Potential benefits of jetting to the HS model

Summary

An experimental evaluation of the airflow aboard a candidate vessel was conducted as part of this investigation. The intention was to quantify a typical flow pattern within a typical pen with an explicit intention to avoid extreme data. This would exclude pens that were immediately adjacent to large scale air exhausts and inlets and pens that were bounded by more than one wall. Moreover, pens that were essentially in the middle of the deck were favoured where the middle is taken in the forward – aft axis. In total three pens were measured. It was found that the average velocity measured was higher than the nominal PAT by factors of 3.2, 8.5 and 10.4.

Caution needs to be exercised when interpreting these factors. It was found that the flow in the centre of the pens was highly blustery, giving an overall increase in mean velocity, above the nominal PAT. However this blustery flow results from air movement, that has already been exposed to the hot animals and is therefore expected to give less cooling potential than air issuing directly out of air distribution outlets. As such, it may be prudent to give some weighting factor based on location within a pen, when evaluating the average. Such a weighting process was not performed in this case.

Secondly, the blustery nature of the flow makes it inherently difficult to model, especially with simple analytical models. Even computational methods generally need some calibration factors to include such levels of variations, and these generally come from experiments, which are prohibitively expensive. The flow was most blustery away from the air outlets and again, it may be prudent to simply exclude such regions from the evaluation of average air velocity.

The intention of this assessment is to try and identify potential benefits that may flow from the inclusion of jetting in the HS model. As such, it is acknowledged that on some voyages, the allowable stocking fractions can be 100% and so in those cases there is no margin for potential improvements. It is only in the marginal cases where potential for improvements can be realised. These marginal cases would include voyages that are run at reduced stocking density or are prevented from sailing. Therefore, in order to equate the measured velocity ratio to potential benefits, a set of typical data was used, for a nondescript vessel that represented a marginal voyage. The conditions used for this evaluation are as follows:

Breed: 25% Bos Indicus Weight: 220 kg Fat Score: 3 Nominal PAT: 150 m/hr Departure Port: Port Hedland Arrival Port: Kuwait
These conditions were chosen as they reduced stocking fractions by 15% in August.
Equivalent temperatures were calculated that were based on equating the animal comfort index of ETI and the convective potential. These equivalent conditions were used with the above data as input to the HS model. It was found that the reduction in stocking fraction could be potentially regained in the month of August. In fact, for the conditions, it showed that 100% stocking fractions would be supported for the whole year.

It was found that the measured velocity ratio varied from 3.2 in the worst case to some 10.4 in the best case. It may be tempting to try to utilise the full potential of each pen, since there is a great difference in these values. However there is a clear complexity in varying the stocking density on a pen-by-pen basis. This would add a good deal of complexity in loading if such an approach was to be adopted. It would also add a good deal of complexity in verification of stocking levels, if such an approach was used. As such, a more simplified approach should be sought, as an alternative.