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GUJARAT TECHNOLOGICAL UNIVERSITY
DIPLOMA ENGINEERING – SEMESTER – IV • EXAMINATION – SUMMER- 2016
Subject Code: 3341902 Date: 12- 05- 2016
Subject Name: Thermal Engineering - I
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make Suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Use of programmable & Communication aids are strictly prohibited.
5. Use of only simple calculator is permitted in Mathematics.
6. English version is authentic.
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Q.1 Answer any seven out of ten. 14
1. What is two phase system? Give two examples of it.
2. Define: (a) Pure substance (b) Evaporation
3. List five industrialapplications of steam.
4. Define: (a) Boiler mountings (b) Boiler accessories
5. List five applications of steam nozzles.
6. Why is compounding of simple steam turbine necessary?
7. List five elements of steam condensing plant.
8. Give four advantages of Hyperbolic cooling tower.
9. Define “Volumetric efficiency” in context with air compressor.
10. Define “Thermal conductivity” and give its unit.
Q.2 (a) Draw only neat sketch of High level jet condenser and labelit. 03
OR
(a) List advantages and disadvantages of surface condenser. 03
(b) Draw only neat sketch of Babcock-Wilcox boiler and label it. 03
OR
(b) List advantages and disadvantages of Lancashire boiler. 03
(c) State four differences between Natural draft and Artificialdraft in context with steam boiler. 04
OR
(c) Explain Bourdon tube pressure gauge with neat sketch. 04
(d) State four differences between Reciprocating and Rotary aircompressors. 04
OR
(d) What is intercooling in context with air compressor? List advantages of intercooling. 04
Q.3 (a) State the function of (1) Blades (2) Casing (3) Governing system in context with steam turbine. 03
OR
(a) Define “Steam nozzle”. Drawneat sketches of two main typesof nozzles along with velocity and pressure distribution curves. 03
(b) Explain working principle of Impulse steam turbine with neat sketch. 03
OR
(b) State advantages and disadvantages of velocity compounding. 03
(c) Derive an equation for outlet velocity of steam through nozzle by applying steady flow energy equation. 04
OR
(c) Steam enters a nozzle with a velocity of 350 m/s at a pressure of 4 bar with
dryness fraction of 0.95, and expands isentropically to 2.2 bar. Using
following table, find out change in enthalpy and exit velocity of steam.
(d) State advantages of multistage air compression. 04
OR
(d) With the help of p-v diagram, explain intercooling in 2 - stage air compression. 04
Q.4 (a) State and explain in briefvarious modes of heat transfer. 03
OR
(a) On a substance, 54.5 KW energy is incidenting out of which the radiation absorbed is 21.6 KW and the radiation reflected is 11 KW. Calculate Reflectivity, Transmissivity and absorptivity of the substance. 03
(b) Differentiate between Free convection and Forced convection. 04
OR
(b) Define “Heat exchanger”. With the help of neat sketches explain in brief the parallel flow, counter flow and cross flow heat exchangers. 04
(c) In a boiler, 525 Kg/hr of coal is used to produce 5200 Kg/hr of steam at a pressure of 15 bar and temperatureof 250º C. The feed water temperature is 27º C and the CV of fuel is30000 KJ/Kg. Assuming Cp of water =4.2 KJ/KgK and Cp of steam = 2.1 KJ/KgK, calculate: (1) Equivalent evaporation (2) Boiler efficiency (3) Boiler power.
At 15 bar pressure, specific enthalpy of steam (gas) is 2789.9 KJ/Kg and saturation temperature of steam is 198.3º C. 07
Q.5 (a) Explain in brief:
(1) Stefan-Boltzmann’s law of total radiation (2) Emissivity 04
(b) Draw the Mollier chart. Show Throttling process and Critical point in it. 04
(c) Explain in brief the working ofEconomiser with neat sketch. 03
(d) Using following table, find out the enthalpy and entropy of5 Kg of steam at
14 bar pressure and 300º C temperature. Take Cp of steam = 2.1 KJ/KgK.
Saturation temperature at14 bar pressure is 195º C.
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