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Air-Side Velocity Distribution in Finned-Tube Heat Exchangers.


pdf icon 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.