Amount Of Mass Transfer Research Articles

A modified dynamic Lee model for two-phase closed thermosyphon (TPCT) simulation

A modified model consisting of a dynamic Lee model, volume of fluid model, and continuum surface force model is developed. The modified model investigates heat transfer characteristics of the vapor–liquid phase change process and details of the two-phase flow during operation of a two-phase closed thermosyphon. The mass transfer time relaxation parameters for the Lee phase change model are the most critical coefficients which determine the rate of the vapor–liquid phase change. A dynamic adjustment of the mass transfer time relaxation parameters for the Lee phase change model is realized based on the amount of mass transfer between the vapor and liquid phases and the values of the mass transfer time relaxation parameters become stabilized. The relative error between the modified model and experimental data for the temperature distribution is 5%, representing an acceptable agreement. Compared with the original model, the maximum thermal resistance errors in evaporation section and condensation section are reduced by 19.3% and 107.1%, respectively. These results indicate that the modified model can provide good corrections with high accuracy.

Production and Solubility of Ectoine: Biochemical and Molecular Dynamics Simulation Studies

In this study, ectoine is produced by Streptomyces. sp IBRC-M PTCC 10615. Fermentation parameters such as flow regime, gas hold up, mass transfer coefficient, and mixing time were optimized by statistical analysis. Streptomyces. sp produced a maximal ectoine concentration of 270 mmol/kg at optimal conditions of ectoine and L-aspartic acid. Also, the amount of mass transfer, gas hold up, and mixing time were determined 0,41/s ,0.3, and 40 s, respectively. The amount of ectoine was measured by HPLC. Furthermore, Molecular Dynamics (MD) simulation was used for studying the solubility of ectoine in aqueous media. Equilibrium data such as temperature, potential energy, and volume graphs showed that the solubility of ectoine is 25%more than glycerol. Also, all the achieving graphs from the equilibrium of simulation were confirmed the appropriate structure of the system.

Mass transfer during transient condensate vaporization: Experimental and modeling study

The gas condensate reservoirs, which are a major source of energy, usually experience an unwanted phenomenon called liquid drop-out. Gas injection as a proven effective remedy is generally employed to diminish the liquid loss. The condensate recovery by gas injection is typically estimated by assuming local equilibrium. This assumption is not valid in porous media when the limited contact area, high velocity, and low residence time are involved, particularly in near-wellbore region. In this study, we attempt to calculate mass transfer coefficient of the gas condensate systems in porous media at the transient state. Hence, a number of experiments are performed where the tests include three injection gases (CO2, N2, and CH4), three liquid types as condensate components (C5, C6, and C7), and three mean grain sizes (150–300 μm) within a wide range of gas velocity (0.00472–0.0283 cm/s). The experiments are modeled numerically and analytically based on the effluent concentrations. The obtained mass transfer coefficients are then employed to introduce new models such that Sherwood number (Sh) is correlated to Peclet (Pe) and Schmidt (Sc) numbers, and other physical/operational parameters. Based on a systematic sensitivity analysis as well as the modeling results, both analytical and numerical modeling approaches are promising and viable. The statistical parameters are calculated to be 97.13% (R2) and 0.0044 (mean squared error or MSE) for the analytical method, and 97.33% (R2) and 0.00303 (MSE) for the numerical solution, confirming the accuracy and reliability of the employed models. The mass transfer coefficients are then fitted well using three correlations with R2 values of 95.29%, 97.04%, and 96.73%, and absolute relative deviation or ARD magnitudes of 13.22%, 11.73%, and 11.44%. The new proposed correlations can be simply implemented in numerical/analytical modeling and commercial software packages to obtain the non-equilibrium mass transfer coefficients of components in the gas phase. The sensitivity analysis also reveals that condensate shrinkage has a significant effect on the amount of mass transfer and vaporization. Methane shows a relatively higher potential to strip the liquid condensate in comparison with other gases in the experiments. Among the liquid hydrocarbons, pentane has a higher tendency to evaporate into the flowing gas phase, followed by hexane and heptane. It is also found that porous system cases with larger mean grain size offer more suitable conditions for enhancement of mass transfer. The findings of this study can help to better understand the mass transfer during gas injection in gas condensate reserves under transient condition.

Mass transfer in a novel passive micro-mixer: Flow tortuosity effects

Hydroynamic fluid tortuosity is a parameter to describe the fluid streamlines average elongation. The motivation of the present study is introducing a new concept for theoretical predictions of dynamic tortuosity effects on mass transfer in a novel three-dimensional passive T-shape micro-mixer both experimentally and by numerical simulation. In the numerical analysis, continuity, motion, and diffusion-convection equations were solved, and the amount of mass transfer and the fluid tortuosity was calculated for different rectangular winglet angles. The Reynolds number is considered in the range of 0.1–93. The results show that when the angle of winglet tends to 22.5°, the fluid tortuosity, lateral velocity, and fluid mass transfer tend to maximum values. Furthermore, the effect of fluid tortuosity on the fluid stretching as a theory of chaotic mixing is investigated.

Toward a universal mass‐momentum transfer relationship for predicting nutrient uptake and metabolite exchange in benthic reef communities

AbstractHere we synthesize data from previous field and laboratory studies describing how rates of nutrient uptake and metabolite exchange (mass transfer) are related to form drag and bottom stresses (momentum transfer). Reanalysis of this data shows that rates of mass transfer are highly correlated (r2 ≥ 0.9) with the root of the bottom stress under both waves and currents and only slightly higher under waves (~10%). The amount of mass transfer that can occur per unit bottom stress (or form drag) is influenced by morphological features ranging anywhere from millimeters to meters in scale; however, surface‐scale roughness (millimeters) appears to have little effect on actual nutrient uptake by living reef communities. Although field measurements of nutrient uptake by natural reef communities agree reasonably well with predictions based on existing mass‐momentum transfer relationships, more work is needed to better constrain these relationships for more rugose and morphologically complex communities.

New Insights into the Pelletization Mechanism by Extrusion/Spheronization

Pellet manufacturing by extrusion/spheronization is quite common in the pharmaceutical field because the obtained product is characterized by a high sphericity as well as a narrow particle size distribution. The established mechanisms only consider deformation of the initially fractured particles but do not account for mass transfer between the particles as a factor in achieving spherical particles. This study dealt with the visualization of mass transfer during spheronization. Therefore, two common pelletization aids, microcrystalline cellulose and kappa-carrageenan, were used alone as well as in combination with lactose as a filler. This study proves that mass transfer between particles must be considered in addition to plastic deformation in order to capture the spheronization mechanism. Moreover, it is evident that there are regional distinctions in the amount of mass transfer at the particle surface. Therefore, the commonly espoused pelletization mechanisms need to be extended to account for material transfer between pellet particles, which has not been considered before.

Study of the Cryolite Formation during the Zinc Phosphating of Aluminium

SUMMARYTo improve the corrosion resistance and the adhesion properties of aluminium, chemical conversion processes, such as zinc phosphating, are applied. During zinc phosphating of aluminium the co-precipitation of cryolite often occurs. Cryolite needs to be formed in solution to remove Al3 ions, which have a poisoning effect on the phosphating process, away from the surface. Cryolite formation on the surface must be avoided, since it leads to a decrease of the corrosion resistance and of the adhesion properties. In this paper, the influence of mass transport on this co-precipitation competition is reported. The resulting conversion layers are investigated by SEM/EDX. It can be concluded that the amount of mass transfer has a large influence on the formation of both the phosphate and cryolite crystals. Hence, this competition in precipitation is explained in terms of mass transport of the different species involved in the chemical reactions at the surface.

The Characteristics of Millisecond Pulsar Emission. I. Spectra, Pulse Shapes, and the Beaming Fraction

The extreme physical conditions in millisecond pulsar magnetospheres, as well as an evolutionary history that differs from that of normal pulsars, raise the question whether these objects also differ in their radio emission properties. We have monitored a large sample of millisecond pulsars for a period of 3 yr using the 100 m Effelsberg radio telescope in order to compare the radio emission properties of these two pulsar populations. Our sample comprises a homogeneous data set of very high quality. With some notable exceptions, our findings suggest that the two groups of objects share many common properties. A comparison of the spectral indices between samples of normal and millisecond pulsars demonstrates that millisecond pulsar spectra are not significantly different from those of normal pulsars. This is contrary to what has previously been thought. There is evidence, however, that millisecond pulsars are slightly less luminous and less efficient radio emitters than normal pulsars. We confirm recent suggestions that a diversity exists among the luminosities of millisecond pulsars, with the isolated millisecond pulsars being less luminous than the binary millisecond pulsars, implying that the different evolutionary history has an influence on the emission properties. There are indications that old millisecond pulsars exhibit somewhat flatter spectra than the presumably younger ones. We present evidence that, contrary to common belief, the millisecond pulsar profiles are only marginally more complex than those found among the normal pulsar population. Moreover, the development of the profiles with frequency is rather slow, suggesting very compact magnetospheres. The profile development seems to anticorrelate with the companion mass and the spin period, again suggesting that the amount of mass transfer in a binary system might directly influence the emission properties. The angular radius of radio beams of millisecond pulsars does not follow the scaling predicted from a canonical pulsar model applicable for normal pulsars. Instead, they are systematically smaller, supporting the concept of a critical rotational period below which such a scaling ceases to exist. The smaller inferred luminosity and narrower emission beams will need to be considered in future calculations of the birthrate of the Galactic population.

Estimating diffusion coefficients of dense fluids

Gas injection (hydrocarbon, nitrogen, or carbon dioxide) into oil and condensate reservoirs may be attempted to recover more in situ hydrocarbons. In some cases, particularly in naturally fractured reservoirs, there has been a need for information on the rate and amount of mass transfer by diffusion. The most important property, to obtain such information, is the diffusion coefficient at reservoir conditions. A simple and generalized correlation in terms of viscosity and molar density is proposed to estimate diffusion coefficients for hydrocarbon systems. The correlation can be used for both gases and liquids up to a pressure of about 400 bar (6,000 psia). It has been shown that the proposed method may also be used to estimate effective diffusion coefficients in multicomponent systems with a reasonable degree of accuracy. Although the proposed correlation is based on experimental data in hydrocarbon systems, preliminary evaluations have shown that it is also satisfactory for non-hydrocarbon systems as well. The proposed equation predicts diffusion coefficients in gases with an absolute average deviation of 8% and in liquid systems with an absolute average deviation of 15%. The input parameters for the correlation are molecular weight, critical properties, and acentric factor of components in the system; mixturemore » molar density; low-pressure gas viscosity; and actual viscosity. The last three properties may be predicted from appropriate correlations.« less

MASS TRANSFER AND CHEMICAL REACTION IN A POWER-LAW SPHERE AT INTERMEDIATE REYNOLDS NUMBERS

Abstract The relevant mass transport equations have been numerically solved to determine the effect of power-law behavior in the dispersed phase. It is concluded that increased pseudoplasticity in the dispersed phase causes decreases in the total amount of mass transferred, C¯lt, to the droplet because of reduced circulation velocities. Maximum decreases in C¯lt, with increasing pseudoplasticity are realized for larger Peclet number, larger values of the ratio of the viscosity of the dispersed to continuous phase and for smaller Reynolds number. Substantial increases in the total amount of mass transfer are predicted as the regime changes from creeping to that of intermediate Reynolds number flow due to increased contribution of forced convection.

Study of metal adhesion by secondary ion mass spectroscopy

The amount of mass transfer in bimetallic ribbons produced by cold-cladding is measured by secondary ion mass spectroscopy. The studies included measurement of the variation of the amount of mass transfer versus relative deformation of the metals after cladding, the nature of the metals, and the means of surface preparation. Bimetallic ribbons were investigated in which Al was clad with Cu, Ni, Fe, Ta, and Nb, while Cu was clad with Ni and Fe. A linear relationship between the amount of mass transfer and the degree of relative deformation of the metals is established and for small deformations a deviation from a linear function is observed. The amount of mass transfer of aluminum for an identical degree of deformation increases in proportion to the increase in the hardness of the base metal. The amount of mass transfer of both cladding metals is observed to be similar when metals with similar mechanical properties, Ni-Cu and Fe-Cu, are used.

Motion of dispersed drops and mass transfer in pulsed column.

The relationship between the motion of drops and mass transfer in a pulsed column was investigated by taking high speed photographs. The rising motion of drops in the column was found to be divided into jetting, forced rising and free rising periods, whereas the falling motion was divided into forced falling and free falling periods. With use of the observed results, it was confirmed that the drop velocity and the distance of moving drop predicted from the equation of drop motion were satisfactorily compared with the corresponding observed values. On the basis of the results, the overall mass transfer coefficient in the pulsed column was derived, which was found to be valid in the course of calculation of the amount of mass transfer in the pulsed column.

X-ray equatorial analysis of crab striated muscle in the relaxed and rigor states.

The structure of muscle projected along the fiber axis was studied by equatorial X-ray diffraction. The electron-density distributions in axial projection of muscle were derived by the Fourier syntheses to a resolution of 7 nm in the relaxed and rigor states. The structure of the thick filament backbone (diameter about 21.5 nm) has a nearly smooth cylindrical surface and a low electron-density core (diameter about 7 nm) in the center. In the relaxes state, the center of gravity of th myosin heads is situated at a radius of 19.6 nm from the center of thick filament, lying just between the surface of the thick filament backbone and the surface of the thin filament (diameter about 8.4 nm). From the electron-density distributions in two states, the amount of mass transfer from the thick filament to the thin filament was estimated. It was in accordance with that predicted from the structure derived by the X-ray layer-line analyses.

A Study of Corrosion and Mass Transfer Of Nickel by Molten Sodium Hydroxide

Abstract The usefulness of nickel as a container material for molten sodium hydroxide is severely hampered at high temperatures by the occurrence of corrosion and mass transfer whenever a temperature gradient is present in the system. Free convection studies at other laboratories and preliminary studies at the National Advisory Committee for Aeronautics Lewis laboratory showed that the amount of mass transfer is strongly affected by variables such as temperature level, temperature gradient, flow conditions, atmosphere and the chemical composition of both the caustic and the nickel. It was found that normal care in the control of these variables resulted in reproducibility of the order of 200 to 300 percent. A free convection test was developed which yielded results reliable to ±10 percent and made it possible to study the effects of the different variables and to investigate the effectiveness of additives. The relations between mass transfer rate and temperature gradient were established in the temperatur...