Sensible heat storage is a method of thermal energy storage that involves storing heat in a material without changing its phase. The process relies on increasing the temperature of the storage medium, and the amount of heat stored is directly proportional to the temperature change. Sensible heat storage is widely used in various solar thermal applications, such as solar water heating systems and solar space heating. Here are the principles and common materials used in sensible heat storage:
Principles of Sensible Heat Storage:
1. Heat Capacity: The ability of a material to store heat is determined by its specific heat capacity, which is the amount of heat required to raise the temperature of a unit mass of the material by one degree Celsius (or Kelvin). Materials with higher specific heat capacity can store more heat energy per unit mass.
2. Temperature Differential: The amount of heat stored in sensible heat storage is directly proportional to the temperature difference between the initial state of the storage medium and its final state after energy is stored. The greater the temperature difference, the more heat energy can be stored.
3. Heat Transfer: Sensible heat storage involves heat transfer between the storage material and the fluid (e.g., water or air) that passes through the storage system. During charging (heat absorption), the fluid transfers its heat to the storage material, raising its temperature. During discharging (heat release), the stored heat is transferred back to the fluid.
Common Materials Used in Sensible Heat Storage:
1. Water: Water is one of the most commonly used materials for sensible heat storage due to its high specific heat capacity (4.186 J/g°C). Water can be stored in insulated tanks, and it is particularly effective for low to medium-temperature applications, such as solar water heating for domestic and industrial purposes.
2. Rocks and Gravel: Rocks and gravel are abundant and low-cost materials that can be used for sensible heat storage. They have relatively high specific heat capacities and can be used in rock beds or underground caverns to store thermal energy for longer durations.
3. Concrete: Concrete is a widely used construction material that also possesses good thermal properties, making it suitable for sensible heat storage applications. Concrete can be used in the form of blocks or as part of building structures to store heat.
4. Bricks: Bricks are another common material used for sensible heat storage. They have decent thermal properties and can be used in various configurations, such as brick walls or brick-filled containers, to store heat.
5. Phase Change Materials (PCMs): Although PCMs are typically associated with latent heat storage, some materials can also be used for sensible heat storage. Certain PCMs have a specific heat capacity comparable to water, making them suitable for sensible heat storage applications.
6. Air: In some applications, air can be used as the storage medium for sensible heat. Air-based systems are typically used for lower temperature storage and can be more suitable for space heating applications.
The selection of a suitable material for sensible heat storage depends on factors such as the desired operating temperature range, the amount of heat to be stored, the duration of storage, and economic considerations. Sensible heat storage systems are relatively simple and cost-effective, making them a practical solution for various solar thermal applications.