| Summary: | To address the scarcity of natural convection research for
the tube array with three or more columns of horizontallyaligned cylinders, this paper conducts RANS/URANS
simulations for multiple cylinder columns in one or two rows,
validated by particle-image velocimetry and heat transfer
measurements. Parametric study with varying horizontal and
vertical pitches is implemented by RANS with transition SST
model. Key findings are then substantiated and examined by
URANS. It is found that the horizontal pitch influences the
balance between the chimney effect and the blockage effect,
thus has an optimum with respect to the natural draft velocity.
For all the vertical distances computed in the two-row thermal
chimney model, the flow pattern stays in a plume-dominant
mode at the large horizontal pitch and a chimney-dominant
mode at the small horizontal pitch. Interestingly, at the
intermediate horizontal pitch (pitch/diameter2.5), the flow
pattern switches from plume-dominant to chimney-dominant
over a minor increase of the vertical pitch (from 4.5 to 6
diameters), leading to significant augmentation in natural draft
velocity and heat transfer on cylinder surfaces. This distinct
thermo-flow behavior, identified for the first time to the
authors’ knowledge, may be harnessed to improve the
performance of passive heat exchangers.
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