2 direction heat transfer

[ruecel]

hi, I have a metal heater which is contact with water and air (Metal heater is kind of plate). The metal heater energy supplied from external heat source or it is connected with power supply to produce resistance.
In that case, how I calculate total heat transfer? I am confused because heater will supplied to right and left.

 

[IRstuff]

What's the issue? The air and water interfaces are in parallel. You only have to determine if the thickness of your plate implies that the surface temperatures on the two sides are different or the same.

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[LittleInch]

The devil is in the detail on this one. If your plate is thick enough that you have a uniform temperature across the surface then heat load will be a combination of the heat transfer from the water and the air. If these are simple convection currents or if there is a flow in one or the other will make a huge difference as will the relevant masses and heat transfer actually going on.

If the temperature of the plate block is < 27C then you've got heat transfer from the air to the plate to the water complicating life.

It's likely that the heat transfer to the water far exceeds that to the air to the extent you might just allow for it by a few percent additional heat transfer.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ruecel]

Hi,
Thank you for your responds and sorry for unclear message.

So, I want to use a metal heater (I want to set the heater constant which is 70oC) to heat water in a closed system. However, this closed system consists of still / stagnant water, metal heater, and air.

Due to the purpose of a metal heater is to heat the still water. So I there will be a heat loss in air part.

Because of that, I want to calculate heat loss and supply energy needed of the metal heater (It will be supplied from electricity).

However, so far I know the heat transfer calculation has gradually temperature gradient.

Thank you

 

[ruecel]

This is the profile temperature might be of my system.
Thank you

 

[IRstuff]

Why not immerse the heater completely?

How much water? How fast?

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[ruecel]

I think the air space could reduce heat loss there.
Water volume: 6 cm3
It is stagnant water, so there will be no circulation speed.

 

[IRstuff]

if you immerse the heater completely, then you are only heating water. Ideally, however, you want the heater at the bottom of the water so that convection currents within the water will distribute the heat.

TTFN
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[LittleInch]

I didn't understand your last attachment.

You have tow surfaces with a surface temp of 70C. Just calculate the heat loss into the water and into air.

Your possible issue is that the water will gradually heat up if it's a closed system so you have a transient analysis going on there.

Why not insulate the air side?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.