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

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

GHFM-01 features

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 RS (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:

GHFM-The-Fourier-Law
The above equation is linear in form, and is the working equation of the instrument. Constants F (m2•K/W) and Rint (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)

Direction

Through-thickness

Thermal conductivity (W/m·K)*

0.1 to 100

Sample diameter (mm)

50 to 50.8

Sample thickness (mm)

Up to 25 | Thin-films down to 0.1 mm with optional software

Test time (minutes)

40 to 60

Accuracy (Thermal conductivity)

3%

Repeatability (Thermal conductivity)

1 to 2%

Temperature range (°C)**

-20 to 310

Pressure (kPa | psi)

Automated up to 379 kPa (55 psi)

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

Heat Flux Module

Easy to Change Heat Flux Stack

No tools are required to change the lower Heat Flux Stack, 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

thickness measurement ghfm

Thickness Measurement

Our proprietary gimbal design has the advantage of either automatic determination of sample thickness for rigid materials or a user defined sample thickness for compressible materials.

Sample thickness is measured using digital optical encoder technology.

Temperature Control

Temperature Control

Optimally selected heaters cooled by heat exchangers matched with thermocouples are positioned in the upper and lower stack to accurately control plate temperatures.

Lateral heat loss is minimized with the use of a guard oven. Upper and lower plates along with guard oven temperatures are controlled by the convenient software.

Clamping Control GHFM

Clamping Control

Plates automatically clamp together for optimum sample contact for rigid materials. When testing compressible materials, the desired height, force, or pressure is set in the software and the plate will automatically stop once desired sample height, or pressure is achieved.

Measurement Process

GHFM Step1

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.
GHFM-01 Step 2

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.
GHFM-01 Step 3

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.

GHFM-01 Step 4

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

Pyrex-7740 Graph

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


ghfm-01

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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