Rotating cylinder method

Silverman has defined a number of useful expressions that allow one to utilize the rotating cylinder method with a variety of practical geometries (12,15). Both shear stresses and mass transfer coefficients are included in the derivations described (12). Table 1 in NACE standard TM-0270-72 summarized the various features of experimental systems for studying flow induced corrosion (22). 

Since the flow of liquid determines the interfacial trans -port rate, it is important to have exactly reproducible conditions of stirring if dissolution rates are to be compared. The rotating cylinder method is rather flexible the vessel containing the solution can be of almost any size or shape, and the cylinders of any convenient diameter. Care should be taken to avoid end effects. If baffle plates are placed extremely close to the rotating cylinder the dissolution rates are increased at the same value of U there is a pronounced effect if a thin... 

The rotating cylinder method and modifications, e.g. in which the couple acting on a disc or cylinder hanging in a rotating bath of liquid is measured, is very suitable for use at high temperatures with molten glass, slags, or metals. 

Accelerated long-term ageing/conditioning by the rotating cylinder method (RCAT)... 

CEN EN 15323. 2007. Bitumen and bituminous binders - Accelerated long-term ageing conditioning by the rotating cylinder method (RCAT). Brussels CEN. 

Rotating cylinder viscometers consist of two concentric cylinders, corresponding to the bob and the crucible, one cylinder of which is rotated at a constant speed. The viscosity is determined from measurement of the torque generated. A schematic drawing is shown in Fig. 25. This method is most popular for measuring viscosity at high temperatures and is suitable for melts with high viscosity. The viscosity is calculated from... 

A concentric cylinder method in which the outer cylinder is rotated has been presented by Bockris and Lowe" for measuring the viscosity of silicates up to 1800 C. 

Flow effects on non-neutrally buoyant emulsions and suspensions can be studied in various geometries. For example, flow in rotating cylinder and narrow gap concentric cylinder geometries in both horizontal and vertical orientations can be studied. Flow instabilities in settling suspensions in a horizontal rotating cylinder have recently been reported [84], Measurements of velocity fields have not been reported in the literature, but can be performed by using the methods presented in this work. 

Arias, 1999 Haslbeck and Holm, 2005). Both methods are based on a painted polycarbonate rotating cylinder immersed into a holding tank in which artificial sea water of known composition is kept at relatively constant conditions (see Table 1). At specific time intervals, the cylinder is immersed into a 1.5 litre tank where they are rotated for typically 1 hour, after which the total copper released is determined. In this way, copper release rate vs. time curves are obtained. Typically, the average release rate value between day 21 and 42/45 and the accumulated release rate during the first 14 days of exposure are used to compare the different paint systems. 

The remarkable variations in the viscosity of molten sulphur have already been mentioned. Definite measurements have been made at a series of temperatures by the method of rotating cylinders,5 and it, has been found that exposure of the liquid to air, especially below 160° C., has a marked effect on the viscosity from 160° C. onwards. The viscosity of purified (twice distilled but not gas-free) sulphur lias a value at 123° C. of 0 1094 C.G.S. units this falls to a minimum of 0 0709 at 150° C., rises gradually up to about 159° then rapidly increases above this temperature an exact transition point is not observed, however. The maximum for purified unexposed (gas-frcc) sulphur occurs at about 200° C. and has a value of 215 C.G.S. units. For purified (not gas-free) sulphur after prolonged exposure to the air, the maximum occurs at about 190° C, and may have a value as high as 800 C.G.S. units. Such high viscosity appears to be due to impurities, the chief being sulphuric acid, resulting from exposure to the air sulphur dioxide and ammonia in solution also have an appreciable effect. 

A first approach to analyze such volatiles is the application of the AEDA on extracts prepared by dynamic headspace extraction. An apparatus used for the extraction especially of solid foods is shown in Figure 5 [55]. The powdered material is placed into a rotating cylinder and the volatiles are continuously flushed onto a polymer material (Tenax( )) by using a stream of helium (1 L/min). After 3 hr the volatiles are desorbed from the polymer by elution with a small amount of diethyl ether and evaluated by AEDA after concentration. Since different yields may change the composition of the volatiles during headspace extraction [7], it is essential to sensorially evaluate the flavor of the extracts in comparison with the food flavor itself. The following examples show applications of this method on fresh and stored wheat bread crust [55] and on fresh rye bread crust [P. Schieberle and W. Grosch, unpublished results]. 

Several methods are used to produce fibril-lated film. They are produced in much the same way as slit film, but these techniques take advantage of the tendency of PP to fib-rillate. In one method, a profiled tape is extruded and hot-drawn. It is drawn again to achieve a 10 1 ratio, and the film splits into separate filaments. In another method, called roll embossing, the film is hot-drawn, and then embossed using profiled rollers. The profiled film is drawn again, and fibrillation results. In the pin-roller technique, the film is drawn and cut by knives or pins on a rotating cylinder. This method can produce individual fibers or a controlled web network. 

The behavior of melt viscosity of sulfur-dicyclopentadiene solutions is of obvious interest from the point of sprayable coatings. The melt viscosity behavior has been reported recently, but only qualitatively and over a narrow range of compositions (18). The viscosity of sulfur measured by the capillary method by Bacon and Fanelli (19, 20) is considered to be the best (21). Recently, however, the viscosity of sulfur has been measured by an apparatus containing an electric motor and a rotating cylinder (22). Viscosity of the sulfur-DCP solutions are measured here with the help of a Brookfield synchro-lectric viscometer, which is of the later kind. Viscosity measurements have been carried out to follow the copolymerization reaction and to analyze the viscosity behavior. 

In order to reduce the size of bubbles formed by dispersion through filters, additional methods and devices are used, for example, rotating drums [8], horizontally situated filter pores, rotating cylinders causing solution movement [8], shock effects on the bubbles formed [25], round body devices placed over capillary or pore orifice outlet [26]. Very small bubbles can be formed from thin capillaries with diameter up to 10 - 20 im (sometimes up to 4 pm) or very fine filters. However, the rate of foam formation when such capillaries or filters are employed is very low. Simple injection type devices for generating highly dispersed foam... 

The experimental methods for the determination of liquid viscosity are similar to those used for gases ( 8.VII F) (i) transpiration, through capillaries, (ii) torque on rotating cylinders, or the damping of oscillating solid discs or spheres, in the liquid, (iii) fall of solid spheres through the liquid, (iv) flow of liquid through an aperture in a plate, (v) capillary waves. Methods (i) and (ii) are mostly used for absolute, the others for comparative, measurements. 

A popular method of calculating the shear rate at the surface of the rotating cylinder is to assume that the test fluid follows the simple power law model ... 

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