23-02-2013, 02:22 PM
ADVANCE RESURCH IN SOLAR WATER HEATER BY P.C.M.
ADVANCE RESURCH.docx (Size: 247.38 KB / Downloads: 24)
INTRODUCTION:
There are many sources available to heating the water. But the most convenient method of heating water is solar energy, because of its availability. In ordinary solar water heater works on the principle of sensible heating but our solar water heater works on the principle of latent heat storing by Phase Chang Material(P.C.M.) viz,Paraffin Wax .
Latent heat means, the phase change material can store some amount of heat, and dissipate whenever system necessary. The main application of our project is, it is used mainly where the space restriction limit larger thermal storage units in direct gain or sunspace passive solar system. Latent heat thermal energy storage is one of the most efficient ways to store thermal energy for heating water by energy received from sun. This paper summarizes the investigation and analysis of thermal energy storage incorporating with and without PCM for use in solar water heaters. It has been demonstrated that for a better thermal performance of solar water heater a phase change material with high latent heat and with large surface area for heat transfer is required.
Phase Change Material:
A phase change material (PCM) is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. Heat is absorbed or released when the material changes from solid to liquid and vice versa; thus, PCMs are classified as latent heat storage (LHS) units.
PCMs latent heat storage can be achieved through solid-solid, solid-liquid, solid-gas and liquid-gas phase change. However, the only phase change used for PCMs is the solid-liquid change. Liquid-gas phase changes are not practical for use as thermal storage due to the large volumes or high pressures required to store the materials when in their gas phase. Liquid-gas transitions do have a higher heat of transformation than solid-liquid transitions. Solid-solid phase changes are typically very slow and have a rather low heat of transformation.
Initially, the solid-liquid PCMs behave like sensible heat storage (SHS) materials; their temperature rises as they absorb heat. Unlike conventional SHS, however, when PCMs reach the temperature at which they change phase (their melting temperature) they absorb large amounts of heat at an almost constant temperature. The PCM continues to absorb heat without a significant raise in temperature until all the material is transformed to the liquid phase. When the ambient temperature around a liquid material falls, the PCM solidifies, releasing its stored latent heat. A large number of PCMs are available in any required temperature range from -5 up to 190oC .Within the human comfort range of 20° to 30°C, some PCMs are very effective. They store 5 to 14 times more heat per unit volume than conventional storage materials such as water, masonry, or rock