MULUNGUSHI UNIVERSITY
Pursuing the frontiers of knowledge
SCHOOL OF ENGINEERING AND TECHNOLOGY
MECHANICAL ENGINEERING
MEE 302 – ASSIGNMENT I
Due: 19/03/2023
100 Marks
Question 1[ 20 Marks]
Three heat engines working on Carnot cycle produce work output in proportion of 5: 4: 3 when
operating in series between two reservoirs at 727°C and 27°C.
a) Represent this information on a diagram indicating all energy flows. [5 Marks]
b) Determine the temperature of intermediate reservoirs. [15 Marks]
Question 2 [20 Marks]
A heat pump is run between reservoirs with temperatures of 7°C and 77°C. Heat pump is run
by a reversible heat engine which takes heat from reservoir at 1097°C and rejects heat to
reservoir at 77°C.
a) Represent this information on a diagram indicating all energy flows. [5 Marks]
b) Determine the heat supplied by reservoir at 1097°C if the total heat supplied to reservoir at
77°C is 100 kW. [15 Marks]
Question 3 [20 Marks]
A refrigerator is used to maintain temperature of 243K when ambient temperature is 303K. A
heat engine working between high temperature reservoir of 200°C and ambient temperature is
used to run this refrigerator.
a) Draw a schematic diagram representing this energy flows. [5 Marks]
b) Considering all processes to be reversible, determine the ratio of heat transferred from high
temperature reservoir to heat transferred from refrigerated space. [15 Marks]
Question 4 [20 Marks]
Air expands reversibly in a piston-cylinder arrangement isothermally at temperature of 260°C
while its volume becomes twice of original. Subsequently heat is rejected isobarically till
volume is similar to original. Considering mass of air as 1kg and process to be reversible,
a) Determine net heat interaction, [7 Marks]
b) Determine the total change in entropy. [8 Marks]
c) Show processes on T-S diagram and on a P – V diagram. [5 Marks]
Question 5 [20 Marks]
A heat pump with a coefficient of performance of 3.8 provides energy at an average rate of
75,000 kJ/h to maintain a building at 21C on a day when the outside temperature is 0C. If
electricity costs $0.08 per KWh, Determine,
a) A clear diagram showing the cycle. [3 Marks]
b) The actual operating cost, in $/day [7 Marks]
c) The minimum theoretical operating cost, in $/day. [7 Marks]
d) Compare the results of part (a) with the cost of electrical resistance heating. [3 Marks]