CCB 2024 Chemical engineering thermodynamics Sept 2014

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Tutorial No. 1 (Lecture 1-3)

Questions

1. A mass of 1.2 kg of air at 150 kPa and 12oC is contained in a gas-tight, frictionless piston-

cylinder device. The air is now compressed to a final pressure of 600 kPa. During the process,

heat is transferred from the air such that the temperature inside the cylinder remains

constant. Calculate the work done during this process. Given, the gas constant of air is 0.287

kJ/kg. K.

2. One mole of an ideal gas with Cp=(7/2)R and Cv=(5/2)R expand from P1=8 bar and T1=600K

to P2=1 bar by each of the flowing paths:

(a) Constant volume (b) Constant temperature (c) Adiabatically

Assuming mechanical reversibility, calculate W, Q, ΔU, and ΔH for each process. Sketch each

on a single PV diagram.

3. The reading on a mercury manometer at 25oC (open to the atmosphere at one end) is 56.38

cm. The local acceleration of gravity is 9.832ms-2. Atmospheric pressure is at 101.78 kPa.

What is the absolute pressure in kPa being measured? (The density of mercury at 25oC is

13.534 gcm-3)

4. One kilogram of air is heated reversibly at constant pressure from an initial state of 300K and

1bar until its volume triples. Calculate W, Q, ΔU, and ΔH for the process. (Assume for air that

PV/T = 83.14 bar cm3 mol-1 K-1 and Cp = 29 J mol-1 K-1).

5. One cubic meter of an ideal gas at 600 K and 1000 KPa expand to five times its initial

volume as follows:

(a) By a mechanically reversible, isothermal process

(b) By a mechanically reversible, adiabatic process

(c) By an adiabatic, irreversible process in which expansion is against a restraining

pressure of 100KPa

For each case calculate the final temperature, pressure and the work done by the gas. Cp=21

Jmol-1K-1.

6. One mole of an ideal gas, initially at 30°c temperature (303.15 K) and 1 bar, is changed to

130°c(403.15 K) and 10 bar by three different mechanically reversible processes:

The gas is first heated at constant volume until its temperature is 130°c; then it is

compressed isothermally until its pressure 10 bar

The gas is first heated at constant pressure until its temperature is 130°c; then it is

compressed isothermally to 10 bar

CCB 2024 Chemical engineering thermodynamics Sept 2014

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The gas is first compressed isothermally to 10 bar; then it is heated at constant pressure

to 130°c

Calculate W, Q, ΔU, and ΔH for each case, of the cycle. Take Cp=(7/2)R and Cv=(5/2)R.

alternatively, take Cp=(5/2)R and Cv=(3/2)R.

7. Determine the pressure of water vapor at 350 °C and 0.035262 m3/kg, using

(a) The ideal gas equation, and

(b) The generalized compressibility chart

Which method is suitable if the experimental value of is 7.0 MPa? Justify?

8. Determine Z and V for steam at 250oC and 1800 kPa by the following:

(a) The truncated virial equation with the following experimental values:

B = -152.5 cm3mol-1 C = -5800 cm6mol-2

(b) The steam tables.