The Measurement Platform-2 (MP-2) is an advanced meter with unique selection of transient thermal conductivity sensors for a variety of applications, with a focus on primary measurements. The transient thermal conductivity sensors share similar principles of operation. 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 (THW and EFF) or by resistance temperature detector device (TLS). For samples of high thermal conductivity, resistance increases more slowly over time; for samples of low thermal conductivity, resistance increases more quickly over time.

Thermtest MP-2 Measurement Platform Portable Meter

Picture 1. Thermtest MP-2 Thermal Conductivity Meter

Thermal conductivity MP-2 users benefit from the convenience and accuracy gained when using primary testing methods. The MP-2 controller auto-detects the connected sensor and loads corresponding testing parameters. Measurements are easily performed with the smart on-board software and transferred to computer with an included Windows utility program.

THW-L3 Sensor

THW-L3 Sensor transient hot wire

Picture 2. Thermtest THW-L3 sensor for use with the MP-2 portable meter.

The Transient Hot Wire – THW-L3 sensor is one of the many sensors offered with the Thermtest Portable Measurement Platform (MP-2). This sensor offers simple yet accurate measurements of liquids, pastes, and powders from 0.01 to 1 W/m/K via the transient hot wire method. The THW-L3 adheres with an internationally recognized standard of testing by complying with ASTM D7896-19. The THW-L3 has a 5% accuracy and a 2% reproducibility of measurement, making it a highly accurate and precise instrument for measuring the thermal conductivity of liquids, pastes, and powders.

The THW-L3 has a detect current setting that determines the appropriate amount of current to apply based on a test measurement. By reading the result of the test measurement, a current will be set that results in an optimal temperature rise of the sample during testing. The accompanying sample holder can be filled with ~15ml of any liquid, and the sensor can subsequently be inserted into the sample holder. An alternative method of measuring the thermal conductivity of a liquid sample is to insert the THW-L3 directly into the vessel containing the sample.

Thermal Conductivity of Acetone and Heptane

Acetone and heptane are both used as solvents in laboratory settings, among many other uses. Most commonly, acetone is used as the main ingredient in nail polish remover and paint thinner. Heptane is a main component in gasoline. The thermal conductivity of these two liquids can be used for characterization, as pure acetone or pure heptane would have a different value than a mixture of either. This application sheet outlines the measurement of these two liquids with the Thermtest THW-L3 sensor.

The sensor was first calibrated with DIUF water, then five measurements were taken to verify the calibration. The thermal conductivity of acetone and heptane can then be measured with a high degree of accuracy.

THW-L3 connected to MP-2 handheld

Figure 1: a) THW-L3 connected to MP-2 handheld with heptane and sample cell (15 ml). b) THW-L3 sensor inserted in sample cell filled with heptane. c) running a thermal conductivity measurement on heptane with the THW-L3. These steps were then repeated with acetone.

Table 1: Results of measuring acetone and heptane on the THW-L3, with DIUF water as a calibration and verification sample.

Sample Average Thermal Conductivity (W/m/K) Standard Deviation (W/m/K)
DIUF Water 0.608 0.008
Acetone 0.160 0.007
Heptane 0.114 0.002

The THW-L3 has a 5% accuracy and a 2% reproducibility of measurement, making it a highly accurate and precise instrument for measuring the thermal conductivity of liquids, pastes, and powders.