Water as a dielectric in capacitors

In summary, water is occasionally used as a dielectric in capacitors, but only for short periods of time due to its tendency to conduct electricity. This can be mitigated by using high purity water and coating the plates with a non-conductive material. Water also has the added benefit of being able to absorb high powers and self-heal in case of circuit failure. However, its use in practical applications may be limited due to the potential for ions to leach into the water and affect its conductivity.
  • #1
Indis Nenhrma
8
0
"water" as a dielectric in capacitors

Homework Statement



Why do you think water is not commonly used as a dielectric in capacitors?
K=80.4
*K=dielectric constant for water

thx for any help
 
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  • #2
The dielectric constant looks great for use in a capacitor. What about the conductivity?
 
  • #3
Water is occasionally used as a dielectric. There are some large coaxial cables under Imperial College in London that use water as a dielectric, but only for a very short period of time, before it starts to conduct.
 
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  • #4
Edward G said:
Water is occasionally used as a dielectric. There are some large coaxial cables under Imperial College in London that use water as a dielectric, but only for a very short period of time, before it starts to conduct.

Really? What for? Now I'm curious.
 
  • #5
Dick said:
The dielectric constant looks great for use in a capacitor. What about the conductivity?

I suspect the issue may not be with the conductivity of pure water itself, but the tendency of materials to leach ions into it, creating much more conductive solutions... (The table at this Wiki article -- http://en.wikipedia.org/wiki/Electrical_conductivity -- is instructive.)
 
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  • #6
Dick said:
Really? What for? Now I'm curious.

You use them in very high power applications like pulse X ray or high power laser sources.
You have to use high purity water to reduce the conductivity and they only work for a very short time before they short. They are able to absorb very high powers and they are self healing. And you get the extra useful feature that if things go very wrong the water boils and disconnects the circuit!
 
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  • #7
dynamicsolo said:
I suspect the issue may not be with the conductivity of pure water itself, but the tendency of materials to leach ions into it, creating much more conductive solutions... (The table at this Wiki article -- http://en.wikipedia.org/wiki/Electrical_conductivity -- is instructive.)

That's what I was trying to lead the OP to discover. And thanks to mgb_phys for filling me in on the benefits of water as a dielectric.
 
  • #8
Thanks for your attention and expository answers. :)
 
  • #9


Why do so many think the plates have to be in physical contact with the water? Capacitors are used as fuel sensors in the A4 Skyhawk aircraft and the dielectric is the fuel. However in this case the plates are insulated from the fuel. The same would logically be the case in a capacitor using water as the dielectric. The plates being insulated from the water the conductivity of the impure water due to ions forming would not be a factor.
 
  • #10


Yeah, as the others have stated, I don't think there is anything wrong with using ideal, or "pure," water. I wouldn't want to do practically because water is a good solvent, so it has the potential to bring ions into it. I guess people actually do it in the applications that mgb stated, but I wonder about it's leakage (parasitic resistance).
 
  • #11


Mindscrape, As my previous post says , the plates do not have to be in contact with the water. You can coat the plates in a non-reactive, non-conductive coating then apply the use of water as a dielectric. The conductivity of the water would not be a factor. Also it doesn't have to be pure water. If your water capacitor were going to be mounted outdoors you could add some anti-freeze ( dielectric constant of 40 ) to keep it from freezing.
 

Related to Water as a dielectric in capacitors

1. What is a dielectric in capacitors?

A dielectric in capacitors is an insulating material that is placed between the two conductive plates of a capacitor. It helps to increase the capacitance and store more electrical energy.

2. Why is water used as a dielectric in capacitors?

Water is a commonly used dielectric in capacitors because it has a high dielectric constant, which means it can store a large amount of electrical charge in a small space. It is also inexpensive and easily accessible.

3. What are the advantages of using water as a dielectric in capacitors?

Some advantages of using water as a dielectric in capacitors include its high dielectric constant, low cost, and non-toxic nature. It also has a high boiling point, making it suitable for use in high-temperature applications.

4. Are there any drawbacks to using water as a dielectric in capacitors?

One drawback of using water as a dielectric in capacitors is its high conductivity, which can lead to leakage currents and decrease the overall efficiency of the capacitor. It is also susceptible to evaporation and can freeze at low temperatures.

5. How is water used as a dielectric in capacitors?

Water is typically used as a dielectric in capacitors by filling a container or coating a surface with it. It can also be mixed with other substances to improve its properties, such as adding salt to increase its conductivity or using a polymer to prevent evaporation.

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