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.
TABLE OF CONTENTS
Abstract – – – – – – – – – – i
Table of Contents – – – – – – – – – ii
Nomenclature – – – – – – – – – – iii
1. Introduction – – – – – – – – – 1
1.1 Objectives of Research – – – – – – – 3
2. Literature Review – – – – – – – – 4
2.2 Solar radiation- – – – – – – – – 8
2.3 The behavior of phase change material for charging periods – – – 13
3. The Energy analysis of the Absorber Plate – – – – – 15
3.1 The Exergy equation of the solar collector – – – – – 19
3.2 The Phase change material – – – – – – – 23
3.3 The Energy Balance Equation of PCM in cylindrical pipe for storing period 24
3.4 The Exergy Balance Equation of PCM – – – – – 26
4. Results and Discussion – – – – – – – 29
5. Conclusions – – – – – – – – – 61
References – – – – – – – – – 62
Appendix A Computer program of the equation models – – 65
Appendix B Tables that show the results of the equation models – – 67
1.1 Solar Energy Storage
Storage of solar energy is an important issue as solar radiation is a timedependent
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
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.
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