UNIVERSITY OF PLYMOUTH
SCHOOL of ENGINEERING
BENG3 THERMAL & FLUIDS ENGINEERING (THER305)
TUTORIAL EXAMPLES in HEAT TRANSFER (Revision)
1.
A furnace wall consists of 250 mm
firebrick, 125 mm insulating brick and 250 mm building brick. The inside wall
is at 600°C and atmospheric temperature is 20°C. Calculate the heat transfer
rate per unit area and the outside wall surface temperature. For the outside
surface of the wall, h = 10 W/m²K and for the firebrick, insulating brick and
building brick l
= 1.4, 0.2 and 0.7 W/mK respectively. [460 W/m², 66°C]
2.
Determine the U-value of a 150 mm thick
solid concrete wall where the inside and outside surface heat transfer
coefficients are 10 W/m²K and 25 W/m²K respectively and the thermal
conductivity of concrete is 1.5 W/mK. Ignore radiation. [4.167 W/m²K]
3.
Determine the heat loss per meter run of
a 22mm copper pipe carrying hot water at 75ºC and insulated with a 60mm O.D.
sleeve made of material with a thermal conductivity of 0.038 W/mK. Assume an
outside surface heat transfer coefficient of 12 W/m²K, and an external air
temperature of –1°C. State any other assumptions needed. If a central heating
system has an output of 12 kW what percentage of this is lost if the total
length of pipe exposed to the low temperature is 20m. [16.4 W/m,
2.73%]
4.
A cylindrical refrigeration chamber 0.9 m
inside height is made from a layer of stainless steel 1 mm thick lagged on the
outside with plastic foam 190 mm thick. The surface heat transfer coefficient
on the inside is 50 W/m²K and on the outside 75 W/m²K. The inner diameter of
the refrigerator is 0.7 m. The thermal conductivity of stainless steel is 41
W/mK and of plastic foam is 0.5 W/mK. Calculate the heat transfer rate from the
chamber when the internal temperature is 190 K and the ambient temperature is
16°C. (Ignore the problems of the corners.) [595W]
5.
A triangular section (shown below) is used to
join two walls of a heating vessel together where one wall is at a temperature
of 20ºC and the other at 50ºC. The inside of the vessel contains liquid at 95ºC
and the surface heat transfer coefficient is 75W/m²K. Determine the heat loss
per meter length through the section.
Use a 2.0 mm orthogonal grid to obtain the temperature distribution. [312 W/m] Click here for Spreadsheet