Applications of Refrigeration

Marine Refrigeration.—Marine refrigeration has four kinds of refrigeration equipment: (I) Fruit carriers require forced cir culation of cool air with some fresh air, .(2) Frozen meats which require no air circulation but do require good insulation and a storage temperature of from to F, (3) Chilled meats require a heavy piping ratio with the pipes located under the ceilings. The temperature of the cold storage rooms must be con trolled within a small temperature variation, (4) Where general cargoes are carried the frozen meats may be carried in the lower holds.

District Cooling.

Large cities which have segregated cold storage warehouses, commission merchants and retail markets find it convenient to have a central cold storage company which will supply refrigeration under contract. Of these the Quincy Market and Cold Storage Warehouse Company of Boston, Mass. and the Merchants Refrigerating Company of New York are the best known. The former started under the direct expansion sys tem but as the company expanded a change was made to brine, and in 1927 there were 1,400 separate services with 1,500 tons of refrigeration of connected load, exclusive of the warehouse service. The Merchants Refrigerating Company has brine at o° F and carries 400 services varying from 200 to 15,000 cu.ft. of cold storage of which 35% is freezer and 65% is cooler space at from 31° to 35°.

The piping, where brine is used, can be full weight steel or wrought iron pipe usually completely welded between man-holes. Expansion joints must be provided every soo ft. at a maximum, located at man-holes, and they may be of the slip joint, the corru gated or of the U type. The pipe must be placed below the frost line, usually from 3 to 7 ft. below the surface.

Ice Making.

The manufactured ice industry of the United States is one that was estimated in 1924 to comprise an investment of $1,000,000,000. Its importance has developed because of the hot summer conditions in the United States and because of the uncertainty and the cost of transportation of natural ice. Al though the fractional tonnage compressor had removed a large number of the larger ice customers and the household refrigerat ing machines have caused a loss of thousands of residential cus tomers, yet the manufactured ice industry has shown an increase of output of about io% yearly. The natural ice trade was almost negligible in 1928 except in certain regions where ice is cut for car icing or similar purposes.

There have been numerous methods of freezing manufactured ice but the only method now installed in the United States is the "can system." In the "can system" the water to be frozen is

placed in galvanized iron cares which are lowered into a brine at a temperature of from 14° to 17° F. The water in the cans may be either distilled water or drinking (so-called raw) water. One of the peculiarities of the American requirements is that the ice must be transparent. With distilled water it is very easy to get a crystal ice, but raw water cannot be made transparent without agitation and water softening because of the air in solution as well as the bicarbonates and other solids in solution in the water.

Raw Water Ice.—The difficulty with raw water ice, as has been mentioned, is in the treatment of the water to be frozen. The problem is not a difficult one if the water is rain water and in some localities even the non-thermal deep wells are not objection able, whereas in other localities as for example in Indiana, Illinois, Iowa, etc., the number of grains of bicarbonates, sulphates, etc., may be as high as 3o to 4o per gallon. As such water is frozen the solids in solution become more and more concentrated until finally some of these are precipitated. In addition there is the air in solution which of itself would cause an opaque ice should freezing be carried out without using some method to prevent the air bubbles from settling on the freezing surface and freezing into the ice. One of the first concerns of the ice manufacturer is that of water purification and softening. The requirements of first quality ice are clearness, firmness and freedom from dis coloration. One of the best methods of securing this is by the use of the lime-soda ash filter (the water being cold of necessity), followed by a sand filter and an alum coagulator. Softening with lime removes the bicarbonates effectively. It is not necessary to remove all the permanent hardness provided that the magnesium which always tends to cause whiteness in the ice is removed. As a general statement if the sum of the sulphates, chlorides and ni trates does not exceed 20 grains per gallon the water may be puri fied for ice making, if the number of grains range from 20 to 40 per gallon the results are doubtful but if they exceed 4o grains the water will be found to be unsatisfactory for ice making. Up to '12 grains per gallon of solids consisting of sulphates, chlorides, nitrates and sodium carbonates the so-called low pressure air agitation sys tem will give good results whereas if the high pressure air system of air agitation is used the solids may be increased to 20 grains and as good results can be obtained as with 12 grains and low pressure agitation.