Inclined tube evaporators

Dealing with evaporators operated under vacuum the static pressure of the liquid at the bottom of the bundle can be high in comparison to the pressure at the top. In such a case it is recommended to use evaporators with an inclined tube bundle, see Fig. 7.1-4. Such an arrangement leads to a reduction of the differences of the boiling temperatures at the bottom and the top of the tube bundle. 

Fig. 7.1-4 Recirculating evaporator with inclined tube bundle...

In an inclined tube evaporator the tubes are inclined, usually 30 to 45 degrees from horizontal. (See Figure 11-9.) In early designs the inclined calandria was mounted directly to the bottom head of a vapor body and the downcomer recirculating the product from the separator back to the bottom of the calandria was incorporated within the steam chest. Circulation in this configuration was sometimes impaired because of heat transfer across the downcomer. A first Improvement was to insulate the downcomer. Circulation was further improved by providing a downcomer external to the evaporator. 

Inclined tube evaporators sometimes perform well in foaming services because of the sharp change in flow direction at the vapor head. It sometimes offers advantages when treating heat sensitive materials. Inclined tube evaporators require low headroom and permit ready accessibility to the tubes. 

Figure 11-9 Natural-circulation Inclined-tube evaporator with downcomer integrel with steam chest. (Bennett, Sons Shears Ltd.).

For evaporation at the boiling point either a conical flask with a short Pyrex funnel in the mouth or a round-bottomed flask inclined at an angle of about 45° may be employed in the latter the drops of liquid, etc., thrown up by the ebullition or by effervescence will be retained by striking the inside of the flask, while gas and vapour will escape freely. When organic solvents are employed the flask should be fitted with a swan-neck tube and a condenser so that the solvent is recovered. 

Procedure, ioo c.c. of the wine are evaporated in a flask to io c.c., allowed to cool and treated with 6 c.c. of the saturated ferrous sulphate solution and 4 c.c. of concentrated sulphuric acid.1 The flask is connected with a vertical condenser about 50 cm. long and heated carefully over a small flame so that excessive frothing of the mass is avoided. The distillate is collected in two or three well-cleaned tubes, each containing 2-3 c.c. of the iodide-starch paste acidified with 2 drops of dilute sulphuric acid the tubes are inclined so that the distillate flows down the walls. In presence of nitrites, a blue ring forms at the zone of separation between the starch and the distillate. 

Directions a) Fill a small test tube with water and invert it in a pneumatic trough nearly full of water. Obtain from an instructor a small piece of sodium in a dry evaporating dish. Caution Never handle sodium with your fingers, as enough moisture is present on them to cause action. Always use pincers. With the left hand raise the inverted test tube till its mouth is about an inch below the surface of the water in the trough. With the right hand quickly insert under the mouth of the test tube the piece of sodium held in the pincers. When the action of the sodium and the water has ceased, place your thumb over the mouth of the tube, carry the tube to the burner and uncover it in an inclined position with the mouth downward and close to the fiame. (1) What occurred (2) What... 

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