CHAPTER
7 
To
minimize these weight losses, the humidity of the air in freezers, chillers
and stores and the rate of chilling and freezing, should be as high as
practicable. The design of the evaporator equipment can help if a relatively
large coil area has been provided for the freezing or cooling duty. The
large area means that the cooling demand can be accomplished with a small
airtemperature drop. This may be seen from the standard equation
For fixed q (determined by the cooling demand) and for fixed U (determined by the design of the freezer) a larger A will mean a smaller DT, and vice versa. Since the air leaving the coils will be nearly saturated with water vapour as it leaves, the larger the DT the colder the air at this point, and the dryer it becomes. The dryer it becomes (the lower the RH) the greater its capacity for absorbing water from the product. So a low DT decreases the drying effect. The water then condenses from the air, freezes to ice on the coils and must be removed, from time to time, by defrosting. Similarly for fixed U and A, a larger q means a larger DT, and therefore better insulation leading to a lower q will decrease weight losses. Drying > SUMMARY, PROBLEMS Back to the top 
