The Transient Hot Wire (THW-L1) is widely used for the accurate measurement of thermal conductivity, thermal diffusivity, and specific heat capacity of liquids, pastes, and powders.
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The THW-L1 following ASTM D7896-19, is widely used for the accurate measurement of thermal conductivity, thermal diffusivity and specific heat of liquids and pastes. This versatility is greatly expanded with the addition of Thermtest’s proprietary Temperature Platform (TP) which is appreciated by academic and commercial users alike.
The transient hot wire (THW) has been used for the testing of liquids for more than 30 years, making it one of the most published methods for measuring thermal conductivity of liquids available.
The Transient Hot-Wire (THW-L1) liquid thermal conductivity equipment is an advanced measurement system for testing the thermal conductivity, thermal diffusivity, and specific heat capacity of liquids, pastes and powders in accordance with ASTM D7896-19. The THW-L1 was designed with speed and operational simplicity in mind. With a single measurement of 1 second in duration, small volumes of liquids, pastes, and powders can be accurately and precisely measured for thermal conductivity, thermal diffusivity, and specific heat. The THW-L1 utilizes a non-stationary measurement approach and rapid test times to limit convective effects of samples with a wide range of viscosities.
The THW sensor consists of a thin heating wire 40 mm in length and is completely inserted into the sample to be tested. The sensor wire is heated using a constant current source (q) and the temperature rise is recorded by monitoring the change in electrical resistance of the wire. The slope (m) from the plot of temperature rise vs. logarithm of time is used in the calculation of thermal conductivity (λ). For liquid samples of high thermal conductivity, the lower the slope. For liquid samples of low thermal conductivity, the higher the slope.
Materials | Liquids, Pastes, and Powders |
---|---|
Measurement Capabilities | Flux Sensors (x2) |
Thermal Conductivity | 0.01 to 2 W/m•K |
Additional Properties | Thermal Diffusivity and Specific Heat |
Viscosity Range | 0.001 to 10,000,000 cP |
Measurement Time | 1 second | < 5 seconds |
Reproducibility | ± 1% |
Accuracy* | ± 5% |
Temperature Range† | -150 to 300°C |
Pressure | Up to 35 bar |
Smallest Volume | 20 mL |
Standard | ASTM D7896-19 |
Models | THW-L1 | THW-L1S | THW-L1E |
---|---|---|---|
Materials | Liquids, Pastes, and Powders | Liquids, Pastes, and Powders | Liquids, Pastes, and Powders |
Measurement Capabilities | Bulk Properties | Bulk Properties | Bulk Properties |
Thermal Conductivity | 0.01 to 2 W/m•K | 0.01 to 2 W/m•K | 0.01 to 2 W/m•K |
Additional Properties | Thermal Diffusivity and Specific Heat | Thermal Diffusivity and Specific Heat | Thermal Diffusivity and Specific Heat |
Viscosity Range | 0.001 to 10,000,000 cP | 0.001 to 10,000,000 cP | 0.001 to 10,000,000 cP |
Measurement Time | 1 second | < 5 seconds | 1 second | < 5 seconds | 1 second | < 5 seconds |
Reproducibility | ± 1% | ± 1% | ± 1% |
Accuracy* | ± 2% | ± 2% | ± 2% |
Temperature Range | 10 to 200°C | -50 to 200°C | -150 to 300°C |
Pressure | Up to 20 bar | Up to 20 bar | Up to 35 bar |
Smallest Volume | 20 mL | 20 mL | 20 mL |
Standard | ASTM D7896-19 | ASTM D7896-19 | ASTM D7896-19 |
External Cooling Apparatus Required | No | Yes | Yes |
*All performance data is verified with ASTM Type II Water (IAPWS)
Models | THW-L2 | THW-L3 | THW-S |
---|---|---|---|
Materials | Liquids, Pastes, and Powders | Liquids, Pastes, and Powders | Insulation and Soft Materials |
Measurement Capabilities | Bulk Properties | Bulk Properties | Bulk Properties |
Thermal Conductivity | 0.01 to 2 W/m•K | 0.01 to 1 W/m•K | 0.01 to 2 W/m•K |
Additional Properties | No | No | No |
Viscosity Range | 0.001 to 10,000,000 cP | 0.001 to 10,000,000 cP | N/A |
Measurement Time | 1 second | < 5 seconds | 1 second | 1 to 5 seconds |
Reproducibility | ± 2% | ± 2% | ± 2% |
Accuracy* | ± 5% | ± 5% | ± 5% |
Temperature Range | -50 to 100°C | 10 to 40°C | 10 to 40°C |
Pressure | Ambient | Ambient | N/A |
Smallest Volume | 15 mL | 15 mL | Min. Sample Size: 50mm x 10 mm |
Standard | ASTM D7896-19 | ASTM D7896-19 | N/A |
External Cooling Apparatus Required | Yes | Yes | N/A |
Approximate Time: < 1 min.
Approximate Time: < 1 min.
Approximate Time: 1 min.
Low back pressure was applied to the fluids, to allow measurements over their boiling point.
Thermal Conductivity deviations from reference values:
Water < 2%
Thermal Diffusivity deviations from reference values:
Water < 2%
Thermal Conductivity deviations from reference values:
Heptane < 3%
Thermal Diffusivity deviations from reference values:
Heptane < 2%
Calculated Specific Heat Capacity deviations from reference values:
Water < 2%
Heptane < 5%
Thermal Conductivity deviations from reference values:
Ethylene Glycol < 1%
Thermal Diffusivity deviations from reference values:
Ethylene Glycol < 1%
Calculated Specific Heat Capacity deviations from reference values:
Ethylene Glycol < 2%
Citation:
Lemmon, E.W., Bell, I.H., Huber, M.L., McLinden, M.O. (2018). NIST Standard Reference Database 23: Reference Fluid Thermodynamic and Transport Properties-REFPROP, Version 10.0. National Institute of Standards and Technology, Standard Reference Data Program, Gaithersburg.
Models | ||||
Materials | Liquids, Pastes, and Powders | Liquids, Pastes, and Powders | Liquids, Pastes, and Powders | Liquids, Pastes, and Powders |
Testing Modules | Bulk | Bulk | Bulk | Bulk |
Other Materials | Solids with TPS | No | No | Solids with TPS, TLS |
Thermal Conductivity | 0.01 to 2 W/m•K | 0.01 to 2 W/m•K | 0.01 to 2 W/m•K | 0.01 to 1 W/m•K |
Sample Size | 20 mL | 20 mL | 15 mL | 15 mL |
Additional Properties | Thermal Diffusivity and Specific Heat | Thermal Diffusivity and Specific Heat | No | No |
Temperature Range | Room Temperature 10 to 200 °C | -50/-15/0 to 200 °C -160/-45/-15/0 to 300 °C | 10 to 200 °C | -50/-15/0 to 200 °C -160/-45/-15/0 to 300 °C | -50 to 100 °C | Room Temperature 10 to 40 °C |
Pressure | Up to 35 bar* | Up to 35 bar* | Ambient | Ambient |
Test Times | 1 second | 1 second | 1 second | < 5 seconds | 1 second |
Data-Points | 400 points/second | 100 points/second | 60 points/second | 60 points/second |
Thermal Conductivity Accuracy | 2 % | 2 % | 5 % | 5 % |
Repeatability | 1 % | 1 % | 2 % | 2 % |
Standards | ASTM D7896-19 | ASTM D7896-19 | ASTM D7896-19 | ASTM D7896-19 |
External Cooling Apparatus Required | No | Yes* | No | Yes* | Yes | Yes |
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