346 



CHAPTER XVIII 



to some place where the pressure is lower, as, for example, to the vapour 

 space of the same cell. Various arrangements of piping are shown in Figs. 

 191, 192 and 193, 



As arranged in Fig. 191, the pipes lead directly from the upper tube plate to 

 the vapour space of the same cell and end flush with the upper tube plate. 

 In this arrangement the degree of opening is not under the control of the 

 operator. As shown in Fig. 192, perforated pipes pass through the calandria ; 

 the collecting pipe passes through the side of the apparatus and on to the 

 calandria of the next cell ; a valve allows the opening to be regulated. 

 As indicated in Fig. 193, collection takes place at the top and the bottom of the 

 calandria, the collecting pipes uniting into one outside the vessel, where 

 a valve is placed. In this arrangement the collection of the gases takes place 

 at a point remote from the steam entry. 



The gases are sometimes vented from cell to cell and sometimes direct 

 from anv cell to the condenser. In the latter case all the steam which 



Fig. 191 



Fig. 102 



Fig. 193 



escapes along ^vith the gases is totally lost ; and, besides, there will always 

 be observed difficulty in regulation, owing to the large difference in pressure 

 between the condenser and the earlier vessels. 



The loss of steam along with the gases has been given by Claassen,^* 



as based on Napier's formula for the flow of gas from an orifice : G = n F ^^JE. 



where G is the rate of flow, F the area of the orifice, p the pressure of the escap- 

 ing gases, V their specific volume, and n a constant. If G is in lbs. per sec, 

 F in sq. ins., p lbs. per sq. in., v cu. ft. per lb., n for circular orifices is about 

 0-3. Claassen shows that with large openings very serious losses of steam may 

 occur, and for apparatus of 10,000 sq. ft. he advises the following openings : — 



First body ^| in. ; second body ^^ — if i"- ' ^^ird body || in.— i in. ; 

 fourth body i^Vi"- ^^ ^^^° advises the use of diaphragms, the setting of 

 which is left to the superintendent and not to the workman. 



The distribution of the temperature fall and rate of working of a multiple 

 effect apparatus can be controlled by means of adjustment of the valves on 

 the incondensible gas pipes. If the valve on the third vessel be opened 

 wide, communication is established between vapour space 2 and calandria 4. 



