Furukawa ElectricNewNew Products
Products

Furukawa Multi-Grooved Tubes

1.

INTRODUCTION

Heat exchangers, a key component of room air-conditioners and packaged air-conditioners, make use of tubes
with grooves on the inner surface to both improve heatexchange performance and decrease power consumption. Furukawa Electric markets these as Furukawa Multigrooved Tubes.
Furukawa multi-grooved tubes are heat transfer tubes
with large number of minute grooves formed on the insidesurface in spiral form, as shown in Figure 1, and they
have a much higher heat transfer coefficient than smoothheat transfer tubes, which have a smooth inner surface.

2.

Toward the late 1980s, however, there was a demand
for air-conditioners that were smaller and more energy
efficient, leading to the use the widespread use of multigrooved tubes with an outside diameter of 7 mm in heatexchangers. To gain higher performance per unit of tube,

Product Evolution

When tubes with a grooved inner surface were originallydeveloped, the groove configuration was, as shown forType A in Table 1 featured and outside diameter of 9.52mm, a shallow groove depth of only 0.15 mm, and anobtuse peak angle.

Table 1Figure 1

Furukawa multi-grooved tube.

Evolution in groove configurations.

Year developedTypeOutsidediameter(mm)

Thicknessat trough(mm)

No. ofgrooves

Lead angle(°)

Depth ofgroove
(mm)

1980

A

9.52

0.28

60

25

0.15

9089.0

B

7.00

0.23

56

14

0.26

15

57.8

C

7.00

0.23

50

30

0.24

1556.3

Peak angle Unit weight
Cross sectional configuration
(°)
(g/m)

1988

2000

αioβ

：depth of groove：thickness at trough
α：peak angle
β：lead angle
o：outside diameteri：inside diameter

Location of measurements

Furukawa Review, No. 32

200766

Furukawa Multi-Grooved Tubes

3.

PRODUCT FEATURES

3.1 Principal Multi-grooved Tube Configurations
Table 2 shows configurations representative of those that
Furukawa Electric can mass-produce. In the last few

years the effects of the rapidly increasing cost of copper
have made reducing the amount of copper used ingrooved tubes and other components of air-conditioning
systems an important issue. We at Furukawa Electric have
reduced tube diameter in an effort to lighten tube weight,and have extended our mass-production capability tooutside diameters of 5 mm. If the grooves formed inside
the tube are of the same configuration, reducing the outside diameter from 7 mm to 5 mm will result in a reductionin unit weight (weight per unit of length) of about 25 %.

109

Heat transfer coeﬃcient（ｋW/m 2K）

a method was then adopted whereby multiple grooves
having a sharper angle, as shown for Type B, were formedon the inner surface of the tube, thereby increasing internal surface area and improving heat transfer performance,and groove depth was increased to 0.26 mm.
Around 1997 air-conditioners using alternative refrigerants (R410A and R407C) came to the market. These alternative refrigerants were developed from a concern for protecting the environment, and did not present a risk ofdamage to the ozone layer, in contrast to the CFC (R12)and FCFC (R22) refrigerants that had been used in airconditioners up till that time. Influenced by this, our company, for its part, marketed the Furukawa multi-grooved
tube, having grooves formed in the inside surface.
Conventionally, improvements in performance were effected by forming deeper grooves in the inside surface, but inthese new tubes, such as Type C, we increased the leadangle (the angle made between the spiral grooves inside
the tube and the axis of the tube), effectively agitating therefrigerant flowing through the tube to promote heat transfer, thereby improving performance. Since the replacement refrigerants were mixtures of two or three refrigerants
of differing saturation temperatures, the technique ofincreasing the lead angle to improve performance proved
extremely effective. At present, almost all Furukawa multigrooved tubes in mass production are of this type.

876Symbol

5−●○△
□
◇

43100200300

TypeA
DEFGH400

Refrigerant ﬂow rate（kg/m2s）

Figure 2

Internal condensing heat transfer coefficient.

Table 2

Measurements and configurations of representative Furukawa multi-grooved tubes.

Type

Outsidediameter(mm)

Thicknessat trough(mm)

No. ofgrooves

Lead angle(°)

Depth ofgroove(mm)A(original)

9.52

0.28

60

25

0.15

90

89.0

100.0

D

9.52

0.28

60

30

0.18

20

81.5

91.6

E

7.94

0.26

65

30

0.15

1263.0

70.8

F

7.00

0.23

65

35

0.15

1150.957.2G

6.35

0.23

55

34

0.18

1247.1

52.9

H

5.00

0.23

52

38

0.15

1337.542.1

Peak angle Unit weight
(°)
(g/m)

Unit weightratio
Cross sectional configuration(%) ** As a percent of the unit weight of Type A

Furukawa Review, No. 32

200767

Furukawa Multi-Grooved Tubes

3.2

Heat Transfer Performance of Multi-grooved
Tubes
Figure 2 shows the internal condensing heat transfer
coefficient of the multi-grooved tubes in Table 2.
Compared to the tubes as originally developed, performance has been improved by as much as 200 %.

4.

PRODUCT DEPLOYMENTMulti-grooved tubes are primarily used in room air-conditioners for household use and for packaged systems forcommercial use, but with greater energy efficiency of various types of heating and cooling equipment, their application has extended to heat exchangers for refrigerators,
automated vending machines, showcases, dryers, and soon. More recently that are also used in electric water heaters and “Ecocute” to heat water for a type of air-conditioner that has recently been seen as a promising
approach to global warming prevention.

5.

CONCLUSION

It is possible to design and deliver multi-grooved tubes
that offer the desired performance and unit weight. We
are also establishing systems that will enable us to provide technical support for tube expansion processing andother peripheral technologies for multi-grooved tubes.
For more information, please contact:
No. 2 Sales Department, Metals Company, Furukawa
Electric		 TEL: +81-3-3286-3836 FAX: +81-3-3286-3663

Furukawa Review, No. 32200768