Erfahrungs- und Forschungsbericht 2012 - Ensi

static.ensi.ch

Erfahrungs- und Forschungsbericht 2012 - Ensi

Figure 2: a) Calibration setup; one can see the water film and some trapped air bubble between the glass window and the

wall mesh sensor. b) Wall mesh sensor front view obtained with the NIR camera; darker spot correspond to thicker film.

c) Superposition of raw data obtained simultaneously with the wall sensor on NIR picture; one can see the improved spatial

resolution obtained with the NIR camera.

Development of instrumentation for NIR and

MWIR techniques for temperature and film

thickness measurements

This section provides the reader with a summary

of the measurement principles to be applied in the

LINX facility. Due to the expected high steam concentration

and considering the intrusiveness of most

measurement techniques, the research focus for the

LINX investigations has been to study the potential

of infrared imagery on application such as 2-D

spatially resolved film thickness measurement. Time

resolved liquid film thickness point measurements

based on infrared absorption techniques has already

been successfully carried out [2]. Based on the same

absorption principle a concept for spatially resolved

measurements (2-D) is being developed.

Figure 1 shows the water optical properties of interest

for infrared measurements. Liquid water has very

low absorption properties in the visible spectrum of

light whereas it possesses an adequate absorption

for thin film thickness measurements in the near

infrared (NIR) region. Using a halogen light source

and IR detector allows for absorption measurement

in pure water. Consequently, no additional bodies

(such as dye or seeding) need to be mixed with the

water, which is a necessary condition to measure

condensing and re-evaporating films. Our first attempt

to measure water absorption in a plane (2-D)

was performed with a NIR camera at the FLIR ATS

production centre in Paris. Results showed a good

correspondence between film thickness and photon

count acquired by the camera [1].

Associated with a near infrared (NIR) camera, a midwave

infrared (MWIR) camera will be used for film

and plate surface temperature measurements. For

wavelengths ranging from 2.5 to 5.1 micrometers,

the water light absorption is so high that only blackbody

emissions from the film surface are transmitted

towards the detector. Thermal measurements

should thus provide the temperature of the water

film surface and the dry areas on the plate surface.

Consequently, information on local heat transfer at

the border between wet and dry areas would also

be accessible. Particularly, when droplet or rivulet

regimes are dominant, the non uniform heat transfer

at the surface could be spa-tially and temporally

evaluated.

Measurement campaign at ETHZ

As of today, cameras were purchased, the light

source was designed and tested, and a first measurement

campaign is ongoing in collaboration with

ETHZ to validate the measurement and calibration

technique as well as to assess the accuracy of the

measurements. The Wall Mesh Sensor (WMS) with

maximal time resolution of 10 kHz allows for a direct

synchronized measurement comparison. The frame

rate used in this experiment is coherent with the

camera capabilities and the requirements for characterization

of a condensate flow. At least 100 frames

per second and an integration time below 1 ms ensure

good tracking of the flow pattern evolution and

sharp images.

In the calibration setup, the water is confined between

a glass window and the wall mesh sensor

plate, Figure 2a). The distance between the glass

window and the wall sensor, meaning the thickness

of the film, is controlled by means of three micro-

ENSI Erfahrungs- und Forschungsbericht 2012 217

Weitere Magazine dieses Users
Ähnliche Magazine