Example:Wind Energy 8.5m/s A site evaluated for a wind farm is observed to have steady winds at a speed of 8.5 m/s.Determine the wind energy (a)per unit mass (b)for a mass of 10 kg,and (c)for a flow rate of 1154 kg/s for air. Solution A site with a specified wind speed is considered.Wind energy per Discussion unit mass,for a specified mass,and for a given mass flow rate of air are to be determined. Assumptions Wind flows steadily at the specified speed. =8.5m/s,12m section, Analysis The only harvestable form of energy of atmospheric air is the Pair=1.2 kg/m3 kinetic energy,which is captured by a wind turbine. (a)Wind energy per unit mass of air is A wind turbine with a V2(8.5m/s)2 1 J/kg e =ke= 2 1m2/s =36.1J/kg wind spanΦl2 m has a 2 power generation (b)Wind energy for an air mass of 10 kg is potential of 41.7 kW. E=me=(10kg)(36.1J/kg)=361J Real wind turbines (c)Wind energy for a mass flow rate of 1154 kg/s is convert about 1/3 of this E=me=(1154kg/s)(36.1J/kg) 1kW potential to electric 1000J/s 41.7kW power. 上海究通大学 March 5,2019 SHANGHAI JIAO TONG UNIVERSITYMarch 5, 2019 7 Example: Wind Energy A site evaluated for a wind farm is observed to have steady winds at a speed of 8.5 m/s . Determine the wind energy (a) per unit mass, (b) for a mass of 10 kg, and (c) for a flow rate of 1154 kg/s for air. A wind turbine with a wind span Φ12m has a power generation potential of 41.7 kW. Real wind turbines convert about 1/3 of this potential to electric power. = 8.5m/s, Φ12m section, ρair=1.2 kg/m3 Discussion