The transfer of heat and mass in capillary-porous materials in the hygroscopic state on drying by means of reduction in pressure

A mathematical model has been developed for the process of removing multicomponent moisture from disperse capillary-porous materials during the second drying period.Translated from Inzhenerno-Fizicheskii] Zhurnal, Vol. 56, No. 2, pp. 276–281, February, 1989.     

An analytic solution to the coupled pressure–temperature equations for modeling of photoacoustic trace gas sensors

Trace gas sensors have a wide range of applications including air quality monitoring, industrial process control, and medical diagnosis via breath biomarkers. Quartz-enhanced photoacoustic spectroscopy and resonant optothermoacoustic detection are two techniques with several promising advantages. Both methods use a quartz tuning fork and modulated laser source to detect trace gases. To date, these complementary methods have been modeled independently and have not accounted for the damping of the tuning fork in a principled manner. In this paper, we discuss a coupled system of equations derived by Morse and Ingard for the pressure, temperature, and velocity of a fluid, which accounts for both thermal effects and viscous damping, and which can be used to model both types of trace gas sensors simultaneously. As a first step toward the development of a more realistic model of these trace gas sensors, we derive an analytic solution to a pressure–temperature subsystem of the Morse–Ingard equations in the special case of cylindrical symmetry. We solve for the pressure and temperature in an infinitely long cylindrical fluid domain with a source function given by a constant-width Gaussian beam that is aligned with the axis of the cylinder. In addition, we surround this cylinder with an infinitely long annular solid domain, and we couple the pressure and temperature in the fluid domain to the temperature in the solid. We show that the temperature in the solid near the fluid–solid interface can be at least an order of magnitude larger than that computed using a simpler model in which the temperature in the fluid is governed by the heat equation rather than by the Morse–Ingard equations. In addition, we verify that the temperature solution of the coupled system exhibits a thermal boundary layer. These results strongly suggest that for computational modeling of resonant optothermoacoustic detection sensors, the temperature in the fluid should be computed by solving the Morse–Ingard equations rather than the heat equation.     

Excitation of Nonlinear Spin Oscillations in an Antiferromagnet under the Action of Pulsed Terahertz Pumping

Technical Physics Letters - We present a model of excitation of nonlinear spin oscillations in an antiferromagnet under the action of terahertz pulses of an electromagnetic field. It is shown that,...     

Heat and mass transfer in chemically reacting media with decrease in partial pressures of vapor

We present a mathematical model of heat and mass transfer in a chemically reacting medium-multi-component vapor-gas mixture system with decrease in partial pressures of vapor-gas components in a free reactor volume. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 5, pp. 1012–1020, September–October, 2000.     

The deactivating effect of carbon dioxide on iron-oxide catalyst in the dehydrogenation of methylbutenes

Characteristics of the most energy-intensive second stage of the two-stage production of isoprene from isopentane, i.e., dehydrogenation of methylbutenes are studied to improve the technical and economic performance of the process. The effect of the carbon dioxide formed during self-regeneration of the ironoxide catalyst (according to the reaction C_coke + 2H₂O → 2H₂ + CO₂) on the conversion of methylbutenes and selectivity with respect to isoprene is investigated. It is found that the presence of CO₂ in the reaction batch has a considerable effect on the conversion of methylbutenes; when the content of CO₂ in the raw material feed is 1.5 wt %, conversion of methylbutenes is reduced by 5–6%. It is demonstrated that CO₂ reversibly deactivates the catalyst and the catalyst activity is restored when its influx is discontined (the yield of isoprene returns gradually to its original value). The recovery rate depends on the concentration and duration of exposure to carbon dioxide. Treatment of the catalyst by steam in the absence of the reaction mixture leads to rapid regeneration of the catalyst. It is concluded that measures to continuously monitor CO₂ in the contact gas during the first stage of dehydrogenation, and to select the optimum modes (temperature, steam/raw materials ratio, etc.) for reducing carbon residue during the operation of iron-oxide catalyst in order to implement the two-stage technology for the dehydrogenation of methylbutenes (the main goal of which is to raise the conversion of methylbutenes to 35–40%) are of special importance.     

Intramolecular hydrogen bond controlled coordination of N-thiophosphorylated thiourea 2,6-Me2C6H3NHC(S)NHP(S)(OiPr)2 with Ni(II)

Reaction of O,O′-diisopropylthiophosphoric acid isothiocyanate (iPrO)₂P(S)NCS with 2,6-dimethylaniline 2,6-Me₂C₆H₃NH₂ leads to the new N-thiophosphorylated thiourea 2,6-Me₂C₆H₃NHC(S)NHP(S)(OiPr)₂ (HL). Reaction of the potassium salt of HL with Ni(II) in aqueous EtOH leads to the complex of formula [Ni(L-N,S)₂]. The molecular structures of the thiourea HL and the complex [Ni(L-N,S)₂] were elucidated by single crystal X-ray diffraction analysis, ¹H and ³¹P NMR spectroscopy and microanalysis. In the complex [Ni(L-N,S)₂], the metal center is found to be in a square-planar N₂S₂ environment formed by the CS sulfur atoms and the P–N nitrogen atoms of two deprotonated L ligands. The ligands are in a trans-configuration.