Phase-Change Thermal Battery for Night Heat Reuse

ISEF Category: Energy: Sustainable Materials and Design

Subcategory: Energy Storage  ·  Difficulty: Intermediate  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

A candle can store heat in a solid block and release it much later. That same idea can help a home keep warmth after sunset. You can test this with materials you can buy online or find in a kitchen. Your project can measure how well a blend holds and releases heat.

What Is It?

A phase-change material, or PCM, stores energy when it melts and gives that energy back when it hardens. Think of it like a thermal sponge. Instead of soaking up water, it soaks up heat. Paraffin wax and coconut oil are both common PCMs because they change phase near room or household temperatures.

A thermal battery uses that behavior to save heat for later use. During the day, the material absorbs warmth as it melts. At night, it cools and releases that stored heat more slowly. If you mix materials, you can shift the melting range and change how much heat the blend can store.

A DIY calorimeter lets you measure latent heat, which is the heat absorbed or released during a phase change. In plain terms, latent heat is the extra energy that goes into melting or freezing, not just warming the material up. That makes it a strong topic for a science fair project, because you can turn a simple kitchen-like setup into real data.

Why This Is a Good Topic

This topic works well because you can change one thing at a time, like blend ratio, container shape, or cooling setup, and measure a clear result. It connects to real problems like keeping homes comfortable with less electricity and storing waste heat from cooking or heating systems. You can learn how to design controls, collect repeatable thermal data, and compare materials with basic statistics. You do not need a fancy lab to start, but you can still make the project feel real and technical.

Research Questions

• How does the paraffin to coconut oil ratio affect the latent heat of the blend?
• What is the effect of blend ratio on the melting and freezing temperature range?
• Does adding a small amount of a filler material change how long the blend stays near its phase-change temperature?
• To what extent does container shape change the heat release rate of the thermal battery?
• Which blend ratio stores the most usable heat near a household comfort temperature?
• How does repeated heating and cooling affect the thermal performance of the blend over time?

Basic Materials

• Paraffin wax or candle wax, in a known amount.
• Refined coconut oil.
• Digital kitchen scale with 0.1 g accuracy.
• Small insulated containers with lids.
• Thermometer or digital temperature probe.
• Hot water bath setup with a heat-safe bowl or pot.
• Stopwatch or timer.
• Stirring sticks or disposable spoons.
• Notebook or spreadsheet for data logging.
• Thermal gloves or tongs for safe handling of warm containers.

Advanced Materials

• Differential scanning calorimeter, if available for validation.
• Thermocouples or temperature probes with data logging.
• Insulated calorimeter vessel with known heat capacity.
• Magnetic stirrer and hot plate.
• Analytical balance.
• Vacuum desiccator for sample preparation.
• DSC reference materials or calibration standards.
• Infrared camera for surface temperature mapping.
• Mold set for identical sample geometry.
• Thermal conductivity measurement setup, if available.

Software & Tools

• Google Sheets: Organizes temperature data, calculates averages, and helps you graph heating and cooling curves.
• Logger Pro: Records probe data in real time if your school has compatible sensors.
• ImageJ: Measures melt-front area or visible phase-change changes from photos.
• Python: Fits curves, compares blend groups, and runs simple statistics on your results.
• PubMed: Helps you find review articles on phase-change materials and thermal storage.

Experiment Steps

1. Define the thermal question you want to answer, and choose one variable to change first, such as blend ratio or container shape.
2. Design a simple comparison method that keeps sample mass, starting temperature, and container type consistent across trials.
3. Build a calibration plan for your DIY calorimeter so you can convert temperature change into stored or released heat.
4. Decide how you will identify the phase-change range, then plan controls that separate melting behavior from ordinary warming and cooling.
5. Set up a repeat-testing plan so you can check whether the material performs the same after several heat and cool cycles.
6. Plan your graphs and statistics before you collect data, so you know whether you are comparing heat capacity, latent heat, or release time.

Common Pitfalls

• Using different container sizes for different blends, which changes heat loss and hides the real material effect.
• Skipping calibration of the DIY calorimeter, which makes your latent heat numbers hard to trust.
• Measuring temperature from the container wall instead of the sample center, which can miss the true phase change.
• Letting the sample composition vary from batch to batch, which makes one blend look better or worse by accident.
• Comparing samples that start at different temperatures, which gives unfair heating and cooling curves.

What Makes This Competitive

A strong version of this project does more than compare two blends. It connects material choice to a clear thermal goal, like keeping a sample near a target indoor temperature for longer. Strong entries also control heat loss well, repeat trials enough to show consistency, and use a clean way to extract latent heat from the data. If you add cycle testing, uncertainty analysis, or a real household use case, the project gets much stronger.

Project Variations

• Test soy wax, paraffin, and coconut oil blends side by side to see which stores the most heat near room temperature.
• Compare the same blend in different container shapes to study how geometry changes thermal release.
• Add a low-cost conductive filler, like graphite powder, and measure whether it speeds heat transfer without hurting storage capacity.

Learn More

• DOE Office of Scientific and Technical Information: Search for review articles on thermal energy storage and phase-change materials.
• NASA Technical Reports Server: Look for reports on latent heat storage, thermal management, and insulation testing.
• NIST Chemistry WebBook: Use it to check physical properties and phase information for common organic materials.
• PubMed: Search for review articles on phase-change materials for thermal storage and household heating applications.
• MIT OpenCourseWare: Find heat transfer and materials science course notes for background on thermal conductivity and energy balance.