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The Transient Hot-Wire (THW-L2) is widely used for the accurate measurement of thermal conductivity for liquids and pastes.

Best For Liquids and Pastes

ASTM D7896-19

Standard Test

– 50°C To 100°C


Ambient Only


The Transient Hot Wire (THW-L2) Liquid Thermal Conductivity Meter is an advanced measurement system for direct determination of the thermal conductivity of liquids and pastes in accordance with ASTM D7896-19. The THW-L2 was designed with speed and operational simplicity in mind. With a single measurement of less than 2 seconds in duration, small volumes of liquids and pastes can be accurately and precisely measured for thermal conductivity. The THW-L2 utilizes a non-stationary measurement approach and rapid test times to limit convective effects for samples with a wide range of viscosities.


The THW sensor consists of a thin heating wire 60 mm in length, fully inserted into the sample to be tested. The sensor wire is heated using a constant current source (q), and the temperature rise is recorded by monitoring the change in electrical resistance of the wire. The slope (m) from the plot of temperature rise vs. logarithm of time is used in the calculation of thermal conductivity (λ). For liquid samples of high thermal conductivity, the lower the slope. For liquid samples of low thermal conductivity, the higher the slope.

transient hot wire equation

  • Follows international standard: ASTM D7896-19
  • Portable, Economical, & Accurate
  • Results without the effects of convection
  • Easy to use
  • Optional thermoelectric dry bath for automated temperature testing


Materials Liquids & Pastes
Measurement Capabilities Bulk Properties
Thermal Conductivity 0.01 to 2 W/m•K
Measurement Time < 2 seconds
Reproducibility Typically better than 2%
Accuracy Typically better than 5%
Temperature Range 1 -50 to 100°C
Pressure Ambient
Smallest Volume 15 ml
Largest Sample Size Unlimited
Standards ASTM D7896-19
1 Requires cooling/heating apparatus.
Testing Sensors
Standard THW-L2 Sensor
Standard THW-L2 Sensor

The THW-L2 comes with the standard 60 mm sensor for the testing of liquids and pastes. The sensor is fully inserted into an isothermal sample, and measurements are made with the push of a button. In less than 2 seconds, results are displayed for thermal conductivity. Sample volumes as small as 15 ml can be tested. The easy to use THW software enables measurements to be controlled via a computer. When used in conjunction with the optional thermoelectric dry bath, the software can even automate thermal conductivity measurements with temperature.

THW-L2 sensor

The THW-L2 is capable of testing low thermal conductivity compressible insulations without the liquid sample holder. Samples with minimum dimensions of 65 mm in length and 2 mm in thickness can be tested in a horizontal configuration, with the sensor sandwiched between the samples. Expanded polystyrene was measured with the THW-L2 and given a result of 0.031 W/m•K, which is within 5% of the literature values.

Sample Measurements
the sample
The Sample

Liquid samples of unlimited size can be tested with the THW-L2. With the small volume cell insert, volumes as low as 15 mL can be measured. The instrument’s ability to control convection, using short test times, allows accurate measurements of a wide range of samples with varying viscosities.

Approximate Time: 1 minute

insert sample
Insert Sample

Once the liquid has been poured into the sample holder, the sensor can be vertically inserted in place. For smaller sample volumes, position the small volume cell into the sample holder, prior to the addition of the sample and sensor.

Approximate Time: < 1 minute

run the experiment
Run Experiment

The instrument can be controlled through the front panel with the push of a button, or Windows-based computer software. Single temperature point measurements, as well as scheduled temperature intervals, may be performed using the easy to use THW software.

Approximate Time: < 1 minute

Exporting Results
Exporting Results

Using the Windows-based software, users can save, print, and export test results to Microsoft Excel, for further processing once testing is complete.

Approximate Time: 1 minute


Thermal Conductivity of Solvents
Thermal Conductivity of Solvents

Thermal conductivities of four commonly used solvents that have similar physical properties.

Thermal Conductivity of DIUF Water
Thermal Conductivity of DIUF Water

Thermal Conductivity of Deionized Ultra-filtered (DIUF) Water with the THW-L2 Transient Hot Wire

Thermal Conductivity and Viscosity of Carbon Black Heat Transfer Nanofluids
Thermal Conductivity and Viscosity of Carbon Black Heat Transfer Nanofluids

Thermal Conductivity and Viscosity of Carbon Black Heat Transfer Nanofluids


PCM Mould

PCM Mould

To cast PCM samples for the THW-L2.


Thermoelectric Dry Bath

Used for testing samples from -10 to 100 °C.


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