Part -1:
1. (a) Explain the differences between fire-tube boilers and water-tube boilers with respect to the following:
• construction
• operation
• main mechanisms of heat transfer
• properties and uses of steam produced.
(b) Discuss the major factors which affect the choice of boiler type for particular applications.
(c) A boiler produces superheated steam at 40 bar and 350°C from feedwater at 30°C. The higher heating value (calorific value) of the fuel is 45 MJ kg-1 and the heat from each kg of fuel generates 13.1 kg of steam. Calculate the boiler efficiency based on the higher calorific value of the fuel.
2. (a) Using brief notes explain the function of the following components which make up a steam production and power plant system:
(1) water treatment plant
(ii) de-aerator
(iii) feedwater pumps
(iv) combustion air pre-heater
(v) economiser
(vi) boiler
(vii) steam drum
(viii) superheater
(ix) turbine
(x) condenser
(xi) generator.
(b) Construct a simple block diagram to show these major components of a steam production and power plant system in their correct sequence.
(c) A surface condenser is to be designed to condense 150 000 kg h-1 of dry saturated steam at 0.05 bar. If the overall heat transfer coefficient is 11.5 kW m-2 K-1 and the inlet and outlet water temperatures are 14°C and 24°C respectively, calculate the heat transfer surface area required.
3. (a) Using simple sketches describe the construction and operating principles of the following:
(i) reciprocating compressors
(ii) centrifugal compressors.
(b) Explain the meaning and importance of the phrase 'multi-stage compression with interstage cooling'.
(c) A three-stage compressor takes air at a pressure of 0.96 bar and delivers it at 12 bar. Assuming the intermediate pressures are in geometric progression, find the two intermediate pressures. Take the gas constant R for air as 0.287 Id kg-1 K-1.
(d) Discuss four examples of the use of compressed air in industry.
4. (a) State the two main groups of compressor in industry and explain the differences between them with respect to method of compression, compression ratio and capacity. Quote an example from each group.
(b) Discuss the factors which affect the choice of a compressor type for particular application.
(c) Select a suitable compressor for each of the following applications; state whether single or multi-stage is indicated.
(i) A capacity of 1000 m3 h-1 at a pressure of 9 bar at a steady non-pulsating flowrate.
(ii) A capacity of 10 000 m3 h-1 at a pressure of 100 bar.
(iii) A capacity of 100 m3 h-1 at 100 bar.
Part -2:
1. (a) Write brief notes to explain the function and importance of the following with respect to steam distribution systems:
(i) thermal expansion devices
(ii) air vents
(iii) steam traps
(iv) pressure reducing valves
(v) pressure relief valves
(vi) insulation (lagging).
(b) Explain why it is important to remove water from steam distribution systems and describe two ways in which it may be achieved.
(c) It is proposed that an existing pipeline, which has a nominal diameter of 100 mm, will be used to return condensate from a new piece of process plant. Operating considerations dictate that the pressure in the pipeline must not fall below 2 bar, and the condensate velocity must not exceed 30 ms-1. If the steam pressure in the process plant is to be 8 bar, what would be the maximum condensate flow rate in the return line?
2. (a) Explain the function of the following with respect to the production and distribution of compressed air:
(i) air intake filter
(ii) air silencer
(iii) air compressor
(iv) intercoolers
(v) after cooler
(vi) receiver
(vii) ring main
(viii) auto-drain trap.
NOTE: you may need to refer to your own experience or standard reference books to fully answer parts of this question.
(b) Draw a block diagram to represent the essential stages in the production and distribution of compressed air to users.
(c) Compressed air is delivered through a pipe which is 60 m long and has a nominal bore of 80 mm. If the air is at 5 bar and 20°C, and experiences a drop in pressure of 4000 N Irr2 as it flows through the pipe, find its mass flow rate. Take the friction factor as 0.007 and the gas constant for air as 0.287 kJ kg-1 K-1.
3. NOTE: You may need to refer to standard reference books or your own experience to answer parts of this question.
(a) Explain the function of the following with respect to refrigeration using the vapour compression cycle:
(i) compressor
(ii) oil separator/filter
(iii) cooler
(iv) expansion valve (throttle valve)
(v) refrigerator/evaporator
(vi) connecting pipework.
(b) Draw a block diagram to represent the essential stages (in the order that they occur) in the vapour compression cycle. Indicate where energy enters and leaves the cycle.
(c) State two industrially important refrigerants used in industry, stating one advantage and one disadvantage for each.
(d) Suggest two signs which would indicate that a vapour compression refrigerator has an insufficient charge of refrigerant.
(e) Explain the operation and uses of heat pumps.
4. A vapour compression refrigerator, with ammonia as refrigerant, works between 2.908 bar and 12.37 bar. The temperature after isentropic compression is 82°C and the condensate is undercooled by 8°C in the condenser. Determine the coefficient of performance of the cycle?
5. Suggest a suitable pressure at which dry saturated steam should be supplied to a calorifier (heater) to maintain a chemical process at 140°C, and calculate how much steam would be condensed to provide heat at the rate of 7000 MJ h-i. Allow a temperature difference of 25°C between the steam and the process fluid for effective heat transfer.
6. What two features of the planned drainage provisions for the vessels A, B and C shown in FIGURE 1 are incorrect?
