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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