To ascertain the Number of Cubic Inches of Water, at any Given Temperature, that must be mixed with a Cubic Foot of Steam to reduce the Mixture to any Required Temperature. RULE. From the required temperature subtract the temperature of the water; then find how often the remainder is contained in the required temperature, subtracted from 1202°, and the quotient is the answer. EXAMPLE. The temperature of the condensing water of an engine is 800, and the required temperature 1000; what is the proportion of condensing water to that evaporated? 100-80-20. Then 1202-100 -=55.1, Ans. Or, let w represent temperature of condensing water, t the required temperature, and h the sum of sensible and latent heats. Then h-t water required. To ascertain the Quantity of Steam required to raise a Given Quantity of Water to any Given Temperature. RULE. Multiply the water to be warmed by the difference of temperature between the cold water and that to which it is to be raised, for a dividend; then to the temperature of the steam add 9900, and from that sum take the required temperature of the water for a divisor; the quotient is the quantity of stean in the came terms as the water. EXAMPLE.-What quantity of steam at 2120 will raise 100 cubic feet of water at 800 to 2120 ? 100X2120-80 21209900-2120 13.3 cubic feet of water formed into steam, occupying (13.3X 1700) 22610.0 cubic feet of space. To ascertain the Specific Gravity of Steam. RULE.-Divide the constant number 829.6 (1700x.488) by the volume of the steam at the temperature or pressure at which the gravity is required. To ascertain the Volume of Steam under a given Pressure, the Temperature answering to that Pressure, in Steam at its Maximum Density for its Temperature being given. 1+.00202x(t-32) 18329 V. When p represents the pressure of the steam in pounds per square inch, t the temperature in degrees (Fah.), and V the volume required. To ascertain the Temperature of Steam. From the pressure in inches of mercury subtract the constant 0.1, divide the logarithm of the remainder by 5.13, and to the quotient add the logarithm 2.132794; find the natural number of the sum of the logarithms, from it subtract the constant 51.3, and the remainder will be the temperature. EXAMPLE. When the pressure is 397.8 inches of mercury, what is the temperature of the steam? Then Natural number, 397.8 Constant temperature, 0.1397.7., log, 397.7 2.599565.13=0.506737 log. 2.132794 436.log. 2.639531 51.30 2.59956. 384.70 temperature required. TABLE of the Elastic Force, Temperature, and Volume of Steam. From a Temperature of 32° to 387.3°, and from a Pressure of .200 to 408. inches of Mercury. To find the mean Pressure by Hyperbolic Logarithms. RULE.-Divide the length of the stroke by the length of the space into which the steam is admitted; find in the table the logarithm of the number nearest to that of the quotient, to which add 1. The sum is the ratio of the gain. EXAMPLE. Suppose the steam to enter the cylinder at the pressure of 40 lbs. per square inch, and to be cut off at of the length of the stroke; what is the mean pressure, the stroke being 10 feet? 10 2.5 4. Hyp. log. of 41.38629+1 Then, as 4: 2.38629;:40: 23.8629 lbs. 2.38629. TABLE of the Density of Steam under different Pressures. 2.30258 21. 3.04452 2.39789 22. 3.09104 The volumes are not direct, in consequence of the increase of heat. STEAM-ENGINE. It is inconsistent with the design of this work to treat of the operation of the steam-engine, and this article will be confined to the exhibition of some rules of construction, the utility of which have been fully tested in the varied purposes of Land, River, and Marine practice. The extremes of proportions here given are for the particular requirements of variations in speed, differences in draughts of water, pressures of steam, &c., &c. CONDENSING ENGINE, A For a range of pressures (indicated by a mercurial gauge) of from 10 to 60 pounds per square inch. 10 Condenser. The capacity of it should be from 3 to 4 that of the steam cylinder. Air-Pump. The capacity of it, exclusive of piston space, should be from to that of the steam cylinder. Steam and Exhaust Valves. Let a represent area of steam cylinder in inches, s stroke of piston in inches, and r number of revolutions axsxr per minute, then the area of the valve = 24000 By experiment, when there were 325 square inches of valye for 290.400 cubic inches in the cylinder, with 26 revolutions, the proportion was found to be a proper one. And 318 inches of valve for 371.000 inches in the cylinder, with 20 revolutions has been used, and the operation, as shown by an Indicator, was held satisfactory Foot Valve. The dimensions of it should give an area of from 1 to s of the capacity of the steam cylinder in inches. 350 Delivery Valve. When a solid piston is used in the air-pump, its dimensions should correspond with that of the foot valve; but when au open piston alone is used, this proportion may not be obtained. Out-board Delivery Valve. The area of it should be from to that of the foot valve. 100 Feed Pumps. Their capacity should be to that of the steam cylinder. Injection Cocks. There should be two to each condenser, the area of each sufficient to supply 70 times the quantity of water evaporated when the engine is working at its maximum; and in marine engines there should be three, viz., a Side, Bottom, and Bilge. The Side and Bottom injections will require (for 20 revolutions) an area in square to the number of cubic feet in the steam cylinder for the for to for the latter.* inches of from mer, and from The Bilge injection is properly a branch of the bottom injection pipe, and may be of less capacity. Piston Rods. Their diameter (if of wrought iron) should be that of the cylinder or air-pump. Cross Heads. Of wrought iron. (Steam cylinders.) For the section at their centre, let a represent area of cylinder in inches, p extreme pressure in pounds per square inch that they may be subjected to, and I their length between the centres of journals in feet; then, where d`represents the depth and w the width of the section. = d2Xw. If the sections are cylindrical, for d2xw read dw×1.7. The proportions here given will admit of a sufficient quantity of water when the engine is in operation in the Gulf Stream, where the water is at times at the temperature of 840, and the quantity of water (when the steam is at 10 lbs. pressure) required to give it and the water of condensation a temperature of 1000; is 70 times tha of the quantity evaporated. |