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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