Experimental and numerical analysis of an oscillating slug flow.

The project is dealing with the fundamental understanding of the thermo-hydraulics and heat transfer mechanism inside a pulsating heat pipe. A closed loop Pulsating Heat Pipe (PHP) is a recent, promising two-phase heat transfer device, applicable for moderate heat fluxes. It consists of a capillary tube closed end-to-end, evacuated and partially filled with a working fluid. It finds a wide applicability field, from electronics up to space applications, due to its flexibility, reduction of required moving elements and low production cost. In spite of its simple structure, the PHP working principles are complex.

First a literature review on Pulsating Heat Pipe will be carried on in order to let the student be acquainted with the topic. An existing apparatus will be optimised and improved in order to measure heat transfer coefficients of a oscillating meniscus, for different roughness and wettability of the channel. The system will be able to measure the variation of the heat transfer convection coefficient up to 10 Hz with different amplitudes. The student will learn how to measure the heat transfer coefficient, and the experimental techniques for this kind of experiment. The experimental campaign will regard four main parameters: filling fluid, heat power, frequency and amplitude of the oscillations, internal wall characteristics. If it will be considered feasible, a proposal will be submitted to the Europeam Space Agency in order to reproduce some of the tests in microgravity conditions on a parabolic flight. In particular the channel could have a larger equivalent diameter. Finally a modified version of the Volume of Fluid (VOF) method in OpenFOAM, will be used for the proposed simulations, taking into account heat-transfer and phase-change. 3D, transient, turbulent simulations will be performed to reproduce the actual behavior of the oscillating slugs on ground and in microgravity conditions. The modified OpenFOAM’s VOF-based solvers account for the reduction of spurious velocities due to inaccurate calculation of interface curvature, validating its performance with literature available experiments on adiabatic bubble dynamics.

The main steps of the overall planned work can be summarized in the following Work Packages:
1. Literature review (2 months)
2. Acquisition of the experimental test-rig, optimization and first tests (6 months)
3. Experimental campaign (6 months)
4. Acquisition of knowledge on OpenFoam (2 months)
5. First simulations with the code (2 months)
6. Validation and benchmarking of the final solver regarding phase-change and heat transfer (saturated conditions) (6 months)
7. Application of the optimum solver to a wide series of parametric simulations on diabatic bubble growth in liquid cross-flows within small channels, for different g-levels and fluids (3 months)
8. Reports and paper submissions (6 months)

Applicants should have a minimum of a 2:2 undergraduate degree and desirably have a Masters degree or equivalent in a relevant subject, with experience during their dissertation/thesis either in CFD or with heat transfer measurements.

For applicants whose first language is not English, the minimum standard of English competence accepted is normally equivalent to IELTS 6.0 in all components.