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Originally posted by gmat
Ohms is an universal impedance unit IIRC. During my thermics courses i remember being told that thermal circuits work just like electrical circuit, as per the 'similarity' physics law. Thus thermal impedance has the same 'value' as electrical impedance, Ohms, as they both represent a potential divided by a current.
Now °C/W is maybe not *exactly* a thermal impedance, but it looks like it's very close. My memories are too distant to remember the units involved but a quick google would help for that. (i'm at work right now)
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The units for ohms are almost always Joule*seconds/coulomb^2. They do not involve temperature or
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(edit) impedance ? resistance? i'm not sure about the english term here.
electrically: U=RI -> R is the 'resistance' (in French), does that translate as an impedance ?
In French 'impedance' is the complex value of 'resistance', called Z and is Z=a+ib (complex number)
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Pretty much the same here. Ohm's law is V=IR.
If there are capacitive or inductive properties in the circuit, you use impedence Z=a+bi.
The inverse of resistance is conductance and the inverse of impedence is admittance, if I recall correctly.
The fact that there is a similar relationship between the forces of heat transfer and the forces of electrical current does not mean they share the same units. These same relationships - where a transfer of something is proportional to some sort of gradient - are common in heat transfer (Forier's and Newton's laws) electrical current (Ohm's law) differential mass transfer (Fick's Law) and momentum transfer (Newton's law).
Clearly, this does not mean that heat transfer coefficients, electrical conductance, diffusivity coefficients, and viscosity all share the same units.
Alchemy