Note on a real gas model for OWC performance

Abstract

a b s t r a c tOscillating water column (OWC) are devices for wave energy extraction equipped with turbines for energy conversion. The purpose of the present work is to study the thermodynamic of a real gas flow through the turbine and its differences with respect to the ideal gas hypothesis, with the final goal to be applied to OWC systems. The effect of moisture in the air chamber of the OWC entails variations on the atmospheric conditions near the turbine, modifying its performance and efficiency. In this work we study the influence of humid air in the performance of the turbine. Experimental work is carried out and a real gas model is asserted, in order to take a first approach to quantify the extent of influence of the airewater vapour mixture in the turbine performance. The application of a real gas model and the experimental study confirmed the deviations of the turbine performance from the expected values depending on flow rate, moisture and temperature.

Thermodynamics of an OWC containing real gas

“…All variables are expressed 240 per mole unit. The reduced temperature range corresponds to that of the experiments conducted by Medina- López et al (2016). Figure 3(a) indicates that entropy progressively increases with temperature, due to an associated increase in heat in the real gas system.…”

“…To validate the proposed thermodynamic model, predictions are compared against experimental data obtained by Medina-López et al (2016) on steady airwater vapour mixture flow through a chamber and turbine. Here, the real gas model is used to predict the change between inner and outer system variables, while preserving mass flow rate continuity through the turbine.…”

“…Medina-López et al (2016)). Among others, Gato & Falcão (1984), Gato & Falcão (1989), Raghunathan (1995), and Sarmento et al (1990) have carried out detailed studies of the technical 20 behaviour of the Wells turbine when used as a PTO device.…”

“…For mass flow and enthalpy to remain conservative over a given pressure drop, the temperature change through the turbine could not be obtained theoretically by Medina-López et al (2016) who assumed an ideal adiabatic polytropic process. A temperature correction had therefore to be applied in accordance with a real gas equation of state based on the virial expansion, Prausnitz (1999).…”

“…This approach has provided a useful methodology by which to calculate the system variables of a real gas in terms of deviations from ideal gas values. A preliminary study by Medina-López et al (2016) has shown that application of real gas formalism to the air-water vapour mixture in an OWC proves to be a 75 valuable tool for the accurate prediction of efficiency.…”