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GUJARAT TECHNOLOGICAL UNIVERSITY
Diploma Engineering - SEMESTER–VI • EXAMINATION – WINTER • 2016
Subject Code: 3361907 Date: 26-10-2016
Subject Name: THERMAL SYSTEM & ENERGY EFFICIENCY
Time: 10:30 am - 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. State different sources of energy
2. State various Thermal systems applicable to industries.
3. Define Cogeneration system.
4. State main provisions of the EC act, 2001.
5. Give classification of Heat Exchanger.
6. What is meant by LMTD?
7. Define Free Air Delivery?
8. Give the classification of industrial furnace.
9. Define ton of refrigeration?
10. What is the relation between COP and kW/ton of refrigeration?
Q.2 (a) List various sources of sensible heat loads in refrigeration. 03
OR
(a) List various sources of Latent heat loads in refrigeration. 03
(b) Explain flywheel effect of building materials. 03
OR
(b) Explain heat gain through glass. 03
(c) A hall to air conditioned foe a sitting capacity 500 persons Indoor condition: 260C dbt and 60% RH. Outdoor condition: 300C dbt and 50% RH. Ventilation air 0.30 m3/person. Calculate the sensible heat load, latent heat load 04
OR
(c) In a coldstorage 20T mango is store at 150C for 20 hr. The outside temperature is 380C and specific heat of mango is 3.4 kJ/kg 0K. Calculate the cooling load. 04
(d) Explain the energy conservation in refrigeration and air conditioning system. 04
OR
(d) Differentiate between infiltration and ventilation air. 04
Q.3 (a) What are the major factors affecting the industrial furnace performance? 03
OR
(a) Explain various industrial furnace losses with sankey diagram 03
(b) What are the various instruments required for performance evaluation of industrial furnace. 03
OR
(b) How do you determine excess air level in an industrial furnace? 03
(c) Oil-fired reheating furnace has an operating temperature of around 1340°C. Average fuel consumption is 400 litres/hour. The flue gas exit temperature is 750 °C after air preheater. Air is preheated from ambient temperature of 40 °C to 190 °C through an air pre-heater. If Specific gravity of oil is 0.92. CV of oil is 10000 kCal/kg. Average O2 percentage in flue gas is 12%. Air Fuel ratio is 14:1 and Specific heat of flue gas is 0.25 kCal/kg0C.Calcute the sensible heat loss. 04
OR
(c) Explain the working of rotary hearth furnace. 04
(d) 12TPH billet is heated in furnaces. The temperature of billet is heated form 400C to 11000C. The consumption of oil in furnaces is 750 liters/hr with specific gravity of 0.92 and CV is 9700 kCal/kg. The billet specific heat is 0.12 kCal/kg0C. Calculate i) % heat loss in furnaces ii) Efficiency of furnaces. 04
OR
(d) Explain with neat sketch why proper heat distribution is required in the furnace system? 04
Q.4 (a) The following are the data collected for a boiler using coal as the fuel. Find out the boiler efficiency and evaporation ratio by direct methodSteam generated :8TPH Quantity of coal consumed: 1.5 TPHSteam pressure: 10 kg/cm2GVC of coal: 3995 kCal/kgTemperature of steam: 1800C Enthalpy of steam: 660 kCal/kgFeed water temperature: 850C 03
OR
(a) Boiler efficiency by indirect method is more useful why? 03
(b) The following are the data collected for a boiler using furnace oil as the fuel.
Ultimate analysis (%) Flue gas analysis (%)
Carbon = 85
Hydrogen = 10
Nitrogen = 0.8
Oxygen = 1.1
Sulphur = 1.1
Moisture = 0.7
Flue gas temperature = 240°C
Ambient temperature = 28°C
CO2% in flue gas by volume = 11
O2% in flue gas by volume = 8
Calculate (1) Theoretical air required (2) Excess Air supplied (EA) (3) Actual mass of air supplied/ kg of fuel (AAS) 04
OR
(b) Calculate the rise of feed water temperature by providing an economizer to boiler; generate the steam of 10T. The inlet and outlet temperature of flue gas is 330°C and 180°C respectively. The air fuel ratio is 21:1 and boiler evaporation ratio 10. Neglecting bolwdowen and condensate recovery. (Cpg= 0.23kCal/kg°C ) 04
(c) The following are the data collected for a boiler. Find out the boiler efficiency by indirect method. 07
Carbon content in fuel (C)= 84%
Hydrogen content in fuel (H)= 10%
Moisture content in fuel (m)= 0.3%
Ambient temperature = 35°C
Flue gas temperature = 190°C
Humidity in ambient air = 0.023kg/kg of dry air
GCV of fuel= 9,600 Kcal/kg
Surface temperature of boiler= 85°C
Sp. Heat of flue gases= 0.23kCal/kg °C
Sp. Heat of super-heated steam=0.45kCal/kg °C
Mass of dry flue gas= 25.36kg/kg of fuel
Actual mass of air supplied/kg of fuel=22.49kg/kg of fuel
Radiation & convection losses= 0.32%
Losses due to incomplete combustion= 0.02%
Q.5 (a)In a double pipe heat exchanger hot fluid is entering at 220°C and leaving at 115°C. Cold fluid enters at 10 deg c and leaves at 75°C. Mass flow rate of hot fluid 100 kg/hr, cp of hot fluid 1.1 kcal/kg°C. Cp of cold fluid 0.95kcal/kg°C. Calculate LMTD i) If the flow is parallel , ii) If the flow is counter current. 04
(b) During the reciprocating air compressor testing following parameters are measured calculate Isothermal Efficiency.Flow coefficient : 1 Temperature before the nozzle 40°C Nozzle diameter : 0.08 metre Pressure drop across the nozzle:0.036 kg / cm2Receiver Pressure: 3.5 kg / cm2Gas constant : 287 Joules / kg KInlet Pressure: 1.04 kg / cm2Motor input power :100 kWInlet air temperature: 30°C Motor and drive efficiency :86 %Pressure before nozzle:1.08 kg / cm2 04
(c) What are the various instruments required for performance evaluation of compressed air systems by nozzle method? 03
(d) Explain fouling factor and state factor affecting on it. 03
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