Number Of Rotor Revolutions Research Articles

Blade-Resolved CFD Simulations of a Periodic Array of NREL 5 MW Rotors with and without Towers

A fully resolved (FR) NREL 5 MW turbine model is employed in two unsteady Reynolds-averaged Navier–Stokes (URANS) simulations (one with and one without the turbine tower) of a periodic atmospheric boundary layer (ABL) to study the performance of an infinitely large wind farm. The results show that the power reduction due to the tower drag is about 5% under the assumption that the driving force of the ABL is unchanged. Two additional simulations using an actuator disc (AD) model are also conducted. The AD and FR results show nearly identical tower-induced reductions of the wind speed above the wind farm, supporting the argument that the AD model is sufficient to predict the wind farm blockage effect. We also investigate the feasibility of performing delayed-detached-eddy simulations (DDES) using the same FR turbine model and periodic domain setup. The results show complex turbulent flow characteristics within the farm, such as the interaction of large-scale hairpin-like vortices with smaller-scale blade-tip vortices. The computational cost of the DDES required for a given number of rotor revolutions is found to be similar to the corresponding URANS simulation, but the sampling period required to obtain meaningful time-averaged results seems much longer due to the existence of long-timescale fluctuations.

Chemometric analysis of alternations in coal ash quality induced by application of different mechano-chemical processing parameters

The coal fly ash mechano-chemical activation conducted via high energy ultra-centrifugal mill was optimized using mathematical and statistical tools. The aim of the investigation was to accent the merits of alternations in ash processing schemes with a referral regarding the enhancement of the ash reactivity that will lead to its higher volume utilization as a cement replacement in concrete design. The impact of the processing parameters sets (number of rotor revolutions, current intensity, activation period, circumferential rotor speed, mill capacity) on the on the product?s quality factors (grain size distribution, average grain size, micronization level, agglomeration tendency, specific surface area) was assessed via Response surface method, Standard score analysis and Principal component analysis in order to obtain the most favorable output. Developed models were able to meticulously predict quality parameters in an extensive range of processing parameters. The calculated r2 values were in the range of 0.846-0.999. The optimal ash sample, that reached the Standard Score as high as 0.93, was produced using a set of processing parameters appropriate to experimental sequence with applied 120 ?m sieve mesh. The microstructural characteristics were assessed using image-processing values and histogram plots of the activated fly ash SEM images.

Experimental investigation and performance modeling of centimeter-scale micro-wind turbine energy harvesters

Centimeter-scale micro wind turbines have been proposed to power small devices. Design models and operating conditions for large scale wind turbines do not directly apply towards these small harvesters. We perform an experimental investigation of a swirl-type micro-wind turbine. We measure the useful power extracted from this turbine in an open circuit suction type wind tunnel facility. The optimal resistive loads for different flow speeds are determined. A model for the friction, torque drive and generated power is derived and validated. The effect of varying the direction of incident flow on the turbine performance is also determined. The results show an optimal combination between the rotor diameter and the number of rotor revolutions. The power density and efficiency of this turbine were found to be larger than previously tested turbines that have slightly larger diameters. This is true over a broad range of free stream speeds. Finally, because of its shape, the swirl configuration is effective in harvesting power for yaw angles of ±30°.

Effects of mechanical activation on the parameters of talc quality for ceramics production – Chemometric approach

Talc is broadly used in the ceramic materials industry, either as a basic raw material, or as filler, due to its chemical inertia, fragmentation proneness, thermal stability, and refractoriness. The mechanical activation is frequently employed in the direct enhancement of talc properties, and thereby in the design of talc based composites with advanced performances. The differences in the set of the process parameters measured before and after talc activation via ultra-centrifugal mill Retsch ZM-1, and their influence on the grain-size distribution related characteristics have been investigated. The mechanical treatments are energetically unsustainable procedures, therefore the talc activation was optimized on basis of assessment of the process variables (number of rotor revolutions, current intensity, activation period, circumferential rotor speed and mill capacity) effect on the final quality of product parameters (mesh sizes, cumulative oversizes, average grain size, level of micronization kinetics, mesh size appropriate to 95% micronized product cumulative undersize and specific surface area). The activated product parameters in all experimental sequences were obtained by the analytical procedure based on Rosin-Rammler-Sperling equation. Response surface method, standard score analysis and principal component analysis were used as a means of the optimization. Developed models showed r2 values in the range of 0.714–0.908 and they were able to accurately predict quality parameters in a wide range of process parameters. Standard score analysis highlighted that the optimal sample was obtained using sieve mesh of 120 μm set of processing parameters (SS = 1.0). Multiple comparison tests revealed that the optimal variation in the processing parameters could reduce the negative effect of talc samples inherent properties on the final score and improve the activation procedure energetic and economic sustainability.

COMPARATIVE ANALYSIS OF PROCESS PARAMETERS OF TALC MECHANICAL ACTIVATION IN CENTRIFUGAL AND ATTRITION MILL

The efficiency of talc mechanical activation by means of two different mechano-activators - centrifugal and attrition mill is investigated in this study and the comparative analysis of the characteristics of obtained talc powders is presented. A new approach for obtaining high-grade talc concentrate with low Fe2O3 content is achieved through effect of mechanical activation of talc accompanied by hydrometallurgical process. The applied mechanical activation process conditions of ultra-centrifugal mill were defined by number of rotor revolutions, sieve mesh size, and current intensity. These operating parameters of the ultra-centrifugal mill were variable. Ultra fine grinding of talc in attrition mill (attritor) was carried out in various time intervals - from 5 to 15 min. The following technological parameters of the mechanical activation were monitored: time of mechanical activation, circumferential rotor speed, capacity of ultra-centrifugal mill, and specific energy consumption. The investigation was based on a kinetic model. The structure and behavior of activated samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, and differential thermal analysis (DTA).

Comparative kinetic study of mechanical activation process of mica and talc for industrial application

Mica and talc have wide areas of application as a raw material in a number of industrial branches. Mechanically activated mica has specific applications such as: capacitors, insulators, and pearlescent pigments. Talc is widely used as either a basic raw material or as filler. This paper presents a comparative analysis of mechanically activated samples of mica and talc in ultra-centrifugal mechano-activator “Retsch ZM-1”. The following mechano-activator parameters were variable: number of rotor revolutions (rpm); sieve mesh size (μm); current intensity (A). In addition, the following parameters were monitored: duration of mechanical activation, t (min); circumferential rotor speed, v (m/s); capacity of mechano-activator, Q (kg/h); and specific energy consumption, We (kWh/t). It was observed that effect of mechanical activation of mica and talc increased with an increase of the load and rotor revolution of ultra-centrifugal mechano-activator. Both mica and talc were successfully treated by mechanical activation procedure. In the processing of mica, mechanical activation is suggested to be applied as a post-treatment, and in the talc processing as a pre-treatment, as the high quality talc is obtained by means of hydrometallurgical concentration method.

Artificial immunity-based induction motor bearing fault diagnosis

In this study, the artificial immunity of the negative selection algorithm is used for bearing fault detection. It is implemented in MATLAB-based graphical user interface software. The developed software uses amplitudes of the vibration signal in the time and frequency domains. Outer, inner, and ball defects in the bearings of the induction motor are detected by anomaly monitoring. The time instants of the fault occurrence and fault level are determined according to the number of activated detectors. Anomaly detection in the frequency domain is implemented by monitoring the fault indicator bearing frequencies and harmonics, calculated using the bearing dimensions and number of rotor revolutions. Due to the constant fault location and closeness to the accelerometer, the outer race fault in the bearing is the easiest fault type to determine. However, the most difficult fault type to detect is the ball defect. By verification of the detection results, the motor load has very little effect on the fault.

Effect of Operating Parameters on the Mechanical Activation Process of Mica Powder

Mechanical activation of mica is a great technological and technical problem because of their specific crystallochemical structure. This is dependent upon the type of equipment used and the type of disintegration process. The paper presents the investigations of kinetics of operational parameters, effect on properties and structure of powder mica, etc. The mica sample was subjected to mechanical activation in ultra-centrifugal mechanoactivator with a peripheral comminution path. During the investigation, some operating parameters, viz. number of rotor revolutions (rpm), sieve mesh size (µm) and current intensity (A), and some technological parameters, viz. time of mechanical activation, t (min), circumferential rotor speed, v (m.s−1), capacity of ultra-centrifugal mechanoactivator, Q (kg.h−1) and specific energy consumption, W e (kWh.t−1) were monitored. Analyzing the results it can be concluded that the rate of mechanical activation of mica was increased with the increasing load and rotor revolution of ultra-centrifugal mechanoactivator with peripheral comminution path. Under these conditions, the powder mica was transformed into amorphous state. It was confirmed by X-ray and thermal analyses.