REFRIGERATION. 792 REFRIGERATION. c^-linder, and the cycle of operations just de- scribed is again performed, rollowing now the course of the sealing and cooling oil, which, as previously mentioned, is heated with the gas during compression, tliis oil is passed from the compression cylinder mingled with ammonia gas into the pressure tank, where most of it separates from the gas and falls to the tank bottom. The heated oil is then conducted through a pipe to the lowermost pipe of the oil cooler, which is similar in construction and operation to the ammonia condenser. After being sufficiently re- duced in temperature in the oil cooler the oil flows through the strainer into the oil pump, which is so constructed that it delivers the cooled oil into the compression cylinder, dis- tributing it to either side of the piston or plunger during its compression stroke when it is being compressed and heated. From the compression cylinder the oil proceeds again through the cycle just descrilied. Most of the oil separates from the ammonia gas in the tank, but any small amount that passes on is taken out when it reaches the separating' tank. The three salient parts of the apparatus described are the com- pressor, the condenser, and the expansion coil. There are numerous compressors of othtr makes, all of which differ .structurally from the De La Vergne and from each other. Condensers Turbine io Operate Agihrtor Cold Water Inlet Uqueried 6as Fig. 3. diagram bkction of condenser for liquefying ammonia 0a8 in comphe3sion system. are of two general types, surface condensers and submerged condensers. In submerged condensers the l)il)e coils are suljmerged in the cooling water, and Fig. 3 shows a vertical section of such a construction. In surface condensers the cooling water is simply allowed to trickle from above onto the pipe coils, whence it falls into a basin and is conducted away. The condensers shown in Fig. 2 are of the surface type. Expansion coils are simply coils of pipe of such section as will give a large amount of radiating surface. Their arrangement depends upon the purpose for which refrigeration is to be employed, whether for cold storage or ice-making or other purposes. Systems of refrigeration which use other refrig- erating agents than ammonia differ from the am- monia system chiefly in the character and con- struction of the compressor. They all have the same cycle of operations — namely, compression, condensation, and expansion — which is constantly repeated. The advantages and disadvantages of ammonia and of the other cooling agents used in refrigeration by the compression system may be briefly sunnnarized as follows: The chief ad- vantages of anhydrous ammonia (see Ammonia) are its possession of greater heat-absorbing power than that of an.y of the others, that it liquefies at a comparatively low temperature, and that it is not as explosive nor as inflammable as ether. The advantage of ether as a refrigerating agent is that it liquefies at low pressure and comparatively high temperature, -which adapts it for hot climates. Its disadvantages are that an ether compressor is about seventeen times as large as an ammonia compressor of the same capacity, and that ether is a highly inflammable and explosive gas when mixed with air. The advantage of sulphurous acid or sulphur dioxide is that it liquefies at a low pressure — not so low as ether, but consider- ably loi'er than ammonia. Its chief disadvantage is that it is liable to form sulphuric acid on ex- ])osure to air, which acid rapidly destroys iron. Carbon dioxide has the advantages of being non- inflammable and having a high specific gravity, which renders its heat of vaporization for a given volume much higher than that of anunonia ; it also has no corrosive action on copper. Its dis- advantages are the high pressure required to liquefy it and its fatality to animal life when present in air in any quantity. Absorption Process. The absorption process of refrigeration was invented by Ferdinand CarrS about the year 1850. It is founded upon the fact of the great capacity possessed by water for ab- sorbing a number of vapors having no boiling points, and of their being readily separable there- from again by heating the combined liquid, hence it is commonly known as the absorption process. The process involves the continuous distillation of ammoniacal liquor and requires the use of three distinct sets of apparatus: (1) A set for distilling, condensing, and liquefying the am- monia ; ( 2 ) a set for producing cold by means of a refrigerator and absorber, a condenser, a con- centrator, and a rectifier; and (3) a pumping plant for forcing the liquor from the condenser into the generator for redistillation. The tliree operations are each distinct from the other, but when the plant is actually working they must be continuous and are dependent upon one another, forming separate stages of a closed cycle of opera- tions. An advantage of the absorption process is that the bulk of the heat required for perform- ing the work is applied direct without being transformed into mechanical power. The first machines constructed on this principle were, how- ever, very imperfect in operation, by reason of the impossibility of securing an anhydrous product of distillation. This w-as owing to the distilla- tion, which is the most important operation and has of necessity to be executed in a rapid man- ner, being, in the first machines, very imperfectly
