Transient vs Steady State Testing Methods for Thermal Conductivity

By Landen MacDonald, Market Research Analyst

Thermal conductivity is a property that describes a material’s ability to conduct heat [1]. It is an important property for many applications, such as insulation, heat transfer fluids, phase change materials, and thermal interface materials. However, measuring thermal conductivity is not always straightforward, as different methods have different advantages and limitations.

One way to classify thermal conductivity methods is based on whether they are in a steady state or transient. Steady-state methods apply a constant heat flux to a sample and measure the resulting temperature difference across the sample. Transient methods apply a heat pulse or a periodic heat source to a sample and measure the temperature response over time. Both methods have pros and cons, depending on the material type, sample size, test conditions, and accuracy requirements.

Steady-state methods are considered the traditional standard in some applications, such as the guarded hot plate method for building materials. They are based on Fourier’s law of heat conduction, which relates the heat flux, the temperature gradient, and the thermal conductivity. However, steady-state methods have some drawbacks, such as:

• They require large samples, exacting sample preparation, and extended test times.
• They are destructive and do not work for liquids or high thermal conductivity materials.
• They are susceptible to radiative and convective heat losses and errors in the sample thickness.

Transient methods have gained popularity over the past three decades due to their flexibility and speed. They are based on the heat diffusion equation, which describes how heat propagates in a material over time. Transient methods have some advantages, such as:

• They can measure small samples, liquids, powders, pastes, and high thermal conductivity materials.
• They can perform tests in minutes or seconds, with minimal sample preparation and non-destructive testing.
• They can account for heat losses and sample geometry more easily.

However, transient methods also have some challenges, such as:

• They require more complex mathematical analysis and data processing.
• They may have lower accuracy and precision than steady-state methods for some materials.
• They may have difficulty measuring materials with low thermal diffusivity or high thermal resistance.

Therefore, choosing the right method for measuring thermal conductivity depends on the specific application and material. Fortunately, there is a solution that offers the best of both worlds: C-Therm’s Trident platform.

C-Therm’s Trident platform is a versatile and powerful tool for thermal conductivity measurement. It combines three different transient methods in one modular package: the modified transient plane source (MTPS), the transient line source (TLS), and the transient plane source (TPS). Each method has its sensor and configuration, allowing users to select the most suitable one for their samples.

The MTPS method is the most straightforward and most accurate. It uses a single-sided, “plug & play” sensor that can test solids, liquids, powders, and pastes. It offers maximum sample versatility and conforms to ASTM D7984.

The TLS method is the most robust. It uses a stainless steel needle sensor that can test granular materials, powders, slurries, gels, and pastes. It offers maximum durability and conforms to ASTM D5334 and D5930.

The TPS method is the most flexible. It uses a double-sided, flexible sensor that can test isotropic and anisotropic materials. It offers greater control over experimental parameters and conforms to ISO 22007-2 and GB/T 32064.

With C-Therm’s Trident platform, users can enjoy the benefits of transient methods without compromising on accuracy, speed, or flexibility. They can also access C-Therm’s expertise and support and a range of resources and tools to enhance their thermal conductivity testing experience.

If you are interested in learning more about C-Therm’s Trident platform, you can request a quote or book a live technical consultation today. You can also browse C-Therm’s website for more information on applications, products, services, webinars, publications, and testimonials. C-Therm is the leader in thermal conductivity measurement, and the Trident platform is the ultimate toolbox for thermal conductivity characterization.

Reference

[1] John Clifford. “What is Thermal Conductivity? How is it Measured?”. C-Therm Technologies. www.ctherm.com/resources/newsroom/blog/what-is-thermal-conductivity/