Effect of sonication time on enhancement of effective thermal conductivity of nano TiO₂–water, ethylene glycol, and paraffin oil nanofluids and models comparisons

Abstract

This paper presents experimental and theoretical determination of the effective thermal conductivity of various base fluids and nano TiO 2 composition. Ultrasonically assisted sol-gel method was used for synthesising anatase TiO 2 nanoparticles and dispersing them into base fluids using sonication for the synthesis of nanofluids. It is observed that thermal conductivity enhancement is significantly higher than that of base fluid. The thermal conductivity shows an increment with the addition of nanoparticles and confirms a 22% enhancement achievable in base fluids. The effect of base fluids is a complex idea and difficult to understand; lower base fluid viscosities were supposed to contribute higher in enhancement of thermal conductivity, but another important factor; i.e. fluid nanoparticles surface interaction, nanoparticles crystal type also contributes in enhancement. In the further study, as the sonication time increases; an improvement in the thermal conductivity of nanofluids is also observed. Except water-based nanofluids, all others show reasonably good agreement with the data predicted by Bruggeman model and the prediction is in the range of 5%. This study is important since it covers base fluids with a wide range of thermal conductivity and viscosity.

Effects of Sequence Preparation of Titanium Dioxide–Water Nanofluid using Cetyltrimethylammonium Bromide Surfactant and Tio2 Nanoparticles for Enhancement of Thermal Conductivity

“…Brownian motion caused the colloidal particles to be uniformly dispersed in the base fluids and TiO2 NPs could not be separated from the dispersion when silenced. This observation provides greater value than previous research, confirming that as much as 5.8% thermal conductivity enhancement is achieved with a 2% volume fraction of TiO2 NPs at 2 hours of sonication time (Sonawane et al, 2015). The increased thermal conductivity was influenced by NPs size, shape, and properties as well as the interaction between NPs and the base fluid surface, which caused cluster formation (Xie et al, 2003;Leong et al, 2006).…”

“…Increasing the CMC of CTAB only decreased the pH, because the concentration of CTAB cationic surfactant caused an increase in positive charge thus the fluid is more acid. Sonawane et al (2015) investigated TiO2-water nanofluid with optimum sonication times of 60 minutes with a 6% volume fraction of TiO2 NPs, confirming a 22% enhancement in thermal conductivity. In this study, a pH of 8, a fourfold CMC, a constant temperature of 25ºC, and sonication for 10 minutes (see Figure 1) were used as control parameter conditions.…”

“…The clustering of NPs started, which accounted for the decrement in primary NPs for heat transport and thermal conductivity. It is believed that heat transfer is a surface phenomenon and that the surface of NPs is used for thermal energy interaction (Sonawane et al, 2015). When the particles started to agglomerate, the effective surface area to volume ratio decreased, resulting in a reduction of the effective transfer area of particles and causing a decrease in the thermal conductivity of the fluid (Sonawane et al, 2015).…”

A comprehensive review on heat transfer characteristics of TiO2 nanofluids

“…This observation clearly indicated that the higher EG loading in the binary base fluids can give rise to lower thermal conductivity of base fluid and higher effective thermal conductivity ratio (k nf /k f ) in TiO 2 nanofluids. However, Sonawane et al [46] found that the relationship between the effective thermal conductivity ratio of TiO 2 nanofluids and that of base fluid was irregular. The thermal conductivity of 1 vol.% TiO 2 nanofluids followed the sequence: paraffin oil based nanofluid > water based nanofluid > EG based nanofluid, while that of pure base fluids followed the sequence: water > EG > paraffin oil.…”

“…Mansel et al [48] found two hours' sonication can increase the thermal conductivity of water based TiO 2 nanofluids due to the percolation effect in the aggregations. Sonawane et al [46] carried out a particular research on the effect of sonication time on the thermal conductivity of TiO 2 nanofluids. They found that for each of the three kinds of base fluids including water, EG and PO, the thermal conductivity of TiO 2 nanofluids increased first and then decreased as the sonication time increases.…”