Maximum Allowable Flux Research Articles

Fast and reliable flux map on cylindrical receivers

The thermal design of external solar receivers is a complex problem, in which the main input is the flux caused by the entire heliostat field on the cylindrical receiver surface. In this work, a fast and reliable model of flux distribution on the cylindrical receiver is proposed. This new cylinder flux map is based on the HFLCAL model for the analytic flux density sent by a heliostat on its image plane and the projection, in the direction of the central reflected ray, of any point in the plane image onto the cylindrical surface. The heliostat flux density includes shading and blocking, cosine of the incidence angle, atmospheric attenuation and effective reflectivity. A differential energy balance supports the coherence of the new model, i.e. the power contained in a differential of area in the image plane has to be equal to the power contained in the projected differential of area onto the cylinder. As an application of this new flux distribution on cylindrical receivers, we present the receiver sizing for a Noor III-like 150 MWe plant, with 7400 heliostats, in which the minimum LCOE gives the receiver diameter and a preliminary receiver height. With the help of the new flux map, this height is analysed to verify the maximum allowable flux. A multi-aiming strategy suggested by Vant-Hull (2002) and put into practice by Sanchez-Gonzalez and Santana (2015) is used to spread the hot spots along the receiver height. The PC CPU time to produce a coherent flux map on the cylinder is around six seconds.

Dynamic fouling behavior and cake layer structure changes in nonwoven membrane bioreactor for bath wastewater treatment

A nonwoven fabric module was used as a solid–liquid medium in a membrane bioreactor for bath wastewater treatment. The flux-step method was performed to define the maximum allowable flux and then was verified over a long period operation under six different imposed fluxes ranging from 8L/(m2h) to 18L/(m2h). During the long-term tests, the treatment performance and filtration characteristics of the nonwoven membrane bioreactor (NWMBR) were investigated. The membrane fouling mechanisms under the different operating phases of the NWMBR were also discussed. Results show that the NWMBR operated in two stages during the six tests. In the early stage, the filling up of the internal structure of the membrane caused the rapid formation of a dense cake layer. In the late stage, the increasing imposed flux changed the morphology of the cake layer and affected the membrane fouling differently. When the flux exceeded the critical flux of 15L/(m2h), a thin but dense cake layer formed rapidly and decreased the membrane permeability. When the flux was lower than the critical flux, a loose filamentous biomass layer formed on the nonwoven membrane surface, which acted as a secondary membrane that prevented the adsorption of extracellular polymeric substances, soluble microbial products, and particles onto the membrane surfaces.

Design of polyphase motors with PM excitation

Design guidelines are presented for synchronous motors with permanent magnet (PM) excitation. A general model is established and the dependence of the electric and magnetic loadings on the angle between the armature and field excitations is put in evidence. For this angle there exists an optimal value which yields maximum torque for maximum allowable flux density in the teeth. Another value yields the minimum volume for the permanent magnets. These values guide the selection of the operating point of the motor and its preliminary design. It is found that, when the pole pitch exceeds a certain value, the magnet requires more space than a current carrying winding.