An experimental study of heat transfer to cryogenic fluids in high speed rotating thermosyphons

Igra, Robert Michael (1988) An experimental study of heat transfer to cryogenic fluids in high speed rotating thermosyphons. University of Southampton, Doctoral Thesis.

Abstract

The use of liquid helium to cool superconducting generators requires an understanding of the effect of rotation on natural convection flows within ducts. Although these flows will primarily be driven by centrifugal acceleration, secondary flows, in particular those due to Coriolis accelerations, may develop and these can result in local variations in temperature and heat transfer coefficient. The effect of heating and rotation, at _peeds of up to 3000rpm, on the local temperature within simple natural convection systems is investigated. Measurements have been made with pressure as well as temperature sensors. The selection and calibration of the sensors is described. A novel method for obtaining thermodynamic data to standards accuracy is outlined. It is observed that Coriolis accelerations acting, at right angles to the centrifugal acceleration vector, give rise to local fluid temperature variations of up to 100 percent. Coriolis effects are observed in both thermosyphon loops, (U-tubes), and single arm thermosyphons. In thermosyphon loops heating was expected to give rise to a directed flow, with the fluid flowing radially inwards along the heated arm. It is observed that above a certain critical heat flux a temperature rise occurs on the unheated arm; suggesting that the directed flow is breaking down. An explanation of this effect is given.

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