Thermal Conductivity and Viscosity: Review and Optimization of Effects of Nanoparticles

Abstract

This review was focused on expressing the effects of base liquid, temperature, possible surfactant, concentration and characteristics of nanoparticles including size, shape and material on thermal conductivity and viscosity of nanofluids. An increase in nanoparticle concentration can lead to an increase in thermal conductivity and viscosity and an increase in nanoparticle size, can increase or decrease thermal conductivity, while an increase in nanoparticle size decreases the viscosity of the nanofluid. The addition of surfactants at low concentrations can increase thermal conductivity, but at high concentrations, surfactants help to reduce thermal conductivity of the nanofluid. The addition of surfactants can decrease the nanofluid viscosity. Increasing the temperature, increased the thermal conductivity of a nanofluid, while decreasing its viscosity. Additionally, the effects of material of nanoparticles on the thermal conductivity and viscosity of a nanofluid need further investigations. In the case of hybrid nanofluids, it was observed that nanofluids with two different particles have the same trend of behavior as nanofluids with single particles in the regard to changes in temperature and concentration. Additionally, the level of accuracy of existing theoretical models for thermal conductivity and viscosity of nanofluids was examined.

Forced Convection Nanofluid Heat Transfer as a Function of Distance in Microchannels

“…As results, the anatase-water nanofluid has higher heat transfer coefficient. As the uniformity of the nanoparticles in the base liquid increases, the possibility of nanoparticle-nanoparticle and nanoparticle-molecule collisions and interactions increase and as a result, the energy transportation across the working fluid increases and consequently would increase the thermal conductivity [8,38] and heat transfer coefficient. Rutile TiO 2 nanoparticles were used to enhance the efficiency of dye-sensitized and perovskite solar cells which can be seen in references [42,43,[48][49][50][51][52][53][54][55][56].…”

“…Decreasing the nanoparticle size may decrease or increase the nanofluid thermal conductivity, however it was observed that in most cases, nanofluid thermal conductivity [ 8 , 38 ] and nanofluid viscosity [ 39 ] increase with decreasing nanoparticle size. It was observed that the heat transfer coefficient increases with increasing thermal conductivity and decreases with increasing viscosity.…”

“…To achieve the best nanofluid for given conditions, it is necessary to engineer the characteristics of the nanoparticles, the base liquid, and any possible surfactants. Recent investigations [ 8 ] indicated that adding nanoparticles would increase thermal conductivity and viscosity of working fluids, as results optimization of effects of nanoparticles on thermal conductivity and viscosity of nanofluids is necessary.…”

“…Simultaneously, nanofluid viscosity increases with concentration of nanoparticles and this increased viscosity may also play a role in explaining the effects of nanoparticle concentration. The detail of effects of nanoparticle concentration on nanofluid viscosity discussed in reference [ 8 ]. Fluctuation of the fluid flow and consequently the energy transportation between fluid layers would be suppressed with nanofluid viscosity.…”

Numerical Study on the Fluid Flow and Heat Transfer Characteristics of Al2O3-Water Nanofluids in Microchannels of Different Aspect Ratio

“…The addition of nanoparticles to high-Prandtl number liquids significantly increases the heat transfer performance of micro heat-sinks [ 5 ]. An increase in nanoparticle concentration can lead to an increase in thermal conductivity and viscosity and an increase in nanoparticle size [ 6 ]. Nanofluids contribute to the improvement of heat transfer processes and reduce and optimize thermal systems.…”