Recent research as part of a collaboration between the University of Pretoria, the Massachusetts Institute of Technology (MIT) and Imperial College London hopes to improve refrigeration equipment and reduce their impact on global warming through the use of nanostructures.

The refrigeration industry contributes significantly to global warming, with it causing an estimated 10 to 15% of CO₂ emissions. The industry does this in two main ways – through the electricity used by our fridges and air conditioners, which is often still powered by CO₂ emitting coal power plants, as well as by the refrigerant chemicals themselves used within the fridges and air conditioners. These refrigerant chemicals can have a big impact on global warming. For example, the commonly used refrigerant R-134a is estimated by some calculations to cause about 1 300 times the global warming the same amount of CO₂ would have caused while in the atmosphere. Refrigerants can leak into the atmosphere over time while being used, or end up there when the equipment is thrown away. So if refrigeration equipment can be made more efficient by improving heat transfer, they will use less electricity, reducing the CO₂ emitted at the power stations. They will also be smaller, which means less refrigerant needed to fill them up.

Another possible option to reduce the global warming impact of the refrigeration industry is to use falling film technology. Instead of traditional refrigeration equipment, where equipment is filled with refrigerant to remove heat and cool our homes, thin falling films of liquid refrigerant can be used inside the refrigeration equipment instead, causing less damage to the environment because less refrigerant is used. The catch though is these falling films of liquid sometimes dry out if the liquid is not spread out evenly.

Nanostructures can help in both these cases. They can increase heat transfer, making refrigerators smaller and more efficient. And they can also, much like a paper towel, spread falling films of liquid out over the surface, preventing dry spots.

Researchers at the University of Pretoria’s Clean Energy Research Group thus teamed up with Prof. Matteo Bucci from MIT’s Red Lab and Prof. Christos Markides from Imperial College London to determine whether nanostructure coatings developed for the nuclear industry could be used to improve the heat transfer on the surfaces of the heat exchangers used in refrigerant equipment. The research, conducted by Dr. Bradley Bock under the supervision of Prof. Josua Meyer and Prof. John Thome (EPFL), found that the coatings did just that, increasing heat transfer by up to three times compared to that of plain copper surfaces they were applied to. And when applied to falling film technology, under certain conditions they were able to reduce the dry spots seen, while still increasing heat transfer.

“This research showed some interesting possible uses of nanostructures in the refrigeration industry, and we are continuing our research as we speak to better understand and apply these technologies,” says Dr. Bock. “And as a side benefit, falling film technology is also used in other places like thermal desalination, so this research will help a number of industries.”

The research was supported, in part, by the MIT International Science and Technology Initiatives (MISTI) programme under an MIT-Africa- Imperial College London seed fund grant, by the UK Department for International Development (DFID) through the Royal Society-DFID Africa Capacity Building Initiative and by the European Union’s Horizon 2020 Research and Innovation Programme within the ThermaSMART network under the Marie Sklodowska- Curie Grant Agreement No. 778104.