Case Study: Thermal Conductivity Analysis of Stainless-Steel Fabrics at Room and Elevated Temperatures
Overview
A global customer operating in the glass and automotive industries contacted us to find a suitable laboratory to characterize the thermal transport properties of proprietary stainless-steel fabric materials.
The projectโs objective was to determine the in-plane and through-plane thermal conductivity as well as thermal diffusivity of the supplied samples under room and elevated temperatures, in accordance with ISO 22007-2 using the Transient Plane Source (TPS) method.
Due to our confidentiality agreement, all data and details regarding the specific application and material formulation remain strictly confidential.
Sample Characteristics
While specific sample compositions remain confidential, the tested materials were:
- Flat-format stainless-steel fabrics with minor fiberglass content
- Materials commonly used in thermal shielding and industrial applications
- Characterized by a dominant knitting direction, though directional differences could not be resolved within the slab method setup
Due to sample self-curling behavior, special mechanical fixtures were used to maintain the structural integrity and uniformity during testing.
Measurement Objective
The goal of this project was to establish reliable, direction-dependent thermal property values of stainless-steel fabric materials, essential for high-performance applications in demanding industrial environments. These measurements would support the customer's thermal modeling and product development processes.
Testing Methodology
Measurements were conducted using a Transient Plane Source (TPS) instrument in anisotropic mode, per ISO 22007-2:2015 standards. This approach is ideal for materials with non-uniform (anisotropic) heat transfer behaviorโcommon in layered or structured fabrics.
Key parameters included:
- Sensor Type: Kaptonโข-coated TPS sensor
- Measurement Environment: High-temperature furnace for elevated temperature conditions
- Clamping Method: Mechanical fixation with brass weights to ensure consistent contact and counteract the self-curling nature of the samples
Testing covered:
- In-plane (radial) thermal conductivity
- Through-plane (axial) thermal conductivity
- Thermal diffusivity
The setup ensured good thermal contact and repeatability, with multiple runs per temperature point to validate the data.
Calculations used:
(๐๐ถ๐)๐๐ฃ๐ = ๐ ๐ โ (๐๐ ๐ โ ๐ถ๐๐ ๐ + ๐fg โ ๐ถ๐fg )
- Where:
- m and V are the mass and the volume of the sample;
- Xss stands for the mass fraction of stainless steel;
- Cpss = Heat capacity of stainless steel at various temperatures;
- Xfg stands for the mass fraction of the fiberglass in the sample;
- Cpfg = Heat capacity of fiberglass
Results & Observations
While the actual conductivity values remain under NDA, we can share the following general outcomes and insights:
- Directional Dependence: Anisotropic testing was validated as appropriate due to structural properties. However, despite the knitting direction, no distinguishable anisotropic behavior in-plane (parallel vs. perpendicular) was observed in practice.
- Temperature Dependence: As expected for metallic-based materials, in-plane thermal conductivity increased with temperature.
- Heat Capacity Estimation: Due to constraints in direct measurement, the volumetric heat capacity was estimated using known values for stainless steel and fiberglass components, validated through customer-provided data.
- According to the literature, the heat capacity of the stainless steel, Cpss, is about respectively 470, 510 and 540 J/(kgK) at RT, 150 and 280 ยฐC, while the heat capacity of the fiberglass, Cpfg, is about respectively 700, 830, 900 J/(kgK) at RT, 150 and 280 ยฐC.
- Slab vs. Anisotropic Method: While the slab method (another TPS configuration) was used successfully at room temperature and supported the anisotropic results, it couldnโt be extended to high-temperature testing due to the lack of suitable high-temperature insulation backing materials.
Conclusions
- The anisotropic TPS method effectively captured direction-dependent thermal properties of structured stainless-steel fabrics across a temperature range.
- Estimations of volumetric heat capacity, although not directly measured, were sufficiently accurate to support the reliability of the calculated thermal conductivity values.
- Thermal conductivity increased with temperature, aligning with expectations for metallic materials, thus validating the suitability of the fabric in high-temperature industrial applications.
- The methodology proved robust for fabric-type samples with complex structures and confirmed the applicability of ISO 22007-2 for advanced textile materials.
References
- Gustafsson, S.E., Karawacki, E., & Khan, M.N. (1981). Determination of the thermal-conductivity tensor and the heat capacity of insulating solids with the transient hot-strip method. Journal of Applied Physics, 52(4), 2596.
- ISO 22007-2:2015. Plastics โ Determination of thermal conductivity and thermal diffusivity โ Part 2: Transient plane heat source method.
- Bogaard, R.H., Desai, P.D., Li, H.H., & Ho, C.Y. (1993). Thermophysical Properties of Stainless Steels. Thermochimica Acta, 218, 373โ393.
- Benichou, N., & Sultan, M.A. (2001). Thermal properties of components of lightweight wood-framed assemblies at elevated temperatures. Fire and Materials, 7th Int. Conference, pp. 447โ458.