Abstract:
In a previous study, heat transfer enhancement using a deformable
wall in a heat exchanger was demonstrated numerically
using CFD calculations in liquid single-phase situation.
This configuration allows the pumping function to be integrated
within the heat exchanger itself. Based on these results, a prototype
has been developed (but with different dimensions than in
the numerical study) in which one of the walls constituting the
channel is subjected to dynamic deformations in the form of a
traveling wave. Electric heaters on the other wall heat the channel.
Actuation is achieved by means of piezoelectric actuators.
Experimentally, the pumping function is observed, for all frequencies
of deformations and for two different fluids (water and
HFE 7000). The heat transfer intensification is also shown, and
this in two experimental configurations:
- a pressure difference (which may be zero) between the inlet and
outlet of the channel is imposed: in this configuration, the traveling
wave imposes the flow-rate. The heat transfer enhancement
is then due both to the increase of the flow-rate and the disruption
of the thermal boundary layers generated by the wave;
- a flow-rate is imposed with a mechanical pump: in this case
actuation has no effect on the pumping, and the measured heat
transfer enhancement is then due only to the effects of the imposed
dynamic deformations.
First experiments with the presence of boiling were also performed.
It was found that boiling can occur even if the fluid
does not reach the saturation temperature within the channel. A
100% increase in the mean heat transfer coefficient was found
when actuating the channel wall.
Description:
Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016.
