18 



BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. 



for, as previously stated, the use of a mixture of salt and ice in a 

 refrigerator does not increase the cooling capacity of a given amount 

 of ice, but the effect is to cause the ice to melt more rapidly and thus 

 absorb heat more quickly. In other words, the melting point of 

 ice is lowered when mixed with salt. One pound of ice in melting 

 absorbs 144 heat units, either with or without salt. With salt the 

 absorption is quickened, hence a lower temperature for a shorter 



time. Therefore there is no gain 

 in efficiency by employing a mix- 

 ture of salt and ice; in fact, there 

 is a loss in efficiency due to the 

 heat of solution. 



Ice bunkers for cooling pur- 

 poses, when located over the 

 compartment to be cooled, 

 should be made in the form of a 

 box with one side removed, as 

 shown in figure 6, in order to 

 assist the air currents. With 

 this form of construction the 

 air, as it is gradually cooled, 

 flows to the left down over the 

 ice, while the warm air rises on 

 the right to take its place. It 

 is obvious that if the bunkers 

 should be made in the form of a 

 rectangular box the air would 

 have a tendency to flow off in all 

 directions and give rise to con- 

 flicting currents which would re- 

 tard the circulation and for the 

 same rate of circulation a greater 

 difference in temperature between the air in the bunker and that 

 in the compartment below would be required. 



Ample spaces for air ducts should be provided between the sides 

 of the bunker and the walls of the cold-storage compartment in 

 order to permit the air to circulate freely. The cross-sectional area 

 of the ducts should be from 10 to 15 per cent of the area of the ceiling. 

 The floor of the bunker and the walls of the air ducts should be well 

 insulated to prevent the too rapid cooling of the relatively warmer 

 ascending air as well as that lying next the floor of the bunker. 

 Rapid cooling of the air at these points tends to check the circula- 

 tion by reducing the difference in temperature between the warm 



Fig. 6. — Overhead ice bunker. 



