Fully digital transmitters (DTXs) have the potential of replacing analog-intensive transmitter (TX) line-ups in future massive multiple-input and multiple-output (mMIMO) systems since they hold the ...promise of higher system integration level and energy efficiency. DTX operation so far has been limited to low RF output powers. This article introduces a concept that enables high-power DTX operation. A DTX demonstrator targeting both high output power and high efficiency is realized as a proof of concept. It is based on a custom <inline-formula> <tex-math notation="LaTeX">{V_{T}} </tex-math></inline-formula>-shifted laterally-diffused MOS (LDMOS) technology, which is utilized to implement a segmented high-power output stage operated in class-BE. A low-voltage high-speed 40-nm CMOS controller drives the individual output stage segments at gigahertz rates. Measurements show the promising results for the proposed high-power DTX concept and provide valuable lessons for future DTX implementations.
The objective of this study is to address the problem that the traditional quality control method of fresh Portland cement concrete cannot allow the workability to be evaluated during the mixing ...process. Based on the rheological theory and observed linear relationship between the shear force and flow deformation of concrete mixtures, a mathematical model was established to characterize the workability of concrete using the stirring power of concrete mixers. In this study, a laboratory-scale two-shaft mixer with a rotation speed control system and a power monitoring system was designed and tested. A LabVIEW program was also developed to process and analyze changes of the stirring power data. Laboratory test results show that the optimal workability of fresh concrete with very different mix designs is usually obtained when the second wave trough of stirring power appears. The test results are also compared to the conventional slump test, which indicate the proposed approach and developed system can be used to evaluate the workability of fresh concrete during mixing and identify the optimal mixing time length.
Portland cement concrete; Fresh concrete; Mixing; Workability uniformity; Mixing power.
•The mixing power requirement of an agitated drum dryer was determined using hulled millet on various moisture content.•A DEM model was developed and validated using laboratory measurements.•A ...friction-cohesion contact model was applied to simulate the moisutre content.•The rolling and twisting resistance coefficients were used as a function of rotational speed and drum loading factor.
In the agricultural, food, chemical and pharmaceutical industries, mixing operations of granular materials frequently occur during which fractions are homogenized or the blockage of particles is prevented. In order to select the appropriate agitator motors, it is necessary to know the rotational speed of the mixer and the power requirements of the drive motor, which remains a major challenge for design engineers to this day.
The main aim of this research was to create a discrete element simulation model (DEM) suitable for determining the mixing power requirements of an agitated drum dryer pilot plant, which can be applied to the modelling of mixing granular materials of various moisture content. In order to validate the results of the model, measurements were conducted by mixing hulled millet in the drum dryer. The parameter sensitivity tests conducted in the DEM environment showed that of the micromechanical parameters applied in the model, it was the Young modulus, and the rolling and twisting resistance coefficients of the contacts which needed to be adjusted as a function of the rotational speed in order for the simulated power requirements to approximate the values measured.
In the laboratory tests conducted on the agitated drum dryer, the mixing power requirement of hulled millet of various moisture contents (9.6–29.5%) was determined at different drum loading factors (10–25%) mixed at various rotational speeds (0.32–1.58 s−1). Test results suggested that a DEM simulation environment could be created to approximate measurement results with acceptable accuracy. Furthermore, the mixing power requirement was highly affected by the moisture content of the material and the rotational speed of the mixing unit, while the mixing torque requirement decreased by increasing the latter. The validated DEM model is suitable for simulations of mixing hulled millet in an agitated drum dryer in terms of both quality and quantity.
The enhanced specific strength of SiC Particulate Metal Matrix Composites (PMMC) has been the major contributing factor which helps to find applications in the aerospace and automotive industries. ...Uniform distribution of the particulates in PMMC controls the attainment of better mechanical properties. The most accepted method for producing such a composite is stir casting in which the homogeneity of particulate reinforcement is a significant challenge. This research work proposes a new method for mixing the particulate reinforcement with the liquid and semi-solid aluminium matrix to ensure a uniform mix of the particulates using a gyro shaker. Gyro shaker is a dual rotation mixer commonly used for mixing high viscous fluids. It rotates about two mutually perpendicular axes which help in thoroughly mixing of the ingredients. Developed Computational Fluid Dynamics (CFD) simulation model of the mixing device in finding the mixing performance while mixing SiC particulates with glycerol. The results of the simulation were also validated by experimentation. Analogue fluid simulation of gyro casting was carried out using water and glycerol/water mixture which are having a closer value of viscosity as that of liquid aluminium and semi-solid aluminium. The mixing time obtained in the water system at gyration speeds of 29.63 rpm, 58.18 rpm, 72.73 rpm and 87.27 rpm was 61.84 sec, 43.44 sec, 26.85 sec and 27.24 sec respectively. The mixing time obtained in glycerol/water system at gyration speeds of 58.18 rpm, 87.27 rpm, 116.36 rpm and 145.45 rpm was 26.34 sec, 15.97 sec, 9.8 sec and 6.26 sec respectively. The distribution of the SiC particulates obtained from simulation was compared with stir casting simulations. The homogeneous distribution of particulates was observed in the gyro casting simulation.
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•Two stage hydrolysis of lignocellulose at high solids content was proposed.•Two stage hydrolysis is applicable for large scale pretreatment reactors.•60% of mixing power was saved in ...the two stage hydrolysis method.
A two stage hydrolysis of corn stover was designed to solve the difficulties between sufficient mixing at high solids content and high power input encountered in large scale bioreactors. The process starts with the quick liquefaction to convert solid cellulose to liquid slurry with strong mixing in small reactors, then followed the comprehensive hydrolysis to complete saccharification into fermentable sugars in large reactors without agitation apparatus. 60% of the mixing energy consumption was saved by removing the mixing apparatus in large scale vessels. Scale-up ratio was small for the first step hydrolysis reactors because of the reduced reactor volume. For large saccharification reactors in the second step, the scale-up was easy because of no mixing mechanism was involved. This two stage hydrolysis is applicable for either simple hydrolysis or combined fermentation processes. The method provided a practical process option for industrial scale biorefinery processing of lignocellulose biomass.
Depending on design capacity, agitators consume about 5 to 20% of the total energy consumption of a wastewater treatment plant. Based on inhabitant-specific energy consumption (kWh PE
a
; PE
is ...population equivalent, assuming 120 g chemical oxygen demand per PE per day), power density (W m
) and volume-specific energy consumption (Wh m
d
) as evaluation indicators, this paper provides a sound contribution to understanding energy consumption and energy optimization potentials of agitators. Basically, there are two ways to optimize agitator operation: the reduction of the power density and the reduction of the daily operating time. Energy saving options range from continuous mixing with low power densities of 1 W m
to mixing by means of short, intense energy pulses (impulse aeration, impulse stirring). However, the following correlation applies: the shorter the duration of energy input, the higher the power density on the respective volume-specific energy consumption isoline. Under favourable conditions with respect to tank volume, tank geometry, aeration and agitator position, mixing energy can be reduced to 24 Wh m
d
and below. Additionally, it could be verified that power density of agitators stands in inverse relation to tank volume.
•A calibration method set for industrial measurements of concrete water content was proposed.•A criterion for identifying the stabilisation of mixer power consumption was suggested.•Correlation ...between mixing power and concrete water content was validated in an industrial environment.•Viscosity agent in SCC increases mixing time and energy consumption.
In ready-mixed concrete plants, the water content of self-compacting concrete (SCC) is generally controlled during the mixing process based on the stabilisation of mixer power consumption. This measurement system is however rarely calibrated, even though its signal is sensitive to the wear of mixers and the temperature of engines.
The aim of this paper is to propose a calibration of mixing power as a measurement of the concrete water content that enables improving water control accuracy. A new approach based on the mixing power evolution is devised for a better determination of the signal stabilisation. The stabilisation time is then defined and considered as the necessary mixing time of each concrete batch. Experimental results obtained from 40 batches of different SCC compositions produced in a full-scale concrete plant have shown that, with the developed calibration method, the stabilisation of power consumption can be considered as a reliable indication of water content with a precision of ±3.8l/m3. It is also observed that the water-to-powder ratio (W/P) and the use of viscosity agent have significant effects on the power consumption evolution during mixing.
Usually, mixing is carried out in a vessel with four baffles and a single impeller. In some applications, however, the use of a baffled vessel is not recommended. One of the stirring methods used ...instead is unsteady agitation with forward‐reverse rotating impellers. The aim of this work was to characterize the agitation characteristics in a baffled and an unbaffled vessel with a turbine impeller. Mixing time and mixing power were evaluated in relation to the presence of baffles and the frequency of forward‐reverse rotation. It was found that the frequency of oscillation does not affect either the mixing time and mixing power values or the drag and added mass coefficients. Power requirements and mixing time were higher compared to the steady mixing conditions in a baffled vessel. The results showed that it is not recommended to use baffles because they have no influence on unsteady mixing.
The mixing process is usually carried out in a baffled vessel. In some applications, however, unbaffled vessels are preferred. The agitation characteristics in a baffled and an unbaffled vessel stirred by a turbine impeller with forward‐reverse revolution were studied. Mixing time and mixing power were evaluated in relation to the presence of baffles and the frequency of forward‐reverse rotation.
In this work, we focus on the most crucial units in a chemical technology, the chemical reactors. Using a commercially available CFD software package, COMSOL Multiphysics, 3D mathematical models of a ...batch reactor with different impeller geometries have been investigated. The reasonable agreement between the experimental and simulation results indicates the validity of the developed CFD model. The effect of the impeller design, e. g. number of blades on the mixing efficiency is evaluated based on the simulation studies. The proposed measure to determine the energy efficiency of mixing (i. e. mixing index) is based on the calculated velocity field and energy usage. The information about the homogeneity of the mixed phase in the system can be extracted from the developed velocity field. Hence, we proposed histograms of velocity fluctuations on a logarithmic scale as an efficient tool to measure the achieved homogeneity of the phase in case of different impellers and rotational speeds.
Mixing performance of two continuous flow millilitre‐scale reactors (volumes 9.5 mL and 2.5 mL) equipped with rotor‐stator mixers was studied. Cumulative residence time distributions (RTD) were ...determined experimentally using a step response method. Distributions were measured for both reactors by varying impeller speed and feed flow rate. The mixing effect was determined by measured RTDs. Computational fluid dynamics (CFD) were used to verify that the residence time distribution in the measurement outlet agreed with the outlet flow. The mixing power of both reactors was determined using a calorimetric method. The reactor inlet flow rate was found to affect mixing performance at 1–13 s residence times but the effect of impeller speed could not be noted. Both milliscale reactors are close to an ideal continuous stirred‐tank reactor (CSTR) at the studied impeller speed and flow rate ranges. The specific interfacial area was found to depend on the reactor inlet flow rate at constant impeller speed for the case of copper solvent extraction.
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