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Originally Posted by Kelvin

The salt water ice will provide more cooling but only by a small amount and only because there is more mass for the same volume in saltwater compared to freshwater (saltwater is denser).

Currently you are only measuring the rate of temperature change and the fresh water is slowly becoming solid. Fresh water freezes at 0 degrees and thus it will continue to read 0 until the water is all frozen.

Yeah cool - thanks for that. This is all pretty interesting

[Kelvin]

https://www.pharmoutsourcing.com/Fea...nge-Materials/



The question is does adding salt to water significantly change the latent heat? We not to look at the amount of energy required rather than the actual temperature

[yellow door 1]

Originally Posted by Kelvin

Here is an interesting question

Take 1kg of water in a plastic bottle, 1kg of saltwater in a plastic bottle, 1kg of oil in a plastic bottle, and 1kg of lead sinkers in a plastic bottle.

Freeze them in a freezer to a temperature of -10 degrees and let them reach a steady state.

Put each of these into a separate bucket of water and wait till the temperature equalises. Assuming all other variables are equal which will be colder?

Without googling I dont really know

Theres so many things I dont know about how different substance retain temp that I'm scared to guess.

But I'm hoping this is a bit like the "which is heavier - a kilo of lead or a kilo of feathers?" question.

If they all have the same mass - they should have the same thermal energy?

[Kelvin]

Looking at latent heat the values I have found are

freshwater 333j/g
seawater 330j/g


ie. the amount of energy required to turn freshwater into ice is slightly more than but very similar to saltwater

[Kelvin]

I am slowly working my way through this as I haven't looked at physics since high school.

It gets more complicated as we also need to look at the concept of Specific heat. Specific heat represents the amount of heat required to change a unit mass of a substance by one degree Celsius. Increasing the salt concentration decreased the specific heat capacity of water.

ie. saltwater will require slightly less energy to change temperature.




I think the physics points to the same mass of saltwater ice being slightly less efficient in cooling compared to the same mass of freshwater ice. However the increase density of saltwater would push the equation the other way and more mass of saltwater would cool more efficiently that the slightly less mass of freshwater. In practice I think the actual measurable difference would be negligible and saltwater ice is very similar to freshwater ice in cooling ability

[yellow door 1]

Originally Posted by Kelvin

I am slowly working my way through this as I haven't looked at physics since high school.

It gets more complicated as we also need to look at the concept of Specific heat. Specific heat represents the amount of heat required to change a unit mass of a substance by one degree Celsius. Increasing the salt concentration decreased the specific heat capacity of water.

ie. saltwater will require slightly less energy to change temperature.




I think the physics points to the same mass of saltwater ice being slightly less efficient in cooling compared to the same mass of freshwater ice. However the increase density of saltwater would push the equation the other way and more mass of saltwater would cool more efficiently that the slightly less mass of freshwater. In practice I think the actual measurable difference would be negligible and saltwater ice is very similar to freshwater ice in cooling ability

Yeah there is alot of anecdotal evidence out there with guys swearing that salt water frozen in a bottle lasts significantly longer - but it seems the science may disagree with that.

I've just made another one that is supposed to match ocean water - 17.5 grams of salt in 500ml of fresh should do it - that dissolved much easier.

[yellow door 1]

Well there has been a dramatic turn of events.

I've strung all the Vids together

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Well after an hour out of the freezer - it would seem the rumors are true.

Because Saltwater can get to much lower temps before freezing - it can give off much lower temps as it thaws.

Once the fresh melts a bit - the water will give a 0.0 degree reading.

Now all I have to find out is which one lasts the longest

[yellow door 1]

Originally Posted by Kelvin

Energy transfer depends on mass.

Salt will change the freezing temperature of the ice but the same mass of saltwater will contain the same thermal energy as normal water.

After 14 hours of producing much colder temps - the ocean water ice is almost all gone, Theres just a bit of slush at the top of the bottle -

the fresh water which hovered around zero the whole time still has heaps of ice - theres a solid thick bar of ice running down the middle of the bottle

[yellow door 1]