Heat flux sensor

Medtherm 64 Series Heat Flux Sensor (Schmidt-Boelter type)... 

Commercially available heat flux sensors with thermopiles sandwiched at the interface were used to measure the local temperatures and heat fluxes that is. Omega Corporation, Model HFS-4 devices. The total thickness of the sensors was nominally less then 0.18 mm, and a schematic of the device is shown in Fig. 5.10. By measuring the temperature difference across the center film (AT) and assuming one-dimentional heat transfer, then the heat flux can be measured using the temperature difference and the thermal conductivity of the film. The local temperature is recorded using the thermocouple nearest the barrel. The senors were calibrated at ambient condition with zero heat flux. 

Perry and Lee [28,29] offer an enhancement of QPA, based upon use of dual heat flux sensors and additional thermocouples in autoclave curing. This enhancement entails determining heat transfer properties during the cure, then using these properties in conjunction with PID regulatory control of autoclave temperature. Using the additional sensors, Perry and Lee employ an on-line Damkohler number in lieu of the second time-derivative of temperature to avoid exothermic thermal runaway within the prepreg stack thermoset resin. The Damkohler number is defined as ... 

Bae et al. [10] at Maryland University (USA) have developed a local heat transfer rates measurement device. The device was built for measuring heat-transfer rates at many points underneath areas of interest in heat transfer systems, in order to determine the heat-transfer coefficient as a function of position and time (Figure 8). The deviee is a planar array of small heaters that also serve as heat-flux sensors. The device enables measurement of the loeal heat transfer from the surfaee, with very high temporal and spatial resolution. The information provided by this, and other similar devices, could be used to validate or improve analytical and numerical models used in eomputational simulations. 

With a thermal resistance heat flux sensor, the presence of the instrument in the environment will disturb the temperature field somewhat and introduce an error in the measurement. Wall-heating systems require a heat source (or sink) and an appropriate heat balance equation to determine the heat flux. The temperature-transient types require a measurement of the temperature variation with time. The energy input or output types require good control or measurement of the temperature of the heat flux instrument. For the fourth type, the properties of the fluid are required. A brief discussion of different types of heat flux sensors is given below. 

The temperature drop across the thermal resistance is usually measured with a multijunction thermocouple (thermopile) to increase the sensitivity of the device. The sensitivity of a heat flux sensor depends on the slab material and slab thickness, which essentially determine Rik, and the number of junctions in the thermopile, which determines the output EMF as a function of A T. 

Heat flux sensors having a large sensitivity (output per unit heat flux) generally have a low maximum allowable heat flux and relatively large physical size (thus slower response time). For example, one commercial unit with a sensitivity of 60 pV per W/m2 has a response time of a few seconds [112] whereas a unit that can accommodate heat fluxes up to 6 x 105 W/m2 has a sensitivity of 0.006 pV per W/m2 and a response time of less than one second [113]. 

Goldstein and Chiang [12], Arai, Matsunami, and Churchill [1], and Okoh and Brown [13] discuss the theory of operation of the heat flux techniques discussed here. Bachmann, Chambers, and Giedt [14] experimentally studied how the installation of heat flux sensors embedded in a surface affects the actual heat transfer in the body. They concluded that proper sensor design can minimize the heat flux measurement errors caused by probe thermal resistance that can disturb the heat... 

Brajuskovic, Matovic, and Afgan [84] and Brajuskovic, and Afgan [85] describe a blow-off heat flux sensor that uses gas flowing through a porous sintered metal disc to measure hemispherical radiation heat flux in a dirty environment that includes high particulate loads. The gas acts to blow off fhe boundary layer at the surface. It also cools the instrument, prevents fouling of the porous... 

Ash, R. L. "Response Characteristics of Thin Foil Heat Flux Sensors." AIAA Journal 7, no. 12 (1969) 2332-35. 

Stradomskiy, M. V., Maksimov, Y. A., and Malyarov, V. S. "Calibration of High-Temperature Heat Flux Sensors." Heat Transfer-Soviet Research 20, no. 4 (1988) 562-68. 

Heat flux measurements are taken to understand the uniformity of heat transfer and hence, efficiency of the oxy-burner. Heat flux probes are commonly used in such measurement. These probes usually have wide angle and measure radiative or total (radiative and convective) heat fluxes. Sensor elements in the probe use a circular foil disk on the front side facing flue gases. The edge of the disk is continuously in contact with a heat sink. The temperature difference between the center of the foil... 

LOW TEMPERATURE HIGH SENSITIVITY TEMPERATURE COMPENSATED HEAT FLUX SENSOR. 

The Desert Tortoise included heat-flux sensors buried just beneath the surface, and Nielsen and Ott (1999) fitted a solution of the suh-surface flux measured at the centerline on 100 m downstream of the source in trial DT3. The best lit indicated that the dimensionless exposure time was F 0.24, implying that the local surface flux decreased to 62% of its initial value (po. 

Heat flux sensors to measure heat flow between the ground and the dispersing cloud were located on the desert surface at locations in the downwind arrays. Type K thermocouples were positioned on the downwind array towers to measure cloud temperature as it moved downwind. Open-path IR sensors for the measurement of LNG concentration were positioned at multiple levels on the downwind arrays. High-speed motion picture cameras and infrared imagers were also positioned to make visual recordings of the experiments. 

The spill area was instrumented with numerous Type K thermocouples to record temperatures at various locations within the vapor barrier fence. These were within the pond and upwind of the billboard. Heat flux sensors were also placed within the vapor barrier fence area as well as at four locations downwind of the spill area outside of the vapor barrier fence. Humidity sensors were located both within and outside the vapor barrier fence. The spill line from the tank farm to the spill area was instrumented to provide instantaneous measurement of the flow rate of LNG to the spill area. 

The dispersal pan was mounted on load cells that allowed determination of total amount of chemical released into the pan. Heat flux sensors were placed at locations downwind and crosswind from the pan containing the released material. These were evidently to measure the amount of radiant heat. These locations had two heights at which measurements were recorded, 3 and 6 ft above ground level. In addition, temperatures were recorded at three locations (1) the air temperature approximately 3 ft above the pan bottom, (2) the reaction temperature approximately 3 in above the chemical level, and (3) the chemical temperature approximately 2 in above the pan bottom. 

Figure 2.6 A textile-based heat flux sensor comprising a thermoelectric wire woven into a textile substrate.

Gidik, H., Bedek, G., Dupont, D., Codau, C., 2015. Impact of the textile substrate on the heat transfer of a textile heat flux sensor. Sensors and Actuators A Physical 230, 25—32. 

Heat flux ( >) can be defined as the rate of heat energy transfer through a given surface (W), and heat flux density q>) is the heat flux per unit area (W m ). The fluxmeter, which measures this density, is called a heat fluxmeter or a heat flux sensor [14,40]. 

Lohle et al. (2007) describe a setup for the characterization and calibration of such a heat flux sensor by the use of short laser pulses. A Nd YAG laser was used to... 

Lohle, S., Battaglia, J.-L., Batsale, J.-C., Enouf, O., Dubard, J., and Filtz, J.-R. (2007) Characterization of a heat flux sensor using short pulse laser calibration. Rev. Sci. Instrum., 78, 053501. 

Haam, S. J., R. S. Brodkey, and J. B. Fasano (1992). Loeal heat transfer in a mixing vessel using heat flux sensors, Ind. Eng. Chem. Res., 31, 1384-1391. 

Figure 13. Schematic sketch of a carousel calorimeter for small insects with 1 LKB air bath thermostat, 9 flight carousel, 12 proximity sensor, 13 microphone, 14 light guides, 15 Peltier heat flux sensors and 17 insect [112].

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