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from the center of the box to the face or faces of the mass of apples where 

 heat was transferred to the air. The most important variables influencing 

 the cooling accomplished by convection are the temperature and quantity of air 

 passing the apples. The provisions for air to enter the box have a great 

 effect on these variables. 



When conduction is the sole means of heat removal, the cooling performance 

 will vary almost as the square of the distance from the center to the nearest 

 face where heat can be transferred to the air. If the heat can be disposed of 

 through more than two parallel faces, the relationship becomes more complex. 

 If the distance from the center to one set of parallel faces is much less than 

 the distance to the other pair of parallel faces, then most of the heat is 

 conducted to the nearest faces and the influence of the farthest pair is 

 slight. All stacks of pallet boxes were placed, as in normal commercial 

 practice, tightly together in the row so that the backs and fronts of the 

 boxes had little access to air. It does not seem reasonable that very much 

 heat can be conducted through these surfaces; therefore, the length of the 

 box does not appear to be a variable entering into these cooling studies. 



The depth of the box may also influence the cooling accomplished by 

 convection. The depth may affect the quantity of air which passes through 

 the fruit. As the air quantity is decreased, the air temperature rise as it 

 passes through the fruit increases. As a result, the temperature difference 

 between the air and the fruit is smaller and the cooling time becomes greater. 



Provisions to let air into the box, to accomplish as much cooling as 

 possible by convection, is of prime importance. For that reason, the boxes 

 selected have a wide variation in the manner in which air may enter. In some, 

 the air passes through the sides, others the bottom, and some through both. 

 Yet the most important cooling function is the total space for air to enter. 

 Such free area has been calculated for the bottom and the sides of each type 

 of box. This calculation deducts the area of cross members where spaced 

 sides or bottoms are used. This measure seems to be the best index to show 

 how accessible the box is to air flow. 



Cooling Rates of Different Pallet Boxes 



Half-cooling time is the time required to reduce the temperature of the 

 fruit one-half the way from the initial fruit temperature to cold storage air 

 temperature. 



Approach temperature is the temperature difference between the cooled 

 commodity and the adjacent air after equilibrium is reached. 



The half-cooling time for the standard boxes showed a considerable 

 difference between the 2 test locations (table 3). Previous tests of the 

 cooling performance of pallet loads of unpacked apples in standard boxes 

 showed half-cooling times that ranged from 15.4 to 23.4 hours. In the light 

 of previous experience, the performance at test location No. 1 approaches the 



