FIGURE 1. YoRK
OLD STYLE “Ak-FRAME”
VERTICAL
SIXGLE-,4CTING
COMPRESSOR DIRECT-CONNECTED TO YORKCROSS-COMPOUND STEAM ENGINE
The Common Refrigerants J. S. BEAMENSDERFER York Ice 3lachinery Corporation, York, Pa.
C
LOSELY related to the ever-expanding
refrigeration industry is the field of chemistry, for all volatile refrigerants are produced by chemical processes. The refrigerating engineer who applies them to a refrigeration system must have more than a casual knowledge of the chemistry of the refrigerants he uSes because there are usually chemical reactions between the refrigerant and other elements of a refrigeration systemlubricating oil, metals, packing, etc.-which must be understood and controlled. Viewed in perspective, the refrigeration industry should present a striking challenge to the chemist-commercially because it has been a remarkably active industry in the recent years of business doldrums, and technically because its chemical requirements demand exacting specifications in matters of purity and freedom from moisture. -41~0,the refrigeration industry is alert for new refrigerants and has fostered a number of research projects which led to development and adoption of new refrigerating fluids. There is probably no other subject which mill invoke more attention and discussion in a refrigeration conrention than refrigerants. The earliest use of refrigeration on a large wale was for the manufacture of ice. The impetus was given by the severe shortage of natural ice in 1890. Early machines used ammonia as a refrigerant since the advantageous properties of this fluid had been known and used since the middle of the eighteenth century. 1027
The refrigerants in common use constitute an interesting variety of chemicals, and their performance in a refrigerating system is always a matter for careful study in connection with compressor, condenser, and evaporator design.
Since about 1873 when experimenters, such as David Boyle in the United States and C. P. G. Linde in Germany, began producing commercially successful ice machines, developments in refrigeration have been closely allied to the history of ammonia. In the past few years several other refrigerants have been utilized and new ones developed to meet needs of the widening field of applications for refrigeration. These early ammonia machines were heavy, well built, and rugged, operating at low speeds from 60 to 90 r. p. m. Whether vertical or horizontal, they were patterned after the current steam engine design with external crank, crosshead, and sliding piston rod working through a stuffing box. Because of the variation of the low and high side pressures as compared to steam practice, the valves were operated by differential pressure instead of mechanical means. As the field of refrigeration application broadened, subsequent designs were necessarily aimed at reductions in space required by the machines. To a large extent this was accomplished by the enclosed machine design of the vertical type and also by increased speed which was attainable with lighter and better valve design. The enclosed-type machine, following gas engine practice
1028
INDUSTRlAL AND ENGINEERING CHEMISTRY
VOL. 27, NO. 9
only as a gas above 88" F. It is therefore classified as a low-temperature refrigerant and can be used in compression cycles to nearly - 70 " F. and as cooling agent in solid form as low as -108" F. a t atmospheric pressure. The rather low critical temperature of 88" F. does not prevent its efficient use when condensing temperatures are above this point, if it is properly handled by superpressuring the condensing side in relation to the existing condensing water temperature. I n a carbon dioxide refrigerating system the machines, pipes, and vessels must be designed to withstand the high pressures encountered. Compressor valves must be designed for the hemy gas to be handled, while the small volumes circulated adapt this refrigerant to reciprocating machines with resultant small cylinder dimensions. Carbon dioxide is not reactive with metals except in the presence of moisture. It is not soluble in oil to any extent, and oil passed out of the compressor will need to be removed from the evaporator by some type of oil return. It is inert, odorless, and nonexplosive. I n general, carbon dioxide refrigeration systems have been used only for low-temperature work industrially and in places where its low toxicity is a factor, as in ships and theaters. Solid carbon dioxide, or dry-ice, is applied commercially FIGURE 2. MODERNSELF-CONTAINED AMMOKIA CONDEKSING with some system of temperature control for foodstuffs such as ice cream and frozen foods. The manufacture of dry-ice UNIT(4-INCHBORE AND INCH STROKE) is accomplished by the compression and condensation of carWith improved designs, compressor speeds have been bon dioxide gas, resulting in liquid carbon dioxide which is stepped up in little more than a quarter of a century from less then expanded to atmospheric pressure, thereby forming than 100 r. p. m. to as high as 1800 r. p. m. with reciprocating carbon dioxide snow. This is pressed into dry-ice blocks. machines, and to 5000 and 10,000 r. p. m. with centrifugal The practical use of carbon dioxide as a gaseous refrigerant machines, the result has been the installation of large refrigerin general should be limited to temperatures above -65" F.; ating capacities within narrow space limits. but dry-ice temperatures as low as - 160" F. may be obtained in vacua. Refrigerants in Common Use Ammonia While many substances have been used to some extent as Ammonia is the oldest refrigerant in practical usage and refrigerating media, those in most common usage in the varistill holds the position of a leader as far as its thermodynamic ous fields of present application are ammonia, carbon dioxide, properties for maximum economy are concerned. On acFreon, sulfur dioxide, methyl chloride, methylene chloride, count of its large refrigerating effect per pound and the relawater (to some extent), trichloromonofluoromethane (F-ll), tively small volume of gas required for circulation, it can be and several other fluorine compounds. Table I lists certain used in a reciprocating compressor with fairly small cylinder properties of the various refrigerants. dimensions. While the standard ton unit of refrigeration has been desigwith trunk piston and with the cranks and connecting rods enclosed in the crankcase became the forerunner of the socalled commercial and household machines, since this design is fundamentally compact and is limited in its reduction of size only by the feasibility of designing valves.
TABLEI. PROPERTIES OF REFRIGERAXT~
con B. p. a t atm. pressure,
F. -108.4 Gage pressure, Ib./sq. in.: 319.7 At 5' F. 1024.3 At 86' F. 553.1 At 40' F. Above critical At 100' F. Refrigerating effect:, F. condensing and 5' F. evaporator temp. 55.5 loOD F. condensing and 40" F. evaporator temp. Refrigerant circulated cu. ft./min./ton: 0.960 86-5O F. conditioks 1012-40' F. conditions -4bove critical a Subatmospheric pressures, in inches of mercury
.....
NHa -28.0 19.6 154.5 58.6 197.2
CCliFz
CH&I
SO2
CChF
-21.7
-10.6
14.0
74.7
5.9" 51.8 12.4 69.8
23.P 3.6 15.5= 9.0
11.8 93.2 37.0 117.0
6.2 80.8 28.1 102.3
CHzClz 104.9 27.39 9.62a 23.07a 2.67a
Hs0 212.0
Solid
28.56" 29.67O 27.990
474.4
51.1
148.7
141.4
65.4
134.6
.....
467.8
51.5
150.8
138.5
67.9
136.0
1008.9
37.0 16.1
74.0 27.6
Solid
3.44 1.696
nated for the conditions of evaporation a t 5" F. and condensation a t 86" F., an evaporation temperature of 40" F. and a condensing temperature of 100" F. have been included for the purpose of permitting comparison a t conditions more nearly met in the field of comfort cooling.
Carbon Dioxide Carbon dioxide is unique among the refrigerants in that it is either a solid or gas at atmospheric pressure, does not exist as a liquid except above 60 pounds per square inch gage pressure (corresponding to approximately - 70" F.), and exists
5.815 3.075
6.10 3.60
9.08 4.17
484.0
Ammonia compressor valves need not be of heavy construction to handle the light gas and hence can be designed to operate quietly. The refrigerant is not reactive with iron and steel, and can be used with brass or bronze when there is no water in the system. Its solubility in oil is comparatively low. I n general, the use of ammonia as a refrigerant should be limited t o temperatures above -50' F. It is widely used in industrial refrigeration plants, in capacities up to hundreds of tons of refrigeration. Until recently the most common source of ammonia was
INDUSTRIAL AXD ENGIKEERING CHEMISTRY
SEPTEMBER, 1933
1029
illuminating gas plants, which produced it as a by-product in the distillation of b i t u m i n o u s coal. Ten or more years ago, however, the synthetic process of manufacturing this refrigerant came into prominence and now produces a large portion of the present ammonia consumed.
Freon During the past few years the greatest activity in new refrigerants has centered around the development of several fluorine derivatives of hydrocarbons. To date the most important of these i s F r e o n (dichlorodifluoromethane) which came into use in 1932-33. Freon is now one of the common refrigerants, with thermodynamic properties which make it suitable for reciprocating machines. The displacement volume requirements are 60 to 70 per cent more than that of ammonia. Since pressures encountered with Freon are somewhat lower, machine construction may be of lighter materials, full-weight pipe or c o p p e r t u b i n g being usable. Compressor v a l v e s must be designed to handle a heavy gas similar to carbon dioxide. FIGunE Freon is an active cleansing agent, so DuTY FREON that any system u s i n g i t m u s t b e FOR LA t h o r o u g h l y cleaned before charging. DITIOFiI It is not miscible with water; hence a DIRECT F r e o n s y s t e m s h o u l d be free from TO S Y I moisture when operating a t temperatures below 32' F. Freon is miscible -with oil in all proportions; consequently e v a p o r a t o r s should be designed to permit easy return of oil with the Freon gas to the compressor crankcase. When this is accomplished, an equilibrium of solubility will be obtained in a short time, so that no oil will be lost from the compressor crankcase. Since it is odorless and nontoxic, Freon is a popular refrigerant in air-conditioning applications. Refrigeration compressors as large in capacity as 500 tons of refrigeration have been designed for use with Freon; smaller self-contained units are employed for such commercial refrigeration as in meat markets. This smaller compressor is of a type now widely used in small and moderate size air-conditioning systems. Freon is also used to a limited extent in household refrigeration. I n general, the practical use of Freon as a refrigerant should be limited to temperatures above -30' F.
Methyl Chloride Methyl chloride has thermodynamic properties that make it usable in reciprocating machines of the smaller sizes and, in comparison, requires a volume displacement about 1.8 times that of ammonia. The pressure characteristics allow the use of light machine construction and copper tubing or full-weight pipe. Oil and methyl chloride are miscible in all proportions; thus an evaporator design which will return oil to the machine is necessary. The use of methyl chloride as a refrigerant is usually limited to comparatively small systems and to temperatures above -20' F. Methyl chloride is used extensively in commercial refrigeration up to 20 or 25 horsepower sizes for business establishments in which meat, fish, ice cream, milk, flowers, etc., must be preserved. It is also used in household refrigeration and
is second only to sulfur dioxide in that field. The use of methyl chloride as a refrigerant became quite common in Europe about 1920. Methyl chloride is made by two basic processes: The first is a reaction, in the presence of a catalyst, of methyl alcohol and hydrogen chloride : CH30H HCl = CHaCl HzO The second method is fractional distillation of natural gas to isolate methane and cause a reaction between methane and chlorine.
+
+
Sulfur Dioxide One of the refrigerants that came into use with the development of small, commercial and household units is sulfur dioxide. Its thermodynamic properties require a machine cylinder volume of 2.5 to 3 times that of ammonia, which allows its use in reciprocating machines of the smaller capacity. Materials may be of light construction, such as copper tubing. Sulfur dioxide is absorbed in oil to a slight extent, but, since it is heavier than oil, any lubricant passing out of the machine to the evaporator will float above the liquid refrigerant, and evaporators must be designed to return this oil to the machine. Extreme care must be taken to make sulfur dioxide systems moisture-free, since water and sulfur dioxide form sulfurous acid which is active in attacking metals. This refrigerant is an irritant, and leaks are easily detectable by the odor. The use of sulfur dioxide as a refrigerant should be limited to temperatures above -20" F. and to small systems. A traditional enemy of refrigeration systems is moisture,
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VOL. 27, NO. 9
INDUSTRIAL AND ENGINEERING CHEMISTRY
and refrigerant manufacturers have gone to great expense to provide a refined and moisture-free product for the refrigeration industry. The ordinary commercial grades of sulfur dioxide, for instance, are not sufficiently pure and dry for refrigeration. Instead, refrigeration grades are furnished. In the case of sulfur dioxide, the moisture content is kept in the neighborhood of 20 p. p. m.
F-11 A member of the new family of refrigerants to w-hich Freon belongs is F-11, first used as a heat-transfer medium in a household absorption refrigerator which was merchandised for a year or so starting in 1932. It has recently been adopted for certain high-temperature air-conditioning work. In general, the chemical characteristics of F-11 (trichloromonofluoromethane) are similar to Freon, although the thermodynamic characteristics are quite different. The volume of gas to be handled is about eleven times that of ammonia; consequently F-11 is not adaptable to the reciprocating type of machine but must be handled in a compressor of either the rotary or centrifugal type in order to circulate sufficient volume of the gas. The pressures encountered are such that all applications result in vacua on the evaporating side, and practically all result in pressures somewhat above atmosphere on the condensing side. On this account, steps must be taken to eliminate air from the system for efficient operation. Oil is miscible in all proportions with F-11, and provision must be made in the evaporator design for the return to the machine of any oil passed through the discharge from the compressor. I n general, the practical use of F-11 as a refrigerant should be limited to temperatures above -5" F.
Methylene Chloride This refrigerant has thermodynamic properties which dictate the use of a refrigerating machine of the centrifugal type, because of the large volumes of gas to be handled. I n comparison to ammonia over twenty times the volume must be circulated. Pressures are almost entirely below atmos-
pheric in the range of application, so that it generally becomes necessary to provide for elimination of air from the system. Compressor speeds necessary to handle the large volumes of methylene chloride are such that increasing gears are frequently introduced to step u p synchronous motor speeds. In order to produce efficiently the pressure differential and ratio of compression between the condensing and evaporating sides, multistaging is employed. This staging is increased as the evaporating temperatures are reduced. The application of methylene chloride has been largely to the field of air-conditioning. However, within the last two years one manufacturer has produced many household refrigerators using this refrigerant. I n general, the practical use of methylene chloride as a refrigerant is limited t o temperatures above 5" F.
Water A substance which for some years has engaged the interest of engineers for a refrigerant is water; just recently a number of air-conditioning installations using water as the refrigerant have been made. Although water would be a cheap refrigerant and its nontoxic features are unquestionable, the thermodynamic properties present several difficult problems. Since water solidifies a t 32" F., it could never be used as a low-temperature refrigerant. The volumes of gas to be handled when refrigerating at 40" F. are in the neighborhood of 285 times that of ammonia. Such tremendous volumes are feasible only with a machine of the high-speed centrifugal type or with a steam jet. The pressures at which evaporation and condensation must take place are, in general, not less than 28-inch vacuum, necessitating a design that becomes extremely sensitive to the presence of air and one which is capable of creating and maintaining high vacua with some reasonable efficiency. As a medium in refrigerating systems, the application is almost entirely in the field of air-conditioning. I n general, the practical use of water as a refrigerant can be limited to temperatures above 40" F. RECEIVED
&lay 10, 1935.
OSE OF THE 400-BARREL BREWING THE BREWIKG CORPORATIOS OF AMERICA
UNITSOF
The brew kettle (left) has E one-piece bottom, the largest ever hammered in this country. The mash tub and grant are shown in the background.
Coiirteiy,
Buffalo F o u n d r y and M a r h z n e Co.
