Experimental center-line temperature

Figure 5.25 Experimental and computed center-line temperature history during heating of an 8 mm thick PMMA plate. The initial temperature To=20°C and the heater temperature Ts=140°C. [7]...

Probability distributions have been measured for Cd and Zn (1) and CdTe (15) for several nozzle dimensions and temperatures yielding effusion rates of 0.01-0.33 g/min. A representative distribution is shown in Figure 11. The curve drawn through the data points in Figure 11 illustrates agreement between the probability distribution F(< )), which was predicted by equations 25 and 26, and the experimental data. The root-mean-square difference between the experimental and predicted probability distribution values is 1-3% of the center line value. This agreement is as good as empirical fits described in the literature that use two or more adjustable parameters (16). 

Fig. 3. Temperature profile at the center-line and inner wall surface of the reactor versus time during pyrolysis at teit erature of 800 °C, Symbols, experimental data ...

Near the line centers, the spectral functions have sometimes been approximated by a Lorentzian. The far wings, on the other hand, may be approximated by exponential functions as Fig. 3.2 might suggest. However, better model profiles exist see Chapters 5 and 6 [421, 102, 320], Model profiles have been useful for fitting experimental spectra, for an extrapolation of measured profiles to lower or higher frequencies (which is often needed for the determination of spectral moments) and for a prediction of spectra at temperatures for which no measurements exist. We note that van der Waals dimer structures (which appear at low frequencies and low pressures) modify the Lorentzian-like appearance more or less, as we will see. 

Figure 2.27. Experimental data (points) and theoretical curves (solid lines) representing changes in temperature (curves 1 and 3) and the degree of crystallinity (curves 2 and 4) during anionic activated polymerization of e-caprolactam in a plate reactor. Width of the reactor is 32 mm Tsur = 150°C (a) 140°C (b) and 130°C (c). Data are shown for the center (curves 1 and 2) and for the wall (curves 3 and 4).

In addition to these publications, software is available that allows the user to determine vapor pressures of a wide variety of compounds at room temperature. The Texas Research Center (TRC) (1996) distributes a PC DOS/Windows database that contains experimentally derived Antoine constants for approximately 6000 chemicals from which vapor pressures at user-selected temperatures can be calculated. Another Windows-based program, MPBPVP by Meylan and Howard (1996), estimates the vapor pressure of organic compounds from their SMILES (Simplified Molecular Input Line Entry System) structure and their boiling points using the Antoine equation, the Grain-Watson method, and the Mackay method. 

One example of a concrete system where one observes optical spectrum caused by the Ai-E electronic transition is the N-V center in diamond. This center consists of a substitutional N atom and three nearest C atoms (one of the nearest C atoms is replaced by the vacancy) and it has a trigonal symmetry. The ZPL line at 637 nm of this center corresponds to the electronic transition between the triplet 3A and the 3E electronic states. In the standard model of this center the electronic states of the center come from the occupation and the splitting of the aj and t2 levels arising from three C radicals. The crystalline field of a trigonal symmetry splits the t2 level into a number of states including the ground (Aj) state and the first excited E-state (see, e.g. Refs. [17-25]). Our experimental study of the optical transition between the E and the Aj electronic states indeed showed the 7 3 dependence of the ZPL width at low temperatures. 

The coke profiles in the reactor bed can be predicted excellently by the model as shown by the solid lines in Figure 1. Figure 2 shows good consistency is also obtained for the average coke content over the reactor bed versus time on stream. Note that within the time period of reactor startup plus one hour of operation, the average coke content of the reactor bed is already at about 5 wt%. The model cannot be applied to this startup and initial period with the rapid transients of temperature, activity "spike" and concentration. However, compensation for this interval can be made by a time translation of the model a model time of 36 hours is fixed at an experimental time of zero. A temperature difference of more than 20C between the center of the bed and outer wall of the reactor in the startup stage has been observed in our laboratory for some experiments. About three-fourths of this difference is across the catalyst bed itself. Startup of the reactor at reasonably lower temperatures in order to control the coke formation and to better maintain the catalyst activity is important, if not critical. 

To experimentally probe the electronic and thermal consequences of flash photolysis, a femtosecond time-resolved near-IR study of photoexcited Mb was undertaken (22). This study probed the spectral evolution of band III, a weak ( max 100 M-1 cm-1) near-IR charge transfer transition (14) centered near 13, 110 cm-1 that is characteristic of five-coordinate ferrous hemes in their ground electronic state (S = 2). Because band III is absent when the heme is electronically excited, the dynamics of its reappearance provides an incisive probe of relaxation back to the ground electronic state. Moreover, because the spectral characteristics of band III (integrated area center frequency line width) correlate strongly with temperature (23-26), the spectral evolution of band III also probes its thermal relaxation. 

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