Tag: Heat load

Reports

Guidelines for precooling of fresh fish during processing and choice of packaging with respect to temperature control in cold chains

Published:

01/12/2010

Authors:

Kristín Líf Valtýsdóttir, Björn Margeirsson, Sigurjón Arason, Hélène L. Lauzon, Emilía Martinsdóttir

Supported by:

AVS Fund of Ministry of Fisheries in Iceland (R-037 08), Technology Development Fund at the Icelandic Center for Research (081304508), University of Iceland Research Fund and EU (contract FP6-016333-2)

Contact

Sigurjón Arason

Chief Engineer

sigurjon.arason@matis.is

Guidelines for precooling of fresh fish during processing and choice of packaging with respect to temperature control in cold chains

The purpose of the guidelines is to assist in the choice between different methods of pre-cooling fresh fish products as well as to assist in the selection of packages with regard to the heat load that the product experiences on its way from producer to buyer. The following pre-cooling methods are discussed: liquid cooling, sludge cooling and skin cooling (CBC, touch and blow cooling). The treatment of products during processing and the effect of different refrigerants on temperature control, quality and shelf life of fillets before packaging the product are also discussed. The guidelines take into account the processing of lean whitefish, such as cod and haddock. The results of research show that a well-designed pre-cooling before packing can result in a shelf life of 3 - 5 days longer due to no pre-cooling before packing. Inadequate fluid exchange during hydraulic cooling with associated cross-contamination can, however, negate the positive effect of pre-cooling. Icelandic fresh fish producers mainly use expanded polystyrene (EPS) and corrugated plastic (CP) boxes for the export of fresh fillets and fillet pieces. Therefore, only the aforementioned packaging types are discussed here. The conclusion is that if the temperature control is inadequate and the temperature fluctuations are high, it is desirable to use foam plastic boxes that provide better thermal insulation than corrugated plastic boxes.

The aim of the guidelines is to provide and assist with choice of different precooling techniques for fresh fish fillets as well as assist with choice of packaging with respect to thermal abuse, which the product experiences during transport and storage from processor to customer. The following precooling techniques are discussed; liquid cooling (LC), slurry ice cooling (SIC) and combined blast and contact cooling (CBCC). In addition, the following is discussed; handling during processing and the effect of applying different cooling media before packaging on temperature control, quality and shelf life of fresh fillets. The guidelines are designed with lean white fish muscle in mind, such as cod and haddock. The results reveal that efficient precooling before packaging can prolong shelf life up to 3 to 5 days compared to no precooling before packaging. If the liquid exchange in the liquid cooler's circulation system is insufficient, cross-contamination can diminish the positive effects of precooling. Icelandic fresh fish processors mainly use expanded polystyrene (EPS) and corrugated plastic (CP) boxes for export of fresh fish fillets. The guidelines are therefore only focused on the above-mentioned packaging types. The conclusion is that if temperature control is unsatisfactory and temperature fluctuations are great, then expanded polystyrene boxes are the preferred alternative because they provide better insulation.

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Reports

Freezing and thawing of Greenland halibut - experiments and CFD simulation

Published:

01/10/2009

Authors:

Björn Margeirsson, Lárus Þorvaldsson, Sigurjón Arason

Supported by:

AVS, TÞS, UI Research Fund

Contact

Sigurjón Arason

Chief Engineer

sigurjon.arason@matis.is

Freezing and thawing of Greenland halibut - experiments and CFD simulation

Freezing and thawing of halibut were studied experimentally and computerized thermodynamics (CFD) models. Whole pallets of semi-frozen halibut were placed in a cold store and the air temperature and halibut temperature in different places on the pallet were measured by thermometers. The time taken for the halibut to freeze from -10 to -5 ° C below -15 ° C ranged from one to four days depending on the location of the pallets. In thawing experiments, both individual bags and twenty bags, stacked on pallets, were examined in the temperature-controlled cold rooms of Matís and UI. The heating of a frozen product was mapped under conditions that may occur during unloading from freezer trawlers or 10 - 20 ° C air temperature. The results of the experiments were compared with the results of three-dimensional heat transfer models, and there was generally good agreement between them. At 10 p.m. storage at 12.6 ° C air temperature raised the temperature in individual bags from about -26 ° C to approx. ‐5 ° C. At such a long temperature load, the temperature in pallet bags rose from -22.5 ° C to from -17 to -3 ° C, which shows how homogeneous the heat distribution can be with prolonged heat load. The results of the CFD model showed that 10 m / s wind during loading significantly accelerates the thawing of frozen fish on pallets.   

Freezing and thawing of Greenland halibut was investigated with experiments and computational fluid dynamics (CFD) models. A whole pallet of half ‐ frozen halibut was put in a frozen storage and ambient temperature and fish temperature at different locations in the stack monitored. The required freezing time from ‐10 - ‐5 ° C down to ‐15 ° C was one to four days depending on the location within the stack. In the thawing experiments, both single, free standing halibut bags and twenty halibut bags stacked on a pallet, were investigated in an air climate chamber. The warm up of full ‐ frozen product was mapped under typical temperature conditions during unloading of products from freezer trawlers, ie at 10 - 20 ° C ambient temperature. A good comparison between the CFD simulation and experimental results was obtained. Fish temperature increased from ‐26 ° C to - 5 ° C inside single bags when thermally loaded for 10 hours at 12.6 ° C ambient temperature. Equally long temperature abuse for the whole pallet, initially at ‐22.5 ° C, resulted in a very inhomogeneous temperature distribution from ‐17 to ‐3 ° C. The results from the CFD modeling showed that 10 m / s wind during unloading seriously accelerates thawing of frozen fish.

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Reports

Thermal Performance of Corrugated Plastic Boxes and Expanded Polystyrene Boxes

Published:

01/01/2009

Authors:

Björn Margeirsson, Sigurjón Arason, Halldór Pálsson

Supported by:

EU ‐ project Chill on (project no. FP6‐016333‐2), AVS Research Fund, TÞS Research Fund and University of Iceland Research Fund

Contact

Sigurjón Arason

Chief Engineer

sigurjon.arason@matis.is

Thermal Performance of Corrugated Plastic Boxes and Expanded Polystyrene Boxes

Experiments were performed on the insulation value of two types of packaging for fresh fish fillets: 1) Corrugated plastic box (CP) and 2) Foam plastic box (EPS). The variable temperature around the packages was controlled in the experimental cold rooms and the temperature development outside and inside the packages was monitored with thermometers. Both individual boxes and whole pallets of boxes were examined, as well as the cooling capacity of ice mats, which are sometimes placed on top of boxes for transport from manufacturer to buyer. The cooling mats (ice mats) proved to be very effective in protecting the fish fillets from heat stress. Furthermore, the results showed the superior thermal insulation of the foam plastic box over the corrugated plastic box regardless of the use of cooling mats. In fact, the difference in insulation value is even more visible when using cooling mats. Experiments with fully stacked pallets of fish boxes (approximately 300 kg per pallet) showed that the average temperature rise of fillets can be double for a corrugated plastic box with a foam plastic box, provided that the surrounding air is 10 ° C hot and has considerable movement. Finally, it was shown that several hours. fluctuations in air temperature around an entire fishing board can cause a very uneven heat distribution within the position on the board.  

Experiments were carried out to compare the thermal performance of two different types of packaging for fresh fish fillets: 1) Corrugated plastic (CP) and 2) Expanded Polystyrene (EPS) boxes. The boxes containing fresh fillets were affected with dynamic thermal loads in air climate chambers. Meanwhile, the fillet temperature was monitored with temperature loggers. Both free standing boxes and whole pallets were affected with dynamic thermal loads in the study and the chilling effect of frozen cooling mats was studied by using them in some of the boxes. The frozen cooling mats proved very efficient for protecting fresh fish fillets against temperature abuse. Furthermore, the results show that the insulating performance of EPS is significantly better than of CP, independent of the usage of cooling mats. The difference in insulating performance between the two packaging types is actually exaggerated when cooling mats are used. The experiments with whole pallets revealed that the mean fillet temperature rise for a whole 300 kg fish pallet can be twofold using CP compared to using EPS, given that the movement of surrounding air is considerable and its temperature is 10 ° C. Finally, it was shown that in dynamic temperature conditions, the temperature distribution in a whole pallet of fish fillets can be far from homogeneous.

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