الفهرس 
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Abstract
The present work experimentally investigates the hydrothermal performance of
staggered semicircular tube (SCT) banks at different airflow rates across the tubes
(1516 ≤ Reo,max ≤ 19340) and compared with that of complete circular tube (CCT)
bundles. Numerous spacing ratios between the SCTs bases (0.126 ≤ ≤ 0.378), attack
angles of the SCTs (0 ≤ ≤ 90), and ratios of longitudinal (1.5 ≤ ≤ 3.5) and
transversal (1.5 ≤ ≤ 3.5) spacings between the SCTs are considered.
During the tests, cooling water are passed through the tubes at constant temperature and
total flow rate of 15C (Pri ≈ 7.95) and 51.7 l/min (Rei ≈ 3256), respectively. Totally,
1386 tests are carried out on the 198 arrangements of the tube bundles; 63 tests are done
with CCTs, and 1323 runs are done with SCTs. The thermal performance results in terms
of air average heat transfer coefficient, average Nusselt number and Fanning friction
factor, in addition to the overall heat transfer coefficient are presented for the different
governing parameters.
For all runs, the outputs assure that just splitting the tubes leads to augmenting the airside heat transfer characteristics in addition to increasing the airflow pressure drop.
Besides, the increases in Nuo and 𝑓o are grown up by increasing the spaces between the
bases of the SCTs. Compared with the CCT bank, the percentage increases in Nuo and
𝑓o are 67% and 23.3%, respectively, at SCT spacing ratio of 0.126, while these are 76.5%
and 30%, respectively, at SCT spacing ratio of 0.378.
Moreover, increasing the longitudinal pitch ratio of the tubes, from 1.5 to 3.5, reduces
Nuo and 𝑓o by 17.7% and 9.45%, respectively. While increasing the transversal pitch
ratio of the tubes, from 1.5 to 3.5, reduces Nuo and 𝑓o by 51.1% and 9.2%, respectively.
These show that the effect of the variation of the transversal pitch of the tubes on the
heat exchange rate is higher than that of the variation of their longitudinal pitch. While
the effect of their variations on the air-side friction factor is nearly close.
Furthermore, the attack angle of SCTs significantly influences the hydrothermal
characteristics of the SCT bank. It is obvious that there are two different trends through
two intervals of the attack angles, where the increases in the Nuo and 𝑓o due to splitting
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the tubes are grown up with increasing the attack angle of SCTs in the range of 0 to
60, and these increases are then damped between 60 and 90. Additionally, their
maximum increases are 102% and 44.5%, respectively, are obtained at attack angle of
60.
In addition, the hydrothermal performance index (HTPI) is assessed to compare the
variation ratio of the air-side Stanton numbers to the variation ratio of their associated
airflow resistance due to using SCTs. The results assure that the HTPI is augmented with
decreasing both the transversal and longitudinal pitch ratios of the SCTs and increasing
the spacing between the SCT bases. Besides, the HTPI is augmented with increasing the
SCT attack angle between = 0 to = 60, while increasing the attack angle from =
60 until = 90 dampens the HTPI. Additionally, the HTPI is augmented with
increasing the airflow rate across the tube bundle.
As well, the maximum recorded value of HTPI is 2.35 obtained at greatest airflow rate
and SCT of = 60, = 0.378, = 1.5, = 2.0. Finally, experimental correlations are
proposed to predict the air-side average Nusselt number and Fanning friction factor
besides the HTPI of the staggered SCT bundle as functions of the investigated
parameters.