Search Results

Self-rewetting fluids, i.e. dilute aqueous alcoholic solutions with unique surface tension behavior, have been proposed as working fluids for terrestrial and space heat pipes. Experiments have been carried out in normal gravity and in low-gravity conditions with tubular heat pipes, thin flat heat pipes for thermal management in electronic devices, and flexible, inflatable and deployable radiator panels for space applications. Self-rewetting heat pipes exhibit, in general, better thermal performances in comparison with water heat pipes. Current developments are focused on self-rewetting brines, studied as candidate potential heat transfer fluids for space applications. Activities are in progress to perform experiments in space with a small technological payload onboard a microsatellite developed by the Italian Space Agency.

A multi-objective optimization model using a piston behavior simulation for the prediction of NV, friction and scuffing was created. This model was used to optimize the piston skirt form, helping to enable well-balanced forms to be sought. Optimization calculations, involving extended analyses and numerous design variables, conventionally necessitate long calculation times in order to achieve adequate outcomes. Because of this, in the present project data was converted into functions in order to help enable the complex piston skirt form to be expressed using a small amount of coefficients. Using the limit values for manufacturability and the degree of contribution to the target functions, the scope of design variables was restricted, and the time necessary for the analysis was significantly reduced. This has helped to enable optimal solutions to be determined within a practical time frame.

The paper presents first a description of the methods used for the analysis of global dynamics of rotating systems like jet engines but also auxiliary power units. Different methodologies are described so to model rotating parts using beam, but also Fourier multi-harmonic, three dimensional models or to take into account cyclic symmetry and multistage cyclic symmetry concepts. Advantages and disadvantages of the different model types are discussed and compared. The coupling of the rotating parts with casings and stators is then discussed both in the inertial frame and in the rotating frame. The effect on global dynamics of bearing and other linking devices is taken into account for different type of analysis from critical speed analysis, to harmonic and transient analysis. The effect of gears and gear boxes coupling different rotors (like it is the case for auxiliary power units in a jet engine) is then discussed and appropriate methods described so to model this coupling effect.