Power Input Measurements Research Articles

Numerical and Experimental Analysis of a Solid Shroud in Multi-arc Plasma Spraying

AbstractPlasma spraying is characterized by high flexibility, but has challenges of high energy consumption and oxidation of the metallic spray particles. Modified plasma spraying processes using a gas or solid shroud have been developed to address these challenges, which aim to reduce the introduction of ambient air into the plasma jet and improve the process efficiency. Prior research mainly focused on single-cathode plasma generators, and the use of a shroud in multi-arc plasma spraying systems has not been thoroughly explored. The primary goal of this study is to analyze the effects of a solid shroud as a nozzle extension on the plasma jet of a three-cathode plasma generator numerically and experimentally. Computational fluid dynamics (CFD) is used to simulate a solid shroud, and the resulting design is constructed for experimental analysis. The experimental setup includes a nozzle extension with a transparent window for diagnostic measurements by a high-speed camera. To isolate the effects of the solid shroud from fluctuations in the power input, current, and voltage measurements are carried out synchronized with the high-speed recordings. Particle diagnostics are also conducted to analyze the properties of the in-flight particles without and with the solid shroud. The developed numerical model can be further used to optimize the shroud geometry for different process parameters.

Reassessing the out-of-phase phenomenon in shake flasks by evaluating the angle-dependent liquid distribution relative to the direction of the centrifugal acceleration.

Shake flasks are still the most relevant experimental tool in the development of viscous fermentation processes. The phase number, which defines the onset of the unfavorable out-of-phase (OP) phenomenon in shake flasks, was previously defined via specific power input measurements. In the OP state, the bulk liquid no longer follows the orbital movement of the imposed centrifugal force, which is for example, detrimental to oxygen transfer. In this study, an optical fluorescence technique was used to measure the three-dimensional liquid distribution in shake flasks. Four new optically derived evaluation criteria for the phase transition between the in-phase and OP condition were established: (a) thickness of the liquid film left on the glass wall by the rotating bulk liquid, (b) relative slope of the leading edge of bulk liquid (LB) lines, (c) trend of the angular position of LB, and (d) very high angular position of the leading edge. In contrast to the previously applied power input measurements, the new optical evaluation criteria describe the phase transition in greater detailed. Instead of Ph = 1.26, a less conservative value of Ph = 0.91 is now suggested for the phase transfer, which implies a broader operating window for shake flask cultivations with higher viscosities.

Power Input Measurements in Stirred Bioreactors at Laboratory Scale.

The power input in stirred bioreactors is an important scaling-up parameter and can be measured through the torque that acts on the impeller shaft during rotation. However, the experimental determination of the power input in small-scale vessels is still challenging due to relatively high friction losses inside typically used bushings, bearings and/or shaft seals and the accuracy of commercially available torque meters. Thus, only limited data for small-scale bioreactors, in particular single-use systems, is available in the literature, making comparisons among different single-use systems and their conventional counterparts difficult.This manuscript provides a protocol on how to measure power inputs in benchtop scale bioreactors over a wide range of turbulence conditions, which can be described by the dimensionless Reynolds number (Re). The aforementioned friction losses are effectively reduced by the use of an air bearing. The procedure on how to set up, conduct and evaluate a torque-based power input measurement, with special focus on cell culture typical agitation conditions with low to moderate turbulence (100 < Re < 2·104), is described in detail. The power input of several multi-use and single-use bioreactors is provided by the dimensionless power number (also called Newton number, P0), which is determined to be in the range of P0 ≈ 0.3 and P0 ≈ 4.5 for the maximum Reynolds numbers in the different bioreactors.

Power Input Measurements in Stirred Bioreactors at Laboratory Scale

The power input in stirred bioreactors is an important scaling-up parameter and can be measured through the torque that acts on the impeller shaft during rotation. However, the experimental determination of the power input in small-scale vessels is still challenging due to relatively high friction losses inside typically used bushings, bearings and/or shaft seals and the accuracy of commercially available torque meters. Thus, only limited data for small-scale bioreactors, in particular single-use systems, is available in the literature, making comparisons among different single-use systems and their conventional counterparts difficult. This manuscript provides a protocol on how to measure power inputs in benchtop scale bioreactors over a wide range of turbulence conditions, which can be described by the dimensionless Reynolds number (Re). The aforementioned friction losses are effectively reduced by the use of an air bearing. The procedure on how to set up, conduct and evaluate a torque-based power input measurement, with special focus on cell culture typical agitation conditions with low to moderate turbulence (100 < Re < 2·104), is described in detail. The power input of several multi-use and single-use bioreactors is provided by the dimensionless power number (also called Newton number, P0), which is determined to be in the range of P0 ≈ 0.3 and P0 ≈ 4.5 for the maximum Reynolds numbers in the different bioreactors.

Investigation of poly(\u03b3-glutamic acid) production via online determination of viscosity and oxygen transfer rate in shake flasks

BackgroundPoly(γ-glutamic acid) (γ-PGA) is a biopolymer with many useful properties making it applicable for instance in food and skin care industries, in wastewater treatment, in biodegradable plastics or in the pharmaceutical industry. γ-PGA is usually produced microbially by different Bacillus spp. The produced γ-PGA increases the viscosity of the fermentation broth. In case of shake flask fermentations, this results in an increase of the volumetric power input. The power input in shake flasks can be determined by measuring the torque of an orbitally rotating lab shaker. The online measurement of the volumetric power input enables to continuously monitor the formation or degradation of viscous products like γ-PGA. Combined with the online measurement of the oxygen transfer rate (OTR), the respiration activity of the organisms can be observed at the same time.ResultsTwo different Bacillus licheniformis strains and three medium compositions were investigated using online volumetric power input and OTR measurements as well as thorough offline analysis. The online volumetric power input measurement clearly depicted changes in γ-PGA formation due to different medium compositions as well as differences in the production behavior of the two investigated strains. A higher citric acid concentration and the addition of trace elements to the standard medium showed a positive influence on γ-PGA production. The online power input signal was used to derive an online viscosity signal which was validated with offline determined viscosity values. The online measurement of the OTR proved to be a valuable tool to follow the respiration activity of the cultivated strains and to determine its reproducibility under different cultivation conditions.ConclusionsThe combination of the volumetric power input and the OTR allows for an easy and reliable investigation of new strains, cultivation conditions and medium compositions for their potential in γ-PGA production. The power input signal and the derived online viscosity directly reflect changes in γ-PGA molecular weight and concentration, respectively, due to different cultivation conditions or production strains.

Air and oil dispersions in a four-phase fermentation model, studied under varying physicochemical conditions and retrofitted constant gassed power input

In this study, experimental power input curves were obtained in a four-phase system. Sauter mean diameter of air and oil dispersions obtained in a four-phase Trichoderma harzianum fermentation model (aqueous salt solution, castor oil, air and T. harzianum mycelia) are presented. Experiments allowed to analyze the effect of varying amounts of surfactant (mixture of proteins coming from the biomass and bovine serum albumin) and solid concentration (mycelial biomass) on gassed power input, mean drop and bubble size distributions. Experimental power input measurements showed that the different mixtures of biomass and protein, keeping constant the agitation rate, affected the gassed power consumption by approximately ±10%. By keeping the gassed power input fixed during the dispersion experiments, it was possible to rule out the effects of the power consumption variation and to discern and analyze the impact of the amount of protein and biomass on the dispersion of air bubbles and oil drops. The protein, due to its surface-active properties, caused a considerable decrease in the Sauter mean diameter of air bubbles compared to the system without protein, regardless of the concentration. Protein did not have an effect on oil drops, which maintained a constant Sauter diameter through the studied concentration range (0–1.36g/L). It was shown that, for comparable biomass concentrations, the gassed power input is the parameter determining the Sauter diameter of air bubbles as well as for the oil drops. It was found that, even by keeping the power input constant, the addition of biomass to the mixtures has additional interactions with the dispersions, decreasing the Sauter mean diameter of bubbles and increasing the value in oil drops.

Development of a method for reliable power input measurements in conventional and single-use stirred bioreactors at laboratory scale.

Power input is an important engineering and scale‐up/down criterion in stirred bioreactors. However, reliably measuring power input in laboratory‐scale systems is still challenging. Even though torque measurements have proven to be suitable in pilot scale systems, sensor accuracy, resolution, and errors from relatively high levels of friction inside bearings can become limiting factors at smaller scales. An experimental setup for power input measurements was developed in this study by focusing on stainless steel and single‐use bioreactors in the single‐digit volume range. The friction losses inside the air bearings were effectively reduced to less than 0.5% of the measurement range of the torque meter. A comparison of dimensionless power numbers determined for a reference Rushton turbine stirrer (N P = 4.17 ± 0.14 for fully turbulent conditions) revealed good agreement with literature data. Hence, the power numbers of several reusable and single‐use bioreactors could be determined over a wide range of Reynolds numbers between 100 and >104. Power numbers of between 0.3 and 4.5 (for Re = 104) were determined for the different systems. The rigid plastic vessels showed similar power characteristics to their reusable counterparts. Thus, it was demonstrated that the torque‐based technique can be used to reliably measure power input in stirred reusable and single‐use bioreactors at the laboratory scale.

Effective shear rates in shake flasks

In bioprocess development and scale-up and scale-down consistent fermentation conditions in shake flasks and stirred tank reactors are crucial. Fermentation broths at elevated viscosities generally show a non-Newtonian flow behavior. The effective shear rate is known to influence apparent viscosity, and, as a consequence, mixing as well as mass and heat transfer. Unknown effective shear rates pose the risk of screening and producing under unfavorable conditions. The present study is the first to systematically investigate the effective shear rate in shake flasks. Based on Buckingham׳s π-theorem a shear rate correlation for 50mL to 1000mL shake flasks as a function of viscosity and volumetric power input is developed. Viscosity and power input measurements for a wide range of pseudo-plastic flow behaviors and a broad spectrum of commonly applied operating conditions were applied. Effective shear rates in shake flasks cover a range from 20s−1 to 2000s−1. To demonstrate the value of the obtained shear rate correlation, effective shear rates over time were calculated for three different exemplary fermentation systems in shake flasks generating elevated viscosities. With the aid of this new source of information the specific courses of the individual fermentations could now be interpreted. Depending on the broth׳s flow behavior, the effective shear rate in shake flasks is at least 1.55 times higher than that in stirred tank reactors operated at the same volumetric power input, leading to a potentially 50% lower apparent viscosity in shake flasks. The obtained shear rate correlation is a valuable tool to explain existing deviations in screening and production results, ultimately assisting bioprocesses development by means of consistent scale-up or scale-down procedures.

Using transient and steady-state SEA to assess potential errors in the measurement of structure-borne sound power input from machinery on coupled reception plates

Isolated reception plates provide an engineering approach to quantify the structure-borne sound power input from machinery through the measurement of the spatial-average velocity level and structural reverberation times. For applications in building acoustics there are practical and economic reasons to consider using coupled reception plates formed by solid heavyweight walls or floors that are structurally coupled to other building elements. This paper uses transient and steady-state statistical energy analysis to investigate how the errors depend upon the building structure to which the coupled reception plate is connected. It is shown that the problem is twofold. Firstly, in the low- and mid-frequency ranges, the steady-state velocity level on the coupled reception plate is increased by energy returning from other coupled plates. Secondly, the structural decays on the coupled reception plate have significant curvature due to returning energy; hence short evaluation ranges are needed to minimise the error when determining the total loss factor. This leads to a problematic situation where the coupled reception plate appears to give the correct answer due to the error in the energy cancelling out the error in the total loss factor. The latter error can be minimised using short evaluation ranges for the structural reverberation time.

Performance evaluation of a variable speed DC compressor

Direct current compressors are strong candidates to be employed in energy-efficient refrigeration systems, especially for renewable energy powered units, as these compressors do not require additional components such as a power inverter that an alternative current compressor would require. This study represents experimental performance analysis of a direct current type refrigeration compressor implemented in a 79 L refrigerator. Energy usage reduction and operational improvement potential of the direct current compressor via variable speed operation were investigated. Experiments were carried out at variable speed operation and four different constant speed operation modes of the compressor. Temperature, pressure, and power input measurements were obtained every 30 s. The experimental data were analyzed in terms of energy and exergy efficiencies. The comparison showed that variable speed operation of the direct current compressor can be much more efficient than constant speed operation of the direct current compressors, especially at higher speeds.

Axial impeller selection for anchorage dependent animal cell culture in stirred bioreactors: Methodology based on the impeller comparison at just-suspended speed of rotation

Animal cells, which are nowadays essential for the industrial production of proteinic compounds, are commonly cultivated inside stirred tank bioreactors. In case of anchorage dependent cells, they are usually fixed on microcarriers. The choice of agitation conditions (impeller type, rotational speed…) in this type of process is not an easy task as it has to fulfil three potentially conflicting goals: (1) maintaining microcarriers in complete suspension, (2) homogenizing the culture medium, and (3) limiting mechanical constraints generated by the hydrodynamics on the cells. The aim of this study is to present an original methodology to select the most appropriate axial impeller for this specific application. Seven propellers are preselected on basis of their characteristics available in the literature. Instead of comparing impellers at a given rotational speed or a given power input, they are compared at their respective minimum impeller rotational speed that leads to a complete microcarrier suspension, i.e. at their respective just-suspended speed N js . They are then compared at higher rotational speeds N, expressed as multiples of N js . The impeller classification is based on the intensity of mechanical constraints they produced, evaluated from: (1) the macro-shear rate quantified by the spatial derivative of time average velocity fields measured by P.I.V., (2) the micro-shear rate characterized by the ratio between the microcarrier diameter to the average Kolmogorov scale computed from power input measurements, and (3) the impact of microcarrier collisions on cells described via the turbulent collision severity index also computed from power input measurements. Results show that the 125 mm diameter TTP impeller (Mixel) and the 150 mm diameter Elephant Ear impeller (Applikon) produce the smallest mechanical constraints at their just-suspended speed (50 and 20 rpm, respectively). Moreover, the mechanical constraints they produce increase more slowly with the N/ N js ratio than the mechanical constraints produced by other impellers. These propellers are thus even more advantageous if rotational speeds higher than the just-suspended speed have to be used.

Development and evaluation of forage yield measure sensors in a mowing-conditioning machine

The main aim of this research was to develop and evaluate sensor system to create forage yield maps on a three-point linkage type of rotary mower-conditioner. The method was based on the mowing machine conditioner's power requirement measured by a torque sensor or on material change in momentum measured by a curved impact plate. Laboratory measurements were taken to determine the dependence of conditioner power input and signals from the impact plate on material mass flow. A mixture of grass and alfalfa was used. There was a very good linear relationship between the conditioner's power, impact force from an impact plate, and material feed rate through the mower. The calculated coefficients of determination ( R 2) were about 0.95. It was possible to differentiate a material feed rate difference 0.5 kg s −1 using either method. The effects of material changes and mower parameters on the accuracy of feed rate measurement were then measured. It was observed that the results form torque sensor was influenced by crop variety, maturity and intensity of conditioning. The same influence was not observed for impact plate. A field of 0.54 ha was then harvested. A comparison of data from the torque sensor and impact plate with data from hand measurement were made by means of statistical and geostatistical analysis. Conditioner power input measurement and crop impact force were used to create grass yield maps.

Feed rate measurement technique and yield maps creating in fodder plant harvesting

The main aim of this article is to evaluate the possibility of forage yield maps creating based on mowing machine&amp;rsquo;s conditioner power input measurement. Strong spatial dependence was observed for conditioner power input data. For the data file from material feed rate measurement the medium spatial dependence was calculated. Relatively low value of variograms range is possible to explain by the type of chosen exponential model. Visual displaying of data distribution is done by the maps. These maps were plotted under kriging method. It is possible to observe distributions of higher and smaller values of conditioner power input and material feed rate measurement by this way. Plotted maps are shown in Figures. The correlation coefficients were calculated 0.419 for filtered data. It follows from this evaluation that conditioner power input measurement can be used for the determination of mowing machine material feed rate.

An analytical model for the prediction of power consumption for shear-thinning fluids with helical ribbon and helical screw ribbon impellers

An approximate analytical model has been developed to predict power consumption for the mixing of shear-thinning fluids with helical ribbon and helical screw ribbon impellers in the laminar flow regime. Extensive data on power input measurements embracing a wide range of flow behaviour index, with strong ( n < 0.4 ) and weak ( 0.4 < n < 1 ) shear-thinning fluid characteristics, available in the literature have been used to demonstrate the applicability of the present model for a wide range of helical ribbon mixer configurations. The model is able to explain the differences in the data reported in the existing literature and to successfully predict the complex dependence of power consumption on the fluid properties and the system geometry. Finally, the proposed correlation only requires a knowledge of the flow behaviour index of the fluid and of the geometrical parameters of the mixing systems (wall clearance, number of ribbons, pitch and width of the ribbons) and one characteristic parameter K p of the mixing system which can be obtained from a single measurement of power for Newtonian liquids in the laminar regime.

Modulated electromagnetic induction calorimetry of reactive metallic liquids

A method for the non-contact measurement of the specific heat capacity, the enthalpy of fusion and thermal transport properties of electromagnetically levitated liquid metallic alloys is described. The method is based on the separation of heating and positioning fields, modulation of the inductive heating power input and pyrometric temperature measurement making highly reactive or undercooled metallic liquids amenable to calorimetric investigation. A heat flow model based on coupled reservoirs is developed from which conditions for the accurate measurement of the specific heat capacity and of the thermal relaxation times are derived. Calibration procedures for the quantification of the modulated heating power input are described from which the specific heat capacity is obtained. Experimental results to demonstrate the principles of the method and some application results from the IML-2 and MSL-1 Spacelab missions are presented.

Quantification of the water boiling heat transfer in micro-structures by image analysis

The heat transfer performance of a micro-vaporizer has been measured by conventional methods (using temperatures, flow rates, effective power input). The study was carried out for laminar flow in channels (5 mm×3 cm×200 μm) micro-structured with square obstacles to increase the specific area. The results show that high heat transfer coefficients (1300– 2500 W m −2/ ∘C −1) can be reached in such a micro-structured channel. Image analysis was done to estimate the volume vapour fraction, which can be converted into the mass vapour fraction using a slip ratio and avoids the need for any temperature or electric power input measurements. The estimation of this slip ratio is discussed in this paper.

Utilization of specific power input measurements for optimization of culture conditions in shaking flasks

Shaking flasks are often used in early stages of bioprocess development, particularly in screening purposes. Their advantages include ease of handling and low cost. The direction of bioprocess development is strongly influenced by the performance of microorganisms at these early stages. Therefore shaking conditions must be monitored carefully for limitations, e.g. oxygen limitations, or ‘out of phase’ conditions. Product formation of the xanthan producing bacterium Xanthomonas campestris is severely impaired by ‘out of phase’ shaking conditions. This could be shown for different shaking diameters and filling volumes. The dimensionless phase number could successfully be applied to prevent unsuitable ‘out of phase’ conditions. Cultures of Pseudomonas putida CA3 grown at ‘in phase’ and ‘out of phase’ hydrodynamic states, but otherwise identical conditions, also shows a lower optical density for ‘out of phase’ conditions. With help of power consumption measurements these unsuitable shaking conditions can be detected and avoided.

Measurement and Simulation of Fluid Flow in Agitated Solid/Liquid Suspensions

Numerical and experimental investigations were carried out to improve the knowledge of the flow field in solid/liquid suspensions in agitated vessels and to examine the ability of the commercial CFD, code CFX 4.2, for this application. The numerical results were compared with our own experimental results of time resolved Laser-Doppler-Velocimeter (LDV) and power input measurements with particle concentrations of up to 15 percent of the volume. To perform LDV measurements within the solid/liquid flow the refractive index matching method was used. Results of the CFD simulation show the necessity to use high grid resolution, the k-ϵ turbulence model and an advanced discretization scheme to achieve a grid-independent solution. Simplifications of the grid geometry were shown to be an acceptable way to minimize the time required for calculation. The comparison of experimental and numerical results shows good agreement for velocities and power input in the single- and in all two-phase flow cases. Good agreement with regard to the kinetic energy k is also apparent, except in the region near the stirrer blades, where local maxima are underestimated by the simulation.

Intraspecific scaling of flight power in the bat Glossophaga soricina (Phyllostomidae).

Aerodynamic theory predicts that power output during flight should vary with body mass by an exponent of 1.56 when wing morphology remains constant (within an individual), and by an exponent of 1.19 when wing morphology changes with body mass (within a species or between species). I tested these predictions by estimating the power input during horizontal flight in three pregnant and two subadult Glossophaga soricina using a multivariate regression model. This analysis yielded power input during resting and flight as well as the energetic equivalent of change in body mass. A comparison of the estimated flight power for pregnant G. soricina, with published data on flight power of nonpregnant adults, revealed that energy turnover in flight is highest for pregnant G. soricina. Flight power of a 13-g pregnant G. soricina was even higher than that of a 16-g non-pregnant Glossophaga longirostris. A least-squares regression analysis yielded the following equations for the intraspecific scaling of flight power with body mass: power input during horizontal flight (Pf) = 24099 body mass (bm; kg)2.15 (r2 = 0.97) for the intra-individual allometry (pregnancy) and Pf = 113 bm(kg)0.95 (r2 = 0.99) for the inter-individual allometry (ontogeny). Both mass exponents are not significantly different from the predicted values for the scaling relationship of flight power within an individual (1.56) and within a species (1.19). This is the first measurement of power input during flight for subadult and pregnant bats.

A new pneumatic bearing dynamometer for power input measurement in stirred tanks

A turntable dynamometer has been constructed for the accurate measurement of power input and mixing applications in bench stirred tank reactors. The main feature of this device is a pneumatic bearing with complementary conical parts. The conical pneumatic bearing permitted to apply eccentric loads without affecting its stability. The static friction torque in the pneumatic bearing was very small, 4 x Nm, and can be neglected in the experimental ranges of measured torques, i.e. from 5 x to 2.21 Nm. In accordance with the instrumentation used, the deviations obtained with the apparatus are less than 10% at low torque readings. At moderate torques, deviations lower than 1 % are routinely obtained. Several power input measurements show that the obtained data scatter is lower than 2.5 % . The power input response in the turbulent regime is in agreement with dimensional analysis: the power input depends on the cube of the impeller speed. In addition, data obtained with a turbine impeller under ungassed conditions agree with the predictions of a published correlation, which takes into account several geometrical parameters.