Title:
Micro Heat Exchangers - "Subros new tech ultra pitched micro fin with modified
aerofoil dimples"
Field of Invention:
This invention relates to the design method and system of a very efficient and compact ultra pitched ultra thin micro heat exchanger which is embodied with our unique invention of dimpled fins and which may be used for all Air Conditioning applications and particularly for automotive applications like Condenser, Heater, Evaporator, Radiator, Charge air Cooler and Oil cooler.
Background of the invention: General Scenario:
Heat exchangers are used for transferring heat in a variety of systems such as chemical industry, Air Conditioning applications, Power generation units and many other applications. Though our disclosed invention put forward by the current patent application may find a number of other embodiments, we are presenting the invention through an embodiment specially applicable to the automotive heat exchangers. Automotive sector has been growing at a fast pace and the quest for efficiency increment and compactness is increasing by each coming day.
Heat transfer thermal circuit:
The prime goal of the designers of automotive heat exchangers is to maximize the convective heat transfer between a working fluid and a solid wall in an effort to make it more compact (The reason for targeting the air side convective heat transfer is because of the fact that almost 75 - 80% resistance offered to the heat transfer thermal circuit is offered by the air side convective heat transfer. The thermal circuit is illustrated in the figure (1of 6). The most obvious way of doing this is by increasing the velocity of the fluid, which enhances the wall convective heat transfer coefficient. However, as per the estimates of Kays and London (1984), while the heat transfer coefficient is directly proportional to the velocity, the power required to drive the flow is proportional to the square of the velocity. This imposes an upper limit on the maximum allowable velocities in

the heat exchanger. Also since the main resistance during heat transferred is offered from air side a significant improvement can be achieved only if we focus on the fin design.
Issues and technicalities with fin designing:
Most compact heat exchangers employ closely spaced fins or similar structures to augment the heat transfer area for a given volume. Additional augmentation requires modifying the wall boundary layer flow, usually with the help of turbulence promoters, such as baffles or wall roughness elements. The principal problem of this solution is that using such turbulence promoters causes a significant drop in flow pressure, thereby increasing the power consumption of the fans. A second drawback is that turbulence promoters often snag solid particles or debris, thereby increasing flow blockage and heat transfer surface fouling in many instances. Due to the high density of fin surface area and tube surface area there always remain a potential problem of frost accumulation. This problem is magnified in the exchangers where the tubes are arranged so that the flat surface is substantially horizontal as the moisture collects and remains on the flat surfaces. The moisture and frost accumulation makes operation of the heat exchanger less efficient by increasing flow resistance and thermal resistance through the heat exchanger. Further, the moisture accumulation causes corrosion and pitting of the tube surfaces, thus decreasing their useful life. The art would well receive a micro-channel heat exchanger configuration which maintains the high surface density of a typical micro-pattern on the heat exchanger fin while reducing the efficiency reduction due to moisture accumulation.
Chronology of fin design generations:
Developments in fin designing (broad categorization) can chronologically be classified into three design generations. Generation 1st of fin design basically relied on the flat extended surfaces. The need of better heat transfer and smaller heat exchangers lead to the evolution of 2nd generation of fin design. This generation designers tried to increase the heat transfer capacity of the fins by increasing the turbulence and turbulence was achieved by using the fins of a rough surface (Dimpled fin, Wavy Fin, Rough Fin etc..) The problem with the 2nd generation design was the high levels of air side pressure drop as the high air pressure drop leads to an overall reduction in the air flow itself and thus reducing the heat rejection capacity because of lesser air flow. The 3rd generation of fin designing
was focused to reduce the air side pressure drop during the heat transfer process. This was achieved by using discontinuous fin structures (Louver fins, Offset fins, etc etc). These discontinuous surfaces rupture the boundary layer periodically and a new boundary layer is developed after each rupture. The quest to make the heat exchangers more compact and more efficient so that the the size of heat exchangers can be reduced even further is still going on. The main theme of approach is to design a fin with can have the feature of both 2nd generation and also 3rd generation of fin deigning. The ultimate target design for the next generation is a fin geometry which can increase the turbulence and also rupture and regenerates the boundary layer. (Figure number 2 of 6) displays a graphical comparison between the different fin design being used currently,
Problem Statement:
There exists a need of a Ultra compact heat exchangers and methods for increasing heat transfer while minimizing, or eliminating the additional flow pressure drop and which also can be used for all heat exchanger applications in general and automotive heat exchangers in particular. The present invention addresses such a need. More particularly, the invention relates to devices and methods employing tailored dimples to enhance thermal performance at a little additional pressure drop.
Prior Art and Disadvantages of Prior art
1. The need for different fin configuration for different applications (Separate heat exchanger configuration for condenser, evaporator, heater etc)
2. Tube and fin configurations used in the prior art are having fine section but not the optimized super fin matrix and thus some heat transfer potential remains still untapped.
3. For very thin sheets there is an increased possibility of a decrease in the corrosion resistance
4. The prior art configuration (Louver type fin) can not be used for off highway application (Tractor / Harvester / excavators etc).
5. Less heat transfer per unit area thus resulting in bigger size.
6. Problem of clogging.
7. Corrosion is a problem with thin sheet (thin sheets are necessary to satisfy the weight target which is now becoming an important requirement form the customers.
8. The walls of the heat exchanger tubes are not so thin (because of not so fine core matrix) and hence the heat transfer capacity eludes the optimum value.
9. Tubes used in automotive heat exchangers (For high operating pressure applications) are manufactured through extrusion and (for low pressure applications) by seam welding. Also, the different fin configurations for different heat exchangers result in multiple core matrix and thus resulting in an increased tooling cost and also the requirement of bigger inventory and complicated supply chain management functions.
10. Tubes made from welding technique are of lesser strength and also the benefit of higher heat transfer by use of extruded tubes is also not availed.
11. Use of welded tubes may sometimes result in less durability specifications and may be an increased warranty costs.
12. Increased cost because of using a wide range of matrix resulting in less child part interchangeability
13. The prior art fin designs are missing in intentionally tailored pressure recovery zones and thus leading to a high pressure drop.
14. Fin enhancements (Dimple, Protrusion, Wavy etc..) leading to high pressure drop
15. Costly because of different tube fin configuration for different applications
SUMMARY OF THE INVENTION:
The heat transfer component as per the current invention has thin-walled and micro-channel tubes, a specially tailor made "Subros Designed" dimple fin with unique geometry defined by a fluid flow direction and wherein the fin geometry design has specially recessed tailored dimples on the fin (Very different from the existing dimple fins and the proposed fin design is different not only in the profile but also in the heat transfer mechanism, a convective surface extending between the upstream end and the downstream end which helps in better heat transfer as well as reducing net pressure drop of air side because of their behavior as pressure recovery zone). Further, the convective surface includes dimples and herein the option of the unique dimple design is disclosed and has the features and the advantages of three typical profiles -'
1. Elliptical Shape
2. Parabolic shape
3. Circular arc section shape
Please refer (Figure no. 3 of 6) for description of these shapes in the pictorial form. Also Figure no. 4 of 6 also describes the aerodynamic flow and the advantages which may be tapped thereof.
The salient features of our current work is using a very fine core matrix, specially designed core which offers a large contact area, micro-channel extruded tubes and custom tailored fin enhancement design for all automotive applications, with other embodiments of the invention, a method for transferring thermal energy comprises providing a thin-walled heat transfer member having an upstream end, a downstream end, and a convective surface extending there between. Thus, embodiment described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices. The various characteristics and features will be better appreciated by those skilled in the art after reading the following detailed description of the most preferred embodiment, and by referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
For a detailed description of the preferred embodiments of the invention, reference will
now be made to the accompanying drawings in which:
Figure 1 of 6:- Thermal resistance circuit and brief analysis
Figure 2 of 6: - Performance comparison of existing fins being used in current generation
Figure 3 of 6:- Aerofoil & oval geometry as disclosed in this invention
Figure 4 of 6:- Flow around wing section
Figure 5 of 6:- Optimum design for a typical aerofoil contour
Figure 6 of 6:- Drag versus Lift Coefficient for a typical aerofoil shape

Detailed Description:
1. According to one aspect of the invention, a micro heat exchanger includes two
manifolds for distributing fluid and a plurality of tubes extending from one manifold
and terminating inside the other manifold. At least one tube of the plurality of these
tubes should possess a curvilinear cross-section and all the tubes includes a
plurality of micro ports extending from a first end of each tube to a second end of
each tube, the ports capable of carrying fluid there through and the walls of the
micro channel ports are kept as thin as possible and defined from the durability
requirements and the manufacturing constraints. The proposed micro heat
exchanger also consist of a plurality of specially tailored fins and are located along
a length of the said tubes. In particular, the height H and length L of each heat
transfer member is substantially greater than its thickness. Herein we will use the
term "thin walled" for such parts which have negligible thickness when compared to
the corresponding height and length. Preferably all the heat transfer members are
arranged parallel to each other and also spaced apart maintaining the uniformity.
To enhance the heat transfer by conduction each component preferably comprises
a material with a relatively high thermal conductivity preferably aluminum.
Aluminum will be preferable because of the added advantages of its relatively low
cost, low weight, and ease of machining. In absence of a proper heat transfer
mechanism to the main sink the thermal energy may be stored and thus make the
heat exchanger as sink itself. Henceforth a cooling or working fluid is made to flow
across the convective surfaces of heat transfer members from upstream ends.
2. Each convective surface includes a plurality of indentations or recessed dimples which has a typical tailored design to achieve our purpose of heat transfer enhancement at the additional cost of a minimal pressure drop. The herein disclosed invention also utilizes both the sides of heat convecting surface for augmentation by indenting the said typical geometry in a staggered but defined pattern. To make most of the augmentations indented on the fin surface.
3. In the most preferred embodiment, the said dimples are not of circular profile and instead the geometry parameters are tailored to meet our specific requirements of high heat transfer and minimal additional pressure drop.
4. The most preferred embodiment of the micro heat exchangers as disclosed in the current invention adopts a combination of features of three shapes - Ellipse, Arc of circle and parabola. The specific nomenclature adopted for the dimples based on their geometrical profiles is - "The modified aerofoil dimple fin".
Micro heat exchangers are typically designed with a unique fin design as disclosed through this invention. Our new fin design which can summarily be described as unique combination of different shapes will here from be referred as "Subros New tech Fin". The uniquely designed fin contour can roughly be considered as a combination of three different shapes viz. Parabolic shape, Elliptical shape and an arc of a circle. Both the elliptical sections intersect with an arc of a circle at a point where there exists a common tangent to both arc of the circle as well as the elliptical section. Also, both the ends of the arc of a circle also intersects with a parabolic surface such there exists a common tangent to both the arc of the circle and the parabola. The distance L / D is called the aspect ratio and this is the parameter which conclusively decides on the dimple shaping (Note: Here, L is the largest length In the X - direction of the dimple and D is the biggest vertical distance for the dimple. The figure shown below illustrates the basics of our dimple design.
The terms and parameters which completely define our design are:
1. Aspect Ratio
2. Angle of attack
3. Basic Shape
4. Type of dimple
5. Angle of attack
6. Dimple Pitch
7. Fin Pitch
The above design parameters may be varied as per the specific design requirements. As a typical example of the dimensional concept we may have:
1. Aspect Ratio- 2 to 7.
2. The angle of attack Is typically taken from -20 to 20.
The typical aspect ratio as disclosed in this invention is between 2 to 7 depending on the type of target application.
5. The fin as disclosed in the current invention comprises of the dimples with the shape of a modified aerofoil. In general, an airfoil comprises of a leading edge, a trailing edge, a pressure side wall and suction side wall. The dimensions of such a dimple as per the disclosure of this invention is mentioned in Figure no. 5 of 6.
6. It is of note that the dimple design as disclosed in the current invention is a tailor made special design having special pressure recovery zones which help in minimization the pressure drop on the air side
7. The characteristic feature of the modified aerofoil shaped dimple fin is that during the downstream flow the air strikes the tube and thus producing a forced convection.
8. Each dimple is oriented with major axis at an angle relative to the fluid flow direction. The preferred angle is between -20° to 20°.
9. The micro heat exchanger disclosed herewith has the orientation of the dimple along the direction of major axis.
10. The dimple design disclosed herewith can be indented on the convective surfaces by stamping, machining, high pressure molding or injection molding.
11. The ratio of dimple pitch to dimple diameter depends on many other factors or constraints of the performance subjected to which the designer has to conclude on the design parameters.
12. Embodiments of micro heat exchanger as disclosed in the current invention are designed for the prime purpose of achieving a compact design which can deliver consistently good performance.
13. Numerical calculations hint that due to the increased turbulence and vortex structures the skin drag is more and hence the pressure drop on the air side is slightly more than the prior art design but they still offer a significant performance
improvement because the increase in heat rejection capacity outweighs the pressure drop increase.
14. The heat transfer is enhanced because these self-organized vortex structures promote mixing, drawing "cold" fluid from outside the thermal boundary layer into contact with the wall, thus improving convective heat transfer. The single most important factor to be taken into account is the optimized design of each parameter or else the design advantages may be off set totally.
15. Thus, the preferred dimple geometry and orientation which are expected to give significant performance enhancement is disclosed through the current invention offering maximum heat rejection at the expense of least pressure drop.
16. While preferred embodiments have been shown and described, modifications thereof can be made by any skilled in the art without departing from the scope or illustrations herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the disclosed current invention.

Claims:
What is claimed is:
1. A heat exchanger for automotive application comprising of tubes, fins, plate headers, tank Headers and side plates with the unique feature of super thin walled (of the order of less than 0.15 mm) tubes which help in heat transfer enhancement and also result in the lowering of weight of the heat exchanger.
2. The heat exchanger design method and process as disclosed in the current invention may be useful for other applications in another embodiment and not limited only to automotive air conditioning/engine cooling which is the prime application of the discussed about our most preferred embodiment.
3. The heat exchanger called as micro heat exchanger as disclosed in the current invention claims to be the next generation design of heat transfer and can deliver more heat rejection than the prior art heat exchanges at a very minimal increment in the pressure drop.
4. Two dimple designs are disclosed herein for the micro heat exchanger fin and both designs offer a prospective heat exchanger technology and the scope of our invention broadly covers both the designs and any variant of the same concept disclosed in the present invention.
5. In this invention, the dimples arranged in the fin are made to gradually change the angle of attack (the angle between the central rotation axis of the dimple and the wind direction) so as to direct the flow of wind such that it leads to jet impingement effect on the tube and adjacent fins which enhances the forced convection on the tube walls.
6. The vortex generation as a result of the enhanced turbulence due to the "Subros New Tech Fin" is concentrated very close to the fin surface and significantly interferes the boundary layer allowing the distant "cool" air to mix with the boundary
layer on the fin and tube thus making the micro heat exchanger much more effective when ratio of capacity to pressure drop is compared with the existing designs.
7. The consecutive protrusions as made on the opposite face in "Subros high Tech Fin" makes the air flow in a wavy (zig-zag) path thus adding the advantage of the wavy fin also in the current design.
8. The micro heat exchangers as disclosed in the current invention has a very unique feature of being capable enough from the heat exchange point of view to be used in any of the automotive heat exchanger application. (Separate heat exchanger configuration for condenser, evaporator, radiator, heater, engine oil cooler, charged air cooler, etc)
9. Yet another salient and unique feature of our current invention is the super fine core matrix being disclosed and designed to give a high heat transfer at the expense of a little pressure drop.
10. The heat exchanger as disclosed in the current invention taps the maximum heat transfer capacity and is thus superior to the prior art heat exchangers
11. The invention disclosed here can be applied with little sheet thickness of the order of 0.005 to 0.04 mm and also displays a good resistance to clogging
12. Against the limitation of prior art to use different configuration for off high way applications the embodiment as discussed in the current patentable be used for all possible heat exchanging application
13. The micro heat exchangers provide more heat transfer per unit area thus resulting in a more compact heat exchanger.
14. Micro heat exchangers as disclosed in the current invention are less prone to clogging and hence may be used for a range of applications from on road to off road applications
15. The problem of corrosion is also addressed by the disclosed invention
16. The walls of the heat exchanger tubes is so thin (because of very fine core matrix) and hence the heat transfer capacity eludes the optimum value.
17. Tubes used in automotive heat exchangers (For high operating pressure applications) are manufactured through extrusion and (for low pressure applications) by seam welding. Also, the different fin configurations for different heat exchangers result in multiple core matrix and thus resulting in an increased tooling cost and also the requirement of bigger inventory and complicated supply chain management functions. The invention disclosed herewith gives a brief idea on the same line and shows that there will be a cost reduction in this invention.
18. Tubes made from welding technique are of lesser strength and also the benefit of higher heat transfer by use of extruded tubes is also availed in this invention.
19. Micro heat exchangers as disclosed in the current invention increases the heat transfer and also provide a better strength thus leading to a reduced warranty targets
20. The invention also discloses a cost cutting option because of Commonization and interchangeability
21. The prior art fin designs are missing in intentionally tailored pressure recovery zones and thus leading to a high pressure drop. This drawback of the prior art is countered with the new invention because it offers separate pressure recovery (rising) zones
22. Fin enhancements (non aerodynamic dimple, Protrusion, Wavy etc..) leading to high pressure drop and hence the current design offers a design which may act both as a turbulator and as a boundary rupture agent.
23. The method of claim further comprising spacing the first row from the second row by an inter-row pitch measured perpendicular between the first median line and the second median line
24. The method of claim further comprising spacing the oval dimples in the first row by a distance measured along the first median line between adjacent dimples in the first row, and spacing the oval dimples in the second row by a distance measured along the second median line between adjacent dimples in the second row.