THE pH AND ELECTRICAL CONDUCTIVITY MEASUREMENT

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CHAPTER 5: THE pH AND ELECTRICAL CONDUCTIVITY OF NANOFLUIDS

INTRODUCTION

The formation of a stable nanofluid is central to its successful implementation in most engineering systems. For instance, the stability of nanofluids has been shown to affect properties such as viscosity and thermal conductivity. Therefore, to ensure stable  nanofluids, a situation where the van der Waals force is lower than the force of repulsion between particles, surface-active agents (surfactants or dispersants) or electrostatic stabilisation have been proposed [271].
In the case of a surface-active agent that is a chemical method, there is no unique formula for adding the chemical surfactant. Consequently, it involves trial and error, which may not be sustainable for the different possible combinations of the available chemical surfactants. Electrostatic stabilisation, on the other hand, is often achieved by modifying the pH of the nanofluids, which affects the ionic state of the nanoparticle surface [224, 225]. Physical preparation methods, such as an ultrasonication assist mechanism, is another factor that has a significant effect in ensuring the stability of nanofluids [272].
In light of the preceding statements, pH modification appears to be the most sustainable stabilisation method, and is a very important parameter that may facilitate investigations of the fundamental nature of nanofluids [215]. Wong and Kurma [233] also stated that evaluating the electrical conductivity of nanofluids would give a better understanding of the transport properties of the heat transfer fluid. Although some efforts have focused on the study of the effect of the pH value of nanofluids on their heat transfer properties, such as thermal conductivity and viscosity, these studies do not examine the influence of temperature on the pH of nanofluids. Since nanofluids are being proposed for use in heat transfer equipment, such as high-temperature heat exchangers, it is important to understand the influence of temperature on the pH of nanofluids.
As stated in Section 2.5, the electrical conductivity and pH of nanofluids may be related because they are both affected by the ionic configuration within the system [224, 225]. With regard to nanofluids, electrostatic forces become extant and the strength of the electrostatic forces depends on the degree of ionisation of the suspension when nanoparticles are dispersed in the base fluid (e.g. water) [223]. This process alters the electrical properties of the base fluid due to interactions with the particle surface charge. Despite the importance of the electrical conductivity of heat transfer fluids to science and technological advancements, thorough investigations of the electrical conductivity of nanofluids have not been explored. Therefore, there is very limited data available on the electrical conductivity properties of nanofluids.

THE pH AND ELECTRICAL CONDUCTIVITY OF MgO-EG NANOFLUIDS

The influence of temperature on the pH and electrical conductivity of MgO-EG nanofluids

The pH of a solution can change with temperature due to the effect of temperature on the dissociation of weak acid and base groups and the splitting of the water component into H+ and OH. Figure 5.1 presents the influence of temperature on the pH of MgO-EG nanofluid at various volume fractions alongside the base fluid. The pH of the base fluid measured at 25 oC was 6.78, which was in agreement with the manufacturer’s reference value (i.e. 6 to 7.5) and the value reported by Timofeeva et al. [273] (i.e. 6.8). Table 5.1 shows the measured pH and electrical conductivity of EG and of nanofluid samples at room temperature. The presence of MgO gave approximately 60 and 53% enhancement  in  the  pH value  for 20 and  100 nm respectively at 3%  volume fraction. However, these values reduced with an increase in temperature.
The trends, as presented in Figure 5.1, show a significant reduction in pH values between 20 and 70 oC. Similar results were published by Konakanchi et al. [223] on PG/water (60:40)-based nanofluids for Al2O3, SiO2 and ZnO. The fact that temperature variation affects the pH value of MgO-EG nanofluid, which is not the case for the base fluid, illustrates the significance of this research on the stability of the nanofluid.

The effect of volume fraction and particle size on the pH and electrical conductivity of MgO-EG nanofluid

As shown in figures 5.5 and 5.6, increasing the volume fraction of MgO nanoparticles significantly increased the electrical conductivity and pH values with regard to the base fluid. In Figure 5.5 (b), the relative electrical conductivity for all the samples of MgO-EG nanofluid with respect to the volume fraction shows that there are significant enhancements in electrical conductivity values, even at a low MgO volume fraction of 0.1%. The enhancement increases with the increase of the volume fraction of MgO. Clearly, in Figure 5.5 (a), the effect of MgO particle size does not have a definitive pattern on the electrical conductivity of the MgO-EG nanofluid. This trend is unlike those reported by Sarojini et al. [33] on Al2O3-water nanofluid and White et al. [37] on Al2O3– PG nanofluid.

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THE pH AND ELECTRICAL CONDUCTIVITY OF SiO2-EG AND SiO2-GLYCEROL NANOFLUIDS

The results presented here are based on the nanofluid formulated from the same SiO2 nanoparticle dispersed separately in EG and glycerol base fluids.

The influence of temperature on the pH and electrical conductivity of SiO2-EG and SiO2-glycerol nanofluids

The electrical conductivity value of both glycerol and EC within the experimental temperature  range  was  less  than  1.0.  As  shown  in  Figure  5.7,  the  addition  of SiO2 .
nanoparticles showed a significant jump, especially in SiO2-glycerol nanofluid. Furthermore, similar to the behaviour of MgO-EG nanofluids presented in Section 5.2, as the temperature of the nanofluid increased, the electrical conductivity also increased for both the SiO2-EG and SiO2-glycerol nanofluids

DECLARATIONi
DEDICATION
ACKNOWLEDGEMENTS
ABSTRACT
TABLE OF CONTENTS
LIST OF FIGURES
LIST OF TABLES
NOMENCLATURE
PUBLICATIONS IN JOURNALS AND CONFERENCE PROCEEDINGS
CHAPTER 1:    INTRODUCTION
1.1BACKGROUND
1.2AIM OF THIS RESEARCH
1.3 RESEARCH OBJECTIVES
1.4SCOPE OF THE STUDY
1.5ORGANISATION OF THE THESIS
CHAPTER 2:    LITERATURE REVIEW
2.1INTRODUCTION
2.2THEORETICAL BACKGROUND OF SUSPENSION RHEOLOGY
2.2.1Classical theoretical viscosity models
2.2.2New theoretical models
2.2.3Empirical models
2.3EXPERIMENTAL STUDIES
2.3.1Methods of preparation of nanoparticles and nanofluids
2.3.2Nanofluid stability
2.3.3Experimental set-ups
2.3.4Parameters involved in the effective viscosity of nanofluids
2.4MODELLING NANOFLUID PROPERTIES WITH ARTIFICIAL INTELLIGENCE
2.5THE pH OF NANOFLUIDS
2.6ELECTRICAL CONDUCTIVITY
2.7CONCLUSION
CHAPTER 3:    METHODOLOGY
3.1INTRODUCTION
3.2MATERIALS AND EQUIPMENT
3.2.1Materials
3.2.2Equipment
3.3NANOPARTICLES’ CHARACTERISATION AND NANOFLUIDS’ PREPARATION
3.4VISCOSITY MEASUREMENT
3.5THE pH AND ELECTRICAL CONDUCTIVITY MEASUREMENT
3.5.1The pH measurement
3.5.2Electrical conductivity measurement
3.6UNCERTAINTY ANALYSIS
3.6.1Uncertainty in viscosity measurement
3.6.2Uncertainty in pH and electrical conductivity measurement
3.7MODELLING
3.8CONCLUSION
CHAPTER 4:    VISCOSITY OF NANOFLUIDS
4.1INTRODUCTION
4.2CHARACTERISATION AND VISCOSITY OF Al2O3-GLYCEROL NANOFLUIDS
4.2.1The characterisation of Al2O3 nanoparticles and nanofluids
4.2.2Influence of ultrasonication energy density
4.2.3Influence of temperature
4.2.4Influence of Al2O3 concentration and size on the dispersion viscosityCHARACTERISATION AND VISCOSITY OF MgO-EG NANOFLUIDS
4.3CHARACTERISATION AND VISCOSITY OF SiO2-GLYCEROL AND SiO2 EG NANOFLUIDS
4.3.1SiO2 nanoparticle and nanofluid characterisation
4.3.2Influence of temperature
4.3.3Influence of volume fraction
4.4EG NANOFLUIDS
4.4.1SiO2 nanoparticle and nanofluid characterisation
4.4.2Influence of temperature
4.4.3Influence of volume fraction
4.5THE EFFECT OF DIFFERENT BASE FLUIDS ON VISCOSITY
4.6THE EFFECT OF DIFFERENT BASE FLUIDS ON VISCOSITY ENHANCEMENT
4.7CONCLUSION AND RECOMMENDATIONS
CHAPTER 5:    THE pH AND ELECTRICAL CONDUCTIVITY OF NANOFLUIDS
5.1INTRODUCTION
5.2THE pH AND ELECTRICAL CONDUCTIVITY OF MgO-EG 103
5.2.1The influence of temperature on the pH and electrical conductivity of MgO-EG nanofluids
5.2.2The effect of volume fraction and particle size on the pH and electrical conductivity of MgO-EG nanofluid
5.3THE pH AND ELECTRICAL CONDUCTIVITY OF SiO2-EG AND SiO2 GLYCEROL NANOFLUIDS
5.3.1The influence of temperature on the pH and electrical conductivity of SiO2-EG and SiO2-glycerol nanofluids
5.3.2The influence of volume fraction on the pH and electrical conductivity of SiO2 EG and SiO2-glycerol nanofluids
5.4THE INFLUENCE OF DIFFERENT BASE FLUIDS ON THE PH AND ELECTRICAL CONDUCTIVITY OF NANOFLUIDS
5.5CONCLUSION AND RECOMMENDATIONS
CHAPTER 6:    MODEL DEVELOPMENT FOR NANOFLUID VISCOSITY
6.1INTRODUCTION
6.2MODELLING THE VISCOSITY OF MgO-EG NANOFLUIDS
6.2.1Modelling the viscosity of MgO-EG nanofluids using non-dimensional analysis
6.2.2Modelling the viscosity of MgO-EG nanofluid using FCM-ANFIS and GA-PNN modelling techniques
6.3MODELLING THE VISCOSITY OF Al2O3-GLYCEROL NANOFLUIDS
6.3.1Modelling the viscosity of Al2O3-glycerol nanofluids using non-dimensional analysis
6.3.2Modelling the viscosity of Al2O3-glycerol nanofluids using the GMDH-NN modelling technique
6.4MODELLING THE VISCOSITY OF SiO2-EG AND SiO2-GLYCEROL NANOFLUIDS
6.4.1Modelling the viscosity of SiO2-EG and SiO2-glycerol nanofluids with non- dimensional analysis
6.4.2Modelling the viscosity of SiO2-EG and SiO2-glycerol nanofluids using the GMDH-NN modelling technique
6.5CONCLUSION AND RECOMMENDATION
CHAPTER 7:    CONCLUSIONS AND RECOMMENDATIONS
7.1SUMMARY
7.2CONCLUSIONS
7.3RECOMMENDATIONS
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