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This process could be continued and possible sequences identified for further consideration. Some possible sequences would he eliminated, narrowing down the number suggested by Table 5.1. 

The reaction uses a fixed-bed vanadium pentoxide-titanium dioxide catalyst which gives good selectivity for phthalic anhydride, providing temperature is controlled within relatively narrow limits. The reaction is carried out in the vapor phase with reactor temperatures typically in the range 380 to 400°C. 

Most enzymes work best within a narrow pH range and are susceptible to a wide variety of compounds which inhibit or sometimes promote the activity. The majority of enzymes work most efficiently at around 40°C and at higher temperatures are rapidly destroyed. 

With the accumulation of results obtained from various and complex analyses of narrow cuts (Waterman method), correlations have been found f ctween refractive index, specific gravity and molecular weight on one hand, and percentages of paraffinic, naphthenic and aromatic carbon on the other. 

This method follows the ASTM D 1159 and D 2710 procedures and the AFNOR M 07-017 standard. It exploits the capacity of the double olefinic bond to attach two bromine atoms by the addition reaction. Expressed as grams of fixed bromine per hundred grams of sample, the bromine number, BrN, enables the calculation of olefinic hydrocarbons to be made if the average molecular weight of a sufficiently narrow cut is known. 

The current calculation methods are based on the hypothesis that each mixture whose properties are sought can be characterized by a set of pure components and petroleum fractions of a narrow boiling point range and by a composition expressed in mass fractions. 

We will use the term petroleum fraction to designate a mixture of hydrocarbons whose boiling points fall within a narrow temperature range, typically as follows ... 

In the petroleum refining and natural gas treatment industries, mixtures of hydrocarbons are more often separated into their components or into narrower mixtures by chemical engineering operations that make use of phase equilibria between liquid and gas phases such as those mentioned below ... 

Their production in a refinery begins with base stocks having narrow boiling ranges and high octane numbers iso C5 cuts (used in small concentrations because of their high volatility) or alkylates are sought for such formulations. 

Crude petroleum is fractionated into around fifty cuts having a very narrow distillation intervals which allows them to be considered as ficticious pure hydrocarbons whose boiling points are equal to the arithmetic average of the initial and final boiling points, = (T, + Ty)/2, the other physical characteristics being average properties measured for each cut. 

Separation Processes that split a feed into simpier or narrower fractions. 

Simple conventional refining is based essentially on atmospheric distillation. The residue from the distillation constitutes heavy fuel, the quantity and qualities of which are mainly determined by the crude feedstock available without many ways to improve it. Manufacture of products like asphalt and lubricant bases requires supplementary operations, in particular separation operations and is possible only with a relatively narrow selection of crudes (crudes for lube oils, crudes for asphalts). The distillates are not normally directly usable processing must be done to improve them, either mild treatment such as hydrodesulfurization of middle distillates at low pressure, or deep treatment usually with partial conversion such as catalytic reforming. The conventional refinery thereby has rather limited flexibility and makes products the quality of which is closely linked to the nature of the crude oil used. 

Measured in MJ/m or Btu/ft, the Wobbe Index has an advantage over the calorific value of a gas (the heating value per unit volume or weight), which varies with the density of the gas. The Wobbe Index Is commonly specified in gas contracts as a guarantee of product quality. A customer usually requires a product whose Wobbe Index lies within a narrow range, since a burner will need adjustment to a different fuel air ratio if the fuel quality varies significantly. A sudden increase in heating value of the feed can cause a flame-out. 

This is consistent with the observation that the largest difference between the oil-water interface and the free water level (FWL) occurs in the narrowest capillaries, where the capillary pressure is greatest. In the tighter reservoir rocks, which contain the narrower capillaries, the difference between the oil-water interface and the FWL is larger. 

Finally, it is worth remembering the sequence of events which occur during hydrocarbon accumulation. Initially, the pores in the structure are filled with water. As oil migrates into the structure, it displaces water downwards, and starts with the larger pore throats where lower pressures are required to curve the oil-water interface sufficiently for oil to enter the pore throats. As the process of accumulation continues the pressure difference between the oil and water phases increases above the free water level because of the density difference between the two fluids. As this happens the narrower pore throats begin to fill with oil and the smallest pore throats are the last to be filled. 

This short-cut method could be repeated to include another variable, and could therefore be an alternative to the previous two methods introduced. This method can always be used as a last resort, but beware that the range of uncertainty narrows each time the process is repeated because the tails of the Input variables are always neglected. This can lead to a false impression of the range of uncertainty in the final result. 

The end product specification of a process may be defined by a customer (e.g. gas quality), by transport requirements (e.g. pipeline corrosion protection), or by storage considerations (e.g. pour point). Product specifications normally do not change, and one may be expected to deliver within narrow tolerances, though specification can be subject to negotiation with the customer, for example In gas contracts. 

When an oil or gas field has just been discovered, the quality of the information available about the well stream may be sparse, and the amount of detail put into the process design should reflect this. However, early models of the process along with broad cost estimates are needed to progress, and both design detail and cost ranges narrow as projects develop through the feasibility study and field development planning phases (see Section 12.0 for a description of project phases). 

In the definition phase options are narrowed down and a preferred solution is proposed. The project becomes better defined in terms of what should be built and how it should be operated, and an assessment of how the project may be affected by changes beyond the control of the company (for example the oil price) should be made. Normally a clear statement should be prepared, describing why the option is preferred and what project specifications must be met, to be used as a basis for further work. 

In order to ensure perpendicular beam incidence on the cylindrical specimen, the circular B-scan profiles were acquired by high frequency (narrow beam) transducers in a synthetic circular aperture array. From these profiles two-dimensional reflection tomograms were reconstructed using a filtered backprojection technique. Straight line propagation was assumed. Several artificial discontinuity types in a cylindrical Plexiglas (Perspex) specimen were compared with similar artificial discontinuities in a cylindrical A/Si-alloy [2]. Furthermore, examples of real discontinuities (an inclusion and a feed head) in the cylindrical AlSi-alloy are presented. 

Measuring surface crack depth is performed by calibration samples made of the same material like the object being tested. Calibration samples are the plates having narrow grooves like slits of various depth 0.2 mm, 0.5 mm, 1.0 mm, 2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm and made by electric erosion method. The samples have dimensions 50 mm X 150 mm x 6 mm and 25 mmx 150 mm x 6 mm and are made of magnetic... 

This type of coil was prepared from copper cladded printed circuit board material by applying photolithographic techniques. The p.c. board material is available with difierent copper thicknesses and with either a stiff or a flexible carrier. The flexible material offers the opportunity to adapt the planar coil to a curved three dimensional test object. In our turbine blade application this is a major advantage. The thickness of the copper layer was chosen to be 17 pm The period of the coil was 100 pm The coils were patterned by wet etching, A major advantage of this approach is the parallel processing with narrow tolerances, resulting in many identical Eddy current probes. An example of such a probe is shown in fig. 10. 

Let us consider a conductive material of conductivity o in which a long, very narrow discontinuity was machined under the examined material surface The surface examination is accomplished with a transducer with orthogonal coils, the coil parallel to the inspected surface serving as emission coil, and the coil perpendicular to the surface being the reception coil. 

As the anodes of the cathode-grounded tubes are cooled through the ceramic insulator, narrower insulators should lead to more heat transferable. For lower voltages, tube designs with twice the actual anode load are feasible. 

First, as the element width is very narrow, and though they have a large elevation, the reflector is placed very close to the elements. That is in violation to the standards rules [1], but experience shows no effect on the frequency spectrum. 

Fig. 4a shows a characteristic narrow banded signal (860 kHz center frequency) from a flat steel surface (reference signal). A steel block was milled in a way that the distance of the upper and graved surface varied from 0 to about 1300 microns (Fig. 5). Moving the probe along the edge (see Fig. 5) about 30 signals have been acquired equidistantly (all 4 mm). Fig. 4b and 4c show two characteristic signals (position 6 and 12). The 30 measured signals have been preprocessed and deconvolved. Fig. 6 shows the evident correlation between measured TOF difference and signal position (depth of milled grave).

The surface viscosity can be measured in a manner entirely analogous to the Poiseuille method for liquids, by determining the rate of flow of a film through a narrow canal under a two-dimensional pressure difference Ay. The apparatus is illustrated schematically in Fig. IV-7, and the corresponding equation for calculating rj is analogous to the Poiseuille equation [99,100]... 

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