Maximum power from fluid flow by applying the first and second law of thermodynamics
The application of equilibrium thermodynamics in the study of thermal plant performance under real operating conditions is a constant challenge. In this paper, an analysis of a reservoir pressure piston working between two linear flow resistances is performing by considering the friction of the piston cylinder system on the walls. The proposed model is developed to obtain the optimum power output and speed of the piston in terms of first law efficiency. If the friction on the piston-cilynder assembly is neglected, the expressions obtained are consistent with those presented in the literature under in laminar regime. It was also demonstrated that for both laminar and turbulent regime with overall size constraints, the power delivered can be maximized by balancing the flow resistances upstream and downstream of the piston. This paper also evaluated the influence of the overall size constraints and flow regime on the performance of the piston cylinder. This analysis is equivalent to evaluate the irreversibilities in an endoirreversible Carnot heat engine with heat loss resistance between the engine and its heat reservoirs. The proposed model introduced some modifications to the results obtained from recent literature and leads to important conclusions. Finally, the proposed model was applied to calculate the lost available work in a turbine operating at steady flow conditions with with an ideal gas as working fluid.