1. (a) A vacuum gauge indicates a pressure of 0.1kgf/cm2 at the exit of a turbine. If the

mercury barometer gives local atmospheric pressure as 750 mm Hg, what is the absolute

pressure at the exit of the turbine in kPa? Take relative density of mercury as 13.6. (4

marks)

(b) An electric generator coupled to a windmill produces an average electric power

output of 15 kW. The power is used to charge a storage battery. Heat transfer from the

battery to the surroundings occurs at a constant rate of 1.8 kW. For 8h of operation,

determine the change in energy stored in the battery, in kJ. (4 marks)

2. (a) 5kg of air is contained in a vertical piston - cylinder assembly. The piston has mass

50 kg and face area 0.01m2 and atmosphere exerts a pressure of 100 kPa on the top of the

piston. Initially air occupies a volume of 5litres and it slowly reduces to 0.002m3 as its

specific internal energy decreases by 260 kJ/kg. Neglecting friction between the piston

and the cylinder wall and kinetic and potential energy changes, determine the heat

transfer to the air, in kJ. (6 marks)

(b) A piston cylinder assembly containing 1 kg of steam at 1 MPa and 60% quality is

heated. The piston does not move until the system pressure reaches 1.5MPa and then it

moves at constant pressure till the temperature becomes 400oC.Plot the process and

determine the work and the heat interactions. (8 marks)

3.a) Derive steady-state steady flow first law of thermodynamics equation for a flow

process (5 Marks)

b) Air, with a mass flow rate of 0.5kg/s, enters a steady flow compressor at 30oC and

leaves at 150oC. Upon leaving the compressor it is cooled in a heat exchanger to 30oC. In

the heat exchanger, water enters at 20oC and leaves at 50oC. Assuming air to be an ideal

gas with Cp = 1.005 kJ/kg, determine (a) the compressor power input and (b) the mass flow

rate of water (8 marks)

4.(a) Water is used as the working fluid in a Carnot cycle heat engine, where it changes

from saturated liquid to saturated vapor at 200°C as heat is added. Heat is rejected in a

constant-pressure process (also constant T) at 20 kPa. The heat engine powers a Carnot-

cycle refrigerator that operates between -15 oC and +20 oC, Find the heat added to the

water per kg water. How much heat should be added to the water in the heat engine so the

refrigerator can remove 1 kJ from the cold space? ( 8 marks)

(b) Water at 200 kPa with x = 1.0 is compressed in a piston cylinder to 1 MPa and 350°C

in a reversible process. Find the sign convention for the work and the heat interactions.

(4 marks)

5. (a)Two air streams both at 200 kPa; one is of 1 kg/s at 400 K, and the other is of 2 kg/s

at 290 K. The two flows are mixed together in an insulated box to produce a single exit

flow at 200 kPa. Find the exit temperature and the total rate of entropy generation. (8

marks)

(b). A large slab of concrete, 5 m x 8 m x 0.3 m, is used as a thermal storage mass in a

solar-heated house. If the slab cools overnight from 23°C to l8°C in an house, what is the

change in entropy of i) the concrete slab, ii) the surroundings and iii) the net change in

entropy if the house is at l8°C? ( concrete = 2200 kg/m3, C concrete = 0.88 J/KgK) (8 marks)

6. State carnot's principles. Prove that for a given hot and cold reservoirs, maximum

efficiency will be for reversible heat engine. ( 5 marks)

7. The compression ratio of an air standard Otto cycle is 9.5.Prior to isentropic

compression process, the air is at 100kPa, 35C,and 600 cm3.the temperature at the end of

isentropic expansion process is 800K.Using specific heat values at room

temperature ,determine (a) the highest temperature and pressure in the cycle ;(b) the

amount of heat transferred in kJ; (c) thermal efficiency ; and(d) the mean effective

pressure.(8 marks)

8. Refrigerant-134 a enters the compressor of a refrigerator as superheated vapor at 0.14

MPa and -10 oC at a rate of 0.12 kg/s, and it leaves at 0.7 MPa and 50 C . the refrigerant

is cooled in the condenser to 24 C and 0.65 MPa, and it is throttled to

0.15MPa.Disregarding any heat transfer and pressure drops in the connecting lines

between the components ,show the cycle on a T-s diagram with respect to saturation

lines, and determine (a) the rate of heat removal from the refrigerated space ,(b) power

input to the compressor ,(c)the isentropic efficiency of the compressor , and (d) the

coefficient of performance. (10 marks)

9. Using the four Gibbs equations, derive the Maxwell relations for a simple

compressible substance. (9 marks)