SURFACE CONDENSERS. 109 
for auxiliaries. This steam contains oil, which, of course, gets on the tubes of the main 
condenser. There is practically no oil from the main turbine, but there is oil from the 
auxiliaries. 
There is a great variation in the coefficient C between what we may call ideal con- 
ditions, with a perfectly clean tube, inside and outside, and without any air in the con- 
denser, and a tube that is dirty, or partially dirty, and where the air conditions are not 
quite as good as they ought to be. Under the ideal conditions 300 into the square root 
of the velocity has been obtained in a number of cases, but under actual service condi- 
tions, about 200 is as good as should be allowed, I think, to secure conservative design 
conditions. It is believed that it should be even lower than that; in other words, be- 
tween 170 and 160 may be taken as a conservative value. This may be lower than neces- 
sary, but I think that most designers would rather err on the safe side and also have 
more surface than they need rather than cut it down to too small an amount. 
In this connection I cannot quite agree with Professor Bragg’s figures reducing the 
surface so much as he has, and I think we should allow from 50 to 100 per cent below 
the ideal conditions to approximate the conditions which actually exist in service. 
There is another point in connection with Mr. Lovekin’s condenser which appears 
to be very good, and that is the method of air extraction. The air must be removed 
from the bottom of the condenser in such a way as not to leave pockets, and it must be 
cooled to a reasonable extent so that the volume of the air will be reduced and all of the 
vapor possible taken out of it, so that the volume of vapor and air handled by the air 
pump will be reduced as much as possible, and so that we will not have to put in an un- 
reasonably large air-extraction pump. Air pockets in the top of the condenser also 
should be avoided. 
The performance of condensers in service is very difficult to obtain accurately, 
because of the difficulty in measuring accurately the various features that we require. 
In the first place, the horse-power and the quantity of steam consumed by a steam turbine 
is difficult to measure, and it is almost impossible to measure them on merchant vessels. 
These two items are absolutely essential to get the proper performance of the condenser. 
The measurement of vacuum is a thing which is done wrong more often than it is 
done right. The ordinary spring gauge is not suitable for measuring vacuum accurately, 
and this gauge is used in the majority of cases by marine engineers in recording the 
vacuum in their logs. Therefore I think that those measurements of vacuum cannot be 
considered as being reliable, and most of the extraordinary results reported from ships 
are results of vacuum measured with spring gauges and are of no value. The most 
accurate way to measure vacuum on board a ship is to take the temperature of the steam 
going into the condenser by means of an accurately calibrated thermometer, which 
is insulated from the exhaust pipe or condenser shell, so that the heat in the sur- 
rounding metal does not influence the temperature of the thermometer. This is a very 
simple way to obtain the vacuum and is accurate beyond all requirements of tests or 
performance. 
There is some difference of opinion as to the vacua that condensers should be de- 
signed for. For turbine vessels the vacuum which can be obtained depends largely 
on the temperature of the inlet water, and with a very high temperature of inlet water 
it is not feasible to maintain very high vacua. 
The following seems to be in fair accordance with common practice-—For 70- 
degree water, design condensing plants for a vacuum of 2814 inches; and for 85-degree 
