Winter 2015 Thermal Engineering - I Question Paper

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GUJARAT TECHNOLOGICAL UNIVERSITY
DIPLOMA ENGINEERING – SEMESTER – IV-EXAMINATION – WINTER 2015
Subject Code: 3341902  Date: 17/12/2015
Subject Name: Thermal Engineering-I
Time: 02:30 PM TO 5:00 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.  Explain Triple Point and Critical Point of  H2O.

2.  Define : (i) Degree of Superheat (ii) Sub- cooled liquid.

3.  Write in brief about “Indian Boiler Act”.

4.  Mention the function of Economiser and Air Pre-heater.

5.  What is Draft ? List any two important advantages of draft.

6.  Differentiate between Black body and Gray body.

7.   List any two properties of good insulating material. Give the value of thermal conductivity of Pure Copper and Glass Wool.

8.  Why small clearance is needed in Reciprocating Air Compressor ?

9.  State the methods for detection of air leakage in Condenser.

10.  State the functions of Steam Nozzle.

Q.2  (a)    Find the change in enthalpy when 4 Kg of water is evaporated from 30oC to dry saturated steam at a pressure of 17 bar. Take specific heat of water (Cpw) = 4.187 KJ/ Kg oK.  03

OR

(a)  1 Kg. of steam initially at a 5 bar absolute pressure and temperature of 200oC is isentropically expanded up to wet steam of 0.84 dryness fraction. Find change in enthalpy and final pressure with the help of Mollier Diagram only.   03

(b)  State the purpose of Super Heater in steam power plant.  03

OR

(b)  State the points for Boiler Inspection and explain any one of them.  03

(c)  Explain Throttling Expansion Process of steam by p-v, T- S and h-s diagram.  04

OR

(c)  Explain measurement of dryness fraction of steam by Combined Separating and Throttling Calorimeter with neat sketch.  04

(d)  Explain the working of Babcock and Wilcox boiler with simple figure.  04

OR

(d)  What do you understand by “Heat Balance” in a boiler ?  04

Q.3  (a)The following data was collected during a boiler trial :
(1) The pressure of steam generated = 12 bar.
(2) Condition of steam = 0.9 dry.
(3) Feed water temperature = 36oC.
(4) Average quality of steam generated = 2500 Kg/hr.
(5) Coal used = 300 Kg/hr.
(6) Calorific value of coal = 28000 KJ/Kg.
(7) Specific heat of water = 4.187 KJ/Kg K.     03

OR

(a)  A boiler producing 5000 Kg steam/hr at a 20 bar pressure. Temperature of steam is 300 o C and feed water is 50oC. Efficiency of boiler plant is 80%. If fuel consumption is 3500 Kg/hr, find out calorific value of a fuel oil. Take specific heat for steam and water as 2.1 KJ/Kg and 4.187 KJ/Kg respectively.   03

(b)  State the purpose of Cooling Tower and explain any one of them with sketch.  03

OR

(b)  State the functions of a Condenser. Draw a neat sketch of a Surface Condenser.   03

(c)  Explain pressure compounding for Impulse Turbine with sketch of general arrangement and graphical presentation of variation of pressure, velocity and specific volume.  04

OR

(c)  Define Prime Mover. Explain the working of simple steam engine with sketch.  04

(d)  Steam super heated by 80 o C and 17 bar pressure is expanded through a convergent- divergent nozzle up to 0.7 bar pressure . If the exit diameter of nozzle is 2.48 cm, then find out the flow of steam in Kg/sec.   04

OR

(d)  Assuming isentropic expansion, Calculate the exit area of nozzle , if steam  04 at a pressure of 12 bar and temperature of 250 o C is expanded in a nozzle to 2 bar . The mass flow rate of steam is 0.21 Kg/sec.

Q.4  (a)  Explain Jet condenser. State its limitations.  03

OR

(a)  What is multistage compression? State its advantages.  03

(b)  0.6 m3/min of air is compressed in a compressor from 1 bar to 10 bar pressure. Considering isothermal efficiency as 80%, determine indicated power of compressor.    04

OR

(b)  1 Kg of air at 1 bar and 27o C is compressed to 16 bar, compression index is 1.3. Assuming R = 0.287 KJ/Kg K and there is a perfect inter-cooling. Neglecting the clearance effect, calculate necessary minimum work done/Kg for compression.   04

(c)  Defferentiate between Reciprocating and Rotery Compressor.  07

Q.5  (a)  Explain Stefan-Boltzman Law of Radiative Heat Transfer. Write its equation indicating units of each symbol.  04

(b)  A boiler shell is made up of M.S. plate 50 mm thick which is insulated by 10 mm logging material. Outside and inside temperature of boiler are 30oC and 260oC respectively. If thermal conductivity of M.S. and logging material are 150 KJ/hr m K and 10 KJ/hr m K respectively, then find overall heat transfer co-efficient and heat transfer/unit area.  04

(c)  Write the basic equation of Convection and state factors which are affecting convective heat transfer.   03

(d)  Define thermal conductivity and explain Fourier , s Law of Conduction.    03

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