The University of the South Pacific Thermo-fluid Dynamics of Renewable Energy Devices Class Test Year: 20XX Semester 2 Time: 2 hours Max Marks: 50 Part A (Answer all questions) 1) Discuss some of the concerns continuously raised by environmentalists on the R&D projects relating to ocean energy and wind energy technologies. (4) 2) Explain why NACA series airfoils proved unsuccessful for wind turbine applications. Draw and discuss alpha vs Cl behaviors of NACA airfoils and the modern airfoils used in wind turbines. (4) 3) Explain, with examples, any two airfoil series that were designed for wind turbine applications, clearly highlighting the design objectives and desired applications. (6) 4) Discuss some of the devices that are developed for extracting energy from the waves. (6) Part B (Answer any two questions) 5) It is proposed to design a 450 m tall solar updraft tower system for generating power. The desired maximum velocity in the constant diameter tower is 15 m/s, with the tower diameter being 60 m. The ambient temperature is 32oC and the average solar insolation at the location is found to be 850 W/m2. What is the temperature difference required between the collector exit and the ambient air to achieve the desired velocity? How much power is available in the system if we ignore the friction in the chimney? What is the efficiency of the tower? How will the power available and the efficiency change if the tower height is increased to 1000 m and the temperature difference is the same? (15) 6) a) State clearly the assumptions made in developing the linear wave theory. (7) b) Starting from the equations of motion in differential form, obtain the linearized Bernoulli’s equation for unsteady motion in terms of the velocity potential. (8) 7) In a closed cycle OTEC plant, ammonia enters the turbine at a rate of 18 kg/s at a temperature of 21 oC as a saturated vapor and exits at a temperature of 10oC. The cold water inlet temperature is 4oC and exit temperature is 9oC. The warm water inlet temperature is 27oC and exit temperature is 24oC. The turbine efficiency is 84%, the generator efficiency is 85%, the water pump efficiency is 85% and the liquid ammonia pump efficiency is 75%. The water flow rate in the condenser is 700 kg/s and the total head loss across the cold water piping system is 22 m. The warm water flow rate is 1500 kg/s. The specific heat for sea water is 3.85 kJ/kg K. The total head loss across the warm water piping system is 8 m. The temperature of ammonia rises by 2oC in the pump. Estimate a) the Generator power, b) the power input for the Ammonia pump, c) the cold water pumping power required, d) the warm water pumping power required, and e) the net power output, and the average heat transfer in the condenser. (15) --------------------
