Flux Probe Installation
Silicon encased heat flux sensor for measurements on rugged surfacesThe can have different origins; in principle convective, radiative as well as conductive heat can be measured. Heat flux sensors are known under different names, such as heat flux transducers, heat flux gauges, heat flux plates.
Some instruments that actually are single-purpose heat flux sensors like for solar radiation measurement. Other heat flux sensors include (also known as a circular-foil gauge), thin-film, and Schmidt-Boelter gauges. In units, the is measured in, and the heat flux is computed in per meter squared.
Contents.Usage Heat flux sensors are used for a variety of applications. Common applications are studies of building envelope thermal resistance, studies of the effect of fire and flames or laser power measurements. More exotic applications include estimation of fouling on surfaces, temperature measurement of moving foil material, etc.The total heat flux is composed of a, and part. Depending on the application, one might want to measure all three of these quantities or single one out.An example of measurement of conductive heat flux is a heat flux plate incorporated into a wall.An example of measurement of radiative heat flux density is a for measurement of.An example of a sensor sensitive to radiative as well as convective heat flux is a or Schmidt–Boelter gauge, used for studies of fire and flames. The must measure convection perpendicular to the face of the sensor to be accurate due to the circular-foil construction, while the wire-wound geometry of the Schmidt-Boelter gauge can measure both perpendicular and parallel flows. In this case the sensor is mounted on a water-cooled body.
Such sensors are used in fire resistance testing to put the fire to which samples are exposed to the right intensity level.There are various examples of sensors that internally use heat flux sensors examples are, etc.We will discuss three large fields of application in what follows. Applications in meteorology and agriculture Soil heat flux is a most important parameter in agro-meteorological studies, since it allows one to study the amount of energy stored in the soil as a function of time.Typically two or three sensors are buried in the ground around a meteorological station at a depth of around 4 cm below the surface. The problems that are encountered in soil are threefold:First is the fact that the thermal properties of the soil are constantly changing by absorption and subsequent evaporation of water. Second, the flow of water through the soil also represents a flow of energy, going together with a thermal shock, which often is misinterpreted by conventional sensors. The third aspect of soil is that by the constant process of wetting and drying and by the animals living on the soil, the quality of the contact between sensor and soil is not known.The result of all this is the quality of the data in soil heat flux measurement is not under control; the measurement of soil heat flux is considered to be extremely difficult.Applications in building physics In a world ever more concerned with saving energy, studying the thermal properties of buildings has become a growing field of interest. One of the starting points in these studies is the mounting of heat flux sensors on walls in existing buildings or structures built especially for this type of research.
Heat flux sensors mounted to building walls or envelope component can monitor the amount of heat energy loss/gain through that component and/or can be used to measure the envelope thermal resistance, or thermal transmittance,.The measurement of heat flux in walls is comparable to that in soil in many respects. Two major differences however are the fact that the thermal properties of a wall generally do not change (provided its moisture content does not change) and that it is not always possible to insert the heat flux sensor in the wall, so that it has to be mounted on its inner or outer surface.When the heat flux sensor has to be mounted on the surface of the wall, one has to take care that the added is not too large. Also the spectral properties should be matching those of the wall as closely as possible. If the sensor is exposed to, this is especially important.
Flux Probe Installation Kit
In this case one should consider painting the sensor in the same color as the wall. Also in walls the use of self-calibrating heat flux sensors should be considered. Applications in medical studies The measurement of the heat exchange of human beings is of importance for medical studies, and when designing clothing, immersion suits and sleeping bags.A difficulty during this measurement is that the human skin is not particularly suitable for the mounting of heat flux sensors.
Also the sensor has to be thin: the skin essentially is a constant temperature heat sink, so added thermal resistance has to be avoided. Another problem is that test persons might be moving.
The contact between the test person and the sensor can be lost. For this reason, whenever a high level of quality assurance of the measurement is required, it can be recommended to use a self-calibrating sensor.Applications in industry. Gardon or Schmidt Boelter gauge showing the instrument main components: metal body, black sensor, water cooling pipe in and out, mounting flange, and cable. Dimensions: diameter housing is 25mm. Photo shows model SBG01.Other parameters that are determining sensor properties are the electrical characteristics of the thermocouple.
The temperature dependence of the thermocouple causes the temperature dependence and the non-linearity of the heat flux sensor. The non linearity at a certain temperature is in fact the derivative of the temperature dependence at that temperature.However, a well designed sensor may have a lower temperature dependence and better linearity than expected. There are two ways of achieving this:As a first possibility, the thermal dependence of conductivity of the filling material and of the thermocouple material can be used to counterbalance the temperature dependence of the voltage that is generated by the thermopile. Another possibility to minimize the temperature dependence of a heat flux sensor, is to use a resistance network with an incorporated thermistor. The temperature dependence of the thermistor will balance the temperature dependence of the thermopile.Another factor that determines heat flux sensor behavior, is the construction of the sensor. In particular some designs have a strongly nonuniform sensitivity. Serious sam the second encounter maps download.
Others even exhibit a sensitivity to lateral fluxes. The sensor schematically given in the above figure would for example also be sensitive to heat flows from left to right.
This type of behavior will not cause problems as long as fluxes are uniform and in one direction only. FHF02SC, a thin self-calibrating heat flux sensor. Sensors that are embedded in construction can sometimes be very troublesome to remove if need to be re-calibrated (in a lab). Some sensors incorporate heaters in order to be able to leave the sensor in place while performing a re-calibration.While heat flux sensors are typically supplied with a sensitivity by the manufacturer, there are times and situations that call for a re-calibration of the sensor. Especially in building walls or envelopes the heat flux sensors can not be removed after the initial installation or may be very difficult te reach. In order to calibrate the sensor, some come with an integrated heater with specified characteristics.
By applying a known voltage on and current through the heater, a controlled heat flux is provided which can be used to calculate the new sensitivity.Error sources The interpretation of measurement results of heat flux sensors is often done assuming that the phenomenon that is studied, is quasi-static and taking place in a direction transversal to the sensor surface.Dynamic effects and lateral fluxes are possible error sources.Dynamic effects The assumption that conditions are quasi-static should be related to the response time of the detector. R.Gardon, 'An instrument for the direct measurement of intense thermal radiation', Rev. Instrum., 24, 366-370, 1953. T.E. Diller, Advances in Heat Transfer, Vol. 23, p.297-298, Academic Press, 1993. C.T.
Kidd and C.G. Nelson, 'How the Schmidt-Boelter gage really works,' Proc. Symp., Research Triangle Park, NC: ISA, 1995, 347-368. FluxTeq Heat Flux Sensors National Lab-Approved Heat Flux Sensors. Retrieved 2017-11-16. (PDF).
(1.0 ed.). 2017 2017-01-01. From the original on 2017-11-23. Retrieved 2018-05-30.