![]() | Fig.D-2 Coefficient used to express the extent of kinetic energy conversion into thermal energy. |
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![]() | Fig.D-3 |
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- this loss is usually small when compared with local loss. However, it increases with length of the
investigated pipeline element and may become very large in very long pipelines. As shown in Fig.D-4,
for a pipe with constant cross-section
it is particularly evident that more complex energetic changes must take place than a simple
. Velocity
(because of
= constant)
and therefore also the kinetic energy
in this case simply cannot vary. If there is, as is the case in Fig.D-4, also
= 0 , there are actually only two variable terms in the
equation,
pressure energy and thermal energy.
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Fig.D-4 Friction loss in a horizontal constant cross section pipe: Castelli Theorem dictates that for constant cross section there is invariant velocity - and hence also invariant kinetic energy. If conversion of some kinetic energy into heat takes place, the decrease must be immediately compensated for by changes in another energy component: because the pipe is horizontal (an there are, therefore, no changes in position energy), the only possible chance is decrease in pressure energy. | ![]() |
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Vaclav TESAR : "BASIC FLUID MECHANICS"