Optical temperature

For most purposes only the Stokes-shifted Raman spectmm, which results from molecules in the ground electronic and vibrational states being excited, is measured and reported. Anti-Stokes spectra arise from molecules in vibrational excited states returning to the ground state. The relative intensities of the Stokes and anti-Stokes bands are proportional to the relative populations of the ground and excited vibrational states. These proportions are temperature-dependent and foUow a Boltzmann distribution. At room temperature, the anti-Stokes Stokes intensity ratio decreases by a factor of 10 with each 480 cm from the exciting frequency. Because of the weakness of the anti-Stokes spectmm (except at low frequency shift), the most important use of this spectmm is for optical temperature measurement (qv) using the Boltzmann distribution function. 

Routine temperature measurement within the Discover series is achieved by means of an IR sensor positioned beneath the cavity below the vessel. This allows accurate temperature control of the reaction even when using minimal volumes of materials (0.2 mL). The platform also accepts an optional fiber-optic temperature sensor system that addresses the need for temperature measurement where IR technology is not suitable, such as with sub-zero temperature reactions or with specialized reaction vessels. Pressure regulation is achieved by means of the IntelliVent pressure management technology. If the pressure in the vial exceeds 20 bar, the... 

The MARS-S is constituted of a multimode cavity very close to domestic oven with safety precautions (15 mL vessels up to 0.5 L round-bottomed flasks, magnetic stirring, temperature control). The magnitude of microwave power available is 300 W. The optical temperature sensor is immersed in the reaction vessel for quick response up to 250 °C. A ceiling mounted is available in order to make connection with a conventional reflux system located outside the cavity or to ensure addition of reactants. These ports are provided with a ground choke to prevent microwave leakage. It is also possible to use a turntable for small vessels with volumes close to 0.1 mL to 15 mL vessels (120 positions for 15 mL vessels). Pressure vessels are available (33 bar monitored, 20 controlled). 

Lundgren et al. [132] showed that the cadmium signal could be separated from a 2% sodium chloride signal by atomising at 820 °C, below the temperature at which the sodium chloride was vaporised. This technique has been called selective volatilisation. They detected 0.03 xg/l cadmium in the 2% sodium chloride solution. They used an infrared optical temperature monitor to set the atomisation temperature accurately. 

Li, E. Wang, X. Zhang, C., Fiber optic temperature sensor based on interference of selective higher order modes, Appl. Phys. Lett. 2006, 89, 091119... 

Figure 9.16. Performance of alexandrite based real time optical temperature sensors versus standard (Neslab RTE-J l IM) Equation 9.107 is used to obtain a working relation between Temperature and r. The fiber optic sensor monitored the bath temperature (—) in equilibrium with the standard (-).

K. T. V. Grattan, R. K. Selli, and A. W. Palmer, Ruby fluorescence wavelength division fiber-optic temperature sensor, Rev. Sei. Instrum. 57, 1231-1234 (1987). 

Table 11.1. Various Fiber Optic Temperature Sensor Schemes...

A variety of optical alignment accessories for the launch of the excitation light into the fiber optic temperature probe, the collection of the fluorescence response, and optical filters used to isolate the excitation and fluorescence emission at the detector and in some cases at the excitation source as well. 

T. Bosselmann, A. Reule, and J. Schroder, Fibre-optic temperature sensor using fluorescence decay time, Proc. of 2nd Conf. on Optical Fibre Sensors (OFS 84), SPIE Proceeding 514, 151-154 (1984). 

J. P. Dakin and D. A. Kahn, A novel fibre optic temperature probe, Opt. Quan. Electron. 9, 540 (1977). 

R. K. Selli, Fibre optic temperature sensors using fluorescent phenomena, Ph.D. thesis, City... 

J. Lin and C.W. Brown, Near-IR fiber-optic temperature sensor, Appl. Spectrosc., 47, 62-68 (1993). 

Fig. 16. Fiber-optic temperature sensor. A thin layer of silicon placed in the optical path exhibits a large change in refractive index with temperature, changing the effective path length. (Yazbak, Foxboro, Massachusetts)...

For both type of microwave reactors, if the reactor is not supplied with a temperature sensor or more likely accurate temperature measurment is prerequisited during an experiment, the fiber-optic temperature sensor is directly applied to the reaction mixture. In order to secure the sensor from harsh chemicals, the sensor is inserted into a capillary that in turn is inserted into the reaction mixture. In such a case, it is strongly advocated to use capillaries that are made of quartz glass and are transparent to microwave irradiation. Any capillary that is made of glass or even borosilicate glass can always slightly absorb microwave energy, in particular, while the reaction mixture does not absorb microwaves efficiently, and in turn lead to failures of fiber-optic thermometer performance. 

Fiber optic sensors are an alternative to thermocouples as embedded temperature distribution mapping sensors. As described in Section 2.2.7, McIntyre et al.104 developed two distinct fiber optic temperature probe technologies for fuel cell applications (free space probes and optical fiber probes). Both sensor technologies showed similar trends in fuel cell temperature and were also used to study transient conditions. 

One of the extraction vessels is equipped with a temperature and pressure sensor/control unit. Figure 3.10 shows the schematic diagram of a control vessel as well as a standard vessel. A fiber-optic temperature probe is built into the cap and the cover of the control vessel. The standard EPA method requires the microwave extraction system to be capable of sensing the temperature to within +2.5°C and adjusting the microwave field output power... 

This monograph, I believe, is unique in that it covers the broader topic of pyrometry the latter chapters on infrared and optical temperature measurement, thermal conductivity, and glass viscosity are generally not treated in books on thermal analysis but are commercially and academically important. I have resisted the urge to elaborate on some topics by using ex-... 

The electric field-stimulated uptake of macromolecules is temperature dependent whereas stimulated adsorption is not. For example, the uptake of BSA-FITC by COS 5-7 cells is almost completely diminished at 4°C and enhanced twofold at 37°C compared with room temperature. When elevating the temperature during exposure, one should take into account that LEF treatment also leads to temperature elevation in the cell suspension. The temperature of the solutions during exposure can be measured using fiber-optic temperature sensors (FISO Technologies, Quebec, Canada). Transient temperature rise by up to 2°C can be measured at the end of 1 min exposure of DMEM-H medium to LEF (20 V/cm, 180 (jls pulse duration, and 500 Hz frequency). 

The fact that isomerization and relaxation processes are sensitive to the temperature of a specimen allows a combined optical-temperature control of azo-polymer third-order susceptibility. The temperature-tuned VPC is just one example of this. Combination of optical excitation and temperature variations may result in more effective governing linear and nonlinear optical properties of azo-dye polymer materials. 

Optical temperature-dependent dephasing, nonlinear optical [33]... 

Optical temperature sensor (opt(r)odes) based on the viscosity-dependent intramolecular excimer formation of l,3bi(l-pyrenyl)propane in [C4mypr][Tf2N] have been developed [33], The relative intensity of the excimer emission was found to gain in intensity with higher temperature. This has been attributed to the generally low viscosity of the ionic liquid. The working temperature of this luminescence thermometer is between 25°C and about 150°C. 

Phillips, R.W. Tilstra, S.D. Design of a fiber optic temperature sensor for aerospace applications. In Temperature Its Measurement and Control in Science and Industry Schooley, J.F., Ed. American Institute of Physics New York, 1992 Vol. 6, Part 2, 721-724. 

Wickersheim, K. A. and Alves, R. B. (1979), Recent Advances in Optical Temperature Measurement, Industrial ResearchIDevelopment, 21, 82. 

Lovett s team at Pratt Whitney (Chapter 17) applied a fuel-control system in an actual aircraft engine combustor to actively control pattern factor. For this purpose, available fuel injectors were properly equipped with miniature valves to make possible spatial control of individual fuel injection sites. Optical temperature sensor probes and a traversing gas-sampling rake were integrated into a test rig to quantify the spatial exit temperature distribution in the combustor. Preliminary results have shown good ability to control pattern factor this way. 

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