1. Home
2. All Testing
3. Thermal
4. Transient Line-Source (TLS)

Transient Line-Source (TLS) Testing of Materials

Significance and Purpose

The Transient Line-Source (TLS) Technique is a widely used method for measuring the thermal conductivity of materials. This method is valued for its ability to provide fast, accurate, and reliable measurements of thermal conductivity without requiring steady-state conditions. It is ideal for polymers and materials with relatively low to moderate thermal conductivities, such as thermoplastics, thermosets, and composites, making it a preferred choice in industries such as electronics, automotive, and construction.

Relevant ASTM and ISO Standards

The TLS technique is governed by internationally recognized standards, ensuring reliable and reproducible measurements. Key standards include:

• ASTM D5930: Standard Test Method for Thermal Conductivity of Plastics by Means of the Transient Line-Source Technique.
• ISO 22007-1: Plastics — Determination of thermal conductivity and thermal diffusivity — Part 1: General principles.

These standards specify the procedure, equipment, calibration, and calculation methods required to ensure accurate and repeatable measurements.

DatapointLabs Tests for Transient Line-Source Testing

Tests in the DatapointLabs test catalog that reference transient line-source testing are as follows:

General Transient Line-Source Testing (inquire regarding material suitability)

Test	Test Description	Standards
T-101	Thermal Conductivity (Melt)	ASTM D5930
T-102	Thermal Conductivity (Solid)	ASTM D5930
T-103	Thermal Conductivity Scan	ASTM D5930

Principle of Operation

The transient line-source technique is based on the heat transfer around a line heat source embedded in the material. It works as follows:

1. Line Heat Source:
   • A needle-like probe with an embedded heating element and temperature sensor is inserted into the sample material.
2. Transient Heating:
   • A constant, short-duration heat pulse is applied through the heating element.
3. Temperature Response:
   • The temperature rise over time is recorded by the temperature sensor embedded in the probe.
4. Thermal Conductivity Calculation:
   • The relationship between the temperature rise and time is modeled mathematically to calculate the thermal conductivity (k). The governing equation assumes radial heat flow and is expressed as:
     $\mathrm{k}=\frac{\mathrm{Q}}{4\mathrm{\pi }\mathrm{\Delta }\mathrm{T}}\mathrm{l}\mathrm{n}\left(\frac{{\mathrm{t}}_2}{{\mathrm{t}}_1}\right)$

     where Q is the heat input and ΔT is the change in temperature between times t₁ and t₂ over a linear-log region of a plot of T vs. t over the measurement period.

The method assumes the material is isotropic and homogeneous, and the sample must be large enough to minimize edge effects.

Typical Procedure

1. Sample Preparation:
   • For polymeric materials that may be melted, pellets are loaded into the barrel chamber of the transient-line source measurement device.
2. Calibration:
   • If not previously done, calibrate the TLS probe using a standard material with known thermal conductivity (e.g., glycerol, water, or a reference polymer).
3. Instrument Setup:
   • Heat the material pellets in the device barrel chamber until molten.
   • Insert the probe into the molten material and apply a static load to maintain good contact.
   • For melt-state measurement, bring the material to the desired temperature. For solid-state measurement, cool the molten material to a desired temperature below its melting point. Multiple temperatures across both melt and solid state may also be selected for scan measurements across different material temperatures.
4. Measurement:
   • Apply a constant heat pulse through the probe’s heating element for a set duration.
   • Record the temperature response over time using the built-in sensor.
5. Data Analysis:
   • Analyze the temperature vs. time data to calculate the thermal conductivity using the mathematical model specified (e.g. as in ASTM D5930).
6. Repeat Testing:
   • Conduct multiple measurements to ensure repeatability and reliability of the results.

Specimen Types

Specimens used by DatapointLabs in transient line-source testing are as follows:

Specimen Type	DatapointLabs Test IDs
Pellets [Details]	T-101, T-102, T-103

Characterization Measurements

The primary measurement provided by the TLS technique is:

• Thermal Conductivity (k): A material’s ability to conduct heat.

The technique may also indirectly provide information about:

• Thermal Diffusivity (α): The rate at which heat propagates through a material. Determination requires the use of additional material property data (e.g., density and specific heat capacity).

These properties are critical for understanding how materials respond to thermal loads and their ability to transfer heat.

Typical Data Reported (see test descriptions for exact details)

The TLS technique produces the following outputs:

• Thermal Conductivity (k): Reported as a single value or as a function of temperature if multiple tests are conducted at different temperatures.
• Temperature vs. Time Curve: Graphical representation of the material’s temperature response to the heat pulse.
• Measurement Conditions: Including sample dimensions, probe configuration, and environmental parameters (e.g., ambient temperature).

Uncertainty and repeatability of the measurements are also reported to verify the reliability of the results.

Suitable Material Types

The TLS technique is highly versatile and can be applied to a wide range of materials, including:

• Polymers and Plastics: Thermoplastics, thermosets, and composites.
• Rubbers and Elastomers: Materials with low to moderate thermal conductivity.
• Composites: Filled and reinforced materials, such as those containing glass or carbon fibers.
• Powders and Granular Materials: Provided that they can be compacted or molded into a solid form.
• Foams and Insulating Materials: Provided the probe can achieve sufficient thermal contact.

Suitable Applications

The TLS technique is widely used in industries and research fields for applications such as:

• Injection Molding Simulation: Informing heat transfer calculations for injection-molding, thermoforming and blow-simulations.
• Material Development: Evaluating new polymers and composites for improved thermal management.
• Electronics: Characterizing thermal interface materials (TIMs), packaging materials, and other components critical for heat dissipation.
• Automotive: Testing materials for thermal insulation and heat shields in engine compartments and electric vehicles.
• Construction: Assessing the thermal conductivity of insulation materials used in buildings and infrastructure.
• Energy Systems: Measuring the thermal properties of battery materials, solar panel components, and heat exchangers.
• Quality Control: Ensuring consistency in the thermal performance of manufactured products.

Conclusion

The transient line-source (TLS) technique is a fast, accurate, and reliable method for measuring the thermal conductivity of plastics and other low- to moderate-conductivity materials. Its versatility and ease of use make it an invaluable tool for material characterization, quality control, and product development in industries such as electronics, automotive, construction, and energy systems. By following ASTM D5930 and ISO 22007-1 standards, this technique ensures high-quality, reproducible results for thermal property measurements.