SE541820C2

SE541820C2 - A heat exchanger comprising a heat transfer element

Info

Publication number: SE541820C2
Application number: SE1651402A
Authority: SE
Inventors: Björn Kylefors; Jonathan Elamzon
Original assignee: Scania Cv Ab
Priority date: 2016-10-26
Filing date: 2016-10-26
Publication date: 2019-12-27
Also published as: SE1651402A1; DE102017009424A1

Description

A heat exchanger comprising a heat transfer element BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to a heat transfer element to be arranged in a flow passage in a heat exchanger according to the preamble of claim 1.

Heat exchangers such as radiators and charge air coolers which are cooled by ambient air in a front portion of a vehicle may be designed with a plurality of parallel tubes arranged in a row directing coolant or charge air from an inlet tank to an outlet tank. The tubes are arranged at a distance from each other such that air flow passages are formed between the tubes. Air is forced through the air flow passages by a radiator fan and ram air during operation of the vehicle. Heat transfer elements in the form of fins may be arranged in the air flow passages in order to enlarge the heat transfer area and increase the heat transfer between the air and the coolant or the charge air in the tubes. Furthermore, the fins may be provided with flow deflecting members in the form of louvers increasing the turbulent flow in the air flow passages. The turbulent flow enhances further the heat transfer between the air and the coolant or the charge air in the tubes. However, there is drawbacks with louvers. The turbulent air flow increases the pressure drop in the air flow passages which results in a higher load on the radiator fan and an increased fuel consumption of the vehicle. Furthermore, the existence of the louvers increases the risk that the air flow passages get clogged with dirt which reduces the cooling capacity of the radiator and the charge air cooler.

It is also common to provide the flow passages in the tubes in a radiator and a charge air cooler with heat transfer elements and flow deflecting members in order to increase the heat transfer in the radiator and the charge air cooler. However, the existence of the flow deflecting members in the tubes of a radiator increases the flow resistance and the load for a coolant pump to circulate the coolant through the radiator. The existence of the flow deflecting members in the tubes of a charge air cooler increases the flow resistance and the load a compressor to direct charge air through the charge air cooler.

It is to be noted that heat transfer elements and flow deflecting members can be arranged in flow passages in heat exchangers of arbitrary kind in order to increase the heat transfer in the heat exchanger.

SUMMARY OF THE INVENTION The object of the present invention is to provide a heat exchanger comprising a heat transfer elements with deflecting members causing an increased turbulent flow in a medium passage only when there is an increased heat transfer demand in the heat exchanger.

The above mentioned object is achieved by the heat exchanger according to claim 1. The heat transfer between two mediums in the heat exchanger can be increased by arranging heat transfer elements in a flow passage for at least one of the mediums. In case a medium to be cooled has a too high temperature when it leaves a heat exchanger, it is suitable to increase the heat transfer in the heat exchanger in order to cool the medium to a lower temperature. The heat transfer in a flow passage is related to the proportion of turbulent flow in the flow passage. The turbulent flow level can be increased by providing the heat transfer elements with flow deflecting members. The flow deflecting members receive a temperature related to the medium in the flow passage. Thus, the heat transfer in the heat exchanger is also related to the temperature of the flow deflecting member. According to the invention, the flow deflecting members are made of a material changing shape in relation to its temperature. The flow deflecting member is configured to change shape in relation to its temperature such that it receives different shapes and different deflecting properties of the medium flow at at least two different temperatures. According to the invention, the heat exchanger comprises at least one zone with a long heating time provided with heat transfer elements which comprise flow deflecting members changing shape in relation to its temperature and at least one zone with a short heating time provided with heat transfer elements which comprise flow deflecting members having the same shape at different temperatures.

According to an embodiment of the invention, it is possible to design such flow deflecting members such that they change shape and deflects the medium flow in the flow passage when the temperature of the flow deflecting members indicates that there is an increased heat transfer demand. It is an increased heat transfer demand in a heat exchanger when a medium is not cooled to a desired temperature. It is a sufficient heat transfer demand in a heat exchanger when the medium is cooled to the desired temperature. The flow deflecting members can be designed to have a shape which do not deflect the medium flow when there is a sufficient heat transfer in the heat exchanger. Consequently, such flow deflecting members makes it possible to increase the turbulent flow and the heat transfer in heat exchanger only when there is an increased heat transfer demand. It is possible to reduce the flow resistance in the flow passage and save energy for directing the medium through the heat exchanger during operating conditions when there is a sufficient heat transfer in the heat exchanger.

According to an embodiment of the invention, the flow deflecting member is configured to project into a flow channel when it is in a deflection position. Such a flow deflecting member provides a turbulent flow in the flow channel in the deflecting position. The heat transfer element may be provided with at least one flow deflecting member for each flow channel. Alternatively or in combination, the flow deflecting member is configured to expose an opening between two adjacent flow channels when it is in a deflection position. In this case, it is possible for medium to flow between adjacent flow channels which further increases the turbulent flow in the flow channels.

According to an embodiment of the invention, the flow deflecting member consists of a partly cut out portion in the heat transfer element and a metal material which is connected to the cut out portion in the heat transfer element. It is possible to provide a flow deflecting member changing shape in relation to the temperature by adding a suitable metal material to a surface of a partly cut portion in the heat transfer element. The metal material may be a metal strip fixedly joined to the partly cut out portion. The metal strip may be fixedly joined to a surface of the partly cut out portion by stamping, forging, brazing, welding, gluing etc. Alternatively, the metal material is a metal layer applied on the cut out portion. Such a metal material may be applied to a surface of the partly cut out portion by spraying, sputtering etc. In this case, it is possible to provide the partly cut out portion with a very thin metal material layer.

According to an embodiment of the invention, the metal in the heat transfer element and the metal material are different metals with different coefficient of thermal expansion. In this case, the metal in the cut out portion and the added metal material create a flow deflecting member with bimetallic properties. Consequently, the flow deflecting member receives a curved shape in relation to the temperature. In this case, the deflection of the medium flow and the heat transfer will be adjusted in a stepless manner in relation to temperature of the flow deflecting member. Aluminum and copper may, for example, be used as materials in heat transfer element and in the added metal material. According to another alternative, the metals may be copper and a ferritic stainless steel.

According to an embodiment of the invention, the metallic material is a shape-memory alloy with two -way memory effect. In this case, the metallic material can receive two different shapes. One shape at a low temperature and another shape at a high temperature. The cut out portion is dimensioned such that it will be curved together with the added metal material. The metal material may, for example, be an alloy of copper-aluminum-nickel or nickel-titanium changing shape at suitable temperatures. In this case, it is only possible to adjust the shape of a flow deflecting member between two positions which may be one deflecting position and one no deflecting position.

According to an embodiment of the invention, the partly cut out portion is designed with a fixed end fixedly connected to the heat transfer element, a free end and two sides connecting the free end and the fixed end. In this case, the flow deflecting member may have a rectangular-shape. The free end will be the part of the flow deflecting member projecting the longest distance into the flow passage. The free end may be located in a downstream position of the fixed end with reference to the intended flow direction through the flow passage. In this case, the medium flow hitting the flow deflecting member will be directed in a more or less transverse direction into the flow channel. Alternatively, the fixed end of cut out portion may be located in a downstream position of the free end with reference to the intended flow direction through the flow passage. In this case, the medium flow hitting the flow deflecting member will be deflected from one flow channel to an adjacent flow channel via an opening between the flow channels.

According to an embodiment of the invention, the heat transfer elements comprise a first section to be fixedly connected to a surface defining one side of the flow passage, a second section to be fixedly connected to a surface defining on an opposite side of the flow passage and an intermittent section having an extension cross the flow channel between said end sections. In this case, the heat transfer element may be waved shaped with a V-profile or a U-profile.

According to an embodiment of the invention, the heat transfer elements is provided with flow deflecting portions arranged in different downstream positions in the flow passage. The temperature of the medium varies along the flow passage. In this case, it is possible that the flow deflecting members provide a different deflection of the medium flow in different downstream position in the flow passage.

Heart transfer elements with flow deflecting members changing shape with the temperature may be arranged in a heat exchanger of arbitrary kind. The heat exchanger may, for example, be a radiator in which coolant is cooled by air or a charge air cooler in which charge air is cooled by air. Heat transfer elements according to the invention may be arranged in one flow passage or two flow passages in the heat exchanger. The heat exchanger comprises at least one zone provided with heat transfer elements according to the invention and at least one zone provided with conventional heat transfer elements. When a thermostat opens in a cooling system and directs hot coolant to the radiator, some zones of the radiator obtain a more rapid heating than other zones. Temperature differences between different zones in a radiator results in thermal stresses which may reduce the life time of the radiator. It is usually known which zones of a radiator having a short heating time and a long heating time. Due to this fact, it is possible to arrange heart transfer elements according to the present invention in zones with a long heating time and conventional heat transfer elements in zones with short heating time in order to equalize the heating times between said zones and reduce thermal stress in the radiator.

BRIEF DESCRIPTION OF THE DRAWING In the following preferred embodiments of the invention is described, as examples, and with reference to the attached drawings, in which: Fig. 1 shows a heat exchanger in the form of a radiator comprising heat transfer elements according to the invention, Fig. 2 shows a part of the radiator in Fig. 1, Fig. 3 shows a cross section view along the plan A- A in Fig. 2 in which the flow deflecting members in a no deflecting position, Fig. 4 shows a cross section view along the plan A- A in Fig. 2 in which the flow deflecting members in a deflecting position, Fig. 5 shows a cross second view through one of the tubes in Fig. 1, Fig. 6 shows a cross section view along the plan B- B in Fig. 5 in which the flow deflecting members in a no deflecting position and Fig. 7 shows a cross section view along the plan B- B in Fig. 5 in which the flow deflecting members in a deflecting position.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 shows a heat exchanger in the form of a radiator 1 which may be arranged in a vehicle. The radiator 1 receives coolant circulating in a cooling system for cooling of components in the vehicle such as a combustion engine. The radiator 1 comprises an inlet tank 2 receiving coolant to be cooled. The coolant is directed from the inlet tank 2 to a heat transfer area 3 of the radiator. The heat transfer area 3 comprises a plurality of tubes 4 arranged in a row in parallel. Air flow passages 5 are arranged in the spaces between adjacent tubes 4. Each tube 4 comprises an inner space defining a coolant flow passage 6 through the heat transfer area 3. The coolant flow is forced through the coolant flow passages by means of a not shown coolant pump. A cooling air flow is forced through the air flow passages in the radiator 1 by means of a radiator fan and ram air. Heat transfer elements 7, which can be designated as fins, are arranged in the air flow passages 5. The existence of the heat transfer elements 7 increase the heat transfer area and thus the heat transfer between the air and the coolant in the tubes 4. The coolant leaving the heat transfer area 3 is received in an outlet tank 8.

Fig. 2 shows a part of the radiator 1 in Fig. 1. The tubes 4 has an elongated cross sectional area. As a consequence, the tubes 4 have a small front surface and a relatively large flat outer surfaces 4a defining the air flow passage 5 between two adjacent tubes 4. The heat transfer elements 7 are formed by a folded thin metal sheet. The heat transfer elements 7 comprise first end sections 7a to be fixedly connected to an outer surface 4a of a tube 4 on one side of the air flow passage 5, second end sections 7b to be fixedly connected to an outer surface 4a of a tube 4 on an opposite side of the air flow passage 5, and intermediate sections 7c each having an extension between a first end section 7a and a second end section 7b. The heat transfer elements 7 divide the air flow passages 5 in a large number of relatively narrow air flow channels 5a arranged in parallel. The heat transfer elements 7 are manufactured of a material having excellent heat conducting properties such as, for example, aluminum or copper. Each intermediate section 7c has side surfaces to be in heat transfer contact with the air in the air flow passage 5. The intermediate sections 7c are provided with a plurality of partly cut-out portions 7d. The partly cut out portion 7d comprises a fixed end 7 e fixedly connected to the heat transfer element 7, a free end 7f and two sides 7g, 7h connecting the fixed end 7e and the free end 7f. A metal material 9 is arranged on a surface of the cut out portions 7d. The partly cut out portions 7d and the metal material 9 form air deflecting members 10. The heat transfer elements 7 comprise several air deflecting members 10 arranged in different downstream positions in the air flow passage 5.

Figs. 3 and 4 show a view in the plane A- A in Fig 2 of two flow channels 5a in the air flow passage 5. The partly cut out portion 7d has an extension in the intended flow direction the in the flow channels 5a between the fixed end 7e and the free end 7f. One side of the partly cut out portion 7d has been provided with the metal material 9 such that the partly cut out portion 7d and the metal material 9 together form the flow deflecting member 10. The heat transfer element 7 and the metal material 9 include different metals which expand at different rates as they are heated. The metal material 9 may be a thin metal strip which is fixedly attached to a surface of the partly cut out portion 7d by brazing, welding, gluing etc. Alternatively, the metal material 9 can be applied to the partly cut out portion 7d by spraying, sputtering such as Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CPD) etc.

The partly cut out portion 7d and the metal material 9 can together form a flow deflecting member 10 in the form of a bimetallic strip with a suitable choice of metals. In this case, the different thermal expansion properties of the metals in the cut out portion 7d and the metal material 9 result in a force which bends the flow deflecting member 10 when it is heated. The metal with the higher coefficient of thermal expansion will be on the outer side of the curved flow deflecting member 10. The two including metals of the flow deflecting member 10 may be aluminum and copper, copper and a suitable stainless steel. In this case, the flow deflecting member 10 receives a continuously increasing curvature in relation to the temperature. Alternatively, the metal material 9 may be a shape memory alloy (SMA) with two way memory effect. A shape memory alloy has one shape at a low temperature and another shape at a high temperature. In this case, it is only possible to adjust the shape of the flow deflecting members 10 between said two shapes. In this case, one shape may define the flow deflecting member 10 in a no deflecting position and the other shape may define the flow deflecting member 10 in a deflecting position.

During operation, air flows through the air flow passages 5 between the tubes 4. The flow deflecting members 10 have a temperature related to the air temperature and the coolant temperature in the radiator. When the flow deflecting members 10 have a low temperature, there is no demand to increase the heat transfer between the air and the coolant in order to provide a more effective cooling of the coolant by the air. The flow deflecting members 10 in the air flow passages 5 are designed such that they are in a no deflecting position when they have a low temperature, which is shown in Fig. 4. In this position, the flow deflecting members 10 do not at all influence on the air flow in the adjacent air channels 5a. As a consequence, the flow resistance in the air flow passage 5 will be low. Thus, the consumption of energy to a radiator fan which forces air through the air flow passage 5 will be low.

When the flow deflecting members 10 have a high temperature, there is a demand to increase the heat transfer in order to provide a more effective cooling of the coolant by the air. The flow deflecting members 10 receives a more or less curved shape when it is heated to a high temperature. The flow deflecting members 10 are now in a deflecting position. In the deflecting position, the flow deflecting members 10 penetrate into an adjacent air flow channel 5a. As a consequence, the flow deflecting members 10 disturb the air flow in the air flow channel 5a. The disturbed air flow will be more turbulent. Furthermore, an opening 12 is created in the intermediate sections 7b allowing air to flow between two adjacent air flow channels 5a. Such an air flow results also results in an increased turbulent flow in the air flow passages 5a. The turbulent air flow in the flow passages 5 increases the heat transfer such that the air provides a more effective cooling of the coolant.

Fig. 5 shows a cross sectional view of one of the tubes 4 in Fig. 1 and the coolant flow passage 6. A heat transfer element 13 is arranged in the tube 4 in the coolant flow passage 6. The heat transfer element 13 has a substantially similar design as the heat transfer element 7 in the air flow passage 5. The heat transfer element 13 is formed by a folded thin metal sheet.

The heat transfer element 13 divides the coolant flow passage 6 in a large number of parallel flow channels 6a. The heat transfer element 13 is manufactured of a material having excellent heat conducting properties such as, for example, aluminum or copper. The heat transfer element 13 comprises first end sections 13a to be fixedly connected to an inner side surface 4b of the tube 4, second end sections 13b to be fixedly connected to an inner side surface 4b of the tube 4 on an opposite side of the coolant flow passage 6, and intermittent sections 13c having an extension cross the coolant flow passage 6 between two end sections 13a, 13b. Thus, the heat transfer element has a wave-sized design in a cross sectional view through the tube 4. The intermittent sections 13c have side surfaces to be in heat transfer contact with the coolant in the flow passage 6. The intermittent sections 13c are provided with flow deflecting members 14.

Figs. 6 and 7 show a view along the plane B-B in Fig. 5 of two flow channels 6a in the coolant flow passage 6 at two different temperatures. Several flow deflecting members 14 are arranged in different downstream positions in the flow channels 6a. Each flow deflecting member 14 comprises a partly cut out portions 13d. The partly cut out portion 13d has an extension in the coolant flow between a fixed end 13e and a free end 13f. One side of the partly cut out portion 13d has been provided with a metal material 16. A partly cut out portion 13d and a metal material 16 form together a flow deflecting member 14. The heat transfer element 13 and the metal material 16 include different metals such that the flow deflecting member 14 form a bimetallic strip. Alternatively, the metal material 16 may be a shape memory alloy (SMA) with two way memory effect.

During operation, coolant flows through the coolant flow passages 6 in the tubes 4. When the coolant has a low temperature, there is no demand to increase the heat transfer between the air and the coolant in order to provide a more effective cooling of the coolant. The flow deflecting members 14 in the coolant flow passages 6 are designed such that they are in a no deflecting position when the coolant has a low temperature, which is shown in Fig. 5. In this position, the flow deflecting member 14 does not at all influence on the coolant flow in the adjacent flow channels 6a. Consequently, the flow resistance in the coolant flow passage 6 as well as in the flow channels 6a will be low. Thus, the consumption of energy for the coolant pump to force coolant through the coolant flow passages 6 will be low.

When the coolant has a high temperature, there is a demand to increase the heat transfer between the air and the coolant in order to provide a more effective cooling of the coolant in the coolant flow passage 6. The flow deflecting members 14 which are in contact with the coolant in the coolant flow passages 6 obtain a temperature related to the coolant temperature. When the flow deflecting members 14 are heated to a high temperature they are moved to a deflecting position. The flow deflecting members 14 receive a curved shape in the deflecting position. Fig. 7 shows flow deflecting members 14 in the deflecting position. In the deflecting position, the flow deflecting members 14 penetrate into an adjacent flow channel 6a such that they disturb the coolant flow. As a consequence, the disturbed coolant flow will be more turbulent. Furthermore, an opening 15 is created in the intermediate section 13c allowing coolant to flow between two adjacent flow channels 6a. Such a flow also increases the turbulent flow in the flow passages 6a. The turbulent coolant flow in the flow passages 6 increased the heat transfer between the air and the coolant which results in a more effective cooling of the coolant.

The invention is not restricted to the embodiments on drawings but may be varied freely within the scopes of the claims. The heat exchanger does not need to be a radiator, it may be a heat exchanger of an arbitrary kind. Further, it is possible to arrange such heat transfer elements in flow passage for one medium in a heat exchanger or in flow passages for two mediums in the heat exchanger. Furthermore, it is possible to arrange heat transfer elements with flow deflecting members changing shape in relation to its temperature in specific zones of a heat exchanger and conventional heat transfer elements with flow deflecting members having the same shape at different temperatures in remaining zones of the heat exchanger in order to reduce temperature differences and thermal stresses in the heat exchanger.

Claims

1. A heat exchanger comprising a heat transfer element to be arranged in a flow passage (5, 6) for a medium in a heat exchanger (1), wherein the heat transfer element (7, 13) is made of a thin corrugated metal sheet having a design such that it divides the flow passage (5, 6) in a plurality of parallel flow channels (5a, 6a), wherein the heat transfer element (7, 13) comprises at least one flow deflecting member (10, 14) to be in contact with the medium in the flow passage (5, 6), and wherein the flow deflecting member (10, 14) is configured to change shape in relation to its temperature such that it receives different shapes and different deflecting properties of the medium flow at at least two different temperatures, characterized in that the heat exchanger comprises at least one zone with a long heating time provided with heat transfer elements which comprise flow deflecting members (10, 14) changing shape in relation to its temperature and at least one zone with a short heating time provided with heat transfer elements which comprise flow deflecting members (10, 14) having the same shape at different temperatures.

2. A heat exchanger according to claim 1, characterized in that the flow deflecting member (10, 14) changing shape is designed to receive a shape in which it deflects at least a part of the medium flow in the flow passage (5, 6) at a temperature indicating that there is a high heat transfer demand and to receive a shape in which it does not deflects the medium flow in the flow passage (5, 6) at a temperature indicating that there is a low heat transfer demand.

3. A heat exchanger according to claim 1, characterized in that the flow deflecting member (10, 14) changing shape is configured to penetrate into an adjacent flow channel (6a, 5a) when it is in a deflection position.

4. A heat exchanger according to any one of the preceding claims, characterized in that the flow deflecting member (10, 14) changing shape is configured to expose an opening (12, 15) between two adjacent flow channels (5a, 6a) when it is in a deflection position.

5. A heat exchanger according to any one of the preceding claims, characterized in that the flow deflecting member (10, 14) changing shape comprises a partly cut out portion (7d, 13d) in the heat transfer element (7, 13) and a metal material (9, 16) to be fixedly connected to a surface of the cut out portion (7d, 13d).

6. A heat exchanger according to claim 5, characterized in that the metal material (9, 16) is a metal strip fixedly connected to the cut out portion (7d, 13d).

7. A heat exchanger according to claim 5, characterized in that metal material (9, 16) is a metal layer applied to a surface of the cut out portion (7d, 13d).

8. A heat exchanger according to any one of the preceding claims 5-7, characterized in that the metal material (9, 16) and the heat transfer element (7, 13) comprise different metals with different coefficient of thermal expansion.

9. A heat exchanger according to any one of the preceding claims 5-7, characterized in that the metal material (9, 16) is a shape-memory alloy with two-way memory effect.

10. A heat exchanger according to any one of the preceding claims 5-9, characterized in that the partly cut out portion (7d, 13 d) comprises a fixed end (7e, 13e) fixedly connected to the heat transfer element (7, 13), a free end (7f, 13f) and two sides (7g, 7h) connecting the fixed end (7e, 13e) and the free end (7f, 13f).

11. 1 1. A heat exchanger according to claim 10, characterized in that the free end (7f, 13f) of the cut out portion (7d, 13 d) is located in a downstream position of the fixed end (7e, 13e) with reference to the intended flow direction through the flow passage (5, 6).

12. A heat exchanger according to claim 10, characterized in that the free end (7f, 13f) of the cut out portion (7d, 13 d) is located in an upstream position of the fixed end (7e, 13e) with reference to the intended flow direction through the flow passage (5, 6).

13. A heat exchanger according to any one of the preceding claims, characterized in that the heat transfer elements (7, 13) comprise first end sections (7a, 13a) to be fixedly connected to a surface (4a, 4b) defining one side of the flow passage (5, 6), second end sections (7b, 13b) to be fixedly connected to a surface (4a, b) defining on an opposite side of the flow passage (5, 6) and intermittent sections (7c, 13 c) having an extension cross the flow passage (5, 6) between said end sections (7a, 7b, 13a, 13b).

14. A heat exchanger according to any one of the preceding claims, characterized in that heat transfer elements (7, 13 ) are provided with flow deflecting members (10, 14) arranged in different downstream positions in the flow passage (5, 6).