THE 3 forms of heat loss from an object or surface at earth's surface are...
04-05-2012, 05:42 AM
RE: THE 3 forms of heat loss from an object or surface at earth's surface are...
Derek, you have known me on this forum long enough to know I'm not a "Troll". That post of yours is I feel is possibly a little out of order, and certainly incorrect. The P/4 thread you posted previously that you alluded to, I still think is essentially a red herring and different to what the Slayers have said. I'm not having a go at you personally, Derek, and do not mean this to be personal, we are merely having a scientific discussion. Let's keep it impersonal and scientific, not personal and insulting!
Sorry, if you don't like your ideas being discussed. Strong, good ideas would stand up to any examination, so my approach should be welcomed. So I apologise if you have taken my posts as personal, that is not the intention! Accusing me of being a "Troll" doesn't support your position!
I have also not disagreed with you on everything you have said, just on the P/4 and these latent heat issues. The discussion is around facts that I feel are not quite right, not about "having a go at Derek" and "disagreeing with everything he says".
We are having a discussion about the relative importance of latent heat versus convection. I have stated the reasons why I think you have overstated the importance of latent heat and understated the importance of convection. And yes, I have read your articles and I don't think they really address my points.
And I have another few points in support of convection as being the most important, certainly more important than latent heat. Consider this- latent heat only acts to cool the very earths surface where water is present in liquid or solid form and can thus evaporate or sublimate to water vapour. Once in the atmosphere as water vapour, further phase changes can only release heat as vapour goes back to liquid and back to solid. Any expansion would be convection mushc like dry convection but perhaps with a slightly greater heat capacity, depending on the % water vapour. Convection on the other hand operates from the earths surface right up into the high atmosphere, cooling both the earths surface and the layers of the atmosphere.
As for your PDF, some of it is right and some of it is clearly wrong such as this statement:-
"Radiation, conduction and latent heat happen BEFORE convection.
In point of actual FACT conduction and latent heat CAUSE convection"
Part right, part wrong.
As convection occurs in a desert, dry polar regions and the dry air on a mountain top where little or no latent heat transport occurs this is clearly wrong. Yes, conduction from the hot air to the ground provides much of the heat to the air to start convection -agree with you on that- but not necessarily latent heat in a dry area. Sorry Derek, you won't like it but some of your statement is not quite right!
Convection occurs when a packet of air is heated, the air expands due to the extra heat and because the air has expanded it becomes less dense than before and therefore rises. No latent heat needed here, this is why you get convection in the desert. Conduction yes, latent heat not necessarily!
"For our thought experiment, firstly imagine "our" hot cannonball in a vacuum.
1) Radiation losses are very little – Your hand, even if a small distance away (ie a couple of feet), can not feel much at all, especially as the distance the hand is from the cannonball is increased (increasing circumference)".
Not quite true! If the cannon ball were colder than your hand, then yes, I agree you would not feel the radiation as it would not warm your hand, but if the cannon ball is warmer than the hand, then yes, heat transfer will occur and in a vacuum radiation is the only means by which the cannon ball can cool. So radiation loss from the hot cannon ball in a vacuum is not "very little" but is 100% of the heat loss. Yes, the increased distance is due to the inverse square law by which radiation density decreases by distance from a hot object. Agree with you on that one.
It seems to me you have specifically got confused between heat transfer by latent heat, i.e. water evaporating and the water vapour cloud rising and heat transfer by convection, i.e. hot ground conducts and radiates to the cooler air, this air warms, then expands and rises. They are similar, but not quite the same thing as latent heat involves a change of state caused by heat and dry convection is merely the expansion of a gas by heating it. No change of physical state occurs in convection, merely an expansion of the gaseous state.
This statement is also not quite true:-
"Evaporation and vapourisation are often used interchangeably, but are in fact different "terms". Evaporation happens when water boils, but the vapourisation of fluid water can happen at any temperature between 0C and 100C."
Not really, a liquid can evaporate at any temperature that is has a vapour pressure at, and with decreased pressure the evaporation rate increases! Evaporation does not just occur at boilling point! You have actually got the terms the wrong way round as vapourisation can be an instant change from liquid to gas and evaporation of a liquid happens gradually.
Sorry Derek, this is not a personal attack, I'm just trying to help you to understand the science better and correct the errors in the PDFs you publish. It is just if you are going to make statements in a PDF and publish them on a blog then they need to be correct statements backed by good science. And we need to be discussing good science all the time otherwise us Realists will be opening ourselves for attack by the Warmermongerers. We don't need mistakes and misunderstanding, we need correct statements and good science. Science is not personal, it is impersonal and either right or wrong without regard to the beliefs and feelings of those who hold those beliefs. A scientific paper has to get everything right, down to the last details and be very clear.
I don't know what your scientific background is, but I have a degree in chemistry and worked as a chemist for 20 years in industry. It is from this education and experience that I draw my ideas and conclusions.
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