﻿16 BULLETIN 17, U. S. DEPARTMENT OF AGRICULTURE. 



In order to give credit to those cars in which low temperatures 

 prevailed at the bunker, H in formula 2 must be a function of the car 

 temperature. The cars were iced 24 hours before loading, and the 

 inside car temperature decreases continually from the time of icing 

 until the door is opened for loading. Therefore 24 of the total 

 number of hours are constant. The variable portion then becomes 

 H 1 where 



H-24 + H 1 (3) 



H 1 represents the number of hours between loading and the time at 

 which the temperature at the bunker begins to rise. 



The bunker should cool the air from the temperature prevailing 

 at the center of the car to that prevailing at the bunker, the temper- 

 ature maintained at the center depending on the insulation of the 

 car and the circulation of air. The total refrigerating effect might 

 be expressed as degree-hours; that is, if the temperature at the 

 center is C and that at the bunker is B and this difference in tem- 

 perature is maintained for H 1 hours, the refrigerating effect is H 1 

 (C — B) degree-hours. If no salt had been used on the ice the 

 bunker air would be 32 ° F.; but the total refrigerating effect is the 

 same whether the ice melts slowly or rapidly, and therefore the 

 degree-hours at this temperature are (C — 32) H 11 . Hence 



(C-B) H 1 



W^m: (4) 



As shown by Table 2, 32° F. (0° C.) is too warm for the best 

 results in poultry transportation. The temperature should be 

 30° F. ( — 1.1° C.) or lower. In determining the efficiency of the 

 car for maintaining a temperature of 30° F., this number should be 

 substituted in the formula, which then becomes 



±i - c _ 30 W 



II 11 represents the number of hours after loading at which the 

 bunker temperature would have started to rise if the bunker had 

 been producing air at 30° F. ( — 1.1° C). This reduces all of the car 

 temperatures to a comparative basis; the compensating formula 

 would then be 



pi 142I + 40.5N 

 ^S (T-0 (24 + H) 11 

 and, by substitution, the efficiency formula becomes 

 R1 _ 142I + 40.5N 



~SCT-0 (« + *&£) 



The efficiency of the car will vary inversely as R 1 , since the greater 

 amount of heat transmitted indicates lower efficiency. If E is the 



index of efficiency, then E = ™ 



