  Forced convection cooling is important in numerous technologies ranging from
microprocessors in data centers to turbines and engines; active cooling is
essential in these situations. However, active transfer of heat or thermal
energy under a large temperature difference promptly destroys the exergy, which
is the free-energy component of thermal energy, and this issue has remained
unaddressed. Herein, we describe a thermoelectrochemical conversion to
partially recover presently lost exergy in forced convection cooling. We design
a test cell in which an electrolyte liquid is forced through a channel formed
between two parallel electrodes and the hot-side electrode simulates an object
to be cooled. Our investigations show that the narrower interelectrode channels
afford higher cooling and power generation performances. The mass transfer
resistance is the most dominant type of resistance for all the conditions
tested and the charge transfer kinetics is likely to be controlled by
viscosity. The dependence of the generated power on the flow rate is caused by
the change in the diffusion coefficient of redox species with temperature. As
an evaluation measure for such forced-flow thermocells, the gain (\Lambda)
--defined as the ratio of the generated power to the hydrodynamic pumping work
required to force the liquid through the cell-- is introduced. \Lambda is above
unity in a certain flow rate region. This demonstrates that such a system can
generate more electric power than the pump work required to drive the liquid
through the cell, suggesting its potential to partly recover presently lost
exergy of thermal energy as electricity.
