Modelling and optimization of the Cavity Transfer Mixer

The blending of different materials is an important process in polymer industry, where a good mixing is essential to guarantee adequate performances of the finished product. In the 80s a new device called the Cavity Transfer Mixer (CTM) was invented and patented by Gale at Rapra Technology Limited, as an add-on to be mounted downstream of existing extruders, in order to improve distributive mixing. The CTM consists of two concentric cylinders, the rotor and the stator, both provided with staggered rows of hemispherical cavities. The inner cylinder (rotor) rotates, while the outer (stator) remains still. At the same time, the pressure load imposed upstream, pushes the fluid through the mixer. The result of the interaction between the moving geometry, the imposed pressure load and the rheology of the fluid is the complex flow field driving the mixing mechanisms inside the device. Because of the variety of the phenomena involved, a clear understanding of the CTM mixing processes is still missing and the system development and optimization encounter noticeable difficulties. In this context, the present work proposes a full three dimensional model of the CTM, able to accurately simulate the device operations. A finite element solver provides the transient velocity field, which is used in the mapping method implementation in order to compute the concentration field evolution. A broad range of simulations is run assessing the impact on mixing of several geometrical and functioning parameters, such as the number of cavities per row, the number of rows, the size of the mixer, the rheology of the fluid and the ratio between the rotation speed and the fluid throughput. Results are used to develop some design and operation guidelines for the CTM

Survey of Biomass Resource Assessments and Assessment Capabilities in APEC Economies

This survey of biomass resource assessments and assessment capabilities in Asia-Pacific Economic Cooperation (APEC) economies considered various sources: academic and government publications, media reports, and personal communication with contacts in member economies

Future of Liquid Biofuels for APEC Economies

This project was initiated by APEC Energy Working Group (EWG) to maximize the energy sector's contribution to the region's economic and social well-being through activities in five areas of strategic importance including liquid biofuels production and development

Critical-point scaling function for the specific heat of a Ginzburg-Landau superconductor

If the zero-field transition in high temperature superconductors such as YBa_2Cu_3O_7-\delta is a critical point in the universality class of the 3-dimensional XY model, then the general theory of critical phenomena predicts the existence of a critical region in which thermodynamic functions have a characteristic scaling form. We report the first attempt to calculate the universal scaling function associated with the specific heat, for which experimental data have become available in recent years. Scaling behaviour is extracted from a renormalization-group analysis, and the 1/N expansion is adopted as a means of approximation. The estimated scaling function is qualitatively similar to that observed experimentally, and also to the lowest-Landau-level scaling function used by some authors to provide an alternative interpretation of the same data. Unfortunately, the 1/N expansion is not sufficiently reliable at small values of N for a quantitative fit to be feasible.Comment: 20 pages; 4 figure

3D Lowest Landau Level Theory Applied to YBCO Magnetization and Specific Heat Data: Implications for the Critical Behavior in the H-T Plane

We study the applicability of magnetization and specific heat equations derived from a lowest-Landau-level (LLL) calculation, to the high-temperature superconducting (HTSC) materials of the YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) family. We find that significant information about these materials can be obtained from this analysis, even though the three-dimensional LLL functions are not quite as successful in describing them as the corresponding two-dimensional functions are in describing data for the more anisotropic HTSC Bi- and Tl-based materials. The results discussed include scaling fits, an alternative explanation for data claimed as evidence for a second order flux lattice melting transition, and reasons why 3DXY scaling may have less significance than previously believed. We also demonstrate how 3DXY scaling does not describe the specific heat data of YBCO samples in the critical region. Throughout the paper, the importance of checking the actual scaling functions, not merely scaling behavior, is stressed.Comment: RevTeX; 10 double-columned pages with 7 figures embedded. (A total of 10 postscript files for the figures.) Submitted to Physical Review

Occupant-Centred Control strategies for Adaptive Facades: A preliminary study of the impact of shortwave solar radiation on thermal comfort

Adaptive facades have the potential to shape resource-efficient and occupant-centred spaces only when their control strategies are tailored to meet transient, local and personal demands. State-of-the-art control algorithms are currently failing to provide occupant thermal satisfaction because the data on occupant response to the thermal environment is not sufficiently granular. This paper presents a preliminary assessment of the use of the adjusted operative temperature, which accounts also for the additional effect of shortwave radiation on occupants, to dynamically devise learning control strategies that meet individual occupant comfort requirements. Shortwave effects of solar radiation on occupant comfort and operative temperature are compared to those considering only longwave radiation and two alternative occupant-centred control strategies are devised and assessed. Lastly, a combined occupant-centred control strategy is also proposed for an open space office

Critical Dynamics of a Vortex Loop Model for the Superconducting Transition

We calculate analytically the dynamic critical exponent $z_{MC}$ measured in Monte Carlo simulations for a vortex loop model of the superconducting transition, and account for the simulation results. In the weak screening limit, where magnetic fluctuations are neglected, the dynamic exponent is found to be $z_{MC} = 3/2$. In the perfect screening limit, $z_{MC} = 5/2$. We relate $z_{MC}$ to the actual value of $z$ observable in experiments and find that $z \sim 2$, consistent with some experimental results

Extreme Type-II Superconductors in a Magnetic Field: A Theory of Critical Fluctuations

A theory of critical fluctuations in extreme type-II superconductors subjected to a finite but weak external magnetic field is presented. It is shown that the standard Ginzburg-Landau representation of this problem can be recast, with help of a novel mapping, as a theory of a new "superconductor", in an effective magnetic field whose overall value is zero, consisting of the original uniform field and a set of neutralizing unit fluxes attached to $N_{\Phi}$ fluctuating vortex lines. The long distance behavior is related to the anisotropic gauge theory in which the original magnetic field plays the role of "charge". The consequences of this "gauge theory" scenario for the critical behavior in high temperature superconductors are explored in detail, with particular emphasis on questions of 3D XY vs. Landau level scaling, physical nature of the vortex "line liquid" and the true normal state, and fluctuation thermodynamics and transport. A "minimal" set of requirements for the theory of vortex-lattice melting in the critical region is also proposed and discussed.Comment: 28 RevTeX pages, 4 .ps figures; appendix A added, additional references, streamlined Secs. IV and V in response to referees' comment