444
MODERN GASWORKS PRACTICE
larger condensers. In shape the modern water condenser is nearly always cylin-drical, this section facilitating the building togetlier of tlie mild steel plates forming the shell. Moreover, the stell of the multitubular type has to withstand the stresses due to water pressure, and the cylindrical shape is better able to do so. Only in the case of the largest condensers is it advisable to work to a rectangular section, and then only in those instances in which the saving of ground space is a consideration. So far as the spacing of tubes is concerned there is no hard and fast rule, but it is as well to remember that the free space in the shell should not be too greatly encumbered;
otherwise stoppage will quickly result. A good basis to work upon is that of arranging the tubes so that they occupy about 18 per cent, of the total area of the tube sheet. For water gas this should be in-creased to 25 per cent.
The modern tubulär con-deaser is most frequently made with. the tubes expanded into the top and bottom tube plates ; but, in Order that expansion and contraction of the tubes may take place without und ne straining of the joint, special methods of making the latter are often employed. It will be ap-preciated, moreover, that some considerable difliculty is entailed in removing an expanded tube when renewals become necessary. The special tube-joint employed by R. and J. Dempster is shown in
g I
-
Fig. 273.—Dbmpsteb’s Special Tube-joint.
Fig. 273. .
In all modern condensers means should be provided whereby the direction of flow of both gas and water may be reversed, the cold-water inlet always being in counter-current to the flow of liot gas.
THE CARPENTER CONDENSER
Dr. Carpenter, in dealing with large units of gas, adopts the liydraulic form of condenser, consisting of a series of vertical cooling tubes placed in a cylindrical vessel •containing water. The tops and bottoms of the tubes are connected by gas cham-bers, and the gas is made to flow upwards through the tubes in one vessel and down-