A combined PLIF/IR thermography technique was
developed and employed towards the measurement of unsteady
and conjugate heat transfer in thin, gravity-driven falling liquid
film flows (with and without flow pulsation) over an inclined
heated metal foil. Simultaneous, local film thickness, film and
substrate temperature, heat flux exchanged with a heated foil
and heat transfer coefficient results are reported for a range of
electrically applied heat input values, flow Reynolds (Re)
numbers and flow pulsation frequencies. Moreover, interfacial
wave velocities were calculated from cross-correlations across
successive thickness profiles. Results concerning the
instantaneous and local heat transfer coefficient variation and
how this is correlated with the instantaneous and local film
thickness variation (waves) suggest that the heat transfer
coefficient experiences an enhancement in thinner films. The
particular observation is most probably attributed to a number
of unsteady flow phenomena within the wavy fluid films that
are not captured by the steady analysis. At low flow Re number
values the mean Nusselt (Nu) was around 2.5, in agreement
with laminar flow theory, while at higher Re values, higher Nu
were observed. Finally, lower wave amplitude intensities were
associated with higher heat transfer coefficient fluctuation
intensities.