Part 17

+-----------+---------------+----------+ |Temperature|Relative Volume|Weight per| | Degrees | Water at 39.2 |Cubic Foot| | Fahrenheit| Degrees = 1 | Pounds | +-----------+---------------+----------+ | 32 | 1.000176 | 62.42 | | 39.2 | 1.000000 | 62.43 | | 40 | 1.000004 | 62.43 | | 50 | 1.00027 | 62.42 | | 60 | 1.00096 | 62.37 | | 70 | 1.00201 | 62.30 | | 80 | 1.00338 | 62.22 | | 90 | 1.00504 | 62.11 | | 100 | 1.00698 | 62.00 | | 110 | 1.00915 | 61.86 | | 120 | 1.01157 | 61.71 | | 130 | 1.01420 | 61.55 | | 140 | 1.01705 | 61.38 | | 150 | 1.02011 | 61.20 | | 160 | 1.02337 | 61.00 | | 170 | 1.02682 | 60.80 | | 180 | 1.03047 | 60.58 | | 190 | 1.03431 | 60.36 | | 200 | 1.03835 | 60.12 | | 210 | 1.04256 | 59.88 | | 212 | 1.04343 | 59.83 | | 220 | 1.0469 | 59.63 | | 230 | 1.0515 | 59.37 | | 240 | 1.0562 | 59.11 | | 250 | 1.0611 | 58.83 | | 260 | 1.0662 | 58.55 | | 270 | 1.0715 | 58.26 | | 280 | 1.0771 | 57.96 | | 290 | 1.0830 | 57.65 | | 300 | 1.0890 | 57.33 | | 310 | 1.0953 | 57.00 | | 320 | 1.1019 | 56.66 | | 330 | 1.1088 | 56.30 | | 340 | 1.1160 | 55.94 | | 350 | 1.1235 | 55.57 | | 360 | 1.1313 | 55.18 | | 370 | 1.1396 | 54.78 | | 380 | 1.1483 | 54.36 | | 390 | 1.1573 | 53.94 | | 400 | 1.167 | 53.5 | | 410 | 1.177 | 53.0 | | 420 | 1.187 | 52.6 | | 430 | 1.197 | 52.2 | | 440 | 1.208 | 51.7 | | 450 | 1.220 | 51.2 | | 460 | 1.232 | 50.7 | | 470 | 1.244 | 50.2 | | 480 | 1.256 | 49.7 | | 490 | 1.269 | 49.2 | | 500 | 1.283 | 48.7 | | 510 | 1.297 | 48.1 | | 520 | 1.312 | 47.6 | | 530 | 1.329 | 47.0 | | 540 | 1.35 | 46.3 | | 550 | 1.37 | 45.6 | | 560 | 1.39 | 44.9 | +-----------+---------------+----------+

Water is but slightly compressible and for all practical purposes may be considered non-compressible. The coefficient of compressibility ranges from 0.000040 to 0.000051 per atmosphere at ordinary temperatures, this coefficient decreasing as the temperature increases.

Table 11 gives the weight in vacuo and the relative volume of a cubic foot of distilled water at various temperatures.

The weight of water at the standard temperature being taken as 62.355 pounds per cubic foot, the pressure exerted by the column of water of any stated height, and conversely the height of any column required to produce a stated pressure, may be computed as follows:

The pressure in pounds per square foot = 62.355 × height of column in feet.

The pressure in pounds per square inch = 0.433 × height of column in feet.

Height of column in feet = pressure in pounds per square foot ÷ 62.355.

Height of column in feet = pressure in pounds per square inch ÷ 0.433.

Height of column in inches = pressure in pounds per square inch × 27.71.

Height of column in inches = pressure in ounces per square inch × 1.73.

By a change in the weights given above, the pressure exerted and height of column may be computed for temperatures other than 62 degrees.

A pressure of one pound per square inch is exerted by a column of water 2.3093 feet or 27.71 inches high at 62 degrees Fahrenheit.

Water in its natural state is never found absolutely pure. In solvent power water has a greater range than any other liquid. For common salt, this is approximately a constant at all temperatures, while with such impurities as magnesium and sodium sulphates, this solvent power increases with an increase in temperature.

TABLE 12

BOILING POINT OF WATER AT VARIOUS ALTITUDES

+--------------+----------------+-------------+---------------+ |Boiling Point | Altitude Above | Atmospheric | Barometer | | Degrees | Sea Level | Pressure | Reduced | | Fahrenheit | Feet | Pounds per | to 32 Degrees | | | | Square Inch | Inches | +--------------+----------------+-------------+---------------+ | 184 | 15221 | 8.20 | 16.70 | | 185 | 14649 | 8.38 | 17.06 | | 186 | 14075 | 8.57 | 17.45 | | 187 | 13498 | 8.76 | 17.83 | | 188 | 12934 | 8.95 | 18.22 | | 189 | 12367 | 9.14 | 18.61 | | 190 | 11799 | 9.34 | 19.02 | | 191 | 11243 | 9.54 | 19.43 | | 192 | 10685 | 9.74 | 19.85 | | 193 | 10127 | 9.95 | 20.27 | | 194 | 9579 | 10.17 | 20.71 | | 195 | 9031 | 10.39 | 21.15 | | 196 | 8481 | 10.61 | 21.60 | | 197 | 7932 | 10.83 | 22.05 | | 198 | 7381 | 11.06 | 22.52 | | 199 | 6843 | 11.29 | 22.99 | | 200 | 6304 | 11.52 | 23.47 | | 201 | 5764 | 11.76 | 23.95 | | 202 | 5225 | 12.01 | 24.45 | | 203 | 4697 | 12.26 | 24.96 | | 204 | 4169 | 12.51 | 25.48 | | 205 | 3642 | 12.77 | 26.00 | | 206 | 3115 | 13.03 | 26.53 | | 207 | 2589 | 13.30 | 27.08 | | 208 | 2063 | 13.57 | 27.63 | | 209 | 1539 | 13.85 | 28.19 | | 210 | 1025 | 14.13 | 28.76 | | 211 | 512 | 14.41 | 29.33 | | 212 | Sea Level | 14.70 | 29.92 | +--------------+----------------+-------------+---------------+

Sea water contains on an average approximately 3.125 per cent of its weight of solid matter or a thirty-second part of the weight of the water and salt held in solution. The approximate composition of this solid matter will be: sodium chloride 76 per cent, magnesium chloride 10 per cent, magnesium sulphate 6 per cent, calcium sulphate 5 per cent, calcium carbonate 0.5 per cent, other substances 2.5 per cent.

The boiling point of water decreases as the altitude above sea level increases. Table 12 gives the variation in the boiling point with the altitude.

Water has a greater specific heat or heat-absorbing capacity than any other known substance (bromine and hydrogen excepted) and its specific heat is the basis for measurement of the capacity of heat absorption of all other substances. From the definition, the specific heat of water is the number of British thermal units required to raise one pound of water one degree. This specific heat varies with the temperature of the water. The generally accepted values are given in Table 13, which indicates the values as determined by Messrs. Marks and Davis and Mr. Peabody.

TABLE 13

SPECIFIC HEAT OF WATER AT VARIOUS TEMPERATURES

+----------------------+--------------------------------+ | MARKS AND DAVIS | PEABODY | | From Values of | From Values of | | Barnes and Dieterici | Barnes and Regnault | +-----------+----------+---------------------+----------+ |Temperature| Specific | Temperature | Specific | +-----------+ Heat +----------+----------+ Heat | | Degrees | | Degrees | Degrees | | |Fahrenheit | |Centigrade|Fahrenheit| | +-----------+----------+----------+----------+----------+ | 30 | 1.0098 | 0 | 32 | 1.0094 | | 40 | 1.0045 | 5 | 41 | 1.0053 | | 50 | 1.0012 | 10 | 50 | 1.0023 | | 55 | 1.0000 | 15 | 59 | 1.0003 | | 60 | 0.9990 | 16.11 | 61 | 1.0000 | | 70 | 0.9977 | 20 | 68 | 0.9990 | | 80 | 0.9970 | 25 | 77 | 0.9981 | | 90 | 0.9967 | 30 | 86 | 0.9976 | | 100 | 0.9967 | 35 | 95 | 0.9974 | | 110 | 0.9970 | 40 | 104 | 0.9974 | | 120 | 0.9974 | 45 | 113 | 0.9976 | | 130 | 0.9979 | 50 | 122 | 0.9980 | | 140 | 0.9986 | 55 | 131 | 0.9985 | | 150 | 0.9994 | 60 | 140 | 0.9994 | | 160 | 1.0002 | 65 | 149 | 1.0004 | | 170 | 1.0010 | 70 | 158 | 1.0015 | | 180 | 1.0019 | 75 | 167 | 1.0028 | | 190 | 1.0029 | 80 | 176 | 1.0042 | | 200 | 1.0039 | 85 | 185 | 1.0056 | | 210 | 1.0052 | 90 | 194 | 1.0071 | | 220 | 1.007 | 95 | 203 | 1.0086 | | 230 | 1.009 | 100 | 212 | 1.0101 | +-----------+----------+----------+----------+----------+

In consequence of this variation in specific heat, the variation in the heat of the liquid of the water at different temperatures is not a constant. Table 22 gives the heat of the liquid in a pound of water at temperatures ranging from 32 to 340 degrees Fahrenheit.

The specific heat of ice at 32 degrees is 0.463. The specific heat of saturated steam (ice and saturated steam representing the other forms in which water may exist), is something that is difficult to define in any way which will not be misleading. When no liquid is present the specific heat of saturated steam is negative. The use of the value of the specific heat of steam is practically limited to instances where superheat is present, and the specific heat of superheated steam is covered later in the book.

BOILER FEED WATER

All natural waters contain some impurities which, when introduced into a boiler, may appear as solids. In view of the apparent present-day tendency toward large size boiler units and high overloads, the importance of the use of pure water for boiler feed purposes cannot be over-estimated.

Ordinarily, when water of sufficient purity for such use is not at hand, the supply available may be rendered suitable by some process of treatment. Against the cost of such treatment, there are many factors to be considered. With water in which there is a marked tendency toward scale formation, the interest and depreciation on the added boiler units necessary to allow for the systematic cleaning of certain units must be taken into consideration. Again there is a considerable loss in taking boilers off for cleaning and replacing them on the line. On the other hand, the decrease in capacity and efficiency accompanying an increased incrustation of boilers in use has been too generally discussed to need repetition here. Many experiments have been made and actual figures reported as to this decrease, but in general, such figures apply only to the particular set of conditions found in the plant where the boiler in question was tested. So many factors enter into the effect of scale on capacity and economy that it is impossible to give any accurate figures on such decrease that will serve all cases, but that it is large has been thoroughly proven.

While it is almost invariably true that practically any cost of treatment will pay a return on the investment of the apparatus, the fact must not be overlooked that there are certain waters which should never be used for boiler feed purposes and which no treatment can render suitable for such purpose. In such cases, the only remedy is the securing of other feed supply or the employment of evaporators for distilling the feed water as in marine service.