Q1A In an air standard cycle, air enters the compressor at 0.13MPa and 14 degrees C. The

pressure leaving the compressor is 1.05MPa. The maximum temperature in the cycle is 1135

degrees C. Determine the pressure and temperature at each point in the cycle, the

compressor work, turbine work and cycle efficiency.Check the efficiency using the basic

formula.

T1 = 287.2 K; T2 = 521.98 K; T3 = 1408.2 K; T4 = 775.0 K; η th = 44.95%

Q1B A gas turbine is 46% efficient. Heat lost is 840kJ/kg. Work done by the turbine is

685kJ/kg. Calculate the work done by the compressor.

Wc = 300.4 kJ/kg

Q1C A gas turbines efficiency is 43%. The ambient air pressure is 0.101 MPa. Calculate the

max compressor pressure.

(P2) = 0.72 MPa

Q1d Show the derivation of the basic equation shown below for calculating the efficiency

of an air standard gas turbine engine

Q1e Using diagrams show the component and process diagrams for a Brayton Cycle gas

turbine engine.

Q2A Steam enters a turbine at a temperature of 440 degrees C at a pressure of 5.0MPa.

The condenser pressure is 25kPa. Show the Rankin Cycle on a steam T-s chart and derive all

the values required to calculate the thermal efficiency of the Rankin cycle and the dryness of

steam at entry to the condenser and indicate the heat flows and region of work done.

h1 = 260 kJ/kg h2 = ?kJ/kg h3 = 3300 kJ/kg h4 = 2270 kJ/kg

S1 = 0.83 kJ/kg S3/4 = 6.8 kJ/kg-k Sfg = 7.82 kJ/kg-k X = 0.86

Q2B Calculate, using the values determined from the chart, the Rankin cycle efficiency and

the nett work determined by calculating the heat rejected in the condenser.

ηth = 33.77%; qL = 2010 kJ/kg; Wnet = 1025 kJ/kg

Q2C Check by calculation from values obtained from the chart, the accuracy of your

dryness fraction value obtained from the chart.

85.41% dry

Q2d Critically discuss the effect of lowering the exhaust (condenser) pressure on the

Rankin cycle and describe the ‘Ideal Reheat Cycle’ cycle.

Q3a Explain how a heatpump works using diagrams where necessary and discuss the

problems inherent with using refrigerant gasses.

Q3b Discuss the pattern of use and applications of heatpumps currently used in the UK.

Q3c For domestic space heating for a hospital for the criminally insane, a ground source

heat pump is being used. The pump uses refrigerant R134a and operates with a vapour

pressure of 1.6 MPa. The condenser saturation temperature is 35 degrees C. The volumetric

capacity of the compressor is equivalent to 0.008m^3/s. Considering compression to be

isentropic, and the fluid exiting the evaporator/entering the compressor to be saturated

vapour, use a P-h chart to show the cycle and indicate key enthalpy values and determine

the ideal heating CoP and ideal heating capacity of the system.

h1 = 390 kJ/kg h2is = 430 kJ/kg h3 = 247 kJ/kg h4 = 247 kJ/kg ρ = 8.1 kg/m^3 V = 0.008m^3/s

Ideal Heating CoP = 4.575; Ideal Heating Capacity = 11.59 kW

Q3d For domestic space heating for a lunatic asylum, a ground source heat pump is being

used. The pump uses refrigerant R134a and operates with a vapor pressure temperature of

(– 30degreesC). The condenser saturation temperature is 40 degrees C.

The volumetric capacity of the compressor is equivalent to 0.009m^3/s. The isentropic

efficiency is known to be 68.5%, and the fluid exiting the evaporator/entering the

compressor is considered to be to be saturated vapor, use a P-h chart to show the cycle and

indicate key enthalpy values and determine the value of h2 and plot this on the chart.

h1 = 380 kJ/kg h2is = 435 kJ/kg h3 = 256 kJ/kg h4 = 256 kJ/kg ρ = 4.8 kg/m^3 V = 0.009m^3/s ηis = 0.685

h2= 460 kJ/kg

Q3eA ground source heat pump is used for domestic space heating. The pump, using

refrigerant R134a, operates with the evaporator at a pressure of 2 bar, and a condenser

saturation temperature of 50 C. The compressor may be considered as having a volumetric

capacity of 0.005m3/s.

1 - Initially, considering compression to be isentropic, and the fluid exiting the

evaporator/entering the compressor to be saturated vapor, determine the ideal heating

CoP for the system, and, hence, the heating capacity. Use the appropriate chart provided to

show the cycle, and indicate key enthalpy values.

h1 = 390 kJ/kg h2is = 436 kJ/kg h3 = 270 kJ/kg h4 = 270 kJ/kg ρ = 10 kg/m^3 V = 0.005m^3/s ηis = 1

Ideal Cycle Heating CoP =3.61; Ideal Heating Capacity = 8.3kW

2 - In practice, with the evaporator exit pipe exposed to warm ambient conditions, the

vapour entering the compressor is found to superheated by 15 C, and the compressor has

an actual isentropic efficiency of 75%. Sketch this more realistic cycle on the chart provided.

Determine the enthalpy of the vapour at exit from the compressor.

h1 = 402 kJ/kg h2is = 4448 kJ/kg h3 = 270 kJ/kg h4 = 270 kJ/kg ρ = 9.2 kg/m^3 V = 0.005m^3/s ηis = 0.75

h2= 463 kJ/kg;

3 - Calculate the heating CoP and heating capacity for the plant operating under these

conditions.

Non ideal, real Heating CoP = 3.16; Non ideal, real Heating capacity = 8.88 kW

4- Considering your answers to questions a), b) and c) above, critically discuss the potential

performance benefits and draw backs of the vapour being superheated before entering the

compressor.

5- Determine and discuss the viability of using the high temperature gas exiting the

compressor for domestic hot water heating in addition to space heating.

Potential hot water heating capacity = 1.296kW

Heating required for 160L tank heated to 50degreesC = 6.53 kWh

Q4a A bio-mass fuel contains by mass 89% C, 7%H2, 1%S and 3% ash (silica). Calculate the

Stoichiometric air.

Stoichiometric ratio = 12.58:1

Q4c For Ethane and Octane, calculate the amount of CO2 produced per kg of fuel burned.

2.93 Kg CO2/kg Ethane burned; 3.09 Kg CO2/kg Octane burned

Q4d If the LCV of Ethane is 47.8MJ/kg and LCV for Octane is 44.4MJ/kg calculate kg of CO2

per MJ.

Ethane= 0.061 kgCO2/MJ

Octane = 0.070 kgCO2/MJ

Q4e Critically discuss the combustion process using diagrams where necessary.

Q5 Part A Using the equivalences and data shown below, calculate the RPM at which

the pump must run to deliver the required flow of water and the diameter of pipe required

to permit this flow using the data given in the following table.

Data obtained from analysis of manufacturers pump curves

NA 1200 RPM

QA = Flow rate (Optimal) 0.032m^3/s

HA = Head (Optimal) 64m

HB = Total head 32m

QB = Flow required 0.0160m^3/s

DA = Rotor diameter 115 mm

Equivalences

96.87 mm pipe is required with the pump running at 1009 RPM

Q5b A fan is pushing air along a 0.25m diameter pipe at a uniform velocity of 0.12m/s.

The air temperature is 25 degrees C and the pressure is 170kPa. Taking the value for R to be

0.287, determine the mass flow rate of the air and QA.

The mass flow rate of the air is 0.0116kg/s

Q5c Briefly define the causes of ‘Cavitation’ in pumps and discuss how evidence of

cavitation might show itself and how this may affect the pump’s performance.

Q5d A centrifugal pump has the following characteristics

QA (m^3/h) 0 23 46 69 92 115

HA (m) 17 16 13.5 10.5 6.6 2

η (%) 0 49.5 61 63.5 53 10

The pump has to pump water from a low reservoir to a high reservoir through a total length

of 800m of pipe which is 15 cm in diameter. The difference between the water levels in the

reservoirs is 8m. Neglecting all losses except friction and assuming f = 0.004, find the rate of

flow between the reservoirs. Also determine the power input to the pump

h = 11.9mQ res = 60m^3/h and Q res also = 0.017m^3/s η = 65% = 0.65

Power of pump = 3.047kW

Q5e The motor of a large feed-water pump draws 30 KW of electrical power from a 3

phase mains supply. The pump has the following operating characteristics. Calculate the

pump efficiency.

Flow rate = 55L/s,

Initial Pressure head (Hp)= 380 KPa

Suction lift = 2m

Head = 5m

57.8%

Q5f Using diagrams where necessary, briefly discuss methods and considerations for pump

selection.