STUPIDSID
1 (a)
Explain briefly the mechanism of conduction, convection and radiation heat transfer.
6 M
1 (b)
With sketches write down the mathematical representation of three commonly used different types of boundary conditions for one dimensional heat equation in rectangular coordinates.
8 M
1 (c)
A plate of thickness 'L' whose one side is insulated and the other side is maintained at a temperature T1 is exchanging heat by convection to the surrounding area at a temperature T2, with atmospheric air being the outside medium. Write mathematical formulation for one dimensional, steady state heat transfer, without heat generation.
6 M
2 (a)
An electric cable of 10mm diameter is to be laid in atmosphere at 20°C. The estimated surface temperature of the cable due to heat generation is 65°C. Find the maximum percentage increase in heat dissipation, when the wire is insulated with rubber having K=0.155 W/mK, take h=8.5 W/m2K.
6 M
2 (b)
Differentiate between the effectiveness and efficiency of fins.
4 M
2 (c)
In order to reduce the thermal resistance at the surface of vertical plane wall(50×50cm). 100 pin fins(1 cm diameter. 10Cm long) are attached. If the pin fins are made of coper having a thermal conductivity is 15 W/m2K, calculate the decrease in the thermal resistance. Also calculate the consequent increase in heat transfer in heat transfer rate from the wall if it is maintained at a temperature of 200°C and surroundings are at 30°C.
10 M
3 (a)
Show that the temperature distribution in body during Nevetonian having or cooling is given by \[\frac{T-T_{0}}{T_{1}-T_{0}}=\frac{\theta}{\theta_{1}}=Exp\left ( \frac{-hA_{s}t}{\rho CV} \right )\].
6 M
3 (b)
The steel ball bearing (K=50W/mK, α=.3×10-5m2/sec), 40mm at diameters are heated to temperature of 650°C, it is then quenched in a oil bath at 50°C, where the the transfer coefficient is estimated to be 300 W/m2K. Calculate:
i)The time required for bearing to reach 200°C.
ii) The total amount of heat removed from a bearing during this time and
iii) The instantaneous heat transfer rate from the bearing, when they are first immersed in oil bath and when they reach 200°C
i)The time required for bearing to reach 200°C.
ii) The total amount of heat removed from a bearing during this time and
iii) The instantaneous heat transfer rate from the bearing, when they are first immersed in oil bath and when they reach 200°C
14 M
4 (a)
With reference to fluid flow over a flat plate, discuss the concept of velocity boundary and thermal boundary, layer with nessary sketches.
5 M
4 (b)
The exact expression for local Nuselt number for the laminar flow along a surface is given by \[Nu_{1}=\frac{h_{1}x}{k}=0.332 R^{1/2}_{ex}\ p^{1/3}\] show that the average heat transfer coefficient from x=0 to x=L over the length 'L' of the surface is given by 2ht where ht is the local heat transfer coefficient at x=L.
5 M
4 (c)
A vertical plate 15 cm high and 10cm wide is maintained at 140°C. Calculate the maximum heat dissipation rate from bothe the sides of the plates to air at 20°C. The radiation heat transfer coefficient is 9.0 w/m2K. For air at 80°C, take r=21.09 × 10-6m2/sec, Pr=0.692, Kf=0.03 W/mK.
10 M
5 (a)
Explain the physical significance of i) Nusselt number ii) Groshoff number.
4 M
5 (b)
Air at 2 atm and 200°C is heated as it flows at a velocity of 12m/sec through a tube with a diameter of 3 cm. A constant heat flux condition is maintained at the wall and the wall temperature is 20°C above air temperature all along the length of the tube. Calculate : i) The heat transfer per unit length of tube. ii) The increase in bulk temperature of air over a 4m length of the tube.
take the following properties of air Pr=0.681.μ=2.57×10-5kg/ms, K=0.0386 W/mK and Cp=1.025 kJ/kg K.
take the following properties of air Pr=0.681.μ=2.57×10-5kg/ms, K=0.0386 W/mK and Cp=1.025 kJ/kg K.
10 M
5 (C)
Obtain a relationship between drag coefficient c∞ and heat transfer coefficient h∞ for the flow over a flat plate.
6 M
6 (a)
Derive an expression for LMTD of a counter flow heart exchanger. State the assumptions made.
8 M
6 (b)
What is meant by the term fouling factor? How do you determine it?
4 M
6 (c)
Engine oil is to be cooled from 80°C to 5°C by using a single pass counter flow , concentric-tube heat exchanger with cooling water available at 20°C. Water flows inside a tube with an internal dia of 2.5cm with a flow rate of 0.08 kg/s and oil flows through the annulus at a rate of 0.16kg/s. The heat transfer coefficient for the water side and oil side are respectively hw1000 W/m2°C and hoil 80W/m2C. The fouling factors is Fw 0.00018m2°C/W on both sides and the tube wall resistance in negligible. Calculate the tube length required.
8 M
7 (a)
Sketch a pool boiling curve for water and explain briefly the various regimes in boiling heat transfer.
6 M
7 (b)
Define mass transfer coefficient.
2 M
7 (c)
A 12 cm outside diameter and 2m long tube is used in a big condenser to condense the steam at 0.4 bar. Estimate the unit surface conductance. i)in vertical position ; ii) in horizontal position. Also find the amount of condense formed per hour per hour in both the cases. The saturation temperature of the steam=74.5°C.
Average wall temperature=50°C.
the properties of water film at average temperature of \[\frac{75.4+50}{2}=62.7°C\] are given below ρ =982.2 kg/m3, hf=24800kJ/kg,K=0.65 W/mK, μ=0.47×10-3kg/ms.
Average wall temperature=50°C.
the properties of water film at average temperature of \[\frac{75.4+50}{2}=62.7°C\] are given below ρ =982.2 kg/m3, hf=24800kJ/kg,K=0.65 W/mK, μ=0.47×10-3kg/ms.
12 M
8 (a)
State and prove Wien's displacement law of radiation.
6 M
8 (b)
The temperature of a black surface 0.2m2 in area is 540°C calculate:
i)The total rate of energy emission
ii)The intensity of normal radiation
iii) The wavelength of maximum monochromatic emissive power.
i)The total rate of energy emission
ii)The intensity of normal radiation
iii) The wavelength of maximum monochromatic emissive power.
6 M
8 (c)
Derive an expression for a radiation shape factor and show that it is function of geometry only.
8 M
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