May 1, 2011

ME 2251 — HEAT AND MASS TRANSFER Fourth Semester APRIL/MAY 2011 Anna University Question Paper

Fourth Semester
Mechanical Engineering
(Regulation 2008)

Time : Three hours  Maximum : 100 marks
(Use of approved Heat and Mass Transfer Data Book is permitted)
Answer ALL questions

PART A — (10 × 2 = 20 marks)
1.  State Fourier’s law of heat conduction.
2.  What is heat generation in solids? Give examples.
3.  What is lumped system analysis? When is it used?

4.  In which mode of heat transfer is the convection heat transfer coefficient
usually higher, natural or forced convection? Why? 
5.  Define bulk temperature.
6.  List the various promoters used for maintaining dropwise condensation.
7.  Define LMTD of a heat exchanger.
8.  What do you understand by thermal radiation?
9.  What does the view factor represent? When the view factor from a surface to
itself is zero?
10.  What is the physical meaning of Schmidt number?

PART B — (5 × 16 = 80 marks)
11.  (a) (i)  Define thermal conductivity. How does it vary with temperature for gases?    (4) 
   (ii)  Derive the general 3-dimensional heat conduction equation in cylindrical coordinates. Assume the material as homogeneous isotropic continues.   (12)
  (b)  A cold storage room has walls made of 23 cm of brick on the outside, 8 cm of plastic foam and finally 1.5 cm of wood on the inside. The outside and inside air temperatures are 22°C and –2°C respectively. The inside and outside heat transfer coefficients are respectively 29 and 12 W/m2.K. The thermal conductivities of brick, foam and wood are 0.98, 0.02 and 0.12 W/m.K respectively. If the total wall area is 90 m2, determine the rate of heat removal by refrigeration and the temperature of the inside surface
of the brick.
12.  (a)  (i)  Define the velocity boundary layer and thermal  boundary layer thicknesses for flow over a flat plate. (4)
   (ii)  Atmospheric air at 150°C flows with a velocity of 1.25 m/s over a  2 m long flat plate whose temperature is 25°C. Determine the average heat transfer coefficient and the rate of heat transfer for a plate width of 0.5 m.   (12)
  (b) A 6 – m long section of an 8 cm diameter horizontal hot water pipe passes through a large room in which the air and walls are at 20°C. The pipe surface is at 70°C and the emissivity of the pipe surface is 0.7. Find the rate of heat loss from the pipe by natural convection and radiation.
13.  (a) Consider laminar film condensation of a stationary vapour on a vertical flat plate of length L and width b. Derive an expression for the average  heat transfer coefficient. State the assumptions made.
  (b) (i) Explain briefly fouling in heat exchangers. (6)
   (ii) Hot gases enter a finned tube, cross flow heat exchanger with a flow rate of 1.5 kg/s and a temperature of 250°C. The gases are used to heat water entering the exchanger at a flow rate of 1 kg/s and an inlet temperature of 35°C. On the gas side, the overall heat transfer coefficient and the area are 100 W/m2.K and 40 m2 respectively. What is the rate of heat transfer by the exchanger and what are the
gas and water exit temperatures? Assume  p C of gas as 1.0 kJ/kg.K. 
 229  229  229 
    11407  3
14.  (a) (i)  Distinguish between irradiation and radiosity.  (4)
   (ii) Consider a cylindrical furnace with outer radius = height = 1 m. The top (surface 1) and the base (surface 2) of the furnace have emissivities 0.8 & 0.4 and are maintained at uniform temperatures of 700 K and 500 K respectively. The side surface closely approximates a black body and is maintained at a temperature of 400 K. Find the net rate of radiation heat transfer at each surface
during steady state operation. Assume the view factor  from the base to the top surface as 0.38.  (12)
  (b) (i)  Considering radiation in gases, derive the exponential-decay formula.   (6)
   (ii) Two very large parallel planes exchange heat by radiation. The emissivities of the planes are respectively 0.8 and 0.3. To minimize the radiation exchange between the planes, a polished aluminium radiation shield is placed between them. If the emissivity of the
shield is 0.04 on both sides, find the percentage reduction in heat transfer rate.    (10)
15.  (a)  (i)  With neat sketches, explain the different types of fins. (4)
   (ii) Air at 1.01 bar and 30°C flows past a tray full of water with a velocity of 2 m/s. The partial pressure of water vapour  is 0.7 kPa and the saturation pressure is 3.17 kPa. The tray measures 40 cm along the flow direction and has a width of 20 cm. Calculate the  evaporation rate of water if the temperature on the water surface is
25°C. Assume the following properties for air: density,  ?  1.2 kg/m3, kinematic viscosity,  ? = 15  × 10-6 m2/s and diffusivity,  D = 0.145 m2/h.   (12)
  (b) Write short notes on the following:  (8 + 8)
   (i)  Analogy between heat and mass transfer
   (ii) Evaporation process in the atmosphere.



Post a Comment

Get Syllabus in your Mail


Accenture Admission Notice - 2010 Admission Notification Anna University Anna University Chennai Anna University Question Papers Anna University Trichy Apparel Technology and Management Aptitude Questions Arts and Science Colleges Biomedical Engineering C and CPP Ebooks Calicut University CBSE Question papers Civil Engineering Civil Service Exams Colleges in India Colleges Result Computer Science Engineering Core Jobs CS R2008 CSE CSIR NET EBooks Download ECE EEE EIE Electives Electrical and Electronics Engineering Electronics and communication Electronics and Instrumentation Engineering Engineering Engineering Colleges in Maharashtra Engineering Colleges in TamilNadu Engineering Admissions Engineering Colleges Engineering Colleges in Karnataka Engineering Jobs Engineering Syllabus Entrance Exam Dates Entrance Exam Results Entrance Examination Exam Time Table Experiencer First Year Syllabus Freshers Full Time Jobs Government jobs in india Hardware and Networking Jobs Hotel Management and Catering Technology IGNOU Information Technology INTEVIEW QUESTIONS IT Jobs JNTU Question Papers Jobs in Bangalore Jobs in Chennai Jobs in Coimbatore Jobs in Delhi Jobs in Hyderabad Jobs in India Jobs in Kerala Jobs in Noida Jobs in Tamilnadu Jobs in TATA Karnataka Educations Lab Manuals Mechanical Engineering Medical Colleges Placement Papers Plus 2 Preparation for exams Private Jobs in India Question Papers Question Papers Download Results Announcement Semester 1 Semester 2 Semester 3 Semester 4 Semester 5 Semester 6 Semester 7 Semester 8 Syllabus Syllabus Download Tamil Movie TCS Placement Papers Teaching Jobs TECH MAHINDRA Textile Technology Top colleges University Results UPSC VICEVESVARAYA TECHNOLOGICAL UNIVERSITY waec Walk-in Interview Web Designers



Anna university Engineering Syllabus

Earn Money From Online

Government jobs in india

Admission Notification

Total Pageviews


Privacy Policy use third-party advertising companies to serve ads when you visit our website. These companies may use information (not including your name, address, email address, or telephone number) about your visits to this and other websites in order to provide advertisements about goods and services of interest to you. If you would like more information about this practice and to know your choices about not having this information used by these companies, click here.