الفهرس 
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Abstract
This study presents an experimental investigation on the hydrothermal attributes of inline complete circular or semi-circular tube bundles at several rates of an airflow across
the tubes, which corresponds to maximum Reynolds number (Reo,max) of the air of
1516 ≤ Reo,max ≤ 19355. Throughout the runs, several attack angles () of the semicircular tubes (0 90), gap between their bases to the tube diameter ratio () of
0.126 0.378, transversal (1.5 ST/dt,o 3.5) and longitudinal (1.5 SL/dt,o 3.5)
pitch ratios are considered.
In the experiments, chilly water, with constant inlet temperature of 15C and total flow
rate of 61.2 l/min, is passed through the tubes while hot air is passed across the tube
bundle. 1386 runs are accomplished using 198 arrangements of the tube banks; sixtythree runs are carried out with complete circular tubes, and 1323 tests are carried out
with semi-circular tubes. 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 experiments, the results state that splitting the tubes augments the heat
exchange rate besides increasing the airflow resistance. It is documented that the
influence of varying the pitch ratio of the tubes in the transversal direction on the heat
exchange rate and the fluid pumping power is greater than that varying the pitch ratio
of the tubes in the longitudinal direction. It is shown that growing the pitch ratio of the
tubes in the longitudinal direction from 1.5 to 3.5 decreases both Nuo and 𝑓o by 17.5%
and 11.2%, respectively. While growing the pitch ratio of the tubes in the transversal
direction from 1.5 to 3.5 decreases both Nuo and 𝑓o by 51% and 65.3%, respectively.
Additionally, increasing the ratio of the gap between the bases of semi-circular tubes to
their outer diameter increases both Nuo and 𝑓o. Compared to the complete circular tube
bundle, the average percentage growths in Nuo and 𝑓o are 58.2% and 13.4%,
respectively, at = 0.126, and are 67% and 21.1%, respectively, at = 0.378.The results assure also that the direction of the semi-circular tube base affects the
hydrothermal attributes with two different trends. In the range, 0 60, the Nuo
and 𝑓o are increased with growing the attack angle. Compared with complete circular
tube, their maximum increases at = 60 are 85.1% and 23.3%, respectively. While in
the range, 60 90, the Nuo and 𝑓o are reduced with growing the attack angle.
Compared with complete circular tube, their increases are dropped to be 22.8% and
9.2%, respectively, at = 90.
Moreover, the hydrothermal performance index (HTPI) is calculated to compare the
variation ratio of the air-side Stanton numbers to the variation ratio of their associated
airflow resistance due to using semi-circular tubes. The HTPI is affected by varying
the semi-circular tube geometrical parameters. It is increased by decreasing the pitch
ratios of the tubes in the transversal or longitudinal directions of the semi-circular
tubes, increasing the gap between the semi-circular tubes’ bases, increasing the semicircular tube attack angle in the range 0 60, decreasing the semi-circular tube
attack angle in the range 60 90, and increasing the airflow rate across the tube
bank.
Furthermore, the resulted documented that the maximum value of HTPI is 2.11,
recorded at maximum airflow rate and = 60, ST/dt,o = 1.5, SL/dt,o = 2 and = 0.378.
Finally, set of experimental correlations are anticipated to assess the Nuo, 𝑓o and HTPI
of the in-line semi-circular tube bank as functions of the examined parameters.