The Thermtest THW-L2 is a thermal conductivity meter based on the Transient Hot Wire method for testing the thermal conductivity of fluids. In this example milk is used to demonstrate the sensitivity of the device.

Testing fluids with a THW-L2 is easy and fast. Each measurement is only ca 1 second long and the sensor wire is gently heated with ca 3 °C during each experiment. However, it is important to allow the sample to reach thermal equilibrium between tests, and it is therefore suggested to wait a few minutes between tests and allow temperature to fully stabilize if testing is performed at several temperatures. In this example, the measurements on each samples were repeated four times at the specified temperature to demonstrate measurement precision.

The analysed milk was produced at the local Wapnö diary outside of Halmstad, Sweden. All three types of milk were processed at the diary within a time period of 24 hours, so quality should be very similar between the batches.

Milk is a popular drink here in Sweden and you can get it in a range of qualities. Most popular is low-pasteurized milk with 0.5 %, 1.5 % or 3.0 % fat. There is also high-pasteurized milk available as well as milk with no lactose etc. But in this little example we will focus on the most popular types, locally referred to as “normal milk”.

As fresh milk should be stored chilled, all measurements were performed at 4 °C. The volume of liquid needed for a test like this is ca 25 ml. The THW sample container and sensor used for these tests can be seen in the picture below.