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HỘI THẢO QUỐC TẾ ATiGB LẦN THỨ CHÍN - The 9 ATiGB 2024 11

Additionally, it can be seen in Fig. 5 that the B. Heat transfer
maximum temperature at outlet of the cold fluid flow As seen in Fig. 7, the friction coefficient of the hot
for case 1, 2, 3 are 294.55K, 294.62K, 294.63K fluid flow decreases with Reynolds numbers of the hot
respectively with Reh = 17000 and the minimum fluid flow increases in all cases. This is because the
temperature at outlet of the hot fluid flow for case 1, 2, increase of Reynolds numbers of the hot fluid flow
3 are 330.95K, 330.88K, 330.84K respectively with leads to velocity of the hot fluid flow in the inner pipe
Reh = 5000. increases, resulting in higher pressure drop. However,
Fig. 6 shows temperature and velocity distribution the increase in velocity is greater than the increase in
at a cross section perpendicular to the centerline of the pressure loss so the hot fluid flow friction coefficient
pipe (at z = 250 mm and Reh = 5000) for the three decreases. Generally, for Reh < 9000, the friction
cases. The hot and cold fluid flow temperature and coefficient of the hot fluid flow in case 3 has the
velocity distribution are evenly distributed largest value, but at Reh > 9000 the friction coefficient
concentrically. of the hot fluid flow in case 3 has the smallest value in
three cases. For example, at Reh = 17000, the friction
coefficient of the hot fluid flow in case 3 is lower than
that in case 1, case 2 by 7.37%, 4.91% respectively;
and at Reh = 5000, the friction coefficient of the hot
fluid flow in case 3 is higher than that in case 1, case 2
by 6.32%, 6.5% respectively.

Fig.7. Effects of Reynolds numbers of the hot fluid
flow on friction coefficient of the hot fluid flow for the
three cases
Fig. 8,9 show effects of Reynolds numbers of the
Fig.5. Effects of Reynolds numbers hot fluid flow on mean Nusselt numbers of the hot and
of the hot fluid flow on hot and cold fluid cold fluid flow for the three cases. It can be seen that
flow temperature at outlet for the three cases mean Nusselt numbers of the hot fluid flow increase
with Reynolds numbers of the hot fluid flow increases
in all cases, but mean Nusselt numbers of the cold
fluid flow has decreased trend. In there, the Nu and
h
Nu of case 1 have smallest value in three cases. For
c
example, at Reh = 17000, Nu in case 2, case 3 are
h
higher than that in case 1 by 11.89%, 6.16%
respectively, and Nu in case 2, case 3 are higher than
c
that in case 1 by 0.75%, 4.84% respectively. Besides,
at Reh > 9000, the Nu of case 1 has increased more
h
and more slowly than in case 2, 3; this is because the
friction coefficient of the hot fluid flow in case 1 has
increased more and more strongly than in case 2, 3 for
Fig.6. Temperature and velocity Reh > 9000.
distribution at a cross section
perpendicular to the centerline of the pipe
(at z = 250 mm and Reh = 5000) for the three cases

ISBN: 978-604-80-9779-0