A solar power plant operates on a Rankine cycle with Refrigerant 134a as its wor

Question

A solar power plant operates on a Rankine cycle with Refrigerant 134a as its

working fluid. The turbine and pump operate adiabatically. The rate of energy input to

the collectors from solar radiation is 0.4 kW/m2 of collector surface area. Determine the

solar collector surface area, in m2 per kW of power developed by the plant. Discuss

possible operational improvements that could reduce the required collector surface area.

Assume isentropic turbine and no pressure drop in condenser or solar collector. P2 = 6

bar.

the answer is

25 m2/kW

Explanation / Answer

Find the thermo properties for the differant states in the cycle. 1) T1=60 C H1=275.99 kJ/kg (Enthalpy for saturated vapor @ 60 C from steam table, your book may be slightly different) Hfg=137.42 kJ/kg (from same table) 2) P2= 6 bar T2=21.58 C (From table, temperature of sat. liquid @ 6 bar) H2=259.19 (From table, enthalpy of sat. liquid @ 6 bar) From the above conditions, the power generated can be found. Wt=H1-H2=275.99-259.19=16.8 kW (using unit mass flow rate of 1 kg/s) 3) After condesing: T3=21.58 C P3= 6 bar 4) After pump: T4=21.58 C (adiabatic) Find power required by solar collector to bring temperature of fluid up to 60 C (state 1) and vaporize the fluid : W=Cp?T + Hfg Cp= 0.857 kJ/kg (found specific heat online but you may want to check with your book) Hfg=137.42 (from Table for condition 1) W=0.857*(60-21.58) + 137.42=170.35 kW Area required: A=170.35 kw/0.4 kw/m^2 A=425.86 m^2 Area/Power generated= A / Wt=425.86 m^2/16.8 kW Area/Power generated= 25.3 m^2/kW

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