SHIEL3D: a tool to determine thermal conductivity
What is SHIEL3D?
- SHIEL3D is a characterisation device which determines thermal conductivity and thermal diffusivity of thermal insulation.
- Heating element is a very thin wire (50μm in diameter) sandwiched between two pieces of the material.
- The material is thermally stimulated and the response to stimulation is studied via tiny fluctuations in resistance of wire to yield the thermal properties.
- Thermal conductivity measurable in the range
1-2000 mW/m-K and -250°C to 1000°C!
- Technology developed under two major space projects:
- AerSUS (FP7 from the EU, 2012-14)
- 3-Omega B (ITI from ESA, 2015-17)
Hot plate method vs SHIEL3D
Why Traditional Hot Plate Methods Fail?
- In the hot plate method, the heat travels through the sample and is measured as a delta temperature on the other side.
- For high conductivity materials, this is fine, but for highly insulating materials, this means that very little heat makes it through, resulting in a weak signal.
- If the resulting delta temperature is then similar in size to the error in the temperature measurement, this can lead to 100% uncertainty in measurement result.
- One solution to this problem is to significantly turn up the heat on the hot plate, resulting in higher delta T across the sample and a larger signal to be measured on the other side.
- However, this then requires much longer times to reach steady state (increased costs) and can result in significant convection & radiation, where the heat loss may be similar to the conducted heat, again resulting in larger measurement errors.
SHIEL3D: Better for Good Thermal Insulators
SHIEL3D is based on the 3-Omega method.
- Here, a heating wire is used instead of a heating surface and the heating wire simultaneously serves as the temperature sensor.
- It is the amount of heat reflected by the sample back to the heating wire which is measured, therefore – for highly insulating materials – the measured signal increases and the measurement becomes more accurate.
- Since the heating wire is embedded in the sample, heat loss and associated measurement errors through heat loss is negligible.