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Sensor for Convective and Radiative Heat Loss

Final Report Summary - CORA (Sensor for Convective and Radiative Heat Loss)

Executive Summary:
In the context of the CORA project measurement instrumentation and detectability of heat transitions separately for convection and radiation of small surface areas was examined.
On this basis a miniature sensor was developed. The heat transfer is determined by commercial Peltier modules and additionally the exact surface temperature is detected with an integrated thermocouple.

The complete sensor element consists of two heat flux sensors. One sensor element is blackened to approach the emission behavior of a black body. This sensor is cooled both by convection and radiation. Via a second sensor with a mirrored surface a pure convection can be determined. This surface was gold plated with 24Kt to get a good resistance against environmental influences in addition to high reflection.

The sensor signals are evaluated through a Keithley K2000DMM with a 10 channel scanner card. Its measurement procedures are controlled through a PC program with graphical user interface and the transfer of measurement data to a PC hard disk archive can be accomplished. Additionally, a data export in CSV format is possible to visualize measurement data.

Project Context and Objectives:
In the context of the CORA project measurement instrumentation and detectability of heat transitions separately for convection and radiation of small surface areas was examined.
On this basis a miniature sensor was developed. The heat transfer is determined by commercial Peltier modules and additionally the exact surface temperature is detected with an integrated thermo couple. Two heat flux sensors based on those of the company RDF are used as the sensor elements. For these sensors calibration data are available, which can be entered into the evaluation software.

One sensor element is blackened to approach the emission behavior of a black body. This sensor is cooled both by convection and radiation. Via a second sensor with a mirrored surface a pure convection can be determined. This surface was gold plated with 24Kt to get a good resistance against environmental influences in addition to high reflection.

Both sensors are glued on 0.4mm thick silver plate which is intended to ensure, beside the mechanical stability, a planar rest on the test surface. Alternatively the sensors also can be affixed directly on the measured object.

Previously, attempts with Peltier elements have been made. The characteristics of peltier elements seemed to be well suited. However, it turned out that the transfer constant was highly non-linear and has a large scatter of output signals. This would have required a very
complex characteristic identification and correction. Moreover there were mechanical disadvantages (e.g. a high overall height).

Therefor we went back to the industrial heat flow sensors from the company RDF. As mentioned above all electric and thermal data for every sensor is attached to a data sheet. These sensors also have a thermocouple for measuring the surface temperature which is integrated into the substrate.

All voltages are switched by a 10 Channel scanner card to a Keithley K2000 DMM. Its measurement procedures are controlled through a PC program with graphical user interface.
First the system parameters (calibration data of the sensors, sampling time etc.) are entered.
After this the measurement procedure can be started. The final data are archived on the PC hard disk. In addition, a data export in CSV format is possible to visualize measurement data,
for example in Excel.

Project Results:
In line with the main objective the main Scientific and technical result of the CORA project was the development of a miniature sensor for convective and radiative heat loss. This is fully in line with the above summary of the project context and objectives. The heat transfer is determined with the CORA sensor development by commercial Peltier modules and additionally the exact surface temperature is detected with an integrated thermocouple. Two heat flux sensors based on those of the company RDF are used as the sensor elements. For these sensors calibration data are available, which can be entered into the evaluation software.

One sensor element is blackened to approach the emission behavior of a black body. This sensor is cooled both by convection and radiation. Via a second sensor with a mirrored surface a pure convection can be determined. This surface was gold plated with 24Kt to get a good resistance against environmental influences in addition to high reflection.

Both sensors are glued on 0.4mm thick silver plate which is intended to ensure, beside the mechanical stability, a planar rest on the test surface. Alternatively the sensors also can be affixed directly on the measured object.

Previously, attempts with Peltier elements have been made. The characteristics of peltier elements seemed to be well suited. However, it turned out that the transfer constant was highly non-linear and has a large scatter of output signals. This would have required a very
complex characteristic identification and correction. Moreover there were mechanical disadvantages (e.g. a high overall height).

Therefor we went back to the industrial heat flow sensors from the company RDF. As mentioned above all electric and thermal data for every sensor is attached to a data sheet. These sensors also have a thermocouple for measuring the surface temperature which is integrated into the substrate.

All voltages are switched by a 10 Channel scanner card to a Keithley K2000 DMM. Its measurement procedures are controlled through a PC program with graphical user interface.
First the system parameters (calibration data of the sensors, sampling time etc.) are entered.
After this the measurement procedure can be started. The final data are archived on the PC hard disk. In addition, a data export in CSV format is possible to visualize measurement data,
for example in Excel.

Potential Impact:
A small surface sensor, which measures energy transport through a surface element, can be utilized in a variety of possible fields of application. For example, by arranging several sensors in a matrix shape, hotspots can be identified and if necessary, eliminated by making constructional modifications. In this way, it is possible to use larger areas for the cooling of components and to purely passively dissipate the resulting heat. A particular advantage arises from the bi-directional properties of the sensor, not only can the heat dissipation at a particular point be measured, but also the heat absorption from the environment.


Furthermore the strengthening of the European aircraft industry and the businesses that are dependent on it is expected when applying the sensor device developed within CORA for the
detection of heat loss, which is especially relevant for future more-electric architectures with their localized heat release. Thereby, safeguarding highly-qualified jobs and bolstering the small and medium sized businesses.

The developed sensor was presented as a prototype system to the interested public on the Exponatec Cologne 2011.

It is envisaged to achieve a market launch for the CORA sensor after 31/12/2014.


List of Websites:
Krah & Grote Messtechnik
Mr. Günter Suchan
Bahnhofstr. 38
83624 Otterfing
Germany

website: www.krah-grote.com