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Fakulti Kejuruteraan Mekanikal & Pembuatan
Universiti Tun Hussein Onn Malaysia
BDA 30603: Heat Transfer – Individual Assignment 6
Topic: 2D Heat Conduction and Lumped System Page 01 of 01
3-130 Hot and cold water pipes 12 m long run parallel to each other in a thick concrete layer. The
diameter of both pipes are 6 cm, and the distance between the centerlines of the pipes is 40 cm. the
surface temperature of the hot and cold pipes are 60 °C and 15 °C respectively. Taking the thermal
conductivity of the concrete to be k = 0.75 W.m-1
.K-1
, determine the rate of heat transfer between the
pipes.
3-132 A row of 1 m long and 2.5 cm diameter used uranium fuel
rods that are still radioactive are buried in the ground parallel to
each other with a center to center distance of 20 cm at a depth of
4.5 m from the ground surface at a location where the thermal
conductivity of the soil is 1.1 W.m-1
.K-1
. if the surface temperature of
the rods and the ground are 175 °C and 15 °C respectively,
determine the rate of heat transfer from the fuel rods to the
atmosphere through the soil.
3-141 Hot water at an average temperature of 90 °C passes through a row of eight parallel pies that
are 4 m long and have an outer diameter of 3 cm, located vertically in the middle of a concrete wall (k =
0.75 W.m-1
.K-1
) that is 4 m high, 8 m long, and 15 cm thick. If the surface of the concrete walls are
exposed to a medium at 32 °C, with heat transfer coefficient of 12 W.m-2
.K-1
, determine the rate of heat
loss from the hot water and surface temperature of the wall.
4-5C Consider a hot baked potato on a plate. The temperature of the potato is observed to drop by 4
°C during the first minute. Will the temperature drop during the second minute be less than, equal to, or
more than 4 °C? Why?
4-6C Consider a potato being baked in an oven. The temperature of the potato is observed to rise by
5 °C during the first minute. Will the temperature rise during the second minute be less than, equal to,
or more than 5 °C? Why?
4-20 A person found dead at 5PM in a room whose temperature is 20 °C. the temperature of the
body is measured to be 25 °C when found, and the heat transfer coefficient is estimated to be at 8 W.m-
1.K
-1. Modeling the body as a 30 cm diameter, 1.7 m long cylinder and using the lumped system as a
rough approximation, estimate the time of death of that person. Take k = 0.617 W.m-1
.°C -1
, ρ = 996
kg.m-3
, and cp = 4178 J.kg -1
.°C-1
4-23 A brick of 203 x 102 x 57 mm in dimension is being burned in a kiln
to 1100 °C, and then allowed to cool in a room with ambient air
temperature of 30 °C and convection heat transfer coefficient of 5 W.m-
2.K
-1. If the brick has properties of ρ = 1920 kg.m
-3, and cp = 790 J.kg
-1 .°C
-1,
and k = 0.617 W.m-1
.°C -1
determine the time required to cool the brick to
a temperature difference of 5 °C from the ambient air temperature.
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