kLa Values Research Articles

3D CFD Simulation of Gas Hold-up and Mass Transfer in a Modified Airlift Reactor with Net Draft Tube

Abstract This paper documents CFD simulations of the gas hold-up (ɛg) and volumetric mass transfer coefficient (KLa) for three kinds of airlift reactors (ALRs) namely, conventional ALR, ALR with net draft tube (ALR-ndt), and packed-bed ALR with net draft tube (PBALR-ndt). The 3D two-fluid Eulerian-Eulerian model was adopted to predict the influence of superficial gas velocity on ɛg and KLa. The simulation results were consistent with the trends described previously in the experimental work regarding ɛg and KLa values and a good agreement was obtained (absolute error less than 20 %). Based on the simulation results, axial flow is the dominant flow in the conventional ALR while in ALR-ndt and PBALR-ndt radial flow streamlines are appeared in the reactors due to the presence of concentric net draft tube which improves their performance. The effective role of the net draft tube is proven since consequence of generation of small bubbles by passing through net draft tube is the entrainment of a larger percentage of gas bubbles from the riser into the downcomer which results in improvement of gas holdup and the KLa values. An exponential correlation is used for relating gas hold-up and mass transfer coefficient. Higher power obtained for ALR-ndt and PBALR-ndt (n ≈ 1.22) compared to ALR (n = 0.95) was indicative of high sensitivity of KLa value to gas hold-up in these reactors due to presence of the concentric net draft tube. The CFD modeling is considered to be an invaluable tool allowing us to analyze and visualize the impact of fluidic forces on hydrodynamic properties and consequently, reactor performance.

Hydrodynamic behavior of an airlift reactor with net draft tube with different configurations: Numerical evaluation using CFD technique

In terms of gas holdup, liquid velocity, and volumetric mass transfer coefficient for oxygen (KLa), the hydrodynamic behavior of four configurations of an airlift reactor (ALR) with a net draft tube (NDT) of different net mesh sizes (ALR-NDT-3, 6, 12, and ALR) have been numerically simulated for a range of inlet air flow rates. The effect of various levels of ratio of height (H) to inner tube diameter (D) of the net draft tube (H/D: 9.3, 10.7, 17.5, and 20) and ratio of inner cross-sectional area of the riser (Ar) to the inner cross sectional area of the downcomer (Ad) (Ad/Ar: 1.3 and 7) for different air flow rates is also evaluated for each reactor configuration operating with an air–water system. The two-fluid formulation coupled with the k–ε turbulence model is used for computational fluid dynamics (CFD) analysis of flow with Eulerian descriptions for the gas and liquid phases. Interactions between air bubbles and liquid are taken into account using momentum exchange and drag coefficient based on two different correlations. Trends in the predicted dynamical behavior are similar to those found experimentally. A good agreement was achieved suggesting that geometric effects are properly accounted for by the CFD model. After a comparison with experimental data, numerical simulations show significant enhanced gas holdup, liquid velocity, and KLa for the ALR-NDTs compared with the conventional ALR. Higher gas holdup values are achieved for ALR-NDT-3 than that for the other ALRs because it acts like a bubble column reactor as the holes present in the NDT are large. Maximum liquid velocities are seen in ALR-NDT-12, which operates like a conventional ALR. Moreover, the interaction between the NDT and upward gas flow leads to cross flow through the net, small bubbles, and high interfacial area as well as good mass transfer. This was significant in ALR-NDT-6 with maximum KLa value of 0.031 s−1. The applied methodology provides an insightful understanding of the complex dynamic behavior of ALR-NDTs and may be helpful in optimizing the design and scale-up of reactors.

Design of a Novel Membrane Draft Tube Jet Loop Reactor (MDJLR) and Treatment of Slaughterhouse Wastewater.

The most important obstacle to the widespread use of membrane bioreactors (MBRs) is membrane fouling. In this study, a high-efficiency compact MBR was developed. Therefore, the draft tube of the jet loop reactor (JLB) was planned for use as a membrane module. The high-velocity jet streams, which are present according to the nature of the JLBs, provide high crossflow (cut-off force) on the membrane surface. Thus, the produced membrane module is operated in submerged membrane mode. This enhanced JLB modification is named the membrane draft tube jet loop reactor (MDJLR). This new system has a KLa value of 139 h−1 (at E/V of 2.24 kW m−3). In the next stage, treatment of slaughterhouse wastewater with the MDJLR was carried out. Under the 5.5 kg COD m−3 d−1 loading rate, efficiencies over 97% were achieved. The system operated continuously for 50 days without membrane backwashing or cleaning. During this period, fluxes of 3 L m−2·h−1 were approximately obtained at operating conditions of 850 mg L−1 MLSS (mixed liquor suspended solids) concentration, 1 bar suction pressure (∆P), and 3000 L h−1 circulation rate. This developed MDJLR will make jet loop membrane bioreactors (JLMBRs) and MBRs more compact and improve their performance.

Design and implementation of an affordable laboratory‐scale bioreactor for the production of microbial natural products

Large‐scale bacteria culturing can present many challenges for small academic laboratories. To address these challenges a cost effective, laboratory scale bioreactor was designed and implemented. The constructed bioreactor addresses common problems that small or teaching‐focused laboratories face when attempting scale up cultures. The design utilizes materials commonly found in standard chemistry laboratories that are easily assembled with minor modifications. The system was validated through the replication of natural product production in shake flasks and the bioreactor. Additionally, measurements were done to ensure the designed bioreactor had comparable kLa values to common shake flask conditions. We anticipate that this design will be of use to other small academic natural product groups as well as teaching laboratories as it offers an economical way to undertake large scale culturing of microorganisms.

Optimized Process and Bioreactor Characterization

AbstractThe mass transfer coefficient (kL)and the value of the interfacial area (a) is used to characterize bioreactor systems for their oxygen transfer capability. The kLa value and the mixing time are amongst the most important performance indicators for bioreactors. Their calculation and modeling is extremely complex in highly aerated systems. This paper describes a new methodology for measuring the kLa value to accurately determine the coefficient. The valuable insights obtained allow for improved bioreactor characterization, thus, making it easier to meet regulatory requirements. Furthermore, examples outlining the benefits in the practical application of the new methodology are presented.

Culture Miniaturization of Lipase Production by Yarrowia lipolytica

Background::The proposal to perform scale-down of culture systems (2 to 4 mL) could be more efficient for screen multiple formulations and operational conditions. For such, is important to evaluate if the kinetic parameters of a bioprocess are comparative to conventional lab-scale reactors. In the present study, the effects of different miniaturized systems were evaluated on growth and lipase production of Yarrowia lipolytica IMUFRJ 50682.Methods::Cultivations were conducted in a mini-scale version of Erlenmeyer flask of 10 mL (10EF); 24 deep-well microplate of 11 ml (24MTP/11 mL) and 24 deep-well microplate of 25 ml (24MTP/25 mL).Results::Similar specific growth rate (μ) was observed between miniaturized cultivations (0.27 h-1). Different lipase productivities values were obtained, the highest was achieved in 10EF (181 U.L-1.h-1). Volumetric oxygen transfer coefficient (kLa) and maximum lipase production were improved with culture miniaturization in comparison with conventional shake-flasks. Bioreactor (1.5 L) cultivation showed similar growth kinetic, pH profile and kLa values, but an increase in the maximum productivity was observed. These finding showed the advantages of Y. lipolytica cultivations scale-down.Conclusion::These findings show the advantages of Y. lipolytica scale-down cultivations, and to perform scale-up for benchtop bioreactor directly from these miniaturized cultivations, without the need of gradual scale-up, representing a reduction in costs and working time. Taking into consideration the rare works about miniaturized cultivation with Y. lipolytica, this work opens the way to a better understanding of bioprocess and alternatives for process conduction.

Production of Recombinant Human Asparaginase from Escherichia coli under Optimized Fermentation Conditions: Effect of Physicochemical Properties on Enzyme Activity

The recombinant human asparaginase (rhASP) plays an important role in the treatment of acute lymphoblastic leukemia. In the present work, volumetric mass transfer coefficient (kLa) values are derived from the E. coli cultivation under different agitation and aeration conditions, in order to improve the rhASP productivity. The aeration and agitation conditions were systematically optimized by the kLa. The maximum biomass (2.4 g/L) and rhASP (1.68 g/L) are achieved with the kLa of 0.024 s-1 at 1.5 lpm and 700 rpm process conditions. The kinetic properties of purified rhASP are also extensively studied and optimized for the maximal enzyme activity. The optimal pH, temperature and incubation duration conditions for accomplishing maximum enzyme activity are found to be 9.0, 40°C, and 30 min, respectively. The optimum substrate concentration and substrate specificity for the highest enzyme activity are of 0.07 M and L-asparagine, respectively. The enzyme activity (204 IU/mL) is significantly improved in the presence of sodium metal (Na+) ions and the inhibitors 2- mercaptoethanol, bromoacetic acid and urea have presented the highest inhibition rate on rhASP activity. The enzyme kinetic parameters Km and Vmax of the purified rhASP are recorded as 2.25 mM and 250 IU/mL, respectively. This work provides the extensive characteristic properties of rhASP enzyme, which enables us to place in a competition for the development of oncology drugs.

Separation of Zn(II) from Zn-Ni-Co sulphate solution by di-(2-ethylhexyl)phosphoric acid (D2EHPA) using a slug flow microreactor

Separation of Zn2+ from sulphate solution containing Ni2+ and Co2+ using di-(2-ethylhexyl)phosphoric acid (D2EHPA) has been carried out in capillary microreactors. Well-defined slug flows are formed at total flow rates of 0.1–4 mL/min, and the slugs size and specific interfacial area are determined. The effects of saponification degree of D2EHPA, extractant concentration, and residence time on extraction and separation of these three metal ions are investigated. Meanwhile, conventional batch experiments at 94 s and equilibrium experiments at 8 h are also done in parallel at different extractant concentrations. Compared with conventional batch experiments, better extraction and separation performance, e.g. 2.7–38.9 times higher of βZn/Ni and 3.9–34.9 times higher of βZn/Co, is obtained in the slug flow microreactor. In addition, the overall volumetric mass transfer coefficient kLa and overall mass transfer coefficient kL are measured. Compared with other microreactors and the batch mixer-settler, the used slug flow microreactor shows higher kLa values of Zn.

Mass transfer characteristics and concentration field evolution for gas-liquid Taylor flow in milli channels

The results of the recent experimental work performed by Butler et al. (2016, 2018) are analysed based on the dominant phenomena: (i) small scale convection by means of Taylor vortices in the liquid slugs and (ii) diffusion in lubrication film. A main result shown here is that the Taylor circulation frequency is able to reflect the global mass transfer rate in gas-liquid Taylor flow through an almost linear relationship, which emphasizes the interest of the circulating motion in the slug, and gives a very simple correlation to predict the kLa value (at large Schmidt number). A mechanism of flow behavior during the bubble formation at the T-mixer is proposed as a possible explanation of unexpected concentration areas (called “islands”). However, despite of these unusual concentration field structures in these cases, the mass transfer rate coefficient kLa is still accurately predicted by the Taylor circulation frequency in the slug.

Local Mass Transfer Phenomena and Chemical Selectivity of Gas‐Liquid Reactions in Capillaries

W. Krieger*, J. Lamsfuß, W. Zhang, N. Kockmann, Chem. Eng. Technol. 2017, 40 (11), 2134–2143. DOI: https://doi.org/10.1002/ceat.201700420 The article reported on a color reaction for determining selectivity in gas-liquid reactions. The stoichiometric values were taken from literature [8] and integrated into the calculations and discussion. Current own stoichiometry and mass balance measurements of the oxidation of leuco-indigo carmine lead to corrected values of a single oxygen molecule only needed for each oxidizing step, shown below. Particularly, the mass transfer coefficients must be corrected towards higher values. The authors apologize for the error and want to correct the publication as follows: Fig. 1 should be as shown below. Leuco-indigo carmine occurs in its deprotonated state due to the alkaline solution. Fig. 2 should be as shown below according to the corrected stoichiometry. The proposed mechanism is supported by [17]. Figs. 10 and 11 should be as shown below due to the corrected stoichiometry. On page 2141, right column, line 7 should read “The attained kLa values range from 7.08 to 16.52 × 10−2 s−1 and are comparable to data from the literature for microchannels and capillaries [22, 23].” On page 2142, left column, lines 22–24 should read “Mass transfer investigations led to kLa values for straight and coiled capillaries in the order of 5–20 × 10−2 s−1, which are in reasonable agreement with data from literature.”

Comparative study of local gas-liquid hydrodynamics and mass transfer between conventional and modified airlift reactors

Modified airlift reactor (MALR) was developed for improving the oxygen transfer coefficient (KLa) by installing the slanted baffles in the riser compartment. MALR can enhance KLa value up to 97% compared to a regular reactor. However, insufficient analysis of the hydrodynamics and other oxygen transfer parameters of this new reactor has been performed to date. Therefore, this paper aims to analyse local gas-liquid dynamics and evaluate the oxygen transfer performance in MALR compared to regular reactors using clean water as a liquid phase. Air bubble distribution was employed in terms of bubble diameter, rising velocity, and interfacial area. Slanted baffles maintained the bubble size between 3.88 and 4.63 mm for the studied superficial gas velocity (Ug), which is smaller than that in airlift reactor (ALR) by approximately 0.2 mm. Bubble rising velocity (UB) is relatively increased with Ug, regardless of reactor classes. New reactor could extend the bubble residence in the water by lengthening the bubble stream path of the slanted baffles leading to decrease UB values about 39% and 52% compared to bubble column reactor (BCR) and ALR, respectively. These performances consequently resulted in an interfacial area almost two times higher than in regular reactors. Oxygen transfer improved in MALR with an extra amount of oxygen transfer efficiency of 1.57% and 0.63% over BCR and ALR, respectively. This resulted in the highest aeration efficiency (AE) compared to other examined reactors, following a trendline expression of AE ˜ 0.046 Ug−0.6. Insertion of slanted baffles produced 5% and 12.8% more dead zone volume than ALR and BCR, respectively. In conclusion, MALR can significantly enhance oxygen transfer performance due to the ability to maintain bubble size and extend the gas-liquid transfer period.

Production of Biomass-Degrading Enzymes by Trichoderma reesei Using Liquid Hot Water-Pretreated Corncob in Different Conditions of Oxygen Transfer

Enzymatic hydrolysis accounts for 20% of the total cost in the conversion process of lignocellulosic biomass into bioethanol. Therefore, production of biomass-degrading enzymes by using lignocellulosic residue as a fermentation substrate may be an alternative to decrease the production costs. In this study, corncob (CC) has been pretreated by liquid hot water (LHW) at 200 °C for 30 min and used as inducer source for production of biomass-degrading enzymes by Trichoderma reesei MUM 97.53. The pretreatment was used to increase the cellulose content and the accessibility to lignocellulosic material. Although the filamentous fungus secreted a broad range of cellulolytic and hemicellulolytic enzymes when grown on untreated CC, higher enzyme productions were obtained when cultured on LHW-pretreated CC in a 2-L stirred tank bioreactor (STB). Besides, the effects of aeration (2 and 4 vvm) and agitation (150 and 250 rpm) rates on enzyme production were studied by submerged fermentation in a batch STB and correlated with the volumetric oxygen transfer coefficient (kLa). Maximal cellulase, xylanase, and β-xylosidase productions were found at 150 rpm and 4 vvm, while the highest β-glucosidase levels were obtained at 150 rpm and 2 vvm, that corresponded to kLa values of 32.50 h−1 and 16.41 h−1, respectively. At higher agitation, a lower enzymatic production was observed probably due to the high shear stress in the fungal hyphae.

Mass transfer estimation for bubble column scale up

The productivity of a bubble column reactor (BCR) critically depends upon gas-liquid mass transfer coefficient, kLa. The prediction of kLa as function of design and operating conditions is central to BCR scale up. A large number of researchers have successfully characterized kLa experimentally in terms of superficial gas velocity, Usg using the power law relation kLa=αUsgβ, with α,β as fit parameters. We probe the applicability of such correlations to the design of a scaled up BCR, which differs from laboratory BCR in two important aspects: (i) the scale of operation, which can be O(102-103) times larger, and (ii) the type of sparger used. To this end, experiments were performed with air and water in a pilot scale (DC=1.6 m diameter) BCR using a coarse bubble sparger. We found that the existing correlations do, indeed, describe kLa over a wide range of BCR sizes, suggesting that these correlations are fairly scale insensitive. However, the correlations provide no means to capture the role of sparger explicitly. We cast our experimental kLa values in terms of a mass transfer efficiency and independently recover the power law relation with β=1. We suggest that the role of sparger design can be incorporated in the definition of α through the well-documented sparger efficiency factors. The α and β estimates thus obtained are in good agreement with the literature.

Aeration step method for kLa measurement under growth conditions in pneumatic bioreactors

AbstractBackgroundDetermination of the volumetric oxygen transfer coefficient (kLa) plays an important role in the design and characterization of bioreactors. Among all methods available, few techniques are suitable for the determination of kLa in pneumatic bioreactors during the course of cultivations. The present work proposes a new aeration step method for kLa evaluation in pneumatic bioreactors during biological consumption of oxygen.ResultsThe aeration step method consisted in promoting step changes in the specific air flow rate (Φair) to change the dissolved oxygen concentration during cultivations, allowing the measurement of both overall oxygen transfer coefficient (kLa) and specific oxygen uptake rate (QO2). These parameters were determined experimentally by employing two microorganisms, one a strict aerobe (Bacillus subtilis) and the other a facultative aerobe (Saccharomyces cerevisiae), for Φair values ranging from 2.0 to 5.0 vvm. For the purpose of comparison, kLa was also determined in experiments using water as the liquid phase, employing a dynamic gassing‐out method. The kLa values during the cultivations ranged from 0.0137 to 0.0545 s−1, while QO2 varied from 0.44 to 10.06 mol kg−1 h−1. The results obtained are shown to be reliable, exhibited excellent reproducibility and are in agreement with other values reported in the literature by different methodologies.ConclusionThe new aeration step method proved to be reliable as an alternative technique for the determination of kLa and QO2 during microbial cultivation in pneumatic bioreactors. © 2019 Society of Chemical Industry

Bioprocess development for (2R,3R)‐butanediol and acetoin production using very high polarity cane sugar and sugarcane molasses by a Bacillus amyloliquefaciens strain

AbstractBACKGROUNDEfficient production of (2R,3R)‐2,3‐butanediol (BDO) and acetoin using the GRAS strain Bacillus amyloliquefaciens from very high polarity (VHP) cane sugar and sugarcane molasses could lead to the development of a sustainable industrial process.RESULTSThe effect of initial substrate concentration, nitrogen source, temperature, inoculum size and pH were evaluated in shake flask cultures. Batch bioreactor cultures showed that (2R,3R)‐BDO production (up to 28 g L−1) with high yield (up to 0.43 g g−1) and productivity (up to 0.93 g L−1 h−1) was favored at low kLa values (17–49 h−1). Increasing kLa values (63–104 h−1) initiated acetoin production (up to 25.6 g L−1) with yields up to 0.4 g g−1 and productivities up to 1.42 g L−1 h−1. Fed‐batch fermentation carried out at kLa value of 49 h−1 with VHP cane sugar resulted in mixed production (127.3 g L−1) of (2R,3R)‐BDO, (2R,3S)‐BDO and acetoin at 122 h with high yield (0.50 g g−1) and productivity (1.04 g L−1 h−1). In a similar fed‐batch fermentation with sugarcane molasses, mainly (2R,3R)‐BDO production (48.7 g L−1 with purity of 87.8%) was achieved at 59 h with yield of 0.4 g g−1 and productivity of 0.83 g L−1 h−1. At 130 h, (2R,3R)‐BDO was converted mainly into acetoin (55.4 g L−1).CONCLUSIONThis study demonstrates that kLa manipulation could be used in batch cultures to divert the bacterial metabolism towards either (2R,3R)‐BDO or acetoin production. Fed‐batch cultures with sugarcane molasses could lead to either (2R,3R)‐BDO or acetoin production with negligible by‐product formation. © 2019 Society of Chemical Industry

Estimation of kLa Values in Bench‐Scale Stirred Tank Reactors with Self‐Inducing Impeller by Multiphase CFD Simulations

AbstractA multiphase computational fluid dynamics (CFD) simulation methodology is developed and proposed for the estimation of the spatial distribution of kLa values in a bench‐scale reactor equipped with a self‐inducing impeller. The importance of estimating an apparent drag coefficient, which considers the effect of turbulence on the gas bubble rising velocity, is also tackled by applying different correlations available in literature, namely, Brucato, modified Brucato, and Pinelli correlations. The spatial distribution of kLa values in the agitated vessel is found from the CFD results using Danckwert's surface renewal model. An analysis of the gas volume fraction distribution obtained from the simulations is performed in order to choose the most suitable drag model. The modified Brucato correction correlation for the drag force exhibits the best agreement with experimental data.

Effect of pH and Gas Flow Rate on Ozone Mass Transfer of Κ-Carrageenan Solution in Bubble Column Reactor

This research was conducted to calculate the mass transfer coefficient value for ozonation reaction of κ-carrageenan solution in the bubble column reactor. Ozone gas was produced using ozone generator type corona discharge. In this study, operating conditions were regulated at ozone gas flow rate 2- 5 L min-1, pH 4-10, and temperature 29 ± 1 oC. Samples were tested every 5 minutes to determine the dissolved ozone concentration. The results showed that dissolved ozone concentrations increased with increasing ozonation time and ozone gas flow rate. However, a very high gas flow rate can increase turbulence so that the mass transfer coefficient (kLa) value decreased. In alkaline conditions, the formation of free radicals (HO*) increases so that the amount of dissolved ozone decreases. The kLa value of ozone gas in κ-carrageenan solution is slightly lower than the kLa value of the ozone gas in the water. The results of this study indicate that (kLa) ozone gas in water is 0.131 / minute while the value (kLa) in κ-carrageenan solution is 0.128 / minute.Keywords: ozone; mass transfer; pH; flowrate

The effect of water type on the absorption and desorption of carbon dioxide in bubble columns

This study investigates the effect of alkalinity and salinity on the transfer rate of carbon dioxide, CO2, from/to several aqueous phases. The CO2 absorption and desorption experiments were performed for several water types including distilled, reverse osmosis, brackish, and brackish reject waters in addition to seawater, inside a bubble column contactor. Findings indicated that the direction of transfer (i.e. absorption or desorption) had a strong influence on the rate of mass transfer with higher values recorded for the absorption experiments. The results also showed that for the absorption and desorption experiments the volumetric mass transfer coefficient, kLa, values always decreased with increased salinity until a “threshold” value was attained, above which kLa increased again. The effect of alkalinity on kLa values was not as conclusive where the experimental results indicated that for adsorption kLa values decreases almost linearly with the increase in water alkalinity while no discernible trends were observed for the effect of alkalinity in the desorption experiments.

Effect of aeration and agitation on yeast inulinase production: a biocalorimetric investigation.

Air flow rate and agitation speed for inulinase production by Kluyveromyces marxianus were optimized based on metabolic heat release profiles. Shear stress and oxygen transfer (kLa) values were compared to assess the effects of aeration and agitation. At agitation rates of ≤ 100rpm, the oxygen mass transfer rates were small and eventually led to less inulinase production, but at agitation rates > 150rpm, loss of biomass resulted in less inulinase activity. Bio-reaction calorimeter (BioRc1e) experiment with aeration rates ≤ 0.5 lpm showed low kLa while at 1.5 lpm frothing of reactor contents caused loss of biomass and inulinase activity. The optimum conditions for aeration and agitation rate for K. marxianus in BioRc1e were 1 lpm and 150rpm. Heat yield values obtained for the substrate, product and biomass reinstated the ongoing metabolic process. The heat release pattern could be a promising tool for optimization of bioprocess and in situ monitoring, with a possibility of interventions during the biotransformation process. At optimized aeration and agitation conditions, a two-fold increase in inulinase activity could be noticed.

Intensification of liquid-liquid extraction in a tubular sono-extractor using 1.7 MHz ultrasound and SiO2 nanoparticles

The purpose of the present study is to investigate the effect of high-frequency ultrasound propagation in a sono-extractor to augment liquid-liquid mass transfer in the presence of SiO2 nanoparticles. For this purpose, four 1.7 MHz ultrasound transducers are placed on the body of the sono-extractor and the effect of transducer locations on the mass transfer characteristics are evaluated. Using ultrasound and nanoparticles showed a higher effect on the increase in the mass transfer characteristics compared with only using ultrasound or nanoparticles. Activation of two bottom transducers is more efficient from viewpoint of lower energy consumption. The effect of increasing the power of ultrasound (P) is investigated and measurable increase in KLa and E are obtained. The effect of various weight fraction of nanoparticles (ϕ = 0.1–2% wt.) on KLa and E is evaluated and ϕ = 2% wt showed higher values. Maximum values of KLa (2.81 × 10−3 1/s) and E (0.943) are achieved for activation of two bottom ultrasound transducers with P = 9.5 W and ϕ = 2% wt.