Exercise 1 ‐ Closed system A failure in the control system of a concentrated solar power plant has immobilized a parabolic mirror and trapped 10 kg of water in the corresponding receiver. The initial water temperature is T0 = 250o C and the pressure is p0 = 12 bar. Solar radiation adds thermal energy at a rate of 1 kW/m2 to the parabolic mirror (surface area 10 m2 ) which is then transferred to the receiver (97% efficiency). The receiver unit contains an emergency release valve that triggers once the internal pressure exceeds 20 bar. What is the available repair time before the valve is first activated?
Exercise 2 ‐ Open systems Exercise 2. 1 ‐ Turbine A turbine in a geothermal power plant receives propane (secondary cycle) at a pressure of 40 bar and a temperature of 160o C. The mass flow rate of the working fluid is 5 kg/s. At the turbine outlet the propane exits as a two phase mixture (quality 95%) at a pressure of 14 bar. Disregarding stray heat transfer and changes in kinetic and potential energy calculate the mechanical power that is extracted by the turbine.
Exercise 2.2 ‐ Heat Exchanger Following the turbine in Exercise 2.1 the propane is cooled in a counter‐flow heat exchanger in order to condensate the two‐phase mixture and decrease the pressure at the turbine exit. After passing through the heat exchanger, the propane should exit as a saturated fluid at a pressure of 12 bar. A nearby river with an average water temperature of 20o C is available as coolant. Calculate the minimum required mass flow rate of the water if its exit temperature must not exceed 27o C.
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