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Air velocity field in an air blast freezing tunnel.

Author(s) : WIDELL K. N., FRYDENLUND F.

Summary

The air velocity field inside an air blast freezing tunnel is important in heat transfer from a product and highly influences freezing time. The freezing time is a function of air properties, air velocity and product characteristics. An uneven air velocity field results in different product freezing times and inefficient energy use by the fan. Compressors and fans are the biggest consumers of electricity in a freezing tunnel, which means it is important to optimize their use. This paper presents simulations of the air velocity field in an existing freezing tunnel using computational fluid dynamics software. The air velocity field in the blast freezer is difficult to measure, but simulations can provide indications of the real conditions in the tunnel. The air velocity distribution in the tunnel is discussed as well as how this output can be used to calculate heat transfer coefficients to predict product freezing times. Alternative tunnel construction options are also analysed. A guide blade in the tunnel was installed to provide a more even air velocity field, which resulted in more uniform product freezing times. Freezing times were calculated with a modified Plank's equation and then used to visualize the influence of air velocity. The freezing times in the tunnel without a guide blade varied between 16 and 32 h. For a tunnel with a guide blade the freezing times were between 17 and 21 h. Freezing times in the existing tunnel were between 13 and 20 h. Future work should include the air velocity field in a numerical model for product freezing.

Details

  • Original title: Air velocity field in an air blast freezing tunnel.
  • Record ID : 2010-0543
  • Languages: English
  • Source: Deutsche Kälte-Klima-Tagung: 2009, Berlin.
  • Publication date: 2009/11/18

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