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The analyses defined that the determining factors for CC thermal
hydraulic characeristics were a flow mode parameter (Reynolds numbers)
and the fin-crossing angle
2
β
, while the pitch ratio and the fin angles
asymmetry proved to be insignificant.
When the tests were conducted and the results were processed, the
following type approximating equations were obtained for THC. The
convective heat transfer rate (i.e. minus finning contribution to the effective
heat transfer) takes the form:
St
= exp(
−
2
.
47 + 0
.
81
β
)
Re
−
0
.
32
Pr
−
0
.
6
or
Nu
=
e
(
−
2
.
47+0
.
81
β
)
Re
0
.
68
Pr
0
.
4
;
a hydraulic drag coefficient can be written as:
ξ
=
e
(5
.
24+2
.
94
β
)
Re
−
1
.
32
+
e
(
−
4
.
7+3
.
46
β
)
,
where Re
= (
ρud
e
)
/μ
is the Reynolds number; Pr
=
μc
p
/λ
is the Prandtl
number;
β
is a half of the fins crossing angle (
2
β
);
u
is the mass average
flow velocity in the interfin channels;
d
e
is the equivalent hydraulic diameter
of the interfin channels. The coolant properties were determined by the mass
average flow temperature in SI system, rad.
Relative thermal hydraulic characteristics for CC can be obtained
by comparing them with characteristics of the reference smooth circular
channel with compatible values of the Re and Pr numbers.
The reference channel characteristics can be presented by the following
dependencies [5]:
Nu
sm
= 0
.
021
Re
0
.
8
Pr
0
.
43
— is a convective heat transfer coefficient,
ξ
sm
= 0
.
348
Re
−
0
.
25
— is a hydraulic drag coefficient, where the similarity numbers Re and
Nu are determined by means of the equivalent hydraulic diameter of
the circular channel
d
sm
= 2
h
and the mass average velocity. Thermal
physical properties of the coolant are determined by the mass average flow
temperature in SI system.
The processing results for relative THC are presented in Fig. 2, where
η
Nu
=
Nu Pr
−
0
,
4
Nu
sm
Pr
−
0
,
4
sm
Re
;
η
ξ
= (
ξ/ξ
sm
)
Re
.
The analysis of the results indicates that with the fins crossing angle
β
increasing, the level of relative THC grows significantly. Moreover,
46
ISSN 0236-3941. HERALD of the BMSTU. Series Mechanical Engineering. 2015. No. 2