Textile: Heat Transfer Coefficient of Fabrics

Why is it important to understand the heat transfer coefficient of fabrics?

The well-being of humans largely depends on clothing (i.e. textiles). Wrong clothing leads to discomfort and in extreme cases, to hypothermia (overcooling) or hyperthermia (overheating).

The organ which is responsible for the heat exchange between a human body and the environment is the skin. It acts as a kind of sensor which measures the heat flux. The heat transfer between skin and the environment is influenced by clothing. Understanding the effects of different textiles on this heat transfer is crucial in designing functional high-tech materials (e.g. firefighting protective gear)

Advantages of gSKIN® Heat Flux Sensors:

  • Small heat flux sensors with high sensitivity, easily integrate into application setups

  • Measure heat flux going in and out of the textile.

  • Possible in-situ measurements of fabrics

  • Enhanced monitoring of thermal processes in fabrics

  • Determining heat transfer coefficients

  • Possible to integrate according to ISO 8301 and ASTM C 518-04

Recent application examples:

ETH project with yarn made from gelatin

ETH researchers used the gSKIN® KIT-2615 C to determine the insulation quality of yarn made from gelatin. The yarn has similar qualities to merino wool fibers and could be an environmental friendly alternative to products made from petroleum, natural gas, or natural fibers. Read the full article on the ETH website in English or German.

In-situ measurements of different textile fabrics

Using gSKIN® Heat Flux Sensors for the measurement of heat transfer coefficients of fabric is simple. After identifying the spot of interest, the sensor is applied using skin-friendly tape. For read-out of the sensor signals, we recommend using our data loggers. Then, the data logger should be wired in such a way that the test subject can move freely. The data logger will log all heat fluxes (in W/m2), which can then be evaluated after the experiment.

Application note: Thermal characterization of footwear. Read the whole paper here

Illustrative image: in order to test thermal properties of textiles it is recommended to use hot guarded plate method.

Structure of gelatin at different levels
Source: „Porous, Water-Resistant Multifilament Yarn Spun from Gelatin”

The thermal insulation quality of different brands of camping air mattresses was tested using greenTEG’s U-Value Kit. The tests were conducted by PZT GmbH, an independent technical test laboratory in Germany and presented in Kassensturz, a Swiss television program dedicated to consumer protection. Watch it here.

A short Q&A is available here. For additional questions please do not hesitate to contact us directly.

We use the gSKIN® Heat Flux Sensors to characterize our thermo-regulating fabrics we develop based on a variety of technologies. The sensors are very easy to use, and deliver great experimental insights. Measuring heat flux helps us creating better fabric materials faster.

Why is it important to measure the core body temperature?

The Core Body Temperature is an important property to know in order to make accurate assessments of the human body’s state. The information can be used in a variety of applications:

  • Performance optimization for athletes

  • Monitoring inside incubators for prematurely born children

  • Alerting people working in highly dangerous environments (e.g. firefighters)

  • Sleep (quality) tracking

In these, and other applications, it is crucial to get reliable data of the core body temperature. Most of today’s measurement concepts use only temperature sensors to do this. These methods give a good approximation, but cannot measure the core temperature directly (unless inserted in the human body). The following section outlines a potential, more accurate method using gSKIN® Heat Flux Sensors and temperature sensors.

Advantages of gSKIN® Heat Flux Sensors:

  • Small heat flux sensor with high sensitivity, easily integrate into application setups

  • Non-invasive measurement technique with the potential to determine core body temperature

  • Easy to mount on the skin, does not disturb the exercise routine or working habits

  • Possibilty to be integrated with an easy read out software which allows for in-depth analysis

Measuring Core Body Temperature

The images on the right side show how a core body measurement is done. By placing a gSKIN® Heat Flux Sensor and a temperature sensor on a spot on the body (e.g. on the chest), the core body temperature can be calculated using this approach:

  1. Install a gSKIN®Heat Flux Sensor and temperature sensor on the chest.

  2. Log the temperature and heat flux measurements (in Watts/m2).

  3. Determine the thermal resistance (in Kelvin/Watt/m2) between the forehead and the core with the calibration measurement (assuming Tcore= 37o C).

  4. Calculate the temperature difference between the chest and core by using
    ΔT = (Heat Flux) x (Thermal Resistance)

  5. Calculate the temperature at the core by using
    TCore= TChest + ΔT

Illustrative image: attach the sensor to the skin with use of double sided tape and then put a bandage around it, allowing free movement.

The picture presents a simplified measurement method

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Thermal Influences in Precision Instruments

Why you should measure thermal influences?

Thermal influences are present in all systems and limit the achievable precision e.g. by inducing thermal expansion. In order to compensate for these effects, it is important to measure the thermal influences.

How to monitor thermal influences

The current approach to control thermal effects is based on multi-parameter models. These models are derived empirically, and are used to measure and predict thermal influences. The most common parameters in such models are temperatures at various locations in the system and situational information (e.g. power consumption of motor). A certain compensation of thermal effects is accomplished with this method. However, in some applications, higher measurement precision and robustness towards external factors like changing ambient temperature is required to obtain a satisfactory compensation. This is where heat flux sensors add a lot of value.

“With gSKIN® Heat Flux Sensors, a customer was able to increase the precision within their measurement product by a factor of 4!”

Specifically, gSKIN® Heat Flux Sensors add value to these three areas where temperature sensors are limited:

  1. Non-linear temperature profile: A large number of temperature sensors are necessary to reconstruct the temperature profile with sufficient accuracy.

  2. Temperature resolution: Standard temperature sensors have a limited temperature resolution, which limits the measurement accuracy.

  3. Heat flow dynamics: The change of incoming or outgoing heat flow is unknown since primarly, it is not determined experimentally. An exact statement about whether the system is heating up or cooling down is therefore difficult.


For whom is it relevant?

The integration of heat flux sensors for optimized thermal control is only relevant to manufacturers of the highest precision systems. Systems that might benefit from heat flux sensors are:

  • Dosing systems

  • Positioning systems

  • Lithography

  • Bonding systems

  • Metrology systems

If you are unsure about the potential benefits in your products, contact us to discuss it.

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Solar Radiation Measurements

Fast and precise solar radiation measurements

greenTEG’s gSKIN® Heat Flux Sensor enables fast and highly precise solar radiation measurements (i.e. ultraviolet and visible radiation). Precise data on solar radiation is indispensable for the optimization of photovoltaic installations, in meteorological research or in building automation systems.

Solar radiation measurement applications

  • Optimization of photovoltaic installations: The power output of a photovoltaic system depends on its alignment towards the sun at any given time. The ability to gather precise data quickly is therefore crucial to optimize the efficiency of photovoltaic installations. The gSKIN® Heat Flux Sensor enables you to collect data on solar radiation, which in turn serves as an important reference for predictions on the power output of PV systems, the monitoring of their efficiency, decisions on maintenance (cleaning) and many more.

  • Precise data in meteorological research: The sun has a profound influence on all meteorological processes. Therefore, precise data on global solar radiation (direct and scattered solar radiation) is the basis for research and predictions in meteorology.

  • Smart building automation systems: To increase the energy efficiency of buildings, smart automation systems gain increasing importance. These systems regulate processes according to many environmental parameters, the most important of which, is solar irradiation. The gSKIN® Heat Flux Sensor can, for example, be used to regulate sun blinds and heating automation in buildings in order to reduce its overall energy consumption.

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To measure solar radiation, the gSKIN® can either be used as is or as a built in part of a pyranometer or other measurement systems. When solar rays hit the black coated sensor they are converted into heat, which in turn is converted into an output voltage by the ultra-sensitive thermopiles of the sensor. To calculate the solar radiative flux, the output voltage is divided by the sensor-specific sensitivity. You can easily read-out the signal with a datalogger or a voltmeter.

Advantages of the gSKIN® Heat Flux Sensor for solar radiation measurements

The following features make the gSKIN® Heat Flux Sensor the ideal tool for solar radiation measurements:

  • Fast rise times (sub-second)

  • A homogenous sensitivity across the sensor surface

  • Absolute flat surface (no topography) for best measurement results

  • Customized sensor designs to ensure best performance for specific applications

  • Measurement of all wavelengths with the same sensitivity

  • The sensor’s output is linear to the measured solar power. This guarantees easy read-out.

If you are unsure about the potential benefits in your products, contact us to discuss it.

Calorimetry (Non-Invasive Measurement)

Where are heat flux sensors used?

gSKIN® Heat Flux Sensors provide calorimetric data instantly and directly. The sensors are designed to measure energy down to 0.03 W/m² (e.g. 0.3 J/m² in 10 seconds). This functionality can be used in research and also integrated into calorimetric devices within the fields of:

Chemical engineering, where calorimetric data is essential for process safety control. The heat release rate of chemical reactions can be measured directly with heat flux sensors.

Material science (e.g. PCM), where engineering of energetic materials like phase change materials for latent heat energy storage relies on precise calorimetric measurements. The same applies for many analytical techniques in materials science like the measurement of heat capacities or the investigation of microstructural changes.

Advantages of gSKIN® Heat Flux Sensors:

  • Customizable dimensions enable the straight-forward integration into complex measurement setups

  • Fast response time increases the productivity of research labs and shortens measurement periods

  • Small size, high sensitivty, and quick response time

  • Non-invasive measurement offering highest precision

  • Easy to integrate with gSKIN® DLOG dataloggers, other relevant equipment, or voltmeter

"Using the gSKIN® Heat Flux Sensors, we were able to improve the measurement of dynamic effects"

Mass Flow Measurement (Non-invasive Measurement)

Why are heat flux sensors important?

Today’s calorimetric mass flow sensors use temperature sensors as the core sensing element. While this type of mass flow sensor is tried and tested, it is nonetheless not the most cost-effective solution. Mass flow sensors can be improved by integrating heat flux sensors into the measurement setup.

Mass flow measurement with gSKIN® Heat Flux Sensors

There are two basic methods for mass flow measurements with heat flux sensors. Here, we describe one of these methods.

  1. Install one gSKIN® Heat Flux Sensor. The heat flux sensor measures the heat that passes through its surface in Watts.

  2. Install two temperature sensors (Text and Tfluid). Text describes the external temperature, and Tfluid the temperature of the fluid. Both temperatures should be measured close to the heat flux sensor.

  3. Determine the heat transfer coefficients of the heat flux sensor to air (Kair-HFS) and the heat conductivity of the heat flux sensor (KHFS).

  4. Calculate the heat transfer coefficient of the heat flux sensor to air (KHFS-fluid) by using
    KHFS-fluid= Heat flux x (Tfluid – Text)-1 – Kair-HFS – KHFS

  5. Determine the parameters a, b, and c of the setup. These parameters are needed for King’s Law
    (KHFS-fluid= a + b x vFc)

  6. Calculate the velocity of the fluid by applying King’s Law vF= ((KHFS-fluid – a)/b)1/c

Advantages of gSKIN® Heat Flux Sensors:

  • Easy to integrate into the measurement setup

  • High precision, starting in the mK temperature range

  • Cost-effective in comparison to high precision temperature sensors

  • Robust design, delivering the same level of resolution as temperature sensors

  • Non-invasive measurement of mass flow

Fouling Detection (Non-invasive Measurement)

How to detect fouling with gSKIN® Heat Flux Sensors?

Fouling is a process that creates a layer on the component where it is deposited (e.g. furring in a water pipe). This layer increases the absolute thermal resistance of the component. The increase of the absolute thermal resistance can be measured by combining a heat flux sensor with two temperature sensors.

Phase Change Material (PCM) Characterization


Fouling is a process that creates a layer on the component where it is deposited (e.g. furring in a water pipe). This layer increases the absolute thermal resistance of the component. The increase of the absolute thermal resistance can be measured by combining a heat flux sensor with two temperature sensors.

Advantages of gSKIN® Heat Flux Sensors:

  • Small heat flux sensor with high sensitivity, easily integrated into the application setups

  • Non-invasive measurement technique for determining fouling

  • Flexible, easy to mount on pipes and boilers

Illustrative image: mounting of a sensor on a pipe

Absolute Thermal Resistance Calculation

The absolute thermal resistance between the T1 and T2 are defined by

Rth = ∆T / HF

Rth = Absolute thermal resistance, in K/W
HF = Heat Flux, in W
∆T = Temperature difference, in

The two figures on the right display a common structure in heat exchangers. As soon as fouling starts to deposit on the heat exchanger fins, the Absolute Thermal Resistance Rth starts to increase. When ∆T and HF are measured, this change can be detected.

While the principle is explained for fouling, it can also apply to any other depositions that need to be detected. Other common examples are ice formation (e.g. on plane wings), and algae formation (e.g. on ship hulls).

Absolute Thermal Resistance without Fouling

Absolute Thermal Resistance with Fouling

gSKIN® Heat Flux Sensors for Research and Development

We offer an array of different products for R&D.These include heat flux sensors in different sizes and data loggers for fast and reliable data acquisition.

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gSKIN® Heat Flux Sensors for OEM Applications

We offer heat flux sensors suitable for OEM applications. Please contact us directly to consult you and discuss your application.

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