This article discusses the importance of the thermal analysis of nanofluids and the thermal analysis techniques used for nanofluids.
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Importance of Thermal Analysis of Nanofluids
Nanofluids are primarily a new class of nanotechnology-based heat transfer fluids produced by dispersing and stably suspending nanometer-sized particles/nanoparticles in conventional heat transfer fluids/base fluids, such as polymer solutions, bio-fluids, oil and other lubricants, ethylene- or tri-ethylene-glycols, and water.
Nanoparticle materials can include nanoparticle-sized metal carbides, oxide ceramic, nitrides, metals, non-metals, and functionalized nanoparticles. Nanofluids possess several novel properties that make them suitable for many heat transfer applications, including fuel cells, microelectronics, engine cooling, hybrid-powered engines, chiller, domestic refrigerators, and heat exchangers.
Adding nanoparticles to the base fluids leads to changes in the thermophysical properties of the resultant nanofluids, as base fluids and nanoparticles possess different properties. Thermophysical properties of nanofluids, such as viscosity, thermal conductivity, and specific heat, are crucial in improving overall nanofluid performance.
For instance, several studies have demonstrated that the suspension of nanoparticle inclusions to improve the thermal conductivity of water can effectively enhance convective heat dissipation.
Thermal Analysis Methods for Nanofluids
Macroscopic modeling approaches based on conventional relations of thermodynamics have been ineffective in analyzing nanofluidic thermophysical properties due to the presence of nanosized materials. Atomistic/computational modeling and simulation have been demonstrated as an effective alternative to macroscopic approaches for the thermal analysis of nanofluids.
For instance, the thermal conductivity of nanofluids can be analyzed successfully using quantum mechanical modeling and molecular dynamics simulation. The effect of thermal conductivity on several parameters, including the nature of particle material, size of the particle, and volume concentration of the fluid, can be formulated computationally.
Studies using computational approaches have demonstrated that adding nanoparticle-sized titanium dioxide, copper oxide, and aluminum oxide of different dimensions in the base fluid can increase the effective thermal conductivity of the nanofluid by improving the heat transfer behavior.
Thus, the addition of nanomaterials can reduce the size of heat transfer systems such as radiators and result in increased fuel and energy efficiency, lower pollution, and higher reliability.
Thermal analysis of nanofluids has also been performed using an infrared camera in microfluidics. In a study published in the journal Lab on a Chip, researchers performed a thermal analysis of a nanofluid containing aluminum oxide nanoparticles using an infrared camera in a microfluidic platform.
The small microchannel dimensions and low flow rates of 120 µl min-1 led to extremely low Reynolds numbers of less than 17.5, representing the practical parameters for a microfluidic cooling platform.
Additionally, the infrared camera allowed three-dimensional, high-resolution, and non-contact temperature profiling. The nanofluid was investigated at different weight concentrations of thermally conductive aluminum oxide nanoparticles to study the heat exchange improvement compared to deionized water/base fluid. All experiment results were verified using computational fluid dynamics simulations.
The microfluidic system was integrated into a high-resolution infrared camera and microheater. Researchers used the microheater to control the system temperature accurately, while the infrared camera was employed to determine the temperatures of any location of the microfluidics, even at very low Reynolds numbers.
The combination of these capabilities was used to display the effect of nanofluids on the microfluidic system’s thermal performance. Thus, the study provided a comprehensive heat transfer analysis in a practical microfluidic system without and with suspended aluminum oxide nanoparticles.
No significant difference in heat transfer was observed between nanofluids and conventional/base fluids at low flow rates of 10 µl min-1 with a 1.45 Reynolds number. However, enhanced heat exchange was observed in the nanofluid at higher flow rates of 120 µl min-1 with a 17.5 Reynolds number compared to conventional fluid. All experimental results were confirmed by the results of numerical simulations.
Recent Studies on the Thermal Analysis of Nanofluids
In a recent study published in Scientific Reports, researchers evaluated the thermodynamic and thermal behavior of a buoyancy-driven evacuated tube solar collector (ETSC) and investigated the nanoparticle dispersion efficacy in the testing fluid.
Researchers also investigated the natural convection process in several vertical sections of the absorber tube. The outputs for the utilized nanofluid and water were compared at different cutting planes along the tube during the simulation. Copper oxide nanoparticles with optimal thermal properties were distributed in the base fluid/plain water to obtain the nanofluid.
The use of copper oxide-water nanofluid led to an increase in mean wall temperature, which indicated the feasibility of the nanofluid in enhancing the thermal treatment of operate fluid through the collector pipe.
Moreover, the irreversibility due to fluid friction increased when the nanofluid was used during the flow time. The heat transfer entropy generation was reduced by 6.3% after one hour of flow time when copper oxide nanoparticles with a 5% volume fraction were used in pure water, whereas the entropy generation by fluid viscosity increased by 23% when the nanofluid was used in the system.
Thus, the irreversibility attributed to fluid viscosity and heating displayed significant differences in value owing to the low-velocity range of the fluid in the natural convection process.
To summarize, nanofluids will play a critical role in providing solutions for cooling issues of more complex systems in the future, which will significantly increase the importance of thermal analysis methods for nanofluids to develop more efficient cooling systems.
References and Further Reading
Namboori, P. K. K., Vasavi, C. S., Gopal, K. V., Gopakumar, D., Ramachandran, K. I., Narayanan, B. S. (2010). Thermal Analysis of Nanofluids Using Modeling and Molecular Dynamics Simulation. AIP Conference Proceedings, 1276, pp. 407-412. Available at: https://www.researchgate.net/publication/234999216_Thermal_Analysis_of_Nanofluids_Using_Modeling_and_Molecular_Dynamics_Simulation
Yi, P., Kayani, A. A., Chrimes, A. F., Ghorbani, K., Nahavandi, S., Kalantar-zadeh, K., Khoshmanesh, K. (2012). Thermal analysis of nanofluids in microfluidics using an infrared camera. Lab on a Chip, 12(14), p. 2520. https://pubs.rsc.org/en/content/articlelanding/2012/lc/c2lc40222j
Tabarhoseini, S. M., Sheikholeslami, M. (2022). Entropy generation and thermal analysis of nanofluid flow inside the evacuated tube solar collector. Scientific Reports, 12(1), pp. 1-16. https://doi.org/10.1038/s41598-022-05263-2