COLLEGE OF ENGINEERING

PUTRAJAYA CAMPUS TEST 2

SEM 2, 2015/2016 PROGRAMME : Bachelor of Mechanical Engineering (Honours) SUBJECT CODE : MEHB 213 SUBJECT : Thermodynamics 1 DATE : Saturday 16th January 2016 TIME : 11am-12:30pm (90 mins) INSTRUCTIONS TO CANDIDATES: 1. DO NOT open the question paper until you are allowed to do so. 2. This paper contains THREE (3) questions and answer ALL questions. 3. Write all answers and their solutions in this booklet. THIS QUESTION PAPER CONSISTS OF 7 PRINTED PAGES INCLUDING THIS COVER PAGE.

MEHB213, Semester 2 2015/16

Name: Student ID:

Lecturer: Section:

Page 2 of 7

QUESTION 1 [15 MARKS] Figure 1 shows a steam turbine that, not only drives a generator but is also used to power an

adiabatic air compressor. Steam enters the turbine at 10 MPa and 550qC at a rate of 20 kg/s

and exits at 10 kPa and a quality of 95%, while having heat loss to the surrounding air at a

rate of 50 kJ/s. Air enters an adiabatic compressor at 100 kPa and 300 K at a rate of 10 kg/s

and exits at 1 MPa and 600 K. Neglecting potential and kinetic energy changes in both

turbine and compressor, determine:

(a) The power required by the compressor (in kW). [5 marks]

(b) The power output of the turbine (in kW). [7 marks]

(c) The power delivered to the generator (in kW). [2 marks]

(d) Provide one way we can increase the power delivered to this generator. [1 mark]

FIGURE 1

1 MPa 600 K

100 kPa 300 K

10 MPa 550qC

10 kPa 95% quality

Generator

50 kJ/s

MEHB213, Semester 2 2015/16

Name: Student ID:

Lecturer: Section:

Page 3 of 7

MEHB213, Semester 2 2015/16

Name: Student ID:

Lecturer: Section:

Page 4 of 7

QUESTION 2 [15 marks]

(a) Can the COP of a refrigerator be less than 1? What about a heat pump? [1 marks]

(b) A refrigeration system uses water-cooled condenser for rejecting the waste heat. The

system absorbs heat from a space at -5 oC at a rate of 24,000 kJ/h. Water enters the

condenser at 15 oC at a rate of 0.65 kg/s. The COP of the system is estimated to be 1.77.

The specific heat of water is 4.18 kJ/kg.oC. Determine:

i. The power input to the system, in kW. [4 marks]

ii. The temperature of the water at the exit of the condenser, in oC. [4 marks]

iii. The maximum possible COP of the refrigeration system. [4 marks]

iv. Draw the schematic diagram of the problem. [2 marks]

MEHB213, Semester 2 2015/16

Name: Student ID:

Lecturer: Section:

Page 5 of 7

MEHB213, Semester 2 2015/16

Name: Student ID:

Lecturer: Section:

Page 6 of 7

QUESTION 3 [20 marks] Air enters a compressor operating at steady state at 100kPa, 300K with a volumetric flow rate of 1 m3/min and is compressed to 400kPa, 600K. The power input is 3.5kW. Ignoring the potential and kinetic energy effects, determine:

(a) The heat transfer rate in kW. (b) The change in specific entropy in kJ/kg.K .

By assuming; (i) Variable specific heat (ii) Constant specific heat.

Which assumption gives more accurate answers (i) or (ii) above?

MEHB213, Semester 2 2015/16

Name: Student ID:

Lecturer: Section:

Page 7 of 7