Thermal transpiration flow: A circular cross-section microtube submitted to a temperature gradient

Thermal transpiration is the macroscopic movement of rarefied gas molecules induced by a temperature gradient. The gas moves from the lower to the higher temperature zone. An original method is proposed here to measure the mean macroscopic movement of gas in the case of a long circular cross-section glass microtube onto which a gradient of temperature is applied. The mass flow rate and the thermomolecular pressure difference have been measured by monitoring the absolute pressure evolution in time at both ends of the capillary using high-speed response pressure gauges. Two gases, nitrogen and helium, are studied and three different temperature differences of 50, 60, and 70 °C are applied to the tube. The analyzed gas rarefaction conditions vary from transitional to slip regime.

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