Frequently Asked Question

Heat Flow Meter

What type of materials can be measured for thermal conductivity by the Thermtest HFM 100?

The HFM 100 is specifically designed for testing thermal conductivity and thermal resistance of insulation and common construction materials.

What makes the HFM 100 unique in the market?

The HFM 100 was designed to combine affordability and highest accuracy possible. This was accomplished by focusing on the most common application range of the heat flow meter thermal conductivity method.

How does the HFM 100 work?

A sample is placed between a hot plate and cold plate, which are held at specific temperatures. Flux sensors which are integrated into each plate, are used to monitor flux until steady-state heat flux is achieved. The average heat flux is used to calculate thermal conductivity and thermal resistance according to Fourier’s Law. The basic design of the HFM 100 is based on the Guarded Hot Plate (GHP), which an absolute measurement of thermal conductivity (no calibration). The HFM 100 has a modified design with the use of two flux transducers and calibration to simplify and speed up the measurement.

How is the HFM 100 calibrated?

The HFM 100 uses Standard Reference Materials (SRM) from NIST and IRMM. For expanded operation, the HFM 100 may be user calibrated with Transfer Standards (TS). Thermtest has ability to measure Transfer Standards by absolute methods for use in calibration of the HFM 100.

What standards does the HFM 100 follow?

HFM 100 follows ASTM C518, ISO 8301, and EN 12667 standards.

When to use the HFM 100 to measure thermal conductivity?

HFM 100 was designed to measure through thickness thermal conductivity and thermal resistance of insulation materials which tend to be heterogeneous in nature. The larger sample size of the HFM 100 measures a true thermal conductivity, which is representative of the whole sample.

What is sample size range for the HFM 100?

The sample size range is 6 x 6 inch (150 x 150 mm) up to 12 x 12 inch (300 x 300 mm). Sample thickness up to 4 inch (100 mm) in height.

How is thickness of sample determined?

The thickness of sample is measured with the use of four optical encoders, which are located on each corner of the top sample plate. This ensures the highest accuracy of thickness measurement possible (0.1mm).

What if sample is not ideally flat?

Each optical encoder (4) controls each of the four stepper motors independently. For samples, which are not ideally flat, the independently controlled motors can adjust to slight thickness variations to ensure optimum sample contact.

What is temperature range of the HFM 100?

The maximum temperature range of the upper and lower plates is -20°C to 70°C. Depending on the application or testing standard used, a delta temperature between upper and lower plate is typically 10°C to 20°C. Example, for a mean temperature of 20°C, the user might set upper plate to 30°C and lower plate to 10°C, which follows ASTM C518 which states 20°C delta.