pipe with various distributions of evaporation and condensation has been solved numerically. The conditions in the condenser section are decidedly more complex. Reverse flows occur in the condenser section and occupy a substantial fraction of the condenser length for high condensation cooling rates. Pressure drops and hydrodynamic entrance lengths are presented for symmetric and asymmetric cases, and practical results of the calculation of pressure losses for low-speed vapor flows in the double-walled concentric heat pipe are given.

Measurement of heat transfer and pressure drop in rectangular channels with turbulence promoters

Abstract: Periodic rib turbulators were used in advanced turbine cooling designs to enhance the internal heat transfer The objective of the present project was to investigate the combined effects of the rib angle of attack and the channel aspect ratio on the local heat transfer and pressure drop in rectangular channels with two opposite ribbed walls for Reynolds number varied from 10,000 to 60,000 The channel aspect ratio (W/H) was varied from 1 to 2 to 4 The rib angle of attack (alpha) was varied from 90 to 60 to 45 to 30 degree The highly detailed heat transfer coefficient distribution on both the smooth side and the ribbed side walls from the channel sharp entrance to the downstream region were measured The results showed that, in the square channel, the heat transfer for the slant ribs (alpha = 30 -45 deg) was about 30% higher that of the transverse ribs (alpha = 90 deg) for a constant pumping power However, in the rectangular channels (W/H = 2 and 4, ribs on W side), the heat transfer at alpha = 30 -45 deg was only about 5% higher than 90 deg The average heat transfer and friction correlations were developed to account for rib spacing, rib angle, and channel aspect ratio over the range of roughness Reynolds number