Lovely Professional University 2009 B.Tech Information Technology Assignment 4- Mechanical Engneering - Question Paper

ASSIGNMENT-4

COURSE CODE- MEC 251


1)A wall of house is constructed from a 11.25cm layer of common brick, followed by a 4cm layer of plaster. What should be the thickness of loosely packed rock wool added in ranging from brick and plaster to decrease the heat loss through wall by 75%.
Thermal conductivity of the brick (Kbrick) = 0.7 W/mK
Thermal conductivity of the plaster (Kplaster) = 0.48 W/mK
Thermal conductivity of rock wool (Krock) = 0.065 W/mK

2)(a) A composite has 2 layers of various materials with thermal conductivity K1 & K2. If every layer has identical thickness, what is the equivalent conductivity of slab?

(b) 2 various metallic slabs of equal areas are joined together and the temperatures of the free surfaces are 400 c and 200 c. The conductivities of 2 metals (K1/K2) are in the ratio 1:3, if the junction temperature in ranging from the 2 surfaces is needed to be 300 c then what must be the ratio of their thicknesses?


3)A 0.5m thick plane wall has its 2 surfaces kept at 3000 c and 2000 c the thermal conductivity of the wall raises with temperature and its values at 3000 c and 2000 c are 25W/mK and 15W/mK respectively then what is the steady heat flux through the wall?


4)A cube at high temperature is immersed in a constant temperature bath. It losses heat from its top, bottom and side surfaces with heat transfer coefficients of h1, h2, and h3 respectively. What is the avg. heat transfer coefficient of the cube?


5)(a) A large spherical encloser has a small opening. The rate of emission of radioactive flux through this opening is 7.35KW/m2. What is the temperature at the inner surface?
(Assume Stefan Boltzmann constant = 5.67*10-8 W/m2K4)

(b) Solar radiation of 1200 W/m2 falls perpendicularly on a gray opaque surface of emissivity 0.5. If the surface temperature is 500 c and surface emissive power is 600W/m2. What is the radiocity of the surface will be?


6)An electrical conductor of copper with diameter of 10mm is covered with a plastic insulation of thickness 10mm, the temperature of its surroundings is 200 c using the subsequent data, obtain what is the max current carried by the conductor so that no part of plastic is above 800 c.
K copper = 400W/mK
K plastic = 0.5 W/mK
Thermal heat transfer coefficient = eight W/m2K
Specific electrical resistance = 3*10-8 ohm-m

Earning:   Approval pending.