Investigations on the thermal and electrical conductivity of polyethylene glycol-based CuO and ZnO nanofluids

TL;DR: In this article, three different types of nanofluids were evaluated for their stability using dynamic light scattering and particle morphological study using scanning electron microscopy, and the results showed that they were stable in terms of particle morphology.

Abstract: In this experimental work, three different types of nanofluids were evaluated for their stability using dynamic light scattering and particle morphological study using scanning electron microscopy....

Summary

1. Introduction

• Nanofluids have shown various interesting properties, and the distinguishing features offer exceptional potential for different industrial applications, such as electronic, transportation, improve recovery in oil and gas well, industrial cooling applications, nuclear systems cooling, etc.
• They used polyethylene glycol (PEG) and sodium dodecyl sulfate (SDS) as dispersing agents.
• The results show that the enhancement in thermal conductivity is due to the concentration of nanoparticles in the base fluids and also the interaction between the particles.
• The experimental measured values of thermal conductivity were compared with different existing models which were accurately fitted with models.
• Stable nanofluids containing CuO and ZnO nanoparticles were prepared through a two-step method.

2.1. Materials

• CuO and ZnO nanoparticles were used in this study.
• The CuO nanoparticles were supplied by Sigma-Aldrich with a spherical shape, diameter of <50nm and with purity of >97%.
• The ZnO nanoparticles were purchased from Sigma-Aldrich chemicals with a spherical shape, diameter of <50nm and with purity of >97%.
• Deionized water was used as a base fluid along with PEG and PVP.
• The properties of nanofluids used in this work are summarized in Table 1, which shows the dispersant, nanoparticles used and the concentration of particles.

2.2. Nanofluids Formulation

• The base fluid was mixed with a measured quantity of nanoparticles in a beaker covered with aluminum foil to ensure that there is no evaporation during sonification.
• The polymer was thoroughly dispersed using a magnetic stirrer to avoid lump formation and to get a stable nanofluid system with a polymeric base.
• The beaker containing the sample is submerged in the water.
• For this study, ultrasonication (Crest Ultrasonic, 25 KHz, and 450 W) was performed at high frequency of 25 KHz and 450 W for one hour.
• Sonification time of one hour is employed for all suspensions prepared homogeneously as seen by visual observation.

2.3. Scanning Electron Microscopy

• Topography, morphology, and arrangement of agglomerated particles were observed in the dispersed state using SEM.
• Scanning Electron Microscope (SEM) was used for morphological characterization of nanoparticles, and micrographs of ZnO and CuO nanoparticles were obtained.

2.4. Dynamic Light Scattering

• The Brownian diffusivity of particles is measured using DLS and is related to their size.
• The particle size is measured by illuminating the particles with a laser and analyzing the intensity fluctuations in the scattered light.
• The DLS measurements were carried out using 90 PlusTM Nanoparticle Size Analyzer by Brookhaven Instruments.
• Measurements were made at 90° scattering angle and at 25° C. DLS works on the principle that when the sample is illuminated by a laser beam, the fluctuations of the scattered light are detected at a known scattering angle by a detector.

2.5. Thermal Conductivity and Electrical Conductivity Meter

• The thermal conductivities of the nanofluids prepared in this study have been measured using the transition hot wire method with KD2 pro®.
• The unit was calibrated using standard samples.
• The KS-1 sensor applies a very small amount of heat to the needle, which helps to prevent free convection in liquid samples.
• Thirty seconds are allowed for temperature equilibration before heating starts, after which heat is applied for thirty seconds, and measurements are taken over the full time.
• Electrical conductivity was measured using the PC 700 Eutech ® Instrument.

3. Results and Discussion

• Table 1 shows the combinations of CuO and ZnO nanofluids prepared in this work.
• Figure 1(a) shows ZnO nanofluid preparation with 5 wt% of PVP in water.
• This is based on the overall size of the particles and their agglomerating tendency.
• The extent of increase in thermal conductivity depends upon the nature of the base fluid.
• Figure 6 and Table 3 shows the information on the electrical conductivities of prepared nanofluids and percentage enhancement of the electrical conductivities of these nanofluids over the base fluid, respectively.

4. Conclusion

• Water-based nanofluids have been formulated, characterized and investigated for thermal and electrical conductivities by dispersing CuO and ZnO nanoparticles, and prepared by a twostep method using PVP as a dispersant.
• The morphology characterization of nanoparticle was performed by using scanning electron microscopy.
• The enhancements in thermal conductivity and electrical conductivity were measured at different concentrations.
• ZnO+PVP+water system shows greater enhancement compared to the other two systems.
• This study has demonstrated the feasibility of formulating stable nanofluids of CuO and ZnO in PEG and provided with the information on thermal and electrical properties of these nanofluid systems, which is not available in the literature.

Figures

Figure 4. DLS curve for 0.5 wt% CuO+5 wt% PVP in PEG

Table 3. Percentage increases in electrical conductivity of the prepared nanofluids

Figure 5. Variation of thermal conductivity with nanoparticle concentration. a) ZnO+PVP+water, b) ZnO+PEG, c) CuO+PVP+PEG.

Figure 1. SEM image for: (a) 0.5 wt % ZnO+5 wt% PVP nanofluid; (b) 0.5 wt% ZnO+PEG 600 nanofluid; (c) 0.5 wt % CuO+5 wt % PVP+ PEG 600 nanofluid.

Table 2. Percentage increases in thermal conductivity of the prepared nanofluids

Figure 6. Variation of electrical conductivity with nanoparticle concentration

Figure 3. DLS curve for 0.5 wt% ZnO+PEG

Figure 2. DLS curve for 0.5 wt% ZnO+5 wt% PVP

Table 1: CuO and ZnO nanofluids studied in the present work+

Full text

1
Research article
Investigations on the Thermal and Electrical Conductivity of Polyethylene
Glycol-based CuO and ZnO Nanofluids
Swaminathan Ponmani,
a,b
Pawan Gupta,
a
Prashant Jadhawar,
c
R. Nagarajan,
d
Jitendra Sangwai
a,*
a
Gas Hydrate and Flow Assurance Laboratory, Department of Ocean Engineering, Indian
Institute of Technology Madras, Chennai- 600036, Tamilnadu, India
b
Department of Petroleum Engineering, AMET University, kanathur, Chennai 603112
c
School of Engineering, University of Aberdeen, UK
d
Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai- 600036,
Tamilnadu, India
*Corresponding Author:
Jitendra S. Sangwai
Email: jitendrasangwai@iitm.ac.in
Phone: +91-44-2257-4825
Fax: +91-44-2257-4802

2
Abstract
In this experimental work, three different types of nanofluids were evaluated for their
stability using dynamic light scattering (DLS) and particle morphological study using scanning
electron microscopy (SEM). The nanofluids used in this study are zinc oxide (ZnO) nanoparticle
in water and 5 wt% polyvinylpyrrolidone (PVP) as a dispersant, and ZnO with polyethylene glycol
(PEG 600) and CuO with PEG 600 with 5wt% PVP at different concentration of 0.1, 0.3 and
0.5wt %. Thermal and electrical conductivities were determined by KD-2 Pro
®
and PC 700
Eutech
®
. The result shows better enhancement in the thermal and electrical conductivity in the
ZnO+PVP+Water system, followed by the CuO+PVP+PEG and ZnO+PEG systems. The highest
percentage enhancement in thermal conductivity found to be 35.5 % of ZnO+ PVP+water systems.
The thermal conductivity results were compared with a theoretical model and show good
agreement with results predicted by the model. The proposed model of Nan et al. (1997) is based
on a hypothesis regarding the physical mechanism in heat transfer for nanofluids. This study is
expected to form the basis for the development of nanofluid-based technologies with PEG as the
primary additive in the upstream oil and gas industry especially in gas hydrates and drilling
technology.
Keywords: Electrical conductivity; Nanofluids; Stability; Thermal conductivity; Nan’s model.

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1. Introduction
Nanofluids have shown various interesting properties, and the distinguishing features offer
exceptional potential for different industrial applications, such as electronic, transportation,
improve recovery in oil and gas well, industrial cooling applications, nuclear systems cooling, etc.
Nanofluids are essentially two-phase systems, viz., solid phase in the liquid phase. Several
industries are in need of a cooling medium to improve the heat transfer performance, and of new
technology to overcome persistent challenges. A solid has a higher thermal conductivity than a
liquid, and hence, to increase the thermal conductivity, nanosized particles suspended in a base
fluid, known as ‘nanofluids’, are used. Nanoparticles have good electrical, magnetic and optical
properties. Accordingly, the mechanism for thermal conductivity enhancement is believed to be
the responsible parameter for enhancing heat transfer in engineering applications. However, the
research on the electrical properties of the nanofluid is very rare. The factors responsible for
enhancing heat transfer of nanofluids are the types of nanoparticle, particle size, aggregation,
Brownian motion of the particles and temperature of the nanofluids. Various mechanisms and
models, based on various assumptions, have been recently developed for explaining the unusually
high thermal conductivity of nanofluids [1-3]. Two significant requirements for measuring the
thermal conductivity are preparation of a homogeneous mixture and long-term stability which can
withsatand the initial equilibrium conditions until measurement. The electrical conductivity of a
suspension depends on the background electrolyte, particle size, charge, and volume fraction [4-
6]. Choi and his group [7] were the first to report that the suspended particles in the base fluid can
significantly enhance the heat transfer and give rise to improvement in the heat exchange systems.
Yu et al. [8] studied the thermal conductivity of copper oxide (CuO) nanofluids with ethylene
glycol and polyvinylpyrrolidone (PVP) as dispersants. The results showed about 46%
enhancement in the thermal conductivity in about 0.5 vol% of particle concentration at 50
o
C, and

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demonstrated that the temperature and Brownian motion of nanoparticles play an important role
in the thermal conductivity enhancement. Mehrali et al. [9] showed that by using graphene
nanoplatelets, a stable nanofluid with distilled water could be prepared without surfactant by
ultrasonic probe dispersion technique. The researchers showed about a 28% enhancement in
thermal conductivity and demonstrated that the stability of nanofluids found to be enhanced due
to ultrasonication. These nanofluids can act as an advanced heat transfer fluid in a medium
temperature applications in solar and heat exchangers. Xie et al. [10] conducted studies using
different nanoparticles, such as silicon carbide (SiC), zinc oxide (ZnO), carbon nanotubes (CNT)
and aluminum oxide (Al
2
O
3
) with base fluids, such as deionized water, glycerol, ethylene glycol
and the mixture of water and ethylene glycol. The results showed that the thermal conductivity
enhancement has been influenced by the volume fraction of the particle and due to temperature.
Fedele et al. [11] studied CuO, titanium oxide (TiO
2
) and single-walled carbon nanohorns
(SWCNHs) with water as a base fluid. They used polyethylene glycol (PEG) and sodium dodecyl
sulfate (SDS) as dispersing agents. They investigated three dispersion techniques, such as
sonification, high-pressure homogenization and ball milling for the formation of nanofluids. The
high-pressure homogenization method was found to yield better stability of the nanofluids.
Kole and Dey [12] prepared stable ZnO-ethylene glycol nanofluids by prolonged
sonification of >62 hours and showed that extended time for sonification gives better
fragmentation and dispersion of the particles. In their studies, they considered both temperature
and nanoparticle concentration for thermal conductivity enhancement. The results showed that
approximately 40% of thermal conductivity enhancement is achieved at 30
o
C and with 3.75vol%
of ZnO. Suganthi et al. [13] investigated a colloidal dispersion of ZnO-propylene glycol. Thermal
conductivity was measured in the temperature range of 10-60
0
C and for various aggregate sizes.

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The researchers observed that the thermal conductivity enhancement depends on temperature and
that higher enhancement is possible at a lower temperature. The result shows that the temperature
and aggregation of particles are major factors in the formation of a solvation layer on the ZnO
nanoparticle surfaces. Jeong et al. [14] showed that for ZnO nanoparticles, the thermal
conductivity and viscosity enhancement depend on the particle shape. The researchers used
spherical and rectangular particles with concentration range of 0.05 to 5 vol%. The results show
about 12% and 18% enhancement in thermal conductivity, respectively, for spherical and
rectangular particles at 5vol%. Moattar and Cegincara [15] used PEG to prepare stable nanofluids
of ZnO which was later characterized using dynamic light scattering. They observed the effect of
ZnO nanoparticles concentration and temperature on the volumetric and transport properties of the
aqueous solution of PEG but did not report information on enhancement in the thermal and
electrical property. Ponmani et al. [5] studied experimentally the thermal and electrical
conductivity of ZnO and CuO nanofluids in xanthan gum. They observed an approximately 25 and
50 % enhancement in thermal and electrical conductivity, respectively. White et al. [16]
investigated the electrical conductivity of propylene glycol-based ZnO nanofluids. The result
showed that a higher volume fraction of the particle gives better enhancement in electrical
conductivity. They observed that for about 7 % volume fraction of nanoparticles, electrical
conductivity showed up to 100-fold increase over the base fluid. Kim et al. [17] prepared stable
nanofluids using aluminum oxide, zinc oxide and titanium oxide nanoparticles with water and
ethylene glycol as a base. They showed that the enhancement in the thermal conductivity increases
linearly in lesser size of the particles when suspended in the base fluids. Khedkar et al. [18]
investigated the thermal conductivity of CuO nanofluids in monoethylene glycol and water. The
results show that the enhancement in thermal conductivity is due to the concentration of