Mechanical Engineering Ebooks

The relationship between alloy chromium content and oxidation rate has been determined for nickel-chromium alloys containing up to 17At% chromium. The tests were conducted at 1096C, under one atmosphere of oxygen. The observed structural and phase changes in the oxide were related to the oxidation rate. It has been found that increasing amounts of chromium in the NiO phase govern the oxidation rate for alloys containing less than 2At% chromium. For alloys of greater than 2At% chromium, a complex exchange of chromium among three phases--NiO, Cr2O3 and the spinel, NiCr2O4--has been detected. This chromium exchange was reflected in the lattice parameter of the NiO phase, and in the rate of increase of oxidation rate with chromium addition to the alloy. The present work indicates that an interstitial diffusion mechanism may become dominant in the oxides of high chromium content. Within the scope of the present work, the high oxidation stability of nickel-chromium alloys has been correlated with the presence of Cr2O3 in the oxide layer.

Variational integrators are a class of discretizations for mechanical systems which are derived by discretizing Hamilton's principle of stationary action. They are applicable to both ordinary and partial differential equations, and to both conservative and forced problems. In the absence of forcing they conserve (multi-)symplectic structures, momenta arising from symmetries, and energy up to a bounded error.

This thesis addresses the problem of inter-particle collisions in a viscous liquid. Experimental measurements were made on normal and oblique collisions between identical and dissimilar pairs of solid spheres. The experimental evidence supports the hypothesis that the normal and the tangential component of motions are decoupled during a rapid collision.

Experimental measurements of the particle pressure were obtained for a liquid fluidized bed and for a vertical gravity driven liquid-solid flow. The particle, or granular, pressure is defined as the extra pressure generated by the action of particles in a particulate multi-phase flow. Using a high-frequency-response pressure transducer, individual collisions of particles were collected and measured to obtain a time-averaged particle pressure. Results were obtained for a number of different particles and for two different test section diameters. Results show that the particle pressure experiences a maximum at intermediate concentrations, and that its magnitude is scaled with the particle density and the square of the terminal velocity of the particles. The particle pressure was found to be composed of two main contributions: one from pressure pulses generated by direct collisions of particles against the containing walls (direct component), and a second one from pressure pulses due to collisions between individual particles that are transmitted through the liquid (radiated component).

The increase, in recent years, in the size and efficiency of gas turbines burning natural gas in combined cycle has occurred against a background of tightening environmental legislation on the emission of nitrogen oxides. The higher turbine entry temperatures required for efficiency improvement tend to increase NOx production. First-generation emission control systems involved water injection and catalytic reduction and were relatively expensive to operate. Dry low-NOx combustion systems have therefore been developed but demand more primary air for combustion. This gives added incentive to the reduction of air requirements for cooling the combustor and turbine blading. This paper reviews the various approaches adopted by the main gas turbine manufacturers which are achieving very low levels of NOx emission from natural gas combustion. Further developments, however, are necessary for liquid fuels.