Heat absorption properties of CuO/TiO2/SiO2 trihybrid nanofluids and its potential future direction towards solar thermal applications

Nur Alya Syamimie Muzaidi; Mohd Amiruddin Fikri; Khairul Nizar Syazwan Wan Salihin Wong; Azfi Zaidi Mohammad Sofi; Rizalman Mamat; Norfatihah Mohd Adenam; Muhamad Yuzaini Azrai Mat Yunin; Hasyiya Karimah Adli

doi:10.1016/j.arabjc.2021.103059

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Original article

2021

:14;

202104

doi:

10.1016/j.arabjc.2021.103059

Heat absorption properties of CuO/TiO₂/SiO₂ trihybrid nanofluids and its potential future direction towards solar thermal applications

Nur Alya Syamimie Muzaidi^{^a}, Mohd Amiruddin Fikri^{^a}, Khairul Nizar Syazwan Wan Salihin Wong^{^b,^d}, Azfi Zaidi Mohammad Sofi^{^a}, Rizalman Mamat^{^c}, Norfatihah Mohd Adenam^{^a}, Muhamad Yuzaini Azrai Mat Yunin^{^a}, Hasyiya Karimah Adli^{^b,^d,⁎}

a Faculty of Bioengineering and Technology, Universiti Malaysia Kelantan, 17600 Jeli, Kelantan, Malaysia

b Institute for Artificial Intelligence and Big Data, Universiti Malaysia Kelantan, City Campus, Pengkalan Chepa, 16100 Kota Bharu, Kelantan, Malaysia

c Department of Mechanical Engineering, College of Engineering, Universiti Malaysia Pahang, Lebuhraya Tun Razak, 26300 Gambang, Kuantan, Pahang, Malaysia

d Department of Data Science, Universiti Malaysia Kelantan, City Campus, Pengkalan Chepa, 16100 Kota Bharu, Kelantan, Malaysia

⁎Corresponding author at: Institute for Artificial Intelligence and Big Data, Universiti Malaysia Kelantan, City Campus, Pengkalan Chepa, 16100 Kota Bharu, Kelantan, Malaysia. hasyiya@umk.edu.my (Hasyiya Karimah Adli)

Received: 2020-9-21, Accepted: 2021-2-1,

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Abstract

In this study, we investigated the physical properties of CuO/TiO₂/SiO₂ trihybrid nanofluids. The physical properties that were investigated included density, crystallite size, and surface morphology. The trihybrid nanofluid density was observed to increase at higher volume concentration, with t1 exhibiting the highest density (2.26 gml⁻¹). X-Ray Diffraction (XRD) spectra showed the main diffraction peaks of individual nanoparticles (CuO, TiO₂ and SiO₂), highlighting the successful formation of trihybrid nanoparticles. The nanofluid's calculated crystallite size showed the formation of smaller trihybrid nanofluid crystallites (5.2 nm) compared to the original nanoparticles. The crystallite size is in good agreement with the SEM surface morphology, which shows the appearance of small particles. The trihybrid solution (t1) had the best thermal properties, based on temperature output, at around 55 °C, as the highest volume concentration of nanofluids was used. The heat absorption of t1 also demonstrated increased temperature output at higher solar radiations with a maximum temperature output at 73 °C under 700 W/m². This study is the first to report on the thermal properties CuO/TiO₂/SiO₂ trihybrid nanofluids for future solar thermal application.

Keywords

Trihybrid

Nanofluids

Heat absorption

Temperature output

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1 Introduction

Cumulatively, fossil fuels accounted for 84% of the world’s primary energy source in 2019. Fossil fuels also dominated about 40% of global electricity generation in the same year (BP Statistical Review of World Energy, 2020). Global electrical energy consumption is typically high, and the demand is growing rapidly at an alarming rate. In an effort to reduce the dependency on fossil fuels, many countries have turned to renewable energy such as solar energy (Grätzel, 2009). Generating electricity with solar power instead of fossil fuels can dramatically reduce greenhouse gas emissions, particularly carbon dioxide (CO₂). Greenhouse gases emitted by fossil fuels have led to increased global temperature and climate change, subsequently contributing to serious environmental and public health issues (Haines et al., 2006).

Solar water heating is currently the most common application of solar energy systems, especially in urban areas. This system is environmentally friendly and harnesses the generated electricity to heat water (Shukla et al., 2013). Basically, this system involves natural solar thermal technology based on simple working principles that require only sunlight to heat the water. The system works by bringing the thermal fluid into contact with a dark surface exposed to sunlight, which then increases the temperature of the fluid (Al-Badi and Albadi, 2012). In a direct system, the fluid may cause the water to heat up directly, or in an indirect system, a heat transfer fluid (e.g., glycol or a water mixture) could be used to pass through some form of heat exchanger (Jamar et al., 2016).

Meanwhile, nanofluids are world-class heat transfer working fluids that have been developed by adding solid nanoparticles to the base fluids (Alawi et al., 2018; Sarafraz et al., 2019). Homogenized mixtures of low-volume-fraction nanoparticles and conventional fluids such as ethylene glycol, glycerine, oil, and water can remarkably increase overall thermal performance (Das et al., 2007; Sarafraz et al., 2016). Due to its potential use in numerous engineering applications, nanofluids are now the focus of an expanding body of research. Additionally, nanofluids are most commonly used in heating and cooling processes prevalently seen in solar cells, solar stills, and other thermal energy storage methods (Khanafer and Vafai, 2018; Sarafraz et al., 2018) and thermal conductivity (Ghalambaz et al., 2020a, 2020b).

Oxide nanofluids such as aluminum oxide (Al₂O₃), titanium oxide (TiO₂), silicon dioxide (SiO₂), and copper oxide (CuO) are mostly used in heat transfer applications either as single or hybrid nanofluids, due to their capability to increase heat transfer in the heat transfer system by up to 60% (Azmi et al., 2019). The investigation into various hybrid nanofluid applications have greatly increased (Fikri et al., 2020b). Hybrid or composite nanofluids are an extension of the body of research on single nanofluids. These hybrids can be made via two or more different nanoparticles: either in the form of a mixture or a composite that disperses in liquid (Minea, 2017). Previous works have reported on the superiority of the thermal and rheological properties of hybrid and composite nanofluids over single nanoparticles. Table 1 presents the summary of respective nanofluids for thermal properties characterization.

Table 1 Summary of experimental results of thermal properties measurement of various nanofluids.

Particle	Type	Base fluid	Enhancement	References
Al₂O₃	Single	Ethylene glycol	The thermal conductivity decreased when the EG content in the mixture increased, but increased when the volume concentration of the Al₂O₃ nanofluids increased	Hamid et al. (2018)
Al₂O₃	Single	Water and ethylene glycol	The average thermal conductivity enhancement from 2.6 to 12.8% as the percentage of ethylene glycol increases	Chiam et al. (2017)
	Single	Ethylene glycol and water	At fixed EG content, the thermal conductivity of nanofluids increased with increasing of temperature	Guo et al. (2018)
SiO₂
	Single	Ethylene glycol	Viscosity linearly increased with the increased of nanoparticles concentration with maximum enhancement with 1.3905 times	Żyła and Fal (2017)
TiO₂	Single	Water, ethylene glycol, paraffin oil	The thermal conductivity increases 22% with the addition of nanoparticles	Sonawane et al. (2015)
	Single	Ethylene glycol	Thermal conductivity and viscosity of nanofluids increased with the addition of nanoparticles to base fluids	Khedkar et al. (2016)

CuO	Single	Water, ethylene glycol, engine oil	Thermal conductivity increases 40%, 27% and 19%, for CuO in water, EG and engine oil, respectively	Agarwal et al. (2016)
CuO	Single	Water	18% increase in thermal conductivity	Nemale and Waghuley (2016)
Al₂O₃, TiO₂, SiO₂ and CuO	Single	Ethylene glycol, water	The thermal conductivity of oxide nanofluids was enhanced up to 40% better than the base fluids (water)	Azmi et al. (2019)
Al₂O₃ and SiO₂	Hybrid	Water	An increase of thermal conductivity with volume fraction and temperature increase	Moldoveanu et al. (2018)
ZnO and TiO₂	Hybrid	Ethylene glycol (0.1–3.5 vol%)	Maximum enhancement (32%) at ϕ = 3.5% and 50 °C	Toghraie et al. (2016)
SiO₂ and TiO₂	Hybrid	Water and ethylene glycol (60:40)	Maximum enhancement of 22.8% obtained at 3.0% volume concentration and 80 °C temperature.	Nabil et al. (2018)
	Hybrid	Water and ethylene glycol (60:40)	The nanofluid viscosity increased with increased volume concentration and decreased with increased temperature	Hamid et al. (2019) and Guo et al. (2018)
	Hybrid	Ethylene glycol and water (40:60)	The maximum enhancement 22.1% at concentration 3.0% and temperature 70 °C	Hamid et al. (2017)
TiO₂ and Al₂O₃	Hybrid	Water	The highest thermal conductivity value of 1.134 W/m K is observed for hybrid nanofluid with mixing ratio of 50:50 at 70 °C, with an average thermal conductivity augmentation of 71% comparative to deionized (DI) water	Wanatasanapan et al. (2020)
TiO₂ and Al₂O₃	Hybrid	Ethylene glycol and water (40:60)	The thermal conductivity is improved by 40.86% at 0.1% volume concentration and 80 °C	Urmi et al. (2020)
Al₂O₃, TiO₂ and SiO₂	Trihybrid	Water and Ethylene glycol (60:40)	Reported trihybrid nanofluids remains stable with a concentration ratio of 80%.	Ramadhan et al. (2019)
Al₂O₃, TiO₂ and SiO₂	Trihybrid	Water and Ethylene glycol (60:40)	The maximum enhancement of the heat transfer coefficient for coolant side is observed at 39.7% at 0.3% volume concentration	Ramadhan et al. (2020)
SiO₂, Al₂O₃ and ZrO₂	Trihybrid	Deionised water and Ethylene glycol (60:40)	Nanofluid viscosity decreases with increasing liquid temperature and increases with increasing of nanoparticles volume concentration	Safiei et al. (2020)

Thus, it can be summarized that oxides have great promise in solar thermal applications and the hybrid nanofluids have superior thermophysical properties over single nanofluids. Based on the above findings, this study aims to develop a novel, trihybrid nanofluids made up of CuO, TiO_2, and SiO₂ and to investigate the physical properties of these materials such as density, crystallite size, and surface morphology, as well as temperature output performance. This is the first study to report on the CuO/TiO₂/SiO₂ trihybrid nanofluid. Thus, this study is the first to report on the thermal properties CuO/TiO₂/SiO₂ trihybrid nanofluids for future solar thermal application.

2 Experimental method

2.1

2.1 Materials preparation

Copper (II) oxide powder (Bendosen) (99.9%, ≤ 160 µm), titanium dioxide (TiO₂) powder (R&M chemicals) (≥99.5%, 1 to 150 nm) and silicon dioxide (SiO₂) powder (HmbG Chemical) (99.9%, 0–2000 μm) were used without further purification. Initially, each nanofluid from the copper oxide (CuO), titanium dioxide (TiO₂), and silicon dioxide (SiO₂) nanoparticles was prepared in 2.5 M that were dissolved in ethylene glycol. Then, the mixture was stirred continuously for 3 days and sonicated for 2 h until a homogenized solution was obtained. Each nanofluid was mixed at a 1:3 vol ratio to finally form 100 mL of the (CuO/TiO₂/SiO₂) trihybrid nanofluids. Different concentrations of the trihybrid nanofluids were prepared in water and ethylene glycol mixture (60:40) which are 0.17, 0.08 and 0.04 M, denoted as t1, t2, and t3 respectively. The overall process is summarized in Fig. A1.

2.2

2.2 Physical characterization

The investigation into the physical properties of the prepared (CuO/TiO₂/SiO₂) trihybrid nanofluids (t1, t2, and t3) was observed via visualization effect (Chakraborty and Panigrahi, 2020). Sedimentation is the most commonly used technique for stability evaluation which based on the formation of sediment at the bottom of the liquid column due to gravity. The longer time taken by the nanofluid for the formation of precipitate is an indication of superior stability of nanofluid. Several researchers have used the sedimentation technique to evaluate nanofluid stability (Chakraborty et al., 2018a, 2018b). The density of the base fluids and the prepared trihybrid nanofluids was checked using a density meter (Radwag Balances and Scales model), and several physical characterizations were conducted via Ultraviolet–visible Spectrophotometer (UV–vis), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). MeaUV–Vis analysis was carried out using a Spectroquant Pharo 300 UV–vis Spectrometer. This analysis was run 10 days in a row with a wavelength set at 400 nm to determine the absorption and the stability of the trihybrid nanofluid. The crystallite size and the crystalline structure of CuO, TiO_2, and SiO₂, as well as the t1, t2, and t3 trihybrid were determined via X-ray diffraction (XRD D2 Phaser, Bruker). The surface morphology was observed using a JEOL JSM IT 100 Scanning Electron Microscope (SEM) at 300× magnification.

2.3

2.3 Heat absorption performance

t1, t2 and t3 trihybrid nanofluids were exposed to 300 W/m² artificial solar radiation to investigate the heat absorption performance of each nanofluid, after which t1 was chosen for further analysis on different solar radiation intensities (300 W/m², 500 W/m², and 700 W/m²). A dimmer switch was installed in the circuit to regulate the solar radiation. The experiment started with a charging process of 16 min and then a discharging process for another 16 min using a thermocouple. The temperature data was recorded every 2 min in a controlled environment. The temperature was displayed by thermocouple and the information was manually recorded. The experimental setup is shown in Fig. A2, with detailed descriptions given in Table A1.

3 Results and discussion

3.1

3.1 Physical properties

The formulation of the trihybrid nanofluids is based on the two-step method outlined by Ramadhan et al. (2019), with the difference of metal oxides and solution concentrations used. The copper oxide (CuO), titanium dioxide (TiO₂), and silicon dioxide (SiO₂) solutions in ethylene glycol were prepared individually before mixing to finally form the (CuO/TiO₂/SiO₂) trihybrid solution. Fig. A1 shows the image of oxide solution and trihybrids solutions.

Ethylene glycol also acts as an antifreeze when mixed with water to form a solution with a relatively good heat transfer (Peyghambarzadeh et al., 2011). Ethylene glycol (EG) has been reported to minimize the damage and increase the shelf-life of water heating systems (Sundar et al., 2014). According to the literature, mixed base fluids have better heat transfer properties with high thermal conductivity and low viscosity. The use of base-water has limited operated temperature range, high vapour pressure and high corrosivity. Besides, ethylene glycol has higher performance in the convective heat transfer compared to water. Thus, a water-ethylene glycol mixture at a 60:40 ratio was used as the base fluid for this study.

The density of the base fluids used in this study was initially checked to compare the density of distilled water with the distilled water-ethylene glycol mixture, as shown in Table A2. Next, the density of the prepared t1, t2, and t3 trihybrid was measured. It was found that the density increased with increasing nanoparticle concentration. According to the rule of mixtures, the density of good heat transfer fluids increases linearly with volume fraction since the addition of a small fraction of solid nanoparticles to the base liquid will enhance the density of the mixture (Chandrasekar et al., 2012; Tahat and Benim, 2017).

Fig. A3 shows the images of t1, t2 and t3 trihybrid nanofluids with concentrations of 0.17, 0.08 and 0.04 M, respectively, at after preparation (day 1) and at day 10. At room temperature, no sedimentation of particles was observed after the solution was prepared but sedimentation started to form on day 10. The sedimentation was occurred due to the effect of gravity on the particles (Sahid et al., 2017). The suspension of these solid particles in the base fluids reported can enhance the energy transmission in the fluids resulting an increase thermal conductivity properties and heat transfer performance (Ganji et al., 2018; Okonkwo et al., 2019).

3.2

3.2 Physical characterization

Fig. A4 displays the X-Ray Diffraction (XRD) patterns of CuO, TiO_2, SiO₂, and the (CuO/TiO₂/SiO₂) trihybrid collected within a Bragg’s angle (2θ) between 10° and 90°. The diffraction pattern in Fig. A4(a) is identical to the single-phase monoclinic CuO observed at 2θ ≈ 32° and 35°, indicating the good crystallinity of the copper oxide nanoparticles. All diffraction peaks of CuO at (32, 35, 38, 48, 53, 58, 61 and 67) ° are in good agreement with the JCPDS card NO. 48-1548 (Siddiqui et al., 2018). Next, the peak of the SiO₂ nanoparticles was observed at 2θ ≈ 24° reported in amorphous phase (Yuvakkumar et al., 2014; Nayak et al., 2019), while the sharp peak of TiO₂ nanoparticles at 2θ ≈ 25°, 38°, and 48° confirm the presence of the anatase phase in concordance with the JCPDS card no.: 21-1272 and 211,276 database (Li et al., 2014; Almashhori et al., 2020; Antić et al., 2012 ). Meanwhile, the XRD spectrum of the (CuO/TiO₂/SiO₂) trihybrid (Fig. A4d) shows the appearance of the main diffraction peaks from the individual nanoparticles (CuO, TiO₂ and SiO₂), highlighting the formation of the trihybrid nanoparticles. The diffraction peaks were observed at 2θ ≈ 25°, 35°, 38°, 48°, and 54°.

The crystallite size of the nanoparticles was identified from XRD patterns according to the peak position (Zak et al., 2012). The crystallite size of the nanofluids was evaluated by measuring the FWHM of the strongest peak (Mohammadi et al., 2017). The average crystallite size was computed using the Debye–Scherrer formula below (Deraz and Abd-Elkader, 2014): $D = k λ / β c o s θ$ where D is the crystallite size (nm), k is a constant equal to 0.9, λ is the wavelength of X-ray radiation (0.15406 nm), β is the full-width at half maximum (FWHM) of the peak (in radians), and θ is peak position (in radians).

Based on the FWHM values, the calculated average crystallite size of CuO, SiO₂, TiO₂, and the trihybrid was 26.4 nm, 0.6 nm, 14.4 nm, and 5.2 nm, respectively. From the results obtained (Table A3), it can be concluded that the trihybrid particles had a smaller crystallite size (5.2 nm) compared to their original nanoparticles.

From Fig. A5(a), the surface morphology of the CuO nanoparticles is spherical and nearly uniform in size, with a similar shape to that reported previously (Ranjbar-Karimi et al., 2010). This spherical nanoparticle form is favorable for the heat transfer of absorbed solar energy within the nanofluid and can increase solar absorption capacity (Subramaniyan et al., 2018). Meanwhile, Fig. A5 (b) and (c) show the images of the SiO₂ and TiO₂ nanoparticles that are also similar in shape to that reported by Ramadhan et al. (2019). The surface morphology of CuO/TiO₂/SiO₂ in Fig. A5(d) appear similar in shape to that of the (CuO, TiO₂ and SiO₂) original nanoparticles, proving the formation of the trihybrid nanoparticles although the size of CuO changed after the trihybrid formation. The spherical, nearly uniform size, and rock-like shape, as well as the smaller crystallite particles, prove that the nanoparticles are loose agglomerates (Akilu et al., 2017).

The absorption spectra of the trihybrid nanofluid in different volume concentrations were determined using a UV–Vis spectrophotometer at 400 nm for up to 10 days at room temperature to optimize the stability of the nanohybrid solutions. The absorbance of the nanofluids was found to linearly increase with an increase in volume concentration. This trend is in agreement with the Beer-Lambert Law (Sharif et al., 2019). The UV–vis absorption of the 0.05% (t3), 0.1% (t2), and 0.2% (t1) concentrations are shown in Fig. A6. From the UV–vis spectrum, t1 clearly recorded the highest UV–vis absorption, as t1 has the highest concentration of the sample series. The mixing solution was confirmed due to the comparison of spectra made based on the literature (Saidina et al., 2020; Kumar et al., 2020; Adam et al., 2020 ). Furthermore, the absorbance of the trihybrid nanofluids in different concentrations was monitored after 24 h up until day 10 (240 h). It was found that the absorbance of the CuO/TiO₂/SiO₂ trihybrid (t1, t2, and t3) decreased over hours (Fig. A7). On day 5, t2 was the most stable trihybrid with only a 10.5% decrease, compared to t3 (60%) and t1 (27.6%). However, nearing 240 h, t1 showed the highest absorption of the series, with only a 62.1% drop in the initial absorbance reading.

3.3

3.3 Heat absorption performance analysis

Fig. A8 shows the comparison of solar absorption and the cooling curve of the base fluids, the distilled water (dw), and the mixture of distilled water and ethylene glycol (w:eg), carried out under 15 min charging and 15 min discharging. The results clearly show w:eg having better base fluid properties so it will store heat better than dw.

In a similar method, the heat absorption performance of the (t1, t2, and t3) trihybrid nanofluids in water-ethylene glycol as the base fluid was investigated under 300 W/m² solar radiation. From the analysis, the temperature gradually increased with time during the charging process and started to decrease during the discharge process (Fig. A9a). Hence, t1 recorded the highest performance due to its highest concentration of nanofluids and thus the best thermal absorber of the series. Under different solar radiation (Fig. A9b), t1 exhibited increasing heat absorption at higher solar radiation (500 W/m²) and 700 W/m²) with a maximum temperature achieved at 73 °C. In summary, the obtained results exhibited improved performance in thermophysical properties, compared to the TiO₂-SiO₂ hybrid nanofluids, which recorded a maximum temperature of 37 °C under 300 W/m² solar radiation (Fikri et al. 2020a, 2020b).

4 Conclusion

A trihybrid nanofluid was successfully prepared from CuO, TiO₂, and SiO₂ and analyzed using XRD, SEM, UV–vis, and thermocouple. t1 recorded the highest density of 2.26 gml⁻¹. The XRD spectra showed the existence of the main diffraction peaks of the individual nanoparticles (CuO, TiO₂, and SiO₂), proving the formation of the CuO/TiO₂/SiO₂ trihybrid. The calculated crystallite size and SEM images demonstrated the smaller size of the trihybrid nanoparticles (5.2 nm) compared to the original size of their oxides. The as-prepared trihybrid nanofluid solution (t1) performed stably for 240 h, with only a 62.1% drop in the initial absorbance reading. From the heat absorption performance, t1 recorded the best performance, achieving maximum temperature at 73 °C under 700 W/m².

Acknowledgement

Author would like to thank Faculty of Bioengineering and Technology, UMK for providing instrumentation facility.

Funding

This study was funded by UMK PRO (Grant No. R/PRO/A1300/01501A/002/2020/00759).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Appendix A

See Figs. A1–A9 .

Preparation of trihybrid nanofluids (t1, t2, t3) from CuO (A), TiO2 (B) and SiO2 (C).

Sedimentation of trihybrid nanofluids from Day 1 until Day 10, which the solutions were kept at room temperature.

XRD spectrum of (a) CuO, (b) SiO2, (c) TiO2 and (d) trihybrid (CuO/SiO2/TiO2).

Surface morphology of (a) CuO, (b) SiO2, (c) TiO2 and (d) trihybrid (CuO/SiO2/TiO2) at 300× magnification (50 μm).

UV–vis absorption of trihybrid nanofluids of t1, t2 and t3.

The absorbance of trihybrid nanofluids up to 240 h.

Solar absorption and cooling curve of base fluids with solar radiation of 300 W/m2.

Temperature output a) of the absorber based on t1, t2 and t3, b) of t1 with solar radiation of 300, 500 and 700 W/m2 respectively.

See Tables A1–A3 .

Table A1 Detail description of the solar radiation test rig.

Number	Specification	Description
1	Switch Socket Outlet (Data Logger & Spotlight Dimmer)	SSO
2	Setting up with pyranometer (300 & 700 W/m²)	Dimmer
3	Halogen 500 W	Spotlight
4	K-type	Thermocouple
5	100 mL	Test tube

Table A2 Density of base fluids and trihybrid nanofluids.

Samples	Density (g ml⁻¹)
Distilled water	0.99
Water-Ethylene Glycol (60:40)	1.69
t3 trihybrid nanofluids	1.86
t2 trihybrid nanofluids	2.06
t1 trihybrid nanofluids	2.26

Table A3 The average crystallite size of nanoparticles.

Nanoparticles	CuO	SiO₂	TiO₂	Trihybrid
Peak position	35.47	24.30	25.49	25.10
FWHM	0.32	14.28	0.57	1.57
Crystallites size (nm)	26.41	0.57	14.39	5.19

Introduction

Experimental method

Materials preparation
Physical characterization
Heat absorption performance

Results and discussion

Physical properties
Physical characterization
Heat absorption performance analysis

Conclusion

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[CrossRef] [Google Scholar]

[62] Żyła G., Fal J., . Viscosity, thermal and electrical conductivity of silicon dioxide–ethylene glycol transparent nanofluids: An experimental studies. Thermochimica acta. 2017;650:106-113.
[CrossRef] [Google Scholar]