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Much of today’s modern technology relies on heat transfer to function. Devices and systems within the fields of air conditioning, power generation, microelectronics, transportation, and more, utilize the action of heat transfer in their functioning.
Recent years have seen much work focused on reducing the size of such devices, as well as updating how they are made in order to bring down operating costs. This has led to engineers exploring ways of enhancing heat transfer in these devices. One particular area of success has been in enhancing heat transfer by using nanoparticles to improve the thermal conductivity of fluids used in these applications.
Since the early 2000s, scientists have been working on developing a new class of fluids known as nanofluids. The purpose of creating these fluids was to enhance their thermal properties, improving on their thermal conductivity by increasing the rate of convection between these fluids and the surface.
Scientists began adding nanoparticles measuring between just 1 nm and 100 nm into fluids to enhance their thermal conductivity. Research has shown that a number of metallic and nonmetallic nanoparticles are useful in increasing the thermal conductivity of a fluid in comparison to the base fluid. Particles such as Al2O3, CuO, Cu, SiO2, TiO2, are those that have successfully been added into fluids to increase their thermal conductivity.
Below we discuss the process that underlies the thermal conductivity enhancing effect of adding nanoparticles to fluids.
How do Nanofluids Work?
A fluid’s ability to transfer heat is governed mostly by its thermal conductivity. The fluids that are generally used in devices of heat transfer have relatively low thermal conductivities in comparison to solid materials. Take water, ethylene glycol, and engine oil, for example, they are fairly poor thermal conductors in comparison to solids such as metals.
Therefore, researchers have been devising ways to boost the thermal conductivity of these fluids, to enhance their heat transfer capabilities. Out of much research, one method has stood out as a particularly successful technique for enhancing a fluid’s thermal conductivity. Numerous studies conducted since the early 2000s have demonstrated the efficacy of adding tiny solid particles into these commonly used fluids.
Because the solid particles have higher thermal conductivities than the fluids that they are added to, their addition has the impact of enhancing the thermal conductivity of the fluid. However, it is not as easy as simply adding the particles into the fluid. The particles first used to create these fluids measured just micrometers in diameter, and adding them into fluids began causing two problems.
The first issue was that adding nanoparticles into fluids was causing an unstable mixture, resulting in sedimentation and sometimes the erosion of channel walls by the particles. Also, the addition of nanoparticles led to a significant drop in pressure in some cases, increasing the power needed to pump the fluid and therefore increasing operating costs.
These problems had to be accounted for and overcome to ensure the functionality of the resultant liquid. The solution was found in reducing the size of the particles to less than 100 nm and preparing the liquids by suspending these tiny particles in the fluids, giving birth to a new breed of fluids, known as nanofluids.
Since their conception, nanofluids have been successfully used in devices of heat transfer because of their enhancing thermal conductivity. These fluids do not have the drawbacks of the earlier prototypes as the tiny size of the particles sees them behaving like particles of fluid, rather than solid, overcoming the clogging and erosion problem.
Numerous studies have confirmed the enhanced thermal conductivity of these fluids in comparison to the base fluids and fluids combined with the larger particles. For this reason, nanofluids have been embraced in many sectors as a useful component of heat transfer devices.
References and Further Reading
Kleinstreuer, C. and Feng, Y. (2011). Erratum to: Experimental and theoretical studies of nanofluid thermal conductivity enhancement: a review. Nanoscale Research Letters, 6(1). https://nanoscalereslett.springeropen.com/articles/10.1186/1556-276X-6-229
Özerinç, S., Kakaç, S. and Yazıcıoğlu, A. (2009). Enhanced thermal conductivity of nanofluids: a state-of-the-art review. Microfluidics and Nanofluidics, 8(2), pp.145-170. https://link.springer.com/article/10.1007/s10404-009-0524-4
Sundar, L. and Sharma, K. (2008). Thermal conductivity enhancement of nanoparticles in distilled water. International Journal of Nanoparticles, 1(1), p.66. https://www.researchgate.net/publication/249923115_Thermal_conductivity_enhancement_of_nanoparticles_in_distilled_water