Air-Side Velocity Distribution in Finned-Tube Heat Exchangers.
Air-Side Velocity Distribution in Finned-Tube Heat
Exchangers.
(3272 K)
Yashar, D. A.; Cho, H. H.
NISTIR 7474; 67 p. December 2007.
Keywords:
heat exchangers; velocity distribution; air
conditioning; computational fluid dynamics; air
velocity; lasers; velocity profiles; ducts; air flow;
simulation; pressure drop; uncertainty
Abstract:
The performance of finned tube heat exchangers is
greatly affected by the distribution of the air that
passes through it. The air side velocity distribution
for finned-tube heat exchangers in residential air
conditioning installations is not very well documented
today because it is difficult to measure accurately. In
this study, we examined the air velocity distribution
approaching finned-tube heat exchangers under three
different common installation configurations. To this
end we used a novel, laser based technique called
Particle Image Velocimetry (PIV) to measure
the velocity profile. The heat exchangers examined in
this study were a vertically oriented single-slab coil,
a single slab coil placed at an angle of 65DG to the duct
wall, and a two slab A-Shaped coil with a 34DG apex
angle. The measurement results show that the velocity
profile for any configuration is strongly influenced by
the features within the duct and the orientation of the
heat exchanger, and therefore each installation
configuration has its own unique velocity distribution.
The information presented here documents the magnitude
and type of this mal-distribution realized in these
systems, what features caused it, and which regions were
most affected. Computational Fluid Dynamics (CFD)
simulations were carried out to simulate the air flow
through the test subjects used for the PIV measurements.
We employed momentum resistance models to simplify the
computational domains and reduce computer time. Our
simulation results showed good agreement with the
measured velocity profiles in each case. This work
suggests that CFD can be accurately applied as a tool to
determine the velocity profile. CFD is preferred to
laboratory experimentation because of its speed and
simplicity.
