- #1
emilynb
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Homework Statement
I have a project for a class of mine that asks me to design a rankine cycle to produce electricity from a lake using temperature differences between the water and the atmosphere.
I have a budget that I must stick with ($40,000), a defined effeciency for the pump (50%) and turbine (80%), obviously I am restrained by the temperatures of the water and air at the lake I use, and I am also given the thermal resistance for the water and air side of the heat exchanger (0.01 m2K/W for the water side and 0.05 m2K/W for the air side). Then I must calculate the payback time assuming that I can sell the electricity at $0.03/kWh. My goal is to produce max power output.
Any suggestions on where/how/what numbers to start with the calculations would be greatly appreciated. Also, where would be a good place to look to determine approximately how much it would cost to build such a machine?
Homework Equations
Pump (1-2) - isentropic compression: -win = v(P2 - P1)
Boiler (2-3) - constant pressure heat addition: qin = h3 - h2
Turbine (3-4) - Isentropic Expansion: wout = h3 - h4
Condenser (4-1) - constant pressure heat rejection: qout = h4 - h1
The Attempt at a Solution
I have the machine set up, but I am having troubles figuring out how to get started with my calculations in order to make the machine be reasonable/justifiable and workable. So far, what I have is pumping water up from a lake, using it to boil the working fluid in a boiler, expanding it through a turbine which will power the generator to produce electricity, then going back through a condenser and starting all over again. For the working fluid, I am considering using organic fluids - propane, ammonia, R-123, etc.