Article

AL-QADISIYAH JOURNALFORENGINEERING SCIENCES 14 (2021) 042–047

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Al-Qadisiyah Journal for Engineering Sciences

Journal homepage: http://qu.edu.iq/journaleng/index.php/JQES

* Corresponding author.

E-mail address: hasan.dawwood@qu.edu.iq (Hasan I. Dawood)

https://doi.org/10.30772/qjes.v14i1.732

A Comparative Study On Stability And Thermal Properties Of Various

Nanofluids

Marwa S.J. , Hasan I. Dawood٭

Chemical Engineering Department -Faculty of Engineering – University of Al-Qadisiyah-Iraq.

A R T I C L E I N F O

Article history:

Received 13 January 2021

Received in revised form 11 April 2021

Accepted 15 April 2021

Keywords:

Heat transfer Enhancement;

Nanofluids;

Thermal properties;

Hybrid nanofluids;

Base fluids.

A B S T R A C T

The attention of researches in convective heat transfer by suspended nanoparticles in base fluids has grown

lately to promote uncommon techniques for enhancing the thermal performance of fluids. In this study, the

stability period and thermal properties of aluminium oxide (Al2O3), silicon dioxide (SiO2) and Al2O3–SiO2

hybrid were investigated at volume concentration 0.1vol.% dispersed in Distilled Water (DW) as a base

fluid. For the hybrid nanofluid, the samples were consisted of (0.025

vol.%Al2O3+0.075vol.%SiO2),(0.05vol.%Al2O3+0.05vol.%SiO2)and(0.075vol.%Al2O3+0.025vol.%SiO2).

The two-step method was adopted to prepare the nanofluid samples by using Ultrasonic device. Three

different ultrasonication times were fitted for preparing the samples (1hr,2 hr and 3 hr).The properties of

single and hybrid nanofluids were evaluated at various temperatures (from 30 °C to 70 °C). The obtained

results demonstrated that the dispersion of nanoparticles was homogeneous and more stable for a longer

period for all samples that prepared at 3 hr of ultrasonication process. Among all samples of nanofluids,

SiO2/DW was found to be the most stable coolant. For all nanofluids, with an increase of temperature, the

thermal conductivity and specific heat were increased significantly while density and viscosity were

decreased.

1. Introduction

Improving warmth move rates by using nanofluids has drawn huge

considerations from analysts around the globe. Ordinary strong

nanoparticles, size of 1-100 nm with high warm conductivities, are

suspended in the base liquids that have low warm conductivities. The

nanofluids have demonstrated an upgrade in viable warm conductivities

and the convective warmth move coefficients of the first base fluid[1].

Nano-fluid, a collection of nanomaterials in a continuous and saturated

liquid, has been known to be capable of achieving significantly higher

thermal conductivity than the associated base liquid, causing an

enhancement in heat transfer coefficients [2].Hybrid2nanofluid as an

expansion of nanofluid is obtained by scattering composite nano-powder or

two diverse nanoparticles in the base liquid. It is accepted that half breed

nanofluid will offer great warm qualities when contrasted with the base

liquid and nanofluid containing single nanoparticles because of synergistic

impacts[3]. A blend of nanofluids happens only utilizing remarkable

techniques like as one stage and two-advance strategies. Steady and quality

nanofluids are integrated utilizing these strategies to use them for any

warmth move and exploratory purposes. According to various authors,

physical properties of nanofluids is influenced by several factors.

Temperature is the most important factor which plays a significant role in

the nanofluid thermal performance.

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MARWA S.J. , HASAN. I. DAWOOD /AL-QADISIYAH JOURNALFOR ENGINEERING SCIENCES 14(2021) 042–047 43

[4] claimed that nano-fluids could be better than traditional working

fluids like Ethylene Glycol (EG) and water due to the more beneficial and

encouraging heat transfer properties of nano-fluids. [5]used

Al2O3 nanoparticles with 4.3 vol.% and noted that an increase in the warm

conductivity of water under fixed conditions by 32.4%. [6] thought about

the warm conductivity between Cu-EG nanofluid and unadulterated EG.

The outcome showed that 40% expansion in warm conductivity of Cu-EG

nanofluid at volume portion of 0.3 vol%. As indicated by [7], a superior

improvement in warm conductivity can be produced by hybridizing silver

nano-particles with Multi-Walled Carbon Nanotube (MWCNT).

Approximately half nanoparticles have demonstrated an astounding

improvement regarding cooling adequacy contrasted with single

nanoparticles and water. [8] arranged suspension of TiO2 and Al2O3

nanoparticles by a two-advance technique by scattering 0.05 vol.% and 0.3

vol.% in the blend of water and EG which was mixed for 30 min utilizing

an attractive stirrer followed by ultrasonication utilizing an ultrasonication

for 2 hr. They proposed that TiO2 more steady than Al2O3 in water/EG

blend. [9] Compared to nano-fluid that have single nanoparticles and water,

hybrid nanoparticles have exhibited a significant improvement in cooling

system performance [10]. Stabilized Single Walled Carbon Nanotubes

(SWCNT) functionalized with the carboxyl group (COOH) –water /EG by.
The functionalized SWCNT with different solid volume fractions were

added to the base fluid, using a two-step method. The finds obvioused that

the nano-fluid samples was stable for two weeks and its had a long stability

with no comprehensible precipitation. [11]inspected thermo-physical

properties (warm conductivity, thickness, consistency and explicit warmth)

of nanofluids containing Al2O3 nanoparticles in water/EG blend (50:50).

The ascent in temperature demonstrated improvement in warm

conductivity and specific heat while the density and viscosity were

decreased.[12] estimated warm conductivity of ZnO-Ag (50 %:50 %)/water

by considering different temperatures (25°C– 50°C) at 2 vol.%. The

maximum thermal conductivity was achieved at 50°C. [13]analyzed the

thermal behavior of a functionalized graphene nanoplateletplatinum (GNP-

Pt) hybrid nano-fluid at temperatures ranging from 20°C to 40 °C. They

mentioned that the hybrid nano-fluid density was correlated with the

temperature . GNP-Pt/water hybrid nano-fluid density decreased with the

rise in temperature from the observational investigation. From the findings

of Yarmand et al[14]on the activated carbon/grapheme (ACG)/EGG hybrid

nano-fluid. It was established that when the temperature increases

significantly, the specific heat of nano-fluids was greater than that of the

base fluids. For thermal performance testing, nano-fluid viscosity is a

parameter as important as thermal conductivity, density and specific heat.

Dardan et al[15]demonstrated the viscosity relationship with respect to the

difference of Al2O3-MWCNT/nano-fluid oil temperatures. And as per the

results, with temperature, viscosity was dramatically decreased, with

temperature increase.

The main objective of this paper is to get a nanofluid with promising

advantages by adding Al2O3 and SiO2nanoparticles to DW. Adopting the

two-step method to prepare nanofluid samples and highlighting on the

effect of ultrasonication time on the stability of nano-suspensions. The

thermophysical properties of nanofluids were evaluated at temperatures

from 30 °C to 70 °C.

2. Experimental steps :

2.1. Nanofluids preparation:

Two kinds of oxide nanoparticles were utilized for this investigation:

Al2O3 nanoparticles produced by ( Hongwu, Universal Group.Ltd) and

SiO2 manufactured by US Exploration Nanomaterial's, Inc.

(NovaScientific Assets (M) Sdn. Bhd). Both nanofluids were readied with

DWas base fluid. The properties of these nanoparticles are shown in Table

Table 1:Physical, morphological and thermo- properties of Al2O3 and

SiO2 nanoparticles.

Properties11 (Al2O3) (SiO2)

Color11 White White

Particle size 50 nm 50 nm

Purity 99.99% 99.8%

Morphology1of2Particles Spherical Spherical

Form11 Powder Powder

Density (g.cm-3) 3.9 2.4

Thermal conductivity (K)

(W.m−1 .K−1)

40 [16] 1.4 [17]

Specific heat (cp) (J / kg.k) 773 [16] 745 [17]

The particles shape and microstructure that studied with scanning electron

microscope (SEM) are explain in Fig. 1a-b. The examination was

conducted in the Scientific Research Department / Ministry of Higher

Education and Scientific Research.

The nanoparticle suspensions in DW were subjected to ultrasonic

vibration for 1hr,2hr and 3hr at room temperature as in Fig. 2. The weight

of Al2O3and SiO2 nanoparticles that used to prepare the nanofluid samples

are explained in Table 2.

Table 2:The weights in gm of Al2O3and SiO2 nanoparticles in the

samples.
No. sample Weight

1 0.1 vol.% Al2O3 39.04

2 0.1 vol.% SiO2 24.04

3 0.05 vol.% Al2O3 + 0.05 vol.% SiO2 31.49

4 0.075 vol.% Al2O3 + 0.025 vol.% SiO2 35.24

5 0.025 vol.% Al2O3 + 0.075 vol.% SiO2 27.79

The next step, adequate quantities of DW were added to the underlying

suspensions and altogether blended to accomplish the expected nanofluids.

The volume concentrations of single and hybrid nanofluids are evaluated

from the following equations[18]:

Volume concentration (𝜑) = [

𝑊𝑛𝑝

𝜌𝑛𝑝
𝑊𝑛𝑝

𝜌𝑛𝑝
+

𝑊𝑏𝑓

𝜌𝑏𝑓

] × 100 (1)

Nomenclature

DW Distillate water 𝑛𝑝 nanoparticles

k thermal conductivity (W m-1 K-1) 𝑤 the weight( Kg )

𝐶 specific heat (J kg-1 K-1) 𝜇 viscosity in mpa.s

𝑏𝑓 base2fluid3 𝜌 the density of the nanoparticles ( Kg . m
-3)

𝑛𝑓 nanofluid 𝜑 Volume concentration

44 MARWA S.J. , HASAN. I. DAWOOD /AL-QADISIYAH JOURNALFOR ENGINEERING SCIENCES 14 (2021) 042–047

𝜑 = [
[

𝑊𝑛𝑝

𝜌𝑛𝑝
]

𝐴𝑙2𝑂3
+ [

𝑊𝑛𝑝

𝜌𝑛𝑝
]

𝑆𝑖𝑂2

[
𝑊𝑛𝑝

𝜌𝑛𝑝
]

𝐴𝑙2𝑂3
+ [

𝑊𝑛𝑝

𝜌𝑛𝑝
]

𝑆𝑖𝑂2
+

𝑊𝑏𝑓

𝜌𝑏𝑓

] × 100 (2)

2.2.Evaluation of the physical properties for nanofluids

The thermal conductivity of nanofluids is a significant property when

evaluating warm proficiency. Estimations were performed with

temperature assorted variety between 30 °C and 70 °C. To evaluate the

warm conductivity of nanofluids, KD2 Ace Warm Properties Analyzer

(Decagon Gadgets, USA) was used as in Fig. 3a-b. The examination was

conducted at the University of Babylon / College of Engineering /

Department of Chemical Engineering .The KD2 was adjusted by utilizing

DW at the room temperature before estimations, and the exactness of these

estimations was fated to be inside 1%. The measurements of Physico-

thermal properties for nanofluids (density, specific heat and

Figure 1:a. General shape of Al2O3 and SiO2particles b. SEM of

nanoparticles

Figure 2: Ultrasonic device

viscosity) are necessary to apply for practical applications. Appropriate

correlations to assess the density of single nanofluids were provided by

Pakand Chu [19]that have been identified as follows:

𝜌𝑛𝑓 = 𝜑𝜌𝑛𝑝 + (1 − 𝜑)𝜌𝑏𝑓 (3)

Specific heat of single nanofluids was calculated using Xuan and Roetzel’s

[20] equation:

(𝜌𝐶)𝑛𝑓 = 𝜑(𝜌𝐶)𝑛𝑝 + (1 − 𝜑)(𝜌𝐶)𝑏𝑓 (4)

Figure 3:a. Thermo- Properties Analyzer b. schematic diagram of

thermal conductivity measuring.

To measure the densities and specific heat of hybrid suspensions of

Al2O3and SiO2nanoparticles, the theoretical formulasthat predicted by Ho

et al.[21]were used as follows:

𝜌𝑛𝑓 = [𝜑𝜌𝑛𝑝 ]𝐴𝑙2𝑂3 + [𝜑𝜌𝑛𝑝 ]𝑆𝑖𝑂2 + (1 − 𝜑𝐴𝑙2𝑂3 − 𝜑𝑆𝑖𝑂2)𝜌𝑏𝑓 (5)

(𝜌𝐶)𝑛𝑓 = [ 𝜑𝜌𝐶]𝐴𝑙2𝑂3 + [ 𝜑𝜌𝐶]𝑆𝑖𝑂2 + (1 − 𝜑𝐴𝑙2𝑂3 − 𝜑𝑆𝑖𝑂2)(𝜌𝐶)𝑏𝑓 (6)

To predict the viscosity of nanofluids, the formula derived by Brinkman

[22]was used.All samples that used in this study which have different

component fractions of Al2O3 and SiO2were considered to have the same

viscosity because of particle’s spherical shape and the volume fraction of

samples between 0.01 vol.% and 2 vol.% [23].

𝜇𝑛𝑓 =
𝜇𝑏𝑓

(1−𝜑)2.5
(7)

3. Results and discussion

Tests were performed with DW and various samples of nano-fluids
which were prepared with different ultrasonication times (1hr,2 hr and 3

MARWA S.J. , HASAN. I. DAWOOD /AL-QADISIYAH JOURNALFOR ENGINEERING SCIENCES 14(2021) 042–047 45

hr). The study was carried out with the range of temperature (30,40,50,60

and 70°C) at 0.1vol.%. The observation obtained from the present

investigation is discussed below:

3.1. Dependability time of nanofluids

The impact of ultrasonication times on resting period as appeared in

Table 3. Due to the little size of nanoparticles, it has a high propensity to

shape groups or agglomerates because of van der Waals powers.

Ultrasonication technique helps to break these bonds between the

nanoparticles and increase the random motion of the nanoparticles that

suspended in the base fluid.The augmentation in ultrasonication time lead

to an increment in the random motion of this nano-powder and will create

a slip speed between the particles and the liquid medium[24]. The

experimental results show a good agreement with the previous articles [25,

26]. Besides, the challenge of how to effectively prevent nanoparticles from

agglomeration or aggregation, the key issue is the weight of nanoparticles

that are used to form more stable nanofluids.The best consequences were

gotten for the sample 0.1 vol.% SiO2, where it recorded the longest period

of stability which was about 15 day with ultrasonication time 3 hr.The

reason is due to the total weight of nanoparticles that used in 0.1 vol.% SiO2

is less than weights that utilized in other samples to prepare them with the

same volume concentration, which ensures the possibility of better

distribution and a longer sedimentation time[25].Fig. 4 explain the

sedimentation time for the sample 0.1vol.%of SiO2 after 15day.

Table 3: Stability period (day) of nanofluid samples at room

temperature

Samples Ultrasonication time

1hr 2 hr 3 hr

0.1 vol.% Al2O3 7 9 11

0.1 vol.% SiO2 9 11 15

0.05 vol.% Al2O3 + 0.05 vol.% SiO2 8 10 13

0.075 vol.% Al2O3 + 0.025 vol.% SiO2 7 9 12

0.025 vol.% Al2O3 + 0.075 vol.% SiO2 8 10 13

Figure 4: Sedimentation time for the sample 0.1vol.%of SiO2 after

15day

3.2.Effect of temperature on physical properties

3.2.1.Thermal conductivity

Fig. 5 introduces the variation of nanofluid thermal conductivity as

a function of temperature for DW and all the studied nanofluid samples. By

observing the results, the warm conductivity of the nanofluids increments

with increment in temperature. With the ascent in temperature, while

loosening the intermolecular bonds, the randombehaviour of nanoparticles

- liquid collision will increase [6]. This is known asBrownian motion which

suggested by Xuan and Roetzel [20]. Moreover, these results agree with the

literature [27]. The spontaneous behavior of suspended nanoparticles in

liquid media will increase as temperature goes up ,and weakening

molecular bonds [28]. That is called a Brownian motion as proposed by

Xuan and Roetzel [29]. Besides, the increase in vol.% of Al2O3 at the

component of nanofluids, the thermal conductivity will increase. Due to the

high thermal conductivity of Al2O3 nanoparticles, as compared to SiO2

nanoparticles, it leads to an important role for the better enhancement in the

physical properties of base fluid [16].

Figure 5: Thermal conductivity of DW and various nanofluids as a

function of temperature.

3.2.2.Density

The physical properties of nanofluid is specified by each of

nanoparticles and base fluid. The density of nanofluid is one of these

properties that changes according to the density of nanoparticles and the

base fluid. Since the solid have a density greater than the liquid, the adding

of the nanoparticles will raise the density of the base fluid. Fig. 6 presents

the experimental data of densities that measured for DW andnano fluids

(single and hybrid phase) with different temperatures.The figure shows that

the Al2O3/DW has a higher density than other nanofluids at all

temperatures, because of the high density of Al2O3 nanoparticles[16]. For

the hybrid nanofluids, density increased with increase in the quantity of

Al2O3 nanoparticles due to its high density compared to SiO2

nanoparticles[21]. It is shown also that density decreases with the increase

of temperature to 70 °C for all samples and the decreasing tendency was

slight. With the rise in temperature, the volume usually increases because

the faster-moving molecules are further apart, which is cause a slightly

decreasing in the density [21].

46 MARWA S.J. , HASAN. I. DAWOOD /AL-QADISIYAH JOURNALFOR ENGINEERING SCIENCES 14 (2021) 042–047

Figure 6: Densities of DW and various nanofluids as a function of

temperatures

3.2.3.Specific heat

Heat transfer is significantly influenced by specific heat. Specific heat

of nanofluid as the other physical properties depends on suspended

nanoparticles and the base fluid .Fig. 7 shows the changes in specific heat

for all nanofluids samples at various temperatures. Moreover, as shown in

this figure, the specific heat of DW ishigher than other samples. The lower

specific heat of nanoparticles is the reason that explains why the specific

heat value of the mixture becomes lower than that of base fluid ( 4179.6 J /

kg.k) [11].According to the data of this study, with an increase in

temperature, the specific heat israised steadily and linearly.As the substance

warms up, the normal dynamic vitality of the atoms increments. The

crashes give enough vitality to permit turn to happen, at that point adds to

the inside vitality and raises the particular warmth[30]. It seems that

specific heat of produced nanofluid depends on the type of dispersants

where with increase the volume fraction of SiO2 to Al2O3in base fluid , the

specific heat will decrease . That because of the specific heat capacity of

SiO2 nanoparticles less than Al2O3 nanoparticles[31].

3.2.4.Viscosity

Viscosities of tried examples were estimated in the temperature scope

of 30 °C–70 °C and plotted in Fig. 8. [6, 32] indicated that there is an

immediate connection among temperature and consistency of all trials in

all conditions contrasted with the base liquid. It is observed that expanding

temperature of the nanofluid diminishes its thickness. As the temperature

expands the vitality level of fluid particles increments and the separation

between the atoms increments and causes an abatement in intermolecular

fascination between lessening inconsistency [16].

Figure 7: Specific heat of DW and various samples as a function of

temperatures.

Figure 8: Results of DW and 0.1vol.% sample viscosities relative to

temperatures.

4. Conclusions

In the present experimental study, the stability period of aluminium

oxide(Al2O3), silicon dioxide(SiO2) and Al2O3–SiO2 hybrid was

investigated at various ultrasonication times. Also, thethermal propertiesof

DW and samples have been estimated at five different temperatures. The

conclusions of the study are elaborated below:

The stability period increases with increasing the ultrasonication time

for all samples.

The SiO2 nanofluid was found to be the most stable coolant, while Al2O3

was found the lowest stable nanofluid.For the hybrid samples, the stability

period increases with the increasing volumetric concentration of

SiO2nanoparticles in the nanofluid.

The thermal properties of nanofluids dependent directly on the

temperature. Moreover, with increasing temperature, the thermal

conductivity and specific heat of nanofluid increase,while density and

viscosity decrease.

The outcome of physical properties (thermal conductivity, density and

specific heat) show that 0.1 vol.% Al2O3/DW has good results when

compared to other working fluids.This means that the Al2O3 nanoparticles

had a preferable thermal performance than SiO2 suspensions. For the hybrid

nanofluids, the thermal properties showed good results with expanding the

volume part of Al2O3 nanoparticles in the base fluid.

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