US20030131976A1

US20030131976A1 - Gravity fed heat exchanger

Info

Publication number: US20030131976A1
Application number: US10/339,313
Authority: US
Inventors: Paul Krause; Robert Utter
Original assignee: Brazeway Inc
Current assignee: Brazeway Inc
Priority date: 2002-01-11
Filing date: 2003-01-09
Publication date: 2003-07-17

Abstract

A heat exchanger system having a fluid inlet member, a fluid outlet member, and a plurality of multi-port heat transfer members. Each of the multi-port heat transfer member extends between the fluid inlet member and the fluid outlet member to define a plurality of fluid paths between the fluid inlet member and the fluid outlet member for carrying a refrigerant or coolant. The plurality of multi-port heat transfer members are spaced apart from each other so as to maximize the product of the total air-side surface area and the heat transfer coefficient of the heat exchanger. If necessary for structural rigidity, at least one reinforcing member fixedly interconnects at least some of the plurality of multi-port heat transfer members in a woven pattern to provide both longitudinal and lateral reinforcement.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/347,751, filed on Jan. 11, 2002. The disclosure of the above application is incorporated herein by reference.[0001]

FIELD OF THE INVENTION

The present invention relates to heat exchangers and, more particularly, relates to gravity fed heat exchangers having improved heat transfer capability.

BACKGROUND OF THE INVENTION

As is well known, heat exchangers function in concert with other parts of the system to transfer heat between a hot source and a cold source. Due to the size and system constraints of many applications, heat exchangers are often fabricated using extruded tubing and, more particularly, micro-multi-port (MMP) tubing. In fact, micro-multi-port tubing is used extensively in heat exchangers in the automotive industry and is beginning to be used in many stationary air-conditioning systems.

This micro-multi-port tubing is generally configured to have a flat body with a row of internal, side-by-side passageways, which are separated by internal upright webs. Processing of this micro-multi-port tubing may include extrusion, straightening, cutting to length, assembly, and furnace brazing. Typically, micro-multi-port tubing is extruded to form a long, thin, and narrow section, which is particularly adapted for promoting heat transfer.

Such micro-multi-port tubing is often coupled at its ends between a fluid input member and a fluid output member to form an heat exchanger assembly. Refrigerant or coolant flows within the micro-multi-port tubing to enable heat transfer between the air, or other fluid outside of the micro-multi-port tubing, and the refrigerant or coolant contained therein, thereby acting as a heat exchanger.

Typically, in the aforementioned automotive and stationary air-conditioning applications, the micro-multi-port tubing is conventionally brazed to rows of accordion-folded fins. These conventional fins aid in heat transfer and structural rigidity of the system; however, they also cause an associated air-side pressure drop. This pressure drop must be overcome either by the movement of air caused by the moving automobile and/or by a fan unit.

On the other hand, typical heat exchangers in the refrigeration industry use a round-tube having a plurality of flat fins coupled thereto. This type of heat exchanger is designed for forced-air applications, where a fan unit is used to force air through the heat exchanger. However, the use of forced-air is undesirable in some refrigeration applications where open food spoils prematurely due to the accelerated dehydration caused by the fast-moving air. Moreover, forced-air applications are also undesirable due to the need for an often cumbersome fan unit. When the fan is removed and natural convection is relied upon for air movement, the size of this type of heat exchanger must be dramatically increased to provide the same heat transfer capability. As should be readily understood, the increased size of these heat exchangers require the associated packaging allowances and increased cost.

Accordingly, there exists a need in the relevant art to provide a method of minimizing the physical size and air flow velocity of a heat exchanger, without adversely affecting the heat transfer capacity of the unit. Furthermore, there exists a need in the relevant art to provide a gravity fed heat exchanger capable of providing the necessary heat transfer capacity without requiring a plurality of cooling fins. Additionally, there exists a need in the relevant art to provide a finless, gravity fed, heat exchanger having a plurality of micro-multi-port tubing members being spaced apart a predetermined distance to maximize the convective heat transfer capability of the exchanger system. Still, further there exists a need in the relevant art to provide a gravity fed heat exchanger that overcomes the disadvantages of the prior art.

Further objects, features, and advantages will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.

SUMMARY OF THE INVENTION

According to the principles of the present invention, a heat exchanger system having an advantageous construction is provided. The heat exchanger system includes a fluid inlet member, a fluid outlet member, and a plurality of multi-port heat transfer members. Each of the multi-port heat transfer member extends between the fluid inlet member and the fluid outlet member to define a plurality of fluid paths between the fluid inlet member and the fluid outlet member for carrying a refrigerant or coolant. The plurality of multi-port heat transfer members are spaced apart from each other such that the product of the total air-side surface area and heat transfer coefficient is maximized. If necessary for structural rigidity, at least one reinforcing member fixedly interconnects at least some of the plurality of multi-port heat transfer members in a woven pattern to provide both longitudinal and lateral reinforcement.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: [0012]
FIG. 1 is a perspective view illustrating a gravity fed heat exchanger according to a first embodiment of the present invention; [0013]
FIG. 2 is an end view illustrating micro-multi-port (MMP) tubing; [0014]
FIG. 3 is a front view illustrating the gravity fed heat exchanger of the present invention; [0015]
FIG. 4 is a cross-sectional view of the gravity fed heat exchanger taken along line [0016] 4-4 of FIG. 3;
FIG. 5 is a front view illustrating a gravity fed heat exchanger according to a second embodiment of the present invention; [0017]
FIG. 6 is a cross-sectional view of the gravity fed heat exchanger taken along line [0018] 6-6 of FIG. 5;
FIG. 7 is a graph illustrating the optimal tubing spacing for several tubing widths as a function of the tube-to-air temperature difference.[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. [0020]
Referring now to the drawings, a gravity fed heat exchanger system according to a first embodiment of the present invention, generally indicated at [0021] 10, is provided for transferring heat from one fluid to another. In this case, heat is transferred from air in an enclosed space to a coolant that flows through heat exchanger system 10. The heat is later released according to known thermodynamic principles.
As best seen in FIGS. 1, 3, and [0022] 4, gravity fed heat exchanger system 10 generally includes a pair of parallel fluid headers 12 having a plurality of generally orthogonally-oriented, micro-multi-port (MMP) tubing 14 extending therebetween. As best seen in FIG. 2, each of the plurality of micro-multi-port tubing 14 is comprised of a metal body 16, which is aluminum or an aluminum alloy. Body 16 is made by extrusion and its shape is as shown in FIG. 2. That is, body 16 is generally rectangular having opposite faces 18 and 20 and outwardly facing rounded edge surfaces 22. A plurality of ports or passages 24 extend longitudinally through body 16 in a side-by-side arrangement between faces 18, 20, and edge surfaces 22. In the illustrated example, all of plurality of passages 24 are of the same size and shape, except for the end ports that vary only on one side.
Still referring to FIG. 2, each of the [0023] central passages 24 is defined by a pair of separating webs 26, which extend between opposite faces 18 and 20. Preferably, micro-multi-port tubing 14 is generally flat having a width that is at least three times as long as the height of the body 16. In the present embodiment, body 16 is 2.0 mm thick and 18.0 mm wide and part of a long extrusion, which is coiled for subsequent cutting into strips and straightening.
It is during the coiling/uncoiling, straightening, and cutting operations that the final width, thickness, and length dimensions of micro-multi-[0024] port tubing 14 are achieved. Micro-multi-port tubing 14 is then assembled into a frame and subjected to brazing with a brazing alloy. It should be understood that body 16 may be subjected to additional cold working, such as rolling so as to compress body 16.
As best seen in FIGS. 1, 3, and [0025] 4, the plurality of micro-multi-port tubing 14 extends between the pair of parallel headers 12 in a stacked relationship. Each of the pair of parallel headers 12 is hollow to enable fluid flow therethrough. The plurality of micro-multi-port tubing 14 is coupled to the pair of parallel headers 12 in such a way that the ends of micro-multi-port tubing 14 are in fluid communication with an internal fluid volume of the pair of parallel headers 12. That is, a first open end of micro-multi-port tubing 14 extends within the internal fluid volume of one of the pair of parallel headers 12. The second open end of micro-multi-port tubing 14 then extends within the internal fluid volume of the other of the pair of parallel headers 12.
In operation, fluid, such as a refrigerant or a coolant, enters one of a pair of [0026] connectors 28 extending from a first of the pair of parallel headers 12. Fluid travels into the internal fluid volume of parallel header 12 where it is able to enter and flow through the plurality of passages 24 formed in micro-multi-port tubing 14. During this time, heat is thermodynamically exchanged between the environment surrounding micro-multi-port tubing 14 and the fluid flowing therein. The fluid then exits into the second of the pair of parallel headers 12 and out the second of the pair of connectors 28.
Referring in particular to FIGS. 3 and 4, to further enhance the thermodynamic exchange and, thus, the overall heat exchanger efficiency of the present invention, it is preferable that the plurality of micro-multi-[0027] port tubing 14 is arranged relative to each other to define a tubing spacing A (see FIG. 4). Tubing spacing A is predetermined in order to maximize the heat transfer capability of heat exchanger system 10 and is defined as the space between opposing exterior surfaces of adjacent micro-multi-port tubing 14. That is, tubing spacing A is a distance between exterior top surface 18 of a lower tubing 14 and exterior lower face 20 of an upper tubing 14. In particular, the tubing spacing A is chosen to maximize the product of the total air-side surface area and heat transfer coefficient. This arrangement balances the competing effects of reduced air-side heat transfer coefficient and increased air-side surface area on total heat transfer as tube spacing is reduced. This optimal arrangement was found to be well-described by the following equation. $A_{opt} = \frac{2.714}{P^{0.25}} where: P \equiv \frac{c_{p} \cdot {(\overline{ρ})}^{2} \cdot g \cdot β \cdot Δ T_{0}}{μ \cdot k \cdot W}$
c[0028] _p=air specific heat at constant pressure
{overscore (ρ)}=air average air density [0029]
g=gravitational acceleration [0030]
β=air volumetric coefficient of thermal expansion [0031]
ΔT[0032] ₀=temperature difference between tube and inlet air
μ=air dynamic viscosity [0033]
k=air thermal conductivity [0034]
W=tubing width [0035]
In particular, tubing spacing A is most preferably equal to about 1.2 times the maximum boundary layer height of each micro-multi-[0036] port tubing 14. However, tubing spacing A could be up to about 2.0 times the aforementioned maximum boundary layer height. This arrangement results in a high surface area density without overly restricting the buoyant flow of air between tubing 14, thereby improving the overall heat transfer efficiency. The maximum boundary layer height is defined to be half tubing spacing A when the average heat transfer coefficient on tubing 14 is equal to 99% of the average heat transfer coefficient on a single tube.
As best seen in FIG. 7, the above relationship is depicted in graphical form. Accordingly, the above equations and graph (see FIG. 7) can be used to determine the optimal tubing spacing A given the heat exchanger's tube width and operating conditions. For example, for a heat exchanger with a 25.4 mm tube width in a system with a 22.8° C. temperature difference between the tube and the inlet air, the optimal tubing spacing is 4.53 mm. This arrangement of optimally-spaced finless flat tubes results in a more efficient heat exchanger. [0037]
Therefore, in order to achieve the same heat transfer capacity of a conventional heat exchanger system, [0038] heat exchanger system 10 of the present invention may be made smaller and the cooling fins of the conventional exchanger system may be eliminated. Additionally, by eliminating the cooling fins typically used in conventional applications, the present invention minimizes the air-side pressure drop across the micro-multi-port tubing 14, thereby eliminating the need for conventional fan units. One skilled in the art should appreciate that this elimination of the cooling fins and supplemental fan units reduces the overall size and cost of heat exchanger system 10.
However, it should be understood that as a result of such tubing spacing A, it may be necessary to reinforce the structure of gravity fed [0039] heat exchanger system 10 to maximize the structural integrity thereof. To this end, a reinforcing band 30 is woven between adjacent micro-multi-port tubing 14 to form a webbing or snaking pattern through the plurality of micro-multi-port tubing 14. As best seen in FIGS. 3 and 4, reinforcing band 30 is preferably a single, continuous, thin aluminum band. More preferably, reinforcing band 30 is made of Aluminum Association 1050 aluminum alloy.
As best seen in FIG. 4, reinforcing [0040] band 30 is first fastened, preferably by brazing or other known method, to a first of the plurality of micro-multi-port tubing 14 at 32. Reinforcing band 30 is then routed around a side of the first of the plurality of micro-multi-port tubing 14 until is can be fed in a generally opposite direction to traverse a second of the plurality of micro-multi-port tubing 14, when viewed in cross section (see FIG. 4). This weaving orientation is continued until reinforcing band 30 reached the last of the plurality of micro-multi-port tubing 14. Preferably, reinforcing band 30 is then wrapped about the last of the plurality of micro-multi-port tubing 14, at 34, and woven in a similar fashion through the plurality of micro-multi-port tubing 14. Ideally, reinforcing band 30 is also oriented in a diagonal position such that reinforcing band 30 traverses the length of heat exchanger system 10, when viewed from the front (see FIG. 3).
Accordingly, reinforcing [0041] band 30 increased the structural integrity of heat exchanger system 10 by interconnecting the plurality of micro-multi-port tubing 14 into a single structural member. Moreover, the diagonal and woven orientations further provide both lateral and longitudinal reinforcement of heat exchanger system 10 to resist structural deflection of the system. However, it should be understood that the exact orientation of reinforcing band 30 may change depending upon the specific structural requirements of heat exchanger system 10.
Referring now to FIGS. 5 and 6, a gravity fed heat exchanger system according to a second embodiment of the present invention, generally indicated at [0042] 10′, is provided for transferring heat from one fluid to another. It should be noted that like reference numeral represent like parts of the first embodiment.
In addition to those features described above, [0043] heat exchanger system 10′ further includes a pair of longitudinally extending support brackets 50, which are each secured to corresponding ends of the pair of parallel headers 12. Thus, support brackets 50 are arranged generally parallel to the plurality of micro-multi-port tubing 14. Preferably, supports brackets 50 are made of 90° aluminum brackets.
Accordingly, reinforcing [0044] band 30 is first fastened, preferably by brazing or other known method, to a first of said support brackets 50 at 32′. Similarly as above, reinforcing band 30 is then routed around a side of the first of the plurality of micro-multi-port tubing 14 until it can be fed in a generally opposite direction to traverse a second of the plurality of micro-multi-port tubing 14, when viewed in cross section (see FIG. 6). This weaving orientation is continued until reinforcing band 30 reached the other of the support brackets 50. Preferably, reinforcing band 30 is then wrapped about support bracket 50, at 34′, and woven in a similar fashion through the plurality of micro-multi-port tubing 14. Ideally, reinforcing band 30 is also oriented in a diagonal position such that reinforcing band 30 traverses the length of heat exchanger system 10′, when viewed from the front (see FIG. 5).
It should be understood from the foregoing discussion, that the gravity fed heat exchanger of the present invention provided a number of distinct advantages. That is, the present invention provides a gravity fed heat exchanger that is capable of maximizing the heat transfer efficiency of the system through the proper spacing of the plurality of micro-multi-port tubing. Furthermore, in order to overcome any compromise that may result from such spacing, the present invention utilizes a reinforcing band that is capable of interconnecting the plurality of micro-multi-port tubing to provide additional structural integrity. However, it should also be understood that such reinforcing band may be used in heat exchangers having micro-multi-port tubing that is spaced at some distance other than that specifically recited herein. [0045]
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. [0046]

Claims

What is claimed is:

1. A heat exchanger system comprising:

a fluid inlet member;

a fluid outlet member; and

a plurality of hollow heat transfer members each extending between said fluid inlet member and said fluid outlet member to define a plurality of fluid paths between said fluid inlet member and said fluid outlet member, each of said plurality of hollow heat transfer members having at least two fluid ports extending therethrough, an adjacent pair of said plurality of hollow heat transfer members being spaced apart a distance equal to or greater than about 1.2 times a maximum boundary layer of one of said plurality of hollow heat transfer members.

2. The heat exchanger system according to claim 1 wherein a width of one of said plurality of hollow heat transfer members is between about 10 mm and about 40 mm.

3. The heat exchanger system according to claim 1 wherein said adjacent pair of said plurality of hollow heat transfer members is spaced apart a distance between about 3.3 mm and about 6.2 mm.

4. The heat exchanger system according to claim 1, further comprising:

at least one reinforcing member fixedly interconnecting at least some of the plurality of hollow heat transfer members, said reinforcing member generally traversing at least some of said plurality of hollow heat transfer members to provide a general woven configuration.

5. The heat exchanger system according to claim 4 wherein said at least one reinforcing member generally traverses each of said plurality of hollow heat transfer members and said longitudinally extending support bracket in an alternating pattern to provide lateral structural reinforcement.

6. The heat exchanger system according to claim 4 wherein said at least one reinforcing member generally traverses each of said plurality of hollow heat transfer members in an alternating pattern to provide lateral structural reinforcement.

7. The heat exchanger system according to claim 4 wherein said at least one reinforcing member is further oriented in a diagonal position extending longitudinally along said plurality of hollow heat transfer members to provide longitudinal structural reinforcement.

8. The heat exchanger system according to claim 4 wherein said at least one reinforcing member is fixedly brazed to said plurality of hollow heat transfer members.

9. The heat exchanger system according to claim 4 wherein said at least one reinforcing member is an aluminum alloy band.

10. The heat exchanger system according to claim 1, wherein each of said plurality of hollow heat transfer members is micro-multi-port extruded tubing.

11. The heat exchanger system according to claim 1, further comprising:

a longitudinally extending support brackets fixedly coupling said fluid inlet member and said fluid outlet member.

12. A heat exchanger system comprising:

a fluid inlet header;

a fluid outlet header;

a plurality of hollow heat transfer members each extending generally parallel between said fluid inlet header and said fluid outlet header to define a plurality of fluid paths between said fluid inlet header and said fluid outlet header, a pair of said plurality of hollow heat transfer members being spaced apart a distance equal to or greater than about 1.2 times but less than about 2.0 times a maximum boundary layer of one of said plurality of hollow heat transfer members, each of said plurality of hollow heat transfer members having a plurality of distinct fluid paths extending therethrough, said plurality of hollow heat transfer members being capable of carrying a fluid along said plurality of fluid paths to promote heat transfer; and

at least one reinforcing band fixedly interconnecting at least some of the plurality of hollow heat transfer members, said reinforcing band generally traversing at least some of said plurality of hollow heat transfer members to provide a general alternating connection configuration.

13. The heat exchanger system according to claim 12, further comprising:

a longitudinally extending support brackets fixedly coupling said fluid inlet header and said fluid outlet header.

14. The heat exchanger system according to claim 13 wherein said at least one reinforcing band generally traverses each of said plurality of hollow heat transfer members and said longitudinally extending support bracket in an alternating pattern to provide lateral structural reinforcement.

15. The heat exchanger system according to claim 12 wherein said at least one reinforcing band generally traverses each of said plurality of hollow heat transfer members in an alternating pattern to provide lateral structural reinforcement.

16. The heat exchanger system according to claim 12 wherein said at least one reinforcing band is further oriented in a diagonal position extending longitudinally along said plurality of hollow heat transfer members to provide longitudinal structural reinforcement.

17. The heat exchanger system according to claim 12, wherein each of said plurality of hollow heat transfer members is micro-multi-port tubing.

18. The heat exchanger system according to claim 12 wherein said at least one reinforcing band is fixedly brazed to said plurality of hollow heat transfer members.

19. The heat exchanger system according to claim 12 wherein said at least one reinforcing band is an aluminum alloy band.

20. A heat exchanger system comprising:

a fluid inlet header;

a fluid outlet header;

a plurality of micro-multi-port members each extending generally parallel between said fluid inlet header and said fluid outlet header to define a plurality of fluid paths between said fluid inlet header and said fluid outlet header, said plurality of micro-multi-port members being capable of carrying a refrigerant along said plurality of fluid paths to promote heat transfer, said plurality of micro-multi-port members are spaced apart between about 1.2 times and 2.0 times the maximum external boundary layer surrounding one of said plurality of micro-multi-port members; and

at least one reinforcing band fixedly interconnecting said plurality of micro-multi-port members, said at least one reinforcing band generally traversing each of said plurality of micro-multi-port members in an alternating pattern to provide lateral structural reinforcement, said at least one reinforcing band being further oriented in a diagonal position extending longitudinally along said plurality of micro-multi-port members to provide longitudinal structural reinforcement.