Abstract:
While known to be superior coolants in stand–alone conditions, some scepticism exists with respect to
the hydrodynamic and thermodynamic performance of nanofluids in real life applications. The present
work employs theoretical investigations (supported by simulation results) on the entropy generation
characteristics in parallel microchannel cooling systems (PMCS) employing water and nanofluid as working
fluids. Alumina-water nanofluid of different concentrations and PMCS of three different configurations,
viz. U, I and Z have been employed for the present study. In order to shed more clarity onto the
real thermodynamic performance of nanofluids, an Eulerian–Lagrangian discrete phase approach
(DPM) has also been used to model nanofluids alongside the conventional effective property approach
(EPM). The thermodynamic performance of twin component nanofluid model in PMCS over the base fluid
and single component counterpart has been investigated in view of flow friction generated entropy and
heat transfer generated entropy. To quantify thermodynamic irreversibility of nanofluids in PMCS due to
heat transfer, the Bejan number has been employed. The entropy generation due to particle migration
effects reveal that the effective property model overestimates the entropy generation in case of nanofluids
and essentially nanofluids generate lesser degree of entropy than estimated by use of simplistic models.
The Bejan number analysis reveals that although hydrodynamically inferior to water, nanofluids are
thermodynamically superior fluids when employed as coolants in complex microscale flow systems. The
article sheds insight onto the entropy generation behaviour of such dispersed system flows with respect
to flow and heat transfer characteristics such as particle concentration, flow Reynolds number, and heat
load for proper design of such systems.
