Heat exchange – With coated – roughened or polished surface
Reexamination Certificate
2000-03-01
2001-10-09
Lazarus, Ira S. (Department: 3743)
Heat exchange
With coated, roughened or polished surface
C165S183000
Reexamination Certificate
active
06298909
ABSTRACT:
BACKGROUND TO THE INVENTION
1. Field of the Invention
The present invention relates to a grooved-inner-surface heat transfer tube with fins for enhancing heat exchange efficiency formed in a zigzag shape on the inner surface of a metal tube.
2. Description of the Related Art
This type of grooved-inner-surface heat transfer tube is used mainly as an evaporator tube or a condenser tube in heat exchangers or the like in air-conditioners or cooling apparatus. Recently, heat transfer tubes formed with spiraling fins over the entire face of the inner surface have been widely marketed.
The heat transfer tubes which are currently most popular are manufactured by a method wherein fins are roll-formed over the entire inner surface of a metal tube by passing a floating plug formed with spiral grooves on the outer circumferential surface, along the interior of a seamless tube (with no joins) obtained by a drawing or an extrusion process.
In grooved-inner-surface heat transfer tubes formed with spiral fins of this type, heat transfer liquid which has collected to the bottom of the interior of the heat transfer tube is drawn up along the spiral fins by being blown by a vapor current flowing inside the tube, thereby spreading along the entire circumferential surface inside the tube. Due to this effect, the entire circumferential surface inside the tube is made almost uniformly wet, so that in cases where the tube is used as an evaporation tube for evaporating the heat transfer liquid, the area of the region where boiling occurs can be increased to improve the boiling efficiency. Additionally, in cases where the tube is used as a condenser tube for liquefying heat transfer gas, the condensation efficiency can be increased by increasing the contact efficiency between the metal surfaces and the heat transfer gas due to the tips of the fins being exposed from the surface of the liquid.
However, it is apparent that there is room for further improvement of the effect of increased heat transfer efficiency due to the spiral fins. It is for this reason that the inventors of the present invention have applied electric resistance welding processing methods for the manufacture of heat transfer tubes and have produced many types of grooved-inner-surface heat transfer tubes by changing the patterns of the grooves in the heat transfer tubes, and then carried out experiments to compare their performance. As a result, they discovered that better heat transfer performance can be obtained in comparison to simple spiral patterns and the like, if multiple fins are formed extending in a zigzag pattern around the circumferential direction of the inner surface of the heat transfer tubes.
However, in cases where this type of zigzag patterned fins were formed, there was another problem of a substantial pressure loss due to fluid resistance applied to the fluid when the fluid flows over the bend portions of each of the fins having a convex shape toward the downstream direction.
In order to alleviate this increase in pressure loss, a trial was made involving forming a gap in each of the bend portions of the zigzag patterned fins to have the fluid flow through each of the gaps. However, while there was some reduction in the pressure loss, heat exchange efficiency decreased markedly, so that there arose the problem of not being able to obtain the high heat exchange efficiency of the conventional zigzag patterned fins.
SUMMARY OF THE INVENTION
The present invention takes into consideration the aforementioned situation, with the object of providing a grooved-inner-surface heat transfer tube where pressure loss can be suppressed while increasing heat exchange performance.
In order to achieve this object, with a grooved-inner-surface heat transfer tube according to the present invention, an inner circumferential surface of a metal tube is formed with fins bent at bend portions in a zigzag and extending consecutively around a circumferential direction of the inner circumferential surface, and at at least a part of the bend portions of said fins from said inner circumferential surface is set at 30 to 90% of a height of said fins excluding said bend portions.
According to the grooved-inner-surface heat transfer tube of the present invention, fins are formed bent in a zigzag and extending consecutively around a circumferential direction of the inner circumferential surface, and at at least a part of the fin bend portions the height of, the p inner circumferential surface is set at 30 to 90% of the height of the fins excluding the fin bend portions. Therefore, even at times when the fluid flowing inside the heat transfer tube flows into and collects in the trough side of the fin bend portions, the fluid flows easily over the low fin bend portions so that there is no occurrence of high fluid resistance at the fin bend portions. Moreover, compared with constructions in which gaps are formed in the fin bend portions, as a result of the fluid flowing over the fin bend portions an effective stirring of the fluid takes place whereby there is little incidence of the usual high loss of heat exchange efficiency of zigzag shaped fins. Accordingly, it is possible to effect a well balanced result of reducing pressure loss while increasing heat exchange efficiency which in the past has been difficult to achieve.
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Fukatami Takao
Furuuchi Tetsuya
Kikuchi Shin
Sukumoda Shunroku
Kolisch Hartwell Dickinson & McCormack & Heuser
Lazarus Ira S.
McKinnon Terrell
Mitsubishi Shindoh Co. Ltd.
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