Papers by Keyword: Diffuser

Abstract: Wind energy is the quickest growing sustainable energy resource in present energy crisis scenario. It has been considered as one of the most viable sources of environmental friendly energy. Starting investment cost of the wind turbine plant is exorbitant. Moreover, production cost of the wind turbine blade is about 20% of the wind turbine plant cost. It is fundamental to decrease the life-cycle cost of wind turbine plant by efficient utilization available wind speed. Optimized diffuser (Convergent divergent type and Convergent type) has been developed with highest possible pressure difference between inlet and exit of shroud, Area Ratio of inlet to exit section, wall length, incident angle and various flow qualities to enhance the available wind velocity considerably. The suitable tiny riblets on external layer of turbine blade have been introduced to lessen the skin friction drag force. Moreover, dual rotor blade with various rotor sizes for primary and secondary rotor, direction of rotor rotation, separation distance between them has been studied to augment wind turbine power generation and improvement in cut-in-speed. Moreover, comparative study will be conducted with standard (bare) wind turbine. Based on the above features, available wind speed increased significantly. In addition, various experiments and CFD analysis work still to be done to assess Diffuser based Wind Turbine model which is much closer to realistic product with available interaction. Due to the above additional features of the turbine system, the utilization of wind speed gets augmented with greater power production.

Abstract: The extraction of sugar is one of the first and main stages of sugarcane processing, and obtaining high sucrose extraction efficiencies is essential for the productivity of ethanol and sugar industries. In recent years, the number of diffusers for sucrose extraction has been increasing significantly in Brazil due to several reasons, the main ones being their higher efficiency, lower energy costs and lower maintenance and capital costs. Different factors may influence the sucrose extraction efficiency in industrial diffusers, such as operating conditions that are different from nominal equipment design conditions. Thus, the objective of this work is the modelling of a sucrose extraction process, in a multi-stage sugarcane industrial diffuser. The extraction process was first transformed into a mathematical model using phenomenological equations for the mass and momentum balance considering a lumped parameter model approach. The formulated equations were then modelled in LabVIEW and the model was tested through the analysis of the influence of the input variables in the diffuser’s extraction efficiency. Five scenarios were considered and different imbibition liquid input positions and mass flow rates, as well as different percolation liquid recirculation rates were evaluated. The results show that: (1) the insertion of imbibition liquid in more than one stage decreases the percolation velocities in most of the stages, increasing the concentration of sugar in the megasse but also increasing the concentration of sugar in the final juice; (2) higher imbibition flow rates increases the percolation velocity and, therefore, decrease sucrose concentration in the megasse. However, it dilutes the extracted juice; (3) higher recirculation rates to the same stages increase the percolation velocity and benefit sucrose extraction efficiency, decreasing the sugar concentration in the megasse and increasing the sugar concentration in the juice. Yet, a limit for the increase in recirculation must be respected in order to prevent flooding. All the obtained results were consistent and showed that the model is able to project the operation of a diffuser. In a next stage, a multi-objective optimization will be performed in order to optimize operational conditions of the equipment.

Abstract: The diffuser in wind tunnel plays a vital role to improve flow field quality. Many flow adjusting devices in diffuser were studied by lots of researchers in the world to inhibit flow separation. However, most of them were applied on closed-circuit wind tunnel with high speed. It is necessary to design appropriate flow adjusting device for diffuser in open-circuit wind tunnel with low speed which was increasingly used in aerodynamic experiment. The structure of a new open-circuit wind tunnel with low speed was firstly introduced in this paper. The flow adjusting device was designed, which was composed of three parts, namely contracting cone, air guide plate and screen. On the basis of analysis model for diffuser, the influences of contracting cone, air guide plate and screen on flow field quality were respectively given by CFX simulation that was using multiple reference frames and RNG k-ε turbulence model. Case study showed that the role of single part was limited, combined effect of three parts in flow adjusting device could greatly improve quality of flow field in diffuser. The study results mentioned above are useful for designing flow adjusting device in diffuser of practical open-circuit wind tunnel with low speed.

Abstract: Optical film is an important component for LCDs, cell phones and other mobile devices. It is crucial to ensure an optical films is defect-free. However, derive from the inherent translucent characteristic, many images of defects of optical films are low contrast. Low-contrast defects are notorious for their difficult to be detected. As some low-contrast defects are barely visible to human being without special training, it is indeed a challenging task to capture low-contrast defect images. To overcome the difficulty, we thoroughly investigated various of imaging and lighting technologies. After images have been captured successfully, we devided the captured defects, based on their sizes, into two categories, i.e. macro defects and micro defects. To detect both large and small defects, we set up a macro inspection system and a micro inspection system, respectively. In the study, we provide an easy to understand approach to reveal low-contrast defects. The experimental results showed that the proposed inspection system and method is capable of detecting low-contrast defects such as uneven coatings, streaks, white spots and foreign particles.

Abstract: It is vital to reduce lift generated by a racing car while traveling with high speed for the sake of overall performance and stability. Simplified formula student racing car models with seven diffuser angles and without diffuser were simulated based on CFD technology. Aerodynamic forces and corresponding coefficients were achieved for all eight models. The calculated results show that the lift generated by the car in the high speed can be reduced by a diffuser effectively. The aerodynamic characteristics of a racing car will be greatly improved by adding a rational designed diffuser, which may cut down lift dramatically with only little drag produced. This paper provides theoretically support for improving racing car aerodynamic characteristics.

Abstract: CFD simulation of a tidal current turbine shroud was performed using Ansys FLUENT commercial code and comparison was made with experimental data. The simulation result obtained was in good agreement with the experimental data. The coefficient of velocity, C_v was in the range of approximately 1.2 to 1.4 for both simulation and experiment. The present study gave useful information on the viability of CFD simulation for the initial evaluation of shroud design performance.

Abstract: This article presents the analysis of the flow pattern in the vanes diffuser with discontinuous crossover channels. We observe design features of the crossover channels and their influence on the flow pattern

Abstract: In this paper, diffuser with taper microstructure has been put forward, and the transmission of the light in the taper microstructure has been analyzed. The software of Lighttools has been used to analyze the influence on light intensity distribution of the vertex angle θ, the space between the microstructure L, the diameter ratio of up to down of the microstructure A/B, the cutting output of the microstructure H and the refractive index of the diffuser n1.As a result, the light intensity of the optical axis will increase and visual angle will decrease when the vertex angle θ, the refractive index of the diffuser n1 and the cutting output of the microstructure H increase; the light intensity of the optical axis will increase and visual angle will decrease when the space between the microstructure decrease; with the increasing of the ratio A/B, the light intensity of the optical axis would first increase and then decrease, visual angle would first decrease and then increase. When A/B=0.4, the light intensity gets the maximum value, the visual angle gets the minimum value. The result of the simulation is significant to manufacture and research.

Abstract: The article deals with experimental investigation of subsonic air to air ejector with various configurations of the mixing chamber and the diffuser. A constant mixing chamber, 2° and 4° divergent mixing chambers and 6° diffuser were applied to find differences in the mixing process. Characteristics of the ejector, static pressure distributions and pressure fluctuations were measured to find how the different shape of the mixing chamber affect the efficiency of mixing processes. Pressure fluctuation increased rapidly while the ejection ratio was higher than 1.25 and the highest efficiency of the ejector was obtained when using configuration 4-4-6.

Abstract: Shrouding (diffuser augmented) horizontal axis micro-wind turbine has been shown to be an effective ways to potentially increase the power output of micro wind turbine for applications in built environments. It is well understood that the degree of the performance enhancement depends on several factors including the diffuser shape and geometries, blade airfoils, and the wind condition at the turbine site. The effect of diffuser shape and geometries is reported in this paper. Computational fluid dynamic (CFD) simulations of a small wind turbine with a simple frustum diffuser shrouding have been carried out. The diffuser has been modeled with different shapes with the aim to understand the effect of length and area ratio on power augmentation phenomenon. The simulations provide some parameterized figures which present method to determine the beneficial range of frustum diffuser geometries for diffuser shrouded horizontal axis wind turbines.