Fluxmeter

For the measurement of magnetisation in hysteresis-loop measurements, a search coil consisting of several-turn windings around a specimen is coimected to a fluxmeter whose output can be recoded on thejy-axis of an x,y plotter. The x-axis records the field strength of the primary coil around the specimen. The whole procedure can be done conveniendy in a hysteresigraph, whereby the induction is recorded automatically as the field is varied continuously. 

In the parallel-plate method, the heat flux downward is measured hy a fluxmeter under which the thermal bond material and the molten salt of interest are located. Because the thermal transfer is only conductive if the thermal contacts are perfect, the balance of heat flow through the... 

In this microcalorimeter, the heat sink is not a massive metal block but is divided into several parts which are mobile with respect to each other. Each thermoelectric element (E) and a cell guide (D) are affixed to a fluxmeter holder (C). The holder (C) is mobile with respect to a massive arm (B) which, in turn, rotates around a vertical axle (A). All parts of the heat sink are made of brass. Surfaces in contact are lubricated by silicone grease. Four thermoelectric elements (E) are mounted in this fashion. They enclose two parallelepipedic calorimetric cells, which can be made of glass (cells for the spectrography of liquids are particularly convenient) or of metal (in this case, the electrical insulation is provided by a very thin sheet of mica). The thermoelectric elements surrounding both cells are connected differentially, the Petit microcalorimeter being thus a twin differential calorimeter. 

In a similar method, Ramousse et al. [248] designed a technique wherein the sample material is placed between two copper plates that have thermocouples located at their centers. Copper plates were chosen due to the high thermal conductivity of copper and to ensure a uniform temperature distribution. Fluxmeters to measure the thermal flux between both plates were located beside each copper plate. At each end of fhe apparatus, end plates... 

The accuracy with which the differential heats of adsorption could be measured is ca. 2%. Rapid collection of evolved heat is an important criterion and sometimes, the calorimeter response has to be corrected from the instrumental distortion due to thermal lags. The peak width at half maximum of the signal from the thermal fluxmeters allows comparing the various calorimeters responses [62]. 

R. Rousselet, MAF 22, 649-655 (1948), Use of a fluxmeter by Grassot for measuring initial velocities of projectiles at the testing range... 

Virgin cellulose pellets and cellulose chars produced in the simulated fire apparatus were both examined. Two different measurements were made. One involved measuring the reflected radiation in the mid-infrared from 2.5 to 25 pro (4000 to 400 cm l). These measurements were performed in a diffuse reflectance cell within an FTIR spectrometer. These experiments revealed some wavelength dependence of refleclivity. Reflectance was also measured in-situ in the simulated fire apparatus, by arranging the samples, a fluxmeter. and the heating lamps such that surface reflection of (he incident radiation... 

Class 3-Methods Based on Direct Mechanical Effects. These include the use of acoustical probes [57-71], acoustic impedance measurements [72—75], acoustic fluxmeter [76], the measurement of radiation forces [17,21,77—112], the distortion of liquid surface [ 113-115], surface cleaning, dispersive effects, emulsification [ 116-118], erosion [ 19,22,119-125], mass transfer measurements (electrochemical probe) [26,129], absorption methods [93,132], particle velocity measurements [132], and optical methods [133-141],... 

This method was originally developed as an acoustic fluxmeter for power measurements in air [76], It is based on having two microphones spaced apart at a small distance compared to the sound wavelength. It is possible that this instrument could be adapted for use in liquids, but both plane wave and anechoic conditions would be required. 

The C 80 calorimeter is composed of two identical and symmetrical thermal fluxmeters which are set in a thermoregulated block (Fig. 2). The experimental cells which contain respectively the sample and an inert material, are completely surrounded by the fluxmeters. 

Helmholtz colls Two coaxial parallel flat coils with the same radius placed a distance apart that is equal to the radius. If the same current is flowing in both coils then the value of the magnetic field strength is approximately uniform between the coils. Coils of this type are used to create fields and, in some cases, are employed to counter the effect of the earth s m netic field. Helmholtz coils are also used in m netic measurement, with the coils connected to a "flux-meter. If a small m net is placed between the coils and then removed, the integrated signal on the fluxmeter is proportional to the magnet s m netic moment. 

Thus, this chapter describes an innovative smart textile a heat fluxmeter with a textile auxiliary wall, also called a textile heat fluxmeter (THF), which can detect, analyze, and monitor the heat and mass transfers with minimum dismrbance due to their porosity. It is a yam-based sensor that can be defined as the yarn itself as a sensing element and thus it is easier to be used by conventional knitting and weaving processes [15]. Moreover, it is desirable to use flexible electronics and this is especially tme when they need to be in contact with the human body, in which case the flexibility and nonirritability requirements are of utmost importance (Fig. 19.2) [16]. 

This textile heat fluxmeter consists of a network of thermocouples (assembly of two dissimilar conductor or semiconductor), also called a thermopile, assembled into a textile auxiliary wall. Thus, heat and mass transfer properties of textile substrate used as auxiliary wall will be smdied in the first part of this work. Afterward, the principle and the production technology of the conventional heat fluxmeters and the textile heat fluxmeter will be defined. 

Figure 19.2 Photographs of heat fluxmeters (a) textile heat fluxmeter, and (b) conventional heat fluxmeter (Captec Entreprise, France).

Since a textile substrate is used as an auxiliary wall to create the textile heat flux-meter, die performance of this heat fluxmeter is influenced by textile substrate properties. The first part of this chapter is especially concerned with the complex phenomena of the heat and mass transfers. The following section presents the principles and the production processes of the conventional and textile heat fluxmeters. 

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]. 

The principle of the gradient heat fluxmeter is to observe a heat flux due to the evaluation of the temperature gradient between the two faces of the conducting support, which has known thermal characteristics. This temperature gradient is measured by a thermocouple (assembly of two dissimilar conductors or semiconductors) or rather a number of thermocouples forming a thermopile. 

Fig. 19.4 presents a gradient heat fluxmeter with a thermal conductivity A and a thickness h. The heat flux density in a conduction phenomenon can be defined by Fourier s law (Eq. [19.2]). 

Figure 19.4 Schema of gradient heat fluxmeter with an auxiliary wall [40].

The inverse relationship between the thermal conductivity and thermal resistance is expressed with Eq. [19.1]. Therefore, the temperature gradient between two faces of the heat fluxmeter can be calculated due to the thermal resistance and the heat flux density (Eq. [19.3]). 

In order to increase the signal delivered by the heat fluxmeter, a large number of thermocouples connected electrically in series can be used to form a thermopile. 

Only a few companies commercialize gradient heat fluxmeters and all of them use the same principle described above the transfer of the heat flux generates a temperature gradient on the thermopile, which delivers an output voltage proportional to the heat flux. 

As mentioned previously, there are relatively few companies that commercialize gradient heat fluxmeters. There are three companies in the United States (VateU, Rdf, Omega) and three companies in Europe (Hukseflux, Wuntronic, Captec) (Table 19.2) [43-48]. 

These commercial heat fluxmeters listed in the Table 19.2 use electrochemical deposition process with electroplating technology, which is a deposition process using electrical current to obtain a metallic layer on a sample s surface. The sample is used as the cathode and the anode is made of the depositing material. As the sample to be... 

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