Thermal Analysis Methods in Thermal Energy Storage

By Sarah Ackermann, Laboratory Services Manager

Thermal energy storage (TES) refers to a family of technologies designed to capture heat energy and store or transport it for later use. It includes methods of latent heat storage, such as phase-change materials; methods of sensible heat storage including heat-transfer fluids; and heat storage through reversible chemical reactions, such as adsorption cycles and salt hydrate technologies. As these technologies have improved and matured, the use of thermal analysis methods in thermal energy storage applications has expanded. Now, researchers use thermogravimetric analysis to understand thermal stability and aging, differential scanning calorimetry to understand phase transitions and heat capacity effects, rheology to understand viscoelastic behavior, and thermal conductivity analysis to understand the heat-transfer behavior of these systems.

What is Thermal Analysis?

Thermal analysis is a family of techniques which study the variation of material properties as a function of temperature and the responses of materials to temperatures. These techniques are crucial tools for researchers and engineers in the field of thermal energy storage. It allows them to understand the thermal behavior of materials and their suitability for various applications. In this article, we will review some of the most commonly used thermal analysis methods, including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), rheology, and thermal conductivity.

Differential Scanning Calorimetry

Differential Scanning Calorimetry (DSC) is a technique that measures the heat absorbed or released by a sample as a function of temperature. It is used to determine the heat capacity, enthalpy, and specific heat of a material. DSC is particularly useful in studying phase transitions, chemical reactions, and thermal stability. In the field of thermal energy storage, researchers and engineers can use DSC to determine the heat required to melt a material or the cooling capacity of a certain amount of heat-transfer fluid. This technique can be paired with thermogravimetric analysis, evolved gas analysis or sample observation to shed more light on the behavior of the sample.

In the video above, ethylene glycol, a commonly used ingredient in coolant systems, is frozen and melted in a DSC with sample observation – with the aid of the camera, the viewer can see how much faster the freezing process is compared to the melt and how the glycol freezes from the nucleation sites along the edge of the pan in towards the center, but it melts more uniformly. Understanding freeze-melt kinetics like this can impact the suitability of a phase-change material for different applications.

Thermogravimetric Analysis

Thermogravimetric analysis (TGA) is a method of thermal analysis in which the mass of a sample is measured over time as the temperature changes. TGA provides information about physical phenomena associated with mass changes such as decomposition, adsorption, and desorption. Researchers and engineers can use TGA to evaluate the thermal stability of a material, determine its upper use temperature, and analyze characteristic decomposition patterns. TGA as a technique can be paired with DSC or Differential Thermal Analysis (DTA), sample observation, and evolved gas analysis to understand more about the reactions of the material.

In the video above, PET is heated and decomposed, illustrating the use of TGA – coupled with sample observation and DTA – to understand the thermal stability of a material.x

Rheometry

Rheometry is the applied practice of rheology to measure a material’s rheological properties, such as a fluid’s resistance to flow (viscosity) or viscoelastic behavior of non-Newtonian fluids and soft solids. Viscosity is a fundamental property of liquids and gases and is related to the internal friction within the fluid. It is an important parameter in the design of heat exchangers, pumps, and other fluid handling equipment. Researchers and engineers can use rheometry measurements to determine the flow behavior of fluids, optimize the performance of heat transfer fluids, and evaluate the stability of emulsions and suspensions. Rheological behavior can be measured on thick materials with dynamic mechanical analysis (DMA), or using rheometers on viscoelastic materials and liquids, while a basic viscometer is appropriate for thin, Newtonian fluids.

The webinar above highlights the use of DMA in identifying the viscoelastic properties of polymer-based heat sinks, showing the role of DMA in better understanding lightweight solutions for heat capture in thermal energy storage systems.

Thermal Conductivity

Thermal conductivity measures a material’s ability to conduct heat. It is a critical parameter in designing thermal energy storage systems, heat exchangers, and other thermal management devices. Researchers and engineers can use thermal conductivity measurements to evaluate the thermal performance of materials, optimize the design of thermal energy storage systems, and analyze the thermal behavior of composite materials. Thermal conductivity testing includes many methods, each of which is suited to different sample thermal conductivity ranges and geometries. Some of the most commonly used in the field of thermal energy storage include Modifed Transient Plane Source, Transient Plane Source, Transient Line Source, and Transient Hot Wire. Details on the methods and their strengths and weaknesses can be found in our Method Selection Guide.

The webinar linked above shows the use of thermal conductivity testing in analyzing and understanding of battery pack cooling systems, used to stabilize battery temperature and performance.

Conclusion

In conclusion, thermal analysis is a powerful tool for researchers and engineers in the field of thermal energy storage. Calorimetry, thermogravimetric analysis, viscosity, and thermal conductivity are just a few of the many methods available for analyzing the thermal behavior of materials. By understanding the principles and applications of these methods, researchers and engineers can develop new materials, optimize existing systems, and advance the field of thermal energy storage.

Next Steps

If you have thermal energy storage materials you need to understand better, we can help! Click the link here to make an appointment with one of our thermal analysis experts to discuss testing solutions, or you can learn more about our thermal analysis equipment here.