Why Does Hot Water Conduct Heat Easier Downwards?

In summary: But you're right, if you want to measure the heat flow in a particular range, you want to measure it with the colder water on top.
  • #1
nishant
95
0
while measuring th thermal conductivity of water the upper part is kept hot,why is this so?
is this so because heat conduction is easier downwards.
 
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  • #2
Cold water is denser than hot water, so it goes down. Since water is a bad heat conductor it takes a long time to equalize the temperature.
When you heat water, the fire is in the down position, so the heated, less dense water, goes up and is replaced by cold water. This phenomenon is called convection.
 
  • #3
So what is the answer:To stop convection or it is easier for the heat to be conducted downward by keeping the upper layer hot?
 
  • #4
nishant,

Good question!

To measure any method of heat flow, you have to eliminate other possible methods. Heat flow by conduction is not affected by gravity. Heat flow by convection is affected by gravity, in fact, it's caused by gravity. So convection can only happen when there is warm water below cold water. Heating from the top eliminates that possibility, so it eliminates convection as a method of heat flow. All that's left is conduction.
 
  • #5
I am still not able to get the answer totally correctly.BY maintaing the upper layer hot our main aim is to stop convection or is it the fact that if we maintain the upper layer hot we will be able to conduct heat downwards quite easily?
 
  • #6
nishant said:
I am still not able to get the answer totally correctly.BY maintaing the upper layer hot our main aim is to stop convection or is it the fact that if we maintain the upper layer hot we will be able to conduct heat downwards quite easily?

It is to prevent convection from happening. If convection happens, you will not be able to measure the conduction. You cannot heat from the bottom without causing convection. Gravity will not make it easier for conduction to happen. If you could prevent convection with some other orientation, the conduction would be the same. But you can't eliminate convection with another orientation.

There is however an exception to this hot on top requirement. Water is most dense at 4C. If you wanted to measure the heat conduction in the range from 0C to 4C, you would want the colder water on top of the warmer, denser water.
 
  • #7
but isn't it the same thing.by keeping the upper layer warm we are actually helping to increase the heat conduction downwards and make it easier?
 
  • #8
nishant,

You're not reading carefully.

Conduction of heat DOESN'T DEPEND ON GRAVITY! Conduction works just as well going up as down, or sideways, or any other direction.
 

Related to Why Does Hot Water Conduct Heat Easier Downwards?

1. Why does hot water conduct heat easier downwards compared to cold water?

The temperature of a substance affects its ability to conduct heat. Hot water has higher kinetic energy and therefore its molecules are moving faster. This results in more collisions between molecules, leading to faster heat transfer and easier conduction downwards.

2. How does the density of hot water contribute to its ability to conduct heat downwards?

As water heats up, it becomes less dense. This means that hot water molecules are more spread out compared to cold water molecules. With more space between molecules, heat can be transferred more easily and quickly, making hot water a better conductor of heat downwards.

3. Is the buoyancy of hot water a factor in its ability to conduct heat downwards?

Yes, the buoyancy of hot water plays a role in its ability to conduct heat downwards. As hot water rises, it displaces colder water which then moves downwards. This creates a continuous flow of water, allowing heat to be transferred more efficiently downwards.

4. Can the composition of hot water affect its ability to conduct heat downwards?

Yes, the composition of hot water can impact its conductivity. For example, water with a high mineral content can conduct heat more efficiently than pure water. This is because minerals act as conductors and facilitate the transfer of heat between molecules.

5. Does the shape of a container holding hot water affect its ability to conduct heat downwards?

Yes, the shape of a container can influence the conduction of heat downwards. A tall and narrow container will have a smaller surface area compared to a wide and shallow container. This means that less heat will be lost through the sides of the container, allowing for more efficient downward heat transfer.

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