Maximum Pressure Head Research Articles

Transport in Flat Heat Pipes at High Heat Fluxes From Multiple Discrete Sources

A three-dimensional model has been developed to analyze the transient and steady-state performance of flat heat pipes subjected to heating with multiple discrete heat sources. Three-dimensional flow and energy equations are solved in the vapor and liquid regions, along with conduction in the wall. Saturated flow models are used for heat transfer and fluid flow through the wick. In the wick region, the analysis uses an equilibrium model for heat transfer and a Brinkman-Forchheimer extended Darcy model for fluid flow. Averaged properties weighted with the porosity are used for the wick analysis. The state equation is used in the vapor core to relate density change to the operating pressure. The density change due to pressurization of the vapor core is accounted for in the continuity equation. Vapor flow, temperature and hydrodynamic pressure fields are computed at each time step from coupled continuity/momentum and energy equations in the wick and vapor regions. The mass flow rate at the interface is obtained from the application of kinetic theory. Predictions are made for the magnitude of heat flux at which dryout would occur in a flat heat pipe. The input heat flux and the spacing between the discrete heat sources are studied as parameters. The location in the heat pipe at which dryout is initiated is found to be different from that of the maximum temperature. The location where the maximum capillary pressure head is realized also changes during the transient. Axial conduction through the wall and wick are seen to play a significant role in determining the axial temperature variation.

Pore water pressure assessment in a forest watershed: Simulations and distributed field measurements related to forest practices

A distributed shallow groundwater model related to slope stability is described to assess the spatial distribution of pore water pressure in steep forested terrain in British Columbia. Additionally, effects of timber harvesting and roads on measured changes in pressure head during rainstorms were evaluated for the first time to assess the need for incorporating different hydrological components in the event‐driven distributed model. Although explicit spatial quantification of pore water pressure requires many measurements for accurate prediction, model performance using average parameter values was reasonable when compared with pressure heads measured at nine spatially distributed sites. Increases in maximum pressure head (varying from 9 to 28 cm) between preharvesting (after road construction) and postharvesting rainstorm events were observed in seven of nine sites. The remaining two sites showed either a small decrease (≈5 cm) or similar peak pressure heads following harvesting. Peak pressure head evaluated at one piezometer located 46 m downslope of the road decreased substantially (≈50 cm) after road construction during moderate rainstorms and then recovered following harvesting. Piezometric responses in sites upslope of the road were not affected by road construction but did increase after harvesting. Moderate storms caused the largest relative increases in pressure head between preharvesting (after roads) and postharvesting conditions; such increases were small during large storms, lending support to the idea that timber harvesting in temperate forests enhances hydrologic response only during small and moderate storms. Since landslides in coastal Pacific Northwest are typically caused by large winter rainstorms, it appears more justified to include better spatial representation of soil physical and engineering parameters in the distributed shallow groundwater model compared to specifying evapotranspiration; road hydrology may, however, need to be included.

Fluid inclusion studies in quartz veinlets in the porphyry copper deposit at Sungun, East-Azarbaidjan, Iran

The porphyry copper deposit (PCD) at Sungun is located in East Azarbaidjan, in the NW of Iran.The Sungun porphyries occur as stocks and dikes ranging in composition from quartz monzodiorite through quartz monzonite and granodiorite to granite. The stocks are divided into two groups (1) Porphyry Stocks I and (2) Porphyry Stock II. Porphyry Stock II, hosting the copper ore, experienced intense hydro-fracturing leading to the formation of stockwork-type and anastomozing veinlets and micro-veinlets of quartz, sulfides, carbonates, and sulfates. Three distinct types of hydrothermal alteration and sulfide mineralization are recognized at Sungun (1) hypogene, (2) contact metasomatic (skarn), and (3) supergene. Four types of hypogene alteration are developed at Sungun, potassic, propylitic, potassic–phyllic, and phyllic. Four types of inclusion are common at Sungun based upon their phase content (1) mono-phase vapor, (2) vapor-rich 2-phase, (3) liquid-rich 2-phase, and (4) multi-phase solid. Halite is the principal solid phase. The distribution pattern, shape, and phase contents of fluid inclusions in quartz veinlets at Sungun are analogous to those from Bingham and Globe-Miami in western USA. The fluid inclusion data at Sungun showed that the liquid–vapor homogenization temperature [ T H(L–V)] values for liquid-rich 2-phase, vapor-rich 2-phase, and halite-bearing inclusions vary from 160 to 580 °C, from 200 to 600 °C, and from 160 to 580 °C, respectively. The ascending unboiled fluid at the onset of the phyllic alteration episode had temperatures ∼580 °C and was moderately saline (∼15 wt%). With the gradual decrease in temperature, the salinity of this fluid gradually decreased, so that its salinity at temperatures of ∼370 and <270 °C were ∼7 and <2 wt%, respectively. Multiple boiling events occurred in Porphyry Stock II during phyllic alteration. With each boiling event the salinity of the residual fluid increased substantially. The first boiling event occurred at temperatures 540–560 °C, and increased the salinity of the residual fluid up to ∼50 wt%. At temperatures >350 °C the residual fluid remained undersaturated (with respect to NaCl) however, at temperatures <350 °C they became saturated. The minimum internal pressures calculated for the inclusions having T s (NaCl)≈ T H(L–V) showed that they were developed under the maximum hydrostatic pressure head of ∼1500 m during the boiling events.

Magnetically suspended centrifugal blood pump with an axially levitated motor.

The longevity of a rotary blood pump is mainly determined by the durability of its wearing mechanical parts such as bearings and seals. Magnetic suspension techniques can be used to eliminate these mechanical parts altogether. This article describes a magnetically suspended centrifugal blood pump using an axially levitated motor. The motor comprises an upper stator, a bottom stator, and a levitated rotor-impeller between the stators. The upper stator has permanent magnets to generate an attractive axial bias force on the rotor and electric magnets to control the inclination of the rotor. The bottom stator has electric magnets to generate attractive forces and rotating torque to control the axial displacement and rotation of the rotor. The radial displacement of the rotor is restricted by passive stability. A shrouded impeller is integrated within the rotor. The performance of the magnetic suspension and pump were evaluated in a closed mock loop circuit filled with water. The maximum amplitude of the rotor displacement in the axial direction was only 0.06 mm. The maximum possible rotational speed during levitation was 1,600 rpm. The maximum pressure head and flow rate were 120 mm Hg and 7 L/min, respectively. The pump shows promise as a ventricular assist device.

NEW PRODUCT DEVELOPMENTS

A micropump combining reciprocating motion of a magnetic ball covered with magnetic fluid and diffusers working as valves was investigated experimentally in this study. The reciprocating motion of the magnetic substance pushes water in order to transport it. The diffusers with different divergence angles serve to pump water in net one direction. In the present micropump experiments, the maximum flow rate achieved with minimum backpressure was 3.89 μl/min and the maximum pressure head achieved was 42.4 mm water.

Magnetically suspended centrifugal blood pump with a self bearing motor.

A magnetically suspended centrifugal blood pump with a self bearing motor has been developed for long-term ventricular assistance. A rotor of the self bearing motor is actively suspended and rotated by an electromagnetic field without mechanical bearings. Radial position of the rotor is controlled actively, and axial position of the rotor is passively stable within the thin rotor structure. An open impeller and a semiopened impeller were examined to determine the best impeller structure. The outer diameter and height of the impeller are 63 and 34 mm, respectively. Both the impellers indicated similar pump performance. Single volute and double volute structures were also tested to confirm the performance of the double volute. Power consumption for levitation and radial displacement of the impeller with a rotational speed of 1,500 rpm were 0.7 W and 0.04 mm in the double volute, while those in the single volute were 1.3 W and 0.07 mm, respectively. The stator of the self bearing motor was redesigned to avoid magnetic saturation and improve motor performance. Maximum flow rate and pressure head were 9 L/min and 250 mm Hg, respectively. The developed magnetically suspended centrifugal blood pump is a candidate for an implantable left ventricular assist device.

Hydraulic Analysis and Optimum Design of Multidiameter Irrigation Laterals

A new analytical continuous-uniform outflow approach that takes into account the effect of the number of outlets on the multidiameter lateral hydraulics is presented. The pressure head profile along the multidiameter pipeline is described by a simple analytical function providing direct calculation of the outlet pressure head along the pipeline. The method is significantly improved by introducing an adjusted spatially variable outflow equation—of power function form—for the errors caused by the assumption of equal outlet discharge. The effect of ground slope on hydraulic computation is also considered. Simple equations are derived for the direct calculation of the maximum, minimum, and inlet pressure head along the multidiameter pipeline. The optimum design problem for two-diameter laterals is also solved analytically. For specified total length of a two-diameter pipeline, a simple algebraic equation is derived to calculate directly the appropriate lengths of the reaches of different diameters in such a way that the total cost of the pipeline is minimized. Comparison tests with an accurate numerical stepwise method indicate that the proposed analytical approach is sufficiently accurate.

A ferrofluidic magnetic micropump

A microfluidic pump is described that uses magnetic actuation to push fluid through a microchannel. Operation relies on the use of magnetically-actuated plugs of ferrofluid, a suspension of nanosize ferromagnetic particles. The ferrofluid contacts but is immiscible with the pumped fluid. The prototype circular design demonstrates continuous pumping by regenerating a translating ferrofluidic plug at the conclusion of each pumping cycle. The flow rate can be controlled by adjusting device dimensions or the velocity of an external permanent magnet that directs the motion of the ferrofluid. The ferrofluidic plugs also serve as valves; if the magnetic actuator is stopped, pressure can be maintained with no power consumption. Flow can also be reversed by switching the direction of actuation. The maximum flow rate achieved with minimal backpressure was 45.8 /spl mu/l/min. The maximum pressure head achieved was 135 mm water (1.2 kPa).

An Ultradurable and Compact Rotary Blood Pump with a Magnetically Suspended Impeller in the Radial Direction

A magnetically suspended centrifugal blood pump has been developed with a self-bearing motor for long-term ventricular assist systems. The rotor of the self-bearing motor is not only actively suspended in the radial direction, but also is rotated by an electromagnetic field. The pump has a long lifetime because there are no mechanical parts such as seals and motor bearings. An outer rotor mechanism was adopted for the self-bearing motor. The stator was constructed in the central space of the motor. The rotor shaped thin ring was set at the circumferential space of the stator. Six vanes were extended from the upper surface of the rotor toward the center of the pump to construct an open-type impeller. The outer diameter and the height of the impeller are 63 mm and 34 mm, respectively. The magnetic bearing method and the servomotor mechanism were adopted to levitate and rotate the rotor. Radial movements of the rotor and rotation are controlled actively by using electromagnets in the stator. Axial movement and tilt of the rotor are restricted by passive stability to simplify the control. The radial gap between the rotor and the stator is 1 mm. A closed-loop circuit filled with water was used to examine basic performance of the pump. Maximum flow rate and pressure head were 8 L/min and 200 mm Hg, respectively. Maximum amplitude of radial displacement of the impeller was 0.15 mm. The impeller could be suspended completely without touching the casing wall during the entire pumping process. Power consumption of the pump was only 9.5 W to produce a flow rate of 5 L/min against a pressure head of 100 mm Hg. We conclude that the pump has sufficient performance for the implantable ventricular assist system.

A SWACROP-based potato root water-uptake function as determined under tropical conditions

The SWACROP root-water uptake function for potatoes was determined in the 1994–95 crop season on a Ferralsol in Havana province, west Cuba. The maximum pressure-heads under which water is optimally extracted by potato roots were very similar to the original Feddes function. Nevertheless, the anaerobiosis point and the wilting point pressure-head in both functions were not in agreement. However, the simulated values of soil water contents in the 0–40 cm soil depth by performing SWACROP runs in the 1995–96 potato crop season using both functions were very similar. The original Feddes function seems to be good enough for predicting soil water contents in the tropics and no specific other functions need to be developed for any particular soil or climate condition.

Valve Closure: Method for Controlling Transients

One of the objectives of this study was to reduce the undesirable dynamic pressure oscillation that occurs in a simple pipeline due to valve closure and to prevent the occurrence of column separation. This is accomplished by maximizing the minimum pressure in the pipeline. The second objective was to minimize the maximum dynamic pressure, and the third objective was to estimate the best (minimum) time of closure, T*c, that results in a pipe stress equal to the maximum allowable stress. The method of characteristics with the time-line interpolation technique was used to solve the transient stresses and pressures in a liquid-filled piping system. Frequency-dependent friction was used in the equation of motion for the fluid and the pipe wall. A nonlinear optimization technique was utilized to generate the optimum valve closure policy. Maximum and minimum pressure heads resulting from the optimal policy were calculated and compared with those resulting from a uniform valve closure. Plots of pressure variation at the valve for these two valve closure policies were also generated. Examples are presented to demonstrate the advantage of the optimum valve closure policy over the uniform valve closure policy. The reduction in the maximum dynamic pressure and stress at the valve for different Tc is also presented.

Maximum Pressure Head Due to Linear Valve Closure

The maximum pressure head resulting from one-speed closure of wide open valves is investigated. The dimensionless variables formulated in this study make the subtle effect of the initial valve head loss explicit and separate from that of the pipe frictional head loss. The maximum head is related to initial pipe frictional head loss, the initial valve head loss, the inherent flow characteristic of the valve, and the closure period by plots of dimensionless variables. The trends of the variation of the maximum pressure head are discussed. An example is used to illustrate the usage of the plots, and to show the advantage of having a global perspective of the phenomenon in the selection and sizing of valves from the water hammer point of view.

Further development of the inclined coil pump

THE COIL PUMP is remarkable in its simplicity: it has only one moving part. The coil pump works by picking up air and water alternately. The pockets of air become compressed and a manometric pressure is set up between each adjacent coil. When added together, the individual pressure differentials arc sufficient to force the 'slugs' of water to the top of the delivery pipe. The maximum pressure head that can be achieved depends upon the number of coils and the mean diameter of the coil. The design of the pump has gone through various stages. In the form described by Morgan!, Stucker and Wilson2, Mortimer and Annable, and others, the axis of the pump was horizontal and the pump incorporated a rotating seal. This feature represented a significant drawback to the design, and made manufacture of the pump almost impossible for most village workshops. alternative to the coil element being driven directly by stream power. The inclined coil pump is therefore more versatile, in that it can be powered by either pedal, animal or wind. Measurement of pump performance by one authority, however, indicated that the overall efficiency of a large diameter pump could be well below that which was desirable, and under certain circumstances was as low as 20 per cent. The indications were that significant energy loss was taking place from the churning of the water caused by the coil's support structure. A further problem with the pump was that the lower shaft bearing had to support a considerable weight, leading to some difficulty in the design of the bearing support structure and significant bearing friction where simple bushes were used.

Charts for water hammer in pipelines resulting from valve closure from full opening only

Maximum pressure head rises, which result from total closure of the valve from an initially fully open position, are calculated and plotted for the valve end and for the midpoint of a simple pipeline. Uniform, equal-percentage, optimum, and parabolic closure arrangements are analysed. Basic parameters such as pipeline constant, relative closure time, and pipe wall friction are considered with closures from full valve opening only. The results of this paper can be used to draw the maximum hydraulic grade line along the pipe with good accuracy for the closure arrangements considered. It is found that the equal-percentage closure arrangement yields consistently less pressure head rise than does the parabolic closure arrangement. Further, the optimum closure arrangement yields consistently less head rise than the equal-percentage one. Uniform closure produces pressure head rise that usually lies between those produced by the parabolic and the equal-percentage closure arrangements, except for the range of low pressure head rise combined with low or zero friction, where the rise due to uniform closure approaches that produced by optimum closure.

Charts for water hammer in high head pump discharge lines resulting from pump failure and check valve closure

Maximum pressure head drops and rises resulting from pump failure and subsequent check valve closure are calculated and plotted for a simple pump discharge line at pump end, midpoint, and three-quarter point. Basic parameters such as pipeline constant, pipe wall friction, complete pump characteristics, and pump inertia constant are accounted for in the analyses. Computer studies indicate that pipe friction, pipeline constant, and pump inertia have a major effect on pressure head drops and rises.Studies indicate further that whereas for large pump inertia the pressure head rise or drop at the midpoint is only moderately larger than one-half of the rise or drop at pump end, for small pump inertia this difference is much greater. For very small pump inertia, the pressure head drop or rise at midpoint approaches the values at pump end. This increase in pressure head drop and rise for very small pump inertia is even more pronounced at the three-quarter point.

ベローズ式液体ヘリウムポンプ

A double acting bellows type liquid helium pump was developed for the cryogenic system of a large thin solenoid magnet. The pump performed the maximum capacity of 900l/hr and the maximum pressure head of 4.4×105Pa while the heat generation in the pump was only 200mW. The fatigue test of the bellows was made prior to the construction of the pump. It endured more than six million pumping cycles in liquid nitrogen temperature. The pulsation of the outlet pressure was largely reduced by use of oil-air cylinder actuation.

Charts for water hammer in low head pump discharge lines resulting from water column separation and check valve closure

Maximum pressure head rises resulting from water column separation and check valve closure are calculated and plotted for a simple low head pump discharge line with one well-defined high point. Basic parameters such as pipeline constant, pipe wall friction, complete pump characteristics, pump inertia constant, and the relative location of the high point are accounted for in the analyses. The results of this paper can be used to determine (a) when water column separation is expected, (b) how to avoid water column separation, and (c) the necessary wall thickness in cases where no protection against water column separation is provided. Computer studies indicate that both the vertical and horizontal location of the high point as well as the pipe friction, the pipeline constant, and the pump inertia have a major effect on pressure head rises. Water column separation does not always constitute a danger to the pipeline. Key words: waterhammer, water column separation, check valve closure, pressure rise, pump discharge line, chart.

Charts for water hammer in pipelines resulting from valve closure

Maximum pressure head rises, which result from valve closure according to (a) uniform, (b) equal-percentage, and (c) optimum valve closure arrangements, are calculated and plotted for the valve end and for the midpoint of a simple pipeline. Basic parameters such as the pipeline constant, relative closure time, and pipe wall friction are considered for closures both from partial as well as from full valve openings. The results of this paper can be used to draw the maximum hydraulic grade line along the pipe for these closure arrangements. It is found that the equal-percentage closure arrangement yields consistently less pressure head rise than does the uniform closure arrangement. Further, the optimum closure arrangement yields consistently less head rise than the equal-percentage one. Closures from partial valve openings increase the pressure head rise considerably and must always be considered.