A flexible air separation process: 1. Design and steady-state optimizations

The flexible operation of energy-intensive processes, such as cryogenic air separation, has economic potential due to increasing fluctuations of the electricity markets. Multiproduct air separation processes with high ratios of liquid product are very promising for flexible operation due to storable products. We present a process design with an integrated liquefication cycle and liquid assist operation, that facilitates a high liquid product ratio and a flexible process operation. We use a mechanistic dynamic process model in steady-state process optimizations covering the wide operational range of the proposed process. The optimization results show that the power demand can be varied in a range from 3.5 to 28 MW without violating operational constraints by changing the nitrogen and oxygen production rates. Thus, the proposed process is a promising air separation candidate for flexible operation with respect to fluctuating electricity markets.     

Physical investigations on Ni doping ZnO thin films along with ethanol response

Journal of Materials Science: Materials in Electronics - Undoped and Ni-doped ZnO thin films were grown on glass substrates at 460 °C using the spray pyrolysis method. All samples...     

On reduced modeling of mass transport in wavy falling films

In many industrial units such as packing columns, falling film reactors, etc., the liquid phase is designed as a falling film. It is well known that the mass and heat transfer in laminar wavy film flows is significantly enhanced compared to flat films. The kinetic phenomena underlying the increase in mass and heat transfer are, however, still not fully understood. For an efficient design of falling film units, computational models that account for these enhanced transport mechanisms are of key importance. In this article, we present a reduced modeling approach based on a long‐wave approximation to the fluid dynamics of the film. Furthermore, we introduce a new two‐dimensional (2D) high‐resolution laser‐induced luminescence measurement technique. Both in the numerical simulation results and in the high‐resolution 2D‐concentration measurements obtained in the experiments we observe similar patterns of high concentrations locally, especially in the areas close to the wave hump. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2265–2276, 2018     

Sol–gel derived mesoporous Cr/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for SCR of NO by ammonia

Catalytic performances of Cr/Al₂O₃ catalysts were investigated in Selective Catalytic Reduction (SCR) of NO by NH₃ in the presence of oxygen. Solids were prepared either by sol–gel method or by impregnation and were characterized by different techniques such as chemical analysis, N₂ physisorption, XRD, ²⁷Al MAS NMR, DRIFT, UV–Vis Diffuse Reflectance (DRS), Raman Spectroscopy and Temperature Programmed Reduction by H₂ (H₂-TPR). The physisorption of N₂ at 77 K reveals that solids are mesoporous. On the other hand, XRD shows that xerogels are amorphous but supercritical drying leads to a nanosized crystallite state. No crystalline α-Cr₂O₃ was found which indicate that metal species reside essentially on the surface of Al₂O₃ and their size measured less than 4 nm. Furthermore, ²⁷Al MAS NMR reveals that part of chromium ions occupies sites on/in Al₂O₃ in close vicinity of tetrahedral ²⁷Al. This, apparently, is not the case for aerogels. DRIFT results show that there is a consumption of hydroxyl groups of alumina after calcination. The esterification reaction between hydroxyl groups and chromium oxide during calcination leads to the formation of anchored (poly-)chromates according to DRS, Raman, and H₂-TPR results. The catalysts are active in the studied reaction by NH₃ and the activity is principally governed by preparation method and operating conditions. When compared to xerogels, aerogels are more active in NO reduction and less selective toward N₂O. Preparation method and drying mode seem to involve the predominance of active species which are essentially mono and polychromates but Cr³⁺ ions incorporated inside alumina seem to be inactive.     

A robust and fast algorithm for three-dimensional transient inverse heat conduction problems

Despite numerous studies of inverse heat conduction problems (IHCP) over the last several decades, their solutions still suffer from the mathematical difficulties and the bottleneck of currently available numerical methods for large-scale problems. In this paper, we present a robust and efficient algorithm for the solution of a specific type of three-dimensional (3D) IHCP commonly involved in various engineering applications. The solution method incorporates the Tikhonov regularization for tackling the severe ill-posedness and the conjugate gradient (CG) method for solving the resulting minimization problems. A model function approach is used to significantly reduce the effort needed to find the optimal Tikhonov regularization parameter. The proposed solution method requires no a priori knowledge of the measurement noise and is much more computationally efficient than the traditional Tikhonov regularization-based inversion approaches. Thus, it can be used for the efficient solution of large-scale practical problems. Two simulation case studies of practical significance are presented to validate and assess the performance of the proposed method. Finally, the solution method is successfully applied to the reconstruction of instantaneous heat fluxes from experimentally measured temperature data.     

On the Integration of Unicast and Multicast Cell Scheduling in Buffered Crossbar Switches

Internet traffic is a mixture of unicast and multicast flows. Integrated schedulers capable of dealing with both traffic types have been designed mainly for Input Queued (IQ) buffer-less crossbar switches. Combined Input and crossbar queued (CICQ) switches, on the other hand, are known to have better performance than their buffer-less predecessors due to their potential in simplifying the scheduling and improving the switching performance. The design of integrated schedulers in CICQ switches has thus far been neglected. In this paper, we propose a novel CICQ architecture that supports both unicast and multicast traffic along with its appropriate scheduling. In particular, we propose an integrated round-robin-based scheduler that efficiently services both unicast and multicast traffic simultaneously. Our scheme, named multicast and unicast round robin scheduling (MURS), has been shown to outperform all existing schemes under various traffic patterns. Simulation results suggested that we can trade the size of the internal buffers for the number of input multicast queues. We further propose a hardware implementation of our algorithm for a 16 times 16 buffered crossbar switch. The implementation results suggest that MURS can run at 20 Gbps line rate and a clock cycle time of 2.8 ns, reaching an aggregate switching bandwidth of 320 Gbps.     

Toward an Integrated Smart Sensing System and Data Interpretation Techniques for Pavement Fatigue Monitoring

Abstract: Currently, pavement instrumentation for condition monitoring is done on a localized and short‐term basis. Existing technology does not allow for continuous long‐term monitoring and network level deployment. Long‐term monitoring of mechanical loading for pavement structures could reduce maintenance costs, improve longevity, and enhance safety. In this article, on‐going research to develop and validate a smart pavement monitoring system is described. The system mainly consists of a novel self‐powered wireless sensor based on the integration of piezoelectric transduction with floating‐gate injection capable of detecting, storing, and transmitting strain history for long‐term monitoring and a novel passive temperature gauge. A technique for estimating full‐field strain distributions using measured data from a limited number of implemented sensors is also described. The ultimate purpose is to incorporate the traffic wander effect in the fatigue prediction algorithms. Preliminary results are shown and limitations are discussed.