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The aim of this work is to analyze experimentally the influence of geometrical parameters and fluid properties on the thermal performances of rectangular single-phase natural circulation miniloops, which could be used for cooling of electronic devices. The present paper analyzes two experimental campaigns performed on two rectangular miniloops (ML1 and ML2), characterized by different heights, when two working fluids (water and FC43) are employed. The temperature trends are measured for different combinations of miniloop inclination and power, and the associated fluid velocities are calculated by means of an enthalpy balance. The experimental data are compared with Vijayan’s model, developed for large scale loops in steady-state conditions, corrected with a parameter that takes into account the loop inclination. The dynamical behavior is always stable. The time of the initial transient is long at high miniloop inclination (close to horizontal) and at low power, while the temperature overshoot grows up with increasing power and inclination. Results show that at the same power the velocity of FC43 is almost twice than that of water, but the thermal performances are worse because FC43 is characterized by low specific heat. Moreover, the velocities of the tallest miniloop are the lowest, probably because the enhancement of shear stresses overcomes the increase in buoyancy forces. For both fluids, the velocity grows almost linearly with power. Experimental data show a good agreement with the modified Vijayan’s model.

This paper deals with the aerodynamic redesigning of a four-stage heavy-duty gas turbine. Traditional design tools, such as through-flow methods, as well as more sophisticated tools, such as three-dimensional RANS computations, were applied in subsequent steps according to a given hierarchical criterion. Each design or analysis tool was coupled with modern optimization techniques, and the overall redesign procedure relies on a neural-network-based approach aimed at maximizing the turbine’s power output while satisfying geometrical and mechanical constraints. A detailed description of the redesign procedure is provided, and the aerodynamic characteristics of the optimized geometry are discussed and compared to the original ones.