|Authors: ||R. Jedermann, W. Lang|
|Keywords: ||temperature mapping, air flow simulation, cold chain, hot spot, reefer container|
Temperature variations in reefer containers with fruits regularly occur due to deviating airflow and cooling conditions (DACCs). There is little knowledge about whether DACCs affect only a small area or the complete container load.
In seven tests in containers from Costa Rica to Europe since 2009, we observed a high level of spatial temperature variation.
Banana pallets are not a perfect rectangular shape and they do not completely fit the inward container dimension, resulting in large variations of gap widths.
The effect is enhanced by the biological variance of respiration activity.
We set up a computational fluid dynamics (CFD) simulation for the airflow and temperature in a container loaded with bananas to provide a better understanding of DACC effects, because detailed experimental evaluation was not feasible in a commercial cold chain.
The complex geometrics of a container with 960 boxes had to be reduced to a two-dimensional model.
Almost all DACCs had a predominant local effect.
For the following DACCs, cooling was slower only in some affected boxes: (a) blocking of a horizontal channel in one pallet and (b) narrow vertical gaps.
Double heat generation by higher respiration activity in part of one pallet also had a predominant local effect.
The temperature was between 1.7 and 4.7°C higher than for the reference case with normal airflow conditions at 48 h after the start of cooling.
Only circulation bypasses by packing mistakes and a reduction of inlet air speed had a significant effect on the average container temperature, of +0.6°C maximum.
Quality problems and losses of full container loads, as regularly reported in ocean transport, cannot be explained by a single DACC according to our simulation results.
A combination of at least two DACCs is necessary to cause severe quality problems.
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