Role of hydrodynamic flow parameters in lipase deactivation in bubble column reactor

The dynamic environment within the bioreactor and in the purification equipment is known to affect the activity and yield of enzyme production. In the present work, the effect of hydrodynamic flow parameters and τ_N,max) and interfacial flow parameters ( and ) on the activity of lipase has been comprehensively investigated in bubble column reactors. Lipase solution was subjected to hydrodynamic flow parameters in 0.15 and 0.385 m i.d. bubble column reactors over a wide range of superficial gas velocity (0.01<V_G<0.4-). The flow parameters were estimated using an in-house CFD simulation code based on k-ε approach. The extent of lipase deactivation in both the columns was found to increase with an increase in hydrodynamic and interfacial flow parameters. However, at equal value of any of these parameters, the extent of deactivation was different in the two columns. The rate of deactivation was found to follow first order kinetics. An attempt has been made to develop rational correlations for the extent of deactivation as well as for the deactivation constant. The rate of deactivation was found to be depending on the average turbulent normal stress and interfacial flow parameters such as bubble diameter and bubble rise velocity.     

Performance of compression ignition engine with mahua (Madhuca indica) biodiesel

The performance of biodiesel obtained from mahua oil and its blend with high speed diesel in a Ricardo E6 engine has been presented in this paper together with some of its fuel properties. These properties were found to be comparable to diesel and confirming to both the American and European standards. Engine performance (brake specific fuel consumption, brake thermal efficiency and exhaust gas temperature) and emissions (CO, smoke density and NO_x) were measured to evaluate and compute the behaviour of the diesel engine running on biodiesel. The reductions in exhaust emissions and brake specific fuel consumption together with increase brake power, brake thermal efficiency made the blend of biodiesel (B20) a suitable alternative fuel for diesel and thus could help in controlling air pollution.     

Synthesis and characterization of silver nanoparticles and their antimicrobial efficacy

An efficient protocol for synthesis of silver nanoparticles (AgNPs) using the combination of aqueous extract of Tinospora cordifolia leaves and 5 mM silver nitrate (AgNO₃) solution was developed. This study revealed that bioactive compounds present in the extract function as stabilizing and capping agent for AgNPs. Scanning electron microscope and transmission electron microscope studies confirm the structure and surface morphology of the AgNPs. The size of synthesized AgNPs was in the range of 30–50 nm having spherical morphology. The crystalline nature of NPs was defined by the X-ray diffraction pattern. The AgNPs were found to be toxic against pathogenic bacteria such as Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), and Staphylococcus aureus (ATCC 29213) and against plant pathogenic fungi Fusarium oxysporum (MTCC 8608) and Sclerotinia sclerotiorum (MTCC 8785). The use of AgNPs as antibacterial and antifungal agent is advantageous over other methods for control of pathogenic microorganisms, and it can be of great importance in developing novel drugs for curing many lethal diseases.     

Wavelet-Based Structural Health Monitoring of Earthquake Excited Structures

Abstract:   The article presents a wavelet-based structural health monitoring technique for structures subjected to an earthquake excitation utilizing the instantaneous modal information. The instantaneous mode shape information is first extracted from the vibration response data collected during an earthquake event by using a wavelet packet sifting process. A confidence index (CI) is proposed to validate the results obtained. The identified normalized instantaneous mode shapes in conjunction with the corresponding CIs can be effectively used to monitor damage development in the structure. The effectiveness of the proposed approach is illustrated for two damage scenarios, sudden stiffness loss and progressive stiffness degradation, and different base excitations including three real earthquake signals and a random signal. Consistently good results were obtained in all cases. Issues related to robustness of the method in the presence of a measurement noise and sensitivity to damage severity are discussed.     

Electrochemically active and robust cobalt doped copper phosphosulfide electro-catalysts for hydrogen evolution reaction in electrolytic and photoelectrochemical water splitting

The area of non-noble metals based electro-catalysts with electrochemical activity and stability similar or superior to that of noble metal electro-catalyst for efficient hydrogen production from electrolytic and photoelectrochemical (PEC) water splitting is a subject of intense research. In the current study, exploiting theoretical first principles study involving determination of hydrogen binding energy to the surface of the electro-catalyst, we have identified the (Cu_0.83Co_0.17)₃P: x at. % S system displaying excellent electrochemical activity for hydrogen evolution reaction (HER). Accordingly, we have experimentally synthesized (Cu_0.83Co_0.17)₃P: x at. % S (x = 10, 20, 30) demonstrating excellent electrochemical activity with an onset overpotential for HER similar to Pt/C in acidic, neutral as well as basic media. The highest electrochemical activity is exhibited by (Cu_0.83Co_0.17)₃P:30 at. % S nanoparticles (NPs) displaying overpotential to reach 100 mA cm^?2 in acidic, neutral and basic media similar to Pt/C. The (Cu_0.83Co_0.17)₃P:30 at. % S NPs also display excellent electrochemical stability in acidic media for long term electrolytic and PEC water splitting process [using our previously reported (Sn_0.95Nb_0.05) O₂: N-600 nanotubes (NTs) as the photoanode]. The applied bias photon-to-current efficiency obtained using (Cu_0.83Co_0.17)₃P:30 at. % S NPs as the cathode electro-catalyst for HER in an H-type PEC water splitting cell (～4%) is similar to that obtained using Pt/C (～4.1%) attesting to the promise of this exciting non-noble metal containing system.     

Active and robust novel bilayer photoanode architectures for hydrogen generation via direct non-electric bias induced photo-electrochemical water splitting

Photo-electrochemical (PEC) water splitting is a promising and environmentally benign approach for generation of hydrogen using solar energy with minimum greenhouse gas emissions. The development of semiconductor materials for photoanode with superior optoelectronic properties combined with excellent photoelectrochemical activity and stability is vital for the realization of viable commercial development of PEC water splitting systems. Herein, we report for the very first time, the study of nanoscale bilayer architecture of WO₃ and Nb and N co-doped SnO₂ nanotubes (NTs), wherein WO₃ NTs are coated with (Sn_0.95Nb_0.05)O₂:N-600 (annealed in NH₃ at 600 °C) layer of different thicknesses, as a potential semiconductor photoanode material for PEC water splitting. An excellent long term photoelectrochemical stability under illumination in the acidic electrolyte solution combined with a solar-to-hydrogen efficiency (STH) of ～3.83% (under zero applied potential) is obtained for the bilayer NTs, which is the highest STH obtained thus far, to the best of our knowledge compared to the other well studied semiconductor materials, such as TiO₂, ZnO and Fe₂O₃. These promising results demonstrate the excellent potential of bilayer NTs as a viable and promising photoanode in PEC water splitting.     

Highly active robust oxide solid solution electro-catalysts for oxygen reduction reaction for proton exchange membrane fuel cell and direct methanol fuel cell cathodes

The identification and development of novel non-noble metals based electro-catalyst exhibiting excellent electrochemical activity and stability than noble metal electro-catalyst is important for commercial development of proton exchange membrane fuel cells (PEMFCs). Such non-noble electro-catalyst with unique electronic structure and superior electrochemical performance will immensely contribute to lowering the capital cost of PEMFCs. Herein, we have identified solid solution electro-catalysts of WO₃ and IrO₂ for oxygen reduction reaction (ORR) in PEMFCs exploiting theoretical first principles approaches. The theoretical results were experimentally validated by generation of nanostructured (W_1-xIr_x)O_y (x = 0.2, 0.3; y = 2.7–2.8) electro-catalysts for ORR. (W_0.7Ir_0.3)O_y demonstrated ～43% improved electrochemical activity than Pt/C with similar loading at 0.9 V (vs RHE), respectively. Moreover, single full cell PEMFC study revealed an acceptable ～81% improved maximum power density for (W_0.7Ir_0.3)O_y than Pt/C combined with excellent long term stability. These results thus, show the potential of (W_0.7Ir_0.3)O_y as ORR electro-catalyst for replacing of Pt/C in PEMFCs and direct methanol fuel cells on the additional grounds of superior methanol tolerance.     

Separation of liquid–liquid dispersion in a batch settler: CFD-PBM simulations incorporating interfacial coalescence

Several commercially important chemical processes involve liquid–liquid phase separation. In the present work, we have developed a multi-fluid Eulerian CFD model using OpenFOAM that incorporates binary and interfacial coalescence processes. We simulated separation of kerosene dispersed in water in a batch settler and validated the predictions using the measurements of time-evolution of coalescing and settling interfaces, local dispersed-phase volume fraction (α_O) and drop size distribution (DSD). Simulations are performed to understand the contributions of binary and interfacial coalescence processes to the phase separation process. While the time-evolution of coalescing and settling fronts can be predicted reasonably well using the two-fluid model with empirically-corrected drag models, local α_O and DSD could not be predicted. We have shown that the comprehensive multi-fluid Eulerian model, which incorporates binary and interfacial coalescence, predicts the time-evolution of the coalescing and settling fronts, local α_O and the DSD in an excellent agreement with the measurements.     

A statistical approach to develop a detailed soot growth model using PAH characteristics

A detailed PAH growth model is developed, which is solved using a kinetic Monte Carlo algorithm. The model describes the structure and growth of planar PAH molecules, and is referred to as the kinetic Monte Carlo-aromatic site (KMC-ARS) model. A detailed PAH growth mechanism based on reactions at radical sites available in the literature, and additional reactions obtained from quantum chemistry calculations are used to model the PAH growth processes. New rates for the reactions involved in the cyclodehydrogenation process for the formation of 6-member rings on PAHs are calculated in this work based on density functional theory simulations. The KMC-ARS model is validated by comparing experimentally observed ensembles on PAHs with the computed ensembles for a C₂H₂ and a C₆H₆ flame at different heights above the burner. The motivation for this model is the development of a detailed soot particle population balance model which describes the evolution of an ensemble of soot particles based on their PAH structure. However, at present incorporating such a detailed model into a population balance is computationally unfeasible. Therefore, a simpler model referred to as the site-counting model has been developed, which replaces the structural information of the PAH molecules by their functional groups augmented with statistical closure expressions. This closure is obtained from the KMC-ARS model, which is used to develop correlations and statistics in different flame environments which describe such PAH structural information. These correlations and statistics are implemented in the site-counting model, and results from the site-counting model and the KMC-ARS model are in good agreement. Additionally the effect of steric hindrance in large PAH structures is investigated and correlations for sites unavailable for reaction are presented.