Showing papers on "Pressure drop published in 1984"

Effects of Pin Shape and Array Orientation on Heat Transfer and Pressure Loss in Pin Fin Arrays

Abstract: Modern high-performance gas turbine engines operate at high turbine inlet temperatures and require internal convection cooling of many of the components exposed to the hot gas flow. Cooling air is supplied from the engine compressor at a cost to cycle performance and a design goal is to provide necessary cooling with the minimum required cooling air flow. In conjunction with this objective, two families of pin fin array geometries which have potential for improving airfoil internal cooling performance were studied experimentally. One family utilizes pins of a circular cross section with various orientations of the array with respect to the mean flow direction. The second family utilizes pins with an oblong cross section with various pin orientations with respect to the mean flow direction. Both heat transfer and pressure loss characteristics are presented. The results indicate that the use of circular pins with array orientation between staggered and inline can in some cases increase heat transfer while decreasing pressure loss. The use of elongated pins increases heat transfer, but at a high cost of increased pressure loss. In conjunction with the present measurements, previously published results were reexamined in order to estimate the magnitude of heat transfer coefficients on the pin surfaces relative to those of the endwall surfaces. The estimate indicates that the pin surface coefficients are approximately double the endwall values.

The formation and expansion of a toroidal drop moving in a viscous fluid

Abstract: The deformation of an initially spherical liquid drop moving under the action of gravity in another fluid with which it is completely miscible is investigated under conditions of small values of the drop Reynolds number. It is found experimentally that such a drop evolves into an open torus which subsequently expands, and this phenomenon is examined theoretically for two limiting drop geometries: (i) a slightly deformed spherical drop, and (ii) a highly expanded, slender open torus. Under the assumptions of zero interfacial tension and creeping flow, the theory provides a qualitative description for the initial stages of the drop evolution [case (i)], but is unable to account for the observed drop expansion during latter stages of deformation [case (ii)]. On the other hand, if small inertial effects are retained in the analysis, the theory predicts that a slender open fluid torus possessing an arbitrary cross‐sectional geometry will expand without change of shape to first order in Reynolds number. Quantitative comparisons of theoretically predicted rates of expansion with experimental measurements suggest the possible existence of a small, time‐dependent interfacial tension across the drop interface.

Stratified turbulent‐turbulent gas‐liquid flow in horizontal and inclined pipes

Abstract: A two-dimensional model for stratified turbulent-turbulent gas-liquid flow in inclined pipes is proposed. The gas phase is treated as bulk flow, but an exact solution is carried out for the liquid phase, applying the eddy viscosity theory to model the turbulent viscosity. The interfacial structure is taken into consideration using appropriate correlations for the interfacial shear stress. The model is capable of predicting the liquid velocity field, holdup and pressure drop given gas and liquid flow rates, physical properties, pipe size, and angle of inclination. The results are substantially better than the prediction of Lockhart and Martinelli (1949) correlation and better than the Taitel and Dukler (1976) model for stratified flow.

Effect of mild atherosclerosis on flow resistance in a coronary artery casting of man

Abstract: An in-vitro flow study was conducted in a mildly atherosclerotic main coronary artery casting of man using sugar-water solutions simulating blood viscosity. Steady flow results indicated substantial increases in pressure drop, and thus flow resistance at the same Reynolds number, above those for Poiseuille flow by 30 to 100 percent in the physiological Reynolds number range from about 100 to 400. Time-averaged pulsatile flow data showed additional 5 percent increases in flow resistance above the steady flow results. Both pulsatile and steady flow data from the casting were found to be nearly equal to those from a straight, axisymmetric model of the casting up to a Reynolds number of about 200, above which the flow resistance of the casting became gradually larger than the corresponding values from the axisymmetric model.

Two-phase flowmeter

Abstract: The tubular flowmeter is capable of measuring two different physical parameters in a flowing mixture of liquid and gas (such as wet steam). These measurements are such that they can be used to determine the individual gas and liquid flowrates. The flowmeter comprises first means, such as an orifice plate or a twisted tape, for causing an accelerational or frictional pressure drop in the total flow. Suitable means measure such pressure drop. Downstream of the first means, is positioned means for inducing rotational motion of the total flow, to cause the mixture to separate while remaining within the same conduit into discrete liquid and gas flows. Such means may comprise a rib extending helically along the inner surface of the flowmeter. Means, such as a pitot-static tube assembly, measure a pressure head indicative of the velocity of the gas flow. Downstream from this velocity measurement device, the two phases are permitted to mix freely again, all the time remaining within the same conduit. The total flow pressure drop and gas flow velocity head measurements are used to compute or determine the individual gas and liquid flowrates.

In vitro verification of Doppler prediction of transvalve pressure gradient and orifice area in stenosis.

Abstract: This study was designed to analyze the validity of application of the modified Bernoulli equation (pressure gradient = 4.0 X velocity2) for estimating the pressure drop and valve orifice area from the jet velocity measured by Doppler ultrasound. We used an in vitro model which permitted interchangeable orifices, accurate measurement of the valve area and pressure drop across the valve. An in-line Doppler ultrasound transducer measured jet velocity (VEL D) at various water flow rates at an incident angle of 180 degrees beyond the various tested orifices. Jet velocity was also determined independently by application of a modified Bernoulli equation using the experimentally measured pressure drop (VEL P) and by a standard continuity equation (VEL Q). VEL P correlated very closely with VEL D (r = 0.981, standard error of the estimate [SEE] = 17.0 and slope of the regression = 0.988). VEL Q, corrected for vena contracta effects, correlated with VEL P (r = 0.986, SEE = 21.6), but had a slope of 0.673. To experimentally determine the exponent of velocity in the Bernoulli equation, we plotted pressure drop against VEL D and found a value of 2.11; theory predicts 2.0. Experimental coefficient of velocity was 3.36 torr/m (standard deviation = 0.52), whereas theory predicts 3.75 for water. Orifice area, calculated using VEL D and the continuity equation, was consistently overestimated by 3 to 12% for flows that produced laminar jets. The pressure gradient and orifice areas calculated from Doppler-derived data accurately predict actual pressure gradients and orifice areas.

Liquid circulation, gas holdup and pressure drop in bubble column with draught tube

Abstract: The effects of gas velocity and geometrical dimensions of apparatus on the flow rate QL of circulating liquid, gas holdups and pressure drops in bubble columns with draught tube were examined. It was found that QL increases with increasing gas velocity, column diameter, draught tube length, and height of the lower end of draught tube, and decreases with increasing liquid viscosity. It was also found that the maximum value of QL is observed for constant values of gas velocity and column diameter, when the diameter ratio of draught tube and column is about 0.6. Empirical equations for gas holdups in draught tube and annulus and the pressure drops due to flow reversals, necessary for estimating QL, are proposed.

Well treating method for stimulating recovery of fluids

Abstract: Subterranean oil and gas producing formations are fractured by providing one or more combustion gas generating units using rocket fuel type propellants disposed in a well casing at preselected depths. The well casing is filled with a compressible hydraulic fracturing fluid comprising a mixture of liquid, compressed gas, and propant material and precompressed to a pressure of about 1,000 psi or more greater than the fracture extension pressure at the depth of the zone to be fractured. At least one of the gas generating units is equipped with perforating shaped charges to form fluid exit perforations at the selected depth of the fracture zone. The gas generating units are simultaneously ignited to generate combustion gasses and perforate the well casing. The perforated zone is fractured by the rapid outflow of an initial charge of sand free combustion gas at the compression pressure followed by a charge of fracturing fluid laden with propant material and then a second charge of combustion gas. The column of precompressed fracturing fluid is discharged into the formation until the hydraulic extension pressure is reached and eventually the perforations sanded off.

Heat Transfer and Two-Phase Flow during Shell-side Condensation

Abstract: This paper surveys the evolution of power condenser tube bundle arrangements and examines present-day designs. Condensation heat transfer during shell-side flow is reviewed, including the effects of vapor shear, condensate inundation, noncondensable gases, and enhancement techniques. The difficulties experienced in calculating vapor pressure drop through tube bundles are described, as well as recent attempts to obtain more reliable correlations. The modeling of these phenomena to predict shell-side condenser performance is reviewed, as well as the use of one- and two-dimensional computer codes. Appropriate topics for future research are identified.

Hydrodynamics of cocurrent gas‐liquid‐solid semifluidization with a liquid as the continuous phase

Abstract: The hydrodynamic behavior of a cocurrent gas-liquid-solid semifluidized bed was investigated. A separate investigation was performed on a packed bed and a fluidized bed under gas-liquid flow conditions similar to that for the semifluidized bed. Parameters of the semifluidized bed under extensive study include pressure drop, gas holdup, onset liquid velocity for semifluidization, and the height of the packed bed section and the fluidized section. The pressure drop of the semi-fluidized bed obtained experimentally was compared favorably with that predicted by the model equations.

Heat transfer and fluid flow characteristics for an annulus of periodically varying cross section

Abstract: The fully developed laminar-flow and temperature fields of a double-pipe heat-exchanger with an annular duct of streamwise-periodic-varying cross-sectional area are investigated analytically for Reynolds numbers 50-1000 and Prandtl numbers 2-10. Numerical results are presented graphically and discussed. At Re 1000 and Pr 10, the Nusselt number is found to be four times that of a similar configuration with constant cross section the pressure drop is increased by a factor of two. Nusselt numbers for two different boundary conditions (constant wall temperature or uniform wall heat flux) are shown to differ by only 10-15 percent. 8 references.

Rarefied Gas Flow Through a Circular Orifice and Short Tubes

Abstract: Rarefied gas flow through a circular orifice and short tubes has been investigated experimentally, and the conductance of the aperture has been calculated for Knudsen number between 2 x 10/sup -4/ and 50. The unsteady approach was adopted, in which the decay of pressure in an upstream chamber was measured as a function of time. For flow with high pressure ratio, empirical equations of the conductance are proposed as a function of Reynolds number, or Knudsen number, and length-todiameter ratio of the apertures.

Gas-liquid mass transfer data in a stirred autoclave reactor

Abstract: A novel experimental technique for measuring volumetric mass transfer coefficients in a stirred autoclave reactor is proposed. The method is based on pursuing the instationary pressure drop due to mass transfer under isochoric conditions. The usefulness of the technique is demonstrated for the Fischer-Tropsch slurry system.

Method and apparatus for operating a screw compressor installation

Abstract: In a screw compressor installation cooled by injected oil, in which both the air intake rate of the screw compressor and its preferably electromotive drive are controlled as a function of the pressure, means are provided which act purely pneumatically and which, on reaching a predefinable maximum pressure of the network are able to reduce the intake volume; the maximum pressure of the network at the same time and within a switching period delimited by itself, is used to derive a pneumatic-electrical controlled variable for the screw compressor drive, in such a way that the screw compressor operates at full power below the maximum pressure of the network and on reaching the maximum pressure of the network and a subsequent pressure drop within the switching period runs unloaded, during unloaded running the reduction of the intake volume in conjunction with pressure relief of the pressure vessel being employed for cutting out the drive at definable times. An additional safety device acts as a function of the temperature of the oil separated from the compressed air, preventing the transition from unloaded operation to stopping below a predeterminable oil temperature.

Computer Simulation of the Oil Injected Twin Screw Compressor

Abstract: In this paper a physical model for prediction of oil-flooded twin screw compressor performance is presented and discussed. Calculation results are presented. INTRODUCTION At the 1982 PURDUE Compressor Technology Conference a short survey of the possibilities and advantages of this physical model was reported. The following paper contains mor~ detailed information about the model than was used for the calculations presented at that time. The model has shown itself to be very useful for a deeper understanding of the twin screw compressor. An automatic generation of all appropiate geometrical data is coupled to this physical model, which makes it easier to calculate the influences of changes in housing and rotor shape parameters. The presented calculations in this paper are done in this way. 528 THEORY FOR OIL INJECTED TWIN SCREW COMPRESSORS. Following is a summary of the assumptions, that has shown to give the best agreement with laboratory measurements. The main problem in the understanding and simulation of an oil-injected screw compressor is the behaviour of the internai mass and heat transport of the gas/oil mixture. However, as there are different leakage paths located within the compressor, the behaviour of the gas/oil mixture in and after these paths is very important for twin screw compressor calculations. By comparison with laboratory tests the following assumptions for the different types of leakage paths have been shown to be the most appropriate: 1. The gas/oil mixture in all leakage paths is homogeneous. 2. The gas/oil mixture ratio is the same in all leakage paths and equal to the mixture ratio in the discharge port. 3. The heat transfer between gas and oil in the £O~t~ol yolu~e (compressor thread) is treated in two different ways: a) Leakage over the mesh and the discharge end clearance Because of the high pressure difference and rotor rotation it is assumed that the oil leakage into the control volume is atomized. This assumption leads to a fully developed heat transfer between the oil and the gas. b) Leakage over rotor tips and through the blowhole Due to the centrifugal forces it is assumed that the oil that has leaked into the control volume is located against the housing. This means that only the gas that has leaked into the control volume mixes with the gas already in the control volume. 4. It is assumed that the gas will pass through the outlet port with constant enthalpy. In the case where the outlet port opens before the pressure in the contra 1 vo 1 ume has reach-ed the outlet pressure value, it is assumed that the reverse flowing gas has the same temperature as the gas in the control volume. It is also assumed that the gas/oil mixture is homogeneous during the passage through the outlet port. 5. The cooling of the gas due to heat transfer during the compression phase is calculated by using an average polytropic exponent. The formulas for describing the condition in a compressor thread can now be written as follows: a) Continuity equations 529 . +m evap dm "I • dt w = l'n ·z 111. ., fN ,., 01 ti After integration of the last equation the real thread volume will be V=V . gco,., b). The pressure is calculated according to a polytropic process. (see above assumption 5) p = consf .It~" , where the use of n instead of '¥' will describe the heat transfer between the gas and the surroundings. c) Temperature calculation. From the first law of thermodynamics the following formula for the gas temperature rise in the control volume can be derived When calculating dry compressprs, this equation can be simplified by assuming ld~al ~a~ and fOlY!r~plc_p~o£e~s~ which gives: dT = __ / __ pdV _ 1 'n-1)· dl m·c, df m 1 1 According to the above mentioned assumptions 1. 2 and 3 it can be understood that this equation must be modified before it is able to calculate the gas temperature rise in the control volume of an oil-injected twin screw compressor. This modification will be as follows: fiL: _ _L,p dt't--7;#) _Lin-J\. dl m·c dl ml' I ,. • [(~j'~uf ~ + ~ L[~(n·7l,-T)]. + m Inlet flow + incoming leakage over rotor tips and through blowhole (see as~umption 3 b). +...L[[~elm (c U m/1( = ~mix • R,· ~s obtained from -'-=..2L-+ (1-J ln in In In \r;;,"'n· /n f) Discharge of the compressor thread through outlet port. The same principle as above, but in this case the pressure drop across the outlet is where S'c:1 and Ud are the average density and outlet velocity for a mixture of gas and oil. Equations expressing these parameters are; ( ri-1,:1 + moll J ) t?ct. Rc~ The density s>d is calculated as follows; _L_= __£_+ (/x\ 'Set ~ f? ~//

Pump unit for sampling air

Abstract: An improved pump unit for sampling air that operates at a constant air flow rate in the range of 5-5000 cc/min. having a filter for removing particles or vapors from the air stream, an air accumulator, a variable drive pump optionally with a bypass, an electric motor for driving the pump, an optional air reservoir, an orifice which creates a pressure drop in the air stream, an optional bypass for the orifice and a pressure switch connected in parallel to the orifice which monitors a change in the air pressure drop; the improvement in the pump is the use of a digital circuit electrically connected to the pressure switch and a closed loop control means electrically connected to the digital circuit and motor; a digital signal determines the open or closed position of the switch and the control means and allows current to flow or not flow to the motor driving the air pump to provide a constant flow of air through the unit; the pump unit is worn by a worker or is placed in a work area and at the termination of a period of time, such as a work day, the filter is removed and the contents collected are analyzed by conventional techniques such as gas chromatography to determine a level of exposure of the individual or the level of exposure of people working in that area.

Heat transfer and pressure drop in blade cooling channels with turbulence promoters

Abstract: Repeated rib roughness elements have been used in advanced turbine cooling designs to enhance the internal heat transfer. Often the ribs are perpendicular to the main flow direction so that they have an angle-of-attack of 90 deg. The objective of the project was to investigate the effect of rib angle-of-attack on the pressure drop and the average heat transfer coefficients in a square duct with two opposite rib-roughned walls for Reynolds number varied from 8000 to 80,000. The rib height-to-equivalent diameter ratio (e/D) was kept at a constant value of 0.063, the rib pitch-to-height ratio (P/e) was varied from 10 to 20, and the rib angle-of-attack (alpha) was varied from 90 deg to 60 deg to 45 deg to 30 deg respectively. Two types of entrance conditions were examined, namely, long duct and sudden contraction. The heat transfer coefficient distribution on the smooth side wall and the rough side wall at the entrance and the fully developed regions were measured. Thermal performance comparison indicated that the pumping power requirement for the rib with an oblique angle to the flow (alpha = 45 deg to 30 deg) was about 20 to 50 percent lower than the rib with a 90 deg angle to the flow for a given heat transfer duty.