5 / 12
Fig. 3. Dependency of relative THC
on the angle
β
at
Re
= 10
5
:
—
η
ξ
; —
η
Nu
using the formula
K
Q
=
K
Q
0
A
∗
,
where
K
Q
0
=
η
Nu
η
−
1
/
3
ξ
K
Δ
p
(
K
m
/k
D
)
3
n
−
2
−
m
3
is HTI efficiency with
regard to a convective component in the circular non-finned channel
(
k
D
=
D
1
+
h
D
1
+
h
sm
is the mean diameter correction factor,
K
Δ
р
,
K
m
are
congruence conditions);
A
∗
=
A
f
η
f
is the finning thermal geometric factor
(
A
f
is a channel finning geometric parameter,
η
f
is a finning efficiency
coefficient).
All other conditions being equal, i.e. when hydraulic pressure losses and
coolant consumption are equal (
K
Δ
p
and
K
m
equal unity), the efficiency
criterion
K
Q
0
will be determined mostly by the power-law dependence
on the relative hydraulic characteristic
η
−
1
/
3
ξ
and the coefficient of the
convective heat transfer intensification
η
Nu
.
The channel geometric parameter in case of unidirectional fins is defined
by formula [1]
A
p
=
t
t
+
h
−
1 cos
β
!
3
n
−
m
−
2
3
,
where
t
f
=
t/δ
f
;
h
=
h/δ
f
;
t
and
δ
f
are the fin normal pitch and thickness;
h
is the fin height equalling the channel height;
β
is the fin tilt angle line;
n
and
m
are the power-law approximating coefficients in the equations for
Nu and
ξ
.
Parameter
A
f
was obtained as a result of the relative variables
transformation in both the object and the reference smooth channel.
Assuming that the fin normal pitch ratios on the working (heat releasing)
and the opposite (shaping) surfaces are proportional, they can be considered
equal, i.e.
t
1
≈
t
2
. The channel total height
h
is determined by the sum of
the opposite fins heights, i.e.
h
=
h
1
+
h
2
, while the angle
β
can be assumed
to equal a half of the fins intercrossing angle , i.e.
β
= 0
.
5(2
β
). Thus,
the parameter
A
f
, determined by the way of obtaining and processing the
48
ISSN 0236-3941. HERALD of the BMSTU. Series Mechanical Engineering. 2015. No. 2