Page 157 - Modelling in Transport Phenomena A Conceptual Approach

5.2. RATE OF GENERATION IN ENERGY TRANSPORT 137

Table 5.1 Pressure difference in flow through a pipe with different orientation.

Geometry PA - PB PA - PB

FLOW

The answer to this dilemma lies in the fact that although energy is conserved,
its ability to produce useful work decreases steadily as a result of the irreversibilities
associated with the transformation of energy from one form into another2. These
irreversibilities give rise to energy generation within the system. Typical examples

2Note that 1,000 J at 100°C is much more valuable than 1,000 J at 2OOC.