Tut 5

Energy balance

a)What type of work is done on the gas? Ans: Mechanical work

if the work done on the system is 14800J

Ans: closed system : Q +W =U , isothermal process T is constant → U=0

→ Q +W =Q = -W → Q= -14800 J

Q2) Air is cooled in a constant volume process from T1 to T2. Show that H= ∫T 1

T 2

cpgas dt assume

that the gas at T1 & T2 in the gas phase

Q3) Show that for a steady state open process the energy balance reduces to

mout(H out) – min(Hin) = Q + W (you can neglect PE & KE)

Q4) Three hundred L/h of 20 mole% C3H8, 80% n-C4H10 gas mixture at 0oC and 1.1 atm and 200 L/h of a 40 mole% C3H8-60% n- C4H10 gas mixture at 25C and 1.1 atm are mixed and heated to 227oC at constant pressure.

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b)

Q1)

a) Find n1 , n2, n3

b) Calculate the heat requirement of the process.

Enthalpies of propane and n-butane are listed below. Assume ideal gas behaviour.

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Conversion 60%P

Q5)

a) Calculate the enthalpy for the input and the output streams

b) Make degree of freedom analysis

Use the element material balances & the energy balance to find the unknown stream variables

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