This paper presents numerical predictions
and results of air flow and pressure distribution in
common possible iterations of duct and diffuser having:
1. square, rectangle and circular duct shape, 2. square
duct with side 12in, 15in and 18in and 3. bend radius to
width ratio of 0, 0.5, 1 and 2. The system is designed to
develop an optimal system to reduce the noise levels in a
classroom which are far above the recommended value
of 35dB by WHO in an engineering institution designed
according to the Common Public Works
Department(CPWD) norms while also bridging the gap
between the industry and the consumer.
The iterations were designed on fusion 360 and
tetrahedron meshing was done in ANSYS after defining
the boundaries of geometry of CAD design. The inlet
velocities varied as per the different diffuser size, shape
and angles. The inlet velocity lies in the range of 1.5m/s
to 3m/s.
After setting up the solver and choosing k-omega
SST model for solving, calculation was performed for
3000 iterations using hybrid initialization to reduce the
residuals as much as possible for the results to converge
for accurate results. Material properties of aluminum
and properties of the fluid were set.
Among different groups, results based on different
shapes showed that circular duct displayed gradual
pressure and velocity drop at the lower bend of the wall
than in the case of rectangle or square. While, in case of
duct with different sizes, as size of duct increased,
frictional losses increased, while pressure drop, noise
levels and eddy current formation significantly reduced.
In case of different bend radius to width ratio(r/W), as
r/W increased, eddy formation and boundary layer
separation, pressure drop, turbulence and noise levels
decreased.
Therefore, the study showed that a circular duct,
with a diameter of 15in having r/W ratio of 2 would
significantly reduce the sound levels and be the
optimum solution for the classroom and adding 2-3
vanes would further improve the performance of the
system and maximize the required effort.
Keywords : HVAC; Ansys; CFD; Duct; Diffuser; Pressure drop
