University Of Pune Question Paper
S.E. (Chemical) (Semester – II) Examination, 2011
HEAT TRANSFER
(Common to Bio-Tech.)
(2003 Course)
Time : 3 Hours Max. Marks : 100
Instructions: 1) Solve Q.1 or Q.2, Q.3 or Q.4, Q.5 or Q.6, Q.7 or Q.8,
Q.9 or Q.10 and Q.11 or Q.12.
2) Answers to the two Sections should be written in separate
books.
3) Neat diagrams must be drawn wherever necessary.
4) Black figures to the right indicate full marks.
5) Use of logarithmic tables, slide rule, Mollier charts, electronic
pocket calculator and steam tables is allowed.
6) Assume suitable data, if necessary.
SECTION – I
1. a) State and explain : 9
i) Fourier’s law ii) Newton’s law of Cooling iii) Stefan-Boltzmann’s law.
b) Give the physical significance of the following dimensionless groups : 9
i) Reynolds number ii) Prandtl number iii) Nusselt number.
OR
2. a) Explain in detail “Modes of Heat Transfer”. 6
b) Calculate temperature at an interior point of the wall at a distance 15 cm from
inner surface of wall. The temperatures of the inner and outer surface are
200°C and 80°C respectively. The thickness of the wall is 0.5 m. 6
c) Explain any one method of Dimensional Analysis. 6
3. a) Derive the heat flow equation for steady state heat conduction through
composite cylinder. 8
b) A hollow sphere of 24 mm inner diameter and 36 mm outer diameter is subjected
to constant heat flow of 2.12 kW. In inner surface temperature is 390°K, find the
temperature of outer surface and temperature at a distance of 16 mm from the
centre of the sphere. Thermal conductivity of the material is 85 W/m°K. 8
OR
4. a) Derive the heat flow equation for steady state heat conduction through
composite wall. 8
b) A hollow cylinder of 20 mm inner diameter and 30 mm outer diameter is
maintained at 350°k (outer surface temperature) and 420°k (inner surface
temperature). Determine the heat loss per unit length and also determine the
temperature at a distance of 3 mm from outer surface towards the center.
(Thermal conductivity of material is 50 W/m°K). 8
5. a) Distinguish between : 8
i) Individual and overall heat transfer coefficient
ii) Natural convection and Forced convection.
b) Air at 300°C and atmospheric pressure is heated as it flows through a tube
with a diameter of 25 mm at a velocity of 12 m/sec. Calculate the heat transfer
rate per unit length of tube if a constant heat flux condition is maintained at the
wall which is at 32°C above the air temperature, over entire length of the tube.
Calculate the rise in bulk temperature over a 3.3 m length of the tube. 8
Properties of air are
i) Dynamic viscosity = 29.7×10–6 Kg/m.sec.
ii) Thermal conductivity = 0.0461 W/m°K.
iii) Prandtl Number = 0.674
iv) Cp = 1.047 KJ/Kg°K
v) Density = 0.615 Kg/m3.
OR
6. a) Derive Nusselt’s equation of condensation. 8
b) Air at 27°C and 1 atm. Flow over a flat plate at a velocity of 2 m/sec. The
viscosity of air at 27°C is 1.85×10–5 Pa.s. Assume unit depth. If the plate is
maintained at 60°C. Calculate the heat transferred per unit time in the first
0.4 m of the plate. Properties of air are 8
i) Kinematic Viscosity = 17.36×10–6 m2/sec.
ii) Thermal conductivity = 0.0275 W/m°K.
iii) Prandtl Number = 0.7
iv) Cp = 1.006 KJ/Kg°K.
SECTION – II
7. a) A 50 mm internal diameter iron pipe at 423°K passes through a room in which
the surroundings are at temperature of 300°K. If the emissivity of the pipe
metal is 0.8, what is the net interchange of radiation energy per meter length of
pipe ? The outside diameter of pipe is 60 mm. 9
b) Explain the following : 9
i) Specular and Diffuse Reflection
ii) Radiation shields
iii) Wien’s displacement law.
OR
8. a) It is observed that the value of the radiation emitted by the sun is maximum
wavelength of 0.58 microns. Estimate the temperature of surface of sun and
emissive power. Consider sun to be a black body. 8
b) Discuss the following : 10
i) Electromagnetic spectrum
ii) Black body
iii) Emissive power
iv) Opaque body
v) Emissivity.
9. a) What is LMTD ? Derive LMTD for counter current flow heat exchanger. 8
b) 20 kg/s of water at 360°K entering a heat exchanger is to be cooled to 340°K
by using cold water at 300°K flowing at rate of 25 kg/sec. If the overall heat
transfer coefficient is 1500 w/m2
°k and c
p
for water is 4187 J/Kg°K. Calculate
heat transfer area required in 8
i) Co current flow concentric pipe heat exchanger
ii) Countercurrent flow concentric pipe heat exchanger.
OR
10. a) What is Heat exchanger ? Give the detail classification of heat exchangers. 8
b) In oil cooler 60 gm/sec of hot oil enters a thin metal pipe of diameter 25 mm,
an equal mass of cooling water flows through the annular space between the
pipe and a large concentric pipe, the oil and water moving in opposite directions.
The oil enters at 420°K and is to be cooled to 320°K. If water enters at
290°K, what length of pipe is required ? Take heat transfer coefficient of
1.6 kW/m2
K on the oil side and 3.6 kW/m2K on water side. Specific heat
capacity of oil is 2 kJ/kg°K and that of water is 4.18 kJ/kg°K. 8
11. a) A solution of organic colloids in water is to be concentrated from 8% to 45%
in a single effect evaporator. Steam is available at a gauge pressure of
1.03 atm. A pressure of 102 mm Hg absolute is to be maintained in the vapor
space. The feed rate to the evaporator is 12,000 kg/hr. The overall heat transfer
coefficient can be taken as 2800 W/m2
.°C. The solution has a negligible
elevation in boiling point and a negligible heat of dilution. Calculate (a) steam
consumption (b) the economy and (c) the heating area required. 8
b) What is Evaporation ? Draw a neat sketch and explain any one evaporator. 8
OR
12. a) 1000 kg/hr of a dilute solution is to be concentrated from 10% to 40% by
weight in a single effect evaporator. The feed is available at 25°C. Boiling
point of the solution may be considered as 100°C. Specific heat capacity of
dilute solution is 4180 J/kg°K; Latent heat of vaporization of water is 2239 kJ/Kg,
saturated steam corresponding to 1.8 bar pressure and 117°C is available for
heating purpose. Latent heat of condensation of steam is 2212 kJ/kg. If the
overall heat transfer coefficient for the system is 850 W/m2
°K. 12
Calculate :
i) The quantity of water evaporated
ii) Steam consumed and steam economy
iii) Surface area of the evaporator.
b) Explain multiple effect evaporator with different feed arrangements. 4
————––––––———
S.E. (Chemical) (Semester – II) Examination, 2011
HEAT TRANSFER
(Common to Bio-Tech.)
(2003 Course)
Time : 3 Hours Max. Marks : 100
Instructions: 1) Solve Q.1 or Q.2, Q.3 or Q.4, Q.5 or Q.6, Q.7 or Q.8,
Q.9 or Q.10 and Q.11 or Q.12.
2) Answers to the two Sections should be written in separate
books.
3) Neat diagrams must be drawn wherever necessary.
4) Black figures to the right indicate full marks.
5) Use of logarithmic tables, slide rule, Mollier charts, electronic
pocket calculator and steam tables is allowed.
6) Assume suitable data, if necessary.
SECTION – I
1. a) State and explain : 9
i) Fourier’s law ii) Newton’s law of Cooling iii) Stefan-Boltzmann’s law.
b) Give the physical significance of the following dimensionless groups : 9
i) Reynolds number ii) Prandtl number iii) Nusselt number.
OR
2. a) Explain in detail “Modes of Heat Transfer”. 6
b) Calculate temperature at an interior point of the wall at a distance 15 cm from
inner surface of wall. The temperatures of the inner and outer surface are
200°C and 80°C respectively. The thickness of the wall is 0.5 m. 6
c) Explain any one method of Dimensional Analysis. 6
3. a) Derive the heat flow equation for steady state heat conduction through
composite cylinder. 8
b) A hollow sphere of 24 mm inner diameter and 36 mm outer diameter is subjected
to constant heat flow of 2.12 kW. In inner surface temperature is 390°K, find the
temperature of outer surface and temperature at a distance of 16 mm from the
centre of the sphere. Thermal conductivity of the material is 85 W/m°K. 8
OR
4. a) Derive the heat flow equation for steady state heat conduction through
composite wall. 8
b) A hollow cylinder of 20 mm inner diameter and 30 mm outer diameter is
maintained at 350°k (outer surface temperature) and 420°k (inner surface
temperature). Determine the heat loss per unit length and also determine the
temperature at a distance of 3 mm from outer surface towards the center.
(Thermal conductivity of material is 50 W/m°K). 8
5. a) Distinguish between : 8
i) Individual and overall heat transfer coefficient
ii) Natural convection and Forced convection.
b) Air at 300°C and atmospheric pressure is heated as it flows through a tube
with a diameter of 25 mm at a velocity of 12 m/sec. Calculate the heat transfer
rate per unit length of tube if a constant heat flux condition is maintained at the
wall which is at 32°C above the air temperature, over entire length of the tube.
Calculate the rise in bulk temperature over a 3.3 m length of the tube. 8
Properties of air are
i) Dynamic viscosity = 29.7×10–6 Kg/m.sec.
ii) Thermal conductivity = 0.0461 W/m°K.
iii) Prandtl Number = 0.674
iv) Cp = 1.047 KJ/Kg°K
v) Density = 0.615 Kg/m3.
OR
6. a) Derive Nusselt’s equation of condensation. 8
b) Air at 27°C and 1 atm. Flow over a flat plate at a velocity of 2 m/sec. The
viscosity of air at 27°C is 1.85×10–5 Pa.s. Assume unit depth. If the plate is
maintained at 60°C. Calculate the heat transferred per unit time in the first
0.4 m of the plate. Properties of air are 8
i) Kinematic Viscosity = 17.36×10–6 m2/sec.
ii) Thermal conductivity = 0.0275 W/m°K.
iii) Prandtl Number = 0.7
iv) Cp = 1.006 KJ/Kg°K.
SECTION – II
7. a) A 50 mm internal diameter iron pipe at 423°K passes through a room in which
the surroundings are at temperature of 300°K. If the emissivity of the pipe
metal is 0.8, what is the net interchange of radiation energy per meter length of
pipe ? The outside diameter of pipe is 60 mm. 9
b) Explain the following : 9
i) Specular and Diffuse Reflection
ii) Radiation shields
iii) Wien’s displacement law.
OR
8. a) It is observed that the value of the radiation emitted by the sun is maximum
wavelength of 0.58 microns. Estimate the temperature of surface of sun and
emissive power. Consider sun to be a black body. 8
b) Discuss the following : 10
i) Electromagnetic spectrum
ii) Black body
iii) Emissive power
iv) Opaque body
v) Emissivity.
9. a) What is LMTD ? Derive LMTD for counter current flow heat exchanger. 8
b) 20 kg/s of water at 360°K entering a heat exchanger is to be cooled to 340°K
by using cold water at 300°K flowing at rate of 25 kg/sec. If the overall heat
transfer coefficient is 1500 w/m2
°k and c
p
for water is 4187 J/Kg°K. Calculate
heat transfer area required in 8
i) Co current flow concentric pipe heat exchanger
ii) Countercurrent flow concentric pipe heat exchanger.
OR
10. a) What is Heat exchanger ? Give the detail classification of heat exchangers. 8
b) In oil cooler 60 gm/sec of hot oil enters a thin metal pipe of diameter 25 mm,
an equal mass of cooling water flows through the annular space between the
pipe and a large concentric pipe, the oil and water moving in opposite directions.
The oil enters at 420°K and is to be cooled to 320°K. If water enters at
290°K, what length of pipe is required ? Take heat transfer coefficient of
1.6 kW/m2
K on the oil side and 3.6 kW/m2K on water side. Specific heat
capacity of oil is 2 kJ/kg°K and that of water is 4.18 kJ/kg°K. 8
11. a) A solution of organic colloids in water is to be concentrated from 8% to 45%
in a single effect evaporator. Steam is available at a gauge pressure of
1.03 atm. A pressure of 102 mm Hg absolute is to be maintained in the vapor
space. The feed rate to the evaporator is 12,000 kg/hr. The overall heat transfer
coefficient can be taken as 2800 W/m2
.°C. The solution has a negligible
elevation in boiling point and a negligible heat of dilution. Calculate (a) steam
consumption (b) the economy and (c) the heating area required. 8
b) What is Evaporation ? Draw a neat sketch and explain any one evaporator. 8
OR
12. a) 1000 kg/hr of a dilute solution is to be concentrated from 10% to 40% by
weight in a single effect evaporator. The feed is available at 25°C. Boiling
point of the solution may be considered as 100°C. Specific heat capacity of
dilute solution is 4180 J/kg°K; Latent heat of vaporization of water is 2239 kJ/Kg,
saturated steam corresponding to 1.8 bar pressure and 117°C is available for
heating purpose. Latent heat of condensation of steam is 2212 kJ/kg. If the
overall heat transfer coefficient for the system is 850 W/m2
°K. 12
Calculate :
i) The quantity of water evaporated
ii) Steam consumed and steam economy
iii) Surface area of the evaporator.
b) Explain multiple effect evaporator with different feed arrangements. 4
————––––––———
0 comments:
Pen down your valuable important comments below