thrown into the receiving tank and not mixed with the sample for analysis.

Mixed Samples.-The all-important point is that the gross sample, whatever the manner of sampling, shall be made up of equivalent portions of oil taken at regular intervals of time, so that the sample finally forwarded for analysis will truly represent the entire shipment.

Water or earthy matter settles on standing. Hence, before a large stationary tank or a reservoir is sampled, the character of the contents at the bottom should be ascertained by dredging with a long-handled dipper, and the contents of the dipper should be examined critically. If a considerable quantity of sediment is brought up, it should be cause for rejecting the oil.

CHAPTER XXXV

MEASUREMENT OF STEAM USED IN ATOMIZATION

As has been previously set forth, there are three methods used in pulverizing or atomizing the fuel oil in the industries for heat generating purposes, namely: by compressed air, by steam, and by some mechanical operation.

In any one of these instances the actual expenditure of energy necessary to accomplish this result when converted into heat units should be charged as a loss in furnace operation, when the efficiency of the boiler as a whole is being determined. And if this energy is taken from the steam that is being generated in the boiler, then the net steam energy should be computed by subtracting from the gross production such steam as may be used in atomization.

It then becomes the task of the steam engineer to construct some accurate and convenient apparatus whereby this may be easily and accurately accomplished.

There are steam meters on the market that may be utilized for this purpose, and if a careful design is picked, the measurement may be relied upon. Many engineers, however, prefer the use of a standardized orifice or the construction of an apparatus of their own whereby this important data may be ascertained with

accuracy.

Mathematical Expression for Flow of Steam.-In the mathematical considerations involved in establishing a formula for steam flow through orifices, a rather unique incident is encountered. When the pressure of the lower medium into which the steam empties itself is less than 58 per cent. of the higher pressure, a certain formula applies. And the rather remarkable thing is that below this point the flow is neither increased nor decreased by a reduction of the external pressure, even to the extent of a perfect vacuum. This was the basis upon which Napier's formula was derived in the chapter on Steam Calorimetry, wherein a formula was given to compute the steam utilized for operating the calorimeter. In this formula it was

seen that, if W is the weight of the steam in pounds per second flowing into the atmosphere, p the absolute pressure in pounds per square inch in the steam main, and a the area of orifice in square inches, we have

FIG. 185.-Steam flow meter and draft gage on the left with Venturi meter on the right. This apparatus is at the Redondo Steam Plant of the Southern California Edison Company.

For steam flowing through an orifice from a higher to a lower pressure where the lower pressure is greater than 58 per cent. of the higher, we have the formula

(2)

wherein W is the weight of steam as discharged in pounds per minute, A the area of orifice in square inches, P the absolute initial pressure in pounds per square inch, d the difference in pressure between the two sides in pounds per square inch, and K

is a constant which has a value of 0.93 for a short pipe and 0.63 for a hole in a thin plate or a safety valve.

This latter formula is applicable in the measurement of steam to burner utilized in the atomization of fuel oil. In the following lines a method will be outlined setting forth the necessary apparatus involved in determining the variables in the formula. Instead of actually substituting and solving numerically, however, it is far simpler to construct a chart and pick from this the

FIG. 186.-Steam flow meter with integrating device for registering total quantity of steam passed.

steam consumption for any given steam pressure and pressure. difference in an orifice placed in the main.

Here then is presented a ready and accurate means of steam measurement for atomization purposes. A diaphragm with an orifice opening of 0.5 of a sq. in. in area is inserted in the steam line. On both sides of this diaphragm are drilled holes which are tapped for a 14-inch pipe. The pipes are then connected to both legs of a manometer filled with mercury. A manometer is

nothing more nor less than a U-tube filled with mercury. When these two ends are connected with pipes of varying pressures, the mercury in the U-tube will of course be raised to a higher point in one leg of the U-tube than in the other. The difference in this height represents in inches of mercury the difference in pressure between the two sides of the diaphragm. If now a steam gauge be inserted in the steam main on the boiler side of the diaphragm, we are enabled by means of the atmospheric barometer reading to express these pressures in absolute pressure units as set forth in the chapter on pressures. On the burner

FIG. 187.-Apparatus employed in measuring steam in atomization. The flow of steam through an orifice wherein a slightly lower pressure is maintained on the further side of the orifice, is found experimentally to be proportional to the difference in mercury heights indicated on the manometer shown on the right in the illustration. By calibrating these readings prior to a test the steam used in atomization may be conveniently and readily determined during a test.

side of the steam main a thermometer is inserted as shown in order to measure the temperature of the steam fed to the furnace, as this steam in many instances is superheated and hence the pressure reading does not indicate the temperature existing.

A manometer is accurately calibrated prior to the test by allowing the steam to be discharged into a barrel for a period of time under varying manometer readings. A curve is then plotted similar to the one shown in the illustration, which sets forth the pounds of steam passing per minute for any particular manometer reading in inches of mercury. If, then, readings are taken