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General FAQs

Thermal effusivity is a special quantity relating the thermal conductivity, heat capacity and density of a material. This relation determines heat transfer across material interfaces. Thermal effusivity can be used to measure how a material feels, in terms of coolness or warmth.
No, thermal effusivity should never be used to measure or calculate thermal conductivity due to possibility of significant error as the thermal conductivity included in the quantity is not only heat transfer through conduction.
Anyone who wants to select or design a material to feel cool or warm. Additionally, synthetic materials can be designed to feel more authentic. For example: synthetic composite wood can be designed to feel more like the real wood equivalent.
In addition to the short test time (1 to 3 seconds) noted in ASTM 7984-16, the TPS-EFF can measure 10 seconds as well. The feeling of coolness or warmth can be fully characterized for longer contact – touch times.
Single materials of sufficient thickness will measure the same thermal effusivity. Depending on the thickness of each layer of layered materials, a decrease or increase of thermal effusivity with test time is possible. As heat from sensor penetrates through different layers, the feeling of coolness or warmth may change. This phenomenon can be used to further select or design how a layered material feels with contact – touch time.
The TPS-EFF was designed to be used in the lab or taken to a specific location with the included small carrying case. This portability provides users maximum flexibility at a affordable price with no reduction in accuracy.

ASTM 7984-16 FAQ

Yes
The required probing depth depends on the diffusivity of the material but is generally below 1cm for materials covered by the standard.
The TPS-EFF is calibrated by applying a model of 1D heat transfer with a given sensor heat capacity and backing insulation effusivity to obtain sample effusivity.

Performing tests on known materials and deriving a calibration curve to correct the raw effusivity reading.

No, the TPS-EFF does not require a guard ring. With the TPS-EFF’s larger diameter sensor (30 mm), a guard ring is not required to keep the measurement one-dimensional. The increased area and short test time ensure the heat penetration is one-dimensional for the thermal effusivity covered in standard.
Alongside 2 second tests, 10 second tests are supported as they allow for greater penetration depth, which allows for expanded measurements of contact – touch time to characterize a materials feeling of coolness or warmth. This additional information can be used to alter how a material feels over longer touch times, especially useful for layered textiles and fabrics.
Thermal effusivity is a special quantity relating the thermal conductivity, heat capacity and density of a material. This relation determines heat transfer across material interfaces. Thermal effusivity can be used to measure how a material feels, in terms of coolness or warmth. It is important to understand, as the thermal conductivity included in the quantity is not only heat transfer through conduction, thermal effusivity should never be used to measure or calculate thermal conductivity due to possibility of significant error.
The TPS-EFF can perform 2 second and 10 second tests.
One dimensional heat flow is ensured by using a sensor with a large surface area, limiting the test time to 2-10s, and restricting test materials to those covered by the ASTM standard.
Yes, the TPS-EFF is calibrated. This is necessary due to the construction of the sensor.
Measurements made with the TPS-EFF fall within 5% of known materials.