To info@tutorvista.com
Hi,
One of your videos on the latent heat of fusion of ice has a major error in it.
www.youtube.com/watch?v=M41yEWNyvZkWhen water cools to form ice we find more cooling is required to produce ice than we would expect without there being a latent heat of fusion of ice. During this period of cooling we find the temperature remains constant until the ice is formed.
We do not however observe any release of heat into the surroundings other than the heat that is passing into the surroundings as a result of us cooling the ice.
Your video claims the surroundings become more pleasant because of the freezing of ice. That is not possible. All we experience is that it takes longer to cool the ice than we would expect. The latent heat of fusion is a hidden heat.
Best Regards
Andrew
The rate you are writing these crazy letters the whole world is going to be laughing at you Iceskater.
the whole idea of vegetable protection is to prevent the temperature from dropping below zero in the presence of constant cooling. The latent heat of fusion can maintain the temperature at the level of freezing, raise it if its below the level of freezing and emit heat upwards to ensure the atmosphere above the ice does not cool also (e.g. hold it at zero in the presence of radiative cooling).
In the arctic the freezing point of saltwater is about -2C the atmosphere and the water cools to that level and begins to freeze. In the process of freezing salt is squeezed out of the saltwater and the resulting water will rise in temperature as it freezes and that rise in temperature will also warm the air.
In the agricultural videos the latent heat of fusion is shown to both protect blossoms by encasing them in a constant stream of freezing water to maintain them at a minimum of 0C. It also maintains the air temperature for up to a couple of meters above the ice at that temperature also via rising heat. . . .though to get the latter effect you need to pay attention to special instructions on how to place the water.
Before the heat of fusion kicked in the water was cooling via radiation and the air was conducting heat to the water via conduction and the air was radiating some cooling to space as well. The inversion layer was formed by the speed of conduction of heat to the water.
This cooling of the atmosphere via conduction with the water/ground is a semi-permanent situation in the arctic making for an inversion layer.
In addition in the arctic since the downward conduction has ceased the warmer air above will conduct heat into the inversion layer and warm it. So the temperature spike you see from heat of fusion involves both heat of fusion rising into the inversion layer and heat from above the inversion layer conducting down into the inversion layer. How much from each depends upon a lot of variables.
When using fresh water irrigation water to perform this, you have the same thing happening. The only difference is you will not see a temperature rise in the surface, the surface and the air above it will be held to zero degrees.
But the air above the surface will be kept warm by heat rising from the freezing water from the heat of fusion. The rate of that warming will be to offset radiative cooling of the air to space.
Obviously the heat of fusion cannot warm something warmer than the ice through normal conduction, convection, or radiation. Thats a restriction placed on any object in the world by the 2nd law of thermodynamics for heat transfer (except for the folks who believe that the heat of backradiation causes warm objects to rise in temperature).
However, since the latent heat of fusion in freezing ice and condensing water is an exothermic process there may well be a force that will force warming. A cold stick of dynamite will produce heat when exploded. The molecular bonding in water requires work to separate so those same forces may force heat out of the object. But as we see above we don't need to prove that. But somebody here now wants that to be proven.
Numeruno and Iceskater started out wrong on this topic so in their typical fashion they are madly and sneakily changing the goal posts in a desperate attempt to try to salvage something out of their mistake.
They don't want to talk about the arctic warming, they don't want to talk about super cooled water warming, and they want to even ignore normal heat transfers from radiation that will allow heat to rise from the heat of fusion as described above to maintain local temperatures.
Its obvious that the heat of fusion is able to rise to counter heat losses in the atmosphere. And in the case that started this whole argument, the case of the DMI data showing a sudden spike in temperature from -2 to -1C they don't even want to defend that issue any more or talk about it.
They want a different goal post. Because there, in the arctic, we can see not just the heat from the heat of fusion rising, we can see it increasing the temperature of the air above also.
Of course this latter condition you don't want in crop protection. You don't want water that will allow the temperature to drop below 0C. Fortunately irrigation water has enough other stuff in it to prevent supercooling. And that way it can work to push heat of fusion where its needed to be pushed.
