Steady state tracers

The Chapman-Enskog method has been used to solve for steady state tracer diffusion (. ). According to the method the singlet distribution function for the diffusing species 1, present In a trace amount n nj, 1 1) In an otherwise equilibrium fluid. Is approximated by... 

Nozaki Y, Yamada M, Nikaido H (1990) The marine geochemistry of actinium-227 evidence for its migration through sediment pore water. Geophys Res Lett 17 1933-1936 Nozaki Y (1993) Actinium-227 a steady state tracer for the deep-se basin wide circulation and mixing studes. In Deep Ocean Circulation, Physical and Chemical Aspects. Teramoto T (ed) Elsevier p 139-155... 

A common feature of all models for the upper part of circulating fluidized beds is the description of the mass exchange between dense phase and dilute phase. Analogously to low-velocity fluidized beds, the product of the local specific mass-transfer area a and the mass-transfer coefficient k may be used for this purpose. Many different methods for determining values for these important variables have been reported, such as tracer gas backmixing experiments [112], non-steady-state tracer gas experiments [117], model reactions [115], and theoretical calculations [114],... 

The distribution of natural radiocarbon, with its half-life of —5,000 yr is unique among steady-state tracers as a diagnostic of ocean mixing and circulation. Aside from its long (but not too long)... 

This relation is derived by considering a steady-state tracer exchange between the ascending and descending emulsions and the bubbles, and comparing the resulting equation with that of the diffusion model. Since Ee = mieE s, the above equation is equivalent to the following relation from van Deemter (V2) ... 

C8 = steady-state tracer concentration in purge or step test, lb. moles/ cu. ft. 

The flow difference explains the time required for the intestinal concentration to reach steady state. Tracer in the plasma is quickly convected to... 

The earliest separations of the products of photosynthesis of C 02 by two-dimensional paper chromatography revealed certain amino acids to be rapidly labeled products of C 02 reduction (Stepka et al., 1948). Most important among these are alanine, aspartic acid, serine, glutamic acid, and glycine. Using quantitative steady-state tracer studies. Smith et al. (1961) were able to show that Chlorella pyrenoidosa incoirporate as much as 30% of the C 02 taken up photosynthetically directly into these amino acids. The rate of incorporation of C 02 into alanine by Chlorella pyrenoidosa may exceed the rate of labeling of sucrose. 

EXPERIMENTAL METHODS, 264 Intrusive Probes, 265 Steady State Tracers, 267 Impulse Tracers, 269 Optical Tracers, 274 Chemical Reaction, 276... 

Measurement techniques for the gas phase in CFB risers are becoming increasingly more sophisticated and accurate, and many find application in industrial-size equipment. In this section, we classify the different methods into five categories intrusive probes, steady state tracers, impulse (non-steady state) tracers, chemical reaction, and optical tracers. No single tracer technique is capable of quantifying... 

In Table 4, operating conditions, riser geometry and particle characteristics of a number of studies using steady state tracers is summarized. Generally, most of the data is either directed at operating conditions typical of coal combustors or FCC risers. 

As suggested, RTD measurements should be combined with other techniques to best quantify riser gas-phase hydrodynamics. Injection and detection methods are critical to interpreting the data. Iso-kinetic injection at different radii may help deconvolute inlet boundary conditions and flow structure. Multiple detectors along the riser length also are preferred. However, combining radial gas sampling, as practiced with steady state tracers, with radioactive impulse experiments could provide sufficient data to completely characterize riser gas-phase hydrodynamics. 

A radial gas dispersion coefficient can be obtained from the steady-state tracer method by fitting measured radial profiles of tracer concentration downstream of the injection point to a two-dimensional... 

Gas backmixing is obtained from steady state tracer injection tests in which tracer is injected continuously from one location and its concentration is monitored upstream of the injection point. A one-dimensional vertical dispersion process with a nonadsorbing tracer can be represented by... 

El Temtamy et al. [69] determined the mixing in the liquid phase in a 5 cm. diameter fluidized bed using a steady state tracer technique similar to the one by Vail et al. [68]. Ammonium chloride solution was injected into the fluidized bed at a given level. When a steady state tracer distribution was attained, samples of the liquid upstream from the point of injection were collected. With this information the axial dispersion coefficients were determined in beds of 0.45 mm, 0.96 mm, 2 mm and 3 mm glass beads. No backmixing was detected for 3mm particles. 

Using steady state tracer kinetic techniques in rats, Kurlandsky et al. determined how much of the all-rra 5-retinoic acid present in a given tissue was derived from the circulation [21]. Some of the findings of this study are summarized in Table 1. For the liver and brain, greater than 75% of the all-rran -retinoic acid present in these tissues was derived from the circulation (88.4% for brain and 78.2% for liver). The seminal vesicles, epididymis, kidney, epididymal fat, perinephric fat, spleen, and lungs derived, respectively, 23.1%, 9.6%, 33.4%, 30.3%, 24.5%, 19.0%, and 26.7% of their tissue all-rran -retinoic acid pools from the circulation. Only 2.3% and 4.8%, respectively, of the retinoic acid present in the pancreas and eyes was contributed by the circulation. For all rats studied, the testes did not take up any (<1%) all-tran -retinoic acid from the circulation. Kurlandsky et al. also reported a fractional catabolic rate for d -tmns-retinoic acid in plasma of 30.4 pools/hr and an absolute catabolic rate for all-tran -retinoic acid of 640 pmol/h [21]. These rates are very rapid compared to those of the only other naturally occurring retinoid that has been studied under normal physiological conditions, all-rra 5-retinol [22]. 

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