US20120292004A1

US20120292004A1 - Heat exchanger

Info

Publication number: US20120292004A1
Application number: US13/112,949
Authority: US
Inventors: Ing-Youn Chen; Jhong-Syuan Tsai; Chi-Chuan Wang
Original assignee: National Yunlin University of Science and Technology
Current assignee: National Yunlin University of Science and Technology
Priority date: 2011-05-20
Filing date: 2011-05-20
Publication date: 2012-11-22

Abstract

A heat exchanger includes: an inlet header tube including opposite first and second ends and an inner space formed between the first and second ends; an outlet header tube parallel to the inlet header tube; a plurality of heat exchange tubes transversely extending between and fluidly connected to the inlet and outlet header tubes, each of the heat exchange tubes having a connecting end connected to the inlet header tube; and a baffle tube inserted into the inner space of the inlet header tube. The baffle tube has an open end proximate to the first end, a closed end proximate to the second end, and a plurality of orifices disposed between the open and closed ends to fluidly intercommunicate the inner space of the inlet header tube and the baffle tube. Each of the orifices is disposed in alignment with the connecting end of one of the heat exchange tubes.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to a heat exchanger, more particularly to a heat exchanger that includes a baffle tube inserted in an inlet header tube.
2. Description of the Related Art
Heat exchangers are widely applied to various devices such as condensers, evaporators, boiler furnaces, heat collectors using solar panels, heat radiators of nuclear reactors or electronic equipments, etc. The heat transfer efficiency of a heat exchanger is generally improved by an increase in the heat transfer area of the heat exchanger.
A conventional heat exchanger using gas to dissipate heat has a relatively low heat exchange efficiency and cannot meet current commercial demands. Therefore, it is desired in the art to increase the heat exchange efficiency of a heat exchanger by utilizing liquid to dissipate heat.
FIGS. 1 and 2 show a conventional heat exchanger that is usually used in an electronic equipment or a solar energy water heater. The heat exchanger includes an inflow tube 20, an inlet header tube 21 having an open end 211 fluidly connected to the inflow tube 20, an outlet header tube 22 parallel to the inlet header tube 21, and a plurality of heat exchange tubes 23 transversely extending between and fluidly connected to the inlet and outlet header tubes 21, 22. In use, a first fluid 11 is allowed to flow into the inlet header tube 21 through the inflow tube 20 and is then distributed among the heat exchange tubes 23. A second fluid 12 having a temperature higher or lower than that of the first fluid 11 is allowed to flow externally around the heat exchange tubes 23 so as to transfer heat from the second fluid 12 to the first fluid 11 or vice versa.
Generally, the cross section of the inflow tube 20 is smaller than that of the inlet header tube 21 such that let flow is induced near the open end 211 of the inlet header tube 21. As shown in FIG. 3, because of the inlet jet stream, vortex flow and eddy flow are generated at the open end 211 and even in first and second ones of the heat exchange tubes 231, 232 that are closest to the open end 211, resulting in relatively low flow amounts in the first and second heat exchange tubes 231, 232 compared to that in the remainder of the heat exchange tubes 23. In other words, the flow distribution among the heat exchange tubes 23 is uneven, thereby reducing the heat exchange efficiency of the conventional heat exchanger.
The aforesaid drawbacks may be overcome by moving the heat exchange tubes 23 away from the open end 211 of the inlet header tube 21. However, such an arrangement may result in an increase in the length of the inlet header tube 21, which makes the heat exchanger inapplicable for a small scale device.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a heat exchanger that can overcome the vortex flow and eddy flow problems encountered in the prior art.
According to the present invention, a heat exchanger comprises: an inlet header tube including opposite first and second ends and an inner space formed between the first and second ends; an out 1 et header tube substantially parallel to the inlet header tube; a plurality of heat exchange tubes transversely extending between and fluidly connected to the inlet and outlet header tubes, each of the heat exchange tubes having a connecting end connected to the inlet header tube; and a baffle tube inserted into the inner space of the inlet header tube from the first end to the second end, the baffle tube having an open end proximate to the first end, a closed end proximate to the second end, and a plurality of orifices disposed between the open and closed ends to fluidly intercommunicate the inner space of the inlet header tube and the baffle tube, each of the orifices being disposed in alignment with the connecting end of one of the heat exchange tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invent ion will become apparent in the following detailed description of the preferred embodiments of the invention, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a conventional heat exchanger;

FIG. 2 is a fragmentary enlarged sectional view of FIG. 1;

FIG. 3 shows simulation of velocity vector lines of the conventional heat exchanger;

FIG. 4 is a plot illustrating flow ratios of the heat exchange tubes of the conventional heat exchanger;

FIG. 5 is a perspective view of the preferred embodiment of a heat exchanger according to the present invent ion

FIG. 6 is a fragmentary enlarged sectional view of FIG. 5;

FIG. 7 shows simulation of velocity vector lines of the preferred embodiment according to the present invention;

FIG. 8 is a plot illustrating flow ratios of the heat exchange tubes of Example 1;

FIG. 9 is a plot illustrating flow ratios of the heat exchange tubes of Example 2;

FIG. 10 is a plot illustrating flow ratios of the heat exchange tubes of Example 3;

FIG. 11 is a plot illustrating flow ratios of the heat exchange tubes of Example 4;

FIG. 12 is a plot illustrating flow ratios of the heat exchange tubes of Example 5;

FIG. 13 is a plot illustrating flow ratios of the heat exchange tubes of Example 6; and

FIG. 14 is a plot illustrating flow ratios of the heat exchange tubes of Example 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 5 and 6, the preferred embodiment of a heat exchanger according to the present invention is used for conducting heat exchange between a first fluid 31 and a second fluid 32. The heat exchanger includes: an inlet header tube 4 having opposite first and second ends 41, 42, and an inner space 43 formed between the first and second ends 41, 42; an outlet header tube 5 substantially parallel to the inlet header tube 4; a plurality of heat exchange tubes 6 (nine in the embodiment) transversely extending between and fluidly connected to the inlet and outlet header tubes 4, 5; a baffle tube 7 inserted into the inner space 43 of the inlet header tube 4 from the first end 41 to the second end 42; and inflow and outflow tubes 33, 34.
Each of the heat exchange tubes 6 has a connecting end 60 connected to the inlet header tube 4. The baffle tube 7 has an open end 71 proximate to the first end 41 of the inlet header tube 4, a closed end 72 proximate to the second end 42 of the inlet header tube 4, and a plurality of orifices 73 (nine in the embodiment) disposed between the open and closed ends 71, 72 to fluidly intercommunicate the inner space 43 of the inlet header tube 4 and the baffle tube 7. Each of the orifices 73 is disposed in alignment with the connecting end 60 of one of the heat exchange tubes 6.
The inflow and outflow tubes 33, 34 are respectively fluidly connected to the open end 71 of the baffle tube 7 and the outlet header tube 5 such that a fluid pathway for the first fluid 31 flowing from the inflow tube 33 to the outflow tube 34 through the inlet header tube 4, the heat exchange tubes 6, and the outlet header tube 3 is formed. The second fluid 32 is allowed to externally flow around the heat exchange tubes 6 so as to exchange heat with the first fluid 31 via the heat exchange tubes 6.
In this preferred embodiment, the fluid pathway is classified as a U-type fluid pathway in that the inflow and outflow tubes 33, 34 are disposed at the same side with respect to the heat exchange tubes 6. Alternatively, the inflow and outflow tubes 33, 34 may be disposed at opposite sides with respect to the heat exchange tubes 6 such that the fluid pathway is classified as Z-type.
Preferably, radiator fins (not shown) may be disposed between and connected to the heat exchange tubes 6 to improve the heat exchange efficiency between the first and second fluids 31, 32.
According to the present invention, due to the design of the baffle tube 7 that is inserted inside the inlet header tube 4, no eddy flow is induced in the inlet header tube 4. As shown in FIG. 7, the first fluid 31 is allowed to flow into the baffle tube 7 and subsequently flows into the inner space 43 of the inlet header tube 4 through the orifices 73. A portion of the first fluid 31 directly flows into the heat exchange tubes 6, and another portion of the first fluid 31 which does not directly flow into the heat exchange tubes 6 circulates around the baffle tube 7 and eventually flows into the heat exchange tubes 6. Because no vortex flow or eddy flow is generated in the inlet header tube 4, the flow distribution of the first fluid 31 in the heat exchange tubes 6 becomes relatively uniform as compared to that of the conventional heat exchanger (see FIG. 3), thereby improving the heat-exchange efficiency of the heat exchanger. In this embodiment, the inflow tube 33 and the baffle tube 7 have the same cross sections, i.e., 4 mm in diameter.
Preferably, the inlet and outlet header tubes 4, 5 respectively have a square cross section. Alternatively, the cross sections of the inlet and outlet header tubes 4, 5 may be in the form of any shape.
For the sake of clarity, the nine heat exchange tubes 6 and the nine orifices 73 from the open end 71 to the closed end 72 of the baffle tube 7 are respectively denoted by reference numerals 61 to 69 and 731 to 739. The first heat exchange tube 61 and the first orifice 731 are disposed closest to the open end 71 of the baffle tube 7, and the second heat exchange tube 62 and the second orifice 732 are respectively disposed adjacent to the first heat exchange tube 61 and the first orifice 731 opposite to the open end 71. The remainder of the heat exchange tubes 63, 64, 65, 66, 67, 68, and 69, and the remainder of the orifices 733, 734, 735, 736, 737, 738, and 739 are respectively disposed on one side of the second heat exchange tube 62 and the second orifices 732 that is opposite to the first heat exchange tube 61 and the first orifice 731. It should be noted that the number of the heat exchange tubes 6 and that of the orifices 73 are the same, and are not limited to nine in other embodiments of this invention.
Preferably, in order to further overcome the drawbacks associated with the prior art that the flow amounts of the first and second heat exchange tubes 61, 62 are relatively low, in this embodiment, the first orifice 731 is larger than the second orifice 732, and the second orifice 732 is larger than each of the remainder of the orifices 733-739. Moreover, in order to avoid accumulation of excessive pressure in the baffle tube 7 that may adversely influence the inflow of the first fluid 33, an area of an interior space of each of the heat exchange tubes 6 is preferably designed to be smaller than or equal to an area of the first orifice 731 and to be larger than an area of the second orifice 732.
The performances of a conventional heat exchanger and the preferred embodiment of the heat exchanger according to the present invention were assessed by a numerical simulation using EFD.lab software as described below. The flow ratio (β) of each of the heat exchange tubes 6 of the heat exchangers was calculated by the EFD.lab software and is defined as a ratio of the flow rate in one heat exchange tube to the total flow rate (Q) in all of the heat exchange tubes 6.

COMPARATIVE EXAMPLE

A conventional U-type heat exchanger used in the comparative example has a structure shown in FIG. 1, in which the inlet and outlet header tubes 21, 22 have a square cross section with a width of 9 mm, each of the nine heat exchange tubes 23 has an inner diameter of 3 mm, and the inflow tube 20 has an inner diameter of 4 mm. A distance of an opening of the heat exchange tube 231 from the open end 211 of the inlet header rube 21 is 3.5 mm. The first fluid 11 is water having a temperature of 25° C.
FIG. 3 shows the simulation plot of velocity vector lines of the convent tonal heat exchanger. Inlet jet stream and vortex flow are generated at the open end 211 of the inlet header tube 21 near the first and second heat exchange tubes 231, 232, and even in the first heat exchange tube 231. The inlet jet stream and vortex flow result in relatively low flow amounts in the first and second heat exchange tubes 231, 232. According to FIG. 4, when the total flow rate (Q) is 1-4 L/min, the flow ratio (β) of the first heat exchange tube 231 is smaller than 6% and is quite lower than the flow ratios of the remainder of the heat exchange tubes 23, which indicates an extremely uneven flow distribution in the heat exchange tubes 23 of the conventional heat exchanger.

Examples 1 to 7

The heat exchanger of the present invention used in Examples 1 to 7 has a U-type structure as shown in FIG. 5, in which the inlet and outlet header tubes 4, 5 respectively have a square cross section with a width of 9 mm, each of the heat exchange tubes 6 has a circular cross section with an inner diameter of 3 mm, the baffle tube 7 has a circular cross section with an outer diameter of 6 mm and an inner diameter of 4 mm, and each of the orifices 73 of the baffle tube 7 has a circular shape. A distance of the connecting end 60 of the first heat exchange tube 61 from the first end 41 of the inlet header tube A is 3.5 mm, a center-to-center distance between two adjacent orifices 73 is 10 mm, and a center-to-center distance between two adjacent heat exchange tubes 6 is 10 mm. It should be noted that the inflow tube 31 has the same cross section as that of the baffle tube 7 in Examples 1 to 7. The first fluid 31 is water having a temperature of 25° C.
In Examples 1 to 7, each of the orifices 73 has a hole diameter that is varied (see Table 1) so as to verify the influence of the size of the orifices 73 on the flow distribution in the heat exchange tubes 6. For each of Examples 1 to 7, the total flow rate (Q) varied from 1 to 4 L/min. The flow ratios (β) of the heat exchange tubes 6 in each of Examples 1 to 7 are respectively shown in FIGS. 8 to 14.

TABLE 1

	Orifice
Exam-	Hole diameter of orifices (mm)

ple	731	732	733	734	735	736	737	738	739

1	4	3.7	3.2	3.2	3.2	3.2	3.2	3.2	3.2
2	4	3.5	3	3	3	3	3	3	3
3	3.7	3.2	2.8	2.8	2.8	2.8	2.8	2.8	2.8
4	3.5	3	2	2	2	2	2	2	2
5	3	2.2	1.5	1.5	1.5	1.5	1.5	1.5	1.5
6	2.8	2	1.2	1.2	1.2	1.2	1.2	1.2	1.2
7	3.8	2.2	1.5	1.5	1.5	1.5	1.5	1.5	1.5

Referring to FIG. 8, the flow distribution in the heat exchange tubes 6 slightly decreases as the total flow rate (Q) of the heat exchange tubes 6 increases. The first and second heat exchange tubes 61, 62 have relatively higher flow ratios than those of the third to seventh heat exchange tubes 63-67 because of the relatively large hole diameters of the first and second orifices 731, 732, which allow a larger volume of the first fluid 31 to flow therethrough and into the first and second heat exchange tubes 61, 62. Moreover, because of the effect of the moment of inertia, the first fluid 31 has a higher flow rate near the eighth and ninth orifices 738, 739, thereby resulting in relatively high flow ratios in the eighth and ninth heat exchange tubes 68, 69.
As shown in FIGS. 9 and 10, Examples 2 and 3 have curve profiles of flow ratio similar to that of Example 1. In these two examples, the hole diameters of the orifices 73 were reduced that resulted in an increase of the flow resistance of the first fluid 31 in the baffle tube 7. Because of the increased flow resistance and the moment of inertia, in each of Example 2 and Example 3, the flow ratio of the eighth heat exchange tube 738 is higher.
In Example 4, the hole diameters of the third to ninth orifices 733 to 739 were substantially decreased, i.e., reduced to 2 mm, resulting in a great increase in the flow resistance for the first fluid 31 in the baffle tube 7. Referring to FIG. 11, because of the greatly increased flow resistance, the first fluid 31 tends to flow into the fifth to seventh beat exchange tubes 735 to 737 rather than the eighth and ninth heat exchange tubes 738, 739. Moreover, it is apparent that, in Example 4, the slope of the curve from the fifth to ninth heat exchange tubes 735 to 739 is relatively smaller than that in Examples 1 to 3.
Referring to FIG. 12, in Example 5, when the first orifice 731, the second orifice 732, and each of the remainder of the orifices 733-739 respectively have hole diameters of 3 mm, 2.2 mm., and 1.5 mm, the first fluid 31 is evenly distributed in the nine heat exchange tubes 6. In other words, the differences in the flow ratios among the nine heat exchange tubes 731-739 become relatively small.
Referring to FIG. 13, the flow ratios of the first and second heat exchange tubes 61, 62 are higher than those of the remainder of the heat exchange tubes 63-69 in Example 6. Since the hole diameters of the third to ninth orifices 733-739 were excessively decreased to 1.2 mm, the flow resistance adjacent to the third to ninth orifices 737-739 is extremely high that causes the first fluid 31 to flow into the first and second heat exchange tubes 61, 62 through the first and second orifices 731, 732 where the flow resistance is relatively low.
Referring to FIG. 14, the flow ratios of the heat exchange tubes 6 in Example 7 are similar, which indicates a substantially uniform flow distribution in the heat exchange tubes 6. It is apparent from Examples 5 and 7 that the optimum conditions for the hole diameters of the orifices 73 are respectively 3-3.8 mm for the first orifice 731, 2.2 mm for the second orifice 732, and 1.5 mm for each of the remainder of the orifices 733-739. In other words, the hole diameters of the first, second, and each of the remainder of the orifices 731, 732, 733-739, are respectively 1-1.26, 0.73, and 0.5 times the inner diameter of each of the heat exchange tubes 6, i.e., 3 mm.
According to Examples 1 to 7, it is manifested that the site of the third to ninth orifices 733-739 exhibits greater influence to the flow distribution in the heat exchange tubes 6 than those of the first and second orifices 731, 732. When the size of the third to ninth orifices 733-739 become larger, the flow amounts of the seventh to ninth heat exchange tubes 67-69 are excessively increased. On the other hand, when the size of the third to ninth orifices 733-739 is relatively small, the flow distribution in the heat exchange tubes 6 becomes uniform. However, as shown in Example 6, when the size of the third to ninth orifices 733-739 is excessively reduced, the flow distribution in the heat exchange tubes 6 becomes uneven, i.e., the first and second heat exchange tubes 61, 62 have higher flow ratios.
In conclusion, with the baffle tube 7 in the inlet header tube 4, the vortex flow and eddy flow problems may be alleviated. According to FIGS. 8 to 14, each of the heat exchange tubes 6 has a flow ratio larger than 7%, which is much larger than that of the conventional heat exchanger in Comparative Example (the lowest one is 2%). Moreover, the flow distribution in the heat exchange tubes 6 of the present invention can be controlled to be uniform by controlling the sixes of the orifices 73, thereby improving the heat exchange efficiency of the heat exchanger.
Additionally, the heat exchanger according to the present invention may be configured for application to a large scale heat exchange system such as a heat exchanger in a nuclear power plant, a small size heat exchanger disposed in a small scale electronic device, or any other heat exchange devices known to those skilled in the art.
While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretations and equivalent arrangements.

Claims

1. A heat exchanger comprising:

an inlet header tube including opposite first and second ends and an inner space formed between said first and second ends;

an outlet header tube substantially parallel to said inlet header tube;

a plurality of heat exchange tubes transversely extending between and fluidly connected to said inlet and outlet header tubes, each of said heat exchange tubes having a connecting end connected to said inlet header tube; and

a baffle tube inserted into said inner space of said inlet header tube from said first end to said second end, said baffle tube having an open end proximate to said first end, a closed end proximate to said second end, and a plurality of orifices disposed between said open and closed ends to fluidly intercommunicate said inner space of said inlet header tube and said baffle tube, each of said orifices being disposed in alignment with said connecting end of one of said heat exchange tubes.

2. The heat exchanger of claim 1, wherein said orifices of said baffle tube include a first orifice disposed closest to said open end of said baffle tube, and a second orifice disposed adjacent to said first orifice oppositely of said open end, a remainder of said orifices being disposed on one side of said second orifice opposite to said first orifice, said first orifice being larger than said second orifice, said second orifice being larger than each of said remainder of said orifices.

3. The heat exchanger of claim 2, wherein an area of an interior space of each of said heat exchange tubes is smaller than or equal to an area of said first orifice and is larger than an area of said second orifice.

4. The heat exchanger of claim 3, wherein said first, second, and each of said remainder of said orifices have hole diameters that are respectively 1-1.26, 0.73, and 0.5 times an inner diameter of each of said heat exchange tubes.

5. The heat exchanger of claim 4, wherein said inner diameter of each of said heat exchange tubes is 3 mm, and said hole diameters of said first, second, and each of said remainder of said orifices are respectively 3-3.8 mm, 2.2 mm, and 1.5 mm.

6. The heat exchanger of claim 5, wherein said hole diameter of said first orifice is 3.8 mm.

7. The heat exchanger of claim 6, wherein said baffle tube has a circular cross section with an inner diameter of 4 mm.

8. The heat exchanger of claim 7, wherein a distance of said connecting end of said heat exchange tube from said first end of said inlet header tube is 3.5 mm, a center-to-center distance between adjacent ones of said orifices being 10 mm, a center-to-center distance between adjacent ones of said heat exchange tubes being 10 mm.

9. The heat exchanger of claim 1, further comprising an inflow tube fluidly connected to said open end of said baffle tube.

10. The heat exchanger of claim 1, wherein said inlet header tube has a square cross section.

11. The heat exchanger of claim 10, wherein said square cross section of said inlet header tube has a width of 9 mm.