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Many limitations exist within the development of energy efficient heat transfer fluids; however, low thermal conductivity of these fluids is the main issue. In order to improve the thermal conductivity of these heat transfer fluids, researchers in this study performed strenuous research and ultimately created a new and improved fluid. In this newly designed material, nanoparticles and carbon-nanotubes (CNTs) were suspended within the fluid, aiming to increase the fluids thermal conductivity. Multiple variations of the new and improved heat transfer fluids were created in this research, in order to accommodate for multiple applications.
Researchers have determined the potential of increasing the thermal conductivity of insulating polymers by adding conductive fillers. One common application this may be used for, is fuel cell bipolar plates. In this article, researchers tested varying amounts of three different carbon fillers (black carbon, synthetic graphite particles, and carbon nanotubes), by adding them to polypropylene. Both single fillers and combination fillers were studied for their potential effects on the thermal conductivity of insulating polymers. When analyzing the effects of single fillers, synthetic graphite caused the largest increase in the thermal conductivity, while with the combinational fillers, composites containing 80 wt% synthetic graphite had an in-plane thermal conductivity of 28.0 W/m·K.
This article evaluates the thermal conductivity of heat transfer nanofluids containing nickel coated single wall carbon nanotubes. The results concluded that with the introduction of a magnetic field, the thermal conductivity of the heat transfer nanofluid is improved. Researchers attribute this improved thermal conductivity to the ability of the nickel coated nanotubes to form aligned chains under the force of a magnetic field, allowing for better contact and ultimately a higher thermal conductivity. Researchers also determined that once the nanofluids have reached their maximum thermal conductivity, under a reduced magnetic field strength, the thermal conductivity can be maintained for longer periods of time, than when in the absence of the magnetic field.
The researchers in this paper were the first to report that the thermal conductivity of the heat transfer nanofluids has the ability to be enhanced by an external magnetic field. This is possible due to carbon nanotubes and magnetic-field-sensitive nanoparticles of Fe2O3. It was discovered that the Fe2O3 nanoparticles form chains when exposed to magnetic fields, which allows the nanotubes to connect. As the nanotubes connect, the thermal conductivity of the nanofluid improves drastically. Researchers also discovered that when large clumps form, instead of chains, the thermal conductivity of the nanofluid decreases.
The thermal conductivity of heat transfer nanofluids has been determined to increase by 10%, when containing metal oxide nanoparticles and carbon nanotubes. The fluid viscosity of the nanofluids is relatively the same as water, and therefore cannot not account for the increase in thermal conductivity. However, the fashion in which the metal oxide particles conglomerate within the fluid could be a potential explanation for the spike. Results show that under the influence of a strong outside magnetic field, the thermal conductivity value decreases. The thermal conductivity value also decreases when the pH is shifted from 7 to 11.45.
