andieje
asked on
conduction, convection and radiation trivia
Hi
I have a few conduction/convection/radi
1 Why is the element at the bottom on an electric kettle
Convection currents means cold water at the bottom of kettle
2. Why is freezer box at top of fridge
Don't know. I would have thought it would be warmest at the top due to convection
3. Why is it more likely to be fristy on a clear night than cloudy night
Clouds stop heat escaping
4. Why is back of refrigerator painted black
I don;t know, do they mean the inside or outside of a fridge? Black is a better radiator and absorber of radiation. If the outside of the fridge was black would radiate more heat but also absorb more too. If inside of fridge was black this would absorb more heat out of the fridge i guess. In either case, why just the back? Why not sides too?
5. What would happen if you sprinked black soot on ice in the antartic
Don;t understand the relvance of the antartic but presumbaly the ice would be more likely to melt
6. Why are heat sinks black, with large aluminium fins
Fins gives large surface area; black will absorb the heat better, aluminium will conduct heat away
Many thanks
I have a few conduction/convection/radi
1 Why is the element at the bottom on an electric kettle
Convection currents means cold water at the bottom of kettle
2. Why is freezer box at top of fridge
Don't know. I would have thought it would be warmest at the top due to convection
3. Why is it more likely to be fristy on a clear night than cloudy night
Clouds stop heat escaping
4. Why is back of refrigerator painted black
I don;t know, do they mean the inside or outside of a fridge? Black is a better radiator and absorber of radiation. If the outside of the fridge was black would radiate more heat but also absorb more too. If inside of fridge was black this would absorb more heat out of the fridge i guess. In either case, why just the back? Why not sides too?
5. What would happen if you sprinked black soot on ice in the antartic
Don;t understand the relvance of the antartic but presumbaly the ice would be more likely to melt
6. Why are heat sinks black, with large aluminium fins
Fins gives large surface area; black will absorb the heat better, aluminium will conduct heat away
Many thanks
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2 You have to work to cool the freezer, so you might as well use its escaping cool air to cool the fridge below.
4 outside, to radiate
Lee
4 outside, to radiate
Lee
SOLUTION
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2. Why is freezer box at top of fridge
Don't know. I would have thought it would be warmest at the top due to convection
It's more convenient - they make models with the freezer below. (2 doors)
Don't know. I would have thought it would be warmest at the top due to convection
It's more convenient - they make models with the freezer below. (2 doors)
>>2. Why is freezer box at top of fridge
The normal construction places the motor compressor in the base of the "box", so that the bottom is heavier than the top and it won't fall over when knocked.
This means that the compressor forces the coolant into the radiator at the bottom. The top of the radiator is where the coolant then goes into the nozzle which reduces the pressure and hence cools the coolant down even further. It then makes sense to feed the cold coolant directly into the freezer part since the coolant is at it's lowest temperature. After going into the freezer, where it will warm up, it is then passed into the refigerator and finally back down into the compressor. Thereofre the freezer box is at the top of the fridge box.
The normal construction places the motor compressor in the base of the "box", so that the bottom is heavier than the top and it won't fall over when knocked.
This means that the compressor forces the coolant into the radiator at the bottom. The top of the radiator is where the coolant then goes into the nozzle which reduces the pressure and hence cools the coolant down even further. It then makes sense to feed the cold coolant directly into the freezer part since the coolant is at it's lowest temperature. After going into the freezer, where it will warm up, it is then passed into the refigerator and finally back down into the compressor. Thereofre the freezer box is at the top of the fridge box.
>>5. What would happen if you sprinked black soot on ice in the antartic
You'd be arrested, since there is an international agreement not to pollute the antartic. Everybody must take their rubbish home with them.
You'd be arrested, since there is an international agreement not to pollute the antartic. Everybody must take their rubbish home with them.
>>6. Why are heat sinks black, with large aluminium fins
because they are cheaper than heat sinks with copper fins.
because they are cheaper than heat sinks with copper fins.
@BigRat
Re: 5. Who would arrest you? The penguins? :-)
Lee
Re: 5. Who would arrest you? The penguins? :-)
Lee
@Lee
Probably the US military.
Probably the US military.
ASKER
many thanks
ASKER
I still dont understand 2 and 4.
Cool air is denser so falls to the bottom of the fridge i get that. This the coldest part of the fridge is at the bottom so wouldn't it be easier then to have the freezer box at the bottom as it would take less energy to keep it cold?
Regarding the fridge again, do you know if it is black on the inside or outside of the fridge?