Such is the apparatus which has been called the rafraichis-soir or refrigerator; it is very simple in its construction, nor is its action less remarkable. By this method, we have no operation of the pulverising of water: a system of a complex and often unhealthy nature, particularly if in the hands of ignorant and negligent persons.
The utility of the apparatus consists in the perforated plate, which presents a large plane of action. It is to be remarked that the same air can be reintroduced into the apartment where its beneficent effects are required. In fact, if the fresh air introduced by the apparatus seizes upon the noxious gas, it will be definitively expelled; on the other hand, if it have only conquered some degrees of heat, it can again be taken up by the ventilator and again conducted to the perforated plate, there to leave in the water the hurtful particles, and again recommence its course. Well- or spring-water will supply the liquid at the required temperature; the temperature, in fact, can be lowered to about 53} F. (12°C); if a lower temperature is required, this can be obtained by placing ice or frigorific materials on the perforated plate. In all places coolness exists under the surface, no matter what the temperature of the climate; and it is sufficient to simply extract this cold naturally represented by water obtained from a certain depth, to produce fresh and even cold air.
Several thousand cub. yd. of air per hour may be cooled; and for this purpose a plate measuring 1 sq. yd. is sufficient. (Jonglet.)
The principle of Mignon et Rouart's process lies in the cooling of the air by contact with refrigerating liquids. They undertook to maintain at a uniform temperature one of the buildings of the Royal Candle Factory at Amsterdam during the hot months of the summer and autumn. This building is over 50 yd. in length by 14} yd. wide, and 13 1/2 ft. in height, and some 30,000 lb. of oil, at a temperature of about 140°F. (60° C.), are passed in daily to be crystallised into stearic acid. The problem was to maintain during the hot weather a temperature not exceeding 54° F. (12° C). This was accomplished in the following manner. A concentrated solution of lime chloride prepared with ammonia solution, which gave 60,000 negative calories per hour, was made, and a fan was provided for driving the air at the rate of 20,000 cub. yd. per hour, the capacity of the building being upwards of 3000 cub. yd. A large cylinder was so fitted with internal plates fixed to the sides, and also with a vertical axis carrying plates or paddles arranged so as to pass between the plates affixed to the sides of the cylinder, that when the refrigerating liquid was poured in at the top, and the vertical axis revolved, the mixture was carried by the centrifugal force of rotation against the sides of the cylinder, and being prevented from rising by the plates fixed therein, was forced down to the plate next below, where a similar effect was produced upon it.
The result of this arrangement and motion of the apparatus was to produce a finely-separated spray or slowly-falling cascade of the cooling liquid, which constantly filled the interior of the cylinder. The air was drawn by the fan from the lower part of the heated building, and, after passing through the cooling apparatus, was driven in from above. It was found that from the 20,000 cub. yd. driven through it hourly, the apparatus abstracted nearly 60,000 calories, and the result of the experiment was so far satisfactory that during the hottest part of the summer and autumn, the temperature of the building was kept down to an average of 54° F. (12°C), the readings scarcely ever varying more than 2° or 3°. The inventors do not furnish any details of the cost, so as to compare results with any of the refrigerating machines at present in use; but it will be seen that this method of producing cool air promises to be largely useful in many industries. The lime chloride solution becomes impoverished to a certain extent by use, owing mainly to the absorption of a large amount of watery vapour from the heated air drawn from the building.
Fig. 17 illustrates Boyle's arrangement for cooling the air entering a room in hot weather. It consists of an air inlet tube of bracket-form, made of iron. The part which penetrates the hole in the wall has an outer casing, so that a space of about } in. is left between, which is packed with a non-conducting substance, for the purpose of preventing the heat from the wall penetrating into the interior of the opening and acting upon the blocks of ice, which are placed in a movable drawer, and kept in position by means of open galvanised iron or copper wire netting. The front of of ice, and from thence on to the ice at the bottom of the drawer, and thence up the tube into the room. The air is not only cooled, but purified thoroughly from dust.
Cooling and. Freezing Water. - Refrigeration, or the artificial production of ice, consists simply in transferring the heat of the water (or other body to be frozen) to some other body. Water at 60° F. (151/2° C.) contains an excess of heat beyond that of an equal weight of ice at 32° F. (0° C.) amounting to 170.65 heat units for each lb., therefore, to reduce the water from the first temperature to the second will necessitate the abstraction of that amount of heat from it; to reduce 1 ton of water will require the removal of 62,720 heat units, or 2240 lb. X 28 (the difference between 32° and 60° F.). It would still be water. To convert it into ice, it is further necessary to abstract the latent heat, which determines the liquid state of water, amounting to 142.65 heat units for each lb. of water; or, for 1 ton, 2240 lb. x 142-65 = 319,536 heat units, bringing the total to 332,256 heat unit). It is thus evident that about 5 times greater expenditure of power is necessary to transform water at the freezing-point into a solid condition (ice), than is necessary to reduce its temperature from the ordinary point to the freezing-point; and this fact must be borne in mind in the practical application of refrigeration to commercial purposes, where a low temperature will often be as effective as the actual production of ice.