Industry demand for high heat transfer capability, efficient thermal control, flexibility and low cost has motivated our researchers to develop a new generation of passive systems mainly based on fluid phase-change. This project proposes the modelling and the experimental characterisation of a novel wickless heat transfer device applicable both on the ground and in space. The name Hybrid Heat Pipe (HyHP) comes from the fact that the well-established loop thermosyphon (TS) is transformed into a plain serpentine device with one evaporator for each turn, as a pulsating heat pipe (PHP).
The Engineering and Physical Sciences Research Council (EPSRC) has awarded a research grant of £907k to the project team led by Professor Marco Marengo. The project is being run in collaboration with three industrial partners: Libertine FPE which develops technology in the automotive sector; Sustainable Engine Systems Ltd which develops heat exchangers; and Kayser Space, one of the most important companies in the European space sector. It is expected that the primary beneficiary of this research will be the space industry; however, advantages are not confined to this specific field, as the support of two ground-based companies indicates.
Why do we need a new wickless heat device?
Two-phase heat transfer devices play an important role in a variety of engineering fields; thermosyphons, for example, are already successfully implemented in nuclear and solar plants, while heat pipe applications range from electronics cooling to the automotive sector. But the actual systems have two major problems:
- dissipation of high thermal powers maintaining high heat fluxes has significant limits connected to the upscale of the internal wick and the system dimension
- the deployability or the flexibility of the passive two-phase systems is quite reduced.
How does HyHP work?
The vertical operation in gravity, as well as the distinctive location of the heating and the cooling sections, causes the fluid to circulate regularly in a preferential direction guaranteeing stable operation and homogeneous temperature distribution of the system. The combination between channel dimension and working fluid is chosen in such a way that the device will operate in thermosyphon mode on the ground and, in the case of weightless conditions, in capillary mode, meaning that the liquid completely fills the tube section and therefore vapour expansion and contraction cause an oscillation of the liquid/vapour patterns.
Why do we need a new project on HyHP?
In 2014, a first HyHP prototype was already built and the first ground and microgravity experiments were successfully carried out, but we are far from understanding all the physical phenomena inside a HyHP and our ability to simulate the processes involved is still quite limited; we are not able to design a HyHP to manage heat within given boundary conditions. Moreover, since the final design of the Pulsating Heat Pipe experiment on the International Space Station is still under investigation, further microgravity experiments with different configurations are still necessary. The HyHP contributes to the definition of the correct heat pipe geometry for this important experiment.
Numerical analyses are fundamental to understanding the possible advantages and drawbacks of the HyHP and to predict its performance. The development and the use of innovative numerical tools and theoretical approaches will provide an insight into the physical phenomena and the governing mechanisms of a HyHP, opening the route to more efficient and customised design of thermosyphons, pulsating heat pipes and heat pipes in general.
The overarching aim of the project is to address a critical lack of knowledge; we need to be able to predict HyHP thermal behaviour with different geometrical characteristics and boundary conditions. We aim to develop advanced numerical tools and theoretical approaches to provide deep insight into the underlying physical phenomena and the complex governing mechanisms of this innovative device, opening the route to a better customised modelling for space and ground applications.
This novel transformative research offers significant potential, since the knowledge that will be acquired in simulating the HyHP can be transferred to a wider range of applications and beneficiaries, such as heat exchangers and other kinds of heat pipes. The development of mathematical models and sub-models able to numerically describe two-phase micro-scale phenomena will enhance present knowledge in several academic fields, from engineering, to physics of fluids, chemistry and even pharmaceutics.
We plan to conduct:
A state-of-the-art simulation of this new kind of PHP, which shows different behaviours under different gravity levels, with the following sub-objectives:
- the development of state-of-the-art numerical methods/treatments for the simulation of oscillating bubbles in capillary slug flows and in stratified conditions, including
- the evaporation and condensation at the three-phase contact line (vapour-liquid-solid) as well as the bulk liquid flow
- conjugate heat transfer between solid and fluid regions, and
- adaptive mesh refinement.
- the implementation of the proposed methods/treatments in an open source CFD code (OpenFOAM) and the performing of high-resolution numerical runs, using a powerful workstation, for a realistic comparison with the experimental data.
- the development of sub-models in terms of heat transfer coefficient (sensible heat and phase transition in oscillating flows), bubble and liquid film dynamics for a lumped parameter model.
The experimental characterisation of the HyHP at various gravity levels, including transient 0-g conditions using parabolic flights and the potential use of the future Thermal Platform on the International Space Station.
The HyHP will further contribute to the development of the existing world-leading research base in thermal management at the University of Brighton and enhance the focus on both heat pipe production and the space sector within the UK.