Heat dissipation using evaporative cooling processes
When using evaporative cooling methods, the evaporation heat of the water can be used to cool the air. This is done by spraying a fine aerosol of water into the air where it completely vaporizes if possible. This is often achieved with a fan where the water is sprayed into the air flow produced by the fan, or compressed air is used to create the aerosol. Today, typical applications include: greenhouse and shopping mall cooling systems (e. g. in the USA).
This method of heat dissipation can, in principle, also be applied to refrigerated containers. There are a number of particular benefits:
  • Refrigerated containers are designed to be operated under damp conditions anyway (rain/sea spray).
  • Condensation is to be expected in the hold of a ship carrying refrigerated containers, which means that paintwork etc. must be waterproof anyway. Holds are always designed with bilge sumps to pump off any water.
  • As a result of the space limitations with regard to installing ventilation ducts, this procedure is the only way of dissipating more heat in conjunction with the existing ventilation system. It is thus particularly suitable when upgrading a vessel.
The water sprayed into the air for evaporation must be obtained on board using a suitable treatment method to produce fresh water. It would be tempting to use sea water, but this would lead to serious problems in terms of erosion of the spray nozzles and salt deposits in the hold.
Obviously, evaporative cooling systems must be accompanied by ventilation of the hold using fresh air, but this can be at a lower level than when using air cooling systems alone. When using a combined system like this, the quantity of fresh air can be reduced from 60 m³/h to 30 m³/h compared with cooling systems using fresh air only. Despite evaporation, the relative humidity drops (!) from 70% at the air inlet to 52.1% at the air outlet.
The quantity of water necessary for evaporation will only be required during normal operation for a few hours a day because the ambient temperature drops at night. Since water is easy to store, the system can be run with a buffer.
This method is particularly interesting if an existing ventilation system is required to extract more heat than is possible with a fresh air cooling system alone.

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