Suchergebnisse

AbstractThe solubility of oxygen in a liquid is limited/restricted by the gas–liquid film that prevents gas from dissolving in wastewater. Oxygen in the biological aeration unit (BAU) is required by microorganisms to survive and eliminate organic and inorganic matter. This study developed a volumetric mass transfer coefficient (KLa) model using Artificial Neural Network (ANN) algorithm. The performance of the KLa model was evaluated using coefficient of determination (R2), mean squared error (MSE), and root mean squared error (RMSE). KLa model produced R2 (0.852), MSE (0.0006), and RMSE (0.0245) during the testing phase. Biomass concentration (22.29%), aeration period (20.55%), and temperature (19.63%) contributed the highest towards the KLa model. KLa model showed that the BAU should be operated at high temperatures (35°C), low biomass concentration (1.65 g/L), and low aeration period (1 h) instead of high airflow (30 L/min). Temperature should be included in the modelling of the BAU, to achieve optimum KLa.

AbstractThis study demonstrates evidence that the mass transfer process of an enzyme (a biocatalyst) is the rate‐limiting step in the starch hydrolysis reaction during food digestion. The significance of this work has been to compare the reaction rate of starch hydrolysis by salivary enzymes with the mass transfer rate of rate‐limiting enzymes. This research has applied mass transfer and reaction engineering theory in a quantitative study of starch hydrolysis, and a dimensionless group, the Damköhler number (Da), has been calculated based on glucose measurements from a beaker and stirrer system. The values of the Da number in this study (0.3–19) indicate that both the time constant for mass transfer and the time constant for reaction are significant parameters. Scanning electron microscopy images emphasize that compression (simulated mastication) helps to break the plant cell wall of starch. Mass‐transfer resistance needs to be considered during food digestion studies. The Da numbers are significantly affected by both compression forces (internal mass‐transfer coefficients) and stirrer speeds (external mass‐transfer coefficients) in this beaker and stirrer system.

The results of modeling and experimental study of heat and mass transfer in a dense blown layer of plant materials under cyclic microwave exposure are presented. The two-dimensional mathematical model consists of the equations of conservation of the mass of the gas phase, filtration, heat and mass transfer in phases, which take into account the internal resistance to heat and moisture transfer in the particles when determining the heat and mass transfer coefficients. In this case, the dependences of the heat of the phase transition on the humidity of the particles, their shrinkage during dehydration, and the dependences of the effective coefficients of thermal conductivity of the gas and vapor diffusion on the filtration rate are taken into account. The simulation results of drying chopped potatoes in a dense layer with a cyclic microwave convective energy supply are presented. The possibility of intensifying the process of moisture dehydration and reducing its duration compared with the convective method is shown. Comparison of calculated data with experimental data confirms the adequacy of the model.

The present work analyses the carbon dioxide absorption process in aqueou alkylpyrrolidones solutions, from the point of view of hydrodynamic studies as well as mass transfer, using a bubble column contactor. An analysis of the influence of solute concentration and gas flow-rate is complemented by the study of the effect caused by the alkyl group on the hydrodynamics and mass transfer. The presence of this kind of substance produces a decrease in mass transfer rate, but on the basis of interfacial area and mass transfer coefficient values, ethyl-2-pyrrolidine (EP) shows suitable characteristics to replace methyl-2- pyrrolidine (MP) in gas separation processes due to its lower safety problems ; The authors thank the Consellería de Economía e Industria of Galicia regional government (Xunta de Galicia) for funding the research through the research project 10MDS265021PR. Diego Gómez Díaz gratefully acknowledges the Ministerio de Innovación y Ciencia of Spain for the support under a "Ramón y Cajal" position ; SI

Abstract
Background
In this research work, a coupled heat and mass transfer model was developed for salt recovery from concentrated brine water through an osmotic membrane distillation (OMD) process in a hollow fiber membrane contactor (HFMC).The model was built based on the resistance-in-series concept for water transport across the hydrophobic membrane. The model was adopted to incorporate the effects of polarization layers such as temperature and concentration polarization, as well as viscosity changes during concentration.

Results
The modeling equations were numerically simulated in MATLAB® and were successfully validated with experimental data from literature with a deviation within the range of 1–5%. The model was then applied to study the effects of key process parameters like feed concentrations, osmotic solution concentration, feed, and osmotic solution flow rates and feed temperature on the overall heat and mass transfer coefficient as well as on water transport flux to improve the process efficiency. The mass balance modeling was applied to calculate the membrane area based on the simulated mass transfer coefficient. Finally, a scale-up for the MD process for salt recovery on an industrial scale was proposed.

Conclusions
This study highlights the effect of key parameters for salt recovery from wastewater using the membrane distillation process. Further, the applicability of the OMD process for salt recovery on large scale was investigated. Sensitivity analysis was performed to identify the key parameters. From the results of this study, it is concluded that the OMD process can be promising in salt recovery from wastewater.

Cooling or heating an agitated liquid is a very common operation in many industrial processes. A classic approach is to transfer the necessary heat through the vessel jacket. Another option, frequently used in the chemical and biochemical industries is to use the heat transfer area of vertical tube baffles. In large equipment, e.g. fermentor, the jacket surface is often not sufficient for large heat transfer requirements and tube baffles can help in such cases. It is then important to know the values of the heat transfer coefficients between the baffles and the agitated liquid. This paper presents the results of heat transfer measurements using the transient method when the agitated liquid is periodically heated and cooled by hot and cold water running through tube baffles. Solving the unsteady enthalpy balance, it is possible to determine the heat transfer coefficient. Our results are summarized by the Nusselt number correlations, which describe the dependency on the Reynolds number, and they are compared with other measurements obtained by a steady-state method.

Proceedings of: 14th International Conference on Fluidization: From Fundamentals to Products. Noordwijkerhout, Netherlands, 26-31 may 2013. ; This work presents an experimental study to determine the capacity of a Phase Change Material (PCM) in granular form to be used in a bubbling fluidized bed for thermal energy storage. The experimental measurements are focused on the determination of the heat transfer coefficient between a heated surface and the granular PCM in fluidized state. The results obtained indicates that the heat transfer coefficient notably increases (up to values three times higher) when the granular PCM is in solid form because it changes its phase when touches the heated surface ; This work was partially founded by the Spanish Government (Project ENE2010-15403), the regional Government of Castilla-La Mancha (Project PPIC10-0055-4054) and Castilla-La Mancha University (Project GE20101662). ; publicado