Boiling heat transfer tube

Details Boiling heat transfer tube Boiling heat transfer tube

1999-02-22

2001-01-23

Lazarus, Ira S. (Department: 3743)

Heat exchange

With coated, roughened or polished surface

C165S179000, C165S184000

Reexamination Certificate

active

06176302

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a boiling heat transfer tube which is incorporated in an flooded evaporator of a vapor compression refrigerating machine, such as a centrifugal type chiller, a screw type chiller, immersed in a liquid refrigerant (for example, freon, liquid nitrogen or the like) and used for heating and boiling a liquid refrigerant and particularly, to a boiling heat transfer tube which is improved on its heat transfer performance for a low density refrigerant.
2. Related Prior Art
Several kinds in shape of heat transfer surface have heretofore proposed as boiling heat transfer tubes of this kind. For example, as disclosed in the published Examined Japanese Patent Application Nos. Sho 53-25379 and Hei 4-78917, fins are formed on the outer surface of the tube, cuts to form holes are given in the tip of each fin and the tips of fins are turned down to form useful cavities for boiling heat transfer.
Besides, for example, as described in the published Examined Japanese Patent Application No. Sho 64-2878 and the published Unexamined Japanese Patent Application No. Hei 8-219674, after fins in a spiral fashion are formed on the outer surface of the tube, the tips of the fins are deformed by compression to form cavities in directions of a tube periphery and a tube axis and gaps of 0.13 mm or less in width are provided for communication between the cavities and the outside.
Furthermore, for example, as described in the published Unexamined Japanese Patent Application Nos. Hei 4-236097 and Hei 7-151485, in order to improve a heat transfer performance, not only is boiling in a cavity accelerated but turbulence of a liquid refrigerant and gasified refrigerant on the tube outer surface are also encouraged.
While these heat transfer tubes are improved in heat transfer performance when a refrigerant, such as trichlorofluoromethane, chlorodifluoromethane, or 1, 1-dichloro-2,2,trifluoroethane, is used, there has been a problem, when a low density refrigerant, such as 1,1,2-tetrafluoroehtane is used, that a heat transfer performance is reduced since a conventional heat transfer tube has a small opening (a gap) where a cavity and the outside are communicated, which resists flowing-in of a liquid refrigerant into the cavity, and makes a space in the cavity dried.
In order to avoid this problem, a method can be considered that a quantity of a liquid refrigerant charged in a flooded evaporator is increased, but it has a fault that a charge cost of a liquid refrigerant is increased and in addition, a requirement arises that a volume of an heat exchanger is larger, which in turn makes a cost further increased.
SUMMARY OF THE INVENTION
The present invention was made in light of the above problems and it is, accordingly, an object of the present invention to provide a boiling heat transfer tube which can improve its heat transfer performance when a low density refrigerant is used.
A boiling heat transfer tube according to the present invention comprises: a heat transfer tube body; and fins formed on an outer surface of the tube body in a specified pitch along an axial direction thereof while being disposed in an extending manner along tube peripheral directions, wherein each of fins has recesses and protrusions disposed alternately, a protrusion coming after a recess or vice versa, along its length direction and an opening width (W) between protrusions of adjacent fins is 0.13 mm<W≦0.40 mm.
In the boiling heat transfer tube, it is preferred that an opening width at a top end of a cavity between an adjacent pair of the fins is narrowed by mutual, inward jutting-out of the fins at either recesses or protrusions.
Besides, a profile of each of the protrusions in section perpendicular to the tube axis can assume a trapezoid. It is preferred that in section perpendicular to the tube axis, an angle (&thgr;) formed between opposed side surfaces of each recess is 55 degrees or less; in section perpendicular to the tube axis, a pitch (P
1
) of the recesses or the protrusions in a peripheral direction is 0.28 mm≦P
1
≦0.55 mm; or in section including the tube axis, a pitch (P
2
) of the cavities is 0.50 mm≦P
2
<0.90 mm. Furthermore, it is preferred that ribs are provided on an inner surface of the tube body in a spiral fashion, wherein a lead angle (&agr;) of a rib to the tube axis is 41 degrees≦&agr;≦50 degrees, a rib height (h) is 0.22 mm≦h≦0.45 mm and a pitch (P
3
) of the ribs in a tube axial direction is 2.6 mm≦P
3
≦6.5 mm.


REFERENCES:
patent: 3326283 (1967-06-01), Ware
patent: 4166498 (1979-09-01), Fujie et al.
patent: 4313248 (1982-02-01), Fujikake
patent: 4660630 (1987-04-01), Cunningham et al.
patent: 5186252 (1993-02-01), Nishizawa et al.
patent: 5513699 (1996-05-01), Menze et al.
patent: 5690167 (1997-11-01), Rieger

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