Phase Change Materials and Solar Water Heaters
A TECHNICAL REPORT ON PHASE CHANGE MATERIALS &
SOLAR WATER HEATING USING PHASE CHANGE MATERIALS
INDEX
1. Introduction 2. Types of Phase Change Materials 3. Selection criteria 4. Principle of solar water heater with phase change materials 5. Heat transfer analysis between water and PCM’s 6. Results 7. Conclusion
CHAPTER – 1
INTRODUCTION
PHASE CHANGE MATERIALS: The materials which undergo either boiling or condensing by absorbing heat from a medium or liberating heat to a medium are called as phase change materials.
Characteristics
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 rise 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 190 oC. 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.
CHAPTER –
SOLAR WATER HEATING USING PHASE CHANGE MATERIALS
INDEX
1. Introduction 2. Types of Phase Change Materials 3. Selection criteria 4. Principle of solar water heater with phase change materials 5. Heat transfer analysis between water and PCM’s 6. Results 7. Conclusion
CHAPTER – 1
INTRODUCTION
PHASE CHANGE MATERIALS: The materials which undergo either boiling or condensing by absorbing heat from a medium or liberating heat to a medium are called as phase change materials.
Characteristics
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 rise 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 190 oC. 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.
CHAPTER –