CANE SUGAR. 



(b) A steam belt completely encircling the calandria. 



(c) Division of the main steam or vapour pipe into two or more branches, 

 which may lie in the same horizontal or vertical plane, or four branches may 

 be used, two in the same horizontal and two in the same vertical plane. 



(d) The use of an internal vapour pipe passing down through the lead 

 box of a vessel and connecting with the calandria at the position often 

 occupied by the central juice circulating tube ; in this design an annular space 

 is arranged between the calandria and the shell of the vessel. 



Circulation of the Juice.* The circulation in an evaporator may 

 be either positive or induced ; the former when the circulation is obtained by 

 means of pumps withdrawing juice from and returning it to a vessel and 

 the latter when the circulation is obtained by the skill of the designer. In 

 the earlier evaporators the central circulating tube (shown in Fig. 158) was 

 absent and circulation too was restricted; 

 the addition of this tube probably acts 

 in the following way. Owing to the 

 absence of heating surface the juice 

 therein contained is cooler than that 

 in the tubular cluster and tends to 

 sink ; its place is taken by hotter j uice 

 from the tubes and a regular circulation 

 from centre towards the periphery is 

 induced. In some apparatus the tube is 

 placed at the side remote from the 

 steam entry and it may be replaced 

 by a space formed by cutting away a 

 segment of the calandria on the side 

 remote from the steam entry. The 

 circulation so induced may be aided by 

 asymmetry in the design of the shell ; 

 thus the saucer instead of sloping equally in all directions may be bellied 

 on one side. 



The utilization of temperature difference to induce a circulation has been 

 further developed by the combined use of live and of exhaust steam; in 

 Heckman's circulator, Fig. 17!j., a small tubular cluster is arranged without, 

 "but connected to, the main calandria, and is heated with live steam; in 

 Rohrig's and Konig's design live steam is also used, the calandria taking the 

 form of a small annular cluster arranged symmetrically with the vertical axis 

 of a vessel. 



* Just before sending his MSS. to the press the author read Prof. Perry's The Steam Engine; 

 in Chap. XXXIII. (edition of 1907), entitled "How Fluids give up Heat and Momentum," he 

 discusses the importance of circulation of both hot gases and water as affecting the efficiency 

 of the boiler: between the evaporator and the boiler there is a difference of degree only; 

 his remarks on boilers are equally applicable to evaporators and should be studied carefully 

 .by all sugar house engineers. 



304 



Fm. 174. 



