INGENIEUR
Testing Standards The thermal conductivity test is applicable to any number of different materials of various thicknesses and conductivity levels . The Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus ( C518-17 ), published as an updated version by The American Standards for Testing Materials ( ASTM ) in 2017 , is used as the guide for the tests conducted at MRL .
Specimen Selection An example of a typical building material is the flexible elastomeric foam open cell which has nitrile rubber as part of its constituents . This material is used as acoustic insulation for heating , ventilating , air-conditioning and refrigeration ( HVAC / R ) equipment . Due to its thermal properties , it is applied as external insulation for the supply and return air ducts in an air-conditioning system to prevent heat loss from conditioned air , the physical features of this are shown in Figure 1 .
Figure 2 : Climate chamber
Figure 3 : Conditioning sample in climate chamber
ASTM C518-17 Standards , before being taken out for the testing , shown in Figure 3 .
Figure 1 : Typical specimen ( open cell nitrile rubber insulation )
Sample Conditioning The material sample must be conditioned to comply with required standards prior to the actual test . The sample is first stored in the climate chamber , shown in Figure 2 .
The condition inside the chamber is then set at a temperature of 22 ° C and relative humidity of 50 % for a period of 24 hours as required by the
Heat Flow Meter The equipment used for the testing is the Fox 314 Heat Flow Meter , shown in Figure 4 . It consists of two isothermal plate assemblies that are outfitted with a dedicated cooling system . It also has a central and peripheral group of thermoelectric elements , which are controlled independently to eliminate radial temperature gradients in the plates . The heat flow meter operations are controlled by the Digital Signal Processor ( DSP ).
The heat flow meter is a two heat flux transducers-type , the assembly of which is shown in Figure 5 .
The transducers are made of small thermocouples to provide high sensitivity . These thermocouples are positioned next to the surfaces
72 VOL 89 JANUARY-MARCH 2022