Wind Chill question
- Thread starter hisilver
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That's a good question,because they'll say "Temperature is 30 degrees,but feels like 10 degrees". If it feels like 10 degrees,isn't it in fact 10 degrees? Or maybe in layman's terms,the actual temperature is a fluctuation between ambient temperature and wind chill temperature?
According to the National Weather Service.
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It is different than the effects on humans. Until detailed research can be done, the exact effects are too complex to determine
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It is different than the effects on humans. Until detailed research can be done, the exact effects are too complex to determine
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No, the closer to ambient temperature of an item the less "wind chill" it experiences. A tree is at the same temperature as the air (more or less depending on sunshine I guess) and feels no effect.
Wind Chill is the added cooling effect on a warm object the moving air has, but wind cannot cool an object below the temperature of the air.
Wind Chill is the added cooling effect on a warm object the moving air has, but wind cannot cool an object below the temperature of the air.
Originally Posted By: bepperb
No, the closer to ambient temperature of an item the less "wind chill" it experiences. A tree is at the same temperature as the air (more or less depending on sunshine I guess) and feels no effect.
Wind Chill is the added cooling effect on a warm object the moving air has, but wind cannot cool an object below the temperature of the air.
This seems right. Wind removes warm from warm things, but if the thing is cold and doesn't
produce its own heat, wind chill would have little effect.
No, the closer to ambient temperature of an item the less "wind chill" it experiences. A tree is at the same temperature as the air (more or less depending on sunshine I guess) and feels no effect.
Wind Chill is the added cooling effect on a warm object the moving air has, but wind cannot cool an object below the temperature of the air.
This seems right. Wind removes warm from warm things, but if the thing is cold and doesn't
produce its own heat, wind chill would have little effect.
Originally Posted By: bepperb
No, the closer to ambient temperature of an item the less "wind chill" it experiences. A tree is at the same temperature as the air (more or less depending on sunshine I guess) and feels no effect.
Wind Chill is the added cooling effect on a warm object the moving air has, but wind cannot cool an object below the temperature of the air.
+1
No, the closer to ambient temperature of an item the less "wind chill" it experiences. A tree is at the same temperature as the air (more or less depending on sunshine I guess) and feels no effect.
Wind Chill is the added cooling effect on a warm object the moving air has, but wind cannot cool an object below the temperature of the air.
+1
Originally Posted By: bepperb
No, the closer to ambient temperature of an item the less "wind chill" it experiences. A tree is at the same temperature as the air (more or less depending on sunshine I guess) and feels no effect.
Wind Chill is the added cooling effect on a warm object the moving air has, but wind cannot cool an object below the temperature of the air.
Unless the object is wet. I got my hands wet this morning brushing snow off the car in -20C and 20mph wind, and that chilled them off real quick! Going through 2 changes of state accelerated by the wind pulls alot of heat out of your hand.
For trees specifically, wind does increase the "freezer burn" effect in sensitive trees like fruit trees. But thats more of a sublimation issue.
No, the closer to ambient temperature of an item the less "wind chill" it experiences. A tree is at the same temperature as the air (more or less depending on sunshine I guess) and feels no effect.
Wind Chill is the added cooling effect on a warm object the moving air has, but wind cannot cool an object below the temperature of the air.
Unless the object is wet. I got my hands wet this morning brushing snow off the car in -20C and 20mph wind, and that chilled them off real quick! Going through 2 changes of state accelerated by the wind pulls alot of heat out of your hand.
For trees specifically, wind does increase the "freezer burn" effect in sensitive trees like fruit trees. But thats more of a sublimation issue.
I would say no since the orchards near here with both citrus and avocados use wind machines when the temps drop below 30.
Originally Posted By: bepperb
No, the closer to ambient temperature of an item the less "wind chill" it experiences. A tree is at the same temperature as the air (more or less depending on sunshine I guess) and feels no effect.
Wind Chill is the added cooling effect on a warm object the moving air has, but wind cannot cool an object below the temperature of the air.
...unless it is evaporating water off its surface. The phase change removes heat from the surface.
No, the closer to ambient temperature of an item the less "wind chill" it experiences. A tree is at the same temperature as the air (more or less depending on sunshine I guess) and feels no effect.
Wind Chill is the added cooling effect on a warm object the moving air has, but wind cannot cool an object below the temperature of the air.
...unless it is evaporating water off its surface. The phase change removes heat from the surface.
Originally Posted By: morepwr
I would say no since the orchards near here with both citrus and avocados use wind machines when the temps drop below 30.
I think that is to remove frost pockets. Apple orchards here have rented helicopters for a night to mix the air up if there is a chance of frost. The choppers just fly over the trees blowing warmer air down onto them. On our land you can feel how cold in gets in the valley as the air stratifies when the sun goes down.
I would say no since the orchards near here with both citrus and avocados use wind machines when the temps drop below 30.
I think that is to remove frost pockets. Apple orchards here have rented helicopters for a night to mix the air up if there is a chance of frost. The choppers just fly over the trees blowing warmer air down onto them. On our land you can feel how cold in gets in the valley as the air stratifies when the sun goes down.
"Wind Chill" happens when the air closest to your skin is always rapidly being removed. The air closest to your skin is warmer than the air 2 feet from your skin because your body heat radiants and warms the air closest to your skin. Also, water evaporates from your skin and "saturates" the air closest to your skin. Evaporation slows down and stop once saturation is achieved.
So, the faster the air is moving by your skin, your body is radiating warmth into the air. Your body cannot create a warm blanket of air around it. This is how a real blanket (like on your couch or bed) works. It traps the warmth your body radiates close to your skin....thus keeping you warm.
Also, if the air is being rapidly removed, the water from your skin is at maximum evaporation all the time. And the faster evaporation occurs, the greater the cooling effect.
This is how wind chill works.
And of course, every animal, every organism has it's own unique skin/hair/exoskeleton structure (which effects the manner in which moving air can remove/strip away the immediate warm air blanket surrounding you) and also each organism has it's own rate of surface water evaporation.
So, the faster the air is moving by your skin, your body is radiating warmth into the air. Your body cannot create a warm blanket of air around it. This is how a real blanket (like on your couch or bed) works. It traps the warmth your body radiates close to your skin....thus keeping you warm.
Also, if the air is being rapidly removed, the water from your skin is at maximum evaporation all the time. And the faster evaporation occurs, the greater the cooling effect.
This is how wind chill works.
And of course, every animal, every organism has it's own unique skin/hair/exoskeleton structure (which effects the manner in which moving air can remove/strip away the immediate warm air blanket surrounding you) and also each organism has it's own rate of surface water evaporation.
Think of the opposite extreme; are people in Arizona 110 degrees when it is 110 out? No, the evaporation from their bodies cools them to below 110. The latent heat of phase change is where the energy goes.
A 32F bag of ice and a 32F bag of melted ice don't store the same energy; it takes a boat load of energy to get from ice to water, and there is no increase in the temp of the material
A 32F bag of ice and a 32F bag of melted ice don't store the same energy; it takes a boat load of energy to get from ice to water, and there is no increase in the temp of the material
A block of steel left outside is the same temp as air temp (assuming all temp changes are gradual and no sun) and wind chill does not come into play.
Its really things that product heat like people.
Its really things that product heat like people.
Originally Posted By: simple_gifts
A 32F bag of ice and a 32F bag of melted ice don't store the same energy; it takes a boat load of energy to get from ice to water, and there is no increase in the temp of the material
You lost me. Ice and water are both H2O, how do the two different states have two different amounts of energy?
A 32F bag of ice and a 32F bag of melted ice don't store the same energy; it takes a boat load of energy to get from ice to water, and there is no increase in the temp of the material
You lost me. Ice and water are both H2O, how do the two different states have two different amounts of energy?
Originally Posted By: RamFan
Originally Posted By: simple_gifts
A 32F bag of ice and a 32F bag of melted ice don't store the same energy; it takes a boat load of energy to get from ice to water, and there is no increase in the temp of the material
You lost me. Ice and water are both H2O, how do the two different states have two different amounts of energy?
Latent heat of fusion. It's been precisely measured but it takes a bunch of BTU's of heat or cold to make or melt ice.
Quote:
To heat one kilogram (about 1 litre) of water from 283.15 K to 303.15 K (10 °C to 30 °C) requires 83.6 kJ.
However, to melt ice and raise the resulting water temperature by 20 K requires extra energy. To heat ice from 273.15 K to water at 293.15 K (0 °C to 20 °C) requires:
(1) 333.55 J/g (heat of fusion of ice) = 333.55 kJ/kg = 333.55 kJ for 1 kg of ice to melt
PLUS
(2) 4.18 J/(g·K)· 20K = 4.18 kJ/(kg·K)· 20K = 83.6 kJ for 1kg of water to go up 20 K
= 417.15 kJ
Or to restate it in everyday terms, one part ice at 0 °C will cool almost exactly 4 parts water at 20 °C to 0 °C.
Originally Posted By: simple_gifts
A 32F bag of ice and a 32F bag of melted ice don't store the same energy; it takes a boat load of energy to get from ice to water, and there is no increase in the temp of the material
You lost me. Ice and water are both H2O, how do the two different states have two different amounts of energy?
Latent heat of fusion. It's been precisely measured but it takes a bunch of BTU's of heat or cold to make or melt ice.
Quote:
To heat one kilogram (about 1 litre) of water from 283.15 K to 303.15 K (10 °C to 30 °C) requires 83.6 kJ.
However, to melt ice and raise the resulting water temperature by 20 K requires extra energy. To heat ice from 273.15 K to water at 293.15 K (0 °C to 20 °C) requires:
(1) 333.55 J/g (heat of fusion of ice) = 333.55 kJ/kg = 333.55 kJ for 1 kg of ice to melt
PLUS
(2) 4.18 J/(g·K)· 20K = 4.18 kJ/(kg·K)· 20K = 83.6 kJ for 1kg of water to go up 20 K
= 417.15 kJ
Or to restate it in everyday terms, one part ice at 0 °C will cool almost exactly 4 parts water at 20 °C to 0 °C.
Originally Posted By: eljefino
Originally Posted By: RamFan
Originally Posted By: simple_gifts
A 32F bag of ice and a 32F bag of melted ice don't store the same energy; it takes a boat load of energy to get from ice to water, and there is no increase in the temp of the material
You lost me. Ice and water are both H2O, how do the two different states have two different amounts of energy?
Latent heat of fusion. It's been precisely measured but it takes a bunch of BTU's of heat or cold to make or melt ice.
Quote:
To heat one kilogram (about 1 litre) of water from 283.15 K to 303.15 K (10 °C to 30 °C) requires 83.6 kJ.
However, to melt ice and raise the resulting water temperature by 20 K requires extra energy. To heat ice from 273.15 K to water at 293.15 K (0 °C to 20 °C) requires:
(1) 333.55 J/g (heat of fusion of ice) = 333.55 kJ/kg = 333.55 kJ for 1 kg of ice to melt
PLUS
(2) 4.18 J/(g·K)· 20K = 4.18 kJ/(kg·K)· 20K = 83.6 kJ for 1kg of water to go up 20 K
= 417.15 kJ
Or to restate it in everyday terms, one part ice at 0 °C will cool almost exactly 4 parts water at 20 °C to 0 °C.
http://www.spaceflight.esa.int/impress/text/education/Solidification/index.html
Originally Posted By: RamFan
Originally Posted By: simple_gifts
A 32F bag of ice and a 32F bag of melted ice don't store the same energy; it takes a boat load of energy to get from ice to water, and there is no increase in the temp of the material
You lost me. Ice and water are both H2O, how do the two different states have two different amounts of energy?
Latent heat of fusion. It's been precisely measured but it takes a bunch of BTU's of heat or cold to make or melt ice.
Quote:
To heat one kilogram (about 1 litre) of water from 283.15 K to 303.15 K (10 °C to 30 °C) requires 83.6 kJ.
However, to melt ice and raise the resulting water temperature by 20 K requires extra energy. To heat ice from 273.15 K to water at 293.15 K (0 °C to 20 °C) requires:
(1) 333.55 J/g (heat of fusion of ice) = 333.55 kJ/kg = 333.55 kJ for 1 kg of ice to melt
PLUS
(2) 4.18 J/(g·K)· 20K = 4.18 kJ/(kg·K)· 20K = 83.6 kJ for 1kg of water to go up 20 K
= 417.15 kJ
Or to restate it in everyday terms, one part ice at 0 °C will cool almost exactly 4 parts water at 20 °C to 0 °C.
http://www.spaceflight.esa.int/impress/text/education/Solidification/index.html
The best way to look at it is the molecular level
A solid is a phase where the molecules of a substance are bound in a lattice, so that none of the molecules can escape each other. The temperature of the solid is immaterial. As energy is added to the solid, the temperature of the solid rises. This is manifested itself by the molecules in the solid vibrating (motion) The appearance of the solid may change (e.g. when cold steel is heated to red hot).
If enough energy is added, the molecules in a substance will break free with enough vibration, but still be under the influence of the other molecules in proximity; this is know as a liquid. The temperature of the substance will not increase; all the energy is devoted to "breaking free" from the solid. The molecules and moving around influencing each other, but they are free to move. (this enables things like flow)
The transition from liquid to gas is the same concept. If enough energy is added, molecules will "break free" from the influence of "any" of the molecules in a liquid, thus changing to a gas.
Boiling water is an example. A pan of water on the stove is 212F. Any additional energy added does not raise the F of the water. It is "taken up" by the water molecules in a phase change and the water is converted to steam.
Any transition from one phase to another requires an input of energy for the atom to reach the next phase.
A solid is a phase where the molecules of a substance are bound in a lattice, so that none of the molecules can escape each other. The temperature of the solid is immaterial. As energy is added to the solid, the temperature of the solid rises. This is manifested itself by the molecules in the solid vibrating (motion) The appearance of the solid may change (e.g. when cold steel is heated to red hot).
If enough energy is added, the molecules in a substance will break free with enough vibration, but still be under the influence of the other molecules in proximity; this is know as a liquid. The temperature of the substance will not increase; all the energy is devoted to "breaking free" from the solid. The molecules and moving around influencing each other, but they are free to move. (this enables things like flow)
The transition from liquid to gas is the same concept. If enough energy is added, molecules will "break free" from the influence of "any" of the molecules in a liquid, thus changing to a gas.
Boiling water is an example. A pan of water on the stove is 212F. Any additional energy added does not raise the F of the water. It is "taken up" by the water molecules in a phase change and the water is converted to steam.
Any transition from one phase to another requires an input of energy for the atom to reach the next phase.
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Back in the day, they used to give us "dry bulb", and "wet bulb" temperatures.
Dry bulb is exactly that, a dry bulb, same as the sump in your vehicle.
Wet bulb had the bulb surrounded in a damp sponge, with the sponge evaporating water off, and running cooler than the dry bulb. (look at old desert and Aussie films, and there was a canvas water bag swinging on the front of the vehicle to provide cool water, relying on this effect.
The difference between the dry and wet bulbs tells you something about the humidity of the air (the closer they are together, the more humid it is, and the less evaporation can take place)...e.g. 100F "dry heat", and 100F coastal humid feel massively different, because your sweat can evaporate in the dry heat, and can't in the humid...exactly why your swamp cooler works in the desert and doesn't at the coast.
Wind chill is the additional temperature drop that a moist body (like us) can experience in dry, mobile air...and we love it in hot weather.
As a big example, some power stations are dry cooled (like car radiator, only footbll fields worth), and others have the traditional cooling towers...there will be a 20-30F difference in operating temperatures between the two...the tower being more efficient (cooler), but evaporating 5-6MG/day to do it.
Dry bulb is exactly that, a dry bulb, same as the sump in your vehicle.
Wet bulb had the bulb surrounded in a damp sponge, with the sponge evaporating water off, and running cooler than the dry bulb. (look at old desert and Aussie films, and there was a canvas water bag swinging on the front of the vehicle to provide cool water, relying on this effect.
The difference between the dry and wet bulbs tells you something about the humidity of the air (the closer they are together, the more humid it is, and the less evaporation can take place)...e.g. 100F "dry heat", and 100F coastal humid feel massively different, because your sweat can evaporate in the dry heat, and can't in the humid...exactly why your swamp cooler works in the desert and doesn't at the coast.
Wind chill is the additional temperature drop that a moist body (like us) can experience in dry, mobile air...and we love it in hot weather.
As a big example, some power stations are dry cooled (like car radiator, only footbll fields worth), and others have the traditional cooling towers...there will be a 20-30F difference in operating temperatures between the two...the tower being more efficient (cooler), but evaporating 5-6MG/day to do it.
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