KR100324065B1 - A heat transfer tube and method of manufacturing same - Google Patents

Abstract

The present invention relates to a heat transfer tube (10) having an outer surface configured to improve heat transfer performance in both refrigerant evaporation and condensation applications and a method of manufacturing the heat transfer tube (10). This heat transfer tube is suitable for use in, for example, shell and tubular air conditioning condensers, flooded evaporators, release film evaporators, or combinations of flooded and release film evaporators. The heat transfer tube has at least one fin line 20 extending helically around its outer surface 13. The notches 30 of a predetermined pattern extend at an angle of inclination α across the pin line at intervals around the circumference of the tube. There is a split spike 22 with two distal tips 23 between each pair of adjacent notches. The pin lines, notches and split spikes are the first between the mandrel and the gang of the pinning disc 63, the second between the mandrel and the notching wheel 66, and the third between the mandrel and the split wheel 67. It is formed in the tube by rotating the wall of the tube. Because of the interaction of rotating and advancing the tube and the notching wheels, during the manufacture of the tube, the maximum width W _t of the spike is greater than the width W _r of the proximal portion of the fin line.

Description

Heat transfer tube and its manufacturing method {A HEAT TRANSFER TUBE AND METHOD OF MANUFACTURING SAME}

The present invention relates generally to heat transfer tubes. In particular, the present invention relates to heat transfer tubes having a refrigerant surface configuration suitable for use in air conditioning and refrigeration system heat exchangers in both evaporation and condensation applications, as well as methods of making the same.

Shell and tube type heat exchangers have a plurality of tubes contained within the shell. Typically, the tube is arranged to provide multiple parallel flow paths for one of the two fluids that are required to exchange heat. In a flooded evaporator, the tube is submerged in a second fluid flowing through the heat exchanger shell. Heat travels from one fluid to another through the wall of the tube. Many air conditioning systems include shells and tubular heat exchangers. In air conditioning applications, fluid, typically water, flows through the tube and the refrigerant flows through the heat exchanger shell. In evaporator applications, the refrigerant cools the fluid by heat transfer from the fluid through the walls of the tubes. The transferred heat evaporates the refrigerant in contact with the outer surface of the tube. In condenser applications, the refrigerant is cooled and condensed through heat transfer to the fluid through the walls of the tubes. The heat transfer capacity of such a heat exchanger is mainly determined by the heat transfer characteristics of each tube. The external configuration of each tube is important for achieving total heat transfer characteristics.

Many methods are known for improving the heat transfer efficiency of heat transfer tubes. One of these is to increase the heat transfer area of the tube. One of the most common methods employed to increase the heat transfer area of a heat exchanger tube is by placing fins on the outer surface of the tube. The fins may be manufactured separately and attached to the outer surface of the tube, or the walls of the tube may be machined by some process to form fins on the tube outer surface.

In refrigerant condensation applications, in addition to the increased heat transfer area, finned tubes provide improved condensation heat transfer performance compared to tubes with smooth outer surfaces for other reasons. The refrigerant to be condensed forms a continuous film of liquid refrigerant on the outer surface of the smooth tube. The presence of the film reduces the rate of heat transfer across the tube wall. The resistance to heat transfer across the film increases with film thickness. The film thickness at the fin is generally small compared to most of the tube surface due to the surface tension effect, resulting in low heat transfer resistance through the fin.

In refrigerant evaporation applications, increasing the heat transfer area of the tube surface also improves the heat transfer performance of the heat transfer tube. In addition, a surface configuration that enhances nuclear boiling on the surface of the tube in contact with the boiling fluid improves performance. In the process of nuclear boiling, the heat transferred from the heated surface evaporates the liquid in contact with the surface, and the vapor is formed into bubbles. Heat from the surface superheats the vapor with bubbles and bubbles grow in size. When the bubble size is sufficient, the surface tension is overcome and the bubble comes off the surface. When the bubble leaves the surface, the liquid enters the space from which the bubble escapes, and the vapor remaining in the space has an additional source of liquid that evaporates to form another bubble. With the convective effect of vapor bubbles rising through the liquid and mixing the liquid, continuous formation of bubbles at the surface, release of bubbles from the surface, and rewetting of the surface improve the heat transfer rate to the heat transfer surface. .

The nuclear boiling process can be enhanced by constructing a heat transfer surface to provide a location for the capture of steam and to have a nucleation zone that promotes the formation of vapor bubbles. For example, merely roughening the heat transfer surface provides a nucleation zone that can improve the heat transfer properties of the surface compared to similar smooth surfaces. The re-entrant type nucleation zone produces stable bubble columns and good surface heat transfer properties. The reentrant nucleation zone is a surface cavity whose opening in the cavity is less than the subsurface volume of the cavity. Excessive inflow of the surrounding liquid may lock the reentrant nucleation zone and render the nucleation zone inoperable. By having a relatively large communicating subsurface channel with a relatively small opening to the surface, flooding of the vapor capture zone or nucleation zone can be reduced or prevented and the heat transfer performance of the surface can be improved.

In a falling film type evaporator, the spreading of the liquid film on the heat transfer surface and the enhancement of the thin film are important to improve heat transfer.

It is logical to have a heat transfer tube with an external heat transfer surface with good heat transfer performance in both refrigerant condensation and evaporation applications in both flooded and evaporator modes so that a single tube configuration can be used in both condensers and flooded evaporators. It is preferable from a manufacturing viewpoint.

The present invention is a heat transfer tube having an outer surface configured to provide improved heat transfer performance in both refrigerant condensation, flood evaporation and film evaporation applications, and a method of making the heat transfer tube.

1 is a perspective view of a tube of the present invention.

Figure 2 shows how the tube of the present invention is made.

Figure 3 is a plan view of a portion of the outer surface of the tube of the present invention.

4 is a plan view of a portion of a single fin convolution of the tube of the present invention.

Figure 5 is a general, cross-sectional view of two adjacent pin lines of the tube of the present invention.

<Explanation of symbols for the main parts of the drawings>

10: heat transfer tube

20: pin line

22: pin spike

23: Tips

30: notch

60: peening machine

63: pinning disc

64: mandrel

66: notching disc

67: split disk

The tube has one or more fin convolutions formed on the outer surface. A notch extends at an angle around the circumference of the tube across the pin line at an angle of inclination. The portion of the pin line between adjacent notches in the pin line forms a spike. The distal tip of the spike is divided into two tip portions. Each tip portion extends outwardly from the proximal base of the pin toward the divided pin tip in the adjacent pin line.

Notched and split spike tips further increase the outer surface area of the tube as compared to conventional finned tubes. The grooves between adjacent pin lines, through which the divided pin tips extend, form a reentry cavity to promote refrigerant pool boiling in the flooded evaporator.

In condensation applications and dural evaporation applications, relatively sharp spike tips enhance drainage and dispersion of refrigerant from the fins. In most equipment, the tubes in the shell and tubular air conditioning heat exchanger extend horizontally or almost horizontally. With a horizontal tube, the notched and split fin configuration promotes drainage of condensed refrigerant from the fin into grooves between the fins of the upper portion of the tube surface, and condensed refrigerant from the tube is drained from the tube. Promote becoming In the film evaporation mode, the sharp tip and notch and the low surface tension of the refrigerant help the liquid to spread along the tube axis on the tube surface. This promotes good wettability in horizontal shell and tube dural evaporators.

Fabricating finned tubes of notched and split tips is a type of pinning machine of the kind that pins on the outer surface of the tube by rotating the tube wall between the inner mandrel and the outer pinning disk. Economics can be achieved by adding notching disks and splitter disks to a group of tool gangs. The notching tool is configured to impart a twist to the normal spike to facilitate the splitting of the spike tip.

The accompanying drawings form part of this specification. Throughout the drawings, like reference numerals refer to like elements.

1 is a perspective view of a heat transfer tube 10. The tube 10 includes a tube wall 11, a tube inner surface 12 and a tube outer surface 13. Outer fin spikes 22 extend from the outer surface of the tube wall 11. The tube 10 has an outer diameter D ₀ as measured from the outer surface 13 except for the height H _f of the pin spike 22.

The tube of the present invention can be easily produced by a rolling process. Figure 2 illustrates this process. In FIG. 2, the pinning machine 60 works on a tube 10 made of a soft metal such as copper to produce both inner ribs and outer fins on the tube. The pinning machine 60 has one or more tool arbors 61, each tool mandrel comprising a group of tools 62 consisting of a number of pinning disks 63, a notching disk 66, and a split disk. (67). Mandrel shaft 65 to which mandrel 64 is attached extends into the tube.

The wall 11 is pressed between the mandrel 64 and the pinning disc 63 as the tube 10 rotates. Under pressure, the metal enters into the grooves between the pinning discs to form a ridge or pin on the outer surface of the tube. As the tube rotates, the tube 10 advances (from left to right in FIG. 2) between the mandrel 64 and the group of tools 62, forming many spiral pin lines on the tube. The number of convolutions is a function of the number of pinning discs 63 and the number of tool mandrel 61 in the group of tools 62 when used in the pinning machine 60. At the same pass and immediately thereafter, a group of tools 62 form a pin convolution on tube 10, and notching wheel 66 imprints a notch inclined into the metal of the fin convolution. Subsequent to the formation of the inclined notch, the dividing disk 67 divides the tip of each pin line into two parts.

The mandrel 64 can be constructed in a manner that imprints any kind of pattern with the inner surface 12 of the wall of the tube passing over the mandrel as shown in FIG. An exemplary pattern is one or more spiral rib lines. This pattern can improve the heat transfer rate between the fluid flowing through the tube and the tube wall.

3 shows a part of the outer surface of the tube in a plan view. Many pin lines 20 extend from the outer surface 13 of the tube 10. A predetermined pattern of notches 30 are inclined to extend at intervals across each pin line. Between each adjacent pair of notches in a given pin line there is a pin spike 22 with two end tips 23.

4 is a plan view of a portion of a single pin line of a tube of the present invention. The inclination angle of the notch base 31 from the tube longitudinal axis A _T is an angle α. The inclination angle of the distal tip 23 of the pin spike 22 from the longitudinal axis A _T of the tube is angle β. During manufacture of the tubes (see FIG. 2), the interaction between rotating the tube 10 and the notching wheels 66 and advancing them causes the pin spike 22's axis to appear as shown in FIG. 4. Slightly distorted from the angle between teeth and the pin line, causing the tip axis angle β to be inclined with respect to angle α, ie β ≠ α. However, it may be β = α as a specific case. This skewed spike allows the split disk 67 to reliably split the spikes because the notched spikes provide a wider face for splitting than the notched pin lines.

It has been found that if the angle of the notching wheel is greater than 40 ° and the spacing between adjacent teeth on the notching wheel is less than 0.3175 mm (0.0125 inch), the spikes will be twisted. The twisting of the spikes allows the splitting of the spikes to be carried out more efficiently. Specifically, without torsion, the pin tip thickness will be too small to reliably divide the spikes. By twisting, the shape of the spike just after splitting just before the notching is basically parallelogram. After the division, this parallelogram is divided along its diagonal to form two triangles.

5 is a schematic cross-sectional view of two adjacent pin lines of the tube of the present invention. The term " model " was used because the cross section cut through any portion of the pin line does not appear exactly as the cross section shown in FIG. However, this figure serves to represent most of the features of the tube. The pin lines 20A, 20B extend outward from the tube wall 11. The pin lines 20A, 20B have a proximal portion 21 and a spike portion 22. A notch with notch base 32 extends through pin line 20A. The total height of the pin lines 20A, 20B is H _f . The width of the proximal portion 21 is W _r and the width of the spike portion 22 at its widest dimension is W _t . The outermost distal end of the spike 22 has two distal tips 23. The notch penetrates into the fin line at height H _n above the inner wall surface 13.

It should be noted that the notching wheel 66 (FIG. 2) does not cut the notch from the pin line during the manufacturing process but rather imprints the notch into the pin line by displacing the material from the notch zone. The surplus material from the notched portion of the fin line moves into the region between adjacent notches and outwards from the side of the pin line toward the tube wall 11 on the side of the pin line. As a result, W _t is greater than W _r . The distance or pin pitch between similar points on adjacent pin lines is P _f . The angle or split angle between the two distal tips 23 on the spike portion 22 is the angle δ. The distal tip extending from one side of the pin line extends toward an adjacent pin line on the side, leaving a gap g between the tips.

A relatively large number of sharp end tips promote condensation on the surface of the tube when the tube is used for condensation applications. Because the distal tip is located above the space between adjacent fin conduits, a reentry cavity is formed, forming a tube surface that promotes evaporation.

Two groups of prototype tubes made according to the instructions of the present invention were tested using refrigerant R-134a. The relevant parameters of the two prototypes are as follows.

Prototype A Group:

Nominal outside diameter (D ₀ )-1.9 cm (3/4 inch),

Pin pitch (P _f )-0.6 mm (0.024 in) or 16.5 pins per cm (42 pins per inch),

Pin Height (H _f )-0.79 mm (0.031 in),

Notch base height (H _n )-0.58 mm (0.023 in),

Notch angle (α)-50 °, 30 °, 45 °,

Split angle (δ)-70 °, 90 °, 110 °,

Notch density, or number of notches in pin convolution per tube circumference-80, 140.

Prototype B Group:

Nominal outside diameter (D ₀ )-1.9 cm (3/4 inch),

Pin pitch (P _f )-0.45 mm (0.018 inches) or 22 pins per cm (56 pins per inch),

Pin Height (H _f )-0.58 mm (0.024 in),

Notch base height (H _n )-0.35 mm (0.014 in),

Notch angle (α)-50 °,

Split angle (δ)-90 °,

Notch density, or number of notches in pin convolution per tube circumference-140.

The inventors compared the performance of two prototypes with the performance of a tube with a smooth outer surface over a range of heat flux conditions. For evaporation applications, the performance of prototype A group is about 2.5 times the average of smooth tube performance, and the performance of prototype B group is about 3 times the performance of smooth tube. In condensation applications, the performance of prototype A group is about 19 times the performance of the smooth tube, and the performance of the prototype B group is about 23 times the performance of the smooth tube.

Extrapolation from the test data indicates that similar performance is obtained in tubes having an outside diameter of nominal 12.5 mm (1/2 inch) to 25 mm (1 inch). here,

a) pin pitch is 0.38 to 0.76 mm (0.015 to 0.030 inch), or 0.38 mm ≤ P _f ≤ 0.76 mm (0.015 inch ≤ P _f ≤ 0.030 inch),

b) the ratio of fin height to tube outer diameter is 0.026 to 0.067, or 0.026 ≦ H _f / D ₀ ≦ 0.067,

c) notch density is from 60 to 190,

d) the angle between the notch axis and the tube longitudinal axis is 20 to 65 °, or 20 ° ≦ α ≦ 65 °,

e) the height of the notch base is 0.50 to 0.8, or 0.50 <H _n / H _f <0.8 of the pin height,

f) The angle between the two distal tips on the spike is 70 ° to 130 °, or 70 ° ≦ δ ≦ 130 °.

The prototype tested has three lines or "starts". The optimal number of pin circuits or starts depends more on the ease of manufacture than on the effect of the number on heat transfer performance. A large number of starts increases the rate at which pin lines can form on the tube surface.

The outer surface formed in the heat transfer tube according to the present invention improves heat transfer performance in both refrigerant condensation, flood evaporation and film evaporation applications.

Claims (8)

A method of forming a heat transfer surface on an outer wall of a tube, Rotating the wall between the inner mandrel and the group of pinning discs to form a pin line, Notching the pin lines at intervals around the circumference of the tube to form spikes in the pin lines; Dividing the spike to form two distal tips within each spike, And said notching comprises twisting said spikes. The notch formed by the notching step has a notch base axis angle, the distal tip has a tip axis angle, and the step of twisting the spikes is such that the tip axis angle is relative to the notch base axis angle. And twisting the distal tip to be inclined. 3. The method of claim 2, wherein the notching step displaces material to form the distal tip, wherein the displaced material produces a spike width W _r at the distal end of the spike. A heat transfer surface formed by the method of claim 1. In an improved heat transfer tube 10 having an outer surface, At least one pin line 20 spirally disposed around the outer surface, And notches 30 radially extending into the pin line at intervals around the circumference of the tube, Each notch has a base axis that makes an angle α with respect to the longitudinal axis A _T of the tube, The notches divide the pin line into a split spike 22 having two end tips 23 and a proximal portion 21, The distal tip has a tip axis angle, the spike tip axis angle β is inclined relative to the angle α, Wherein said split spike is between said adjacent pair of notches and has a maximum width (W _t ) greater than the maximum width (W _r ) of said proximal portion. 6. The pin pitch P _f is from 0.38 to 0.76 mm (0.015 to 0.030 inch), the tube has an outer diameter D ₀ , the pin line has a fin height H _f , and the The ratio of fin height H _f / D ₀ is 0.026 to 0.067, the number of the notches in the fin line per tube circumference is 60 to 190, the angle between the notch axis and the tube longitudinal axis is 30 ° to 65 ° And the notch has a base 32 having a notch base height H _n between 0.50 and 0.8 of the pin height, the distal tips extending outwards from each other at a split angle δ and the spike tip axis angle β The improved heat transfer tube, characterized in that 20 ° to 65 °. 7. The improved heat transfer tube according to claim 6, wherein the splitting angle δ is 70 ° to 130 °. 7. The method of claim 6, wherein the pin pitch is 0.42 to 0.60 mm, the notch angle is 50 °, the number of notches in the fin convolution per tube circumference is 110 to 140, and the notch base height is 0.50 to 0.80 of the pin height. An improved heat transfer tube, characterized in that.