Ammonia is a chemical compound made up of one part nitrogen and three parts hydrogen and is expressed by the chemical symbol NH₃. It has some peculiar characteristics being analogous to water. It will assume a solid, liquid and gaseous form, at -115° F. and -28¹⁄₂° F. for solid and liquid respectively and will modify to a gaseous form at any temperature above -28¹⁄₂° F. under “atmospheric” or conditions of no pressure.
Water, as is known, changes from a liquid to a solid at 32° F. and changes to a vaporous form at 212° F. but here the analogy ceases.
Ammonia has further peculiar advantages for use in refrigerating production that it becomes a liquid at variable pressures and temperatures; for example, when the temperature is reduced to 60° F. under a pressure of 92 pounds, when reduced to 80° under a pressure of 139 pounds and at 100°, under a pressure of 200 pounds; with variables above, between and below these conditions. Ammonia, as will be seen, has variable forms and capacities under the conditions imposed upon it. Substances passing from a liquid to a gaseous form require heat to make this change and consequently absorb it; the complement to the giving up of heat when the process is reversed and the substance changed from a gaseous to a liquid form. The adoption or harnessing of these principles is the nucleus upon which mechanical refrigerating effect is built. A pound of water passing to steam will absorb about one thousand degrees of heat, ammonia has the same characteristic to a different degree. They both return the heat when the process is reversed.
Type of Machine Illustrated.
—The [diagram] illustrates a single acting pump showing its piston, a liquifier or condenser where the ammonia is modified in form from a gas as received therein to a liquid; a receiver to which it flows and a cooler in which it is expanded and where the heat brought to it by the returning brine is picked up by the ammonia and carried to the condenser. The arrows indicate the direction of flow.
Compressor.
—The “Compressor” is a pump, a cylinder fitted with a piston which withdraws the ammonia from the tank in which it is expanded. The piston is tightly fitted and when it travels in one direction, the gas flows in, filling the space, like any ordinary pump whether it be a water or gas pump. Upon the return stroke, the gas is compressed in the cylinder until the pressure in the piston is sufficient to equal or overcome that exerted against it accumulated in the condenser, when it is discharged thereto. There are spring actuated valves interposed in the line of gas travel which close and retain in the condenser that gas which has been discharged, allowing the piston and compressor to repeat the just described performance many times per minute.
Condenser.
—The use of this element is to liquify the ammonia, really to extract the heat absorbed by the ammonia in the cooler and the heat generated in the compression. This condensing operation changes the form of the substance from gaseous to liquid. The most simple style of condenser is a series of pipes stacked together with ammonia on the inside of the several pipes, and water flowing over the outside. The gas on leaving the compressor is hot and at a high temperature, frequently as high as 250° F. or more, and the pressure from 140 to 220 lbs., depending upon the water supply, its temperature and quantity, and the area of the surface of the condenser.
The water flowing over the condenser absorbs the heat from within, the ammonia becoming cooled by contact with the comparatively cool walls of the pipe while flowing from one end to the other of the condensing coil, gradually changing from a gaseous to a liquid form.