10.3.2   Storage temperatures in the container
10.3.2.1 Influence of solar radiation
10.3.2.2 Depth of penetration of temperatures
If the correct decision as to the suitability of a container for transporting a product without causing damage is to be made, it is essential to have sufficient information about the anticipated climatic conditions in the container. Fig. 9 shows factors which have an influence on the cryptoclimate in the container.
 
Figure 9: Factors influencing container cryptoclimate [42]

 
The four decisive influencing factors are:
  • weather conditions during the voyage
  • the type of cargo with which the container is packed
  • the type of container
  • the container stowage space
Clarifying the complex thermodynamic processes occurring in containers, especially in containers exposed to radiation, was the objective of the hold meteorology study group at the Warnemünde-Wustrow University of Seafaring (Fig. 10), where cryptoclimate was investigated in two containers, both on a test rig and on board commercial vessels. The investigations were carried out on two standard containers, each of which was equipped with an air lock to prevent disturbing the cryptoclimate when monitoring and making measurements and a weather station. The containers were packed with hygroscopic goods, in particular sawdust in one case and packets of sugar wrapped in paper in the other.
 
Climatic conditions during the voyage are determined by the route, season and current weather events. Consequently, it is not entirely straightforwardly possible to transfer the experience gained from one voyage or one route to another as the stresses vary between the different routes and individual voyages. Solar radiation, air temperature and wind are of significance to thermal stress.
 
The temperatures encountered in containers are primarily determined by heat exchange across the steel boundary surfaces, with inward and outward radiant transfers predominating.
 
Figure 10: Hold meteorology study group of Warnemünde-Wustrow University of Seafaring, 1970: container with air lock and weather station;
Svenson [54]

 
Good heat-transfer properties, especially through the metal walls, and the relatively large ratio of container surface area to container volume have a favorable impact in this respect (20' container, approx. 1.80 m²/m³).
 

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