A Study of Mass Transfer Around Oil Sand Fragments in High Temperature Atmospheres

1989 ◽  
Vol 111 (2) ◽  
pp. 97-99
Author(s):  
M. A. Abdrabboh ◽  
G. A. Karim
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Reynolds Number ◽  
High Temperature ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Oil Sands ◽  
Simple Expression ◽  
Convective Mass Transfer ◽  
Oil Sand

An approximate approach was formulated to estimate the coefficient of convective mass transfer from small preshaped rectangular fragments of oil sands when subjected to hot streams of products of combustion of lean mixtures to hydrogen in air at low Reynolds number and at temperatures up to 1000 K. A simple expression which was derived to correlate the mass transfer coefficient in terms of the connective stream temperature was shown to fit the experimental data well.

scholarly journals Effective diffusivity and convective mass transfer coefficient during the drying of bananas

2012 ◽  
Vol 32 (2) ◽  
pp. 342-353 ◽  
Author(s):  
Cleide M. D. P. da S. e Silva ◽  
Wilton P. da Silva ◽  
Vera S. de O. Farias ◽  
Josivanda P. Gomes
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Boundary Condition ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Effective Diffusivity ◽  
Convective Boundary Condition ◽  
Drying Kinetics ◽  
Convective Mass Transfer ◽  
Convective Boundary

In this article, a methodology is used for the simultaneous determination of the effective diffusivity and the convective mass transfer coefficient in porous solids, which can be considered as an infinite cylinder during drying. Two models are used for optimization and drying simulation: model 1 (constant volume and diffusivity, with equilibrium boundary condition), and model 2 (constant volume and diffusivity with convective boundary condition). Optimization algorithms based on the inverse method were coupled to the analytical solutions, and these solutions can be adjusted to experimental data of the drying kinetics. An application of optimization methodology was made to describe the drying kinetics of whole bananas, using experimental data available in the literature. The statistical indicators enable to affirm that the solution of diffusion equation with convective boundary condition generates results superior than those with the equilibrium boundary condition.

Mass Transfer Coefficients during Steel Decarburization in a RH Degasser

2008 ◽  
Vol 273-276 ◽  
pp. 679-684
Author(s):  
Roberto Parreiras Tavares ◽  
André Afonso Nascimento ◽  
Henrique Loures Vale Pujatti
Keyword(s):  
Mass Transfer ◽  
Reynolds Number ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Gas Flow ◽  
Vacuum Chamber ◽  
Volumetric Mass Transfer Coefficient ◽  
Gas Flow Rate ◽  
Rh Process ◽  
Kinetics Of

The RH process is a secondary refining process that can simultaneously attain significant levels of removal of interstitial elements, such as carbon, nitrogen and hydrogen, from liquid steel. In the RH process, the decarburization rate plays a very important role in determining the productivity of the equipment. The kinetics of this reaction is controlled by mass transfer in the liquid phase. In the present work, a physical model of a RH degasser has been built and used in the study of the kinetics of decarburization. The effects of the gas flow rate and of the configurations of the nozzles used in the injection of the gas have been analyzed. The decarburization reaction of liquid steel was simulated using a reaction involving CO2 and caustic solutions. The concentration of CO2 in the solution was evaluated using pH measurements. Based on the experimental results, it was possible to estimate the reaction rate constant. A volumetric mass transfer coefficient was then calculated based on these rate constants and on the circulation rate of the liquid. The logarithm of the mass transfer coefficient showed a linear relationship with the logarithm of the gas flow rate. The slope of the line was found to vary according to the relevance of the reaction at the free surface in the vacuum chamber. A linear relationship between the volumetric mass transfer coefficient and the nozzle Reynolds number was also observed. The slopes of the lines changed according to the relative importance of the two reaction sites, gas-liquid interface in the upleg snorkel and in the vacuum. At higher Reynolds number, the reaction in the vacuum chamber tends to be more significant.

scholarly journals Aeration / Stripping of n-Butyl Mercaptan in aqueous environment

2013 ◽  
Vol 8 (2) ◽  
pp. 103-112
Keyword(s):  
Experimental Data ◽  
Water Quality ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Chemical Equilibrium ◽  
Reaction Rate ◽  
Reaction Parameter ◽  
Ph Values ◽  
Neutral Compound

Μany applications in water quality management have a common key water quality parameter, dissolved oxygen, resulting to the critical role of aeration. On the other hand, in municipal and industrial wastewater, especially where aeration is applied, the presence of volatile organic compounds (VOCs) causes several concerns including a direct threat to humans, partly due to their emission from treatment tanks. pH, temperature and Henry’s Law govern VOCs’ speciation and consequently their emission characteristics. Limited data and simplifications of available mass-transfer models pose obstacles to a realistic approach, especially in the presence of a chemical equilibrium, for example in the case of mercaptans. In the present study the importance of oxygen transfer and stripping of a VOC (n-butyl mercaptan) on aeration’s overall effectiveness are examined separately. Clean water oxygenation and stripping of mercaptan to an inert gas (nitrogen) were studied aiming to consider mass transfer aspects and to investigate the influence of chemical equilibrium between ionic and neutral form of the target compound in neutral and alkaline solutions. Using appropriate mass transfer relationships (dynamic method), experimental data were analyzed for the determination of overall mass transfer coefficient ( kOL,O2α ) of oxygen. Correlating kOL,O2 α with the corresponding mass transfer coefficient of n-butyl mercaptan in neutral solutions (calculated according the model proposed by Matter-Muller et al. [1]), a value of ratio βy of 0.566 is found, close to the reported values of other VOCs with similar values of Henry’s constant. At alkaline pH however the conventional simplified model fails to predict realistic values of mass-transfer coefficients. A coupled differential algebraic equation system, based on mass balances, taking into account dissociation of the compound to be stripped and assuming chemical non-equilibrium conditions during stripping, was developed. Reaction parameter k2 was calculated with non-linear least-squares analysis. The model predicts satisfactorily the experimental data and it provides a useful tool for the semibatch stripper design in situations where a reversible reaction is involved. At pH values below 8.5 mercaptan concentration falls exponentially whereas above 10.5 it tends to linearity. The bubble equilibrates and mercaptan transferred depends upon solubility and not diffusivity. Especially after depletion of initial neutral compound, transport depends upon neutral/ionic form speciation. The effectiveness of stripping n-butyl mercaptan, at a given pH, is mainly determined by a proportionality constant considered as “fugacity capacity” (removal effect on the process) and by a reversible reaction rate constant k2 (kinetic effect on the process). The ‘’fugacity capacity” is determined by hydrophobicity (i.e. low solubility and high limiting activity coefficient) rather than pure-component volatility (i.e. vapor pressure or boiling point). High limiting activity coefficient promotes mercaptan emission due to established vapor-liquid equilibrium, while the low reaction parameter k2, controls neutral compound quantity. At high pH, where ionic form predominates, experimental data showed that stripping was almost independent of the gas flow rate applied. A strong sensitivity of the model to uncertainty of γ∞ was found: γ∞ controls emission rate and through this the dynamic variations of neutral/ionic concentration profiles whereas reaction rate law parameter k2 controls the neutral/ionic transformation and it is the crucial quantity which governs the process at high pH values.

scholarly journals A novel two-phase model for bubbling fluidized-bed CO-methanation reactor

2020 ◽  
Author(s):  
Quancong Zhang ◽  
Zhikai Cao ◽  
Songshou Ye ◽  
Yong Sha ◽  
Bing Hui Chen ◽  
...  
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Fluidized Bed ◽  
Gas Flow ◽  
Flow Distribution ◽  
Co Methanation ◽  
Interphase Mass Transfer ◽  
Proposed Model

Fluidized bed reactor is promising for CO methanation owing to its excellent heat transfer performance. The gas flow distribution between the bubble and emulsion phases and mass transfer are important for such a solid-catalyzed fast reaction in fluidized bed but these are described simplistically in most conventional models. In this work, a novel model contemplating the gas flow distribution influenced by circulation flow and the interphase mass transfer coefficient influenced by bubble size variation is proposed. The simulation results of the proposed model and the classic Kunii–Levenspiel model were compared with experimental data of fluidized bed CO methanation. It was shown that the results of the proposed model have better agreement with experimental data. To evaluate the roles of gas flow distribution and interphase mass transfer coefficient, sensitivity analysis was carried out. The results indicated that in the proposed model, the effect of gas flow distribution is more important.

Convective Mass Transfer Coefficient at Wooden Surface in Jet Drying of Veneer

Holzforschung ◽  
1999 ◽  
Vol 53 (2) ◽  
pp. 204-208 ◽  
Author(s):  
Antti Hukka ◽  
Olli Oksanen
Keyword(s):  
Mass Transfer ◽  
Moisture Content ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Heat And Mass Transfer ◽  
Correction Factor ◽  
Average Moisture Content ◽  
Correction Coefficient ◽  
Convective Mass Transfer ◽  
Wooden Surface

Summary The relationship between heat and mass transfer at wooden surface is investigated experimentally by drying 1.6 mm thick birch veneers in constant conditions in a laboratory-scale roller dryer. By intermediate weighing of the samples a drying curve is established for each specimen. The drying curves are formulated in a functional form to produce the drying rate as a function of wood moisture content. Based on that and the measured heat-transfer coefficient a correction factor is calculated for the mass transfer coefficient predicted by the boundary layer theory. The results show that the convective mass transfer coefficient for wooden surfaces substantially deviates from that given by the analogy between heat and mass transfer. The correction factor describing the internal resistance for evaporation is strongly dependent on wood temperature within the range 50–90°C, but for practical purposes not dependent on the average moisture content of the veneer (range 40–70%). The numerical value of the correction coefficient established is somewhat lower than published earlier by other researchers.

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