CANE SUGAE. 



of the level of the upper tube plate ; the contained juice creeps up the sides 

 of the tuhes, and in this form permits a rapid exchange of heat. Claassen's 

 observations give the following coefficients of transmission : 



Tubes full ..'.... ,.. .. .. . 2-50 



Tubes two-thirds full . . 3'00 



Tubes one-third full . . . . 3'60 



Euissellement 2'90 



Entrainment. By entrainment is meant the carrying over of sugar 

 along with the vapours and its consequent loss. Entrainment may take place 

 in two distinct ways : in the first case the loss is entirely mechanical, and is 

 due to splashing following on a vigorous ebullition, particles of juice being 

 projected into the vapour pipe of the vessel. In the second case, loss is caused 

 by vescicular transference ; by this term is meant the formation of bubbles of 

 liquid, which being very light in proportion to their bulk are readily earned 

 forward with the stream of vapour. 



FIG. 176. 



The first cause of entrainment is capable of control ; the more vigorous 

 the ebullition the greater is the height to which particles of juice will be 

 projected ; with vessels having tubes of great length bubbles of steam formed 

 at the lower layers will burst with greater force on reaching the vapour space 

 than where the tubes are shorter ; further, tubes of short length imply vessels 

 of large diameter and consequently a less velocity to the current of vapours 

 moving forward to the next vessel. Losses due to splashing may be entirely 

 prevented by the use of bafflps, and better still by an amplo vapour space. 



The best known contrivance to prevent loss in vescicular transference is 

 the Hodek Ralentisseur, Fig. 176, very extensively used in the beet sugar 

 industry, but not often found in cane sugar factories, the island of Mauritius 

 being an exception, and upon which many other designs have been based. 

 The Hodek Ralentisseur consists of a vessel of considerably greater diameter 

 than the vapour pipe, and of length generally about twice its diameter; it is 



306 



