Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.
Compact Heat Exchangers (CHEs) play an important role in
a wide range of applications, e.g. in windmill gear units,
machine tools, mobile hydraulic systems and so on. For each
field, specific requirements are needed (i.e. heat transfer rate,
mass, size and pressure drop), which are achieved also through
different types of configuration for the fin geometry in both the
oil and the air channel.
By means of CFD simulations of a small part of the CHE
core, it is possible to know how a certain coupling of air and oil
channels performs. However, when the number of
configurations to be analysed is consistent, it is preferable to
choose the smallest meaningful computational domain, in order
to reduce computational resources while keeping all important
physical phenomena.
The purpose of this paper is to demonstrate that, despite oil
flow can lead to convective heat transfer coefficient several
times higher with respect to air flow, a change in the fin
geometry affects significantly the “conjugate heat transfer” and
the CHE performance. Besides, it is presented a simplified
model for the heat exchanger element where the oil channel
conductive and convective heat exchange are modelled by
using a fixed temperature boundary condition and an effective
thermal resistance. 3-D simulations were carried out
considering a fixed fin geometry for the air channel and five
different fin geometries for the oil channel. Two cases of
operative conditions were taken into account. Furthermore, for
each coupling of channels, the simplified model was applied.
Results demonstrate that a change in the fin geometry for
the oil channel affects the overall heat transfer, and this
influence is greater or smaller depending on the operative
conditions. Secondly, the reduced model is shown to yield
results with a reduction in accuracy that can not be neglected.
