Analysis of the HTF fluid in thermal solar power plants

01 Dec 2016
In: News


Analysing high temperature heat transfer fluids (HTF) as a diagnostic tool for maintaining solar thermal power plants is essential for this type of facility to operate under optimal conditions.

The most common analyses are often on the new HTF fluids for classification with the following:

Analysis Specification
Appearance Clear and clean
Composition Biphenyl and diphenyl ether
Humidity 300 ppm
Chlorine <10 ppm
Sulphur <10 ppm
Neutralisation Number <0.2 mg KOH/g sample
Copper corrosion (ASTM D 130) <<1a
Inflammation point V/A (ASTM D 92) 124 ºC
Inflammation point V/C (ASTM D 93) 110 ºC
Combustion point (ASTM D 92) 127 ºC
Self-combustion temperature (ASTM E 659) 621 ºC
Kinematic viscosity at 40 ºC 2.48 cSt
Kinematic viscosity at 100 ºC 0.99 cSt
Density at 25 ºC 1060 kg/m3
Thermal expansion coefficient at 200 ºC 0.000979/ºC
Average molecular weight 166
Crystallisation point 12 ºC
Contraction volume on freezing 6.27%
Expansion volume on melting 6.69%
Surface tension in air at 25 ºC 36.6 din/cm
Fusion heat 97.3 kJ/kg
Boiling point 257 ºC
Vaporisation heat at the maximum use temperature of 400 ºC 206 kJ/kg
Specific resistivity at 20 ºC 6.4*1011 ohm/cm
Optimal use range, liquid 12 ºC a 400 ºC
Optimal use range, vapour 260 ºC a 400 ºC
Maximum temperature of the film 425 ºC
Pseudocritical temperature 499 ºC
Pseudocritical pressure 33.1 bar
Pseudocritical density 327 kg/m3

Table. Classification analysis of the new fluid

It must be taken into account that a series of tests are usually carried out as primary indicators of the state of the fluid, while others are used to confirm the results obtained in these primary indicators.

Primary indicators

  • Humidity
  • Percentage of “low and high boilers”
  • Insoluble

Secondary indicators

  • Density
  • AN
  • Viscosity
  • Fire point

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