THW-L2 Transient Hot-Wire

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

The Transient Hot Wire (THW-L2) Liquid Thermal Conductivity Meter is a portable measurement system for direct determination of the thermal conductivity of liquids and pastes. The THW-L2 follows international standard ASTM D7896-19, and was designed with speed and operational simplicity in mind.


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 and is completely 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.

THW equation



Liquids & Pastes

Measurement Capabilities

Bulk Properties

Thermal Conductivity

0.01 to 2 W/m•K

Measurement Time

< 2 seconds


Typically better than 2%


Typically better than 5%

Temperature Range*

-50 to 100°C



Smallest Volume

15 ml

Largest Sample Size



ASTM D7896-19

* Requires cooling/heating apparatus.

Testing Sensor & Applications

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.
Thermal Conductivity of Nanofluids

Thermal Conductivity of Nanofluids

The THW-L2 is capable of testing the thermal conductivity of almost any kind of liquid including nanofluids, nanopowders, emulsions, and pastes using the same sensor and measuring cell. The sensitivity of the sensor can record even the smallest thermal conductivity changes when solid particles are settling inside a liquid mixture.
Dry Bath

Optional Dry Bath

The optional dry bath allows for automated measurements of thermal conductivity with temperature (-10 to 90°C or 0 to 100°C). The THW software automatically controls the increments of temperature steps between the desired start and end temperatures to ensure isothermal conditions and test results are free of temperature drift effects. For wider temperature ranges, additional cooling/heating options are available.

Liquids vs. Temperature

THW Graph

Using the Thermoelectric Dry Bath, the Thermtest THW-L2 is capable of testing liquids over a wide temperature range. In this  application, deionized ultra-filtered (DIUF) water was tested from 10 to 70 °C, using the THW-L2. All test results were within 5% of the literature values.

Measurement Process

thw 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 min.
insert sensor

Insert Sensor

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 min.

run 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 min.

export 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 min.


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