JPS63156994A - Finned type heat transfer pipe having longitudinal fine wave surface - Google Patents

Abstract

PURPOSE:To enhance a heat transfer characteristic of a heat transfer pipe by a method wherein a wavy surface having fine and accute angle corrugations at inner and outer surfaces of the wall of a straight pipe is longitudinally formed on a pipe. CONSTITUTION:A sectional shape of a heat transfer pipe 1 is a starshape having six fins (p). Member of each of the fins (p) is bent in a finepitch, corrugated portions in a longitudinal direction are applied, an area-multiplication rate with respect to a smooth surface pipe is calculated, a bending angle of the corrugation is made as an accute angle and a condensation of steam is promot ed. Partition plates 8 are arranged at the heat transfer pipe 1 with a pitch l, condensation liquid drip 10 flowing along the trough of the fin (p) is collected and discharged. With this arrangement, the heat transfer pipe having fins has a high heat transfer characteristic and at the same time a wall thickness of the heat transfer wall can be made quite thin, so that it is advantageous when an expensive anti-corrosion material is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a shaped heat exchanger tube useful for use in a condenser and having a finely corrugated surface in the longitudinal direction.

[Conventional technology and its problems]

Various types of heat transfer tubes for condensers have been proposed in the past.
Although it has been put to practical use, no one that is fully satisfactory is known yet. Therefore, the inventors of the present invention first had smooth straight pipe parts at both ends, formed a plurality of uneven folds protruding inward between the straight pipe parts, and placed a core body in the center of the folds. He invented a pleated tube made by inserting the tube, and is currently applying for a patent (Patent Application No. 134793, 1985). Although this folded heat transfer tube has a larger heat transfer area than a normal heat transfer tube and can produce considerable effects, it is desirable that it be improved as a heat transfer tube for a condenser.

[Means for solving problems]

The present invention has been made for the purpose of improving the above-mentioned pending invention and providing a molded heat exchanger tube with higher heat exchange efficiency. In a heat exchanger tube formed by forming a plurality of concave and convex folds protruding inwardly between the tube parts and inserting a metal core into the center of the folds, minute and acute-angled peaks and valleys are formed on the inner and outer surfaces or outer surfaces of the folds. The tube is characterized by a wavy surface consisting of uneven stripes formed in the longitudinal direction of the tube.

That is, the present invention is an improvement of a heat transfer tube for a condenser, and its main purpose is to increase the heat transfer area by providing fine irregularities in the longitudinal direction of each covering part, in addition to increasing the heat transfer area by using pleats. At the same time, the angles between the peaks and valleys of this uneven surface are made as acute as possible, increasing the probability that vapor molecules that collide with this slope and are reflected will be encouraged within this depression and condense again. The aim is to further promote this, and the details are as follows.

In order to achieve the above object, the inventor of the present invention experimentally measured the heat transfer characteristics of the heat transfer tube of the prior application and made various studies. When a cored metal is used, the stirring effect of the cored metal is particularly remarkable.
It has been learned that the heat transfer coefficient on the cooling water side inside the tube is several times higher than the heat transfer coefficient on the steam outside the tube (for example, steam at a vacuum level of 712 mm and 11 g). Therefore, from the viewpoint that it is expected that the heat transmission coefficient can be further increased by increasing the heat transfer coefficient on the steam side, as a means to do so, the members of each fold are bent at a fine pitch to form a mountain in the longitudinal direction. The heat transfer on the outer surface of the tube is improved by applying unevenness in the shape of a wave with grooves and valleys to increase the area magnification compared to a smooth tube, and by making the bending angle of the unevenness acute, which has the effect of promoting steam condensation. They succeeded in dramatically increasing the rate.

Next, we will explain the phenomenon in which sharp uneven surfaces promote steam condensation.
This will be conceptually explained by comparing the figure and FIG. 2.

Figure 1 shows a heat transfer surface with acute irregularities, Figure 2 shows a smooth surface,
Small circles represent vapor molecules, arrows indicate their direction of motion, and semicircles represent condensation of molecules.

In Fig. 1, if the pitch of the concavities and convexities is shorter than the mean free path of the molecule, the molecule that collides with one slope of concavity a and is reflected will reach the other surface directly, as in concavity a, and there. It can be thought that once a molecule enters a dent, it will definitely condense, because it will either condense or be further reflected and be pushed back to the original surface and condense.

Therefore, if the pitch of the concavities and convexities is longer than the mean free path of the molecules, there is a high probability that the molecules that have collided will come out of the concavity again, as shown in concavity B, but some molecules will not move as shown in concave C. It is possible to follow the same process as for the depression a.

In Figure 2, in order for a molecule that has been reflected to return to its original plane, it must collide with another molecule, be reflected, and return successfully, and the probability of this happening is shown in Figure 1. You can see that it's small.

It can be seen that as the angle α of this unevenness becomes more acute and the wave pitch becomes smaller, the probability that molecules reflected from one surface will reach the heat transfer surface and condense without colliding with other molecules increases. .

However, there is a limit to this due to the condensate discharge, and the angle α and the pitch are determined in consideration of the pitch of the liquid discharge partition plate, which is one of the factors of the present invention. I'll explain more about that later.

The shape of the unevenness may be a triangular waveform as shown in FIG. 1, or the corners may be rounded.

Figure 3 shows a shape in which the peaks and valleys of the unevenness are rounded. Although the height and pitch of this wave are the same as in FIG. 1, the area magnification is slightly larger than in FIG. 1 due to the roundness, and the condensation promotion effect remains the same.

In the case of a wave composed of a curved surface as described above, when a line connecting the vertices of a crest and a trough forms an acute angle α, the wave is referred to as an acute-angle wave.

FIG. 4 shows the case where the angles between the peaks and valleys in the above sense are right angles, and it clearly shows that the probability that molecules are attracted to the condensation surface is smaller than in FIGS. 1 and 3.

Since the area magnification m for a smooth surface is determined by the following formula (%), it is unrelated to the wave height and pitch, and the reason for choosing a fine pitch is based on the above-mentioned molecular motion theory.

In order to make the pitch of the waves finer, if the board is bent, the thickness of the board must be made as thin as possible.

Fig. 5 shows a process using a combination of bending and shearing force with little slippage, and Fig. 6 shows a process using a roller for sharpening, and the method is selected depending on the relationship between pitch and plate thickness.

Next, a method for quickly discharging the condensed liquid to prevent liquid from accumulating in the recesses or grooves and inhibiting heat transfer will be described.

FIG. 7 shows a longitudinal section of a part of a heat exchanger tube having a structure similar to that described in the specification and drawings of the earlier application, with minute waves 9 formed in the longitudinal direction of the covering part; a chrysanthemum-shaped heat transfer surface consisting of folds P, 2 adapted on one side to the contour of the chrysanthemum-shaped heat transfer surface 1 and a base adapted to a circular hole in the tube plate 3 on the other side, 4 a spiral 5; A core bar 6 is an adapter that fixes the core bar 4 to the base 2 and has a fluid communication hole.

7 is Natsuto.

Reference numeral 8 denotes partition plates for discharging condensate flowing along the valleys of the folds p, which are arranged at a pitch Q.

The effect of this partition plate 8 is as shown in FIG.
Collect the liquid and discharge it as shown in step 11, so that the heat transfer surface is not covered with the liquid as much as possible. However, it is important to consider the shape of the partition plate 8 so that the partition plate 8 completely drains the liquid and falls down without touching the bottom.

FIG. 9 shows an embodiment in which six pieces of partition plates 8 are attached to six folds p. The reason that the pleats P are represented by dotted lines means that each pleat P consists of fine grooves 9, as shown in FIG.

In FIG. 10, 12 indicates that the gap between the cap 2 and the groove 9 is closed by brazing or welding. However, this is not necessary if the contour of the partition plate 8 is made jagged so that it can be fitted from the tube end.

In Fig. 10, the reason why the wave height on the inner surface is lower than that on the outer surface is to make it easier to work with.Furthermore, it is also possible to create waves only on the outer surface and not on the inner surface, for example. Suitable for fluorocarbon-based refrigerants, etc.

It is preferable to leave the valley bottom of the fold P smooth without providing the groove 9, from the viewpoint of the flow of cooling water in the pipe, and also because it allows the joint in the longitudinal direction of the pipe to be located there. .

In this way, the seams can be overlapped and easily sealed by resistance welding.

Although it is also possible to seal at the tips of the folds p.

In the case of 10, a smooth part without some waves is required.

Heat transfer coefficient hokcal/m on the steam side condensing on the vertical wall
h'c is given below.

Here, L: height of vertical wall or outer diameter of horizontal pipe mΔθ:
Difference between condensation temperature and heat transfer wall temperature °Cτ: Latent heat of liquefied fluid Kcal/Kgγ: Specific weight of liquefied fluid
g/mlλ: Thermal conductivity of liquefied fluid Kcal/m
, hr, 'cη: viscosity coefficient of liquefied fluid Kg, h/
++fC is a constant and is 0.943 for a vertical wall. 0 for horizontal pipes
．． 725 Assuming that the partition plate 8 works perfectly in a vertical pipe, L can be taken as the pitch Q of the partition plate, and if the temperature condition remains unchanged, equation (1) becomes as follows.

ho = /L''' (2) However, if the temperature is constant, the smaller the constant pitch α is, the larger ho will be given, but at the same time, the liquid flow in the groove 9 will fill the groove and impede heat transfer. For example, by making the shape of the groove on the steam side an equilateral triangle,
When the length of the negative side is ant, the heat transfer area A1++'' of one groove with respect to the length Lm is as follows.

A1 = 2 a L The fluid is steam, and the heat transfer coefficient on the steam side is, for example, 10.0.
00Kcal/+m”h”C1 If the difference between steam temperature and wall temperature is 10℃, and the latent heat of condensation is 556Kcal/Kg, then 1
The condensate flow rate GxKg/hr at the lower end of the book groove is given below.

At every second, G1=0.1a LKg/5ec== a L
X 10-' m3/The speed at which the see liquid flows down is U
If rn/see, the cross-sectional area of the liquid flow in the groove S
1(++”) becomes as follows when it reaches the partition plate.

L - 8mm = -XIO' The cross-sectional area of the groove is roughly equal to 9 of an equilateral triangle with sides of a (m), but the value of U is L≧0 due to frictional resistance due to the groove, etc.
．． If we estimate that it will not become more than about 0.1m/sec and become constant at 0.02m, then if we try to keep it below S1/5ti-0.05.

Now, if a = 0.001, then L≦0.
22m = 220m, so if the partition plates 8 are provided at this pitch and the minute gaps between the partition plates 8 and the grooves 9 are closed, the drain will be well discharged and there will be almost no interference with heat transfer. I understand that.

The smaller the pitch Q of the partition plate, the h in equation (1)
Although this is preferable from the standpoint of increasing o.

Since the labor involved in attaching partition plates increases, there is a limit to this, and the optimum pitch should be selected in consideration of the balance between heat transfer characteristics and manufacturing costs.

If the pitch of the partition plates is reduced to about 50 degrees, the grooves 9 can be made at a more acute angle, for example, 30 degrees, and the pitch can be reduced to less than 0.5 m, thereby further increasing the area magnification.

The partition plate 8 reduces the vertical wall height L in equation (1) to increase the extra-tube heat transfer coefficient ho, and at the same time prevents the fine grooves 9 from being filled with liquid, thereby increasing the heat transfer area. It is very important because it has the dual effect of making it work effectively.

As can be understood from the above example, if the partition plates are provided densely enough, the groove angle α can be made smaller than 60 degrees to some extent, but this lower limit has to be set in consideration of manufacturing issues. Since it is determined, I cannot generalize.

Setting the angle α to 60 degrees or more makes the work easier, but it is not preferable because the effectiveness decreases even though the number of steps remains the same. In particular, it should be avoided to make the angle α an obtuse angle, that is, 90 degrees or more, as this will rapidly reduce the above effect.

As described above, the shaped heat exchanger tube of the present invention having a finely wavy surface in the longitudinal direction has significantly greater heat transfer characteristics than a smooth tube of the same diameter.

As a comparison, we considered a vertical multi-tube heat exchanger using smooth circular tubes, and compared the case where separate plates were installed as partition plates every 500 m and an example of the present invention with the following specifications. Take a look.

Comparison of an example of the present invention and a smooth tube: tube outer diameter 40 nm, heat transfer surface thickness 0.4 nwn, number of folds in dosage form 8, inner diameter screw core outer diameter = 13 mm, wave angle α = 60
'.

Assuming that the pitch of the partition plates is 20 mm, the heat transfer area magnification for the smooth circular tube is: 2. Multiplier due to dosage form 2. Multiplier due to waves 2. Total area multiplier 2X2=4 Synergistic effect of the above = 4 X 2.2448.9 This is the problem here. To simplify the equation, the synergistic effect is assumed to be 1 because the molecular kinetic effect of the groove is greater than 1, although the effect of the partition plate 8 is actually inferior to the theoretical value.

Next, a comparison will be made between a multi-tubular heat exchanger using horizontal smooth tubes and the present invention. In the case of a horizontal pipe, assuming for convenience that the outside diameter of the pipe is 20 mm, which is equivalent to the pinch of the partition plate, the only difference between vertical and horizontal in equation (1) is the coefficient C,
Therefore.

Note that no matter how many layers of horizontal pipes are used, the lower pipes will be covered by droplets from above, so the ho
A decrease in The average decrease due to this is usually 80
It is said that it is about %.

Effect of not using horizontal multilayer = - = 1.250.8 Also, since the total area magnification = 4, the synergistic effect of the above = 1.3 x 1.25 x 4 =
6.5 The heat transfer coefficient hi on the inner surface of the tube must be increased to the same degree as the above-mentioned ho.

As stated at the beginning, the pleated heat exchanger tube of the present invention provides a heat transfer coefficient hi several times higher than that of a smooth circular tube, so there is no problem with this point.

〔Effect of the invention〕

The molded heat transfer tube of the present invention having a finely wavy surface in the longitudinal direction has high heat transfer characteristics as compared to 1 or more, and at the same time, the heat transfer wall can be configured to have a very thin wall thickness. This is extremely advantageous when using an expensive corrosion-resistant material such as titanium, and it is considered to be particularly suitable for applications that require high performance, low cost, and corrosion resistance, such as ocean temperature difference power generation.

So far, we have explained that it is for use in condensers, but it can also be used as a boiler for recovering waste heat from petroleum and chemical plants by passing pure water through the pipe and evaporating it. Heat can be recovered in the form of steam and used for preheating crude oil or charging materials, heating tanks, and pressurizing it for stripping steam, etc.

In addition, it is also possible to use it as a double pipe heat exchanger without installing a partition plate.

[Brief explanation of the drawing]

Figures 1 to 4 are conceptual diagrams for explaining the phenomenon in which uneven surfaces with minute and acute-angled peaks and valleys formed on the inner and outer surfaces of folds promote condensation of steam in the present invention, and Figure 5 and FIG. 6 is a diagram showing a processing method for forming the uneven surface, FIG. 7 is a partially sectional view showing an example of the implementation of the present invention, and FIG. 8 is a diagram showing the function of the partition plate. 9 is a diagram showing a state in which six partition plates are attached to six folds, and FIG. 10 is a partially enlarged view thereof.

Claims (1)

[Claims] 1. In a heat exchanger tube that has smooth straight pipe parts at both ends, a plurality of uneven folds are formed between the straight pipe parts, and a core bar is inserted in the center of the folds. 1. A pleated heat exchanger tube having a finely wavy surface in the longitudinal direction, characterized in that a wavy surface consisting of uneven striations having fine and acute-angled peaks and troughs is formed in the longitudinal direction of the tube on the inner and outer surfaces or the outer surface of the tube.