The quest for thermal systems that are more efficient in removing heat is never ending, with design improvements of heat exchangers being one of the main areas of focus. Water has been the working fluid of choice for years for several reasons; it is clean, readily available and has fairly good thermal properties for heat removal. Over a century ago micro-sized particles with high thermal conductivity were investigated as a way to increase the thermal characteristics of working fluids.
However, micro-sized particles can be abrasive and can precipitate out due to their higher density. Nano-sized particles introduced into a base liquid have also been studied and called “nanofluid”. This concept of using copper, aluminum, or carbon nanoparticles to create colloidal suspension fluids has been accepted as a new avenue for enhancing coolant's thermal characteristics. Because heat transfer enhancements are due to particle size and dispersion isometry; the key technical challenge in implementing this technology is to understand the fundamental physics responsible for enhancing the transport of heat, which can lead to the knowledge based development of a stable nanofluid with maximum thermal conductivity.
Due to the necessity of compact thermal management systems many researchers have begun to investigate the benefits of the nanofluids on the heat transfer in the thermal management system. Scientists have reported varying degrees of increase in thermal performance with the addition of the nanoparticles to the thermal fluid. The earlier studies were primarily on the enhancements of the thermal conductivity. Most studies reported very good enhancements of the thermal conductivity even with small volume percent concentrations. Researchers have investigated the addition of nanoparticles made of highly conductive materials such as aluminum, carbon, diamond and copper with varying positive results.
Many prior researchers have focused on the use of copper (II) oxide (CuO) nanoparticles to form the nanofluid due to the favorable thermal properties of copper (II) oxide powders. However, nanofluids formed with copper (II) oxide suffer from several drawbacks that can impede its commercial use in a thermal system. For example, fluids containing copper (II) oxide nanoparticles have a tendency to mix with and retain air and oxygen within the fluid, which adversely affects the thermal properties of the fluid and can create problems in the thermal system. Additionally, the copper (II) oxide nanoparticles tend to agglomerate and/or stick to the container of the fluid in the thermal system, which can lead to impairment and fouling of fluid flow in the system.
As such, a need currently exists for a commercially viable nanofluid that can be easily mass produced, has effective thermal properties, and is relatively stable during use.
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