Temperature Control Tubes

Figure 5.1 The Knowles water electrolysis cell Key A, steel cell tank B, temperature control tubes C, electrodes D, leads E, gas collection bells F, insulating sleeves G, sealing and safety tubes H, J, insulating caps (top, bottom) K, copper connections M, gas take-off pipes N, drain tubes O, S-pipes ...

High-quality and also expensive molds can be manufactured using the porous nickel-galvanos. In the special procedures, porous galvanic molds with thicknesses up to 2 mm can be manufactured. These molds are backfilled, and if necessary provided with temperature control tubes. 

The temperature control tube (Figure 2.88) is introduced into a core bore hole and is supplied by a feeding unit. The temperature control medium (e.g., water or air) flows through the tube, exits at the front side, and flows between the core bore hole and the temperature control tube back into the outlet. 

FIGURE 2.88 Temperature control tube (source STRACK Norma GmbH)... 

Drawing of the dried fibers was carried out continuously in a temperature controlled tube furnace at 105 °C. The draw ratio was varied up to a maximum of about 6 by changing the relative speed of the feed and take up spools at either end of the heated tube. The speed of the feed spool varied from 3 to 6 cm/min, while take up varied from 8 to 32 cm/min, depending on the desired draw ratio. The length of the heated zone of the tube furnace was =12 cm. 

Generally speaking, temperature control in fixed beds is difficult because heat loads vary through the bed. Also, in exothermic reactors, the temperature in the catalyst can become locally excessive. Such hot spots can cause the onset of undesired reactions or catalyst degradation. In tubular devices such as shown in Fig. 2.6a and b, the smaller the diameter of tube, the better is the temperature control. Temperature-control problems also can be overcome by using a mixture of catalyst and inert solid to effectively dilute the catalyst. Varying this mixture allows the rate of reaction in different parts of the bed to be controlled more easily. 

The thermal expansivity of Ni—Fe alloys vary from ca 0 at ca 36 wt % Ni (Invar [12683-18-OJ) to ca 13 x 10 / C for Ni. Hence, a number of compositions, which are available commercially, match the thermal expansivities of glasses and ceramics for sealing electron tubes, lamps, and bushings. In addition, the thermal expansion characteristic is utilized ia temperature controls, thermostats, measuriag iastmments, and condensers. 

Fig. 5. Vacuum caUbrator for pipe and tubing extmsion A, molten tube from die B, tank C, hinged cover with gasket D, siting rings E, circulated and temperature controlled water E, water level G, vacuum and H, inside of pipe open to atmospheric pressure (15).

Phthalic anhydride. Naphthalene is oxidized by air to phthalic anhydride in a Bubbling flmdized reaclor. Even though the naphthalene feed is in liquid form, the reaction is highly exothermic. Temperature control is achieved by removing heat through vertical tubes in the bed to raise steam [Graham and Way, Chem. Eng. Prog., 58, 96 (Januaiy 1962)]. 

Acrylonitrile. Acrylonitrile is produced by reacting propylene, ammonia, and owgeu (air) in a single flmdized bed of a complex catalyst. Known as the SOHIO process, this process was first operated commercially in 1960. In addition to acrylonitrile, significant quantities of HCN and acetonitrile are also produced. This process is also exothermic. Temperature control is achieved by raising steam inside vertical tubes immersed in the bed [Veatch, Hydrocarbon Proce.ss. Pet. Refiner, 41, 18 (November 1962)]. 

Figure 2.2.4 (Berty 1983) shows a tubular reactor that has a thermosiphon temperature control system. The reaction is conducted in the vertical stainless steel tube that can have various diameters, 1/2 in. being the preferred size. If used for fixed bed catalytic studies, it can be charged with a single string of catalytic particles just a bit smaller than the tube, e.g., 5/16 particles in a l/2 O.D. tube. With a smaller catalyst, a tube with an inside diameter of up to three to four particle diameters can be used. With such catalyst charges and a reasonably high Reynolds number— above 500, based on particle diameter—this reactor...

Figure 4-8 shows a continuous reactor used for bubbling gaseous reactants through a liquid catalyst. This reactor allows for close temperature control. The fixed-bed (packed-bed) reactor is a tubular reactor that is packed with solid catalyst particles. The catalyst of the reactor may be placed in one or more fixed beds (i.e., layers across the reactor) or may be distributed in a series of parallel long tubes. The latter type of fixed-bed reactor is widely used in industry (e.g., ammonia synthesis) and offers several advantages over other forms of fixed beds. 

The oldest technology involved in the elastomer blending and vulcanization process is essentially a temperature controlled two roll mill as well as internal mixers followed by an optimum degree of crosslinking in autoclave molds (compression, injection, etc.) in a batch process or in a continuous process such as continuously heated tube or radiated tubes. A few examples of laboratory scale preparation of special purpose elastomeric blends is cited here. 

Exiting steam from the roof and convection-pass cooling sections is collected in headers and typically passes through a primary superheater tube bundle, where a controlled amount of superheat is provided. In the superheater the steam discharges through an outlet header and across a spray attemperator (which provides the steam temperature control) and is then delivered to the control valves for distribution and subsequent use in a turbine or other items of process equipment. 

A perfect temperature-controlled heat-transfer surface is difficult to achieve, but it is closely simulated in practice by using a control fluid on one side of, for example, a metal tube. The tube wall should be thin and, ideally, the heat-transfer resistance comparatively large for the other fluid on the working side of the tube the latter surface is then effectively temperature-controlled and responds only to changes in the control fluid. 

The continuous polystyrene process which was commercialized successfully in 1952 (2) is illustrated schematically in Fig. 16. It is characterized by three vertical elongated reactors in series, the contents of which are gently agitated by slowly revolving rods mounted on an axial shaft. Temperature control is provided by horizontal banks of cooling tubes between adjacent agitator rods. Such a reactor, called a "stratifier-... 

The maximum rate of polymerization has been confirmed to occur at the laminar-turbulent flow transition. The rate of polymerization was observed to be maximum at the transition for both straight reactors as well as for the helically-coiled reactor for which the transition is at a Reynolds number higher than that of the straight tube. The helically coiled tubular reactor is of industrial interest since it is much more compact and, consequently, the cost and the temperature control problems are more tractable. 

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