Microgas turbines are a widespread technology in cogenerative and propulsion applications. Bearings are a key factor in their design and development. The aim of the present research work is the development of the support system for a typical microturbine intended for power generation. To this goal, the present chapter defines the typical requirements of the machine and, afterward, describes the different technologies available to develop the support system of a reliable microturbine. Conventional (rolling element and oil-film) supports and cutting-edge (magnetic, aerodynamic, and aerostatic) bearings are reviewed. Particularly, their suitability to the operating conditions is compared by means of a literature review and elaboration of the relevant data. By analyzing all this information, a new concept for the design of a micro-GT support system is devised. Instead of using a single type of bearing as usual, the new system includes different types in order to take advantage of the best characteristics of each one and, simultaneously, to minimize the effects of the relevant flaws. The innovative support system requires a suitable bearing arrangement, which is compared with the conventional ones. The conceptual design of the innovation is completed by a discussion of its advantages, drawbacks, and prospective improvements.
Although elliptical pocket bearings are widely used in turbomachineries, the influence of their design on performance has not been specifically investigated. A lot of works about tribological models are available, but few of them focus on their application to bearing design at industrial level. \ud
The purpose of the work is to conceive a fast method to verify design and performance of elliptical pocket journal bearings. \ud
The computer-aided verification of pocket journal bearings is performed by means of a suitable finite element analysis method.\ud
The results of sample analyses indicate that the machining tolerances are very influential on elliptical pocket bearing performances and they must be included among the input data
We monitored the evaporation kinetics of drops from solid surfaces and the resulting cooling of the surfaces. To do this we deposited water drops with diameters smaller than 100 µm onto atomic force microscope (AFM) cantilevers. Due to the surface tension of the liquid, the Laplace pressure inside the drop, the change of the interfacial stress at the solid-liquid boundary and evaporative cooling, the cantilevers are deflected by typically some hundred nanometers. We used pure silicon and gold-coated silicon cantilevers in order to be able to separate and quantify the cooling effect from that due to the surface tension. We measured the bending of the cantilevers along their longitudinal axis versus time with an AFM-like setup, and monitored the contact angle and radius of the evaporating drops with video microscopy. We developed a FEM model for the bending of a cantilever as a result of surface forces and evaporative cooling. Experimental results are reproduced by FEM simulations.
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