ABSTRACT
Energy and exergy analysis of solar air heater with phase change material energy storage is considered in this research work. Energy and exergy models for component systems like flat plate solar collector and phase change material in one-dimensional heat conduction in a cylindrical pipe, for storing periods were obtained. Exergy analysis, which is based on the second law of thermodynamics, and energy analysis, which is based on first law, was applied to improve system efficiency. Measured data, like hourly insolation, collector temperature, PCM temperature, environmental temperature and air flow rate were used as an input on the energy and exergy models to determine system performance. The Software, Engineering Equation Solver (EES) was used to solve the generated equation models. The results of the analysis revealed that the average energy and exergy efficiencies were 48% and 35% respectively.
CHAPTER ONE
INTRODUCTION
1.1 Solar Energy Storage
Storage of solar energy is an important issue as solar radiation is a time- dependent energy source. Thermal energy can be stored as sensible heat (water and rock), latent heat (water, ice and salt hydrates), heat of reaction, etc. Parameters such as storage period required, economic viability or operating conditions are important in the selection of these methods.
Latent heat storage system through phase change material (Paraffin wax) is
selected in this study. The reason for this selection is the fact that, the use of PCMs for the thermal energy storage in solar heating systems has received considerable attention in the literature. Major advantages of the system are that, PCMs can store large amounts of heat, changing the phase from solid to liquid. The most important PCMs include Glauber’s salt, calcium chloride hex-hydrate, sodium thiosulphate, sodium carbonate decahydrate, fatty acid, and paraffin wax. PCMs are used in application to heat up buildings, dry food stuff for storage etc. The analysis of quality and quantity of energy in a thermodynamic system is important for energy saving and obtaining efficiency of the system. In this context, the second law of thermodynamics assesses the quality of energy, but the first law focuses on the quantity of energy.
Exergy by definition is the maximum work obtained in a reversible system interacting with the environment to attain, equilibrium, considering the environmental parameters (such as temperature and pressure) at the reference state.
There is an increasing interest in the combined utilization of the first and second laws of thermodynamics, using such concepts as exergy (availability, available useful quality energy), entropy generation and irreversibility (exergy destruction) to evaluate the efficiency with the available energy being consumed. Energy analysis allows a thermodynamic evaluation of energy conservation. It provides the necessary tool for a clear distinction between energy losses to the environment and internal irreversibility in the process. Exergy analysis acknowledges the fact that, energy cannot be created nor destroyed, it can be degraded in quality eventually reaching a state in which it is in complete equilibrium with the surroundings and hence of no further use for performing useful task.
Furthermore, a comprehensive exergy analysis assessing the magnitude of exergy destruction identifies the location, the magnitude and the source of thermodynamic inefficiencies in a thermal system. This knowledge is useful in directing the attention of process design researchers and practicing engineers to those components of the system being analyzed, that offer the maximum opportunities for improvement.
In addition, exergy analyses are a method that uses the conservation of mass and energy principles together with the second law of thermodynamics for the design and analysis of energy system. It can reveal whether or not, it is possible to design more efficient energy system by reducing inefficiencies in the system. The exergy method gives information on the quality of the energy transferred in latent heat energy storage systems such as PCMs and finally obtain the energetic and exergetic performance efficiency of PCMs.
1.2 THE OBJECTIVES OF THIS PROJECT ARE;
(1)The objective of this research work is to present results obtained from energy and exergy model for an air heater with phase change material energy storage,
(2)To determine how much energy can be stored for a day, using paraffin wax as phase change material,
(3)To show that exergy method is a better method to improve system performance than energy method.
This material content is developed to serve as a GUIDE for students to conduct academic research
EXERGETIC EFFICIENCY OF PASSIVE SOLAR AIR HEATER WITH PHASE CHANGE ENERGY STORAGE MATERIAL
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