L. G. Limpus (lglimpus@coastnet.com)
Fri, 11 Jun 1999 07:25:29 -0700
Dear Andrew,
Technically I agree with you. I remember Gorden telling me that the data
on commercial ice was taken when they first installed the ice pumping
system in either Grimbsby or Hull in the late 50's or early 60's. I am
sure there have been technological improvements since then to reduce ice
heat loss. However, in many developing countries (and perhaps even
developed ones) ice is shipped in blocks (and is not sub-cooled by the time
it arrives) to a point
where it is crushed (either mechanically or manually) where there is
further heat loss. I wonder if in such circumstances, it may be better to
use a lower figure than the technically correct 80 kcal/kg.
L. G. Limpus
At 07:30 AM 11/06/99 -0300, Andrew Strak wrote:
>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 - 07:28:46 PDT