Heat Transfer B.Tech Question Paper : vardhaman.org
College : Vardhaman College Of Engineering
Degree : B.Tech
Department :Mechanical Engineering
Semester : VI
Subject : Heat Transfer
Document type : Question Paper
Website : vardhaman.org
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Heat Transfer Question Paper :
Hall Ticket No: Question Paper Code : A1326
VARDHAMAN COLLEGE OF ENGINEERING
(AUTONOMOUS)
Four Year B. Tech VI Semester Regular Examinations June – 2014
(Regulations: VCE-R11)
(Mechanical Engineering)
Date: 3 June, 2014
Time: 3 hours
Max Marks: 75
Answer ONE question from each Unit
Related : Vardhaman College Of Engineering Air Pollution & Control Methods B.Tech Question Paper : www.pdfquestion.in/6383.html
Unit – I :
1. a) Write explanatory notes on modes and mechanism of heat transfer 10M
b) An electric current is passed through a wire 1mm in diameter and 10cm long. The wire is submerged in liquid water at atmospheric pressure and the current is increased until the water boils. For this situation h = 5000W/m2.0C, and the water temperature will be 1000C. How much electric power must be supplied to the wire to maintain the wire surface at 1140C. 5M
2. a) Suppose a person stated that heat cannot be transferred in vacuum. How do you respond? 7M
b) Explain the sequence of events which would happen when
i. A copper plate is heated
ii. A vessel containing water is heated 8M
Unit – II :
3. a) A thin metal sphere of diameter 300 mm is used to store a liquefied gas at -200 0C. To reduce the heat leakage from atmosphere at 30 0C, it is insulated by two layers of insulation each 30 mm thick. The first layer of insulating material has a thermal conductivity 0.06 W/m. 0C and the second layer has the thermal conductivity of 0.6 W/m 0C. Determine the heat leakage:
i. When the better insulator is next to sphere
ii. When the better conductor is immediately next to sphere 8M
b) A 5 cm thick iron plate (k = 60 W/m 0C, CP = 460 J / kg C, ? = 7850 kg/m3, a =1.6×10-5m2/s) is initially at Ti = 225 0C. Suddenly both surfaces are exposed to an ambient at T8 = 25 0C with heat transfer co-efficient of 500 W/m2 .0C
i. Calculate the centre temperature at t = 2 min after the start of cooling
ii. Calculate the temperature at a depth of 1 cm from the surface at t = 2 min after the start of cooling 7M
4. a) A furnace wall is made up of three layers of thickness 250mm, 100mm, 150mm with thermal conductivities of 1.65, K, 9.2 W/m 0C respectively. The inside is exposed to gases at 1250 0C with convective coefficient of 25 W/m2 0C and the inside surfaces at 1100 0C. Outside surface is exposed to air at 25 0C with convection coefficient of 12 W/m2 0C
Determine :
i. The unknown thermal conductivity ‘K’
ii. The overall heat transfer coefficient
iii. All surface temperatures 8M
b) A 5 cm diameter sphere k = 60 W/m 0C, CP = 460 J / kg 0C, ? = 7850 kg/m3, a =1.6×10-5m2/s Initially Ti = 225 0C suddenly both surfaces are exposed to an ambient temperature at T8 = 25 0C, with heat transfer co-efficient of 500 W/m2 .0C
i. Calculate the centre temperature at 1 min after the start of cooling
ii. Calculate the temperature at a depth of 1 cm from the surface, 1 min after the start of cooling 7M
Unit – III :
5. a) Using Buckingham theorem obtain the correlation in terms of Nusselt number, Reynolds
number and Prandtl number.
8M
b) A fine wire having a diameter of 0.02 mm is maintained at a constant temperature of
54 0C by an electric current. The wire is exposed to air at 1 atm. and 0 0C. Calculate the
electric power necessary to maintain the wire temperature if the length is 50 cm.
7M
6. a) Sketch temperature and velocity profile of natural convection of vertical wall. 7M
b) A water at mean temperature Tm =25 0C and mean velocity of um =1.5 m/s enters a brass condenser tube L =6 m long, 1.34 cm ID, 1.58 cm OD and K=110 w/m0C. The heat transfer coefficient for condensation at the outer surface of the tube is ho= 12,000 w/m2 0C. Calculate the overall heat transfer coefficient Uo based on the outer surface. (Assume fouling factor fi=fo=0) 8M
Unit – IV :
7. a) A heated brass plate is submerged in a container of water at atmospheric pressure. The plate temperature is 1170C. Calculate the heat transfer per unit area of the plate. 8M
b) Write explanatory notes on regimes of pool boiling. 7M
8. a) Discuss the classification of heat exchanger. 7M
b) Saturated water at 100 0C is boiled with a copper heating element. If the surface heat flux is 400 kW/m2 , calculate the surface temperature. 8M
Unit – V :
9. a) Two parallel black plates 0.5 by 1m are spaced 0.5m apart. One plate is maintained at 10000C and the other at 5000C. What is the net radiant heat exchange between the two plates? 7M
b) Explain the following terms and state the applications of each one of them:
i. Gray body
ii. Radiation shape factor 8M
10. a) Two concentric cylinders having diameters of 10 and 20 cm have a length of 20cm. Calculate the shape factor between the open ends of the cylinders. 10M
b) Discuss the following laws:
i. Stefan Boltzmann’s law
ii. Laws of Planck 5M