NUMERICAL STUDY OF CROSS FLOW FAN PERFORMANCE IN AN INDOOR AIR CONDITIONING UNIT

In this study, a detailed characterization is carried out on a typical cross flow fan
used in the HVAC industry, in order to understand the fan design in detail. The study
is carried out numerically followed by experimental validation. The challenge in the
study lies in the large number of variables involved and the geometric complexity.
The numerical simulation is carried out by use of the software FLUENT. The
geometry of the flow domain is created in the preprocessor and the governing
equations of fluid flow are identified along with the appropriate boundary conditions.
This is followed by appropriate grid size selection. The RMS error is less than 7% for
the 2D model and less than 20% for the 3D model. From the 2D study, it is concluded
that the optimum number of blades is 37 for the fan with diameter of 102 mm. The
thickness of the blade determines the total flow area and flow rate delivered. When
the internal blade angle is at 90°, shock free entry is incurred and maximum flow rate
can be achieved. Finally, the external blade angle should be within 20 to 45 degrees,
to avoid rapid drop of pressure coefficient and efficiency. It is concluded from the 3D
study that the straight impeller provides better performance than the twisted impeller.