Vacuum flow


Vacuum fuel stripping  [c.4]

Throughput (vacuum flow) Pa - mVs ILf - ftVs  [c.629]

Vacuum Flow When gas flows under high vacuum conditions or through very small openings, the continuum hypothesis is no longer appropriate if the channel dimension is not very large compared to the mean free path of the gas. When the mean free path is comparable to the channel dimension, flow is dominated by collisions of molecules with the wall, rather than by colhsions between molecules. An approximate expression based on Brown, et al. J. Appl. Phys., 17, 802-813 [1946]) for the mean free path is  [c.640]

Vacuum flow is usually described with flow variables different from those used for normal pressures, which often leads to confusion. Pumping speed S is the actual volumetric flow rate of gas through a flow cross section. Throughput Q is the product of pumping speed and absolute pressure. In the SI system, Q has units of Pa m vs.  [c.641]

Strain-gauge pressure transducers are manufactured in many forms for measuring gauge, absolute, and differential pressures and vacuum. Full-scale ranges from 25.4 mm of water to 10,134 MPa are available. Strain gauges bonded direc tly to a diaphragm pressure-sensitive element usually have an extremely fast response time and are suitable for high-frequency dynamic-pressure measurements.  [c.762]

Design vessel to accommodate maximum vacuum (full vacuum rating)  [c.48]

Design vessel to accommodate maximum vacuum (full vacuum rating)  [c.48]

Design vessel to accommodate maximum vacuum (full vacuum rating)  [c.56]

Excessive liquid Design vessel to accommodate maximum withdrawal rate vacuum (full vacuum rating)  [c.56]

Discharge coefficient for orifice and nozzles Diameter correction factor, vacuum flow. Figure 2-43 Diameter correction factor, v acuum flow. Figure 2-4.3  [c.154]

Temperature correction factor, vacuum flow. Figure 2-43  [c.154]

Temperature correction factor, vacuum flow. Figure 2-43  [c.154]

In the 1970 s, heavy fuel came mainly from atmospheric distillation residue. Nowadays a very large proportion of this product is vacuum distilled and the distillate obtained is fed to conversion units such as catalytic cracking, visbreaking and cokers. These produce lighter products —gas and gasoline— but also very heavy components, that are viscous and have high contaminant levels, that are subsequently incorporated in the fuels.  [c.241]

The visbreaking process thermally cracks atmospheric or vacuum residues. Conversion is limited by specifications for marine or Industrial fuel-oil stability and by the formation of coke deposits in equipment such as heaters and exchangers.  [c.378]

Applied to vacuum residue, its purpose is to reduce the viscosity of the feedstock to a maximum so as to minimize the addition of light diluents for production of fuel-oil for industrial uses.  [c.378]

The coking process produces electrode quality coke from vacuum residues of good quality (low metal and sulfur contents) or coke for fuel in the case of heavy crude or vacuum residue conversion having high impurity levels.  [c.380]

There have been numerous reviews of photoelectrochemical cells for solar energy conversion see Refs. 181-184 for examples. Figure V-14 shows a typical illustrative scheme for a cell consisting of an n-type semiconductor electrode as anode and an ordinary metal electrode as cathode separated by an electrolyte solution. The valence and conduction bands of the semiconductor are bent near the interface, and as a consequence, the electron-hole pair generated by illumination should separate, the electron going into the bulk semiconductor phase and thence around the external circuit to the metal electrode and the hole migrating to the interface to cause the opposite chemical reaction. Current flow, that is, electricity, is thus generated. As the diagram in Fig. V-14 indicates, there are a number of interrelations between the various potentials and energies. Note the approximate alignment of the solid-state and electrochemical energy scales, the former having vacuum as the reference point and the latter having the H /Hj couple as the reference point.  [c.204]

The study of the friction between metals turns out to be almost two subjects—that relating to truly clean metal surfaces and that involving metals with adsorbed gases or oxide coatings. If metal surfaces are freed of all surface contamination by electron bombardment of the heated surface in a vacuum, then, in the cases of tungsten, copper, nickel, and gold, the coefficients of friction can be quite large. Similarly, nickel surfaces so treated seized when placed in contact and rubbed slightly against each other. That is, a firm metal-meal weld occurred such that it was necessary to piy the pieces apart [19] iron surfaces gave a n value of 3.S at room temperature, but seized at 300°C. Machlin and Yankee [20] using fresh surfaces formed by machining in an inert atmosphere, again found that seizure usually occurred. With two dissimilar metals, however, this may not always happen if the two metals are mutually insoluble. Thus cadmium and iron, which are mutually soluble, did weld together on mbbing, but not silver and iron. The welds that form when seizure occurs appear to be of full strength, that is, for two like metals the strength of the weld is essentially that of the metal itself. An interesting correlation reported by Buckley [21] is that n decreases with increasing d-bond character to the metal-metal bond.  [c.439]

For example, energy transfer in molecule-surface collisions is best studied in nom-eactive systems, such as the scattering and trapping of rare-gas atoms or simple molecules at metal surfaces. We follow a similar approach below, discussing the dynamics of the different elementary processes separately. The surface must also be simplified compared to technologically relevant systems. To develop a detailed understanding, we must know exactly what the surface looks like and of what it is composed. This requires the use of surface science tools (section B 1.19-26) to prepare very well-characterized, atomically clean and ordered substrates on which reactions can be studied under ultrahigh vacuum conditions. The most accurate and specific experiments also employ molecular beam teclmiques, discussed in section B2.3.  [c.899]

Electron transport processes at surfaces often involve electron-tunnelling transport. For example, in tire scanning tunnelling microscope (STM) (see section B1.19 and figure C3.2.3), electrons flow between delocalized initial and final states. Depending on tire experimental design, tire tunnelling can proceed tlirough vacuum or tlirough attached atoms and molecules. In closely related photochemical experiments, electrons are driven from a delocalized electrode state to a localized molecular species or anotlier electrode tlirough an insulating molecular monolayer [10].  [c.2973]

Graham himself clearly recognized the shortcomings of his experiments on effusion through mechanically formed orifices, and in later work i.87] he studied effusion into a vacuum through a thin plate of pencil lead graphite. In this case he claims that Che pores are sufficiently small Chat effusion cakes place by a "molecular mechanism" -- what we should now call Knudsen streaming-- in contrast to his earlier work with stucco plugs and punched orifices. Of course, the length of the pores in the graphite plate Is such that collisions between molecules and the pore walls generate the main resistance to flow, so conditions are still such Chat no test of the kinetic theory formula (A.2.1) is possible. A direct test of this equation had to await the development of vacuum techniques, which permit the upstream pressure to be reduced to a point where the mean free path is long compared with the orifice dimensions. The critical experiments were finally performed by M. Knudsen [3]. Recognizing that equations (A.2.2) and (A.2.3) predict an identical dependence of the effusion rate on upstream temperature and pressure, Knudsen made careful microscopic measurements of the area of his orifice, in order to determine from his experiments the factor multi-plying A(T/M) in Che expression for the effusion rate. As the upstream pressure decreased, this was found to converge accurately to the value of  [c.188]

To make the HCN/THF the chemist is going to have the setup as described in place, under the hood and the vent from the vacuum source must be channeled way, way outside (the vacuum is not on at this point mind you). In the preweighed receiving flask is placed a 300g of THF. In the reaction flask is placed 113g sodium cyanide (NaCN) and 500mL water and the stoppers are immediately put back in place. The vacuum hose, which is connected to the vacuum adapter is going to have a hose damp on it so that vacuum flow can be regulated. With the hose pinched shut by the clamp, the vacuum is turned on and the flow is slowly started by adjusting the clamp. What the chemist wants to see is a slow bubbling coming from the inlet tube in the reaction flask and also from the bubbling tube in the receiving flask. The vacuum flow should not be any stronger than what is needed to cause this  [c.282]

For gas flow through porous media with small pore diameters, the slip flow and molecular flow equations previously given (see the Vacuum Flow subsec tion) may be applied when the pore is of the same or smaller order as the mean free path, as described by Monet and Vermeulen (Chem. E/ig. Pi og., 55, Symp. Sei , 25 [1959]).  [c.666]

Failure of vacuum Design vessel to accommodate maximum system control vacuum (full vacuum rating) resulting in possi-. , elief system bility of vessel collapse pressure alarm and interlock to inert gas supply Select/design vacuum source to limit vacuum capability ASME VIII CCPS G-23 CCPS G-39  [c.79]

Vacuum distillation of the atmospheric residue complements primary distillation, enabli r.ecoyery of heavy distillate cuts from atmospheric residue that will un r o further conversion or will serve as lube oil bases. The vacuum residue containing most of the crude contaminants (metals, salts, sediments, sulfur, nitrogen, asphaltenes, Conradson carbon, etc.) is used in asphalt manufacture, for heavy fuel-oil, or for feed for others conversion processes.  [c.367]

Apart from the cooling structures described before an additionally applied layer ensures the blade surface against the oxidative and corrosive stress The coating consists of a NiCoCrAlY layer and is applied by vacuum plasma spraying (VPS) The thermally particularly highly stressed blades are coated with an additional ceramic heat-insulating layer Such a blade therefore consists of at least two layers the outside ceramic (Zr02) layer, which reduces the heat flow due to the bad heat conductivity into the blade and a metallic bond layer, which originates usually from the NiCoCrAlY family [3]  [c.405]

These spectroscopic probes have been complemented by studies using the crossed molecular beams teclmique. In tliese experiments, two well collimated and nearly monoenergetic beams of H2 and F atoms cross in a large vacuum chamber. The scattered products are detected by a rotatable mass spectrometer, yielding the angular distribution of the reaction products. The experiment measures the transitional energy of the products via time of flight. Thus, one obtains the fiill transitional energy and angrilar distribution, ( ., 0), for the HE products. The first experiments of this type on the F + D2 reaction were carried out by Lee [42] in 1970. Subsequent work by the Lee [43, 44] and Toennies [45, 46] groups on the F + H2, D2 and HD reactions has yielded a very complete characterization of the P E, 0) distribution.  [c.876]

Most electronic transitions of interest fall into the visible and near-ultraviolet regions of the spectmm. This range of photon energies commonly corresponds to electrons being moved among valence orbitals. These orbitals are important to an understandmg of bonding and stmcture, so are of particular interest in physical chemistry and chemical physics. For this reason, most of this chapter will concentrate on visible and near-UV spectroscopy, roughly the region between 200 and 700 mn, but there are no definite boundaries to the wavelengths of interest. Some of the valence orbitals will be so close in energy as to give spectra in the near-infrared region. Conversely, some valence transitions will be at high enough energy to lie in the vacuum ultraviolet, below about 200 mn, where air absorbs strongly and instmmentation must be evacuated to allow light to pass. In this region are also transitions of electrons to states of higher principal quantum number, known as Rydberg states. At still higher energies, in the x-ray region, are transitions of iimer-shell electrons, and their spectroscopy has become an extremely usefiil tool, especially for studying solids and their surfaces. However, these other regions will not be covered in detail here.  [c.1119]

Flow which fluctuates with time, such as pulsating flow in arteries, is more difficult to experimentally quantify than steady-state motion because phase encoding of spatial coordinate(s) and/or velocity requires the acquisition of a series of transients. Then a different velocity is detected in each transient. Hence the phase-twist caused by the motion in the presence of magnetic field gradients varies from transient to transient. However if the motion is periodic, e.g., v(r,t)=VQsin (n t +( )q] with a spatially varying amplitude Vq=Vq(/-), a pulsation frequency co =co (r) and an arbitrary phase ( )q, the phase modulation of the acquired data set is described as follows  [c.1537]

The first study in which a full CASSCE treatment was used for the non-adiabatic dynamics of a polyatomic system was a study on a model of the retinal chromophore [86]. The cis-trans photoisomerization of retinal is the primary event in vision, but despite much study the mechanism for this process is still unclear. The minimal model for retinal is l-cis-CjH NHj, which had been studied in an earlier quantum chemisti7 study [230]. There, it had been established that a conical intersection exists between the Si and So states with the cis-trans defining torsion angle at approximately a = 80° (cis is at 0°). Two  [c.305]

The explicit definition of water molecules seems to be the best way to represent the bulk properties of the solvent correctly. If only a thin layer of explicitly defined solvent molecules is used (due to hmited computational resources), difficulties may rise to reproduce the bulk behavior of water, especially near the border with the vacuum. Even with the definition of a full solvent environment the results depend on the model used for this purpose. In the relative simple case of TIP3P and SPC, which are widely and successfully used, the atoms of the water molecule have fixed charges and fixed relative orientation. Even without internal motions and the charge polarization ability, TIP3P reproduces the bulk properties of water quite well. For a further discussion of other available solvent models, readers are referred to Chapter VII, Section 1.3.2 of the Handbook. Unfortunately, the more sophisticated the water models are (to reproduce the physical properties and thermodynamics of this outstanding solvent correctly), the more impractical they are for being used within molecular dynamics simulations.  [c.366]

Meanwhile fit up an apparatus for ether distillation precisely similar to that shown in Fig. 64 (p. 163), except that a 100 ml. Claisen flask is used instead of the simple distillation-flask shown in the figure, f.e., as in Fig. 23(E), p. 45. The droppingTunnel is fitted to the main neck of the Claisen flask, the side-neck being corked. Filter the dry ethereal solution through a fluted filter-paper directly into the dropping-funnel, finally washing the conical flask and the calcium chloride with a few ml. of fresh ether. Then distil off the ether in the usual way, allowing the solution to fall from the droppingTunnel into the flask as fast as the ether itself distils over—observe all the usual precautions for ether distillations. When the distillation of the ether is complete and only the crude ester remains in the Claisen flask, fit up the latter for vacuum-distillation, using the simple apparatus shown in Fig. 12(a), (p. 29) or a Perkin triangle with condenser (Fig. 14, p. 31) or the condenser and pig shown in Fig. 23(F), p. 46, and heating the flask in an oil-bath. The ethyl malonate usually distils as a sharp fraction boiling over a range of about 2-3° it may be recognised from the following b.p.s 93°/i6 mm., io5°/26 mm. Yield, about 35 g. If necessary the ethyl malonate may be distilled at atmospheric pressure, at which it has b.p. 198° slight decomposition occurs in these circumstances, however, and the distillate, although colourless, has a slightly acrid odour.  [c.274]

The angles ot, p, and x relate to the orientation of the dipole nionient vectors. The geonieti y of interaction between two bonds is given in Fig. 4-16, where r is the distance between the centers of the bonds. It is noteworthy that only the bond moments need be read in for the calculation because all geometr ic features (angles, etc.) can be calculated from the atomic coordinates. A default value of 1.0 for dielectric constant of the medium would normally be expected for calculating str uctures of isolated molecules in a vacuum, but the actual default value has been increased 1.5 to account for some intramolecular dipole moment interaction. A dielectric constant other than the default value can be entered for calculations in which the presence of solvent molecules is assumed, but it is not a simple matter to know what the effective dipole moment of the solvent molecules actually is in the immediate vicinity of the solute molecule. It is probably wrong to assume that the effective dipole moment is the same as it is in the bulk pure solvent. The molecular dipole moment (File 4-3) is the vector sum of the individual dipole moments within the molecule.  [c.125]

The product of a chemical reaction, isolated by solvent extraction and subsequent removal of the solvent, which should normally be crystalline, is sometimes an oil, due to the presence of impurities. It is usually advisable to attempt to induce the oil to crystallise before purifying it by recrystallisation. Methods 1 and 2 (previous paragraph) may be applied method 2 cannot always be used because of the difficulty of securing the necessary seed crystals, but should these be available, successful results will usuaUy be obtained. Another procedure is to add a small quantity of an organic solvent in which the compound is sparingly soluble or insoluble, and then to rub with a stirring rod or grind in a mortar until crystals appear it may be necessary to continue the rubbing for an hour before signs of solidification are apparent. Another useful expedient is to leave the oil in a vacuum desiccator over silica gel or some other drying agent. If all the above methods fail to induce crystallisation, direct recrystallisation may be attempted the solution should be boiled with decolourising carbon as this may remove some of the impurities responsible for the difficulty of crystal formation. Occasionally, conversion into a simple crystalline derivative is applicable subsequent regeneration of the original compound will usually yield a pure, crystalline solid.  [c.130]

Formation of an adsorption column. In order to obtain satisfactory results, the tube must be uniformly packed with the adsorbent. Uneven distribution leads to the formation of cracks and channels. If there is any doubt concerning the uniformity of the adsorbent powder, it should be sifted before use. The necessary support for the column (glass wool or cotton wool plug perforated porcelain plate, or sintered glass plate, with filter paper circle, etc.) is placed in the tube, the latter is clamped or held vertically, and the adsorbent added portionwise. The first portion should be about twice the size of those that follow. For tubes up to one cm. diameter, the individual portions are pressed down with a fiattened glass rod. For wider tubes, a cylindrical wooden pestle (walnut wood is recommended), slightly convex in the centre (Fig. II, 46, 6), is used the area of the conical end should be two thirds to three quarters of that of the tube. The adsorbent is pressed down by a short vigorous tapping from a height of 3 to 6 cm. With certain adsorbents, a slight vacuum is created as the pestle is raised and a cloud of fine powder may be formed this is avoided if a slight rotary movement is given to the pestle as it is raised, or by slightly turning the glass tube with the left hand each time the pestle is lifted. From one-fifth to one third of the tube should be left empty. The amount of adsorbent is usually generous compared with the quantity of material to be adsorbed.  [c.160]

Equip a I litre three-necked flask with a mechanical stirrer and a thermometer, and immerse the flask in a bath of ice and salt. Place 306 g. (283 ml.) of acetic anhydride, 300 g. (285 ml.) of glacial acetic acid and 25 g. of p-nitrotoluene in the flask, and add slowly, with stirring, 42 5 ml. of concentrated sulphuric acid. When the temperature has fallen to 5°, introduce 50 g. of A.R. chromic anhydride in small portions at such a rate that the temperature does not rise above 10° continue the stirring for 10 minutes after all the chromium trioxide has been added. Pour the contents of the flask into a 3 litre beaker two-thirds filled with crushed ice and almost fill the beaker with cold water. Filter the solid at the pump and wash it with cold water until the washings are colourless. Suspend the product in 250 ml. of cold 2 per cent, sodium carbonate solution and stir mechanically for 10-15 minutes filter (1), wash with cold water, and finally with 10 ml. of alcohol. Dry in a vacuum desiccator the yield of crude p-nitrobenzal diacetate is 26 g. (2),  [c.695]

Preparation of aluminium isopropoxide. Place 27 -5 g. of clean aluminium foil in a 1 litre round-bottomed flask containing 300 ml. of anhydrous isopropyl alcohol (e.g., refluxed with and distilled from lime) and 0-5 g. of mercuric chloride. Attach an efficient (for example, double surface) reflux condenser carrying a calcium chloride (or cotton wool) guard tube. Heat the mixture on a water bath or upon a hot plate. When the liquid is boiling, add 2 ml. of carbon tetrachloride (a catalyst for the reaction between aluminium and dry alcohols) through the condenser, and continue the heating. The mixtime turns grey and, within a few minutes, a vigorous evolution of hydrogen commences. Discontinue the heating it may be necessary to moderate the reaction by cooling the flask in ice water or in running tap water. After the reaction has slowed down, reflux the mixture until all the metal has reacted (C-12 hours). The mixture becomes dark because of the presence of suspended particles. Pour the hot solution into a 500 ml. Claisen flask attached to a water condenser with a 250 ml. filter flask or distilling flask as leceiver. Add a few fragments of porous porcelain and heat the flask in an oil bath at 90° under slightly diminished pressure (water pump). When nearly all the isopropyl alcohol has distilled over, raise the temperature of the bath to 170° and lower the pressure gradually to the full vacuum of the water pump. Immediately the temperature of the distillate rises above 90°, stop the distillation and remove the condenser. Attach a 500 ml. distilling flask directly to the Claisen flask, add a few fresh boihng chips and distil use either an oil bath at 180-190° or an air bath (Fig. II, 5, 3). The aluminium isopropoxide passes over as a colourless viscid liquid at 140-150°/12 mm. the yield is 190 g. Pour the molten aluminium isopropoxide into a wide-mouthed, glass-stoppered bottle and seal the bottle with paraffin wax (or with cellophane tape) to exclude moisture. Generally the alkoxide (m.p. 118°) crystallises out, but the substance exhibits a great tendency to supercool and it may be necessary to cool to 0° for 1-2 days before solidification occurs.  [c.883]


See pages that mention the term Vacuum flow : [c.627]    [c.1877]    [c.1910]    [c.2426]    [c.10]    [c.206]    [c.188]    [c.625]    [c.106]    [c.116]    [c.121]    [c.696]   
Applied Process Design for Chemical and Petrochemical Plants, Volume 1 (1999) -- [ c.0 ]