Three-phase modeling and optimization of benzene alkylation in commercial catalytic reactors

The main object of this research is heterogenous modeling of benzene alkylation in three phase reactors based on the mass and energy balance equations by coupling the kinetic and equilibrium models and optimization the process conditions to enhance production capacity. In the first step, the alkylation reactors are simulated considering a three-phase model including heat and mass transfer resistances in the solid catalyst, gas and liquid phases. To prove the accuracy of developed model and adopted assumptions, the simulation results are compared with the plant data. Based on the simulation results, the benzene conversion and ethylbenzene selectivity in the alkylation reactors are 15.03 and 94.60% at the conventional condition. In the second step, considering the temperature of inlet streams to the reactors as decision variables, an optimization problem is formulated to maximize the ethylbenzene production rate as the objective function. Based on the simulation results, applying optimal condition on the system improves the ethylbenzene production by 1.33% at the same ethylene conversion compared to the conventional condition.

A Simple Condition Monitoring Method for Gearboxes Operating in Impulsive Environments

Reliable condition indicators are necessary to perform effective diagnosis and prognosis. However, the vibration signals are often corrupted with non-Gaussian noise and rotating machines may operate under time-varying operating conditions. This impedes the application of conventional condition indicators. The synchronous average of the squared envelope is a relatively simple yet effective method to perform fault detection, fault identification and fault trending under constant and time-varying operating conditions. However, its performance is impeded by the presence of impulsive signal components attributed to impulsive noise or the presence of other damage modes in the machine. In this work, it is proposed that the synchronous median of the squared envelope should be used instead of the synchronous average of the squared envelope for gearbox fault diagnosis. It is shown on numerical and experimental datasets that the synchronous median is more robust to the presence of impulsive signal components and is therefore more reliable for estimating the condition of specific machine components.

Significant changes in yields of 7-hydroxy-coumarin-3-carboxylic acid produced under FLASH radiotherapy conditions

Yield of 7-hydroxy-coumarin-3-carboxylic acid (7OH–C3CA) significantly decreases at FLASH condition with the dose rate of >40 Gy s−1, compared to that at conventional condition of 0.05 Gy s−1, due to the oxygen depletion in the solution.

Checkerboard artifacts free convolutional neural networks

It is well-known that a number of convolutional neural networks (CNNs) generate checkerboard artifacts in both of two processes: forward-propagation of upsampling layers and backpropagation of convolutional layers. A condition for avoiding the artifacts is proposed in this paper. So far, these artifacts have been studied mainly for linear multirate systems, but the conventional condition for avoiding them cannot be applied to CNNs due to the non-linearity of CNNs. We extend the avoidance condition for CNNs and apply the proposed structure to typical CNNs to confirm whether the novel structure is effective. Experimental results demonstrate that the proposed structure can perfectly avoid generating checkerboard artifacts while keeping the excellent properties that CNNs have.

Investigation of Carrot Reduction Effect on 4H-Silicon Carbide Epitaxial Wafers with Optimized Buffer Layer

We investigated the carrot-defect reduction effect by optimizing the buffer layers of 4H-Silion Carbide (SiC) epitaxial wafers. The SiC epitaxial wafer with the 0.5 μm-thick optimized condition-B buffer layer show the carrot-defect density of 0.13 cm-2, since that with the conventional-A buffer layer were 0.68 cm-2. Although the average bunching length with the optimized condition-B buffer layer was 7-times longer than those with the conventional condition-A buffer layer, we could reduce the bunching length by applying the optimized condition-B only to the initial 0.05 μm-thick buffer layer. Finally, with the initial 0.05 μm-thick optimized condition-B buffer layers, we could achieve the SiC epitaxial wafers with only half the carrot-defect densities of those with the conventional condition-A buffer layers, while the average bunching lengths were less than 100 μm. With this condition, we could achieve the estimated yield of 90.1% with 4 x 4 mm chips, while that with the conventional condition-A buffer layer was 81.9%.

Simplified Approach for Fracture Integrity Assessment Procecedure of Flawed Weld Joint Under Non-Conventional Condition

Welded pipes are widely employed in many oil and gas applications. Engineering Critical Assessment (ECA) shall be performed in order to establish acceptance levels for revealed or postulated flaws in new or existing constructions. Although methods for assessing the acceptability of flaws in all types of structures are presented in codes and standards, such as BS7910 [1], API579-1 [2], R6 [3], DNV OS-F101 [4], the approaches are typically derived by simplified geometries as plate solutions, simplified material assumption, and simplified load condition as uniaxial load condition. Dedicate numerical solution are more accurate and would improve the assessed results. But the use of appropriate conditions in the full ECA requires several specific Finite Element Analysis (FEA) which are able to identify the Crack Driving Force (CDF) for each postulated defect geometry, material assumption and load conditions. The purpose of this paper is to propose a simplified method, into a standard procedure (similar to BS7910 [1]), minimizing numerical analyses, to guaranty the safety against fracture of many kind of weld joint under non-conventional condition (such as generic weld joint geometry and/or weld joint subjected to combined axial force, bending moment and internal over pressure which are not contemplate in current code and for which dedicated FEA are recommended).

Finite Element Analysis of the Roller Bearing Used in Rolling Mill

The loading roller number and maximum stress of the bearings can not be calculated accurately through conventional methods because support manner of the roller bearings used in rolling mill is different from that of the roller bearings used in conventional condition. Based on characteristic of the bearings, the model of the bearing is made combining contact mechanics with finite element method. The loading roller number and maximum stress of the bearings are calculated through FEA. The work of this paper offers a reference to design and manufacture this kind of bearings.

Utilizing Data from a Sensorless AC Variable Speed Drive for Detecting Mechanical Misalignments

Conventional condition monitoring techniques such as vibration, acoustic, ultrasonic and thermal techniques require additional equipment such as sensors, data acquisition and data processing systems which are expensive and complicated. In the meantime modern sensorless flux vector controlled drives can provide many different data accessible for machine control which has not been explored fully for the purpose of condition monitoring. In this paper polynomial models are employed to describe nonlinear relationships of variables available from such drives and to generate residuals for real time fault detection and performance comparisons. Both transient and steady state system behaviours have been investigated for optimal detection performance. Amongst 27 variables available from the drive, the torque related variables including motor current, Id, Iqcurrents and torque signals show changes due to mechanical misalignments. So only these variables are explored for developing and optimising detection schemes. Preliminary results obtained based on a motor gearbox system show that the torque feedback signal, in both the steady and transient operation, has the highest detection capability whereas the field current signal shows the least sensitivity to such faults.