PRECOOLING 



37 



fected. Consequently, if the process has to be discontinued 

 before the bulk of the load has been cooled, the general aver- 

 age effect may be less satisfactory where extremely cold air 

 is used than where more moderate temperatures are utilized. 

 There is undoubtedly an optimum of temperature and volume 

 of blast which will yield most economical and efficient results. 



So far, the most satisfactory system of car precooling has 

 been found to be a straight circulation of cold air through 

 the car. In the Bureau equipment, the air is introduced 

 through an ice hatch at one end and is withdrawn at the op- 

 posite end. Facilities for reversing the air blast are pro- 

 vided, and the current is reversed whenever the produce near 

 the entering air becomes chilled to the danger point. This 

 reversal of the air current is extremely important where a 

 straight circulation system is employed, as it enables both 

 ends of the car to be given maximum treatment. 



A number of mechanical problems enter into the construc- 

 tion of a car precooling plant. These are the problems of 

 the refrigeration engineer, however, and a discussion of them 

 here will not be attempted. 



In connection with the utilization of precooling by different 

 industries, several processes which purport to give an in- 

 creased rate of cooling have been devised and introduced. 

 None of these, however, warrant the extra expense and roy- 

 alties which may be demanded for the use of any patented 

 process now being exploited. 



One of these processes is at present being actively exploit- 

 ed by the company owning the patent. This process implies 

 the utilization of a vacuum for increasing the rate of cooling 

 within the carload. The claims of the process are based 

 upon the withdrawal of the air of the car, exhausting it into 

 the outer air, and thus supposedly creating a partial vacuum 

 within the car and later replacing the exhausted warm air 

 by cold air. No advantage has been found to result from 

 this process over a straight circulation system, for the reason, 

 that it is practically impossible to obtain a sufficient vacuum 

 to be effective within the ordinary refrigerator car without 

 drawing into the car considerable volumes of air, through 

 innumerable crevices, and this air must likewise be re- 



