High-Accuracy Quality Control Tool in Measuring the Thermal Conductivity of Insulation
Expanded Polystyrene Board (EPS Foam) is a widely used plastic for applications in packaging and building insulation. It has a very low thermal conductivity property, and therefore is an ideal material for providing thermal insulation.
C-Therm’s TCi thermal conductivity measurement is based on the modified transient plane source (MTPS) technique. The MTPS method provides a fast, highly-accurate, and easy way to measure the thermal conductivity of insulation samples with no sample preparation or contact agents required. For this reason it has become a very popular tool for rapid quality control in the manufacturing of EPS and other insulation products.
Is it as accurate as traditional steady-state methods such as guarded hot plate (GHP) or guarded heat flow (GHF)?
Chart 1 below shows the TCi’s results on a certified reference sample material of EPS provided by the National Institute of Standards and Technology (NIST) measured via the guarded hot plate (GHP) technique. GHP is a highly accurate and reliable method for measuring thermal conductivity – but it takes hours to run a sample and the wait-time for results - coupled with the onerous sample size requirements – can add up to a significant burden for some users. As graphically presented in Chart 1, the average test results generated with the C-Therm TCi Thermal Conductivity Analyzer on the NIST reference sample is 0.0329 W/mK with an RSD of 0.19%. This represents a difference of 2.13% from the stated NIST value measured with GHP of 0.0337. All testing was done at approximately 24◦ Celsius. In testing within 2.13% of the stated reference value, the test results fall within the 2.4% uncertainty noted on the NIST certificate for the reference standard material. These test results exemplify the high accuracy clients typically achieve in characterizing a wide range of sample materials with the C-Therm TCi Thermal Conductivity Analyzer.
Quality Control Applications
Having demonstrated the high accuracy of the TCi’s MTPS method in testing the NIST sample, the following testing results highlight application of the tool in quality controller testing. A sample of EPS was sourced from the local Home Depot store in Fredericton, New Brunswick. The TrueFoam™ sample was tested in 10 different locations in assessing both the overall quality of the insulation material, and also the sample homogeneity. In Chart II these results are plotted – note that this time the X-axis plots different locations of measurement in contrast to Chart I above that plots multiple measurements on the same location. Test results demonstrate the product provides excellent insulation quality with an average thermal conductivity of 0.033 W/mK and is highly homogeneous in its performance across multiple locations with a relative standard deviation 0f 0.6%. As the product has a specification of better than 0.0363 W/mK, C-Therm found the insulation to surpass the stated performance specification for the product. All testing was completed within 10 minutes (each measurement took less than 3 seconds with a 60-second interval period between measurements).
In manufacturing, the C-Therm TCi Thermal Conductivity Analyzer offers added insight in being able to accurately and quickly measure the thermal conductivity of product so production can understand if they are meeting specifications consistently. In this example, the test results tested better than the stated thermal conductivity and the sample material is of excellent consistency.
Overall, C-Therm TCi's Modified Transient Plane Source (MTPS) technique offers a broad range of testing capabilities in both thermal insulators and highly-conductive metals.
For more information on the C-Therm TCi Thermal Conductivity Analyzer click here.
TrueFoam specifications stated thermal insulation performance as thermal resistance. Thermal resistance is equal to the thickness of the material divided by thermal conductivity. For more information on the relationship between thermal conductivity and thermal resistance see http://www.ctherm.com/products/tci_thermal_conductivity/helpful_links_tools/thermal_resistance_thermal_conductance/