Effect of tube size and obstacles on explosion limits in flowing gases.

In a large pilot plant the upper explosion limit of ethene-air-nitrogen mixtures was experimented in 3.0-m-long and 21-, 50-, and 100-mm-dia. tubes at different flow rates, pressures, and temperatures. The upper explosion limit, influenced by the gas velocity, becomes smaller and shifts to higher oxygen concentrations for increasing flow rates. The results of these tubes could be correlated based on the tube Reynolds number. A cooling effect of the tube wall, which might influence the explosion region, was not observed. An increase in pressure lowers the critical oxygen content as does an increase in temperature, thus the explosion region becomes larger. Different obstacles were tested, which alter the hydrodynamics. Reaction fronts could only propagate for increased oxygen concentrations through a structured Sulzer laboratory gauze packing or a sudden reduction in diameter from 50 to 20 mm. In the experiment, where the tube was completely filled with glass spheres, propagation of reaction fronts through this packed bed was not possible, even at very low gas velocities and very high oxygen concentrations. In a deep dead zone connected to the tube, the gas was ignited and reacted without igniting the gas outside the dead zone. After some time the reaction stopped because of oxygen starvation. However, dead zones with another geometry, where renewal of the combustible gas can occur, still may be dangerous

Influence of hydrodynamics on the upper explosion limit of ethene-air-nitrogen mixtures

A large pilot plant was constructed to study the upper explosion limit of ethene-air-nitrogen mixtures under conditions of flow in a tube. Experiments were performed at pressures of 0.5, 1.0, and 1.5 MPa, gas temperatures between 298 and 573 K, and with ethene concentrations between 20 and 40 vol. %. A cylinder-symmetrical 2-D model developed simulated the experimentally obtained ignition and flame propagation phenomena. The commercial computational fluid dynamics code AEA-CFX 4.1 was used to solve this model, to which reaction kinetics for a scheme of two consecutive reactions were added. The model predicts the experimental explosion points within 0.5 vol. %. The explosion limit is influenced by the gas velocity: it becomes smaller and shifts to higher oxygen concentrations at increasing flow rates. In practice this means that partial oxidation reactions can safely be operated at high oxygen concentrations, provided the gas is kept flowing at high flow rates

InP-based generic foundry platform for photonic integrated circuits

The standardization of photonic integration processes for InP has led to versatile and easily accessible generic integration platforms. The generic integration platforms enable the realization of a broad range of applications and lead to a dramatic cost reduction in the development costs of photonic integrated circuits (PICs). This paper addresses the SMART Photonics generic integration platform developments. The integration technology based on butt joint active-passive epitaxy is shown to achieve a platform without compromising the performance of the different components. The individual components or building blocks are described. A process design kit is established with a comprehensive dataset of simulation and layout information for the building blocks. Latest results on process development and optimization are demonstrated. A big step forward is achieved by applying high-resolution ArF lithography, which leads to increased performance for AWGs and a large increase in reproducibility and yield. The generic nature of the platform is demonstrated by analyzing a number of commercial multiproject wafer runs. It is clear that a large variety of applications is addressed with more than 200 designs from industry as well as academia. A number of examples of PICs are displayed to support this. Finally, the design flow is explained, with focus on layout-aware schematic-driven design flow that is required for complex circuits. It can be concluded that generic integration on InP is maturing fast and with the current developments and infrastructure it is the technology of choice for low cost, densely integrated PICs, ready for high-volume manufacturing