GHFM-01 Guarded Heat Flow Meter

GHFM-01 Guarded Heat Flow Meter is designed to test the thermal resistance and thermal conductivity of both homogeneous and heterogeneous materials.

Best for Metals, Polymers, Composites, and Pastes

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The Guarded Heat Flow Meter (GHFM-01) follows ASTM E1530-19 for testing thermal resistance and thermal conductivity of solids, such as metals, polymers, composites and paste from -20 °C to 310 °C. The Thermtest proprietary testing stack, replaces the traditional pneumatic movement with advanced motor control, which allows automated control of testing sample thickness, force or pressure applied.

Features

Basic and advanced functions are easy with GHFM-01 Windows Software.
Full computer control of GHFM-01; mean temperature, sample thickness, force or pressure applied.
Programmable mean temperatures from -20 °C to 310 °C.
Multiple high resolution (0.01 °C) thermocouples for accurate measurement of thermal resistance and thermal conductivity.
Thickness is measured to an accuracy of 0.0254 mm, with use of a digital optical encoder.
Integrated force sensor with feedback loop for controlling stepper motor.
High performance stepper motor enables plate clamping to be automated or set to a user defined thickness – ideal for compressible materials.
Flux modules are easily changed, with no tools needed.
Follows international standard; ASTM E1530-19.

The advanced GHFM-01 is a primary measurement of thermal resistance—thermal conductivity for solids, such as metals, polymers, composites and paste. Specifically, the calculation of thermal conductivity from measurement of thermal resistance is the most accurate method of testing the true thermal conductivity of heterogeneous materials. The steady-state measurement of thermal resistance represents the full sample thickness and mature heat transfer properties.

According to the method, the sample is subjected to a steady-state through-thickness temperature gradient. The thermal conductivity of the sample is obtained by measuring the temperature difference across it, and one additional temperature.

The testing stack is made up of a heater – upper plate, with integrated temperature sensor and heat sink—lower plate with integrated temperature sensor on each side of the sample. Additional temperature sensors are placed near the top and bottom surface of the sample.

Once steady-state temperature across the sample is achieved, the Fourier law equation can be applied. The ratio R_S (m²•K/W), equal to the thickness of the sample, d (m) to its thermal conductivity, λ (W/m•K), can be obtained from the temperatures measured:

The above equation is linear in form, and is the working equation of the instrument. Constants F (m²•K/W) and R_int (m²•K/W), can be obtained by calibration of the instrument. To this effect, calibration samples of known thermal conductivity and hence, thermal resistance, are employed. Calibrated results for thermal resistance and thermal conductivity are reported.

Specification

Following international standards, the GHFM-01 is designed for testing both homogeneous and heterogeneous materials.

Materials	Metals, Polymers, Composites, and Pastes
Type of Sensors	Thermocouples (x6)
Applications	General Testing
Direction	Through-Thickness
Thermal Conductivity Range*	0.1 to 100 W/m•K
Measurement Time	40 to 60 min.
Accuracy	± 3%
Repeatability	± 1 to 2%
Plate Temperature Range**	-20 to 310 °C
Pressure	Automated up to 7 KPa (55 psi)
Sample Diameter	50 to 50.8 mm
Sample Thickness	Up to 25 mm \| Thin-films down to 0.1 mm with optional Software
Standard	ASTM E1530-19

*Above 60 W/m·K, the material should be a minimum of 12.5 mm thick
**Chilled circulator included with each system

Highlights

Easy to Change Heat Flux Module

No tools are required to change the lower flux module, which forms a calibrated heat flux transducer. Housing multiple thermocouples to monitor temperature for confirmation of steady state condition of the temperature gradient across the sample is achieved.

Temperature Control

Optimally selected heaters cooled by heat exchangers matched with thermocouples, which have a resolution of 0.01 °C are positioned in the upper and lower stack are used to accurately control plate temperatures.

Thickness Measurement

Accurate sample thickness is required for determining thermal conductivity of a material from the measurement of thermal resistance. The GHFM-01 features a proprietary gimble design, which has the advantage of either an automatic determination of sample thickness, for rigid materials, or a user defined sample thickness, force or pressure applied for compressible materials. Sample thickness is measured using digital optical encoder technology, ensuring the most accurate (± 0.025 mm) measurement of sample thickness.

Operation

The GHFM-01 offers a feature packed Windows based software included with each system. The simple to use software offers unlimited automation steps of temperature along with thickness force or pressure settings. Basic testing and calibration steps are fully automated, as well as additional functions like saving, exporting, and printing of measurement results.

Clamping Control

For rigid materials, the GHFM-01 plates automatically clamp together for optimum sample contact. When testing compressible materials, the desired height, force or pressure (up to 80 kg, 379 kPa – 55 psi) applied may be set in the software and the plate will automatically stop once desired sample height or pressure is achieved.

Calibration

All conditions of calibration, such as management of reference materials, temperature steps and pressure are fully automated with the GHFM-01 software. Verification of calibration is performed through built in validation routines.

Measurement Process

The Sample

GHFM-01 samples should be 50 to 50.8 mm in diameter. The top and bottom surfaces should be flat and parallel. A thin layer of contact paste is added to the top and bottom of the sample surface.

Approximate Time: 1 min.

Place Sample on GHFM-01 Testing Stack

Sample then can be loaded into the testing stack. For rigid materials, upper stack will close to a default pressure. For soft materials, the user can define a specific pressure or required thickness. Pressure and thickness testing parameters can be controlled within the testing schedule.

Approximate Time: 1 min.

Measurement

Using the GHFM-01 Software, the user is able to schedule unlimited temperature steps up to 300 °C. Internal red backlight signals testing in progress.

Approximate Time: 40 to 60 mins.

Export Result Calculations

Temperatures from upper and lower plates are monitored by the GHFM-01 software for temperature stability. Measured thermal resistance and calculated thermal conductivity results are tabulated and available for export to excel. Internal blue backlight signal testing is complete and stack safe to touch.

Approximate Time: 1 min.

Accuracy

Thermal Conductivity of Pyrex^(R) 7740

Demonstrating the performance of the GHFM-01, measurements on Pyrex 7740 were made up to 300 °C and compared to literature values.

Accuracy of all results < 2%.

Thermal Conductivity (W/m•K)

Temperature ( °C)	25	40	60	80	100	120	140	160	180	200	220	240	260	280	300
Direct Measured Values	1.134	1.172	1.192	1.223	1.246	1.261	1.280	1.307	1.325	1.343	1.361	1.386	1.401	1.426	1.451
Literature Values	1.143	1.164	1.214	1.236	1.236	1.257	1.276	1.295	1.313	1.330	1.348	1.366	1.385	1.404	1.426
Error (%)	0.80	0.71	0.11	0.71	0.75	0.33	0.27	0.96	0.92	0.99	0.98	1.44	1.19	1.54	1.78

Guarded Heat Flow Meter (GHFM) Model


Models	GHFM-01
Materials	Metals, Polymers, Composites, and Pastes
Measurement Capabilities	Through-Thickness
Applications	General Testing
Thermal Conductivity Range	0.1 to 100 W/m•K *
Sample Diameter	50 to 50.8 mm
Sample Thickness	Up to 25 mm \| Thin-films down to 0.01 mm with optional Software
Maximum Thickness	25.4 mm / 1 in.
Temperature Range	-20 to 310 °C **
Pressure	Automated up to 379 kPa (55 psi)
Measurement Time	30 to 45 minutes
Accuracy	± 3 %
Repeatability	± 1 to 2 %
Standards	ASTM E1530-19

*Above 60 W/m·K, the material should be a minimum of 12.5 mm thick
**Chilled circulator included with each system

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GHFM-01 Guarded Heat Flow Meter

Features

Specification