||A Thermodynamic Study on Residential Ammonia Water Absorption Cooling Technology
||International Master Degree Program on Energy Engineering
||Wani Jamaal Morgan
Coefficient of Performance
Conjugate Gradient Method
Humankind currently faces a global challenge in the form of global warming. The root cause of global warming has been attributed to excess atmospheric CO2 caused by burning fossil fuels for energy. To alleviate the impacts of global warming, the demand on fossil fuels must be reduced. Conventional vapor compression refrigeration is an energy demanding process which accounts for up to 20% of the global energy demand. A more carbon neutral alternative to vapor compression is that of absorption refrigeration. Absorption refrigeration is a promising alternative capable of utilizing low grade solar energy for cooling. This paper first uses the first law of thermodynamics to model the steady state performance of this system using the numerical modelling software Engineering Equation Solver (EES). Subsequent to modelling the system was optimized using a conjugate method algorithm. The aim of the optimization was to identify the optimal parameter combination that promotes the highest Coefficient of Performance. Via optimization, the Coefficient of performance of the has been shown to increase by 7.8% when compared to the base line model proposed by Aman et al. In this study a One-at-A-Time sensitivity analysis was also carried out to investigate how each input parameter impacts the optimal performance of the system. It was shown that COP increases with increasing absorber temperature, evaporator temperature and heat exchanger efficiency. Conversely, COP decreases with increasing condenser temperature. The generator temperature uniquely increases the COP until a certain plateau point, subsequent to the plateau point COP decreases with further increase in generator temperature. This study also explores the potential of combining an ejector with the traditional ammonia water absorption model. The ejector proved to be a promising addition to the ARS as it increased the systems COP from 0.65 to 1.33. Furthermore, it was showed that the ejector is uniquely suitable for residential cooling where evaporator temperatures of 16-24oC are required.
List of Figures v
List of Tables vii
Nomenclature and Abbreviations ix
Chapter 1. Introduction 1
1.1 Background 1
1.2 Thermal Comfort 2
1.3 Global Air Conditioning Status 3
1.4 Vapor Compression Refrigeration Systems (VCRS) 3
1.5 Motivation 6
1.6 Study Flow Chart 8
Chapter 2. Absorption Refrigeration Cycles 9
2.1 Three Fluid Absorption Refrigeration System 9
2.2 Two Fluid Absorption Refrigeration System 11
Chapter 3. Thermodynamic Model of Traditional Model of a Single Effect Absorption Refrigeration System 15
Chapter 4. Optimization 23
4.1 Introduction to Optimization 23
4.2 Designing Optimization Problems 23
4.3 Conjugate Gradient Method 24
4.4 Parameter Design 25
4.5 Results and Discussion 26
Chapter 5. Hybrid Absorption Refrigeration Model 35
5.1 First Law Analysis of Hybrid-ejector Model 36
5.2 Operational Parameters 39
5.3 Results and Discussion 40
Chapter 6. Ejector Study 46
6.1 Ejector 46
6.2 Ejector modelling 49
6.3 Model optimization 49
6.4 Results of Ejector Optimization 51
Chapter 7. Conclusions and Future Work 54
Appendix A-Huang’s 1-D model for an Ejector 60
Appendix B-EES Numerical model of the Traditional Absorption Refrigration System 62
Appendix C-EES model of the Hybrid Ejector Ammonia System 67
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