Humidity motor (cycle) in the container
The intensity of container sweat is determined by the temperature gradient between the cargo and container wall. If this gradient is steep and ventilation is not possible in the standard container, a humidity motor (cycle) is formed, as is shown in Fig. 28. The temperature of the external air is 12°C and the temperature of the cargo 20°C.

TA - temperature, external
φR - rel. humidity in hold
TL - cargo temperature
φA - rel. humidity, external
R - dew point, hold
A - dew point, external
TR - hold temperature
TS - temperature of side wall  

Figure 28: Humidity motor (cycle) in the container between the cargo and the container wall;
U. Scharnow [46]

During thermal circulation, the container air cools down to below its dew point on the container wall and a proportion of the water vapor condenses because the temperature is below the dew point. As a result of the thermal circulation, this air returns to the cargo, where it warms up and picks up water vapor, before cooling back down again on the container wall.

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