Numerical investigation on heat transfer characteristics of Taylor Couette flows operating with CO2

Abstract

An accurate prediction of heat transfer characteristics is essential for the design of bearings in supercritical CO2 power cycles, where the flow at the rotating surface is characterised as Taylor Couette flows. However, the high pressure CO2 leads to Taylor numbers exceeding the applicable range of existing empirical correlations, challenging the suitability. Few studies are found to consider this issue. In this paper, the heat transfer characteristics and windage losses of Taylor Couette flows are investigated. Two representative pressures of 1.4 MPa and 7.8 MPa are studied. It is demonstrated that the heat transfer performance is significantly enhanced at high operation pressures, in particular for the operation temperature towards the critical regime, while a reasonable windage loss is maintained. This is attributed to the increased Taylor number and abrupt changes of thermophysical properties near the critical regime. In addition, empirical correlations underpredict the heat transfer performance, particularly for high operation pressures. The difference is up to three times. The effect of annual gap, cylinder radius and axial length are further compared. This work provides the insight into heat transfer characteristics of Taylor Couette flows operating with CO2. The outcome can be used to the design of CO2 bearings.