Exergetic efficiency of passive solar air heater with phase change energy storage material

Thesis Overview

<p> INTRODUCTION<br>1.1 Solar Energy Storage<br>Storage of solar energy is an important issue as solar radiation is a timedependent<br>energy source. Thermal energy can be stored as sensible heat (water<br>and rock), latent heat (water, ice and salt hydrates), heat of reaction, etc.<br>Parameters such as storage period required, economic viability or operating<br>conditions are important in the selection of these methods.<br>Latent heat storage system through phase change material (Paraffin wax) is<br>selected in this study. The reason for this selection is the fact that, the use of<br>PCMs for the thermal energy storage in solar heating systems has received<br>considerable attention in the literature. Major advantages of the system are that,<br>PCMs can store large amounts of heat, changing the phase from solid to liquid. The<br>most important PCMs include Glauber’s salt, calcium chloride hex-hydrate,<br>sodium thiosulphate, sodium carbonate decahydrate, fatty acid, and paraffin wax.<br>PCMs are used in application to heat up buildings, dry food stuff for storage etc.<br>The analysis of quality and quantity of energy in a thermodynamic system is<br>important for energy saving and obtaining efficiency of the system. In this context,<br>the second law of thermodynamics assesses the quality of energy, but the first law<br>focuses on the quantity of energy.<br>Exergy by definition is the maximum work obtained in a reversible system<br>interacting with the environment to attain, equilibrium, considering the<br>environmental parameters (such as temperature and pressure) at the reference<br>state.<br>14<br>There is an increasing interest in the combined utilization of the first and second<br>laws of thermodynamics, using such concepts as exergy (availability, available<br>useful quality energy), entropy generation and irreversibility (exergy destruction) to<br>evaluate the efficiency with the available energy being consumed. Energy analysis<br>allows a thermodynamic evaluation of energy conservation. It provides the<br>necessary tool for a clear distinction between energy losses to the environment and<br>internal irreversibility in the process. Exergy analysis acknowledges the fact that,<br>energy cannot be created nor destroyed, it can be degraded in quality eventually<br>reaching a state in which it is in complete equilibrium with the surroundings and<br>hence of no further use for performing useful task.<br>Furthermore, a comprehensive exergy analysis assessing the magnitude of exergy<br>destruction identifies the location, the magnitude and the source of<br>thermodynamic inefficiencies in a thermal system. This knowledge is useful in<br>directing the attention of process design researchers and practicing engineers to<br>those components of the system being analyzed, that offer the maximum<br>opportunities for improvement.<br>In addition, exergy analyses are a method that uses the conservation of mass and<br>energy principles together with the second law of thermodynamics for the design and<br>analysis of energy system. It can reveal whether or not, it is possible to design more<br>efficient energy system by reducing inefficiencies in the system. The exergy method<br>gives information on the quality of the energy transferred in latent heat energy storage<br>systems such as PCMs and finally obtain the energetic and exergetic performance<br>efficiency of PCMs.<br>15<br>1.2 THE OBJECTIVES OF THIS PROJECT ARE;<br>(1)The objective of this research work is to present results obtained from energy<br>and exergy model for an air heater with phase change material energy storage,<br>(2)To determine how much energy can be stored for a day, using paraffin wax as<br>phase change material,<br>(3)To show that exergy method is a better method to improve system performance<br>than energy method.<br>16 <br></p>