Relative humidity above 100 °C


An accurate control and monitor of relative humidity in a wide range of temperatures and pressures is required in many industrial processes. Since 2015 the VSL relative humidity facility offers the possibility to calibrate relative humidity and air temperature sensors in the temperature range from -40 ⁰C to 180 ⁰C and in the pressure range 70 kPa to 500 kPa, with a maximum dew-point of 95 ⁰C (97 %rh at 95 °C, but only 8 %rh at 180 °C).

In the framework a of the EMPIR project “Humidity measurements at high temperatures and transient conditions” (HIT) the dew-point temperatures will be extended up to 150 ⁰C. Such extension is not trivial from the technical point of view, as it implies saturation of air with water at temperatures higher than 100 ⁰C, a condition in which relative humidity is not even unambiguously defined.

VSL approach in generating dew-point temperatures up to 150 ⁰C is based on the combination of the sub-chamber concept (in which an external chamber controls only the temperature of an internal chamber) with a pre-saturation stage outside the external chamber (at lower temperature) and a final saturation stage inside the external chamber (at the temperature of the external chamber), before entering the internal chamber.

The development of this facility is proceeding in parallel with the R&D on prototype sensors being developed by two industrial partners in the HIT project (Michell Benelux and Innovation Handling). In a later stage of the project, the developed prototype sensors will be tested in real industrial environments (milk powder industry and paper industry).