Stability and Thermal Conductivity Characteristics of Carbon Nanotube based Nanofluids

Abstract

Water, ethylene glycol and engine oil are commonly used in heat exchanger applications. However, these fluids possess low thermal conductivity. The technology advancement in nanotechnology has enabled nano size particles to be included in a base fluid. This new generation of fluids is known as nanofluids. Producing a stable nanofluid with improved thermal conductivity is a challenging process. In the present study, multiwalled carbon nanotubes (MWCNT) based nanofluids with or without surfactant were investigated for their stability and thermal conductivity. The study indicates that nanofluids with added polyvinylpyrrolidone (PVP) surfactant exhibit better stability than nanofluids without surfactant. About 22.2% thermal conductivity improvement was observed for water containing 0.5wt% of MWCNT and 0.01wt% of PVP surfactant. The thermal conductivity also increases with increase of the MWCNT's weight fraction. It can be concluded that the addition of PVP and MWCNT into base fluid (water) is vital to produce a stable nanofluid with improved thermal conductivity.

Thermal conductivity and viscosity of deionised water and ethylene glycol-based nanofluids

“…A lower weight percentage of PVP was chosen in this study because a high weight percentage of surfactant in base fluid can decrease thermal conductivity of nanofluid [20]. Moreover, data reported here was supported by a previous research claim that 10% PVP from the weight percentage of MWCNT-OH gives an effective stability to the MWCNT-OH-based nanofluids, where the sample was tested with 0.1 wt % of MWCNT-OH and 0.01 wt % of PVP, and was proven to be stable even after one month [19]. Figures 2 (a) and (b) show thermal conductivities of deionised water and ethylene glycolbased nanofluids.…”

“…The most stable nanofluids that do not have any sedimentation or agglomeration can provide the best results in a thermo-physical test. According to previous research, PVP acts as dispersant agent, and the use of PVP in nanofluids formulation can increase stability thus overcome agglomeration of solid particles nanofluids [1,19]. Meanwhile, a vital process that can maintain particles dispersion and stability of nanofluids for a long period of more than 100 hours is ultrasonication process.…”

“…Literature on thermal conductivity has highlighted that the addition of nanoparticles, such as Al2Cu and Ag2Al, at concentrations of 0.2 vol% to 1.5 vol% to ethylene glycol and deionised water has resulted in an enhancement of about 50% to 150% higher than that of standard base fluid, whereas enhancement of 12.7% at 1.0 vol% of CNT was reported for ethylene glycol-based nanofluids [2,9,[15][16][17][18]. Studies conducted by researchers have found that the inclusion of a surfactant in nanofluids influences effective thermal conductivity, where enhancement was about 22.2% at 0.5 wt% of CNT and 0.01 wt% of PVP [19]. In addition, thermal conductivity value of CNT was between 1800 W/m.K to 2000 W/m.K [20].…”

“…This is due to the hydrophobic nature of CNTs, which have higher tendency to agglomerate in conventional fluids [23][24][25][26][27][28]. Stability is the main factor that contributes to thermo-physical performance [29].…”

Effect of Temperature on Heat Transfer Coefficient of Titanium Dioxide in Ethylene Glycol-Based Nanofluid

“…Later, Eastman et al [6] focused on the thermal conductivity of nanofluids. Many researchers have conducted studies on the thermal properties of nanofluids such as thermal conductivity and rheological behavior that affect their performance [4,7,8]. According to a review study by Ravisankar and Chand [9] and Azmi et al [3], the study of nanofluid properties is important as they contribute significantly to heat transfer performance.…”