(A) Study on Heat and Mass Transfer Enhancement by Binary Nanofluids and Nanoemulsions for Absorption System Application

다국어 초록 (Multilingual Abstract)

As one of the most renowned refrigeration system, the vapor compression systems still occupy most of the refrigeration systems. The CFCs refrigerants used for these systems have environmental problems such as global-warming and ozone-layer-depletion, which are critical problems throughout the world. For this reason, many countries have developed various policies and reinforced regulations. A great deal of research is being conducted to study alternative energy and new regeneration energy, and now it faces a major turning point for energy field. The absorption refrigeration system using the binary mixture such as NH3/H2O or H2O/LiBr is considered as an alternative to the vapor compression system which causes the environmental problems such as global warming and ozone-layer-depletion. Absorption system is the thermal-driven cycle which can be used as the heat sources as waste heat, solar and geothermal energy.
The absorption heat transfer performance of the absorption system could be greatly improved with advanced refrigerant such as binary nanofluids or binary nanoemulsions. Nanofluids are defined as a fluids in which nano-particles below 100 nm in diameter are stably suspended in the basefluids. Also binary nanofluids are defined as the nanofluids in which the base fluid is a binary mixture, such as NH3/H2O. Nano-technology has been applied to the absorption area to improve the heat and mass transfer performance. It has been reported that the effective thermal conductivity of working fluids can be improved greatly by adding nanoparticles. In addition, nanoemulsions were suggested to solve the problems such as sedimentation, cohesion and corrosion which happen conventionally in heterogeneous solid/liquid mixture with solid particles. Up to now, most studies for nanoemulsions have focused on application to the drugs, cosmetics, etc. but it has only recently become the study to improve the heat and mass transfer performance. Nanoemulsions mean stable fluids that have dispersed immiscible nano sized droplets in base fluids.
In this paper, the relation between the dispersion stability and the absorption heat transfer for binary nanofluids/nanoemulsions are analyzed. In addition, absorption heat transfer and dispersion stability characteristics of binary nanoemulsions are compared with the binary nanofluids. The concentration and the ratio of nano particle, oil and surfactants are considered as the key parameters. The dispersion stability of binary nanofluids/nanoemulsions is evaluated by the droplet size and Tyndall effect analysis.
For the NH3/H2O binary nanofluids, the heat transfer rate and absorption rate with 0.02 vol% Al2O3 nano particles were found to be 29% and 18% higher than those without nanoparticles, respectively. For the NH3/H2O nanoemulsions, the heat transfer rate and absorption rate with 0.04 vol% n-Decane are found to be 26% and 22% higher than those without the nano size oil droplets, respectively. It is experimentally found that a strong relationship between the dispersion stability and the heat and mass transfer performance should be existed. It is expected that this study will give some basic idea to understand the heat and mass transfer enhancement mechanism in multi-components nanofluids.

목차 (Table of Contents)

• TABLE OF CONTENTS
• ABSTRACT i
• TABLE OF CONTENTS iii
• LIST OF FIGURES vi
• LIST OF TABLES ix
• NOMENCLATURE x
• CHAPTER 1. INTRODUCTION 1
• 1.1 Background and Motivation 1
• 1.2 Scope and Objectives of Research 2
• 1.3 The Constitution of Thesis 3
• CHAPTER 2. ABSORPTION SYSTEM 4
• 2.1 Absorption System for Various Refrigerants 6
• 2.2 Advanced Absorption System Cycles 8
• 2.2.1 H2O/LiBr absorption cycles 8
• 2.2.2 NH3/H2O absorption cycles 16
• 2.3 Summary of Chapter 2 26
• CHAPTER 3. BINARY NANOFLUIDS/NANOEMULSIONS 27
• 3.1 Binary Nanofluids/Nanoemulsions as Next Generation Refrigerant 27
• 3.2 Theoretical Background 29
• 3.2.1 Heat and mass transfer enhancement mechanisms 29
• 3.2.2 Dispersion stability and destabilization mechanisms 30
• 3.3 Summary of Chapter 3 37
• CHAPTER 4. DISPERSION STABILITY EVALUATION 38
• 4.1 Experimental Procedures 38
• 4.1.1 Binary nanofluids/nanoemulsions preparation 38
• 4.1.2 Dispersion stability evaluation methods 44
• 4.2 Experimental Result 46
• 4.2.1 Dispersion stability visualization 46
• 4.2.2 Particle and droplet size analysis 49
• 4.2.3 Tyndall phenomenon analysis 63
• 4.3 Summary of Chapter 4 65
• CHAPTER 5. EXPERIMENT OF ABSORPTION HEAT TRANSFER 67
• 5.1 Experimental Equipments and Procedures 67
• 5.2 Data Reduction 72
• 5.3 Result and Discussion 74
• 5.3.1 Ammonia concentration verification 74
• 5.3.2 Absorption performance 76
• 5.3.3 Heat transfer performance 82
• 5.4 Summary of Chapter 5 87
• CHAPTER 6. ABSORPTION HEAT TRANSFER ENHANCEMENT MODEL 88
• 6.1 Heat and Mass Diffusion on the Pool Type Absorption Process 88
• 6.2 Enhanced Diffusion Area Model 91
• 6.3 Experimental Validation 93
• CHAPTER 7. CONCLUSIONS 101
• 7.1 Dispersion Stability 102
• 7.1.1 Binary nanofluids 102
• 7.1.2 Binary nanoemulsions 103
• 7.2 Absorption Heat Transfer 104
• 7.2.1 Binary nanofluids 104
• 7.2.2 Binary nanoemulsions 105
• 7.3 Concluding Remarks 106
• LIST OF REFERENCE 107