Printed Pages:
Sub Code: NME-504
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PAPER ID: 4049
Roll No.
B.TECH. ODD SEMESTER EXAMINATION (2017-18)
HEAT & MASS TRANSFER
Total Marks: 100
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Time: 3 Hours
Note: Be precise and scientific in writing.
SECTION – A
1. Attempt ALL questions in brief. (2X10=20)
- What do you understand by overall heat transfer coefficient?
- What is the significance of heat transfer?
- Explain effectiveness and efficiency of fin.
- Explain the significance of Heisler's charts.
- Define Gray body.
- Define Prandtl number.
- What is intensity of radiation?
- What is radiation shield?
- Define condensation and their types.
- How heat exchangers are classified?
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SECTION – B
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2. Attempt any THREE parts of the following. (10X3=30)
- A furnace wall is composed of 220 mm of fire brick. 150 mm of common brick, 50 mm of 85% magnesia and 3mm of steel plate on the outside. if the inside surface temperature is 1500°C and outside surface temperature is 90°C, estimate the temperature between layers and calculate the heat loss in Kj/h-m². Assume, k (for fire brick) = 4kJ/m-h. °C, k (for common brick) = 2.8kJ/m-h. °C, k (for 85% magnesia) =2.4kJ/m-h. °C, k (steel) =240kJ/m-h. °C.
- Derive an expression of rectangular fin in case of heat dissipation from an infinite long fin. What are advantages and application of fins?
- Castor oil at 25°c flows at a velocity of 0.1 m/s past a flat plate, in a certain process. If the plate is 4.5 m long and is maintained at a Uniform temperature of 95°c, calculate the following using exact solution:
i. The hydrodynamic and thermal boundary layer thicknesses on one side of the plate,--- Content provided by FirstRanker.com ---
ii. The total drag force per unit width on one side of the plane,
iii. The local heat transfer coefficient at the trailing edge, and the heat transfer rate - Explain diffuse emitter and radiation shape factor.
- Define pool boiling and also explain regimes of pool boiling with the help of diagram.
SECTION – C
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3. Attempt any ONE part of the following. (10X1=10)
- A carbon steel plate ( K = 45 W/m°K) 600 mm x 900mm x 25 mm is maintained at 310°C. Air at 15°C blows over the hot plate. If convection heat transfer coefficient is 22 W/m²°C and 250 W is lost from the plate surface by radiation, calculate the inside plate temperature.
- Derive a general heat conduction equation in case of cylindrical co-ordinate.
4. Attempt any ONE part of the following. (10X1=10)
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- Prove that for a body whose thermal resistance is zero, the temperature required for cooling or heating can be obtained from the relation (t-ta)/(tt-ta ) = exp[-Bi Fa], where the symbols have their usual meanings
- A large metal plate of thickness 5cm is initially at 460°C. It is suddenly exposed to fluid at 100°C with a convection coefficient of 142.5W/m².K. Find the time needed for its mid plane to reach a temperature of 316°C and surface temperature at the same instant of time. Take k= 21.25W/m K and = 1.2*10-5 m²/sec.
5. Attempt any ONE part of the following. (10X1=10)
- Derive the equation for boundary layer thickness.
- A 350mm long glass plate is hung vertically in the air at 24°C while its temperature is maintained at 80°C. Calculate the boundary layer thickness at the trailing edge of the plate. If a similar plate is placed in a wind tunnel and air is blown over it at a velocity of 5 m/s, find the boundary layer thickness at its trailing edge. Also determine the average heat transfer coefficient, for natural and forced convection for the above mentioned data.
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6. Attempt any ONE part of the following. (10X1=10)
- A small convex object of area A1, temperature T1 and emissivity €1 is enclosed within a large enclosure at temperature T2 and emissivity €2. Derive an expression for the net heat exchange between the two objects.
- Consider two large parallel plates one at t1=27°c with emissivity €1=0.8 and other at 227°c with emissivity €2=0.4. An aluminum radiation shield with an emissivity, €5=0.05 on both sides is placed between the plates. Calculate the percentage reduction in heat transfer rate between the two plates as a result of shield. Use o=5.67×10-8 W/m²K4.
7. Attempt any ONE part of the following. (10X1=10)
- In a counter-flow double pipe heat exchanger; water is heated from 25°c to 65°c by oil with a specific heat of 1.45KJ/Kg K and mass flow rate of 0.9 Kg/s. The oil is cooled from 230°c to 160°c. If the overall heat transfer co efficient is 42070W/m°c, calculate the following
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i. the rate of heat transfer
ii. the mass flow rate of water and
iii. the surface area of the heat exchanger - Derive an expression for LMTD by NTU method for parallel flow.
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This download link is referred from the post: AKTU B-Tech Last 10 Years 2010-2020 Previous Question Papers || Dr. A.P.J. Abdul Kalam Technical University
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