Question

An ideal gas (C_p = 30 kJ / kmol.K) at 1 MPa and 295 K, enters a thermally and mechanically isolated device. Half of the gas with the flow rate of 1 kmol / s is leaving the device at 355 K and 100 kPa, the other half of the gas is leaving the device at 235 K and 100 kPa. Is this process suitable for thermodynamic laws?

Answer 1

To be suitable for thermodynamics laws, here the enthalpy balance should be valid. Hence we will enthalpy balance on the above system and see

Since there is no heat transfer and also no work done. Entjaloy at inlet should equal enthalpy outlet

Let inlet Enthalpy be H 1, out enthalpy 2 be H2 and outlet enthalpy of other stream be H3

By enthalpy balance. H1 = H2 + H3

For this we will do H = Cp*dT

Now we can take any reference temperature as per our choice

To simplify calculation will take T =295 K as reference temperate.

Now stream is itself entering at 295 K

Hence H 1= Cp(295-295)=0

Now let us evaluate other two enthalpy

H2=Cp*(355-295)= 60*Cp

H3 = Cp*(235-295) = - 60*Cp

Now we will apply an overall enthalpy balance

H1 = H2 + H3

0 = Cp*60 - Cp*60=0

Since the enthalpy balance is getting satisfied

The energy balance is satisfied and the above system does follow thermodynamic law