Calculate the enthalpy of 3 kg of fluid that occupies a volume of
| Calculate the enthalpy of 3 kg of fluid that occupies a volume of 1.5 m3/kg, if the internal energy is 3.5 MJ/kg and the pressure is 0.3 MN/m2
A. 3.95 MJ
B. 3.65 MJ
C. 10.95 MJ
D. None of these
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Right Answer is: D
SOLUTION
\(Enthaply(H)\; = \;U + PV\; = \;m\left( {u + Pv} \right)\; = \;3\left( {3.5 + 0.3 \times 1.5} \right)\; = \;11.85\;MJ\)
Mistake Point
when P is in Pa and V is in m3 then the unit of work done is (W = PV) J.
when P is in Pa and V is in m3/kg then the unit of work done is (W = PV) J/kg.
Here internal energy is specific internal energy (MJ/kg) but PV work is also in MJ/kg.
That's why with (u + Pv), we get specific enthalpy which is multiplied with mass to get enthalpy.
h = u + Pv
H = U + PV = m(u + Pv)