Numerical modelling of stationary and radial rotating heat pipes

Abstract

This thesis focuses on the CFD simulation of two-phase flows within stationary and rotating radial heat pipes (RRHPs). These heat pipes, especially RRHPs, have demonstrated their potential for a wide range of industrial applications. However, their development is hindered by a limited understanding of the complex flow fields and heat transfer phenomena inside them. This study begins by validating the Rensselaer Polytechnic Institute (RPI) wall boiling model alongside various bubble size models against two subcooled boiling flows in vertical cylindrical pipes. For this purpose, a bubble size model was implemented in OpenFOAM. The effects of non-uniform heating conditions on the subcooled boiling flow were examined using one of the validation cases. Following this, a comparative analysis between the performances of the RPI model and the Lee phase change model in simulating pool boiling phenomenon was conducted. Further exploration involves the CFD simulation of the two-phase flow in a stationary two-phase closed thermosyphon (TPCT) using the Lee model. To maintain the mass balance within the TPCT, a mass-balance algorithm was implemented in OpenFOAM. The predicted results show good agreement with experimental data and capture the features of two-phase flow. Non-uniform heating conditions have demonstrated their effects on the flow field and heat transfer in the TPCT, either increasing or reducing the overall thermal resistance of the TPCT depending on the particular non-uniform heating pattern applied. Finally, the aforementioned CFD model has been further developed for the simulation of an RRHP, taking into account the effects of rotational forces and the time-varying direction of the gravitational force when solving in a rotating frame of reference. The predicted wall temperature of the RRHP agrees well with that reported in the literature. The effects of secondary flow on the phase distribution and heat transfer in the RRHP have been analysed and discussed in detail. It was found that the asymmetry in phase distribution and heat transfer in the RRHP is significant, even when the rotational speed is relatively low compared to practical applications. In the present study, the vapour flow in the condenser section begins to be significantly influenced by the Coriolis force when it is approximately 0.756 times the gravitational force.

Date of Award	6 Jan 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Timothy Craft (Supervisor)