The Transient Hot Wire Liquid Thermal Conductivity Meter (THW-L1) is a precision analytical instrument for directly measuring the thermal conductivity, thermal diffusivity and specific heat of liquids and low viscosity pastes, from -150 to 300°C.  The THW-L1 is available in three models:

10 to 200°C -50 to 200°C -100 / -150°C to 300°C

Thermtest THW-L1 Liquid Thermal Conductivity Instrument

Picture 1. Thermtest THW-L1 Liquid Thermal Conductivity Meter.

The Thermtest Transient Hot Wire (THW-L1) Liquid Thermal Conductivity Meter is an advanced measurement system for direct determination of the thermal conductivity liquids and pastes in accordance with ASTM D7896-19 – Standard Test Method for Thermal Conductivity of Engine Coolants and Related Fluids by Transient Hot Wire Liquid Thermal Conductivity Method.

The THW-L1 Meter was designed with speed and operational simplicity in mind. With a single measurement of 1 second in duration, small volumes of liquids and low viscosity pastes can be accurately and precisely measured for thermal conductivity, thermal diffusivity, and specific heat. The THW-L1 Meter uses a non-stationary measurement approach and rapid test times, limiting convective effects for samples with a wide range of viscosities (0.1 to 10,000,000 mPa·s).


For the measurements of the Phase Change Materials (PCM), a novel cell (THW PCM Cell) with easy to load access is used (Picture 2a). The unique spring design allows sample expansion and contraction while ensuring the sample is in constant contact with the THW wire during the measurements.  The spring on the bottom of the cell allows thermal conductivity measurements over temperatures for fluid thermal expansion up to 15 %.


PCM AC-1200

The AC-1200 is a microencapsulated phase-change material used in bedding textiles and gives the preferred cooling effect during sleep. The phase change range of AC-1200 is between 20 to 25 oC which is lower temperature than the human body. While the AC-1200 is going from the solid to the liquid phase, the endothermic procedure absorbs heat from the human body giving feeling of cooling and comfort during sleep.

Thermal Conductivity of PCM sample AC-1200 

The thermal conductivity of the PCM sample AC-1200 was measured with a THW-L1 sensor from 5 oC to 105 oC. The sample was shaken, heated up to 100 oC and poured in the warm measuring cell. Then the novel spring-bottom lid is screwed into the cell and the measurements of the PCM started from 105 oC down to 5 oC. The measurements repeated for the increasing temperature run. The measurements from 105 oC to 5 oC repeated and they were repeatable with the first run.

Figure 1 shows the cooling and melting runs of the PCM sample AC-1200. As shown, there is an “anomalous” thermal conductivity increase in the freezing/melting region because of the exothermic/endothermic reactions taking place. In addition, the expected sharper thermal conductivity increase during the melting region of the PCM sample can be seen.


Figure 1. Thermal Conductivity measurements of PCM sample AC-1200