Civil Engineering Reference
In-Depth Information
As in the case of bare pipelines, the above expressions are modified if the
insulated pipeline outside surface is taken as reference.
In all the foregoing relationships, average values of temperatures must be
introduced in the following situations:
• When a fluid enters a pipe at one temperature (
t
in
) and leaves at another (
t
out
)an
average temperature must be equal to (
t
in
+
t
out
)/2 at any point along the pipe (see
• When the value of the parameter k for insulation material varies significantly
with the temperature, the mean temperature between the two faces of the
insulation must be considered. The mean value is calculated as half the sum of
the temperatures on either side of the insulation.
Since the same amount of heat
flows through each layer of a multilayer
wall or pipeline, the temperature difference between the surfaces of
each layer is proportional to the thermal resistance of each layer
Δ
t
Layer
¼
Q
R
th
Layer
Q
.
8.3.3 Tanks, Other Equipment
In these cases specialized handbooks should be consulted to ascertain the
relationships and coefficients related to the shape of the structure to insulate and
to the operating temperature.
8.4
Thermal Energy End Users
At the end of thermal distribution pipelines, end users can be grouped as follows:
• Furnaces and ovens where fuels are burned directly;
• Systems where steam or hot water is released to make direct contact with the
products (steam to heat a water tank, steam to sterilize food products, etc.). In
this case, because of possible contamination during the process, the condensate
is generally discarded; potential recovery and thus potential energy saving must
be considered carefully in each individual case;
• Heat exchangers where the heat medium (steam, water, oil, etc.) transfers energy
to a colder fluid (air, water, or other fluids) by reducing its temperature or by
changing its state as in steam condensation (see Chap.
15
);
As a general rule, the steam consumed in the final users can be calculated by
using a few basic relationships.
