Question

water at 400 kpa and 500 k is cooled to 200 kpa and 400 k what the enthlpy change

Answer 1

SOLUTION.

Water at given temperature and pressure is Given we have to calculate the enthalpy change during the cooling of water.

Since water is at high temp and pressure.

The enthalpy of water can be found by the Steam table.

Here are the values from steam table.

Property	state 1	state 2
Temp,K	500	400
Pressure, kPa	400	200
Enthalpy , h,kj/kg	2,916.86	2,720.54

Thus changes in enthalpy of water during cooling Process =enthalpy at state 2 - enthalpy at state 1

∆h=h2-h1 = 2720.54-2916.86 =-196.32 kJ/kg

Thus as we cools the water its enthalpy decrease by -196.32 kJ/kg.

Since enthalpy is Fuction of temp , Cooling decreases the temp and hence enthalpy have -ve sign.

ANSWER .

The enthalpy change of water is -196.32 kJ/kg.

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