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DARK0717

What things are thermally conductive but not electrially?

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So, im looking for maybe paste, or a pad, or a liquid that can conduct heat very well and doesnt let electriity to pass through. Any material/brand/or whatever out here that can  achieve both at the same time? 

I was thinking of thermal paste (for computers) but they are electrically conductive as well.

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3 hours ago, DARK0717 said:

So, im looking for maybe paste, or a pad, or a liquid that can conduct heat very well and doesnt let electriity to pass through. Any material/brand/or whatever out here that can  achieve both at the same time? 

I was thinking of thermal paste (for computers) but they are electrically conductive as well.

Diamond is best but beryllium oxide is excellent for this. It is extremely toxic but it seems it is being replaced by aluminum nitride.

There are various other solutions - provide more information or look for how a problem similar to yours has been solved.

 

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7 hours ago, DARK0717 said:

So, im looking for maybe paste, or a pad, or a liquid that can conduct heat very well and doesnt let electriity to pass through. Any material/brand/or whatever out here that can  achieve both at the same time? 

I was thinking of thermal paste (for computers) but they are electrically conductive as well.

Any fluid or squashy substance, liquid or paste,  will not work for you since  they do not prevent the metal conductive parts contacting.

Since you haven't told us your application here is a solution for certain types of power transistor.

https://uk.rs-online.com/web/p/heatsink-mounting-accessories/7128225?cm_mmc=UK-PLA-DS3A-_-google-_-PLA_UK_EN_HVAC+%26+Fans+%26+Thermal+Management_Whoop-_-Heatsink+Mounting+Accessories_Whoop-_-PRODUCT_GROUP&matchtype=&pla-339395015021&s_kwcid=AL!7457!3!413164769885!!!g!339395015021!&gclid=EAIaIQobChMInKmxiLmw6AIVRcjeCh2kYAeQEAYYASABEgJvUvD_BwE&gclsrc=aw.ds

 

This has a thermally conductive/electrically isolating mounting slip and also an isolating sleeve for the mounting bolt.

 

At one time these were made from mica, but now various proprietary artifical materials are available.

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9 hours ago, DARK0717 said:

I was thinking of thermal paste (for computers) but they are electrically conductive as well.

 

There is a couple different thermal pastes for computers. Silicone, with silver and with copper. The one with the best properties in thermal conductivity are with silver and copper.

Try silicone one..

On every computer paste there is mentioned thermal conductivity in W/m × K.

Search net for thermal grease and you will know their properties and will be able to compare.

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16 minutes ago, Sensei said:

There is a couple different thermal pastes for computers. Silicone, with silver and with copper. The one with the best properties in thermal conductivity are with silver and copper.

Try silicone one..

On every computer paste there is mentioned thermal conductivity in W/m × K.

Search net for thermal grease and you will know their properties and will be able to compare.

 

But they will not (cannot) guarantee electrical isolation.

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11 minutes ago, studiot said:

But they will not (cannot) guarantee electrical isolation.

But what can guarantee electrical isolation? It is just a matter of exceeding breakdown voltage of whatever medium we are taking into consideration.

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The white thermal compound is Aluminum Oxide in Silicone oil carrier.
Aluminum Oxide has good thermal conductivity but poor electrical conductivity.

As Studiot mentions, however, in paste or grease form, it is squishy and will allow metal to metal contact.

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1 hour ago, Sensei said:

But what can guarantee electrical isolation? It is just a matter of exceeding breakdown voltage of whatever medium we are taking into consideration.

But if you stay within the breakdown voltage, a paste cannot guarantee isolation while a solid barrier can.

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7 hours ago, Carrock said:

Diamond is best but beryllium oxide is excellent for this. It is extremely toxic but it seems it is being replaced by aluminum nitride.

There are various other solutions - provide more information or look for how a problem similar to yours has been solved.

 

thanks, tho they seem to be too expensive

4 hours ago, studiot said:

Any fluid or squashy substance, liquid or paste,  will not work for you since  they do not prevent the metal conductive parts contacting.

Since you haven't told us your application here is a solution for certain types of power transistor.

https://uk.rs-online.com/web/p/heatsink-mounting-accessories/7128225?cm_mmc=UK-PLA-DS3A-_-google-_-PLA_UK_EN_HVAC+%26+Fans+%26+Thermal+Management_Whoop-_-Heatsink+Mounting+Accessories_Whoop-_-PRODUCT_GROUP&matchtype=&pla-339395015021&s_kwcid=AL!7457!3!413164769885!!!g!339395015021!&gclid=EAIaIQobChMInKmxiLmw6AIVRcjeCh2kYAeQEAYYASABEgJvUvD_BwE&gclsrc=aw.ds

 

This has a thermally conductive/electrically isolating mounting slip and also an isolating sleeve for the mounting bolt.

 

At one time these were made from mica, but now various proprietary artifical materials are available.

right, so the application for this is to make a water heater that in which when dipped, and touch the water, it wont electrify you. My family company is about those water heaters using 2 plates than dont touch. It directly plugs in to the wall and dip under water then it boils, im sure u guys already know about the principle behind it, so yea, im thinking of a way to make it so that its completely safe to touch (the water) my idea is have the 2 plates encased with high boiling point liquid (or probably water) in aluminum, around that aluminum is thermally conductive and non electrically conductive material and those 2 are encased in more aluminum. So the point is, boil the water inside, transfer the heat outside (to boil water) and keep the current in.

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The power generated by this heater is equivalent to V^2/R in a constant current situation.
But you can also vary the current, keeping the voltage constant, in which case it is equivalent to I^2*R.
IOW increasing the current while keeping voltage low, is your best bet to keep it safe with adequate insulation.

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Posted (edited)
8 minutes ago, MigL said:

The power generated by this heater is equivalent to V^2/R in a constant current situation.
But you can also vary the current, keeping the voltage constant, in which case it is equivalent to I^2*R.
IOW increasing the current while keeping voltage low, is your best bet to keep it safe with adequate insulation.

it has no electronics, its plugs straight to the wall, tho if anyone is worried, its completely safe, until u add too much salt, or used the wrong type of heater depending on the water, but if u used the standard one (which is yellow) it works with all types of waters tho some water takes much longer to boil. The worst thing that happened in my experience is it tripped the breaker lol

Edited by DARK0717

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Posted (edited)

I think you might want to use a heat pipe.  These are used in computer cooling systems among other things.  You can isolate the electronics from the heat delivery and have a very fast thermal conductivity in the system.  You heat water or oil outside the heat pipe, not the pipe itself, and the pipe will transfer that heat to the secondary bath lickety split.  19th century technology still in use today.

Edited by quixotic

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7 minutes ago, quixotic said:

I think you might want to use a heat pipe.  These are used in computer cooling systems among other things.  You can isolate the electronics from the heat delivery and have a very fast thermal conductivity in the system.  You heat water or oil outside the heat pipe, not the pipe itself, and the pipe will transfer that heat to the secondary bath lickety split.  19th century technology still in use today.

wont heat pipes conduct electricity since theyr made of brass or copper

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On 3/23/2020 at 4:01 PM, DARK0717 said:

right, so the application for this is to make a water heater that in which when dipped, and touch the water, it wont electrify you. My family company is about those water heaters using 2 plates than dont touch. It directly plugs in to the wall and dip under water then it boils, im sure u guys already know about the principle behind it, so yea, im thinking of a way to make it so that its completely safe to touch (the water) my idea is have the 2 plates encased with high boiling point liquid (or probably water) in aluminum, around that aluminum is thermally conductive and non electrically conductive material and those 2 are encased in more aluminum. So the point is, boil the water inside, transfer the heat outside (to boil water) and keep the current in.

I see you are still interested in this subject.

I don't know where you are in the world, but the UK wiring regulations has a section on such direct water heaters.
They are used in large scale heaters.
I would advise any company manufacturing these to read the appropriate section.

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2 minutes ago, studiot said:

I see you are still interested in this subject.

I don't know where you are in the world, but the UK wiring regulations has a section on such direct water heaters.
They are used in large scale heaters.
I would advise any company manufacturing these to read the appropriate section.

well, we live here in the Philippines, worry not, the company passed wiring regulations of our country otherwise our company wont be able to sell the heaters commercially.
Im just exploring ways to make the design better

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Just now, DARK0717 said:

well, we live here in the Philippines, worry not, the company passed wiring regulations of our country otherwise our company wont be able to sell the heaters commercially.
Im just exploring ways to make the design better

I don't worry.

I just happen to know that the UK regs offer substantial advice on just the subject you are asking about.

I would have to dig out the detail, but I would expect for commercial reasons any company to do the due diligence themselves.

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On 3/23/2020 at 2:09 PM, Sensei said:

But what can guarantee electrical isolation? 

Not using a conductor like silver is probably a good start.

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On 3/23/2020 at 5:01 PM, DARK0717 said:

right, so the application for this is to make a water heater that in which when dipped, and touch the water, it wont electrify you. My family company is about those water heaters using 2 plates than dont touch. It directly plugs in to the wall and dip under water then it boils, im sure u guys already know about the principle behind it, so yea, im thinking of a way to make it so that its completely safe to touch (the water) my idea is have the 2 plates encased with high boiling point liquid (or probably water) in aluminum, around that aluminum is thermally conductive and non electrically conductive material and those 2 are encased in more aluminum. So the point is, boil the water inside, transfer the heat outside (to boil water) and keep the current in.

If you are isolating the water that is used to generate the heat from the water that is being heated, then I can't see any point in retaining the water used to generate the heat. Just use resistive wire (as used in old-fashioned electric heaters). Any advantage that comes from using the water as a heating element (whatever that might be - I struggle to imagine) is gone once you are no longer directly heating the water with the electric current. It sounds like you are trying to solve a non-existent problem.

Encase the electric heating elements in a metal surround and ensure that the element cannot come into contact with it. (And ground it for safety, obviously.) It is called an "immersion heater".

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10 hours ago, Strange said:

If you are isolating the water that is used to generate the heat from the water that is being heated, then I can't see any point in retaining the water used to generate the heat. Just use resistive wire (as used in old-fashioned electric heaters). Any advantage that comes from using the water as a heating element (whatever that might be - I struggle to imagine) is gone once you are no longer directly heating the water with the electric current. It sounds like you are trying to solve a non-existent problem.

Encase the electric heating elements in a metal surround and ensure that the element cannot come into contact with it. (And ground it for safety, obviously.) It is called an "immersion heater".

Can I use magnetic induction to accomplish what i wanna accomplish?
/\ I cant think of a proper design atm that is small and can simply be immersed in water

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10 hours ago, DARK0717 said:

Can I use magnetic induction to accomplish what i wanna accomplish?
/\ I cant think of a proper design atm that is small and can simply be immersed in water

What benefit would magnetic induction provide? What benefit does using water as the heating element provide?

Small? You can buy immersion heaters that fit in a mug (for making hot drinks). So thee don’t seem to be any size constraints. 

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1 hour ago, Strange said:

What benefit would magnetic induction provide? What benefit does using water as the heating element provide?

Small? You can buy immersion heaters that fit in a mug (for making hot drinks). So thee don’t seem to be any size constraints. 

I knew there was a special term for this type of device.

I looked it up and they are called 'Electrode boilers'

Note

They are AC only, single or polyphase.

They are used for generating steam as well as just heating water and are usually operated well above atmospheric pressure 10bar being typical.

https://en.wikipedia.org/wiki/Electrode_boiler

 

You would not use this method to heat a cup of water.

 

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On 4/3/2020 at 6:11 PM, studiot said:

I knew there was a special term for this type of device.

I looked it up and they are called 'Electrode boilers'

Note

They are AC only, single or polyphase.

They are used for generating steam as well as just heating water and are usually operated well above atmospheric pressure 10bar being typical.

https://en.wikipedia.org/wiki/Electrode_boiler

 

You would not use this method to heat a cup of water.

 

i see, thank you

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