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ENHANCING THE HEAT ENERGY USING PHASE CHANGE MATERIAL

 

Phase Change Materials (PCMs) are widely used in solar air heaters to improve their efficiency by storing excess thermal energy during the day and releasing it during periods of low or no solar radiation (e.g., nighttime or cloudy weather). This ability to store heat helps to smooth out temperature fluctuations and maintain a more consistent air temperature in solar heating systems.

Here’s a breakdown of how PCMs are integrated into solar air heaters:

MATERIAL SELECTION:

PCMs absorb, store, and release latent heat during the phase change, typically between solid and liquid phases. For solar air heaters, suitable PCMs are selected based on:

  • Melting Point: The PCM’s melting temperature should match the desired operational temperature of the solar air heater. Typical PCMs used in solar applications melt at temperatures between 30°C and 80°C.
  • Thermal Storage Capacity: PCMs with high latent heat storage capacity allow efficient energy storage.

Common PCMs:

  • Organic Compounds (e.g., paraffin wax): Widely used due to their moderate melting points, non-corrosiveness, and stability.
  • Inorganic Compounds (e.g., salt hydrates): Have higher energy densities but may suffer from issues like phase segregation or corrosion.
  • Eutectic Mixtures: Combine organic and inorganic components for optimized performance across specific temperature ranges.

WORKING PRINCIPLE:

  • During the day: The solar air heater collects solar radiation, heating the air inside. The PCM absorbs the excess heat as it changes from solid to liquid (latent heat storage), preventing overheating and maintaining a balanced temperature.
  • During the night or low solar radiation: As the air temperature drops, the PCM solidifies and releases the stored heat, warming the air that passes through the system.

SYSTEM DESIGN CONSIDERATIONS:

  • Placement of PCM: The PCM is typically integrated into the back of the absorber plate or in separate thermal storage chambers. It is crucial to ensure that the airflow comes into contact with the PCM to maximize heat exchange.
  • Heat Transfer Enhancements: The rate of heat exchange between the air and PCM can be increased through finned surfaces or by using materials with higher thermal conductivity.

ADVANTAGES:

  • Improved Efficiency: By storing thermal energy, the solar air heater can supply heat even after sunset or during cloudy conditions.
  • Temperature Stability: PCMs help in maintaining a more uniform temperature, which is beneficial for various applications, such as drying processes or space heating.

CHALLENGES:

  • Cost of Materials: Some PCMs, especially advanced ones, can be expensive, impacting the overall system cost.
  • Thermal Conductivity: Many PCMs, especially paraffin-based ones, have low thermal conductivity, which can limit the rate of heat transfer.
  • Long-Term Stability: Some PCMs may experience degradation or phase separation over time, affecting their performance.

APPLICATIONS:

  • Residential and Commercial Space Heating: Solar air heaters with PCMs can provide reliable heating for buildings, reducing dependence on conventional energy sources.
  • Solar Dryers: PCMs in solar dryers can help maintain a steady temperature, improving drying efficiency for agricultural products.
  • Industrial Heating: Processes requiring consistent heat over time can benefit from PCM-enhanced solar air heaters.

Incorporating phase change materials into solar air heaters allows for more efficient thermal energy management, making them a valuable technology for enhancing solar energy applications.

Phase Change Materials (PCMs) are widely used in solar air heaters to improve their efficiency by storing excess thermal energy during the day and releasing it during periods of low or no solar radiation (e.g., nighttime or cloudy weather). This ability to store heat helps to smooth out temperature fluctuations and maintain a more consistent air temperature in solar heating systems.

Material Selection: PCMs absorb, store, and release latent heat during phase transitions between solid and liquid states. For solar air warmers, appropriate PCMs are selected based on:

• Melting Point: The PCM should match the solar air heater's required operating temperature. PCMs used in solar applications typically melt at temperatures ranging from 30°C to 80°C. They have significant latent heat storage capacity, enabling effective energy storage.

Common PCMs include organic compounds such as paraffin wax, which are widely employed due to their low melting points, non-corrosive properties, and stability.

• Inorganic compounds, such as salt hydrates, have higher energy densities but may suffer from phase segregation or corrosion.

• Eutectic Mixtures: Combine organic and inorganic components for optimal performance throughout temperature ranges.

The solar air heater heats the indoor air by collecting solar energy during the day. The PCM absorbs surplus heat as it transitions from solid to liquid (latent heat storage), preventing overheating and maintaining a steady temperature.

• During nighttime or low solar radiation, the PCM freezes and releases heat, warming the air passing through the system.

The following factors are taken into account while designing a system: 

• PCM placement: Usually, the PCM is integrated into the absorber plate's back or is housed in distinct thermal storage chambers. For the PCM to receive as much heat exchange as possible, the airflow must come into touch with it.

• Heat Transfer Enhancements: Finned surfaces and materials with better thermal conductivity can both speed up the rate of heat exchange between the air and PCM

PCM advantages are Improved Efficiency: Because the solar air heater can store thermal energy, it can stay warm in cloudy or dusk conditions.

A multitude of applications, such as space heating and drying processes, benefit from temperature stability, which is facilitated by the use of PCMs.

PCM usage and challenges Expense of Materials: Certain PCMs, especially complex ones, can have an impact on the price of a system.

The speed at which heat is transmitted may be restricted by the low thermal conductivity of certain PCMs, especially those based on paraffin.

Long Term Stability: Phase-separated PCMs may degrade over time, reducing their usefulness.

APPLICATIONS: 

• Residential and Commercial Space Heating: By utilizing photovoltaic cells (PCMs), solar air heaters may dependablely heat buildings, hence mitigating reliance on traditional energy sources.

• Solar Dryers: By assisting in the maintenance of a constant temperature, PCMs in solar dryers can increase the drying efficiency of agricultural products.

• Industrial Heating: PCM-enhanced solar air heaters are beneficial for processes that need constant heat over an extended period of time.

Phase change materials are a useful technology for improving solar energy applications because they enable more effective thermal energy management in solar air heaters.


Author Bios:

1. R.Arivazhagan, ASP/Mech

2. Antony Jerish.M, IV/Mech

3. Hariharan.K, IV/Mech


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