3248 



STORAGE 



STORAGE 



is that it must be comparatively inexpensive and must 

 be within the means of utilization by a comparatively 

 simple apparatus. Ammonia, sulfur dioxide, and carbon 

 dioxide are in general use in about the order named. 

 Ammonia is the most common, and is in many respects 

 the easiest to handle. It may be liquefied at a lower pres- 

 sure and a higher temperature than either carbon dioxide 

 or sulfur dioxide. Carbon dioxide is, therefore, somewhat 

 less efficient to the extent that the high pressure requires 

 more power, there is greater friction to overcome, and 

 colder water is needed for condensation. These condi- 

 tions are not always obtainable within ordinary means. 

 Carbon dioxide has the advantage of being a non-irritat- 

 ing and non-poisonous gas. If leaks occur in the system, 

 there is no great danger of serious injury either to the 

 operators of the machinery or to the goods stored in 

 the rooms. If leaks occur in the ammonia system or in 

 the sulfur dioxide machines, there is very great danger 

 of injury to the workmen about the plant and the food 

 commodities exposed to these gases may be very ser- 

 iously injured, even with a slight leakage. Neverthe- 

 less, the greater ease with which the ammonia machines 

 can be manipulated is considered a sufficient advan- 

 tage, and this type of machine is much the commonest 

 now in use. 



The system of operation of the refrigerating plant is 

 comparatively simple although rather complicated 

 machinery is required. It is not essential that the fruit- 

 grower who contemplates the erection of a refrigerating 

 plant be conversant with all of the complicated details. 

 It is well, however, that he understand the principles 

 upon which the machines are designed. For the erec- 

 tion and planning of a complete storage plant depend- 

 ing on refrigerating machinery, the services of a 

 competent refrigeration engineer are essential. While 

 it may be possible for a mechanically inclined fruit- 

 grower to design and have erected a complete refriger- 

 ating plant, it must not be forgotten that slight errors 

 in the calculation of the power required and the capa- 

 city of the machinery necessary to yield given results 

 will frequently render the operation of the plant very 

 much more expensive than need be, or the efficiency of 

 the plant may be very seriously impaired. Refrigerating 

 machinery is, of necessity, expensive; it is likewise 

 delicate in many respects. 



There are many styles and designs of refrigerating 

 machines. All, however, are dependent upon the same 

 general principles. There is, first of all, the motive 

 power which may be either the gasoline or electric 

 motor, or the steam engine, which furnishes the power 

 to operate the compressor. The compressor exerts 

 pressure on the gas, heating it to a rather high tempera- 

 ture. If the machine is operating with ammonia gas, 

 the compression results in a dense hot vapor. From 

 the compressor, this hot vapor passes to the condenser, 

 which is a system of pipes arranged in such a way that 

 streams of cooling water may be passed continuously 

 around the pipes containing the hot gas. The absorp- 

 tion of the heat from the dense vapor condenses it into 

 liquid ammonia. This liquid is ordinarily run into a 

 receiver or reservoir, where it is kept for use as needed. 

 From the receiver, the liquid ammonia is forced into 

 what is known as expansion coils. These coils consist 

 of series of pipes into which the liquid ammonia is 

 allowed to enter. The liquid boils at a low temperature 

 and changes from the liquid to the gaseous state, and 

 in changing its state and expanding absorbs consider- 

 able heat from the surrounding medium; in this way 

 the refrigeration is obtained. After expansion, the 

 ammonia gas is passed back to the compressor where 

 it is again compressed and afterwards liquefied, the 

 same gas being used over and over again. 



Instead of the compressor, the same effect can be 

 obtained from what is known as the absorption system. 

 This is a combination of a chemical and mechanical 

 process. No compressor is used. Dense aqua-ammonia, 



which is simply a strong solution of ammonia gas in 

 water, is heated in a reservoir, and as the ammonia 

 escapes from the solution, it is under heavy pressure 

 and becomes a dense vapor. From this tank the gas 

 is passed through condensing coils and liquefied, just 

 as is done in the compression system. After liquefac- 

 tion, it is allowed to expand in coils and the gas is 

 then returned to a tank or a series of tanks known as 

 absorbers. These absorbers contain cool water which 

 readily absorbs or dissolves the ammonia gas. From 

 the absorber, the solution is pumped into the heating 

 tank, again heated, and the process repeated. 



When one contemplates the installation of refriger- 

 ating machinery, one of the most important factors to 

 consider is the supply of water needed for condensing. 

 This is ordinarily of very much greater importance 

 than is appreciated. Large quantities of water are 

 needed unless the temperature of the water is very low. 

 The higher the temperature of the water-supply, the 

 larger the quantity needed. The same water may be 

 used continuously if there is some means at hand to 

 cool it after it has served to absorb the heat from the 

 condensing ammonia. In large refrigerating plants this 

 is taken care of by means of large racks or towers 

 located in some exposed place. In these towers, the 

 water is run through screens which break it into many 

 fine streams, thus increasing the evaporation and cool- 

 ing the water by the absorption of its heat. Unless 

 some means is at hand to cool the water, a constant 

 supply must be provided; otherwise, the efficiency of the 

 machinery will be very greatly reduced. This point is 

 of the utmost importance when refrigerating plants 

 are to be located in fruit-growing districts. In fact, 

 the practicability of operating the refrigerating plant 

 successfully depends primarily on the presence of a 

 sufficient supply of water for condensation. 



Ice systems. 



Refrigeration may be obtained from the use of ice 

 alone. In this instance, however, only cool-storage 

 effects can be obtained, except in winter and in climates 

 where the outdoor temperature is low enough to offset 

 the lack of refrigerating effects from the ice. The 

 minimum temperature obtainable from ice is its melt- 

 ing point, which is just above 32 F. or, under the very 

 best conditions, about 33 or 34. Generally, ice-cooled 

 chambers cannot be maintained below a temperature 

 of 38 or 40 and these temperatures are obtainable 

 only under the most favorable conditions. To obtain 

 a low temperature from ice, the addition of salt is 

 necessary. The mixing of salt with the ice lowers the 

 melting-point and, consequently, the temperature is 

 lowered, although the rapidity with which the ice is 

 consumed is very greatly increased. When the mixture 

 of ice and salt is used, the quantity of ice necessary for 

 storage is much greater. A lower temperature is neces- 

 sary to hold the storage chambers at 32 F. because of 

 the heat leakage into the chambers through the walls. 



There are two methods of obtaining refrigeration 

 from ice and salt. One of these is the indirect method, 

 known as the gravity-brine system, and the other is 

 the direct circulation of air through the ice and salt 

 mixture. 



The gravity-brine system, the invention of Madison 

 Cooper, acts as the reverse of a hot-water heating 

 system. It depends on the principle of the greater 

 density of a cold liquid, and its consequent downward 

 flow when confined in a system of pipes. The system 

 consists, first of all, of coils of pipes filled with a strong 

 solution of calcium chloride brine. One end of the pipe 

 system is contained in a tank which holds ice and 

 salt. The cooling effect of the ice and salt results in 

 greatly reducing the temperature and increasing the 

 density of the brine. From these "primary" coils the 

 brine is conducted into what is known as secondary coils 

 which are placed in the rooms or chambers to be cooled. 



