Water is drawn from a river at 17 degree C and has to be heated to 64 degree C.

Question

Water is drawn from a river at 17 degree C and has to be heated to 64 degree C. Calculate the advantage of using the heat pump plant described below over direct heating of the water. Assume t a heat source above 450 degree C is available. R-12 heat pump: Compressor driven by steam turbine; condenser temperature = 60 degree C and evaporator temperature = -5 degree C; R-12 compressor as saturated vapour and enters throttle valve as saturated liquid. Steam turbine plant: Steam pressure and temperature leaving the boiler at 30 bar and 450 degree C respectively; condenser temperature = 76 degree C. Take 100% efficiency for turbine and compressor and neglect all heat losses. The water drawn from the river passes through the refrigerant condenser and then through steam condenser.

Explanation / Answer

TURBINE:

At T1 = 450 C and P1 = 30 bar , h1 = 3344.65 KJ/Kg and s1 = 7.085 KJ/KG.K

as the turbine is 100% efficient, s2 = s1 = 7.085 KJ/Kg.K

At T2 = 76 C and s2 = 7.085 KJ/Kg.K, from steam table :

h2 = 2433.22 KJ/Kg

Work delivered by turbine = h1 - h2 = 3344.65 - 2433.22 = 911.43 KJ/Kg

PUMP:

I will need property table of R-12 whichI dont have.

I can xplain the process but

At 60 C find the value of hf and sf

Now after finding sf, note that sf will be equal to s@ -5 C

At Sf abd -5 C calculate h2

Now pump work = hf - h2 = Q (say)

Heat given to system = Q + 911.43

advantage = ( Q + 911.43 ) / 911.43

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