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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

)

is the Reynolds number; Pr

=

μc

p

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