GUJARAT TECHNOLOGICAL UNIVERSITY -...
Transcript of GUJARAT TECHNOLOGICAL UNIVERSITY -...
GUJARAT TECHNOLOGICAL UNIVERSITY
BRANCH NAME: Mechanical Engineering
SUBJECT NAME: Advance Heat Transfer
SUBJECT CODE: 2171911
B.E. 7th SEMESTER
Type of course: Elective
Prerequisite: Engineering Thermodynamics, Fluid Mechanics, Heat Transfer
Rationale: The course is prepared to provide the detailed understanding of conduction,
convection, radiation and phase change. This course is design to learn techniques for heat transfer
enhancement and usage of numerical methods for solving heat transfer problems.
Teaching and Examination Scheme:
Teaching Scheme Credits Examination Marks Total
Marks L T P C Theory Marks Practical Marks
ESE
(E)
PA (M) ESE (V) PA
(I) PA ALA ESE OEP
3 0 2 5 70 20 10 20 10 20 150
Content:
Sr. No. Content No. of
Hrs.
%
Weightage
1 Heat conduction with heat generation: Plane wall and cylinder
with uniform heat generation, applications. Two-dimensional
steady state conduction.
6 14
2 Transient and multi dimensional heat conduction: Exact
solution, use of Heisler and Grober chart, integrated method
6 14
3 Heat Transfer through extended surfaces: Steady state analysis
and optimization, radial fins of rectangular and hyperbolic profiles-
longitudinal fin of rectangular profile radiating to free space.
7 17
4 Convective Heat Transfer:
Forced convection: Introduction, heat transfer in high velocity
flow, empirical relations for pipe and tube flow, flow across
cylinders, spheres and tube banks, liquid-metal heat transfer
Natural Convection: Introduction, empirical relations for free
convection, free convection from vertical planes, cylinders,
horizontal cylinders, horizontal plates, inclined surfaces, spheres
and enclosed space, non-newtonian fluids, combined free and
forced convection
10 19
5 Convection with change of phase: Condensation: Laminar film on a vertical surface, Turbulent film
on a vertical surface, Film condensation in other configurations,
Drop condensation, effect of non-condensable gases in condensing
equipments
Boiling: Pool boiling regimes, Nucleate boiling and peak heat flux,
Film boiling and minimum heat flux, Flow boiling
6 17
6 Radiation heat transfer: Radiation effect on temperature
measurements, radiation properties of a participating medium,
emissivity and absorptivity of gases and gases mixtures, heat
transfer from the human body, radiative exchange and overall heat
transfer in furnaces.
8 19
Suggested Specification table with Marks (Theory):
Distribution of Theory Marks
R Level U Level A Level N Level E Level C Level
10 15 15 15 10 5
Legends: R: Remembrance; U: Understanding; A: Application, N: Analyze and E:
Evaluate C: Create and above Levels (Revised Bloom’s Taxonomy)
Note: This specification table shall be treated as a general guideline for students and teachers.
The actual distribution of marks in the question paper may vary slightly from above table.
Reference Books:
1. D.P. Incropera, P.P. and Dewitt, Fundamentals of Heat and Mass Transfer, Wiley
Eastern
2. Adrian Bejan, Convective Heat Transfer, Wiley India.
3. Cengel Y A, Heat Transfer – A Practical Approach, McGraw Hill
4. Kays, Crawford and Weigand, Convective Heat and Mass Transfer, McGraw Hill.
5. Siegel and Howell, Thermal Radiation, McGraw Hill.
6. Kraus A.D., Aziz, A., and Welty, J., Extended Surface Heat Transfer, McGraw Hill
7. Adrian Bejan, Allan D. Krams, Heat Transfer Handbook, John Wiley & Sons.
8. J. P. Holman, Heat Transfer, McGraw Hill
Course Outcome:
After learning the course, the students should be able to:
Develop ability to apply the basic principles of classical heat transfer in real engineering
application
Analyze the analytical and numerical solutions for heat transfer problem.
Understand the basic concepts of turbulence and their impact on heat transfer
List of Experiments:
1. Experiment on “Heat transfer through composite wall at different temperature”
2. Experiment on “Thermal conductivity of insulating powder (Asbestos powder) ”
3. Experiment on “Heat transfer in turbulent flow”
4. Experiment on “Heat transfer by forced convection”
5. Experiment on “Heat transfer coefficient in natural convection”
6. Experiment on “Heat transfer by radiation: Stefan-Boltzmann Law”
7. Experiment on “Thermal conductivity of metal rod ”
8. Experiment on “Drop and Film wise condensation”
9. Experiment on “Unsteady state conduction heat transfer”
Design based Problems (DP)/Open Ended Problem:
1. Comparison of composite wall made of different materials
2. Calculate cooling capacity of domestic refrigerator
3. Calculate the effect of different fins in heat transfer
Major Equipment:
1. Conduction through Composite Wall
2. Heat Transfer in Natural convection
3. Heat Transfer in Forced Flow
4. Pin-Fin (Natural and Forced Convection)
5. Stefan Boltzmann Constant
6. Emissivity of test plate
7. Drop and Film wise condensation
8. Unsteady state conduction heat transfer
List of Open Source Software/learning website:
1. nptel.ac.in
2. www.learnerstv.com
3. cosmolearning.org
ACTIVE LEARNING ASSIGNMENTS: Preparation of power-point slides, which include
videos, animations, pictures, graphics for better understanding theory and practical work – The
faculty will allocate chapters/ parts of chapters to groups of students so that the entire syllabus
to be covered. The power-point slides should be put up on the web-site of the College/ Institute,
along with the names of the students of the group, the name of the faculty, Department and
College on the first slide. The best three works should submit to GTU.
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Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VII (NEW) - EXAMINATION – SUMMER 2017
Subject Code: 2171911 Date: 29/04/2017 Subject Name: Advance Heat Transfer(Department Elective - I) Time: 02.30 PM to 05.00 PM Total Marks: 70 Instructions:
1. Attempt all questions. 2. Make suitable assumptions wherever necessary. 3. Figures to the right indicate full marks.
Q.1 (a) What is the difference between film and drop wise condensation? Which is a
more effective mechanism of heat transfer?
07
(b) Explain the function of extended surfaces with classification. 07
Q.2 (a) Derive Temperature distribution relation for cylinder with Steady state and
uniform heat generation.
07
(b) A chemical reaction takes place in a packed bed (k=0.6 W/m 0C) between two
coaxial cylinders with radii 15 mm and 45 mm. the inner surface is at 580 0C
and it is insulated. Assuming the reaction rate of 0.6 MW/m3 in the reactor
volume, find the temperature at the outer surface of the reactor.
07
OR
(b) Obtain an expression for the steady state temperature distribution of two
dimensional rectangular fin having constant thermal conductivity. The fin has
thickness of L in Y-direction and is semi infinite in X- direction. The base
temperature of fin and ambient temperature are t0 and t∞ respectively. Assume
the heat transfer coefficient to be large
07
Q.3 (a) What is lumped system analysis? Derive equation for lumped parameter
Analysis
07
(b) Water in a tank is to be boiled at sea level by a 1-cm-diameter nickel plated
steel heating element equipped with electrical resistance wires inside. .
Determine the maximum heat flux that can be attained in the nucleate boiling
regime and the surface temperature of the heater surface in that case.
Take following properties of water at saturation temperature of 100 0C
ρ l= 957.9 kg/m3, ρ v = 0.6 kg/m3, Prl= 1.75, hfg= 2257 × 103 J/ kg, μl= 0.282 ×
10 -3 kg m/s, Cpl= 4217J / Kg 0C and Csf = 0.006 , n=1, Ccr =0.12
07
OR
Q.3 (a) Draw the boiling curve and identify the burnout point on the curve. Explain
how burnout is caused. Why is the burnout point avoided in the design of
boilers?
07
(b) An ordinary egg can be approximated as a 5-cm-diameter sphere with
approximately 75% water. The egg is initially at a uniform temperature of 5°C
and is dropped into boiling water at 95°C. Taking the convection heat transfer
coefficient to be h =1200 W/m2 °C, determine how long it will take for the
center of the egg to reach 70°C. Take thermal conductivity and diffusivity of
eggs at the average temperature of 37.5°C; k = 0.627 W/m °C , α = 0.151×10-6
m2/s, λ1 = 3.0753 and A1 = 1.9958
07
Q.4 (a) Define: Nusselt Number, Reynolds Number, Prandtl Number and give
conventional generalised basic equation for forced convection using these
numbers.
07
2
(b) Air at 20 0C and 1.013 bar flows over a rectangular container, with top surface
750 mm long in direction of flow and 1 m wide, at 35 m/s. determine the heat
transfer from the top surface maintained at 60 0 C.
use following properties of air at average temperature of 40 0C:
µ= 1.906X10-5 kg/ms, Cp = 1.007 kJ/kg 0C and k= 0.0272 W/m 0C, and
following correlations for finding average heat transfer coefficient
Nu = 0.664 (ReL)0.5 (Pr)0.33 if ReL ≤ 5 × 105
Nu = [0.037 (ReL)0.5 – 850] (Pr)0.33 if ReL > 5 × 105
07
OR
Q.4 (a) Explain briefly Flow boiling regimes. 07
(b) Air at 2 bar and 40 c is heated as it flows through a 30mm diameter tube at a
velocity of 10m/s. If the wall temperature is maintained at 100 0C all along the
length of the tube, make calculations for heat transfer per unit length of the
tube. Proceed to calculate the increase in bulk temperature over one meter
length of the tube. Use Nu=0.023 (Re0.8 )(Pr0.4)
And take following thermo-physical properties of air at the average film
temperature of 70 0C
µ=20.6×10-6 Ns/m2, Cp=1.009 kJ/Kg 0C, k=0.0297 W/m 0 C and Pr=0.694
07
Q.5 (a) Explain all the different mechanisms of heat transfer from the human body (a)
through the skin and (b) through the lungs.
07
(b) Explain effect of radiation on measurement of temperature by a bare
thermometer. A bare thermometer measuring the temperature of a gas body
reads 600 K. The surrounding walls are 500K. The thermometer bulb is 3mm in
dia and is spherical, its surface emissivity being 0.7. The convective heat
transfer coefficient over the surface is 40 W/ m2K. Determine the gas
temperature and error involved.
07
OR
Q.5 (a) Write a short note on Emissivity and absorptivity of gases and gas mixtures 07
(b) Consider a man of surface area 1.8 m2 and convective heat transfer coefficient
4 W/m2 0C wearing summer clothes whose thermal resistance is 0.93 m2 0C/W.
The man feels very comfortable (33 0C) while standing in a room maintained at
22°C with same air temperature. The air motion in the room is negligible. If this
man were to stand in that room unclothed, determine the temperature at which
the room must be maintained for him to feel thermally comfortable. Take indoor
radiation heat transfer coefficient 4.7 W/m2 0C
07
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Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VII(NEW) • EXAMINATION – WINTER 2016
Subject Code:2171911 Date:18/11/2016
Subject Name: Advance Heat Transfer(Department Elective - I)
Time: 10.30 AM to 1.00 PM Total Marks: 70 Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Tables for properties of air and water are permitted.
Q.1 (a) Write the finite-difference equations under steady-state conditions for the
following situations:
(i) (ii) (iii)
07
(b) In a wind tunnel, air at 5 m/s flows over a flat plate and 15oC, 1 m x 0.8 m in
size. The surface temperature of plate is 35oC. One of the side of the plate is
arranged parallel to the flow direction, such that the heat transfer is lesser,
estimate:
(i) Rate of heat transfer from the one side of plate
(ii) Initial rate of cooling per hour of the plate, if mass of the plate is 5 kg
and specific heat is 875 J/kg.K.
(iii)If the flow is turned off, compute the heat flow rate from the upper
surface of the plate in still air at 15oC.
(iv) What is the percentage change in heat flow rate?
The thermo-physical properties of air are as follows:
ρ= 1.1707 kg/m3 , = 15.172 x 10-6 m2/s , k= 0.02614 W/mK, Cp=1007 J/KgK,
Pr = 0.7075
Use the following correlations:
For free convection: Nu= 0.27 (Gr. Pr) 0.25
For forced convection: Nu= 0.664 (Re) 0.5 (Pr) 0.33
07
Q.2 (a) A cylindrical furnace whose height and diameter are 5 m contains gases at 1200
K and a total pressure of 2 atm. The composition of the gases is determined by
volumetric analysis to be 85 percent N2, 8 percent H2O, 7 percent O2.
Determine the effective emissivity of the gases. Consider L = 0.6D
Make use of following charts
07
2
(b) Consider three consecutive nodes n - 1, n, and n + 1 in a plane wall. Using the
finite difference form of the first derivative at the midpoints, show that the
finite difference form of the second derivative can be expressed as
07
OR
(b) Define these terms used in the finite difference formulation: node, nodal
network, volume element, nodal spacing, and difference equation. 07
Q.3 (a) What is an irregular boundary? What is a practical way of handling irregular
boundary surfaces with the finite difference method? 07
(b) In a production facility, large brass plates of 4 cm thickness that are initially at a
uniform temperature of 20°C are heated by passing them through an oven that
is maintained at 500°C. The plates remain in the oven for a period of 7 min.
Taking the combined convection and radiation heat transfer coefficient to be h
= 120 W/m2.°C, determine the surface temperature of the plates when they
come out of the oven using Heisler charts (given at end of paper).
The properties of brass at room temperature are k = 110 W/m·°C, ρ = 8530
kg/m3, Cp = 380 J/kg · °C, and α = 33.9 10-6 m2/s
07
OR
Q.3 (a) Define fin efficiency and fin effectiveness. Why is the insulated-tip solution
important for the fin problems? 07
(b) Explain radial fins of rectangular and parabolic profiles. 07
Q.4 (a) Explain the mechanism of laminar film condensation on a vertical plate. 07
(b) The water flows at 20oC enters a 2 cm diameter tube with a velocity of 1.5 m/s.
The tube is maintained at 100oC. Find the tube length required to heat the water
to a temperature of 60oC.
The properties of water are:
ρ = 992.2 kg/m3 , = 0.659 x 10-6 m2/s , k= 0.634 W/mK ,Cp= 4.174 kJ/KgK,
Pr= 4.31
07
OR
Q.4 (a) Discuss the various regimes of pool boiling with neat sketch. 07
(b) Explain heat transfer in high velocity flow with neat sketch. 07
Q.5 (a) What is Beer’s law?
Why do surfaces absorb differently for solar or earthbound radiation?
07
3
(b) How is the insulating effect of clothing expressed? How does clothing affect
heat loss from the body by convection, radiation, and evaporation? How does
clothing affect heat gain from the sun?
07
OR
Q.5 (a) What is latent heat? How is the latent heat loss from the human body affected
by (a) skin wettedness and (b) relative humidity of the environment? How is the
rate of evaporation from the body related to the rate of latent heat loss?
07
(b) A long, circular aluminum rod is attached at one end to a heated wall and
transfers heat by convection to a cold fluid.
(i) If the diameter of the rod is tripled, by how much would the rate of heat
removal change?
(ii) If a copper rod of the same diameter is used in place of the aluminum, by
how much would the rate of heat removal change?
07
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