RR320306-HEATTRANSFER

8/12/2019 RR320306-HEATTRANSFER

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Code No: RR320306 RR Set No. 2

III B.Tech II Semester Examinations,APRIL 2011

HEAT TRANSFER

Common to Mechanical Engineering, Automobile Engineering

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

1. (a) Water at 200C was flowing over a plate of uniform heat flux of 9000 w/m2.The flow velocity was 200 m/s. The length of the plate was 1.3 m. Determinethe temperature of the plate.

(b) A hot plate of 2m at constant temperature of 900

C was placed in air with hugespeed of 60 km/hr. at 70C. Determine the heat transfer co-efficient, only inthe region, where the air flows with turbulency. [8+8]

2. Heat at the rate of 0.5 MW/m3 is generated in a 50 mm thick wall having thermalconductivity 18 W/mK. One side of the wall exposed to environment at 500C witha heat transfer coefficient of 450 W/m2K. Calculate the maximum temperature inthe wall if the outer side of the wall is insulated? [16]

3. (a) Write a note on thermal and hydrodynamic boundary layer.

(b) Determine the rate of heat loss from a 100 mm diameter steam pipe placedhorizontally in ambient air at 300C. The length of pipe is 4 m and wall tem-perature tw = 1700C. [8+8]

4. (a) A vertical plate 3m high is maintained at 550C in the presence of a saturatedsteam at atmospheric pressure. Estimate the heat transfer rate per unit width.

(b) Dry steam at 1000C condenses on the outside of surface of a horizontal pipeof OD = 2.5cm. The pipe surface is maintained at 850C by circulating waterthrough it. Determine the rate of formation of condensate per meter lengthof the pipe. [10+6]

5. (a) The surface of steel plate measuring 0.9m long x 0.6m wide x 0.025m thick ismaintained at a uniform temperature of 3000C, and the plate loses 250 wattby radiation. If air at 150C temperature and 20 w/m2K con vective heattransfer coefficient blows over the plate, calculate the temperature on insidesurface of the plate. Take thermal conductivity of plate as 45w/m K.

(b) Derive expressions for temperature distribution during steady sate heat con-duction in a solid sphere with internal heat generation. [8+8]

6. (a) Define the term overall heat transfer coefficient? And explain its significance.

(b) An aluminium fin (200 W/mK) of 3 mm thick and 75 mm long protrudes

from a wall at 3000

C. The ambient temperature is 500

C with heat transfercoefficient of 10 W/m2K. Calculate the heat loss from the pin for unit depthof material. Also calculate its effectiveness and efficiency? [8+8]

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7. (a) Define the terms

i. absorptivityii. reflectivity and

iii. transmissivity.

(b) Differentiate between specular and diffuse reflections.

(c) Derive Stefan-Boltzmanns law from Planks law. [6+4+6]

8. In a petrol engine arranged for evaporative cooling, the steam formed at 1000C iscondensed in the radiator where it is surrounds the tube through which coolingair at 180C is made to flow with a mean air velocity of 5.5 m/Sec . The radiatorconsists of 12.5 cm long parallel tubes and 8mm diameter tubes. This is connected

to an engine which develops 8.75 KW of power with brake thermal efficiency of 20percent. If 35 percent of heat supplied to the engine is dissipated at the radiator,calculate number tubes and temperature of air at exit of the radiator . For air ;Cp= 1005 J/kg K ; P = 1.4 kg/m

3 and overall heat transfer coefficient through thetube = 19 W/m2-K. [16]

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HEAT TRANSFER





1. In a petrol engine arranged for evaporative cooling, the steam formed at 1000C iscondensed in the radiator where it is surrounds the tube through which coolingair at 180C is made to flow with a mean air velocity of 5.5 m/Sec . The radiator

consists of 12.5 cm long parallel tubes and 8mm diameter tubes. This is connectedto an engine which develops 8.75 KW of power with brake thermal efficiency of 20percent. If 35 percent of heat supplied to the engine is dissipated at the radiator,calculate number tubes and temperature of air at exit of the radiator . For air ;Cp= 1005 J/kg K ; P= 1.4 kg/m





i. absorptivity

ii. reflectivity and




4. (a) The surface of steel plate measuring 0.9m long x 0.6m wide x 0.025m thick ismaintained at a uniform temperature of 3000C, and the plate loses 250 wattby radiation. If air at 150C temperature and 20 w/m2K convective heattransfer coefficient blows over the plate, calculate the temperature on insidesurface of the plate. Take thermal conductivity of plate as 45w/m K.




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6. Heat at the rate of 0.5 MW/m3 is generated in a 50 mm thick wall having thermalconductivity 18 W/mK. One side of the wall exposed to environment at 500C witha heat transfer coefficient of 450 W/m2K. Calculate the maximum temperature inthe wall if the outer side of the wall is insulated? [16]


(b) A hot plate of 2m at constant temperature of 900C was placed in air with hugespeed of 60 km/hr. at 70C. Determine the heat transfer co-efficient, only inthe region, where the air flows with turbulency. [8+8]

8. (a) Define the term overall heat transfer coefficient? And explain its significance.(b) An aluminium fin (200 W/mK) of 3 mm thick and 75 mm long protrudes

from a wall at 3000C. The ambient temperature is 500C with heat transfercoefficient of 10 W/m2K. Calculate the heat loss from the pin for unit depthof material. Also calculate its effectiveness and efficiency? [8+8]

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HEAT TRANSFER





1. In a petrol engine arranged for evaporative cooling, the steam formed at 1000C iscondensed in the radiator where it is surrounds the tube through which coolingair at 180C is made to flow with a mean air velocity of 5.5 m/Sec . The radiator

consists of 12.5 cm long parallel tubes and 8mm diameter tubes. This is connectedto an engine which develops 8.75 KW of power with brake thermal efficiency of 20percent. If 35 percent of heat supplied to the engine is dissipated at the radiator,calculate number tubes and temperature of air at exit of the radiator . For air ;Cp= 1005 J/kg K ; P= 1.4 kg/m



(b) A hot plate of 2m at constant temperature of 900C was placed in air with hugespeed of 60 km/hr. at 70C. Determine the heat transfer co-efficient, only inthe region, where the air flows with turbulency. [8+8]




(b) An aluminium fin (200 W/mK) of 3 mm thick and 75 mm long protrudes

from a wall at 3000C. The ambient temperature is 500C with heat transfercoefficient of 10 W/m2K. Calculate the heat loss from the pin for unit depthof material. Also calculate its effectiveness and efficiency? [8+8]


i. absorptivity





6. Heat at the rate of 0.5 MW/m3 is generated in a 50 mm thick wall having thermalconductivity 18 W/mK. One side of the wall exposed to environment at 500C with

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a heat transfer coefficient of 450 W/m2K. Calculate the maximum temperature inthe wall if the outer side of the wall is insulated? [16]

7. (a) The surface of steel plate measuring 0.9m long x 0.6m wide x 0.025m thick ismaintained at a uniform temperature of 3000C, and the plate loses 250 wattby radiation. If air at 150C temperature and 20 w/m2K convective heattransfer coefficient blows over the plate, calculate the temperature on insidesurface of the plate. Take thermal conductivity of plate as 45w/m K.


8. (a) A vertical plate 3m high is maintained at 550C in the presence of a saturated

steam at atmospheric pressure. Estimate the heat transfer rate per unit width.(b) Dry steam at 1000C condenses on the outside of surface of a horizontal pipe

of OD = 2.5cm. The pipe surface is maintained at 850C by circulating waterthrough it. Determine the rate of formation of condensate per meter lengthof the pipe. [10+6]

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HEAT TRANSFER






(b) A hot plate of 2m at constant temperature of 900

C was placed in air with hugespeed of 60 km/hr. at 70C. Determine the heat transfer co-efficient, only inthe region, where the air flows with turbulency. [8+8]


i. absorptivity






(b) An aluminium fin (200 W/mK) of 3 mm thick and 75 mm long protrudesfrom a wall at 3000C. The ambient temperature is 500C with heat transfercoefficient of 10 W/m2K. Calculate the heat loss from the pin for unit depthof material. Also calculate its effectiveness and efficiency? [8+8]

4. Heat at the rate of 0.5 MW/m3 is generated in a 50 mm thick wall having thermalconductivity 18 W/mK. One side of the wall exposed to environment at 500C witha heat transfer coefficient of 450 W/m2K. Calculate the maximum temperature in

the wall if the outer side of the wall is insulated? [16]



6. (a) The surface of steel plate measuring 0.9m long x 0.6m wide x 0.025m thick ismaintained at a uniform temperature of 3000C, and the plate loses 250 wattby radiation. If air at 150C temperature and 20 w/m2K con vective heattransfer coefficient blows over the plate, calculate the temperature on inside

surface of the plate. Take thermal conductivity of plate as 45w/m K.


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8. In a petrol engine arranged for evaporative cooling, the steam formed at 1000C iscondensed in the radiator where it is surrounds the tube through which coolingair at 180C is made to flow with a mean air velocity of 5.5 m/Sec . The radiatorconsists of 12.5 cm long parallel tubes and 8mm diameter tubes. This is connectedto an engine which develops 8.75 KW of power with brake thermal efficiency of 20

percent. If 35 percent of heat supplied to the engine is dissipated at the radiator,calculate number tubes and temperature of air at exit of the radiator . For air ;Cp= 1005 J/kg K ; P = 1.4 kg/m


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RR320306-HEATTRANSFER