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Comparative analysis of the theoretical models of ideal propulsor, ideal fluid brake, ideal screw propeller and ideal axial wind turbine

Koronowicz T., Szantyr J. A.

Polish Maritime Research

2013

nr 2

3--12

The article presents a detailed discussion of the theoretical models of four different fluid dynamic devices: an ideal propulsor, an ideal fluid brake, an ideal screw propeller and an ideal turbine. The four models are presented with all relevant mathematical formulae regarding the forces, the power and the efficiency. It is demonstrated that the application of the model of an ideal optimum fluid brake according to the Betz theorem for determination of the maximum effectiveness coefficient of an axial wind turbine is not correct. In the case of a turbine the inclusion of important rotational flow losses may increase the maximum value of the turbine effectiveness coefficient above the level defined by Betz. Therefore the model of an ideal turbine should be an inversion of the model of an ideal screw propeller. This conclusion is supported by numerical calculations. It may influence the design procedures of wind turbines and may lead to increase in their efficiency.

Determination of maximum efficiency position of a slip-ring induction motor

Banach H.

Zeszyty Naukowe. Elektryka / Politechnika Łódzka

1998

z. 92

199--204

A simple method to calculate an efficiency maximum position of slip - ring induction motor is presented. This method is based on the knowledge of no-load test losses at the rating voltage and locked - rotor losses by the rating rotor current.

W artykule przedstawiono sposób na określenie położenia maksimum sprawności w silniku indukcyjnym pierścieniowym w funkcji mocy wydawanej. Sposób ten oparty jest na znajomości strat biegu jałowego przy napięciu znamionowym oraz strat zwarcia wyznaczonych dla znamionowej wartości prądu wirnika.