Temperature measurement application

Measurement of the hotness or coldness of a body or fluid is commonplace in the process industries. Temperature-measuring devices utilize systems with properties that vaiy with temperature in a simple, reproducible manner and thus can be cahbrated against known references (sometimes called secondaiy thermometers). The three dominant measurement devices used in automatic control are thermocouples, resistance thermometers, and pyrometers and are applicable over different temperature regimes. 

The noncontact measurement principle, usually called optical or radiation temperature measurement, is based on detecting electromagnetic radiation emitted from an object. In ventilation applications this method of measurement is used to determine surface temperatures in the infrared region. The advantage is that the measurement can be carried out from a distance, without contact with the surface, which possibly influences the heat balance and the temperatures. The disadvantages are that neither air (or other fluid) temperature nor internal temperature of a material can be measured. Also the temper-... 

J. B. Ott and J. Rex Goates, "Temperature Measurement with Applications to Phase Equilibria Studies," in Physical Methods of Chemistry, Vol. VI. Determination of Thermodynamic Properties B. W. Rossiter and R. C. Baetzold, eds, John Wiley Sons, New York, 1992, pp. 463-471. 

This discussion follows closely a description of ITS-90 provided by one of the authors as part of J. B. Ott and J. R. Goates, Temperature Measurements with Application to Phase... 

Product yields may also be determined by magnetic measurements, as in the formation of ferrites [340], where kinetic data were obtained at reaction temperature. Quantitative applications of Mossbauer spectroscopy have also been described [326]. 

Subsequent studies and applications with ether carboxylates have been published [73]. Phase inversion temperature measurements, which can be used to select surfactants for enhanced oil recovery, showed good results when the phase inversion temperature of the system was just below the reservoir temperature [184]. 

We attempt here to describe the fundamental equations of fluid mechanics and heat transfer. The main emphasis, however, is on understanding the physical principles and on application of the theory to realistic problems. The state of the art in high-heat flux management schemes, pressure and temperature measurement, pressure drop and heat transfer in single-phase and two-phase micro-channels, design and fabrication of micro-channel heat sinks are discussed. 

Since 1986, when the very first reports on the use of microwave heating to chemical transformations appeared [147,148], microwave-assisted synthesis has been shown to accelerate most solution-phase chemical reactions [24-27,32,35]. The first application of microwave irradiation for the acceleration of reaction rate of a substrate attached to a solid support (SPPS) was performed in 1992 [36]. Despite the promising results, microwave-assisted soHd-phase synthesis was not pursued following its initial appearance, most probably as a result of the lack of suitable instriunentation. Reproducing reaction conditions was nearly impossible because of the differences between domestic microwave ovens and the difficulties associated with temperature measurement. The technique became a Sleeping Beauty interest awoke almost a decade later with the publication of several microwave-assisted SPOS protocols [37,38,73,139,144]. There has been an extensive... 

CombiCHEM System (Fig. 3.9) For small-scale combinatorial chemistry applications, this barrel-type rotor is available. It can hold two 24- to 96-well microtiter plates utilizing glass vials (0.5-4 mL) at up to 4 bar at 150 °C. The plates are made of Weflon (graphite-doped Teflon) to ensure uniform heating and are sealed by an inert membrane sheet. Axial rotation of the rotor tumbles the microwell plates to admix the individual samples. Temperature measurement is achieved by means of a fiber-optic probe immersed in the center of the rotor. 

After some considerations relating to microwave technology, we will examine microwave ovens and reactor background. The limits of domestic ovens and temperature measurements will be analyzed, as well as design principles of microwave applicators. Next, a brief overview of laboratory, experimental and industrial equipment will be given. 

Synthetic chemists desire well defined reaction conditions. Process chemists demand them. Nonuniform heating and difficulties with mixing and temperature measurement are technical constraints that initially limited the scale of microwave chemistry with dry media and have not yet been overcome. Poor reproducibility also has been reported, probably resulting from differences in performance and operation of individual domestic microwave ovens [13-15]. Consequently, most, if not all, of the disclosed applications of dry media are laboratory-scale preparations. However, as discussed in other chapters, this does not prevent their being interesting and useful. 

EXAFS (Extended X-ray Absorption Fine Structure) measurements using synchrotron radiation have been successfully applied to the determination of structural details of SCO systems and have been particularly useful when it has not been possible to obtain suitable crystals for X-ray diffraction studies. Perhaps the most significant application has been in elucidating important aspects of the structure of the iron(II) SCO linear polymers derived from 1,2,4-triazoles [56]. EXAFS has also been applied to probe the dimensions of LIESST-generated metastable high spin states [57]. It has even been used to generate a spin transition curve from multi-temperature measurements [58]. 

For capacity measurements, several techniques are applicable. Impedance spectroscopy, lock-in technique or pulse measurements can be used, and the advantages and disadvantages of the various techniques are the same as for room temperature measurements. An important factor is the temperature dependent time constant of the system which shifts e.g. the capacitive branch in an impedance-frequency diagram with decreasing temperature to lower frequencies. Comparable changes with temperature are also observed in the potential transients due to galvanostatic pulses. 

The application of a more precise expression for enthalpy, at least as a function of temperature and composition, requires a new categorization of enthalpy flowrates. They can be divided into three categories depending on the combination of total flowrate, composition, and temperature measurements, as indicated in Table 2. 

Consider temperature as an example. Temperature measurement is needed in a variety of laboratory applications and, in the modern laboratory, is done with a temperature sensor, such as a thermocouple. A thermocouple is a junction of two metals that produces a voltage proportional to temperature that can be measured via electrical connections to the two metals. The voltage difference between the two connections can be amplified by the difference amplifier discussed in Section 6.3.3. 

Gas law experiments generally involve pressure, volume, and temperature measurements. In a few cases, other measurements such as mass and time are necessary. You should remember that AP, for example, is NOT a measurement the initial and final pressure measurements are the actual measurements made in the laboratory. Another common error is the application of gas law type information and calculations for non-gaseous materials. Typical experiments involving these concepts are numbers 3 and 5 in the Experimental chapter. 

Hewlett Packard Application Note 290 (1997) Practical Temperature Measurements. 

Of course, the temperature probes discussed could be further classified according to specific applications, e.g., biomedical temperature measurement, high temperature sensing up to >500°C, and the pyrometry range (> 500°C).The development of the temperature probes for such applications cited is discussed where specific applications are concerned. 

K. A. Wickersheim and W. D. Hyatt, Commercial applications of fiberoptic temperature measurement, SPIE Proc. 1267, 84-96 (1990). 

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