Patent Publication Number: US-2012024510-A1

Title: Heat exchanger, in particular a heating element for motor vehicles

Description:
This nonprovisional application is a continuation of International Application No. PCT/EP2010/051232, which was filed on Feb. 2, 2010, and which claims priority to German Patent Application No. DE 10 2009 007 619, which was filed in Germany on Feb. 5, 2009, and which are both herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a heat exchanger, in particular a heater core for motor vehicles. 
     2. Description of the Background Art 
     Document EP 0 710 811 B1, which corresponds to U.S. Pat. No. 5,564,497, made known a heat exchanger that is used as a heater core of an air conditioning system for motor vehicles. The known heater core comprises a block formed of flat tubes and corrugated fins, and a collecting tank on the inlet side and on the outlet side for the inflow and outflow of coolant of a cooling circuit of an internal combustion engine. Coolant flows through the flat tubes of the heater core in only one direction. The coolant is therefore not redirected along the width or the depth. The heater core is optimized such that the same amount of heat is output, to the greatest extent possible, when coolant throughput through the heater core is low, e.g. when the internal combustion engine idles, and when coolant throughput rates are higher. The flat tubes of the heater core block have an inner diameter of 0.6 to 1.2 mm, and the corrugated fins between the flat tubes have a height of 3 to 6 mm; this corresponds to a ratio of corrugated fin height to inner tube diameter of 5.0. 
     Document DE 101 27 084 A1, which corresponds to U.S. Pat. No. 6,892,806, and which is incorporated herein by reference discloses a single-row flat tube and a heat exchanger comprising corrugated fins for motor vehicles, wherein a coolant of a cooling circuit of an internal combustion engine flows through the flat tubes. To increase the heat transfer on the coolant side, longitudinal vortex generators arranged in the shape of a “V” are formed in the flat sides of the flat tubes. The vortex generators are arranged in rows transverse to the flow direction of the coolant, and are inclined at an angle of approximately 20° relative to the flow direction. The vortex generators have a height which extends into the flow cross-section of the flat tubes and is in the range of 5 to 40% of the width of the flat tubes. 
     The known heat exchangers often have a low output/weight ratio, i.e. the weight of the heat exchanger is relatively high compared to the output thereof. This is due to the fact that greater output is obtained using more weight: For example, if the number of tubes of the heat exchanger is increased (reduction of lateral distribution), greater output is obtained since the heat-dissipating surface is greater, but the heat exchanger becomes heavier. Increasing the depth of the heat exchanger also has an unfavorable effect on the output/weight ratio. 
     SUMMARY OF THE INVENTION 
     It is therefore an objection of the present invention to provide a heat exchanger that has the highest possible output/weight ratio, i.e. a high ratio of output of the heat exchanger to the weight thereof. A further problem addressed by the invention is that of ensuring that the heat exchanger has a low pressure drop on the air side and on the coolant side, in particular a favorable ratio of air-side pressure drop to coolant-side pressure drop. Finally, it should be possible to manufacture the heat exchanger at low cost and using a reliable process. The problem addressed by the invention is therefore also that of reducing the fuel consumption of the motor vehicle (reducing the blower and coolant pump output that is taken up). 
     According to an embodiment of the invention, the flat tube has an inner diameter L in the range of 0.9 to 1.2 mm, preferably 1.0 mm, and the corrugated fins have a height H in the range of 6.3 to 8.0 mm, preferably 6.3 mm. Preferably, the ratio of corrugated fin height H to inner diameter L is in a range of 5 to 9, in particular in a range of 6.3 to 7.2. The advantage of a high output/weight ratio is therefore obtained, in combination with a low pressure drop of the heat exchanger on the air side and on the coolant side. Due to the high output/weight ratio, material for the heat exchanger is saved, thereby making it possible to lower the manufacturing costs. 
     According to an embodiment, the flat tubes comprise vortex generators which extend inwardly into the flow cross-section of the flat tubes, are longitudinal, and are arranged in the shape of a “V” in rows transversely to the flow direction of the coolant. The vortex generators have been optimized in respect of their dimensions (length, width, depth), their number, and their inclination angle relative to the coolant flow in respect to the coolant-side pressure drop and heat transfer. Due to the vortex generators which have been dimensioned according to the invention, the output can therefore be increased while maintaining a justifiable coolant-side pressure drop. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
         FIGS. 1 and 1   a  show a heater core in one view and in a 3-D representation; 
         FIG. 2  shows a corrugated fin with fins, as seen from above; 
         FIG. 3  shows a corrugated fin, as seen from the front (in the direction of air flow); 
         FIG. 4  shows a cross section through a folded flat tube; 
         FIG. 5  shows a cross section through a folded flat tube comprising embossed vortex generators; 
         FIG. 6  shows a longitudinal cross-section through a flat tube comprising vortex generators; 
         FIG. 7  shows an enlarged section of a flat tube comprising vortex generators; 
         FIG. 8  shows, in a graphic representation, the influence of depth W of the vortex generators on the ratio of output to coolant-side pressure drop; 
         FIG. 9  shows, in a graphic representation, the influence of depth W of the vortex generators on the ratio of output to air-side pressure drop; 
         FIG. 10  shows, in a graphic representation, the influence of inner diameter L on the ratio of output to air-side pressure drop; 
         FIG. 11  shows, in a graphic representation, the influence of inner diameter L on the output/weight ratio (specific output); and 
         FIG. 12  shows, in a graphic representation, the influence of corrugated fin height H on the ratio of output to the product of coolant-side and air-side pressure drop. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a heat exchanger in the form of a heater core  1  which comprises a block  4  formed of flat tubes  2  and corrugated fins  3 , and a collecting tank  5  on the inlet side, and a collecting tank  8  on the outlet side. Heater core  1  is part of a heating system or air conditioning system of a motor vehicle, which is not depicted, and coolant of a cooling circuit of the internal combustion engine of the motor vehicle, which is not depicted, flows therethrough. Ambient air flows over corrugated fins  3  disposed between flat tubes ( 2 ) (see also  FIGS. 2 ,  3 ), is heated in heater core, and is then supplied to a vehicle interior of the motor vehicle. 
       FIG. 1   a  shows heater core  1  in a perspective depiction, wherein it is clear that heater core  1  is formed as a single row, i.e. it comprises only one row of flat tubes  2 . Collecting tanks  5 ,  6  do not have any partition walls. As indicated by an arrow E, the coolant enters lower collecting tank  5 , flows through all flat tubes  2  from the bottom to the top, i.e. in the same direction, is collected in upper collecting tank  6 , and leaves it as indicated by arrow A. Components  2 ,  3 ,  5 ,  6  of heater core  1  are composed of aluminium materials and are soldered together. The design and production of heater core  1  are therefore relatively simple for attaining a high level of process reliability and lowering costs. Due to the simple flow through the heater core on the coolant side, i.e. omitting redirections in the width and the depth, a relatively low pressure drop results on the coolant side. 
       FIG. 2  shows a corrugated fin  3  in a view from above, in which fins  3   a,    3   b  having different adjustments are shown. 
       FIG. 3  shows corrugated fin  3  in a view from the front, i.e. as seen in the direction of air flow. Corrugated fin  3  comprises fin arches  3   c,    3   d,  at which they are soldered to flat tubes  2  which are not depicted here. The height of corrugated fin  3 , which corresponds to the distance between adjacent flat tubes  2 , is labelled as H. According to an embodiment, the height of the corrugated fin is in a range of H=6.3 to 8.0 mm. 
       FIG. 4  shows a flat tube  2  in a cross section, wherein flat sides are labelled as  2   a,    2   b.  Flat tube  2  is designed as a folded tube, i.e. it is made by forming a piece of sheet metal, and comprises a fold  2   e  composed of two segments  2   c,    2   d  in the center thereof. The flow cross-section of flat tube  2  is therefore subdivided into two chambers A 1 , A 2 . The outer dimension of the flat tube is labelled as T in the depth direction, which is also referred to as depth, and the inner diameter of flat tube  2  is labelled as L. According to an embodiment, the depth is in a range of T=15 to 35 mm, and the inner diameter is in a range of L=0.9 to 1.2 mm. A range for the ratio of corrugated fin height to inner diameter can be H/L=5 to 9, in particular 6.3 to 7.2. 
       FIG. 5  shows a cross section of flat tube  2  comprising vortex generators  7 ,  8 , which are embossed inwardly into the flow cross-section, on both flat sides  2   a,    2   b . Vortex generators  7 ,  8  have a depth W which is indicated using arrow heads and, in an embodiment, lies in a range of W=0.15 to 0.35 mm. 
       FIG. 6  shows a section of flat tube  2  in a longitudinal cross section, wherein rows of vortex generators  7  are shown. The flow direction of the coolant is indicated by arrows S; a cross-sectional plane, perpendicular to flow direction S, is indicated by line q. The number of vortex generators in one row is labelled as W A , wherein each row comprises six vortex generators in the embodiment shown. 
       FIG. 7  shows a section of flat tube  2  with a top view of vortex generators  7  which are disposed in the shape of a “V” relative to flow direction S and have an inclination angle α with respect to flow direction S. Vortex generators  7  are longitudinal: they have a longitudinal axis a, a length W 1 , and a width W 2 . Angle α is defined by longitudinal axis a and flow direction S. 
     According to an embodiment, vortex generators  7 ,  8  have the following dimensions: depth W (see  FIG. 5 ) is in a range of 0.15 to 0.35 mm—given an inner diameter L of flat tube  2  of 0.9 to 1.2 mm. Length W 1  of vortex generators  7 ,  8  is in a range of 1.5 to 4.0 mm, and width W 2  is in a range of 1.0 to 2.5 mm. The number W A  of vortex generators  7 ,  8  per row and transversely to flow direction S is 4 to 10. Inclination angle α of vortex generators  7 ,  8  is in a range of 15 to 25°. 
     In an embodiment, vortex generators  7 ,  8  can have the following dimensions: W 1 =2.5 mm; W 2 =1.25 mm; W=0.25 mm; α=20°; W A =6. 
     Dimensions of the flat tube can be: L=1.0 mm and T=26 mm. 
       FIG. 8  shows a diagram in which a specific output of the heat exchanger, i.e. output Q 100  relative to coolant-side pressure drop dp 1 , is plotted in percent over depth W of the vortex generators. The vortex generators serve to improve the heat transfer by forming a turbulence flow, thereby increasing the output. At the same time, coolant-side pressure drop dp 1  increases. Starting at a certain depth of W=0.25 mm, the output increases insubstantially despite the greater pressure drop. Range W=0.15 to 0.35 mm is the preferred range for a favorable ratio of Q 100 /dp 1 . The measurement on which the diagram is based was carried out using a flat tube having an inner diameter of L=1.0 mm. 
       FIG. 9  shows a diagram in which a specific output, i.e. output Q 100  relative to air-side pressure drop dp 2 , is plotted in percent over depth W of the vortex generators. Air-side pressure drop dp 2  is influenced practically not at all by the vortex generators since the vortex generators are embossed toward the inner side of the flat tube, i.e. in the flow cross-section of the coolant. The ratio Q 100 /dp 2  increases as depth W increases. The preferred range of depth W of the vortex generators can be determined by the ratio Q 100 /dp 1 , however, as shown in  FIG. 8 . 
       FIG. 10  shows a diagram in which the specific output Q 100 /dp 2 , i.e. the output based on the air-side pressure drop, is plotted over inner diameter L of flat tube  2 . Three curves are shown for different corrugated fin heights, namely H=4.5 mm (symbol: square), H=6.3 mm (symbol: triangle), H=8.0 mm (symbol: circle). The investigation was based on a depth of the vortex generators of W=0.25 mm. The depiction shows the influence of corrugated fin height H on the ratio of output to air-side pressure drop. As corrugated fin height H increases, air-side pressure drop dp 2  decreases. Given an increase in corrugated fin height of 4.5 to 6.3 mm, the air-side pressure drop decreases by approximately 20%, and by approximately 10% if the corrugated fin height increases from 6.3 to 8 mm. An increase in corrugated fin height typically results in a reduction in output since fewer flat tubes (and therefore less heat-transferring surface) are present. It has been shown, however, that similar output is attained by using a corrugated fin having a height of 6.3 mm compared to a corrugated fin height of 4.5 mm. The reason for this is the higher speed of the coolant in the flat tube and, therefore, better heat transfer. This results in a marked improvement of the Q 100 /dp 2  characteristic curve for fin height H=6.3 mm compared to fin height H=4.5 mm. Measurable output is reduced even given a corrugated fin having a height of 8 mm since a further reduction in surface (since there are fewer flat tubes) is noticeable. In this case, however, the reduction in the air-side pressure drop results in further improvement of the Q 100 /dp 2  characteristic curve. This results in a preferred range of corrugated fin height H between 6.3 and 8.0 mm. 
       FIG. 11  shows a diagram in which the specific output, i.e. the output relative to the weight of the heater core, is plotted in percent over inner diameter L of the flat tube. Three curves are shown for different corrugated fin heights of 4.5; 6.3; 8.0 mm. The characteristic value Q 100 /weight defines the effectiveness of the heat exchanger, wherein the effectiveness also affects the costs of the heat exchanger. The lower the weight is, the lower amount of material is that is consumed, wherein the material costs for a heat exchanger comprise more than 50% of the total manufacturing costs. The two upper curves for corrugated fin height 6.3 mm (symbol: triangle) and the corrugated fin height 8.0 mm (symbol: circle) confirm—as already explained with reference to FIG.  10 —the preferred range of corrugated fin height of H=6.3 to 8.0 mm. 
       FIG. 12  shows a diagram in which a further specific output is plotted against height H of the corrugated fins. The specific output is based on the product of coolant-side and air-side pressure drop, and is referred to as Q 100 /(dp 1 ·dp 2 ). The diagram shows a family of curves comprising six curves for different inner diameters L of 0.8 to 1.3 mm, each of which is depicted for corrugated fin heights of 4.5; 6.3; 8.0 mm. The ratio Q 100 /(dp 1 ·dp 2 ) increases as the inner diameter increases. The main reason therefor is the decreasing coolant-side pressure drop which affects this characteristic value to a greater extent than does the decreasing output. The curves of the diagram first show—in the region of the corrugated fin height of 4.5 to 6.3 mm—a strong increase, while the ratio Q 100 /(dp 1 ·dp 2 ) stops increasing past this point. 
     With consideration for the two ratios Q 100 /(dp 1 ·dp 2 ) and Q 100 /dp 2  (see  FIG. 10 ), a preferred range of L=0.9 to 1.2 mm results for the inner diameter. This diagram also confirms the preferred range for the corrugated fin height of H=6.3 to 8.0 mm. 
     The aforementioned diagrams and the associated explanations show that the heater core according to the invention has a high output/weight ratio, thereby combining low material usage and low material costs. The heater core according to the invention is also highly efficient. The low air-side pressure drop results in low blower output and, therefore, lower current uptake, thereby reducing fuel costs. The low coolant-side pressure drop results in a lower current uptake of the coolant pump in the cooling circuit and, therefore, higher output of the internal combustion engine. 
     Further dimensions of a preferred embodiment are: Fin density, i.e. the number of fins per dm (decimeter=10 cm), is in a range of 85 to 105 fins/dm. The material thickness of the flat tubes is in a range of s tube 0.15 to 0.3 mm, in particular 0.20 mm. The material thickness of the corrugated fins is in a range of s fin =0.06 to  0 . 10  mm, in particular in a range of 0.07 to 0.08 mm. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.