Summary

The Electrowetting Heat Pipe (EHP) is a new cooling technology capable of transporting high heat loads over long distances. The working fluid evaporates in the evaporator (which is in contact with the heat source), thereby removing heat. This vapor then condenses in the condenser (cold region) and the condensate is returned to the evaporator. Conventional heat pipes are limited in their ability to transport high heat loads over long distances.

The EHP solves this issue acting disruptively in two ways: i) using electrowetting-based pumping to move the condensate back to the evaporator, and ii) utilizing electrically enhanced evaporators to enhance heat transfer and prevent dry-out in the evaporator. In this project, the heat transfer enhancement in the evaporator was studied via experiments and numerical analysis.

The project mainly showed that evaporation characteristics can be increased by further enhancing the wetting properties of the evaporator surface (working as the dissipator). The model further provided interesting features on the boiling regime and on the mechanisms explaining such heat transfer enhancement. The results also show that the use of nanofluids offers a potential increase to the boiling heat transfer. However, stability issues limit the concentration of the nanoparticles to be used, thus limiting the enhancement effects. On the other hand, the team at IN+/IST-ID could develop (in collaboration with FEUP) and characterize new sets of stable nanofluids, with potential use in the heat transfer enhancement for several cooling applications. Finally, from the practical side, model and experiments suggest that this heat pipe configuration can be used for cooling purposes in the electric motorizations and in the batteries.

This work is now expected to enable future development of a new class of heat pipes with much higher performance than current heat pipes, with a very low power consumption. This can favourably impact the energy efficiency in many thermal systems. One of the major goals of Electrowave was to evaluate how this disruptive technology could be used in the thermal management of electric vehicles. In fact, efficient thermal management in these vehicles, particularly considering batteries is a real obstacle towards their broader implementation in the mass mobility market, given the current limitations in fast charging. Electrowave showed that such EHP technology is able to cope with the specificthermal management requirements of this important market.