Liquids thermal conductivity measurement
The thermal conductivity of a liquid defines its ability to transfer heat. It is expressed in W/m/K.
Along with heat capacity and density, it is one of the quantities used to characterize the thermal behavior of fluids as a function of temperature. These quantities are particularly used to size the heating of the fluid in question, but also for so-called heat transfer fluids whose function is to transfer heat between two points of a system.
Examples of thermal conductivity values
The order of magnitude of the conductivity of liquids varies between 0.01 and 2 W/m/K. The thermal conductivity of polar liquids (water, ammonia, etc.) is generally higher than that of other liquids, especially organic liquids. The table below gives some examples of thermal conductivities measured on common liquids:
Measurement Method: Hot Wire
At Calnesis, the method used to measure the thermal conductivity of liquids is that of the hot wire. The measurement consists of placing the liquid in a temperature-regulated container between 0 and 100°C. A probe equipped with a conductive wire is placed in the thermostated liquid.
For approximately one second, a current travels through the hot wire and heats the fluid located around it. The temperature variation measured during this heating makes it possible to determine the thermal conductivity of the fluid at this temperature. This is therefore a so-called transitional measure.
The reduced measurement time makes it possible to overcome undesired heat transfer modes that occur in fluids, in particular the main one: convection.
The accuracy of this type of measurement is about 5%
Conditions necessary for thermal conductivity measurement
The fluid must be thermally stable over the entire desired measurement temperature range. The measurement temperature(s) must not be too close to the boiling temperature to avoid degassing or the formation of gas bubbles in the fluid.