Andrew Strak (abstrak@accesswave.ca)
Fri, 11 Jun 1999 07:30:56 -0300
It is obvious for that reason that 'melting ice' described below is no more
ice but rather slush and should be designated properly and any ice made of
fine particles gives away free water more slowly than larger cubes or
chunks. Although any slush always has some proportion of water unlike 'cold
ice' at temperature below 0C, however its initial cooling effect may be
faster due to a better surface contact with the product. Most benefits of
chilling effect of ice come from its change of transition at a melting point
of 0C that absorbs so many calories without temperature change and it is
indeed 80kcal/kg. When the boat buys flake ice it is usually fresh from
factory and several degrees below the freezing point of water, otherwise it
is not 'blowable' anymore. As such it has enthalpy of 80 kcal/kg plus
whatever is its temperature below the freezing point let's say -5C
multiplied by its specific heat appro. 0.5 kcal/kg/1C. Therefore, any
refrigerated capacity of 1 kg of such ice would be appro. 82.5 kcal/kg of
ice.
Andrew
-----Original Message-----
From: L. G. Limpus <lglimpus@coastnet.com>
To: abstrak@accesswave.ca <abstrak@accesswave.ca>; luispasp@usp.br
<luispasp@usp.br>; seafood@ucdavis.edu <seafood@ucdavis.edu>
Date: Friday, June 11, 1999 1:46 AM
Subject: Re: ice on fish boats
>Dear Coleagues,
>
>With regard to the use of ice on fish boats and Andrew Strak's comment that
>there is no difference between various types of ice, and other comments
>that a lot of work was done a number of years ago, I remembered a quote
>from Gordon Eddie (formarly with the White Fish Authority in England) in an
>old FAO Technical paper No: 232 "Road transport of fish and fishery
>products", in which he makes the following statement:
>
>"---However, it should be noted that, in practice, the refregerating effect
>of crushed ice is never as high as 80 kcal/kg, unless the ice is
>sub-cooled, for the simple reason that commercial crushed ice is always
>wet, that is, it is a mixture of ice and water. A more realistic figure is
>67 kcal/kg of the misture as purchased."
>
>>
>>There is no difference between various types of ice concerning their
>>enthalpy or heat content. However, any finer ice of a larger surface such
as
>>flake ice will be cooling your catch faster but will also melt faster
giving
>>some impresion that it is not so 'cold' as slow melting one due to a lower
>>surface/volume ratio for ice cubes. Please also remeber that almost 100%
of
>>the cooling 'power' of the ice comes from its melting action where it
>>absorbs 80 cal/g still being at OC and that is equivalent to raising
>>temperature of 1 g of water from 0C to +80C. The specific heat of ice is a
>>relatively low though, and if you have some freshly made ice at -30C it
will
>>need only 13 cal/g to be raised to the temperature OC.
>>
>>Best regards,
>>
>>Andrew Strak
>>
>>
>
>
This archive was generated by hypermail 2.0b3 on Fri Jun 11 1999 - 03:33:44 PDT