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The position of vent holes affects cooling

World population is expected to reach 9.1 billion people in 2050, so it is absolutely necessary to guarantee the future of food security. A first step is certainly the reduction of post-harvesting waste, which is estimated at 15-30% on a global level.

Bad temperature management and physical damage are considered the main and most common causes of post-harvesting waste. This loss could be reduced by using the cold chain correctly and employing more efficient packaging to facilitate temperature regulation during the pre-cooling phase and protect the produce against bruising.

Packaging ventilation must therefore be designed keeping in mind various parameters such as: type of packaging, type of holes, external and internal packaging structure, type of product, product shape and size, etc. 

Generally, cardboard boxes are palletized to make their management easier and improve pre-cooling, transport and storing. Packaging and pallet structures, however, create barriers between the produce and refrigerated air, hindering cooling and affecting quality. Certainly, making more holes on the packaging is not a solution!

Forced-air cooling (FAC) is used to remove heat quickly and guarantee a better quality. Boxes are ventilated to favour uniform cooling and reduce the energy used by cooling fans. The efficiency depends on the area and hole configuration. However, the position of ventilation holes may also reduce the compression strength of the cardboard. This way, additional panels are needed and cardboard manufacturing costs are higher.

A group of South African, Swiss and Belgian researchers studied 4 types of crates, analysing the holes and type of cardboard used.

Cardboard boxes with different holes.

Researchers calculated Computational Fluid Dynamics (CFD) behaviour to assess airflow resistance, uniformity and energy consumption. Experiments were carried out to quantify box compression strength. 

Computational Fluid Dynamics (CFD) calculation to simulate the horizontal flow of cooling air through an apple box.

Results showed a negative linear relationship between carton strength and vent hole area. The effect of vent hole configuration on the compression strength depends on the type of corrugated cardboard.

Multivent types used 58% less energy and improved cooling uniformity with respect to standard types. They also needed a smaller ventilation area. The significant improvement in energy efficiency also led to an improvement of the compression resistance of boxes.

This study demonstrates how a multi-parameter approach can favour a better and more efficient packaging development.

Source: Tarl M. Berry, T.S. Fadiji, Thijs Defraeye, Umezuruike Linus Opara, 'The role of horticultural carton vent hole design on cooling efficiency and compression strength: A multi-parameter approach', 2017, Postharvest Biology and Technology, Vol. 124, pag. 62–74.
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