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GUJARAT TECHNOLOGICAL UNIVERSITY
DIPLOMA ENGINEERING – SEMESTER –VI • EXAMINATION – WINTER 2015
Subject Code: 3361907 Date: 14/12/2015
Subject Name: Thermal systems and Energy Efficiency
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.
7. Use of Psychrometric chart is permitted in T.S.E.E.
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Q.1 Answer any seven out of ten. 14
1. List the main parameters on which the choice of HVAC components depends on?
2. Why CFC's are phased out? which are the alternatives to CFC's.
3. Name the parameters that a psychometric chart provide for an air conditioning Engineer?
4. How do you calculate TR across the air conditioning units.
5. What is heat flux in a heat exchanger?
6. What is capacity ratio in Heat exchanger?
7. What are the methods of waste heat recovery in a furnace ?
8. Define Boiler efficiency ?
9. Why energy cost of a compressor is evaluated ?
10. What is free air delivery in a compressor ?
Q.2 (a) As a means of performance evaluation, explain the difference between efficiency and evaporation ratio ? 03
OR
(a) What is controllable and uncontrollable losses in a boiler ? 03
(b) What is the need for performance assessment of a heat exchanger ? 03
OR
(b) What instruments are required for indirect efficiency testing in a boiler ? 03
(c) Distinguish between heat exchanger efficiency and effectiveness ? 04
OR
(c) What is meant by LMTD ? Express it Mathematically. 04
(d) Why furnaces operate at low efficiency? What are the methods by which furnace efficiencies can be improved ? 04
OR
(d) How is the furnace performance evaluated by indirect method ? 04
Q.3 (a) Explain the term recuperator ? 03
OR
(a) What are the advantages and disadvantages of operating the furnace at a positive pressure ? 03
(b) What are the major losses in a furnace ? 03
OR
(b) How does the ceramic coatings help in reducing energy consumption ? 03
(c) What care should be taken for proper heat distribution in a furnace ? 04
OR
(c) What are the factors that affects the boiler performance ? 04
(d) Discuss some of the practical difficulties in optimizing the loading of the furnace ? 04
OR
(d) List down the adverse impacts of operating the furnace at temperatures higher than required ? 04
Q.4 (a) Explain the principle of vapour compression system with a neat sketch ? 03
OR
(a) Differentiate between vapour compression refrigeration system and vapour absorption refrigeration system ? 03
(b) What are the different factors considered in load estimation sheet for comfort application? 04
OR
(c) The following data relates to the office air conditioning plant having maximum seating capacity of 25 occupants:Outside design conditions =340DBT,280WBT
Inside design conditions =240
DBT,50% RH
Solar heat gain =9120W
Latent heat gain per occupant=105W
Sensible heat gain per occupant=90W
Lightening load=2300W
Sensible heat load from sources=11630W
Infiltration load=14m3/min
Assuming 40% fresh air and 60%recirculated air passing through the
evaporator coil and by-pass factor of 0.15,
find the dew point temperature of the coil and capacity of the plant. 07
Q.5 (a) Calculate the radiation loss through a opening in the furnace for a period of Eight hours from the data given belowA reheating furnace with walls 460mm(X) thick has a billet extraction outlet which is 1m high and 1m wide. Furnace operating temperature is 13400Celsius. The factor total radiation for the opening is 0.71.(Blackbody radiation corresponding to 13400Celsius=36.00kcal/cm2/hr)
(b) Explain how you would undertake an energy audit of a batch type heat treatment furnace ?
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