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Thermtest TPS-EFF thermal effusivity meter

TPS-EFFusivity Meter

A portable Thermal Effusivity Meter for the Measurement of Textiles, Fabrics, and Solids. TPS-EFF uses a single-sided TPS sensor along with 2 and 10 second test times to fully understand measurement of comfort with touch time.

ASTM D7984-16

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Featured Transient Plane Source Capabilities

Thermal Effusivity (W√s/m2K) is described as a materials ability to exchange heat with its surroundings. Surface haptics is a branch of psychology, describing the sense of touch, localized to the skin surface. The feeling of warmth and coolness (thermal effusivity) makes up the feeling of comfort, or the desired effect, which goes into the touched material surface. This is an important field of measurement for textiles, fabrics and solids.
  • Follows International Standard ASTM D7984-16
  • Portable, Economical, and Accurate
  • Easy to use
  • Test time 2 and 10 seconds
  • No user calibrations required
Thermtest-TPS-EFF-Thermal-Effusivity-Meter-with-Case
The TPS-EFF (Transient Plane Source-EFFusivity) is a portable meter for direct determination of thermal effusivity of textiles and other low effusivity materials, in accordance with ASTM D7984-16. With a single measurement of 2 or 10 seconds in duration, materials can be accurately measured for thermal effusivity.

The TPS-EFF uses a single-sided 30 mm diameter TPS sensor and short test times, to ensure one-dimensional heat flow. During the measurement, the sensor is heated using a constant current source, while the temperature rise of the sample is simultaneously recorded with time, by monitoring the change in electrical resistance of the wire spiral. The slope of temperature against a special function of time, is used to calculate the thermal effusivity of the material. For materials of relatively high effusivity, the slope will be lower, than materials of low effusivity.

TPS-EFF Thermal Effusivity Meter equation graph
Mathematically, thermal effusivity equates to the square root of the product of thermal conductivity (W/m•K), Density (kg/m3) and Heat Capacity (J/kg•K). For certain materials, like textiles, there are often other modes of heat transfer, such as convection and radiation. These modes of heat transfer alter the thermal conductIVITY to thermal conductANCE. The resulting term used for measurement of materials like this is referred to as Thermal Effusance.

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TPS-EFFusivity Meter SPECIFICATIONS

Materials Textiles, Fabrics and Solids
Measurement Capabilities 1-Dimensional
Thermal Effusivity Range 35 to 1700 W√s/m2K
Measurement Time 2 and 10 seconds
Reproducibility 2%
Accuracy 5%
Temperature Range1 -10 to 50°C
Minimum Sample Size 35 mm diameter x thickness dependent on Effusivity
Maximum Sample Size Unlimited
Moisture Range 0 to 90% (non-condensing)
Sensor Diameter 30 mm
Standards ASTM D7984-16
Test Method Transient Plane Source (TPS)

1 Requires cooling/heating apparatus

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Portable. Economical. Accurate.

TPS EFF 30mm Sensor Thermal Effusivity Meter for Textiles, Fabrics and Solids

Standard TPS-EFF Sensor

The TPS-EFF comes with a standard 30 mm diameter, single-sided sensor for testing textiles, fabrics and solids. The spring loaded sensor can be used in two testing configurations; sample on top of sensor, or sensor on top of sample. At the push of a button, samples can be measured at 2 and 10 second test times. The additional 10 second test time allows for superior characterization of materials feeling of warmth, or coolness. Ambient temperature and results are conveniently displayed on the test screen. Results can then be saved and exported to Excel.

Compression, Humidity and Temperature

Several application and environmental specific conditions can affect the thermal effusivity (feeling of warmth or coolness) of a material. When used with a compression stand and environmental chamber, the TPS-EFF is able measure the effect of compression, humidity and temperature on a materials thermal effusivity.

TPS-EFF Thermal Effusivity Compression, Humidity and Temperature
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SAMPLE MEASUREMENT

Sample fabric step1
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The Sample

Using the TPS-EFF, samples of unlimited size can be tested, sample should be at least 30 mm in diameter to allow contact with TPS-EFF sensor. Measurement on various textiles, fabrics and solids are possible. Care should be taken to ensure sufficient thickness of sample, the divergence technique may be used to confirm this.

Approximate Time: < 1 minute

TPS-EFFusivity Sensor with brass piece and fabric sample step2

2

Place Sample on Sensor

Once a sample has been prepared, measurements may be configured in one of two ways; sample placed on top of sensor, or sensor placed on top of sample.

Approximate Time: < 1 minute

tps-eff-press-button

3

Measurement

From the portable TPS-EFF, a test time of 2 or 10 seconds may be selected and test activated with the push of a button.

Approximate Time: <2 minute

 

tps-eff-meter-export-data-to-excel

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Result Calculations

Upon completion of tests, temperature and thermal effusivity results are displayed on screen. Results can then be exported from the TPS-EFF to Excel, via Micro-SD or USB.

Approximate Time: 1 minutes

 

Sample fabric step1

1

 

The Sample

Using the TPS-EFF, samples of unlimited size can be tested, sample should be at least 30 mm in diameter to allow contact with TPS-EFF sensor. Measurement on various textiles, fabrics and solids are possible. Care should be taken to ensure sufficient thickness of sample, the divergence technique may be used to confirm this.

Approximate Time: < 1 minute

TPS-EFFusivity Sensor with fabric sample step2

2

 

Place Sample on Sensor

Once a sample has been prepared, measurements may be configured in one of two ways; sample placed on top of sensor, or sensor placed on top of sample.

Approximate Time: < 1 minute

Activate Measurement TPS-EFFusivity Meter Step 3

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Measurement

From the portable TPS-EFF, a test time of 2 or 10 seconds may be selected and test activated with the push of a button.

Approximate Time: <2 minute

 

TPS-EFFusivity meter export results step 4

4

 

Result Calculations

Upon completion of tests, temperature and thermal effusivity results are displayed on screen. Results can then be exported from the TPS-EFF to Excel, via Micro-SD or USB.

Approximate Time: 1 minutes

 

EFFUSIVITY – EFFUSANCE OF TEXTILES, FABRICS AND SOLIDS

As the measured thermal effusivity of textiles and fabrics encompasses various modes of heat transport (conductivity, convection and radiation), the results are referred to as thermal effusance. The measurement of solids, where the main heat transport property is thermal conductivity, results are properly referred to as thermal effusivity.

EFFUSIVITY - EFFUSANCE OF TEXTILES, FABRICS AND SOLIDS

TEST TIMES TO SIMULATE TOUCH TIME

To simulate the feeling of prolonged cool to touch sensation, each material was prepared in sufficient thickness and individually measured for thermal effusivity at 2 and 10 seconds. This experiment was then repeated by layering Fabric 1 on top of Wadding 2. Results of the experiment show with sufficient thickness, an individual material feels the same at different touch – test times, different from material to material. Additionally, when one layer of higher effusivity material, Fabric 1, is placed on top of a lower thermal effusivity material, Wadding 2, the different touch – test times shows a decreasing feeling of coolness with time. This testing capability allows TPS-EFF users to layer different types of materials, to achieve a desired feeling of coolness, or warmth, with varying touch times.

TEST TIMES TO SIMULATE TOUCH TIME
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Applications using the TPS-EFF

Thermal Effusivity

Thermal Effusivity of Multiple Layers and Force

Discovering the feeling decays with test time (touch time) as heat from the sensor (your skin) is dominated by the lower effusivity layer when a more effusive layer is placed over a more insulative layer and measured.

Thermal Effusivity applications

Testing Thermal Effusivity with Force

Testing Thermal effusivity of Memory Foam with a compression force of 1 lb and 2 lb

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Frequently Asked Questions

General FAQ

1. What is thermal effusivity?
Thermal effusivity is a special quantity relating the thermal conductivity, heat capacity and density of a material. This relation determines heat transfer across material interfaces. Thermal effusivity can be used to measure how a material feels, in terms of coolness or warmth.
2. Can thermal conductivity be calculated from thermal effusivity?
No, thermal effusivity should never be used to measure or calculate thermal conductivity due to possibility of significant error as the thermal conductivity included in the quantity is not only heat transfer through conduction.
3. Who is interested in measuring thermal effusivity?
Anyone who wants to select or design a material to feel cool or warm. Additionally, synthetic materials can be designed to feel more authentic. For example: synthetic composite wood can be designed to feel more like the real wood equivalent.
4. How can 2 second and 10 second tests be used to better characterize a material for the feeling of coolness or warmth?
In addition to the short test time (1 to 3 seconds) noted in ASTM 7984-16, the TPS-EFF can measure 10 seconds as well. The feeling of coolness or warmth can be fully characterized for longer contact – touch times.
5. Do materials measure the same thermal effusvity for 2 and 10 second test times?
Single materials of sufficient thickness will measure the same thermal effusivity. Depending on the thickness of each layer of layered materials, a decrease or increase of thermal effusivity with test time is possible. As heat from sensor penetrates through different layers, the feeling of coolness or warmth may change. This phenomenon can be used to further select or design how a layered material feels with contact – touch time.
7. Why is the TPS-EFF portable?
The TPS-EFF was designed to be used in the lab or taken to a specific location with the included small carrying case. This portability provides users maximum flexibility at a affordable price with no reduction in accuracy.

ASTM 7984-16 FAQ

1. Does the TPS-EFF comply with ASTM 7984-16?
Yes
2. How does thickness relate to thermal effusivity?
The required probing depth depends on the diffusivity of the material but is generally below 1cm for materials covered by the standard.
3. How is the TPS-EFF calibrated?
The TPS-EFF is calibrated by applying a model of 1D heat transfer with a given sensor heat capacity and backing insulation effusivity to obtain sample effusivity.

Performing tests on known materials and deriving a calibration curve to correct the raw effusivity reading.

4. Does the TPS-EFF have a guard ring?
No, the TPS-EFF does not require a guard ring. With the TPS-EFF’s larger diameter sensor (30 mm), a guard ring is not required to keep the measurement one-dimensional. The increased area and short test time ensure the heat penetration is one-dimensional for the thermal effusivity covered in standard.
5. Why does the TPS-EFF also measure 10 seconds?
Alongside 2 second tests, 10 second tests are supported as they allow for greater penetration depth, which allows for expanded measurements of contact – touch time to characterize a materials feeling of coolness or warmth. This additional information can be used to alter how a material feels over longer touch times, especially useful for layered textiles and fabrics.
6. What is thermal effusivity?
Thermal effusivity is a special quantity relating the thermal conductivity, heat capacity and density of a material. This relation determines heat transfer across material interfaces. Thermal effusivity can be used to measure how a material feels, in terms of coolness or warmth. It is important to understand, as the thermal conductivity included in the quantity is not only heat transfer through conduction, thermal effusivity should never be used to measure or calculate thermal conductivity due to possibility of significant error.
7. Does the TPS-EFF measure within 1 to 3 seconds? Does it measure longer?
The TPS-EFF can perform 2 second and 10 second tests.
8. How does the TPS-EFF ensure one dimensional heat flow?
One dimensional heat flow is ensured by using a sensor with a large surface area, limiting the test time to 2-10s, and restricting test materials to those covered by the ASTM standard.
9. Is the TPS-EFF calibrated?
Yes, the TPS-EFF is calibrated. This is necessary due to the construction of the sensor.
10. Does the TPS-EFF measure within 5% of known materials?
Measurements made with the TPS-EFF fall within 5% of known materials.
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