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I'm looking for thermophysical properties of Galden LS 230, a liquid polymer (PFPE) produced by Solvay (https://www.solvay.com/en/markets-and-products/featured-products/Galden.html) at temperatures above 25 °C. Solvay only publishes properties at 25 °C.

I asked them for properties at higher temperatures, with no answer in three weeks. I also couldn't find other free online sources (this is a vapor phase soldering hobby project).

The properties published at 25 °C are:

  • boiling point: 230 °C
  • density: 1820 kg/m³
  • kinematic viscosity: 4.4 cSt = 4.4 × 10-6 m²/s
  • vapor pressure: 453.3 Pa
  • specific heat: 973 J/kg K
  • heat of evaporation at boiling point: 63 kJ/kg
  • thermal conductivity: 0.07 W/mK
  • coefficient of expansion: 0.0011 1/K
  • surface tension: 20 dyne/cm = 0.02 N/m
  • average molar weight: 1020 a.m.u
  • some others that I don't expect to need for thermodynamics: dielectric strength, dielectric constant, volume resistivity.

Vapor density

Using the ideal gas law to calculate the density of saturated vapor at 1 bar yields about 24.4 kg/m³, which is within the range I found in some other inofficial sources and also in a pretty hard to read plot in a solvay presentation.

Viscosity

the wikipedia page on the temperature dependence of liquid viscosity (https://en.wikipedia.org/wiki/Temperature_dependence_of_liquid_viscosity) lists a number of models that might also apply to Galden, but I'm not sure which ones would yield reasonable results. I'd be glad if someone could shed some light on this. The solvay FAQ (https://www.solvay.com/en/markets-and-products/featured-products/galden-pfpe-faq.html) shows a plot of viscosity vs. temperature for Galden HT 230, which has the same nominal boiling point as the "LS" grade, but has higher tolerances for the molecular weight distribution. The HT grade also starts with the same viscosity at 25 °C as the LS grade. If all else fails, I might use that value.

Specific heat

I'm not sure if it's reasonable to assume specific heat to remain close to constant. My gut feeling is "probably".

Thermal conductivity

Since Galden is a non-metal, I'd expect thermal conductivity to remain more or less constant, or to increase slightly. How large or how significant the change would be, I don't know.

Surface tension

I expect surface tension to decrease with increasing temperature, according to the Eötvös Rule (https://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_rule), but to really calculate values I'd need information about the critical point of this polymer (if that even exists, anyway).

A bit more technical background

In vapor phase soldering, a printed circuit board with solder paste and components is immersed into high temperature vapor (such as that of Galden). To create this vapor, the liquid has to be heated and evaporated. This must be done carefully because Galden starts to decompose at 290 to 300 °C. All the properties above are required to calculate a Nusselt number for nucleate boiling, so that I can determine the actual temperature at the heating surface, which will be higher than 230 °C.

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  • $\begingroup$ Would it be easier if you boiled at a fixed temperature below 290C and above 230C, would that be sufficient? If you don't bug the company, they tend not to get to requests from non-corporate sources. $\endgroup$ – J. Ari Jan 4 '18 at 20:48
  • $\begingroup$ Unfortunately with my current hardware it's not possible to heat the Galden in such a way that I can measure the temperate at the surface where the actual vaporization takes place, which is an immersed power resistor. That's why I want to look closer at the actual heat transfer to figure out an upper limit to the heat flux. $\endgroup$ – Christoph Jan 4 '18 at 21:22
  • $\begingroup$ What Nusselt number relationship are you thinking of using? If you don't get literature from the company or from journals (even data for similar molecules will be okay), you'll have to make an engineering judgement whether the worst case scenario for you is conservative or will lead to failure. $\endgroup$ – J. Ari Jan 5 '18 at 14:26
  • $\begingroup$ @J.Ari I thought about using correlation from Stephan and Preußer for nucleate boiling above horizontal plates, which is said to be suitable for organic fluids close to atmospheric pressure. This would be a rather bad heat transfer situation (with rather high wall temperature) when compared to, say, boiling at the wall of a horizontal cylinder, which is closer to what I have in mind. $\endgroup$ – Christoph Jan 12 '18 at 21:12
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    $\begingroup$ @J.Ari I did not consider dual stage heating because I want the device to stay as simple as possible. One fact that makes this question somewhat obsolete is that I just found out that the Galden FAQ contains a section about proper heater sizing, which states that the lower end of the safe region is around 4 - 5 W/cm². If all else fails, I'll have to use that value. $\endgroup$ – Christoph Jan 15 '18 at 14:24

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