Mass transfer coefficient

About: Mass transfer coefficient is a research topic. Over the lifetime, 7827 publications have been published within this topic receiving 168354 citations.

Combined heat and mass transfer along a vertical moving cylinder with a free stream

Abstract: The mixed convection flow over a continuous moving vertical slender cylinder under the combined buoyancy effect of thermal and mass diffusion has been studied. Both uniform wall temperature (concentration) and uniform heat (mass) flux cases are included in the analysis. The problem is formulated in such a manner that when the ratio λ(= u w/(u w + u ∞), where u w and u ∞ are the wall and free stream velocities, is zero, the problem reduces to the flow over a stationary cylinder, and when λ = 1 it reduces to the flow over a moving cylinder in an ambient fluid. The partial differential equations governing the flow have been solved numerically using an implicit finite-difference scheme. We have also obtained the solution using a perturbation technique with Shanks transformation. This transformation has been used to increase the range of the validity of the solution. For some particular cases closed form solutions are obtained. The surface skin friction, heat transfer and mass transfer increase with the buoyancy forces. The buoyancy forces cause considerable overshoot in the velocity profiles. The Prandtl number and the Schmidt number strongly affect the surface heat transfer and the mass transfer, respectively. The surface skin friction decreases as the relative velocity between the surface and free stream decreases.

Oxygen transfer phenomena in 48-well microtiter plates: determination by optical monitoring of sulfite oxidation and verification by real-time measurement during microbial growth.

Abstract: Oxygen limitation is one of the most frequent problems associated with the application of shaking bioreactors. The gas-liquid oxygen transfer properties of shaken 48-well microtiter plates (MTPs) were analyzed at different filling volumes, shaking diameters, and shaking frequencies. On the one hand, an optical method based on sulfite oxidation was used as a chemical model system to determine the maximum oxygen transfer capacity (OTR(max)). On the other hand, the Respiration Activity Monitoring System (RAMOS) was applied for online measurement of the oxygen transfer rate (OTR) during growth of the methylotropic yeast Hansenula polymorpha. A proportionality constant between the OTR(max) of the biological system and the OTR(max) of the chemical system were indicated from these data, offering the possibility to transform the whole set of chemical data to biologically relevant conditions. The results exposed "out of phase" shaking conditions at a shaking diameter of 1 mm, which were confirmed by theoretical consideration with the phase number (Ph). At larger shaking diameters (2-50 mm) the oxygen transfer rate in MTPs shaken at high frequencies reached values of up to 0.28 mol/L/h, corresponding to a volumetric mass transfer coefficient (k(L)a) of 1,600 1/h. The specific mass transfer area (a) increases exponentially with the shaking frequency up to values of 2,400 1/m. On the contrary, the mass transfer coefficient (k(L)) is constant at a level of about 0.15 m/h over a wide range of shaking frequencies and shaking diameters. However, at high shaking frequencies, when the complete liquid volume forms a thin film on the cylindric wall of the well, the mass transfer coefficient (k(L)) increases linearly to values of up to 0.76 m/h. Essentially, the present investigation demonstrates that the 48-well plate outperforms the 96-well MTP and shake flasks at widely used operating conditions with respect to oxygen supply. The 48-well plates emerge, therefore, as an excellent alternative for microbial cultivation and expression studies combining the advantages of both the high-throughput 96-well MTP and the classical shaken Erlenmeyer flask.

Silicone oil: An effective absorbent for the removal of hydrophobic volatile organic compounds

Abstract: BACKGROUND: Hydrophobic volatile organic compounds (VOCs), such as toluene, dimethyl sulfide (DMS) and dimethyl disulfide (DMDS), are poorly soluble in water and classical air treatment processes like chemical scrubbers are not efficient. An alternative technique involving an absorption step in an organic solvent followed by a biodegradation phase was proposed. The solvent must fulfil several characteristics, which are key factors of process efficiency, and a previous study allowed polydimethylsiloxane (or PDMS, i.e. silicone oil) to be selected for this purpose. The aim of this paper was to determine some of its characteristics like absorption capacity and velocity performances (Henry's constant, diffusivity and mass transfer coefficient), and to verify its non-biodegradability. RESULTS: For the three targeted VOCs, Henry's constants in silicone oil were very low compared to those in water, and solubility was infinite. Diffusivity values were found to be in the range 10 -10 to 10 -11 m 2 s -1 and mass transfer coefficients did not show significant differences between the values in pure water and pure silicone oil, in the range 1.0 × 10 -3 to 4.0 × 10- 3 s -1 for all the VOCs considered. Silicone oil was also found to be non-biodegradable, since its biological oxygen demand (BOD 5 ) value was zero. CONCLUSION: Absorption performances of silicone oil towards toluene, DMS and DMDS were determined and showed that this solvent could be used during the first step of the process. Moreover, its low biodegradability and its absence of toxicity justify its use as an absorbent phase for the integrated process being considered.