THW-L1 Transient Hot Wire

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.

Best for 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.

Features

Follows international standard ASTM-D7896-19
Automated, powerful & accurate
Minimum effects of convection
Cell Pressure up to 35 bar
Integrated temperature control
Unique wire clamping for easy replacement

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.

Specifications

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

^*All performance data is verified with ASTM Type II Water (IAPWS)
^†Based on THW-L1 model used

Transient Hot-Wire Models (Non-portable)

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)

Transient Hot-Wire Models (Portable)

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

Optional THW-L1 Accessories

Paste and PCM Cell

Special Phase Change Materials (PCM) with easy to load access. Unique spring design allows sample expansion and contraction, while ensuring sample is in constant contact with THW wire during measurement.

Observation Cell

THW-L1 observation sample cell is used for liquids, powder, and paste testing. The cell has convenient glass ports for observing what is happening with your sample. Typical applications are phase separation, boiling or particle settling to name a few.

Ambient Density Powder Cell

The THW-L1 Ambient density Powder Cell is suitable for basic powder sample testing and ambient pressure.

Variable Density Powder Cell

THW-L1 test cell with screw-type compression system for varying the density of powder samples, can also be used to ensure powders stay in contact with THW wire.

Vertical Cell Mount

Convenient THW cell mount that can be attached to your THW-L1 for vertical sample loading. Ideal for the Paste/PCM and all Powder Cells.

Cooling Options

Measurement Process

The Sample

The liquid is poured into the sample cell, the required volume is 20 ml. The THW-L1’s ability to limit convection, using short test times, allows accuracy measurements of a large range of samples, widely varying viscosities. The sample cell can then be back filled to pressures up to 35 bar, for testing liquids past their boiling points.

Approximate Time: 1 min.

Insert Sensor

For testing with temperature, the liquid cell is inserted into the integrated temperature platform.

Approximate Time: < 1 min.

Run Experiment

The THW-L1 Software automatically controls isothermal steps of temperature from -150 to 300°C.

Approximate Time: < 1 min.

Exporting Results

Smart THW-L1 Windows Software verifies quality of results and recommends changes if needed. Results report can be generated, saved, and exported to excel. For convenience results may also be emailed.

Approximate Time: 1 min.

THW-L1 Applications

Low back pressure was applied to the fluids, to allow measurements over their boiling point.

Thermal Conductivity of Water

Thermal Conductivity deviations from reference values:
Water < 2%

Thermal DIffusivity of Water

Thermal Diffusivity deviations from reference values:
Water < 2%

Thermal Conductivity of Heptane

Thermal Conductivity deviations from reference values:
Heptane < 3%

Thermal Diffusivity of Heptane

Thermal Diffusivity deviations from reference values:
Heptane < 2%

Calculated Specific Heat Capacity deviations from reference values:
Water < 2%
Heptane < 5%

Thermal Conductivity of Ethylene Glycol

Thermal Conductivity deviations from reference values:
Ethylene Glycol < 1%

Thermal Diffusivity of Ethylene Glycol

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.

Transient Hot Wire (THW) Models Comparison


Models	MP-1 with THW	THW-L1	THW-L2	MP-2 with THW-L3
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

*Depending on the Model used

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