Hydrodynamics and Mass Transfer in a Concentric Internal Jet-Loop Airlift Bioreactor Equipped with a Deflector

The gas–liquid hydrodynamics and mass transfer were studied in a concentric tube internal jet-loop airlift reactor with a conical bottom. Comparing with a standard design, the gas separator was equipped with an adjustable deflector placed above the riser. The effect of riser superficial gas velocity uSGR on the total gas holdup εGT, homogenization time tH, and overall volumetric liquid-phase mass transfer coefficient kLa was investigated in a laboratory bioreactor, of 300 mm in inner diameter, in a two-phase air–water system and three-phase air–water–PVC–particle system with the volumetric solid fraction of 1% for various deflector clearances. The airlift was operated in the range of riser superficial gas velocity from 0.011 to 0.045 m/s. For the gas–liquid system, when reducing the deflector clearance, the total gas holdup decreased, the homogenization time increased twice compared to the highest deflector clearance tested, and the overall volumetric mass transfer coefficient slightly increased by 10–17%. The presence of a solid phase shortened the homogenization time, especially for lower uSGR and deflector clearance, and reduced the mass transfer coefficient by 15–35%. Compared to the gas–liquid system, the noticeable effect of deflector clearance was found for the kLa coefficient, which was found approx. 20–29% higher for the lowest tested deflector clearance.

Study on the Key Technology of Electrochemical Machining Flow Field in Aero-Rotor Blades

With the rapid development of aerospace industry in recent years, the use of aero-rotor engine blades with new special alloy materials and high distortion and thin-walled structure has been paid more and more attention. Aiming at the problems of poor tool accessibility, serious tool loss and easy deformation of blade profile in NC milling technology, electrochemical machining can realize the processing of complex special structure products with advanced materials by means of non-contact electrochemical etching process. However, in the process of electrochemical etching, the flow channel structure of electrochemical machining affects the stability of the distribution of electrochemical etching characteristics in various parts of the machining surface and ultimately acts on the forming quality by controlling the liquid phase mass transfer process in the machining gap. Therefore, reasonable design and optimization of the flow channel is of great significance in the process of electrochemical machining. In this paper, based on the existing traditional vertical single-axis feed machining mode and combined with the traditional side flow processing blade flow characteristics, innovatively proposed two kinds of electrolyte flow schemes under the vertical machining mode; Then, based on the above two flow channel structures and the energy loss characteristics of viscous fluid during liquid phase mass transfer, a mathematical model of liquid phase mass transfer flow field is established, which combines the viscosity loss characteristics of electrolyte, and by introducing a optimized flow channel structure that combined with the characteristics of positive flow and side flow and adjusting the parameters of electrolyte inlet / outlet, the optimal design channel structure and uniform flow field of aero-rotor blades are realized. Finally, the accuracy and rationality of the proposed scheme are verified by electrochemical machining verification test, which lays a research foundation and guarantee for the feasibility and accuracy of vertical electrochemical machining machine tool in aero-rotor blades.

Gas–liquid mass transfer using advanced optical probe in a mimicked FT slurry bubble column

Gas-liquid volumetric liquid-phase mass transfer coefficient (kLa) was studied in a slurry bubble column at the conditions mimicking Fischer–Tropsch synthesis. To avoid the hydrodynamic disturbances due to the gas switching, oxygen enriched air dynamic absorption method was used. Influence of reactor models (CSTR, ADM and RCFD) on the volumetric mass transfer coefficient was investigated. Effect of operating pressure, superficial gas velocity and solids loading were investigated. From the reactor models investigated, it is recommended to use ADM model for kLa study. If the CSTR model is used, applicability of the model should be checked. With increase in the superficial gas velocity and operating pressure, volumetric liquid-phase mass transfer coefficient increases, while it decreases with the solids loading corroborating with the literature.

EFFECTS OF TEMPERATURE-pH ON LIQUID PHASE MASS TRANSFER AND DIFFUSION COEFFICIENTS AT LEACHATE TREATMENT IN ANAEROBIC BIOREACTOR

- Leachate contains complex dissolved organic and inorganic substrates that are biodegradable and non-biodegradable. Principally, anaerobic treatment utilizes anaerobic bacteria to degrade the dissolved organic matters. Anaerobic treatment is very sensitive towards the change of temperature and pH. This research used an anaerobic bioreactor with volume of 160L, with a ratio of leachate:biogas was 70:30. Seeding, acclimatization and leachate treatment were executed at temperature 35°C; pH ambient, temperature 45°C; pH ambient, temperature 35°C; pH 7.2 and temperature 45°C; pH 8.0. Based on this research, that there is dependency on mass of solutes organic substrate (COD) in the leachate, at all operating conditions of leachate treatment in anaerobic bioreactor. Hence, the organic substrate concentration (COD) will affect the VFA, the liquid phase mass transfer and diffusion of solute organic. Consequently, the higher the temperature-pH, the higher the liquid-phase mass transfer, but lower diffusion coefficients is. Keywords: anaerobic bioreactor, diffusion, leachate, liquid-phase mass transfer

Mass Transfer of Anthocyanins during Extraction from Pre-Fermentative Grape Solids under Simulated Fermentation Conditions: Effect of Convective Conditions

The colour of red wine is largely determined by the concentration of anthocyanins that are extracted from grape skins during fermentation. Because colour is a key parameter in determining the overall quality of the finished product, understanding the effect of processing variables on anthocyanin extraction is critical for producing a red wine with the desired sensorial characteristics. In this study, the effect of convective conditions (natural and forced) on the mass transfer properties of malvidin-3-glucoside (M3G) from pre-fermentative grape solids was explored at various liquid phase conditions representing stages of fermentation. A mathematical model that separates solid and liquid phase mass transfer parameters was applied to experimental extraction curves, and in all cases, provided a coefficient of determination exceeding 0.97. Calculated mass transfer coefficients indicated that under forced convective conditions, the extraction process was controlled by internal diffusion whereas under natural convection, both internal diffusion and liquid-phase mass transfer were relevant in determining the overall extraction rate. Predictive simulations of M3G extraction during active fermentation were accomplished by incorporating the current results with a previously developed fermentation model, providing insight into the effect of a dynamic liquid phase on anthocyanin extraction.

EFFECT OF pH ON LIQUID-PHASE MASS TRANSFER AND DIFFUSIVITY COEFFICIENT AT LEACHATE TREATMENT OF MUNICIPAL WASTE LANDFILL IN ANAEROBIC BIOREACTOR

Leachate is a liquid waste resulted from physical, biological and chemical decomposition of landfill waste. Leachate contains complex dissolved organic and anorganic substrate which are biodegradable and non-biodegradable. Anaerobic treatment principally utilizes anaerobic bacteria in order to degrade the dissolved organic substance into biogas. Anaerobic treatment is very sensitive towards the substrate cocentration, temperature, and pH. This research used anaerobic bioreactor with the volume of 160 L, the ratio of the leachate: biogas is 70:30. Seeding and acclimatization steps were done, respectively for 10 days, leachate treatment was done in 21 days. Seeding, acclimatization, and leachate treatment were done on the pH ambience of 7.2 and 8.0 and ambient temperature. COD and VFA analysis were done every two days. The objective of this research is to decide the pH effect on the coefficient of liquid-phase mass transfer: kL, and the diffusivity of the dissolved substace, DL. pH affects the degradation of the concentratio of dissolved organic substrate in the leachate. The higher the pH is, the higher the obtained VFA concentration is. VFA concentration is affected by pH; however, it still considers the optimal pH condition of the substrate biodegradation. pH affects the average rate of mass transfer, rkL and diffusivity of the dissolved substance, DL in the anaerobic treatment of leachate. pH affect the concentration of dissolved organic substrate which subsequently influenes the coefficient of liquid-phase mass transfer of the leachate, kL and the diffusivity of the dissolved substance, DL. The higher the pH is, the more increasing the kL is and the more decreasing the DL is.

Hydrogen Sulfide Removal from Biogas Using Digester Effluent Absorbent in a Continuous Vertical Column

HYDROGEN SULFIDE REMOVAL FROM BIOGAS USING DIGESTER EFFLUENT ABSORBENT IN A CONTINUOUS VERTICAL COLUMN. Gas-Liquid mass transfer is one of the most commonly used phenomena in the chemical process, such as absorbtion. This research evaluates the value of liquid phase mass transfer coefficient of hydrogen sulfide removal from biogas in a continous contactor column for digester effluent-biogas system. This study was carried out by contacting biogas at certain flow with digester effluent continously in a counter-current flow packed bed column. Samples were taken in steady state condition. This research used raschig rings, large balls, and small balls as packing materials with surface areas are 0.9269 m2/m3, 0.6279 m2/m3, and 0.2992 m2/m3 respectively at volumetric flow rates of biogas from 0.1109 m3/h to 0.8846 m3/h. The results show that the relationship between the variables and mass transfer coefficient gives following mathematical model This model is valid in the range of (As·dt) and (Vg/dt·DL) respectively from 0.03 to 0.09 and from 237,267.08 to 3,307,522.67. Average error is 17.85%.