Hydrocarbon dielectric heat transfer fluids for microwave plasma generators
A process and apparatus for cooling a plasma tube generally includes flowing a hydrocarbon dielectric heat transfer fluid into a space defined by the plasma tube and a concentric tube surrounding the plasma tube. In one embodiment, the hydrocarbon fluid is selected to have a dissipation factor less than 0.002 and a thermal efficiency coefficient greater than or equal to 1.30 kJ/kg*K.
1. A plasma apparatus comprising:
a plasma tube extending from a gas source through a microwave cavity to a process chamber;
a microwave power source arranged to couple microwave energy to gas flowing through the tube within the microwave cavity;
a concentric tube disposed about the plasma tube, wherein the concentric tube defines a space; and
a hydrocarbon dielectric fluid in fluid communication with the space, wherein the hydrocarbon dielectric fluid is an aliphatic hydrocarbon.
2. The plasma apparatus of claim 1 , wherein the hydrocarbon fluid is selected to have a dissipation factor less than 0.002 and a thermal efficiency coefficient greater than or equal to 1.30 kJ/l*K.
3. The plasma apparatus of claim 1 , wherein the dissipation factor is less than 0.001.
4. The plasma apparatus of claim 1 , wherein the dissipation factor is less than 0.0005.
5. A plasma apparatus comprising:
a plasma tube;
a concentric tube paced apart from and surrounding the plasma tube; and
a dielectric heat transfer fluid comprising a hydrocarbon fluid, wherein the hydrocarbon fluid is selected to have a dissipation factor less than 0.002 and a thermal efficiency coefficient greater than or equal to 1.30 kJ/l*K.
6. The plasma apparatus of claim 5 , wherein the dissipation factor is less than 0.001.
7. The plasma apparatus of claim 5 , wherein the dissipation factor is less than 0.0005.
8. The plasma apparatus of claim 5 , wherein the hydrocarbon fluid has a dielectric constant less than 4.0.
9. The apparatus of claim 1 , wherein the hydrocarbon fluid is non-polar and has a vapor pressure less than 133 Pascals.