COOLING HOT-BOTTLED PASTEURIZED MILK. 17 



BY FORCING THE AIR FROM THE TOP DOWNWARD. 



As it is natural to expect, tlie results -^ obtained by admitting the 

 air at the top of the box, forcing it downward through the stacks of 

 crates, and out near the bottom of the box, show that it is by far 

 the best method. With this arrangement the liquid in the upper 

 part of the bottles is cooled first, and of course, owing to its greater 

 density, settles to the bottom of the bottles, allowing the warmer and 

 therefore lighter liquid to rise to the top and take its place. The 

 convection currents are thus taken advantage of, with the result 

 that the extreme difference in temperature between the lower quarts 

 and the upper pints is only a few degrees. Iii view of this fact 

 the possibility of some of the bottles being insufficiently cooled, 

 while others in extreme cases may be frozen, is remote when this 

 arrangement is used. Furthermore, the rate of cooling was found 

 to be considerably increased by this method as compared with the 

 other two methods. In addition to giving a more nearly uniform 

 temperature throughout the stack, the variation in the temperature 

 of different parts of the same bottle was more nearly the same when 

 the air was forced downward than when blown upward. 



From the temperature curves in figure 11 it will be noted that 

 the incoming air is at an average temperature of 40° F. (4.4° C)^ and 

 that with an air velocity of 2,512 feet a minute the time required 

 to reduce the temperature of the lower quart to 50° F. (10° C.) was 

 2 hours and 10 minutes. The average difference in temperature 

 between the lower quart and the upper pint was only 8.9° F, (4,9° C). 

 In this experiment, as in others, there was some variation in the initial 

 temperature of the liquid before cooling was commenced. In this 

 case the variation amounted to 8° to 10° F. (4.4° to 5.6° C). 



The curves in figure 12 show more plainly the results of cooling 

 by blowing air downward through the stack than those in figure 11, 

 for in the former case the initial temperature of all bottles is prac- 

 tically the same. The average difference in temperature between 

 the lower quart and upper pint (cui:ves 3 and 4, respectively, figure 

 12), representing extreme conditions both as to size and location 

 of bottles, was only 2.49° F. (1.4° C), while the maximum difference 

 in temperature between these bottles was only 4.5° F. (2.5° C). 

 There was a difference of only 2° F. (1.1° C.) between the average 

 and the maximum, showing that the cooling throughout the stack 

 was practically uniform and that with this method all danger that 

 some of the bottles arc not thoroughly cooled is eliminated. If the 

 temperature is taken in any one bottle it is safe to assume that the 

 temperatures of the others are within a few degrees of the one taken 

 when the crates are arranged as in the experiment. The average 

 temperature of the incoming air was about 30° F. (—1.1° C), and 

 SSa??**— Bull. 420—16 3 



