I want construct a heating element by screen printing a flat coil pattern of conductive paste onto an insulated substrate. This conductive paste consists of a powder of conductive metal contained in a viscous epoxy paste. The pieces of metal are held together by the paste to form a conductive pathway. There are several options for the type of conductive metal filler - so far I have found silver, silver and copper mixed, carbon, graphite and nickel.

What material characteristics should I be looking at in trying to assess the best filler material? I want to make a heating element that will heat up as quickly as possible with the least amount of electric current being put through the heating element. The max temperature of the heating element will be 100 C.

I am thinking that the two most important qualities for generating heat with the least electric current are Resistivity and Thermal Conductivity. Is this correct?

These are the specs on some pastes I have found. It seems like the Nickel paste would be best - is that right?

Nickel Volume Resistivity <0.004 ohm. cm Thermal Conductivity 1.44 W/M-K

Graphite Volume Resistivity 0.004 ohm. cm Thermal Conductivity 0.24 W/M-K

Silver Volume Resistivity 3.00 E -3 ohm. cm Thermal Conductivity 1.45 W/M-K

Carbon Volume Resistivity < 40 ohm. cm Thermal Conductivity 0.25 W/M-K

Silver/Copper Volume Resistivity 3.70 E-2 ohm. cm Thermal Conductivity 1.15 W/M-K

  • $\begingroup$ High thermal conductivity to spread heat faster. Low coefficient of thermal expansion to minimize internal stress due to temperature gradients. Also helps with cyclic thermal fatigue. Sufficient corrosion resistance and mechanical property retention in operating temperature range. No phase changes in operating temperature range. Sufficient filler concentration to reach the percolation threshold. Resistivity can be traded off with material usage in terms of material usage efficiency. Higher resistivity, less material for the same resistance and same Joule heating, so material cost is important. $\endgroup$ – wwarriner Oct 10 '19 at 19:28
  • $\begingroup$ What will the heating element heat? The fluid around the element? Only the containing matrix around the wires? Or some complex combination thereof? Also, how do you want to provide power input? Do you want to design a voltage unlimited/current limited system or a voltage limited/current unlimited system? $\endgroup$ – Jeffrey J Weimer Oct 12 '19 at 15:11

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