Download TUTORIAL 3- HEAT TRANSFER- 326-2023

TUTORIAL
1.
Define thermal conductivity
2.
Define the convection heat-transfer coefficient.
3.
Discuss the mechanism of thermal conduction in solids.
4.1
Discuss the mechanism of heat convection.
4.2
Name some good conductors of heat; some poor conductors
5
A flat wall is exposed to an environmental temperature of 38◦C. The wall is
covered with a layer of insulation 2.5 cm thick whose thermal conductivity
is 1.4 W/m・ ◦C, and the temperature of the wall on the inside of the
insulation is 315◦C. The wall loses heat to the environment by convection.
Compute the value of the convection heat-transfer coefficient that must be
maintained on the outer surface of the insulation to ensure that the outersurface temperature does not exceed 41◦C.
6
Consider a wall heated by convection on one side at T1 and cooled by
convection on the other
side at T2. Show that the heat-transfer rate
through the wall is
q= T1 −T2/1/h1A+_x/kA+1/h2A
where T1 and T2 are the fluid temperatures on each side of the wall and h1
and h2 are
the corresponding heat-transfer coefficients.
7
One side of a plane wall is maintained at 100◦C, while the other side is
exposed
to a convection environment having T =10◦C and h=10 W/m2 · ◦C. The wall
has
k =1.6W/m· ◦C and is 40 cm thick. Calculate the heat-transfer rate through the
wall.
8. An aluminum can having a volume of about 350 cm3 contains beer at 1◦C.
Using a lumped-capacity analysis, estimate the time required for the contents to
warm to 15◦C when the can is placed in a room at 20◦C with a convection
coefficient of 15 W/m2·◦C. Assume beer has the same properties as water.
9.
Define the Biot number
15 A stainless-steel rod (18% Cr, 8% Ni) 6.4 mm in diameter is initially at a
uniform temperature of 25◦C and is suddenly immersed in a liquid at 150◦C with
h= 120 W/m2·◦C. Using the lumped-capacity method of analysis, calculate the
time necessary for the rod temperature to reach 120◦C.
10.
A 5-cm-diameter copper sphere is initially at a uniform temperature of
200◦C. It is suddenly exposed to an environment at 20◦C having a heat-transfer
coefficient h=28 W/m2·◦C. Using the lumped-capacity method of analysis,
calculate the time necessary for the sphere temperature to reach 90◦C.
11. An aluminum sphere, 5.0 cm in diameter, is initially at a uniform
temperature of 50◦C. It is suddenly exposed to an outer-space radiation
environment at 0 K (no convection). Assuming the surface of aluminum is
blackened and lumped-capacity analysis applies, calculate the time required for the
temperature of the sphere to drop to−110◦C.
Geoffrey, 2022