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GUJARAT TECHNOLOGICAL UNIVERSITY
Diploma Engineering - SEMESTER–IV • EXAMINATION – WINTER • 2014
Subject Code: 3341902 Date: 28-11-2014
Subject Name: Thermal Engineering-I
Time: 02:30 pm - 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. English version is considered to be Authentic.
Q.1 (a) 1. Define two phase system and show on T-S diagram from 0° C water to superheated steam. 03
2. Define followings
( i ) Dryness fraction
(ii) Sensible heat
(iii) Triple point
(iv) Compressed liquid 04
(b) Explain the process of finding dryness fraction using throttling calorimeter with neat sketch. 07
Q.2 (a) Using steam table find entropy, enthalpy and volume of 5 kg wet steam having dryness fraction 0.86 at 20 bar pressure. 07
(b) 1. Differentiate between fire tube and water tube boiler. 03
2. What is the difference between mounting and accessory explain water level indicator. 04
OR
(b) During trial on a boiler following data has been recorded (i) Steam produced 2500 kg/hr (ii) Coal used 250 kg/hr (iii) Feed water temperature 40° C (iv) Quality of steam dry and saturated (v) Calorific value of coal 30000 KJ/kg (vi) Pressure of steam boiler 12 bar. Find 1. Actual evaporation 2. Equivalent evaporation 3. Thermal efficiency of boiler. 07
Q.3 (a) 1. Draw heat balance sheet of boiler. 03
2. Differentiate between impulse turbine and reaction turbine. 04
(b) Why compounding of steam turbine is necessary? State three types of compounding and explain any one with diagram. 07
OR
Q.3 (a) 1. Define prime movers, give classification of steam turbine. 03
2. Compare jet condenser with surface condenser. 04
(b) What is cooling tower? State types of cooling tower and explain induced draft cooling tower. 07
Q.4 (a) Draw schematic diagram of single stage reciprocating air compressor and explain its working with P-V diagram. 07
(b) Write advantages and disadvantages of multi stage compression and intercooling. 07
OR
Q. 4 (a) Derive an expression for condition of maximum efficiency in case of two stage reciprocating compressor. 07
(b) Find out minimum work required to compressed 2 kg of air in two stages from 10 N/cm2 and 30° C to 160 N/cm2 with perfect inter cooling. Take R=0.287 KJ/kg° K and Index n=1.3 07
Q.5 (a) Explain various modes of heat transfer with examples. 05
(b) Find out rate of heat transfer from an I.C. Engine whose wall temperature is 260° C, area of surface is 0.4 m2,atmospheric temperature is 35° C and heat
transfer coefficient is 60 w/m2 k. 05
(c) Define (i) Absorptivity (ii) Overall heat transfer coefficient (iii) Black body (iv) Emissive power. 04
OR
Q.5 (a) State types of heat exchangers and write application of each of them. 05
(b) A boiler shell is made up of MS plate of 50 mm thick which is insulated by 10 mm lagging material inside the shell. The temperature of outside and inside of boiler are 30° C and 300° C. Considering thermal conductivity of MS plate and insulated material are 160 and 0.15 KJ/h m° K respectively.Find out overall heat transfer coefficient and heat transfer per unit area. 05
(c) State Fourier law for conduction. Why negative sign attach with temperature gradient 04
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