Compare via the experiment, the better efficiency of the
heat transfer is 100 ppm concentration of silver nano-fluid
water solution; the worse one is 450 ppm concentration of
silver nano-fluid water solution. Although the nano-fluid
has the higher heat-conduction coefficient that dispels more
heat theoretically. But the higher concentration will make
the higher viscosity. The higher viscosity makes the bubble
difficult to produce and the force of friction causes obstruction
of the liquid slug with tube wall becomes larger, so
obstruction is relatively greater when the bubble is promoted
and influences the whole efficiency of the heat
transfer.