Course Content
Thermal conductivity
This is a summary of the unit.
0/6
Introduction
03:34
What is thermal conductivity?
03:10
Applications of thermal properties
06:21
Transient methods for measuring thermal properties
05:39
Methods and standards for thermal properties measurements
05:27
Additional reading
Thermal Conductivity
 

Methods and standards for thermal properties measurement

 

Accurate measurements of thermal properties make it possible to understand heat transfer and storage in a wide range of materials, including soils, rocks, liquids, and engineered compounds. This article introduces the instrumentation used in thermal property analysis, focusing on measurement systems, and it reviews the standards that guide thermal measurement practices.

 

The TEMPOS thermal properties analyzer

The TEMPOS analyzer integrates advanced modeling and measurement capabilities into a portable, battery-powered device suitable for both laboratory and field use. It supports four distinct probe types, each designed for specific applications.

 

TEMPOS components:

  • The TEMPOS handheld unit takes accurate readings of thermal conductivity, thermal resistivity, thermal diffusivity, and specific heat in many material types across multiple disciplines.
The TEMPOS thermal properties analyzer
Figure 1. The TEMPOS thermal properties analyzer

Taking measurements with the TEMPOS requires the selection of one of the following needle probes:

TEMPOS TR-3 large single needle: 100 mm long, 2.4 mm diameter; optimized for porous media like soil
Figure 2. TEMPOS TR-3 large single needle: 100 mm long, 2.4 mm diameter; optimized for porous media like soil
  • The TR-3 large single needle is primarily designed for soil and other granular or porous materials and is the preferred choice if a tight hole can be made to accommodate the sensor. In harder samples, appropriately sized holes can be created using drill bits or pilot pins.
TEMPOS RK-3 thick single needle: 60 mm long, 3.9 mm diameter; robust design for dense, solid materials
Figure 3. TEMPOS RK-3 thick single needle: 60 mm long, 3.9 mm diameter; robust design for dense, solid materials
  • The RK-3 needle is explicitly designed for use in hard materials like rock or cured concrete, after using a 4-mm (5/32-in) rotary hammer bit (included in the RK-3 Rock Sensor Package) to drill a pilot hole in the material. The RK-3 Rock Sensor Package also includes thermal grease, which must be used to provide thermal contact with rock and concrete.
TEMPOS KS-3 small single needle: 60 mm long, 1.3 mm diameter; suitable for viscous liquids, solids, and diverse materials
Figure 4. TEMPOS KS-3 small single needle: 60 mm long, 1.3 mm diameter; suitable for viscous liquids, solids, and diverse materials
  • The KS-3 small single needle works best for liquid samples and insulating materials (thermal conductivity <0.1 W/(m × K)). In low-power mode, this sensor applies a very small amount of heat to the needle, which helps prevent free convection in liquid samples and melting in frozen samples. This sensor also works well for soils and other porous materials, but its small size makes it more susceptible to damage when insertion is difficult.
TEMPOS SH-3 dual-needle: 60 mm long, 1.3 mm diameter; Used for simultaneous heating and temperature sensing, enabling precise measurements of thermal conductivity and diffusivity
Figure 5. TEMPOS SH-3 dual-needle: 60 mm long, 1.3 mm diameter; Used for simultaneous heating and temperature sensing, enabling precise measurements of thermal conductivity and diffusivity
  • The SH-3 needle is used to measure the thermal properties of solid materials. The SH-3 is ideal for measuring volumetric specific heat capacity and thermal diffusivity, and it performs well with high-viscosity liquids, moist soil, granular materials, and cured concrete or rock.
TEMPOS TR-4 small single needle: 100 mm long, 1.9 mm diameter
Figure 6. TEMPOS TR-4 small single needle: 100 mm long, 1.9 mm diameter
  • The dimensions of the TR-4 sensor conform to the specifications for the Lab Probe called out by the IEEE 442-1981, Guide for Soil Thermal Resistivity Measurements; the IEEE 442/D3, Draft Guide for Thermal Resistivity Measurements of Soils and Backfill Materials; and, ASTM D5334-22, Standard Test Method for Determination of Thermal Conductivity of Soiled and Soft Rock by Thermal Needle Probe Procedure.

The TEMPOS automates data collection, analysis, and reporting. Its user interface guides the operator through the measurement process, while internal monitoring ensures that measurement conditions meet required standards. Results are available within minutes.

 

Measuring thermal dryout curves

Thermal properties of porous materials, particularly soils, vary significantly with water content. A thermal dryout curve illustrates the relationship between thermal conductivity and water content, providing valuable insight into material behavior under drying conditions.

While the TEMPOS can be used to generate dryout curves by testing multiple samples at varying moisture levels, the VARIOS offers a streamlined alternative:

VARIOS components:

  • A precision balance to measure water loss
  • A stainless-steel cylinder to hold the soil sample
  • A needle sensor to measure thermal conductivity
  • A data logger to record and analyze measurements

As water evaporates from the sample, the balance tracks moisture loss, and the system continuously calculates water content. The needle sensor simultaneously records thermal conductivity. Once the sample is fully dried, the VARIOS produces a complete thermal dryout curve.

 

Standards for thermal property measurement

Standardized procedures ensure consistency and reliability in thermal property measurements. Three primary standards are commonly referenced:

  • ASTM D5334-22: This standard provides comprehensive guidance on measurement and analysis techniques. It supports electronic data recording, regression analysis, and incorporates time offset corrections for improved accuracy.
  • IEEE 442: Reissued in 2017, This standard recommends manual data recording and simplistic analysis techniques, such as manually fitting a line through data. It does not use linear regression or account for time offsets.
  • Soil Science Society of America (SSSA) standard: This standard offers sound guidance but is less widely adopted. It aligns closely with ASTM in terms of measurement duration and data analysis methods.

For more information about calculating thermal properties of porous materials, visit METER’s knowledge base to find in-depth articles, on-demand webinars, and podcasts.

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