Nano-refrigerant for two phase cooling systems

Development of nano-refrigerants for enhancing energy efficiency and boiling performance in thermosyphons for micro data center cooling

Synano participated in the consortium ‘BRAINE’ within the scope of “ECSEL Research and Innovation Action (RIA)- Call 2019”. ECSEL (Electronic Components and Systems for European Leadership) is a partnership between the private and the public sectors for electronic components and systems. BRAINE project’s overall aim was “to boost the development of the Edge Framework and specifically energy efficient hardware and AI empowered software systems, capable of processing Big Data at the Edge, supporting security, data privacy and sovereignty”. In BRAINE, Synano worked closely with consortium partners to develop nano-refrigerants to improve the energy efficiency in thermosyphons to construct a cooling system enabling high performing Big Data Edge computing to become mobile and independent of typical server cooling infrastructure.

Thermosyphons are gravity-assisted heat pipes which operate by using latent heat of vaporization of working fluid. It is a kind of passive heat transfer device that uses phase change to transfer thermal energy. It contains a refrigerant which evaporates by receiving heat at evaporator and the vapor converts into liquid by heat dissipation in condenser. Addition of nanoparticles to the fluid medium in such devices has shown an improvement in heat transfer attributed to increase in boiling heat transfer which is due to

1. formation of nanoparticle layer on the boiling surface which improves surface wettability and
2. presence of nanoparticles in the fluid medium which provides additional nucleation sites for boiling to take place, thus enabling higher heat flux operations at lower superheat temperature of the fluid.

In general, the performance of a thermosyphon/heat pipe depends on several factors, such as, its geometry, working fluid, capillary wicking material, surface roughness, wettability and applied heat flux. At the same time, nanofluid thermal and physical properties such as size, concentration, shape and type of nanoparticles will also have an impact on overall performance.

As a R&D partner in BRAINE, Synano developed several dispersions with graphene, graphene oxide and CNT nanoparticles with refrigerants. Different surfactants and stabilization methods were investigated during this time to develop stable nano-refrigerants.

After 2 years of intensive research, Synano was able to develop a highly stable nano-refrigerant with graphene nanoparticles that had low Global warming potential and is the choice of working fluid for many two-phase cooling applications.

With this nano-refrigerant, synano conducted several inhouse tests to compare performance with base refrigerant (i.e. refrigerant without nanoparticles). It was found that nano-refrigerant boiled at lower superheat temperatures as compared to base refrigerant. At same heat flux, the boiling incipience for nano-refrigerant was lower than base refrigerant showing improved boiling heat transfer performance of the nano-refrigerant.

As shown in the Graphene refrigerant boiling video, we investigate the boiling behavior of pure refrigerant (left tube) and nano-refrigerant (right tube) containing graphene nanoparticles with increasing heat flux and temperatures. Remarkably, while the pure refrigerant demonstrates only forced convection under the same temperature conditions, the nano-refrigerant exhibits vigorous boiling.

The boiling phenomenon observed solely in the nano-refrigerant presents intriguing possibilities for enhanced heat transfer and efficiency in cooling systems. Our findings shed light on the potential of nano-refrigerants in revolutionizing heat exchange technologies and pave the way for more energy-efficient and sustainable cooling solutions.