Refrigerant

“ Evaporation of Nitrous Oxide.
Evaporation of Pure Oxygen.
FIG. 303.—SEPARATION OF LIQUID AIR INTO ITS CONSTITUENTS.
As to the uses of liquid air it may be said that up to the present time it has attained little or no practical application. There are two principal ways in which it may be utilized; one is to employ its enormous expansive force to produce mechanical power, and the other is as a refrigerant. As a means for obtaining motive power it is a fallacy to suppose that any more power can be obtained from its expansion than was originally required to make it. ”

“ Industrial Applications.—While liquid air and liquid hydrogen are being used in scientific research to an extent which increases every day, their applications to industrial purposes are not so numerous. The temperatures they give used as simple refrigerants are much lower than are generally required industrially, and such cooling as is needed can be obtained quite satisfactorily, and far more cheaply, by refrigerating machinery employing more easily condensable gases. ”

“ In the refrigerator the liquid ammonia, in becoming vaporized, will take up the precise quantity of heat that was given off during its cooling and liquefaction in the condenser, plus the amount due to the difference in heat of vaporization, owing to the lower pressure at which the change of state takes place in the refrigerator, and less the small amount due to the difference in temperature between the vapor entering the condenser and that leaving the refrigerator, less also the amount necessary to cool the liquid ammonia to the refrigerator temperature. ”

“ One of these devices employs a gas jet, or lamp light, the heat from which, acting on a kettle filled with chemical compound, produces a low temperature for a small house refrigerator, while the same principle is claimed to be applicable on a larger scale.
The Uses of Artificial Refrigeration are numerous. For cooling and ventilating buildings, aiding in some lines of manufactures, and in chemical works, it has proved its usefulness. In all hot climates it is extensively employed for making ice. In breweries it is applied very extensively, and is practically indispensable. ”

“ In carrying out artificial refrigeration various kinds of machines are used for reducing temperature, in which the desired effect is produced either directly by the condensation and evaporation of suitable materials, such as liquid carbonic acid, ammonia, sulphurous acid, or indirectly by making saline solutions (calcium chloride) , cooled below the freezing point, circulate through a system of pipes fitted on the roof or walls of the space to be cooled. ”

“ A pump draws off the ammonia vapor from the refrigerator coils, and compresses it into the condenser, where, by means of the combined action of pressure and cooling by water, it assumes a liquid form, and is ready to be again passed on to the refrigerator for evaporation. The ammonia compression process is more economical than the absorption process, and with a good boiler and engine about 240,000 thermal units per hour can be eliminated by the expenditure of 100 lb. of coal per hour, with a brine temperature in the refrigerator of about 20° Fahr. ”

“ We have learned how to pump heat and we can make heat vacuums, anywhere and at any time, even in the heart of the tropics, and regions in which no natural ice is ever obtainable have the benefits of refrigeration. Furthermore, we are not dependent upon ice for cooling foods. In many cases it is not necessary or even desirable to reduce temperatures to the freezing point of water. A moderate chilling is all that is required for certain foods. By the proper use of refrigerating machinery any degree of temperature may be obtained and maintained. ”

“ It is this principle that is utilized in refrigeration and ice making. In the absorption system, where aqua ammonia is used, the liquor is contained in a retort to which heat is applied by means of a steam coil, and a great part of the gas which was held in solution by the water is expelled, and carries with it a small amount of water or vapor. This passes into a separator in the top of a condenser, from which the water returns again to the retort, the ammonia gas, under considerable pressure, passing into the coolers. These are large receptacles in which the gas is permitted to expand. ”

“ In fact, the air which issues in a cold state from the tuyère encounters instantly in the furnace a very high temperature, which expands it, and contributes, along with the solid matters with which the furnace is filled, to diminish the facility of the discharge, and consequently to retard the efflux by the nozzles. The oxygen gas consumed is replaced by a like volume of carbonic acid gas, equally expansible by heat. Reason leads us to conclude that less air flows from the nozzles into the furnace than into the open atmosphere. ”

“ In the majority of refrigerating and ice machines ammonia gas is the substance used for producing the refrigeration, although there are other machines in which other material is employed, one of these being anhydrous sulphurous acid, which is also a gas. ”

“ These consist of a motor and a machine for compressing gas, a chamber which is to be cooled, and sometimes coils of pipe containing brine.
When the gas—for example, ammonia or carbon dioxide—is compressed, it heats the pump which compresses it. That is, when a liquid or gas is being compressed, it gives up heat. When a liquid or gas expands, it takes heat from somewhere. In refrigerating plants, the expanding gas is made to take the heat either directly from the refrigerator or storeroom, or from brine which is then used for cooling the refrigerator or room. ”

“ These plants operate by the rapid evaporation of liquefied gases such as carbon dioxide, sulphur dioxide, or ammonia, so arranged as to cool a solution of common salt, which forms the circulating liquor and is returned after use to the refrigerator. Where such plants are used, it is natural that their use should be extended to the drying sheds to cool the air entering in the height of summer. In some factories the cooling is attained neither by cold water nor cooled brine, but merely by cold air. ”

“ Not enough use is made of cooling by evaporation by those who have not ice in the summer. Inexpensive and fairly effective refrigerators may be made, by any mechanic, of lattice-work sides covered with any thick fabric and kept moist, which would keep milk, butter, fruit, vegetables, and cooked meats in good condition if placed in a hallway with a good circulation of air, or in any shady place with good ventilation. ”

“ When the liquid boils, the capsule expands, and by certain mechanical devices regulates the gas supply so as to produce exactly the temperature required.
The procedure is as follows: The jar is filled with milk, and water is run into the copper vessel by the funnel until it runs over at the overflow pipe. The thermostat is lifted off and the full gas supply allowed to pass to the burner, the temperature of the milk brought up to 180° F. and maintained for half an hour at this figure. ”

“ Ammonia Machines. —The use of ammonia refrigeration equipment either absorption or compression has so generally displaced all others for stationary or land use, and particularly in meat plants and cold storage houses, that for the present purpose it is unnecessary to go into a discussion of others. The compression system being so predominant in its use, a description of same is given.
The diagram indicates a compression system in elementary form consisting of:
(1) A pump or compressor which withdraws the gas from the cooler or expansion tank, prepares and passes it to the condenser. ”

“ Cold, even a freezing temperature, is not fatal to bacteria, but it does decidedly retard their growth. Even at the temperature of the ordinary refrigerator (about 10° C. or 40° F.) we find that most organisms multiply very slowly and as a result putrefactive changes are much retarded. Refrigeration is therefore a necessity for the proper keeping of foods, at least during the hot season. But to be efficient the refrigerator must be properly managed. Unless it be kept clean, properly ventilated and well supplied with ice it is practically useless, in fact absolutely dangerous. ”

“ When these chambers have become heated to a high temperature, the waste gases are made to pass through two other similar chambers, and the air and gas necessary for combustion in the furnace are caused to pass through the highly heated regenerators. By causing the ingoing gases to pass alternately, at suitable intervals of time, through each pair of regenerators, a very high and, at the same time, uniform temperature can be obtained in the furnace, without any greater consumption of fuel than in the older methods. ”

“ This is of great convenience in calculating refrigeration required to cool and de-humidify air. For example, suppose it is required to find the refrigeration necessary to cool 1 lb. of air containing 98 grains of moisture and having a dry bulb temperature of 95 deg., to a final temperature of 40 deg. saturated. We find from the chart that the wet-bulb temperature is 75 deg. The total heat corresponding to a saturation temperature of 75 deg. is 37.8 B.t.u., while the total heat at 40 deg. is 15.3 B.t.u. The difference, 22.5 B.t.u. is the refrigeration required per pound of air. ”

“ Color and Roll Treatment. —Color is an important feature of compound, when an odorless oil has been produced. The mixture passed to the rolls is usually at a temperature of 120° F. and this heated body of material amounting to 4000 pounds per hour on an eight foot roll requires a very large capacity of refrigerating equipment.
It is desirable to maintain a brine temperature in the shell of from zero to five degrees above. A fifty-ton refrigerating equipment of commercial rating is inadequate for this duty. Consequently compound manufacturers must have ample refrigerating machine capacity. ”

“ It is not practicable, in any case, to cool the wort sufficiently on the cooler to bring it to the proper temperature for the fermentation stage, and for this purpose, therefore, the refrigerator is employed. There are several kinds of refrigerators, the main distinction being that some are vertical, others horizontal; but the principle in each case is much the same, and consists in allowing a thin film or stream of wort to trickle over a series of pipes through which cold water circulates. Fig. 5, Plate I., shows refrigerators, employed in Messrs Allsopp’s lager beer brewery, at work. ”

“ A refrigerating machine is actually a heat pump with which we produce a partial heat vacuum.
Whenever a gas is compressed, heat is generated. Anyone who has operated a tire pump knows how hot the pump becomes from the heat that is seemingly squeezed out of the compressed air. As was noted in Chapter VIII, heat is liable to give trouble in an air compressor, and sometimes the temperature rises to such a point that there is an explosion of the air and the vapors coming from the oil used to lubricate the machine. ”

“ This experiment has been made use of by M. Carré in his refrigerator (which was described in the Physics’ section) , by which he freezes water. We may, however, just refer to the process. Whenever the condition of a body is changed from that of liquid to a gas, the temperature is greatly lowered, because the heat becomes “latent.” The latest freezing machine consists of an apparatus as shown in the illustrations herewith (figs. 359 and 360) . The machine is of wrought iron, and contains, when ready for action, a saturated [Pg 364] solution of ammonia at zero. ”

“ The best plan is to expose the hot wort for some hours freely to the atmosphere and the cooler, when the loss of heat is most rapid by evaporation and other means, and when the temperature falls to 100°, or thereby, to transmit the liquor through a zig-zag pipe, laid almost horizontally in a trough of cold water. The various methods described under Refrigerator are more complex, but they may be practised in many situations with considerable advantage. ”

“ Every passenger-carrying steamer is provided with refrigerating rooms for the storage of perishable provisions; and as the comfort of the passengers, not to say their luxury, is bound up with these compartments, it will be interesting to glance at the method employed for creating local frost amid surrounding heat.
The big principle underlying the refrigerator is this—that a liquid when turned into gas absorbs heat (thus, to convert water into steam you must feed it with heat from a fire) , and that as soon as the gas loses a certain amount of its heat it reverts to liquid form. ”

“ Now then, when we have the ice-making currents, what happens to the air of varying degrees of temperature? The coldest air is at the bottom of the refrigerator (of course we are always thinking of the best refrigerators) because cold air is heavier than warm air and the warm air rises. Therefore, if you have odorous things do not put them in the ice chamber because the air starting down will carry odors along. Put the odorous things and the things that should be kept coldest on the lower shelves. ”

“ For a same range of temperature between the boiler and the refrigerator, the weight of alcohol which distills in an hour is constant. By the operation of the valve, D, it becomes easy to allow all the liquid condensed in the first refrigerator to pass into the second boiler; and thus the second rectification, which is effected in a more perfect vacuum, is supplied with exactness. The object of this valve, then, is to allow the liquid to pass, and yet to cut off the pressure in such a way as to have a double fall of temperature throughout the whole apparatus ”

“ They buy liquid air.
“Big mills that manufacture locomotives use liquid air. They freeze up whole engine wheels with liquid air, then put on the tires, which are not frozen. When the wheel thaws out it expands and there you have your tire on tight as a drum. Funny business isn’t it?
[149]
“But mostly,” he slid another jug into position, “liquid air is split up before it’s used.”
“Split up?” Johnny stared.
“Sure,” Donald grinned. “Air contains six gases. The principal ones are oxygen and nitrogen. Oxygen is used a great deal, nitrogen very little, except in time of war. ”