APPLICATION OF REFEIGEKATION TO HANDLING OF MILK. 47 

 CONGEALING-TANK SYSTEM. 



There is in use a modification of the brine-storage system known 

 commercially as the " congealing-tank system." The principal 

 advantage of this system is that by using a weak solution of brine 

 a greater amount of refrigeration per cubic foot of brine is obtained 

 by freezing a portion of the brine on the direct-expansion coils. 

 This method, however, is not so efficient as the brine-storage system, 

 due to the fact that the ice formed around the coils acts as an insula- 

 tion. But the advantage gained in being able to store a greater 

 amount of refrigeration in a small space often makes it advisable to 

 install this system. In the operation of the congealing-tank system 

 care should be taken not to let the volume of brine in the tanks 

 freeze solid, for during the hold-over period some of the brine ice will 

 melt, leaving a space between the ice and the sides and bottom of the 

 tanks, and when starting up the refrigerating machine the smaller 

 space between the ice and sides of the tanks will freeze first; con- 

 sequently when the larger volume of brine at the bottom freezes the 

 sides of the tank will be bulged out, due to the expansive force of the 

 freezing brine. Therefore, ample space between the coils and sides 

 of the tanks should be provided in order to allow the requisite amount 

 of brine ice to form around the pipe coils at a safe distance from the 

 sides. When a part of the brine solution is to be frozen, the volume 

 of brine required is necessarily less than that required for a brine- 

 storage tank system of the same capacity. In practice about one- 

 half the volume of the brine storage is allowed for the congealing- 

 tank system. Therefore the case under consideration will require 

 two tanks 8 feet long, 2\ feet deep, and 6 inches wide. The effective 

 surface of the two tanks is 93 square feet. The heat absorbed by 

 each square foot of surface per hour during shutdown period is 



' 1fi = 23.1 B. T. U. Taking the coefficient of heat transmission 



in B. T. U. per degree difference in temperature as 1.5 per square foot 

 per hour, the temperature difference necessary between the brine and 



ZO .1 _, _ . Q 



air is -;-=- = 15.4°. 

 1.5 



With a 15 per cent solution, by weight, of common salt the freezing 

 point is 12.2° F. Then the temperature of brine at the time the plant 

 is shut down will be 12.2°, and at the time of starting up 27.6°. One 

 cubic foot of the brine will absorb 59.2 B. T. U. per degree rise in 

 temperature, and for a 15.4° rise 59.2 X 15.4 = 91 1 B. T. U. The vol- 

 ume of the two tanks is 20 cubic feet, consequently the heat absorbed 

 by the brine will be 911x20 = 18,220 B. T. XL, leaving 34,400- 

 18,220 = 16,180 B. T. U., to be absorbed by brine ice. Taking the 

 latent heat of the brine ice as 122, the amount of brine to be frozen 



on the coils will be ' =132 pounds. With 117 feet of submerged 



