The Transient Hot Wire Liquid Thermal Conductivity Meter (THW-L1) is a precision analytical instrument for directly measuring the thermal conductivity of liquids and low viscosity pastes, from 10 to 200°C.

THW-L1 Liquid Thermal Conductivity Equipment

Figure 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 mPas).

Measuring Accessories

For the measurements of the Phase Change Materials (PCM) a novel cell with easy to load access is used (Figure 2a). The unique spring design allows sample expansion and contraction, while ensuring 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 %.

             A)  novel spring load cell    B)  paraffin wax sample

Figure 2. a) The novel spring load cell and b) the paraffin wax sample

Thermal Conductivity results

The Paraffin wax and the measuring cell with the sensor heated up to 70 oC and fill the cell with the wax. Figure 3 shows the thermal conductivity results of the paraffin wax sample. The first results show measurements from 70 to 20 oC where the wax is in the solid state. Then the sample was heated up and the reversed measurements take from 20 to 70 oC. The results repeatability is very high both in liquid and solid state proving the continuously contact of the wire with the PCM.

Thermal Conductivity of the Paraffin Wax results in two measuring circles.

Figure 3. Thermal Conductivity of the Paraffin Wax in two measuring circles.