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Nanolubricants can be used for thermal engineering. Enhancing the tribological performance of nanoparticle-based lubricants has been a challenge for years, but recent developments have enabled advances. The goal of any nanolubricant is always to reduce the friction and wear processes inherent in any contact mechanical device e.g. the moving parts in cars, refrigeration compressors and more.
Synthesizing a nanolubricant to successfully maximize energy transfer with a minimal heat loss in thermal engineering has been tough, but not impossible.
Tribology goes all the way back to the Stone Age when contact mechanics were discovered. The cutting and polishing of flints and wood along with the friction created when rubbing two pieces together to ignite fire is still as relevant today as it was thousands of years ago.
With thermal engineering, the problem has always remained in a large amount of energy wasted as a result of friction and wear caused by contact mechanics. No matter how efficient the modern car is, it will always need parts replacing and regular maintenance.
Even with most cars today an average of one-third of automobile fuel is used to overcome the unwanted side effects of high friction. The excessive use of fuel and energy loss is not only bad for the natural environment, it has a deleterious effect on human health and negatively impacts all modern economies.
Finding a solution to decreasing energy loss without negatively impacting the environment has been the goal of most thermal engineers throughout their careers. Just a small fraction of wear and friction reduction has become vital for energy savings. The operational lifetime of a car or refrigeration compressor can be increased by applying the right kind of mechanical contact lubricant.
Base lubricants (oils etc.) apply a Band-Aid on the wider problem, but it is the latest nanoparticle-based lubricants that offer the best advantages. Nanofluids consistently show a better heat transfer result. The heat transfer and flow behavior of nanolubricants always depend on the thermophysical properties present in the lubricant as the viscosity of nanolubricants determines the shearing force between the adjacent layers of fluid responsible for viscous friction.
Each property is an important factor for the heat transfer performance of any machine and includes viscosity, but also density, thermal conductivity and specific heat capacity.
In 2011, Madhusree Kole and T.K.Dey reported an increment of nearly three times in the viscosity of a nanolubricant with a dispersion of 2.5% volume fraction of the Cu0 nanoparticles in gear oil. Impressive results back then, but in 2018 the advantages of nanolubricants became more apparent.
In 2019, scientists and engineers used an enhanced atomic intermixing approach to develop a new type of nanolubricant. They developed a 7-to 8 nanometer thick carbon-silicon nitride multi-layer overcoat that demonstrated an extremely high wear resistance along with low friction at all tribological length scales. The new nanolubricant yielded 2 to 10 times better macroscale wear durability than any previously reported thicker overcoats traditionally used on tape drive heads.
In the past thicker nanolubricant overcoats have been used to combat tribological concerns, but with many contact sliding systems, the large thickness has always hindered the mechanical components, degrading functionality and placing a barrier in front of any development. The carbon-silicon nitride development nullified this barrier.
The latest nanolubricants can be used for thermal engineering. The energy loss during heat transfer has been significantly reduced and scientists are confident new lubricants can be further refined. The main advantage of nanoparticles has always been their size which is well adapted for contact mechanics. The next generation of nanolubricants may eventually eliminate energy loss caused by tribological concerns.
References and Further Reading
Boosting contact sliding and wear protection via atomic intermixing and tailoring of nanoscale interfaces - Science Advances – 2019 https://advances.sciencemag.org/content/5/1/eaau7886
Nanorefrigerants for energy efficient refrigeration systems – Journal of Mechanical Science – 2017 https://link.springer.com/article/10.1007/s12206-017-0746-4
Thermophysical and tribological properties of nanolubricants: A review – Anit Kotia - Research Gate – 2018 https://www.researchgate.net/publication/325109845_Thermophysical_and_tribological_properties_of_nanolubricants_A_review
Improved Tribological and Thermal Properties of Lubricant by Graphene Based Nano-Additive – Research Gate – 2016 https://www.researchgate.net/publication/304002491_Improved_Tribological_and_Thermal_Properties_of_Lubricants_by_Graphene_Based_Nano-additive