Aaberg static pressure


For gross flow maldistribution in heat exchangers, modeling is available for heat-transfer performance prediction, but no modeling is available for pressure-drop prediction. This is because, in most of the cases, the static pressure distribution is not uniform at the exchanger inlet and outlet faces, and no modeling or computational fluid dynamic analysis is possible without the boundary conditions. Gross flow maldistribution significantly increases pressure drop. In addition, because there are an infinite number of gross flow maldistributions possible, the only approach is to analyze the problem numerically for idealized uniform pressure boundary conditions.  [c.496]

In order to avoid the need to measure velocity head, the loop piping must be sized to have a velocity pressure less than 5% of the static pressure. Flow conditions at the required overload capacity should be checked for critical pressure drop to ensure that valves are adequately sized. For ease of control, the loop gas cooler is usually placed downstream of the discharge throttle valve. Care should be taken to check that choke flow will not occur in the cooler tubes. Another cause of concern is cooler heat capacity and/or cooling water approach temperature. A check of these items, especially with regard to expected ambient condi-  [c.422]

Gradual velocity reduction method. This method is a variation of the constant friction approach, where a maximum velocity is used for the main and branch ducts. This procedure provides a reasonable solution and choice between the velocity, diameter, and resistance. The method is not useful to provide the same static pressure at each outlet.  [c.786]

Static pressure recovery method. The diameters are selected in such a way that the same static pressure is available before every connection. The duct reduction is selected in such a way that the gain of static pressure is in balance with the friction losses up to the next connection point. This method may result in fewer control devices at connection points or outlets. Low velocities and large diameters at the end of the system may be the result of this design approach.  [c.786]

As stated earUer, the main idea behind supercritical drying is to eliminate the Hquid-vapor interface inside a pore, thereby removing the accompanying capillary pressure which acts to coUapse a gel network. The value of this approach is demonstrated by the fact that aerogels do have higher porosities, higher specific surfaces areas, and lower apparent densities than xerogels, materials that ate prepared by evaporative drying. However, it is incorrect to think that a gel remains static during supercritical drying. Rather, supercritical drying should be considered as part of the aging process, during which events such as condensation, dissolution, and reprecipitation can occur. The extent to which a gel undergoes aging during supercritical drying depends on the stmcture of the initial gel network. Eor example, it has been shown that a higher drying temperature changes the particle stmcture of base-catalyzed siUca aerogels but not that of acid-catalyzed ones (29). It is also known that gels that have uniform-sized pores can withstand the capillary forces during drying better because of a more uniform stress distribution. Such gels can be prepared by a careful manipulation of sol—gel parameters such as pH and solvent or by the use of so-called drying control chemical additives (DCCA) (30). Clearly, an understanding of the interrelationship between preparative and drying parameters is important in controlling the properties of aerogels.  [c.3]

Molten Carbonate Fuel Cell. The MCFC is weU-suited to utilize fuels that are produced in coal gasifiers or from other sources. In one approach. Energy Research Corp. (ERC) is steam-reforming natural gas to form H2 and CO2 in the fuel cell (internal reforming), eliminating the need for a dedicated fuel processor. The reaction is carried out using a catalyst that is located in the fuel manifold near the anode inlet and in the fuel cell stack itself. Because the steam reforming reaction is endothermic, heat that is generated during the production of electrical energy is utilized. The MCFC stacks developed by ERC operate at atmospheric pressure and utilize external gas manifolds.  [c.583]

The gas and process steam mixture can then be introduced into the primary reformer. This reformer is a direct-fired chamber containing single or multiple rows of high nickel-alloy tubes HK-40, HP-Modified, Incoloy 800, or other alloys are selected according to operating pressures and temperatures. The tubes are normally 72—110 mm ID and 10—13 m long. The catalyst contains 5 to 25% Ni (lower contents also include other metal promoters) as NiO supported on calcium aluminate, alumina, calcium aluminate titanate, or magnesium aluminate. Space velocities (SV) are usually on the order of 5000 8000 h based on wet feed. Steam-to-carbon ratios are usually in the range of 3.0—5.0, outlet gas temperatures, 800—870°C, and pressure, 2.16—2.51 MPa (300—350 psig). The outlet gas composition corresponds to a 0—25°C temperature approach to steam-reforming equiUbrium. That is, an equihbrium temperature is lower than actual at start and end of mn catalyst activity. The flue gas temperatures are 980—1040°C exiting the fired section of the furnace. In the convection section, the flue gases are cooled by superheating the steam for drivers, generating steam, preheating the hydrocarbon feed for desulfurization, and preheating the feed-plus-steam mixture before entering the radiant section of the furnace. In order to obtain high overall furnace efficiency, the stack temperature can be lowered to 150—170°C by preheating combustion air for the radiant section burners.  [c.419]

One direct Ic /ms interface is referred to as the particle beam approach based on the Monodisperse Aerosol Generation Interface for Ic (MAGIC) (19,20). The MAGIC is actually a rather simple transport device, similar to a two-stage jet separator, where the solvent vapor is pumped away and the analyte particles ate concentrated in a beam that is allowed to enter the ms ion source to be vaporized and ionized by electron impact. The particle beam interface consists of four main sections nebulizer, desolvation chamber, momentum separator, and transfer probe. In the nebulizer the Ic effluent is joined by a stream of helium and converted into an aerosol of droplets having a narrow range of diameters. As the droplets move through the desolvation chamber, which is held close to ambient pressure and temperature, the solvent is vaporized creating a mixture of helium, solvent vapor, and analyte particles. As the mixture advances toward the lower pressure, two-stage momentum separator, it is focused into a narrow beam that expands at supersonic speed as it exits the jet nozzle entering the momentum separator. In the separator, the lower mass solvent vapor is pumped and skimmed away while the higher mass, and thus higher momentum, particles pass in a narrow beam through the transfer probe into the ms ion source where they strike the heated source wall and are vaporized.  [c.403]

As primary alkaline fuel cells were developed for space appHcations, consideration was given to separate stack rechargeable designs. In these approaches, the product water formed during the discharge of a primary fuel cell is stored, then fed to a separate electrolizer stack during charge. The hydrogen and oxygen gas generated during charge is stored in separate pressure vessels. This approach overcomes the stabiHty problem of the bifunctional oxygen electrode and the respective stacks can be optimized for thek function. This system is stiH rather complex and bulky and has not yet been appHed.  [c.566]

Low pressure rhodium processes which give higher n iso butyraldehyde ratios (eg, 10 1) have gradually replaced cobalt processes, dramatically effecting the isobutyraldehyde supply. Supply restraints and strong demand for certain value added derivatives will limit the overall growth of isobutyraldehyde to about 0.9% annually. The production of isobutyl alcohol the least valued isobutyraldehyde derivative, should actually decline as strong growth for neopentyl glycol and isobutyraldehyde condensation products limits the avaHabiUty of isobutyraldehyde for conversion to isobutyl alcohol. As isobutyl and -butyl alcohol prices approach parity some isobutyl alcohol consumers are expected to switch back to the normal isomer based on better solvency and perceived better performance.  [c.381]

There are two main approaches to its solution. Traditional approach is based on preliminary separation of UGC samples to gaseous and liquid phases and their subsequent analyses [1]. This approach is well-developed and it allows obtaining quite precise results being used properly. However, this method is relatively complicated. Multi-stage procedure is a source of potential errors, then, it makes the analyses quite time consuming. More progressive approach is based on the direct analysis of the pressurized UGC samples. In both cases the determination of heavy hydrocarbons (up to C ) is made by capillary gas chromatography.  [c.184]

On June 3, 1998, in Rotterdam a 165-m cone roof tank containing methyl tertiary butyl ether (MTBE) exploded while being washed, causing a fatality and launching the 1.4 tonne roof a distance of 100 m. The tank was 10 m high by 4.5 m diameter. Initially the tank contained 27% MTBE vapor with the balance nitrogen. However, as washing proceeded a vacuum tmck was used to suck sludge, water, and residual MTBE out of the tank bottom. As the vacuum hose lost contact with the liquid layer, the resulting negative pressure intermittently sucked air into the tank via the top manway, which held a high pressure washing device. Turbulent mixing by the washing jets helped form a flammable mixture in the tank. The explosion occurred during the fourth cleaning cycle and the fatally injured man was blown from the roof shortly after adjusting the washing device. Two static mechanisms considered were a static discharge involving the water mist and a static discharge from an ungrounded vacuum hose. The latter would have to be ruled out before attributing this incident to a charged mist mechanism involving brush discharges or charged water slugs. The company involved had previously ventilated their tanks to the air to reduce flammable vapor concentrations to a safe level, but this approach had been abandoned owing to local emission constraints.  [c.146]

Supplementary fired cycle The recovery of heat from gas turbine exhaust by the generation of steam has, as its basic limiting factor, the approach temperature at the pinch point (see Figure 15.11). The principal pinch point occurs at the cold end of the evaporator and consequently the combination of the steam-generating pressure and the magnitude of the approach determine the amount of steam which can actually be generated for a given gas turbine. In single-pressure systems, the only heat which can be recovered below the evaporator pinch point is to the feedwater, and this, in turn, now determines the final stack temperature. If, however, a small amount of fuel is used to supplement the gas turbine exhaust heat, then while the pinch point  [c.182]

Tube-Axia.IFa.ns, The tube-axial fan is a refinement of the propeller fan ia both wheel design and mechanical strength, having improved capacity, pressure level, and efficiency. Designs are often capable of operating over a greater range of speeds. The cheapest fans may have an open-type propeller wheel with the motor enclosed ia a tube if directly coimected. Belt-drive models are also available. In more refined types, the blades are shorter and of airfoil cross section mounted on a large diameter hub which may approach 50% of the wheel diameter. The hub and motor tube are normally of the same diameter and reduce the back flow of higher pressure air, which might recycle through less effective central portions of the wheel if a smaller hub were utilised. The performance curve (Fig. 10) may have a dip to the left of the pressure peak which would constitute an unstable region for fan operation and which should be avoided. Commercial models are available having static pressures up to 750 Pa (3 ia. of H2O). The general range of appHcation is for  [c.111]

The performance of the natural-draft tower differs from that of the mechanical-draft tower in that the cooling is dependent upon the relative humidity as well as on the wet-bulb temperature. The draft will increase through the tower at high-humidity conditions because of the increase in available static pressure difference to promote air flow against internal resistances. Thus the higher the humidity at a given wet bulb, the colder the outlet water will be for a given set of conditions. This fundamental relationship has been used to advantage in Great Britain, where relative humimties are commonly 75 to 80 percent. Therefore, it is important in the design stages to determine correctly and specify the density of the entering and effluent air in addition to the usual tower-design conditions of range, approach, and water quantity. The performance relationship to humidity conditions makes exact control of outlet-water temperature difficult to achieve with the natural-draft tower.  [c.1169]

Belt Presses Belt presses were fiiUy described in the section on filtration. The description here is intended to cover only the parts and designs that apply expression pressure by a mechanism in adchtion to the normal compression obtained from tensioning the belts and pulling them over rollers of smaller and smaller diameters. The tension on the belt produces a squeezing pressure on the filter cake proportional to the diameter of the rollers. Normally, that static pressure is calculated as P = 2T/D, where P is the pressure (psi), T is the tension on the belts (Ib/hnear in), and D is the roller diameter. This calculation results in values about one-half as great as the measured values because it ignores pressure created by drive torque and some other forces [Laros, Advances in Filtration and Separation Technology, 7 (System Approach to Separation and Filtration Process Equipment), pp. 505-510 (1993)].  [c.1744]

In the development of all these units, increased stage pressures were sought by using high blade cambers and closer blade spacing. Under these conditions the blades began to affect each other, and it became apparent that the isolated airfoil approach was not adequate. Aerodynamic theory was, therefore, developed specifically for the ease of ca airfoils. In addition to the theoretical studies, systematic experii investigations of airfoils in cascade were conducted to provi required empirical design information.  [c.225]

The composition of the materials tested, their heat treatment, and their static and fatigue properties have been reviewed (89). Because fatigue results for cylinders of different diameter ratios subjected to repeated internal pressure can be correlated on the basis of the maximum bore shear stress, it might have been expected that this stress at the fatigue limit would correspond to the fatigue limit for the material in repeated torsion. However, it was found that the limit for the pressure tests was much lower than expected. Attempts to relate the limiting shear stress at the bore of the cylinder to the fatigue or endurance limit of the material in other forms of loading, eg, torsion, were not successhil, and it was necessary to adopt an empirical approach. With the exception of EN56 and titanium, the ratio of the range of shear stress at the bore at the fatigue limit of 10 cycles to the ultimate stress Ar jHes between 0.36 and 0.27. Thus it appears that the limiting maximum shear stress which can be endured indefinitely at the bore of a plain cylinder is about one-third of the ultimate tensile stress at least up to tensile strengths of 1 GPa (145,000 psi). If the material is markedly anisotropic the ratio Ar may  [c.88]

Batch processiag of nylon-6 is generally used only for the production of specialty polymers such as very high molecular weight polymer or master batch polymers for special additives. In a typical modem batch process (147—150), the caprolactam is mixed ia a hoi ding tank with the desired additives and then charged to an autoclave with a small amount (2—4%) of water. During the two-stage polymeriza tion cycle, the temperature is raised from 80 to 260°C. In the first stage, water is held ia the reactor, the pressure rises, and the hydrolysis and addition steps occur. After a predetermined time the pressure is releasedand the final condensation reaction step occurs. The molecular weight of the polymer can be iacreased by means of a vacuum finishing step, if desired. The entire process can take three to five hours. The final polymer is then drained, often with a forcing pressure of iaert gas, through a die to form ribbons of polymer, which are then cooled ia water and cut iato pellets. Because nylon-6 has such a high monomer and oligomer content, 10—12% by weight, ia the cast pellets, which would significantly reduce the quaUty of the final fiber or resia products, it must be extracted. This is usually done ia hot water under pressure at 105—120°C for 8—20 h. Most of the caprolactam and higher oligomers that are released with the steam from the autoclave or extracted from the pellets ia hot water are then recycled. The pellets must be carefully dried because excess water decreases the molecular weight of the polymer duting subsequent melt processiag. The fiaal polymer processed through water extractioa and drying can have an oligomer level of <0.2% and a moisture level of <0.05%. Alow level of total oligomers is necessary because on remelting and further processiag, the oligomers coateat will iacrease owiag to the reestabUshmeat of the equiUbrium distributioa of molecular species that occurs for all coadeasatioa polymers (151). Because the approach to equihbrium progresses at a moderate rate, it is possible to utilize extracted ayloa-6 ia a remelt process without increasing the oligomer coaceatratioa above 2—3% and thus avoiding any significant drop ia fiaal properties.  [c.234]

The amount of inerts which has to be removed by a pumping system after the pump-down stage depends on the in-leakage of air at the various fittings, connections, and so on. Air leakage is often correlated with system volume and pressure, but this approach introduces uncer-  [c.641]

Expression, possibly followed by air (or steam) displacement, is the last stage in mechanically dewatering compressible solids. Expression is used to wring out the last remaining liquid before resorting to thermal (irying or solvent (chemical) extraction of the remaining liquids from the solids, f The goal of this stage of dewatering is maximum removal of liquid rather than creation of a solids-free hquid. The operating costs for expression are much lower than those for heat or solvent recovery, and the former is used in preference to the two latter processes. Tiller estimates that for pressures up to 1000 kPa (10 atm) the mechanical energy required for liquid removal is 400 times less than the thermal energy required for evaporation [Tiller, Yeh, and Leu, Separation Science and Technology, 22, pp. 1037-1063 (1987)]. For sludges intended for incineration, expression can often dewater the material sufficiently to eliminate the need for aimliaiy fuel. For example, in wastewater treatment plants, particularly those that include some form of thermal treatment, the degree of dewatering has a greater impact on the energy balance than any other single unit process [Campbell and Plaisier, Advances in Filtration and Separation Technology, 7 (System Approach to Separation and Filtration Process Equipment), pp. 583-586 (1993)].  [c.1744]

Figure 22-19 shows a one-stage extraction process that utihzes the adjustability of the solvent strength with pressure in a separation process. The solvent flows through the extraction chamber at a relatively high pressure to extract the components of interest from the feed. The produces are then recovered in the separator by depressurization, and the solvent is recompressed and recycled. The produces can also be precipitated from the extract phase by raising the temperature after the extraction to lower the solvent density. In the increasing pressure profihng approach, conditions are set so that only the lightest components in the feed are extracted in the first fraction. The recovery vessel is then replaced, and the pressure is increased to colled the next heavier fraction. In the multistage isothermal decreasing pressure profiling process, all but the heaviest fraction are extraded in the first vessel. The extract then passes through a series of recoveiy vessels held at successively lower pressures, each of which precipitates the next lower molecular-weight fraction in the raffinate. A new process, critical isobaric temperature-rising elution fractionation, is a supercritical variation on temperature-rising elution fractionation in a liquid solvent (McHugh and Krukonis, op. cit.).  [c.2001]

The gas turbine was designed shortly after World War II and introduced to the market in the early 1950s. The early heavy-duty gas turbine design was largely an extension of steam turbine design. Restrictions of weight and space were not important factors for these ground-based units, so the design characteristics included heavy-wall casings split on horizontal centerlines, hydrodynamic (tilting pad) bearings, large-diameter combustors, thick airfoil sections for olades and stators, and large frontal areas. The overall pressure ratio of these units varied from 5 1 for the earlier units to 30 1 for the units in the 1990s. Turbine inlet temperatures have been increased and run as high as 2300° F (1260° C) on some of these units. Projected temperatures approach 3000° F (1649° C) and, if achieved, would make the gas turbine even more efficient. The industrial heavy-duty gas turbines most widely used employ axial-flow compressors and turbines. In most U.S. designs combustors are can-annular combustors. Single-stage side combustors are used in European designs. The combustors used in industrial gas turbines have heavy walls and are veiy durable.  [c.2507]

Each amino acid side chain within a transmemhrane helix has a different hydrophobicity. It is easy to state that side chains such as Val, Met, and Leu are the most hydrophobic and that charged residues such as Arg and Asp are at the other end of the scale. However, to order all side chains according to hydrophobicity and to assign actual numbers that represent their degree of hydrophobicity is not trivial. Many such hydrophobicity scales have been developed over the past decade on the basis of solubility measurements of the amino acids in different solvents, vapor pressures of side-chain analogs, analysis of side-chain distributions within soluble proteins, and theoretical energy calculations. In Table 12.1 two of these hydrophobicity scales are listed. The most frequently used scale, which was introduced by J. Kyte and R.F. Doolittle at University of California, San Diego, is based on experimental data. A more refined scale was developed by D.A. Engelman, T.A. Steitz, and A. Goldman at Yale University. They used a semitheoretical approach to calculating the hydrophobicity, taking into account the fact that the side chains are attached to an a-helical framework.  [c.245]

A number of methods have been devised for producing cellular products from PVC pastes. One approach is to blend the paste with carbon dioxide, the latter either in the solid form or under pressure. The mixture is then heated to volatilise the carbon dioxide to produce a foam which is then gelled at a higher temperature. Flexible, substantially open-cell structures may be made in this way. Closed-cell products may be made if a blowing agent such as azodi-isobutyronitrile is incorporated into the paste. The paste is then heated in a filled mould to cause the compound to get and the blowing agent to decompose. Because the mould is full, expansion cannot take place at this stage. The mould is then thoroughly cooled and the as yet unexpanded block removed and transferred to an oven where it is heated at about 100°C and uniform expansion occurs.  [c.354]

The third stage of the process is the steam moulding operation itself. Here the prefoamed beads are charged into a chest or mould with perforated top, bottom and sides through which steam can be blown. Steam is blown through the preform to sweep air away and the pressure then allowed to increase to about 151bf/in (approx. 0.11 MPa). The beads soften, air in the cells expands on heating, pneumatogen volatilises and steam once again permeates into the cells. In consequence the beads expand and, being enclosed in the fixed volume of the mould, consolidate into a solid block, the density of which is largely decided by the amount of expansion in the initial prefoaming process. Heating and cooling cycles are selected to give the best balance of economic operation, homogeneity in density through the block, good granule consolidation, good block external appearance and freedom from warping. This process may be used to give slabs which may be subsequently sliced to the appropriate size or alternatively to produce directly such objects as containers and flower pots. The steam moulding process, although lengthy, has the advantages of being able to make very large low-density blocks and being very economic in the use of polymer.  [c.458]

Fuel cells can be utilized in electric hybrid vehicles as the means of converting chemical fuel to electricity. Rapid progress has been made in the development of fuel cells, especially proton exchange membrane (PEM) fuel cells, for transportation applications. This progress has resulted in a large reduction in the size and weight of the fuel cell stack and as a result, there is now little doubt that the fuel cell of the required power (20-50kW) can be packaged under the hood of a passenger car. The primary question regarding fuel cells in light duty vehicles is how they will be fueled. The simplest approach is to use high pressure hydrogen as has been done in the most successful bus demonstration to date. This approach is satisfactory for small test and demonstration programs, but the development of the infrastructure for using hydrogen as a fuel in transportation will take many years. Considerable work is underway to develop fuel processors (reformers) to generate hydrogen onboard the vehicle from various chemical fuels (e.g., methanol or hydrocarbon distillates). Most of the hydrogen used for industrial and transportation applications is presently generated by reforming natural gas using well-developed technology. A promising approach to fuel processing to hydrogen (H" and electrons) onboard the vehicle is direct oxi-  [c.637]

While this method of testing has been in use in some laboratories for two decades or more, and has increased in use considerably in very recent years, there remains some scepticism and unfamiliarity with the method. In essence it involves the application of a relatively slow strain or deflection rate (approx 10 s ) to a specimen subjected to appropriate electrochemical conditions. It should be emphasised that the strain rates employed are very much lower than those involved in straining electrode experiments where the object, the measurement of current transients, is totally different. In slow strain-rate corrosion tests the object is to produce stress-corrosion cracks that, metallographically, are indistinguishable from those produced in constant-load or constant-deflection experiments. The object in all these laboratory tests is normally to obtain data in a relatively short period of time and this is frequently achieved by adopting an approach that increases the severity of the test. In stress-corrosion testing this usually takes the form of increasing the aggressiveness of the environment by changing its composition, temperature or pressure, stimulating the corrosion reactions (galvano-static or potentiostatic polarisation), increasing the susceptibility of the alloy through changes in structure, or increasing the severity of the stress by the introduction of a notch or precrack. The application of dynamic straining to a stress-corrosion test specimen comes into this last category also, and, like all of the other accelerating approaches, its justification will vary according to the circumstances in which it is used.  [c.1365]


See pages that mention the term Aaberg static pressure : [c.281]    [c.1402]    [c.4]    [c.451]   
Industrial ventilation design guidebook (2001) -- [ c.1448 ]