Winter 2016 Thermal Engineering - I Question Paper

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GUJARAT TECHNOLOGICAL UNIVERSITY
DIPLOMA ENGINEERING – SEMESTER – IV • EXAMINATION – WINTER - 2016
Subject Code: 3341902  Date:19 -11 - 2016
Subject Name: THERMAL ENGINEERING I
Time: 02:30 PM TO 05:00 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.  Define 1] sensible heat 2] dryness fraction

2.  State four factors affecting the selection of a boiler.

3.  State the function of economizer and fusible plug.

4.  State concept of steam prime-movers.

5.  State the function of condenser and cooling tower in a steam power plant.

6.  Define the following terms with reference to air compressor. 1] isothermal efficiency 2] free air delivered

7.  State four applications of compressed air.

8.  Define 1] conduction 2]convection

9.  State four properties of good insulators.

10.  State the method of measurement of dryness fraction.

Q.2  (a)  What is throttling? Draw throttling process on P-V and T-S diagram.  03

OR

(a)  Explain method of determining dryness fraction by throttling calorimeter with neat sketch.  03

(b)  Find out enthalpy and entropy of steam having pressure of 20 bar and dryness fraction 0.85. Use  mollier chart and also draw sketch.  03

OR

(b)  Explain formation of steam and its various phases.   03

(c)  Explain Cochran  boiler with neat sketch.  04

OR

(c)  Differentiate between boiler mountings and accessories.  04

(d)  Differentiate between induced draft and forced draft fan with reference to boiler.   04

OR

(d)  State the main safety precautions to be taken in boiler house as per IBR.  04

Q.3  (a)  Differentiate between jet condenser and surface condenser.  03

OR

(a)  State the advantages of condensers in steam power plant.  03

(b)  Classify cooling towers and mention why they are used?   03

OR

(b)  Explain natural draught hyperbolic cooling towers with neat sketch.  03

(c)  Derive the condition of maximum discharge through steam nozzle. 04

OR

(c)  Dry and saturated steam at 12 bar pressure enters the nozzle. The pressure is reduced to 1.5 bar. If the expansion if frictionless adiabatic then find out the final velocity.   04

(d)  Differentiate between impulse and reaction turbine.  04

OR

(d)  State the necessity of compounding the steam turbine and explain velocity compounding.  04

Q.4  (a)  Differentiate between reciprocating and rotary compressor.  03

OR

(a)  Explain the need of multistage compression and state its advantages.  03

(b)  A compressor compresses the air from 1 bar to absolute to 7 bar absolute pressure. The clearance volume is 2130 cm3/sec. The compression and expansion is according to PVn= C. If the volumetric efficiency of compressor is 85%, find out the stroke volume. Take n = 1.3.   04

OR

(b)  Draw neat sketch of a single stage reciprocating compressor and explain its working.  04

(c)  Define the following terms. 1] thermal conductivity 2] absorptivity 3] reflectivity 4] emissivity 5] black body 6] emissive power 7] laminar flow  07

Q.5  (a)  A boiler is generating 10 kg of steam/kg of coal. The calorific value of the coal is 35,280 kJ/Kg. The heat content of steam is 2835 kJ/Kg and feed water temperature is 450C. Calculate 1] equivalent evaporation 2] thermal efficiency   04

(b)  State the types of rotary air compressor and explain any one type of air compressor.  04

(c)  State the types of heat exchangers. Describe any one type of heat exchanger with sketch.  03

(d)  State the applications of steam nozzles.  03

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