Tubular Body

The present invention relates to a tubular body which improves the mixed state or heat conduction efficiency of a fluid flowing therein.

It has been common practice to fabricate the heat conduction pipe of, say, a heat exchanger of a material with high heat conductivity or to provide said pipe with fins to increase the area of heat conduction, thereby improving the heat conduction effect. Such a practice has, however, been unable to produce a pipe meeting various requirements for increased efficiency of the heat exchanger.

Aimed at solution of this problem, the tubular body according to the present invention is characterized by being provided on the external surface with a series of periodically wavy recesses of specific depth and angle and accordingly on the internal surface provided with the corresponding series of similarly wavy projections.

The first object of the present invention is to provide a tubular body which improves the mixed state or heat conduction efficiency of a fluid flowing therein.

The second object of the present invention is to provide a tubular body characterized in that a fluid can flow therein with variable velocity distribution or variable temperature distribution to improve the mixed state or heat conduction efficiency of the fluid.

The third object of the present invention is to provide a tubular body characterized in that the profile of the internal wall of said tubular body in contact with a fluid flowing therein is made various to improve the mixed state or heat conduction efficiency of the fluid.

The fourth object of the present invention is to provide a tubular body which has a series of projecting ribs formed on its internal surface.

The fifth object of the present invention is to provide a tubular body in which a series of projecting ribs formed on its internal surface has waviness with specific periodicity.

The sixth object of the present invention is to provide a tubular body in which said projecting ribs have each a specific depth from the external surface of said tubular body and a specific angle to the axial direction of said tubular body.

Several other objects of the present invention will become apparent from the detail description of preferred embodiments and the attached drawings, in which:

FIG. 1 is a front elevation view of a tubular body according to the present invention.

FIG. 2 is an oblique view of a tubular body according to the present invention.

FIGS. 3 and 4 are diagrams illustrating the formation of recesses.

FIG. 5 and 6 are diagrams showing the details of said recesses.

FIG. 7 is a front elevation view illustrating a tubular body according to the present invention applied as the heat conduction pipe of a heat exchanger.

FIG. 8 is a side view corresponding to FIG. 7.

FIG. 9 is an elevation view showing an array of tubular bodies of FIG. 7.

FIG. 10 is an oblique view of an assembly of tubular bodies of FIG. 7.

Next, an embodiment of the present invention is to be described referring to the attached drawings.

In FIGS. 1, 2 and 3, on the external surface 1a of a tubular body 1 are formed spirally a series of periodically wavy recessed ribs 2 (see FIG. 6) of specific depth and angle and thereby on its internal surface 1b are formed the corresponding series of projecting ribs 3 with waviness of specific periodicity (see FIG. 6).

In the embodiment illustrated in FIGS. 1 and 2, said recessed ribs 2 are spirally formed on the external surface 1a of the tubular body 1, but they may be formed in a ring fashion as shown in FIG. 4.

The sectional profile of the tubular body 1 illustrated is circular, but any other profile may be used.

In FIGS. 3 and 4 the recessed rib 2 is indicated by a two dot-chain line.

Now referring to FIGS. 5 and 6, further description is made of said wavy recesses arranged with specific periodicity.

As illustrated in FIG. 5 (a) (b) (c) (d), for spiral formation of said recessed ribs 2 on the external surface 1a of the tubular body 1, a base line S.sub.1 of said series of recessed ribs 2 with waviness of specific periodicity is imagined with a lead angle .alpha.. Thereby .alpha.=1.degree..about.30.degree..

For ring formation of said recessed ribs 2 on the external surface 1a of the tubular body 1, the contact angle formed between said base line S.sub.1 of the series of periodically wavy recessed ribs 2 and the cross section S of the tubular body 1 (cross-sectioned along an axis vertical to the longitudinal axis of the tubular body 1), is taken as .alpha.,.alpha. being in the range of 1.degree..about.30.degree..

In the above description the lead angle .alpha. or the contact angle .alpha. is set in the range of 1.degree..about.30.degree. which is the most desirable, but this range is not the only one available.

As indicated in FIG. 6, the depth d of said recessed rib 2 is set in the range of 0.5.about.5 mm, which is the most desirable, but this range is not the only one available.

In FIG. 5 (a), the waviness is a continuation of circular part R.sub.1 and straight part R.sub.2 ; and a series of recessed ribs 2 with such a waviness are formed on the tubular body 1. In this case the period l of a waveform is set in the range of 3.5.about.50 mm and the angle of intersection .beta. between the straight part R.sub.2 and the base line S.sub.1 is set in the range of 5.degree..about.60.degree.. In FIG. 5(a) the waveform is a continuation of the circular part R.sub.1 and the straight part R.sub.2, but this is not the only form available; it may be a sine wave of Sin .beta. or a cosine wave of Cos .beta., the angle .beta. thereby being set in the range of 5.degree..about.60.degree. and the period l from crest to crest of wave set in the range of 3.5.about.50 mm.

In FIG. 5(b) the waveform is saw-tooth and a series of such saw-tooth recessed ribs 2 are formed with a period l on the tubular body 1, the period l thereby being in the range of 3.5.about.50 mm and the angle .beta. between the saw-tooth wave and the base line S.sub.1 being in the range of 5.degree..about.60.degree..

The ranges set in FIG. 5 (a) (b), i.e., .beta.=5.degree..about.60.degree. and l=3.5.about.50 mm are the most desirable, but they are not the only ranges available.

In FIG. 5(c) the waveform is an alternate succession of the semi-circular part R.sub.3 and its inversion R.sub.4 and a series of recessed ribs 2 with such a waveform are formed on the tubular body 1, the crest-to-crest period l being set in the range of 3.5.about.50 mm and the angle .beta. of intersection between the base line S.sub.1 and the transition line S.sub.3 from the circular part R.sub.3 to the circular part R.sub.4 being set in the range of 1.degree..about.90.degree..

In FIG. 5(d), the waveform is square and a series of recessed ribs 2 with such a square waveform are formed on the tubular body, l thereby being in the range of 3.5.about.50 mm and the angle .beta. of intersection between the square waveform and the base line S.sub.1 being in the range of 1.degree..about.90.degree..

The ranges set in FIG. 5 (c) (d), i.e., .beta.=1.degree..about.90.degree. and l=3.5.about.50 mm are the most desirable, but they are not the only ones available. And other waveforms than illustrated in FIG. 5 can be used.

The results of experiments using a tubular body according to the present invention are described below.

In the experiments the tubular body 1 was externally heated to a specific temperature under a specific rate of air flow; a fluid with a specific temperature was passed through the tubular body 1; and the temperature of the fluid near the exit of the tubular body 1 was measured, thereby comparing the invented tubular body with the conventional one.

In this experiment the heat conduction area was the same for both tubular bodies and the outside temperature of heating was 280.degree. C.

In this experiment the heat conduction area was set at 1/2 of that in experiment A and the heating temperature was lowered to 200.degree. C.

In experiment A the average exit temperature in the invented tubular body turned out 1.5.about.1.6 times that in the conventional one, and in experiment B it was 1.3.about.1.5 times. The result has testified to an improvement of the heat conduction effect in the tubular body 1 according to the present invention.

An example of the tubular body 1 of the present invention being applied as the heat conduction pipe of a heat exchanger is to be described here.

In FIGS. 7 and 8, the two ends 1', 1" of the tubular body 1 are flattened to form a junction 4 which is rectangular in cross section and the two sides 4a, 4b of said junction 4 are equally bulged outward.

As illustrated in FIGS. 9 and 10 numerous tubular bodies 1 are arranged in parallel to form a grid (the arrangement is not limited to this one); and with all tubular bodies assembled at the ends 1',1" the sides of adjacent bodies are welded together transversely 4a to 4a, 4b to 4b as well as longitudinally 4a to 4b. Thereby the gap C between the adjacent bodies is adjustable by changing the amount of bulge at 4a, 4b and thus the flow rate of a fluid passing through the gap C can be increased by appropriately setting the bulge or transverse extension of sides 4a, 4b.

The junctions 4 of assembled tubular bodies 1 are fitted in a framework 5, which sets the positions of these tubular bodies. Then elastically deformable sleeves 6, 7 are inserted into the space formed between the junctions 4 of tubular bodies 1 positioned in the longitudinal direction. Thereby the thermal strain caused in the vertical direction (in FIG. 10) of the junctions 4 by thermal expansion can be absorbed by the deformation of the sleeves 6, 7, while the thermal strain in the transverse direction of the junctions due to welding can be offset by the thermal strain of the framework 5 fabricated of the same material as the tubular body 1. Meanwhile the thermal strain in the longitudinal direction of the tubular body 1 can be absorbed by the gap C (FIG. 9) between adjacent tubular bodies 1. In this example the junction 4 is formed by flattening the ends 1', 1" of the tubular body 1, but it may be formed by enlarging these ends (FIG. 7).

Such being the constitution, the present invention makes the flow velocity and temperature distributions inside and outside of the tubular body variable, thereby improving the heat conduction effect or the mixing effect of a fluid flowing in the tubular body.