Thermal performance

We are one of the world-leading National Measurement Institutes in thermal conductivity measurements, and have developed a range of UK national standard facilities for direct thermal conductivity measurements covering temperatures from -170 °C to 800 °C and thermal conductivities from 0.01 W/(m*K) to 240 W/(m*K). We have a range of thermal conductivity reference materials and transfer standards conforming to ISO 17034, to provide traceability for industry worldwide. All our thermal conductivity measurement services using direct methods are UKAS accredited.

Direct measurement of thermal conductivity uses steady state methods and is limited to 500 °C for high conductivity materials and to 800 °C for insulation, but we can derive the thermal conductivity at higher temperatures (to over 1500 °C) using values of thermal diffusivity, specific heat capacity and density. This provides a relatively fast and cost-effective way of obtaining data over a wider temperature range.

Our thermal diffusivity measurements have been validated against European Certified Reference Material and NMIJ Certified Reference Material. In addition, the Laser Flash (LFA) thermal diffusivity measurements at NPL have been compared with measurements in other National Measurement Institutes (NMIs) in an International Bureau of Weights and Measures (BIPM) Consultative Committee on Thermometry (CCT) Supplementary Comparison, CCT-S3.

Thermal expansion is measured by contact dilatometry and our instruments can cover the range 100 °C to 1550 °C, including measurement of some liquids in a specially designed cell. Phase changes, annealing and hysteresis can be assessed.

Density is measured by the Archimedes method at room temperature and a value for open, or surface porosity can also be determined. By using this and thermal expansion data the density can be calculated over a wide temperature range.

Axial heat flow meter

This flow meter is suitable for measuring thermal conductivity of homogeneous materials.                                                         

• Measurements on metals, alloys and graphite
• Thermal conductivity range: 10 W/m·K to 240 W/m·K
• Mean specimen temperature range: 50 °C to 500 °C
• Conforms to NPL procedure QPDQM/B/411
• UKAS accredited test service (UKAS 0002)
• A single specimen is required 160 mm x diameter 20 mm
• A drawing with the specification for the required specimen is available upon application, including holes necessary for mounting the specimen and positioning thermocouples
• Measurements are carried out in the normal air environment.
• We can help prepare specimens if you do not have a machining facilities

Guarded heat flow meter

This heat flow meter is a commercial apparatus for measuring thermal conductivity or thermal resistance
of medium thermal conductivity materials such as plastics, ceramics and composites.

• Thermal resistance range: 0.001 m²·K/W to 0.03 m²·K/W
• Temperature range -80 °C to 250 °C
• Conforms to ASTM E1530-11
• UKAS accredited test service (UKAS 0002)
• A single specimen is required, thickness: 1 mm to 20 mm, diameter: 50.8 mm, variation in thickness should be less than 0.025 mm
• Maximum mean specimen temperature to be at least 20 °C below the softening point of the test specimen.

High-temperature guarded hot plate

This hot-plate is an NPL designed and built national standard for thermal conductivity or thermal resistance of insulation and refractories at high temperatures.

• Thermal conductivity range: up to 0.5 W/m·K
• Thermal resistance range: greater than 0.07 m²·K/W
• Mean specimen temperature range: 140 °C to 800 °C
• Conforms to ISO 8302:1991
• UKAS accredited test service (UKAS 0002)
• A single specimen is required (Thickness: 25 mm to 50 mm, Diameter: 305 mm, flatness: better than 0.2 mm

Low-temperature guarded hot plate

This guarded hot-plate is an NPL designed and built national standard for thermal conductivity or thermal resistance of insulation at low temperatures.

• Thermal conductivity range: up to 0.15 W/(m·K)
• Mean specimen temperature range: -170 °C to 50 °C
• Conforms to ISO 8302:1991 and EN 12667:2001
• UKAS accredited test service (UKAS 0002)
• An identical pair of specimens is required. (thickness: 25 mm to 50 mm, length and breadth: 305 mm x 305 mm, flatness: better than 0.2 mm)

Thermal conductivity by thermal diffusivity

The laser flash apparatus (LFA) is an instrument used to measure the thermal diffusivity (a) of materials with respect to temperature. This can then be used to calculate thermal conductivity (λ) if the density (ρ) and specific heat (C_p) of the sample as a function of temperature are already known. It has a temperature range from 25 °C to 1600 °C (or 2000 °C with modifications).
                                                                                                                                                                   

The LFA may be used to assess thermal diffusivity of a wide range of materials including metals and alloys (in solid and liquid phases), ceramics, hard metals, coated materials and MMCs.

• Thermal diffusivity range: 0.01 mm²/s to 1000 mm²/s
• Temperature range: 25 °C to 2000 °C
• Sample dimensions: 6 mm, 10 mm or 12.7  mm diameter
• Inert, static and dynamic atmosphere conditions

We are one of the world-leading National Measurement Institutes in thermal conductivity measurements, and have developed a range of UK national standard facilities for direct thermal conductivity measurements covering temperatures from -170 °C to 800 °C and thermal conductivities from 0.01 W/(m*K) to 240 W/(m*K). We have a range of thermal conductivity reference materials and transfer standards conforming to ISO 17034, to provide traceability for industry worldwide. All our thermal conductivity measurement services using direct methods are UKAS accredited.

Direct measurement of thermal conductivity uses steady state methods and is limited to 500 °C for high conductivity materials and to 800 °C for insulation, but we can derive the thermal conductivity at higher temperatures (to over 1500 °C) using values of thermal diffusivity, specific heat capacity and density. This provides a relatively fast and cost-effective way of obtaining data over a wider temperature range.

Our thermal diffusivity measurements have been validated against European Certified Reference Material and NMIJ Certified Reference Material. In addition, the Laser Flash (LFA) thermal diffusivity measurements at NPL have been compared with measurements in other National Measurement Institutes (NMIs) in an International Bureau of Weights and Measures (BIPM) Consultative Committee on Thermometry (CCT) Supplementary Comparison, CCT-S3.

Thermal expansion is measured by contact dilatometry and our instruments can cover the range 100 °C to 1550 °C, including measurement of some liquids in a specially designed cell. Phase changes, annealing and hysteresis can be assessed.

Density is measured by the Archimedes method at room temperature and a value for open, or surface porosity can also be determined. By using this and thermal expansion data the density can be calculated over a wide temperature range.

Thermal conductivity reference materials and transfer standards

NPL transfer standards are measured in one of our national standard apparatus and is provided with a certificate showing traceability to the UK national standards and UKAS accreditation (UKAS 4002) for producing reference materials to ISO 17034:2016.

NPL reference material specimens are cut from a batch of material that has been characterised by a series of measurements on material that is known to have stable and predictable properties. They have a higher calibration uncertainty than the equivalent transfer standard due to the contribution of variation within the batch. They are provided with a certificate showing traceability to the UK national standards and UKAS accreditation (UKAS 4002) for producing reference materials to ISO 17034:2016.

Materials are increasingly required in situations that challenge the thresholds of their thermal capabilities. It is therefore important to understand material behaviour under the influence of thermal loads. Thermal analysis techniques provide important information for the design engineer. The techniques can be used to analyse most materials in use today in a large number of applications such as metals, polymers, composites, coatings, pharmaceuticals, films, fibres, ceramics and even biological materials and foods. NPL's thermal analysis capabilities enable rapid determination of thermal properties over wide temperature ranges and help develop best practice for testing and data analysis of materials.

Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetry (TGA) techniques can provide data for specific heat capacity, mechanical properties and mass change information, over low and high temperature ranges. We can advise on the best methods available for an application. Our current research is improving the reliability and temperature ranges of these measurements when using different methods. NPL is developing procedures based on these techniques that can be used to design products based on existing materials, select the best material for a given application, predict its performance, optimise processing conditions, improve quality, compare properties of similar or competitive materials and characterise newer research materials.

Differential Scanning Calorimetry (DSC) 

DSC is a rapid technique that measures the heat flow associated with material transitions as a function of temperature, time and atmosphere. 

TA Q2000 

Setaram 96 Line EVO 

Netzsch 404 F1  

Modulated Temperature Differential Scanning Calorimetry (MT DSC) 
 
MT DSC helps separate overlapping and complex transitions in a material under test and is a useful complement to the standard DSC analysis.

TA Q2000

Dynamic Mechanical Analysis (DMA)

DMA is a versatile technique that measures the mechanical properties of the material as a function of the time, temperature and frequency. It is widely used to measure the glass transition and other secondary transitions

TA Q800 

RSA G2

Thermo Mechanical Analysis (TMA)
TMA measures dimensional changes in a material as a function of time, temperature and the applied force.

Thermogravimetric Analysis (TGA)
TGA measures weight changes in a material as a function of temperature, time in a given atmosphere. The determination of the absorbed or bound moisture and other volatiles, are important parameters to assess a material for their analyses for product performance and environmental acceptance.

Evolved Gas Analysis (using TGA-FTIR interface)
TGA-FTIR is used to monitor the evolved gas products resulting from a material under test. The results can be an indicator to study the decomposition behaviour of the material and monitor evaporation and other chemical reactions in real time.