HFM – Heat Flow Meter

Overview

The LINSEIS Heat Flow Meter provides a rapid and easy to use instrument to determine the thermal conductivity properties of low thermal conductive insulation materials as well as all other materials with a high level of accuracy. Measurements can be made in minutes due to its unique design.

Peltier heating and cooling technology provides highly accurate temperature control while reducing maintenance and downtime. Excellent long-term stability allows accurate longterm aging studies. Fast measurement cycles of as little as 15 minutes can be achieved, resulting in a high sampling rate.

To enable these fast and accurate sampling intervals, the instrument uses a dual sensor arrangement. Built-in potentiometers for length measurements (μm resolution) provide immediate sample thickness data.

HFM features of the “updated version”:

• Clean system design with improved isolation and optimized electronics
• Unmatched precision and accuracy
• Low power consumption
• Instrument design based on the standards ASTM C518, JIS A1412, ISO 8301, DIN EN 12664 and DIN 12667

Key benefits

Short Test Cycles
The double heat flux sensor configuration ensures shortest possible measurement cycles. A typical measurement for most samples can take as little as 15 minutes until the temperature stabilizes.

Highest accuracy
The instrument has two built-in linear potentiometers, offering automated highest precision sample thickness determination. Two heat flux sensors then measure the heat flow, which is precisely defined between the hot and cold plate.

Zero Maintenance
The rugged system design and unique zero maintenance Peltier heating and cooling cycle ensure minimal maintenance costs.

Unit operation

The heat transfer coefficient can be calculated from the measured heat flow through the sample divided by the cross-sectional area and the applied temperature difference.

For a homogeneous material, the thermal conductivity Lambda is the product of the heat transfer coefficient (U-value) and the sample thickness.

Fourier’s law of heat conduction is the basis for the calculation of thermal conductivity and thermal resistance.

Integrated dew protection system

If the temperature of an object is being cooled below ambient temperature and reaches the dew point of the ambient air, the humidity contained will start to condensate on that object.

This would also be the case for samples that are inserted into the HFM and are supposed to be measured with any temperature below the dew point. The condensed humidity (dew) might be soaked into the sample and change the thermal conductivity of the sample.

To prevent this problem, the surrounding air can be replaced by dry air or nitrogen and with a constant gas flow the condensation throughout the complete measurement duration.

The required components, such as a throttle valve and a flow meter are already integrated into the Linseis HFM. This allows precise, stable and reproducible measurements.

Specifications

Software

The Linseis Heat Flow Meter can be operated through the touch screen front panel. Optional software free of charge is available. This state of the powerful software package enables convenient temperature programming, data storage and instrument control.

Key features:

• The instrument can be operated from the touch screen front panel
• Easy input of measurement parameters
• Measurement data storage and export
• Report printing, layout can be customized
• Multilingual software versions
• Instrument monitoring (plate temperature, thermal conductivity results, and output signal monitoring)
• Optional user log-in and data monitoring

Applications

The present measurement clearly demonstrates the out- standing reproducibility of the LINSEIS HFM series. A repro- ducibility of 0.25% was achieved. The graph display four measurements of an Elastomer Foam in the temperature range 15 to 40°C. The sample was removed and placed into the instrument again after each measurement.

15 Measurement of the IRMM-440 certified reference material (Resin bonded glass fiberboard) with a thermal conductivity of 0.03274+-0.00015 at 30°C and 0.03102+-0.00012 at 15°C. The X-Axis shows the temperature gradient.

The graph shows two measurements of the same glass wool specimen at several temperatures. The black line shows the thermal conductivity according the manufacturer information. The X-Axis shows the temperature gradient.

Compressible materials can change their properties depending on the compression. Also, the thermal conductivity is dependent on the compression. This was demonstrated on a mat of polyester fibers. A sample of size 300 mm x 300 mm and initial thickness of about 60 mm was placed into a Linseis HFM 300 and tested at room temperature.

Using the distance control, the upper plate was moved so that the sample thickness was step by step reduced to 60 mm, 40 mm and 20 mm. At each sample thickness a gradient of 20 K was applied until a stable state was reached. The compression results in a significant reducing thermal conductivity.