pressed air from the former to the latter, its surface was employed to reduce the temperature of that air from the 280 degrees Fahrenheit which it had on entering the pipe to the 56 degrees which it had on leaving the pipe to enter the expanding cylinder; and this cooling was accomplished by exposing part of the surface of the pipe to the air outside of the room containing the machine, but inside the building containing that room, and the remaining part to water constantly flowing through a tank placed on the floor of the room and supplied from the Croton mains, with a temperature of 55 degrees Fahrenheit, which was maintained in the tank. The pipe from the air-compressing cylinders to the tank had, for the length of 22 feet, an outside diameter of 1% inches, and an inside diameter of 1.69 inches, and, for the remaining length of 270 feet, an outside diameter of 2% inches and an inside diameter of 2.65 inches. The aggregate outside surface of this pipe was 214.02150 square feet, and its aggregate inside surface was 197.05162 square feet. The pipe immersed in the tank (in direct continuation of the preceding, the two forming one pipe) was 156 feet long, 11⁄2 inches in outside diameter and 1.33 inches in inside diameter, exposing to the water an outside surface of 61.26120 square feet, and an inside surface of 54.31826 square feet. The pipe from the tank to the air-expanding cylinder (in direct continuation of the preceding and forming with them one pipe) was 20 feet long, 1% inches in outside diameter and 1.69 inches in inside diameter, exposing to the air of the lower portion of the room containing the machine an outside surface of 9.81750 square feet, and an inside surface of 8.84884 square feet. All these pipes were continuous and had their interiors in common. They were distributed in lengths returned upon each other for economy of space, like the pipes of ordinary steam-heaters. From the compressing cylinders a length of pipe rose vertically to a convenient height; thence the remaining pipe was nearly horizontal, being arranged with a slight and uniform inclination to the expanding cylinder, in order to drain whatever water might be deposited from the compressed air as it cooled. The pipe surface, measured on the outside, exposed first to the air, was 214.02150 square feet, and measured on the inside was 197.05162 square feet, and that air had the temperature of 45 degrees Fahrenheit. Then a surface of 61.26120 square feet, measured on the outside of the pipe, and of 54.31826 square feet, measured on the inside, was immersed in the water of the tank, which water entered the tank with the temperature of 50.6 degrees Fahrenheit, and left it with the temperature of 55.2 degrees. Finally, the remaining 9.81750 square feet of pipe surface, measured on the outside, and 8.84884 square feet, measured on the inside, were exposed to air of 55 degrees Fahrenheit temperature in the lower portion of the room containing the machine. The lowest depression of the pipe was just at its entrance into the expanding cylinder, and at that point a water-trap was placed, which delivered the water of deposition from the pipe as fast as it accumulated, and thereby prevented its entrance into the expanding cylinder. Had this water entered the expanding cylinder, the low temperature existing there would have congealed it into very hard ice, whose mechanical obstruction would have rendered the working of the machine impossible. This trap is an absolutely essential part of the airrefrigerating system, which could not be reduced to practice without it. There is one horizontal double-acting air-expanding cylinder of 5 inches diameter, with 9 inches stroke of piston. Its axis is in the same horizontal plane as the axes of the steam cylinder and compressing cylinders, and it lies on the outer side of the compressing cylinders, so that the latter are between it and the steam cylinder. The piston of the expanding cylinder is connected directly to the crank-pin of a single crank on the main shaft, through the usual piston-rod, crosshead between guides, and connecting-rod. The air-expanding cylinder is fitted at each end with two poppet valves worked by cams. One valve, adjustable at will, is for the admission of the compressed air from the pipe, and it closes when any desired fraction of the stroke of the piston has been completed, thus acting as the expansion valve as well as the admission valve of the air. The other valve is for exhausting the air from the cylinder; it opens when the piston has completed the air stroke, and remains open during the exhaust stroke. The air in the cylinder had neither lead nor cushion. The area of the port at each end of the cylinder was I square inch. The portion of the stroke of the piston of the air-expanding cylinder performed while the expansion valve was open was done by the pressure of the air-compressing pistons through the medium of the air in the connecting pipe; the air for this portion of the stroke was therefore used absolutely without expansion. For the remaining portion of the stroke the piston of the airexpanding cylinder was driven entirely by the expansion of the air admitted during the first portion of the stroke; and all the refrigeration below the general temperature of the air in the room containing the machine was produced after the closing of the expansion valve by this expansion of the air in its performance of work upon the main shaft. The air entered the expanding cylinder at the temperature of 56 degrees Fahrenheit, and left it with the temperature of 57 degrees, making a total fall of temperature of 113 degrees Fahrenheit. All the power developed in the air-expanding cylinder was expended on the compression of air in the two air-compressing cylinders. The steam cylinder, the two air-compressing cylinders, and the air-expanding cylinder are situated side by side on the same bed-plate, and had their axes in the same horizontal plane. They were all connected directly to the same main shaft, which extended clear across one end of the bed-plate. The compressing cylinders were between the steam cylinder and the expanding cylinder, so that the whole formed a compact arrangement, occupying a space 10 feet 4 inches long, 6 feet 7 inches wide, and 4 feet 9 inches high. The space occupied by the water-tank was additional to the above, and was 13 feet long, 21 inches wide, and 11 inches high. The water from this tank was carried to the water-jackets of the compressing cylinders, and thence discharged. The space occupied in the air by the pipe connecting the compressing and expanding cylinders was still more additional. The chamber to be refrigerated was constructed with double floor, ceiling and sides of pine boards, and the intervening space was filled with sawdust. This chamber should have no inleakages of air, no outleakages except through the proper delivery, and its floor, ceiling, and sides should be as little heatconducting as possible. The capacity of the chamber was 11,419 cubic feet, equivalent to the capacity of a cube whose sides are 22.519 feet. The chamber had near its top a hole of 34-inch diameter, through which the air delivered by the expanding cylinder escaped into the atmosphere. The pressure in the refrigerated chamber was slightly greater than that of the atmosphere, so that any leakages must have been outward. The barometer in the chamber stood at 30.240 inches, and outside the chamber at 30.106 inches. The exhaust pipe from the expanding cylinder to the refrigerated chamber was 121⁄2 feet long, and had the outside diameter of 4 inches. It was exposed to an air-temperature on its outside of 56 degrees Fahrenheit. It entered the chamber at the height of 7 feet 5 inches above the floor. The 34-inch diameter hole by which the air left the chamber was 9 feet above the floor. The following are the dimensions of the principal working parts of the refrigerating machine : Space in clearance and steam passage at one end of Area of steam-cylinder port (10 inches by 0.6 inch)..... Number of right angles in exhaust pipe. ......... ..... Length of connecting-rod between centres............... .............. Outside diameter of fly-wheels............................................................................................. AIR-COMPRESSING CYLINDERS. Number of air-compressing cylinders (single-acting)... 2 Diameter of piston-rod (no rod at the side of piston Stroke of the pistons...... ......... ............. Space displacement of one compressing piston per stroke........ There is no clearance nor passage to valves. Length of connecting-rods between centres.......... 12 inches. 2 inches. 9 inches. 113.0976 square inches. 0.58905 cubic foot. 2 53 inches. 1 inches. 2 inches. 3 inches. AIR-EXPANDING CYLINDER. I Number of air-expanding cylinders (double-acting)..... Stroke of piston of air-expanding cylinder.... Space in clearance and steam passage at one end of Bulk of the entire refrigerating machine, with the exception of the space occupied by the pipe exposing 285 square feet of outside surface and connecting the air-compressing and the air-expanding cylinders, in its various convolutions to obtain from external air and water the necessary cooling for the air within...... 323. 132 cubic feet. Side of a cube having the capacity of 323.132 cubic ft. 6.862 feet. PROPORTIONS. I.79744 9.79037 Cubic feet of capacity of steam-cylinder per cubic foot BOILER. 1.98104 The steam cylinder was supplied from one boiler having horizontal flues in direct continuation of the furnaces with horizontal tubes returning above the flues and furnaces. There was no steam chimney or other means for superheating the steam; but there was over the centre of the boiler a cylindrical steam drum or reservoir, from the top of which the steam pipe proceeded to the steam cylinder. This pipe was 321 feet long, 3 inches in inside diameter, and had nine right-angled bends. The front portion of the boiler was rectangular in plan, with a semicircular top. The back portion was cylindrical and its upper half was a horizontal extension of the semicylindrical top of the front portion. The following are the principal dimensions and proportions of the boiler, namely: Extreme length of boiler........... Extreme breadth of front portion of boiler... Number of furnaces...................... ........................... ............... Length of grate bars.... Total area of grate surface. ................................... Number of flues (three from each furnace)...... Inside diameter of flues, four of 11 inches and two of 17 inches. Length of flues......... Number of tubes (iron), Outside diameter of tubes........................ .................. .......... Inside diameter of tubes. Area of heating surface in the tubes, calculated for their inside circumference........ Area of all other heating surface.......................... ........................... 8 feet 6 inches. 2 feet 4 inches. 47 feet 6 inches. 83.776 square feet. 3 inches. 520.730 square feet. 251.494 square feet. 856.000 square feet. Cross-area of the flues for draught... 6.038 square feet. 4.148 square feet. 4.276 square feet. Square feet of heating surface per square foot of grate surface.......... 23.778 Square feet of grate surface per square foot of crossarea of flues........ 5.962 Square feet of grate surface per square foot of crossarea of tubes........ 8.679 Square feet of grate surface per square foot of cross area of chimney.... 8.419 The boiler and steam pipe were thoroughly protected from heat radiation by felt and lagging. The feed water was taken from the mains of the Croton Aqueduct, in which the pressure was so great that scarcely any expenditure of power was required to do the feeding. THE EXPERIMENT. With the refrigerating machine as described, an experiment was made on the 18th of November, 1879, of eight hours and fifty-five minutes, consecutively, duration. Indicators were placed permanently on the steam cylinder, on the air-compressing cylinders, and on the air-expanding cylinder, from each end of all which an indicator diagram was taken every half hour; eighteen complete sets of diagrams were thus taken during the experiments and equi-spaced over it. The results hereinafter given are the means of all these diagrams. The variation in the steam pressure (controlled by a governor), and in the revolutions of the main shaft (equalized by two heavy fly-wheels), were so slight that the mean results from the diagrams may be taken to represent accurately the mean performance for the whole time. The number of revolutions made by the main shaft was taken by a counter. Compared thermometers were permanently hung so as to give the temperature of the air in the market building outside of the chamber containing the refrig. erating machine, the general temperature of the air in that chamber, and the local temperature of the air entering the compressing cylinders. Two thermometers were permanently inserted in the pipe connecting the compressing and expanding cylinders, one being placed as close as possible to the air-compressing cylinders so as to give the temperature of the compressed air when leaving them, and the other being placed as close as possible to the air-expanding cylinder so as to give the temperature of the compressed air when entering it. Two other thermometers were permanently inserted in the exhaust pipe of the air-expanding cylinder, one as close to that cylinder as possible to give the temperature of the air leaving it, the other as close as possible to the refrigerated chamber to give the temperature of the air entering it. This exhaust pipe connects the air-expanding cylinder with the refrigerated chamber. A thermometer was placed in the refrigerated chamber 18 inches from the end of the exhaust pipe of the air-expanding cylinder, in order to obtain the temperature of the refrigerated air after it had spread that short distance into the chamber. Another thermometer was so hung as to give the general temperature of the air in the refrigerated chamber. And still another was hung to give the temperature of the air as it left this chamber. The temperature of the water from the Croton mains, used for feeding the boiler and supplying the cooling tank and water-jackets, was also given by permanently placed thermometers, which showed the temperatures of this water when entering and leaving the tank and when entering and leaving the jackets. Compared barometers were placed in the chamber containing the refrigera ting machine and in the chamber refrigerated, to show the difference of pressure in them. Pressure gauges were permanently inserted into the boiler; into the steam pipe near the steam cylinder, but on the boiler side of the throttle-valve; into the pipe connecting the air-compressing and air-expanding cylinders at the point where the compressed air leaves the former, and at the point where the same air enters the latter. All the water passing through the tank and through the water-jackets was measured. This quantity is the same for both tank and jackets, the water being led from the former through the latter. All the water discharged from the watertrap placed in the lowest point of the connecting pipe close to its entrance into the air-expanding cylinder, was measured. The temperature of this water, on emerging, was the same as that of the compressed air at the same place. All of the above quantities were observed every half hour and entered in the columns of a tabular record. The means of these columns will be found below. |