Publication
The Diffusion Hygrometer: A late invention of H. Greinacher
Résumé
The diffusion of gases, dry and moist, had been studied in 1874 by Louis Dufour, who observed a pressure difference across a porous wall separating moist air and a vessel containing either water or a desiccant. 70 years later, Heinrich Greinacher (1880-1974) claimed to have built the first Diffusion Hygrometer, proposed a theory and got a patent for it. Two different models were produced by firms of Lausanne, TESA and Rüeger. Eventually, they were a commercial failure. We found one exemplar of each maker in the collections of our Physics Museum and have tested them. A comparison of the performances with the then currently available hygrometers will be made.
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Concepts associés (5)
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Pressure measurement is the measurement of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure mechanically are called pressure gauges, vacuum gauges or compound gauges (vacuum & pressure). The widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge.
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En mécanique des fluides la pression dynamique est une mesure de l'énergie cinétique d'un fluide par unité de volume. Elle joue un rôle fondamental dans la conservation de l'énergie et sert de référence pour la définition des coefficients aérodynamiques. La pression dynamique est l'énergie cinétique par unité de volume au sein d'un fluide : où est la masse volumique du fluide, son volume et sa vitesse. L'énergie cinétique par unité de volume est donc, en divisant par : La pression dynamique a la dimension d'une pression, d'où son nom.
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