Sizing of tubes

The extended mandrel technique, illustrated in Fig. 6.22b, is highly desirable for fluoropol5miers because it provides internal cooling and support to the tube. The shrinkage of the plastic as a result of cooling causes a tight contact between the tube and the metal mandrel that can extend up to 30 cm beyond the die. Longer mandrels have been difficult to use due to mechanical difficulties. Surfaces will eventually cor- 

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Nusse/t Number. Empidcal correlations can be obtained for a particular size of tube diameter and particular flow conditions. To generalize such results and to apply the correlations to different sizes of equipment and different flow conditions, the heat-transfer coefficient, Z, is traditionally nondimensionalized by the use of the Nusselt number, Nu named after Wilhelm Nusselt,... 

Determine the number and size of tubes required to calculate this area. Also set the number of tube passes and tube pitch. 

If this value is not reasonable, reassume the tube length, and/or the size of tubes. Try to keep the number of passes fewer than 8 except in special cases, as construction is expensive. 

Assume or estimate a unit size (number and size of tubes, shell, etc.). 

There are three important dimensions of any tubular product outside diameter (OD), inside diameter (ID) and wall thickness. Sizes of pipe are listed by the nominal, or approximate, ID and the wall thickness. The actual OD and the wall thickness list sizes of tubing. 

These meters have been very useful for handling liquid metal coolants where the conductivity is high though they have now been developed for liquids such as tap water which have a poor conductivity. Designs are now available for all sizes of tubes, and the instrument is particularly suitable for pharmaceutical and biological purposes where contamination of the fluid must be avoided. 

Equations (3) and (4) are accurate for any size of tube but since the radius of curvature b is very difficult to measure, they cannot be used until a relation between b and the radius of the tube is obtained. 

One reason for the popularity of peristaltic pumps is their versatility they can be programmed for low or high speeds. Tubes vary in diameter to cover a variety of flow rates. The various sizes of tubes are color coded for diameter and output rate. Another advantage is ease of cleaning After a run, just throw out the inexpensive tubes and put in clean ones. The tubes can also be capped and preserved with the container of color to be used the next time it is run. Peristaltic pumps are self-priming, and a cycle is included in the programming of the pump to fill the output tube up to the extruder or molder quickly. 

Comments. Methods for obtaining melting-points are not usually given in the specifications, but it is absolutely necessary that a definite procedure and definite apparatus be agreed upon. The following points should be taken into consideration calibration and stem correction of thermometers, size of tubes, amoimt of substance taken, rate of melting and vessel of liquid to be used as bath. 

There is some limitation to the size of tubing that can be wound on any given former. It has been found that tubing will be appreciably distorted if it is more than one-quarter of the diameter of the spiral former. Since a small amount of distortion, or flattening, of the mbe makes no difference to the performance of the spiral and very little difference to its appearance, the ratio of former diameter to tube diameter may be taken as 3 to 1. 

A selection of cork stoppers to fit the sizes of tubing in stock. 

C. The catalyst will consist of 0.20 by 0.20-in. cylinders, and the bulk density of the packed bed may be taken as 50 Ib/ft for each size of tube. The superficial mass velocity of g es through each tube will be 400 lb/(hr) (ft tube area). Use the one-dimensional design procedure. 

Knowledge of these operations is useful as a guide for work in the laboratory, where short lengths of tubes for special purposes may be easily made out of any other size of tubing available. In fact, very often a short length of tube wider or narrower than the tube worked on may easily be formed out of the tube itself, and thus an unsightly joint saved. 

The size of tubing is indicated by the outside diameter. The wall thickness is specified by the BWG (Birmingham wire gauge), ranging from 24 (very light) to 7 (very heavy). Sizes and wall thickness of tubing are listed in Perry s "Chemical Engineers Handbook, 3d ed., pp. 417, 42 38. 

Various sizes at this erKi to fit various sizes of tube (Oisposabre, reusable)... 

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