BOILER ACCESSORIES: CALORIMETERS Steam from a boiler is generally accompanied with more or less moisture. This, being mechanically suspended in the steam, cannot readily be measured without the use of special apparatus. An instruwent by means of which the percentage of moisture in steam can be determined, is generally called a calorimeter. There are several different types of this instrument, only three of which wil1 be described.
The Barrel Calorimeter. This was invented by the distinguished engineer, Mr. G. A. Hirn, and is not only one of the earliest of these devices, but is by all means the simplest and most inexpensive form of calorimeter in practical use. It is shown in Fig. 67. The essential apparatus consists of a barrel holding about 400 lbs. of water, scales for weighing—and nothing more. A pipe with suitable connections leading from the boiler or steam main, conveys the sample of steam to be tested. This pipe should be provided with a valve, and on the end should be a piece of rubber hose which can readily be inserted in the barrel or removed. The principle of this calorimeter is extremely simple.
As steam flows through the pipe, it is condensed by the water in the barrel, and the increase in the weight of the barrel after the test indicates the total amount of moist steam condensed, while the rise in temperature of the water in the barrel is an exact measure of the quantity of heat obtained from this moist steam.
The steam tables give the number of B.T.U. in dry steam and hot water at various temperatures and pressures; and with this data and the above-mentioned observations made in the barrel, the percentage of steam and moisture can readily be determined.
The sampling pipe usually projects into the steam main a few inches, the end being perforated so that the sample will be drawn from a point near the middle of the pipe. An agitator should be placed in the barrel, so that the water may be thoroughly stirred and a uniform temperature maintained during the test.
To test a sample of steam by this method, fill the barrel about two-thirds full of cold water; place it on platform scales, and carefully note its weight and temperature. The weight of the barrel and
fittings, when empty, should of course be known, so that the weight of the water alone can be determined. With the hose removed from the barrel, allow steam to blow through the pipe until it has become thoroughly heated If the sampling pipe is long, it should be wrapped with hair felt or some form of lagging, to prevent condensation during the test. As soon as the pipe line has become thoroughly heated, plunge the hose into the barrel and allow the steam to blow through the water until it has become well heated. Shut off the steam, and carefully note the weight and temperature.
Suppose W = Final weight of water in barrel; w = Weight of cold, condensing water before steam is turned on; = Temperature of the cold water; t2 = Temperature of the hot water; P = Absolute pressure of steam in steam pipe (gauge pressure + atmospheric pressure).
From the steam tables in the back of the book may be found: q, the B. T. U. in one pound of the liquid contents of the moist steam; q1, the B. T. U. in one pound of the cooling water, before the steam was added; q2, the B. T U. in one pound of this water after the steam has been added; r, the heat of vaporization corresponding to the absolute e., B. T. U. given up by one pound of steam condensed into water.
If x equals the percentage of dry steam contained in the supply pipe, 1 — x will represent the amount of priming.
x (W — w) = the total amount of dry steam condensed; (1 — x) (W — w) = the total amount of moisture brought into the barrel by the moist steam.
If q, equals the heat in one pound of cooling water, then qw will equal the total heat in the barrel at the beginning.
For the same reason will equal the total heat after the steam has been condensed, and q2 W - q, w will equal the total amount of heat gained by the water in the barrel.