US20090038562A1

US20090038562A1 - Cooling system for a vehicle

Info

Publication number: US20090038562A1
Application number: US12/190,168
Authority: US
Inventors: Ho Chang Sim; Sun An Jeong; Gil Woong Jun; Byoung Sun Cho; Sang Yul Lee; Kwang Yong Jung
Original assignee: Halla Climate Control Corp
Current assignee: Hanon Systems Corp
Priority date: 2006-12-18
Filing date: 2008-08-12
Publication date: 2009-02-12

Abstract

Disclosed is a cooling system for a vehicle, in which coolant coolant, a blend of an antifreezing solution and water flowed into a radiator generates turbulent flow when a vehicle is in a state of a critical driving mode of a vehicle for example, a hill-climbing mode, thereby enhancing heat radiating performance and reducing pressure drop amount at the same time.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 11/640,605, filed on Dec. 18, 2006.

TECHNICAL FIELD

The present invention relates to a cooling system for a vehicle, in which a coolant, a blend of an antifreezing solution and water flowed into a radiator generates turbulent flow when a vehicle is in a state of a critical driving mode of a vehicle for example, a hill-climbing mode.

BACKGROUND ART

In U.S. Pat. No. 4,332,293 there is suggested a numerical range in that the length of a fin in a direction of air flow should be 12 to 23 mm, the pitch of the fin should be 1.5 to 3.3 mm, and the pitch of a tube should be 8.5 to 14 mm as elements of a radiator mounted within a range of a limited core mounting space so as to overcome air resistance generated as the length of the fin is lengthened in the direction of air flow in the radiator with a tube arrangement of 2 or 3 rows and reduction of heat transfer performance according thereto.
However, the conventional radiator is focused on heat radiation performance of an outer side of the tube through which air passes. Further, in order to prevent a coolant-side pressure drop, the caliber of the tube is set not to be small, and the height of the fin is simultaneously set to be relatively high considering an air-side pressure drop amount.
In such conventional radiators, coolant-side pressure drop amount is not simultaneously considered together with air-side heat radiation performance. Particularly, there are some limitations in suggesting a preferred deign object of exchanger tubes in a critical operation condition such as alpine regions with many inclines or cold or arctic regions.
This requires more thorough observation on flow of a coolant in a radiator tube and the heat transfer characteristic to the inside thereof, and more researches and experiments on radiators with more effective heat radiating performance.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a cooling system for a vehicle, i.e., a highly efficient thin radiator for reducing production costs by decreasing the weight of a heat exchanger, reducing energy loss due to a pressure drop of a coolant-side in a case of being mounted in a real vehicle, and enhancing heat radiation performance.
It is another object of the present invention to provide an optimal design condition for enhancing heat radiation performance of a radiator in a coolant flow rate region corresponding to a hill-climbing mode that is a critical driving mode of a vehicle and reducing a coolant-side pressure drop amount.
It is a further object of the present invention to provide a preferred a design condition of a lightweight thin radiator, wherein heat radiation performance of a conventional radiator with a broad width and a heavy weight can be maintained, and a coolant-side pressure drop amount almost identical with that of the conventional radiator can also be maintained when comparing the heat radiation performance and coolant-side pressure drop amount of the conventional radiator.
It is a still further object of the present invention to provide a preferred design range of each main component of the radiator, which can meet the optimal design range.
To achieve these objects of the present invention, there is provided a cooling system for a vehicle, in which a coolant, a blend of an antifreezing solution and water which passed through an engine by a pump flows through a pair of tanks 240, 250 and a radiator 200 including a header 290 at one side coupled with the tank 240 at one side to which the coolant is supplied, heat exchange tubes 280 which is structurally fastened to and communicated with the header 290 at one end portion thereof, a header 290 at the other side coupled with the tank 250 at the other side which is structurally fastened to and communicated with the other end portion of the heat exchange tubes 280 to discharge the mixed solution to the engine, and fins fixedly brazed between the heat exchange tubes 280, wherein the cooling system includes a thermostat 300 for adjusting opening/shutting depending on the temperature of the coolant which passed through the engine to prevent overheating of the engine 100 and cause the coolant to be flowed into the radiator 200 in a flow rate of 60 to 80 L/min when the engine 100 is operated in a high rpm and in less flow rate when the engine 100 is not operated in the high rpm, the radiator 200 has a core 260 width (Td) of 12 to 15 mm, a distance between outmost tubes 280 of 300 to 600 mm, a tube outer width (Th) of 1.7 to 1.9 mm, and a tube material thickness (Tth) of 0.15 to 0.24 mm, and the tube 280 is made of aluminum material, and the mixed ratio of the antifreezing solution and water in the coolant is 1:1, and the flow of the coolant is a completely developed turbulent flow region having a Reynolds number of 2,100 or more when the flow rate is 60 to 80 L/min and a transition from laminar flow to turbulent flow at a flow rate of 40 L/min or less.
Preferably, when the flow rate of the coolant is in the range of 60 to 80 L/min and the temperature thereof is 100° C., the pressure drop amount of the coolant at an exit side of the heat exchanger is 150 mmHg.
Preferably, Fh the height of the fin is in the range of 5.3 to 5.8 mm, and the thickness of the fin is in the range of 0.05 to 0.06 mm for the purpose of reducing a weight and maximizing a heat transfer rate.
Preferably, the heat exchange tube is a flat type with no dimple in an interior thereof, and the heat exchanger is a cross flow type.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view showing a cooling system of a vehicle according to the present invention;

FIGS. 2( a) and 2(b) are a perspective view and an exploded perspective view, respectively, of a down flow type radiator that is a general heat exchanger, respectively;

FIGS. 3( a) and 3(b) are a perspective view and an exploded perspective view, respectively, of a cross flow type radiator that is a general heat exchanger, respectively;

FIG. 4 is a graph illustrating characteristics of heat radiation and pressure drop of radiators according to the present invention and prior arts;

FIG. 5 is an enlarged perspective view showing a coupling feature of a tube and a fin in the radiator;

FIG. 6 is a graph illustrating a change in heat transfer rate and pressure drop of the radiator depending on the height of the fin in the present invention;

FIG. 7 is a graph illustrating a change in heat transfer rate pressure drop of the radiator depending on the outer width of the tube in the present invention; and

FIG. 8 is a graph illustrating a change in heat transfer rate and pressure drop of the radiator depending on the material thickness of the tube in the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As shown in FIG. 1, a cooling system for a vehicle according to the present invention includes an engine 100 in which coolant is flowed along a passage formed in outer wall of a cylinder block, a heater core 400 through which high temperature coolant discharged from the engine 100 is flowed, a radiator 200, a thermostat 300 which controls flow direction of the coolant discharged from the engine 100 and a water pump 500 which receives power from a crank shaft (not shown) of the engine 100 to forcedly circulate the coolant.
In the cooling system for a vehicle, by an action of the water pump 500 operably connected to the crank shaft (not shown), the coolant heated at the engine 100 is cooled by exchanging heat with external air during it passes through the heater core 400 and the radiator 200 and then is flowed again into the engine 100 to perform the heat exchange with the high temperature engine 100.
Since the engine can maintain an appropriate temperature by the cooling system for a vehicle, the engine 100 is prevented from being damaged by high temperature combustion heat.
During the process in that the coolant is circulated through the engine 100, before the engine is heated to the appropriate temperature, i.e. when the temperature of the coolant is a predetermined temperature, the heater core 400 and the radiator 200, the coolant is circulated to the engine 100 via the heater core 400 through an inlet 410 and outlet 420 of the heater core 400 by the thermostat 300 for quick preheating of the engine 100. When the temperature of the engine 100 is more than the appropriate temperature, i.e. when cooling is required, the coolant is flowed into the radiator 200 through an inlet 210 of the radiator 200 by the thermostat 300 and the high temperature coolant flowed into the radiator 200 is cooled by heat exchange with the external air and then circulated to the engine 100 through an outlet 220 of the radiator 200.
The thermostat 300 performs a function which causes the coolant discharged from the engine to be flowed to the heater core 400 when the temperature of the coolant is less than 90° C. but to be flowed to the radiator 200 for heat exchange with the external air when the temperature of the coolant is more than 90° C. Further, the thermostat 300 largely increases the amount of the coolant flowed into the radiator 200 when the engine is in a state of a general critical driving in which the engine is rotated in high rpm, e.g. a hill-climbing mode, but decreases the amount of the coolant when the engine is in a normal driving mode.
Particularly, the thermostat 300 causes the coolant to be flowed into the radiator 200 in a flow rate of about 60 to 80 L/min when the engine is in the hill-climbing mode, and in less flow rate, conventionally a flow rate of about 40 L/min and when the engine is in a normal driving mode.
Practical and presently preferred embodiments of the present invention are illustrative as shown in the following Examples and Comparative Examples.
However, it will be appreciated that those skilled in the art, on consideration of this disclosure, may make modifications and improvements within the spirit and scope of the present invention.
In a case of a radiator, although a heat transfer rate by air-side heat conduction occupies the largest portion of the heat transfer rate by heat transfer, variation of a heat radiation characteristic in accordance with structure modification of a component of the radiator is not so large. On the other hand, although a heat transfer rate by heat conduction in a heat exchange tube, which is a high temperature side, is low at a rate occupying in the entire heat transfer rate, a change in heat radiation characteristic in accordance with structure modification of a component of the radiator is sensitive, and its variation is also relatively large. Accordingly, elements of the radiator and heat radiation performance in accordance therewith can be determined.
Particularly, since a plurality of tubes constituting a radiator are generally formed as a duct with a flat shape, the flow of a coolant flowing into the tube can be classified into a duct flow which is not opened. Although such a flow into a duct is greatly influenced by a cause such as illumination intensity of a wall surface of the duct or a flow change in an entry flow, a main cause is a Reynolds number. In a circular duct, if a Reynolds number reach about 2,300, a flow generally starts forming a “mass” or “puff” and approaching a region of a turbulent flow. Through experiments by the inventors, it has been found that a flow transits from a laminar flow to a turbulent flow near a Reynolds number of about 2,100 in a case of a duct with a flat section, of which width at one side is relatively very wide like a heat exchange tube employed in a radiator according to the present invention. Further, if the flow in the duct exceeds a Reynolds number of 2,100 through a flow condition to be a completely developed turbulent flow, the momentum of the flow and the transfer of energy are accelerated. Particularly, a conduction heat transfer coefficient is largely increased, and thus heat radiation performance of a heat exchanger is enhanced.
Meanwhile, in a case of a flow in a tube of which path is relatively long like a heat exchanger, since loss of pressure caused by the path of the flow result in the increase of power consumption in a water pump, the fuel efficiency of a vehicle is lowered. Thus, a condition of pressure loss should be considered as well as a condition of a turbulent flow in a tube. The aforementioned pressure loss may be divided into an influence by elements of a heat exchanger and a tube and an influence by a property of a flow. However, in a case of a straight tube with a fixed cross-sectional area like a cross flow type radiator of the present invention, since a surface shear stress is increased on a wall surface of a tube if the flow of a coolant in the tube becomes a turbulent flow, the surface shear stress influences a change in pressure loss rather than the influence by elements of the heat exchanger and tube. Therefore, a configuration such as a dimple may be added on a surface of a heat exchange tube to accelerate the turbulent flow of a coolant flow. In this case, since coolant-side resistance becomes large due to the existence of the dimple, the advantage by the turbulent flow may be offset. As a result, there may be no advantage in a thin radiator in which the width of a core has a range of 12 to 15 mm.
Accordingly, in a design of a heat exchanger for enhancing efficiency of an air conditioning system, it is required to consider not only a heat radiation characteristic of the heat exchanger itself but also loss of a power source due to the increase of power consumption in a water pump by coolant-side resistance and the lowering of fuel efficiency of a vehicle.
In the present invention, a turbulent flow condition of the flow of a coolant flowing into a heat exchange tube and the influence of pressure loss are simultaneously considered to enhance such a heat radiation characteristic of a heat exchanger itself, so that there can be provided design elements of the heat exchanger for a more effective cooling system.
Further, a radiator 200 of the present invention can be applied to both a down flow type in which heat exchange tubes 280 are arranged in a vertical direction as shown in (a) and (b) of FIG. 2 and a cross flow type in which heat exchange tubes 280 arranged in a horizontal direction as shown in (a) and (b) of FIG. 3. Particularly, the radiator 200 of the present invention can perform superior performance in a cross flow type heat exchanger in which a flow speed in the tube is relatively fast.
Hereinafter, a radiator of the present invention will be described in detail.
FIG. 4 is a graph illustrating characteristics of heat radiation and pressure drop of radiators according to the present invention and prior arts. Prior arts A and B show heat radiation characteristics and pressure drop characteristics for two kinds of existing radiators, respectively. In the testing condition of a radiator in FIG. 4, the composition of an antifreezing solution and water is 1:1 in a coolant flowing into a core portion, the temperature of the coolant is 100° C., the temperature of inflow air is 40° C., and the front area of the same core 260 is 636×485. Further, the radiator according to the present invention is set such that Td the width of a core 260 is in the range of 12 to 15 mm and the height thereof is in the range of 300 to 600 mm. As such, the reason why Td the width of the core 260 is limited as within the range of 12 to 15 mm is that the component package of the radiator 200 can be minimized and air-side pressure drop can be lowered. Further, the thickness of a fin 230 is set to be in the range of 0.05 to 0.06 mm so that the increase of the entire weight of the radiator 200 can be prevented and the heat transfer rate can be maximized.
The radiator 200 according to the present invention has an advantage in that a driving region with a coolant flow rate from 60 to 80 L/min is set as a major interval in critical and real driving conditions including a hill-climbing mode so that heat radiation performance in a region including the driving region can be enhanced and a pressure drop amount can be reduced.
First, it can be seen that the pressure drop characteristic is satisfactory, but a transition starts from a point at which an inflection point of the graph exists near a coolant flow rate of 60 L/min in a case of the existing radiator A. That is, it can be seen that, since a transition occurs from a laminar flow to a turbulent flow in a region of a coolant flow rate from 60 to 80 L/min that is an interesting region of the present invention, a turbulent flow region which is not completely developed is formed. Thus, since such a transition region is formed near a coolant flow rate of 60 L/min, heat radiation performance of the existing radiator A is lowered as compared with the present invention. As such, the reason why the heat radiation characteristic of the existing radiator A is lowered under the aforementioned condition is that although the width of a tube 280 is lager as compared to the present invention such that a much amount of the coolant flows, but causing delay in transition of a turbulent flow. That is, since a much amount of the coolant flows, a heat transfer rate is identical with or larger than the present invention in an interval except 60 to 80 L/min, but the heat transfer rate is lowered as compared with the present invention due to the existence of the transition region in the range of 60 to 80 L/min. The present invention can maintain a width narrower than conventional radiators, and perform relatively superior performance to conventional thick radiators in a range of 60 to 80 L/min which is a critical driving region.
Meanwhile, it can be seen that, since a transition occurs before a region of a coolant flow rate of 60 L/min and a completely developed turbulent flow region is formed in a region of a coolant flow rate from 60 to 80 L/min in a case of another existing radiator B, the absolute value is decreased but a relative heat radiation characteristic is generally satisfactory. However, in a pressure drop characteristic, it can be seen that the existing radiator B has relatively much high pressure loss in the entire flow rate region as compared with any other radiators. Further, the reason why the heat radiation characteristic is relatively satisfactory and the pressure drop amount is relatively high in the existing radiator B is that an influence of coolant-side pressure drop on fuel consumption of a vehicle may not considered when mounting the radiator in a real vehicle. However, the main reason is that, since an inner flow channel of a tube is set to be smaller than the radiator of the present invention, the pressure drop excessively occurs.
On the contrary, a completely developed turbulent flow region is formed in a region of a coolant flow rate from 60 to 80 L/min, and a pressure drop characteristic also has a satisfactory distribution in a case of the radiator according to the present invention. Particularly, it is important that the radiator of the present invention is designed such that a transition occurs in a region of a coolant flow rate of 40 L/min or less. Accordingly, the radiator of the present invention is configured such that a completely developed turbulent flow region is formed in a region of a coolant flow rate from 60 to 80 L/min, which is an important region for a critical driving condition, and the pressure drop amount in the aforementioned region maintains 150 mmHg or less.
FIG. 5 is an enlarged perspective view showing a coupling feature of a tube 280 and a fin 230 in the radiator. b is the inner width of the tube 280, and Td is the outer height of the tube 280, which corresponds to the width of a core portion.
FIG. 6 is a graph illustrating a change in heat transfer rate pressure drop of the radiator depending on height Fh of the fin 230 with respect to a case where height Th is respectively 1.60 mm, 1.80 mm and 2.10 mm in the present invention. Here, Q is heat transfer rate of the radiator, i.e., Q₀is a minimum required heat transfer rate of the radiator for cooling the engine. That is, in FIG. 6, the left vertical axis is Q/Q₀value showing a minimum required heat transfer rate, and the right vertical axis shows a coolant-side pressure drop amount. At this time, the solid line of the graph indicates a heat transfer rate ratio, and the dotted line indicates a coolant-side pressure drop amount. Fh Height of the fin in the present invention can be set to have a preferred range from the graph of FIG. 6.
In the previously suggested testing condition, since a coolant flow may move to a laminar or transition region in a case where Fh the height of the fin is out of a range of 5.3 to 5.8 mm when driving a vehicle in a hill-climbing mode, it is difficult to obtain an appropriate heat transfer rate with which an optimal driving condition can be met. Further, in a case where the thickness of the fin is set to be too thin, the fin can be buckled.
Further, there is a caused problem in that the number of stacked fins and tubes becomes excessively large at below 5.3 mm so that the weight of the radiator is largely increased and fins and tubes work as a resistance to the flow of air, and what is worse a foreign substance is excessively stacked due to a high density of the fin in an traveling condition of a real vehicle so that air passing through the radiator is not smoothly flowed. Thus, Fh height of the fin is set to be 5.3 mm≦Fh≦5.8 mm as a preferred region within a range where the heat transfer rate is maintained as a sufficiently high value and the pressure loss in the tube is not rapidly increased with reference to the required condition and the characteristic of FIG. 6.
FIG. 7 is a graph illustrating a change in heat transfer rate pressure loss of the radiator depending on Th height of the tube when Fh height of the fin is respectively 5.3 mm, 5.5 mm and 5.8 mm in the present invention. Th Height of the tube of the radiator of the present invention can be set to have a preferred range from the graph of FIG. 7. That is, there is a problem in that, in a case where Th height of the tube exceeds 2.10 mm, a coolant flowing in the tube is difficult to become turbulent flow so that the heat transfer rate is dropped below the minimum required heat transfer rate, and an additional process of forming a means for accelerating a turbulent flow, such as a dimple in the tube, should be added to satisfy a required heat transfer rate.
On the contrary, in a case where Th height of the tube is below 1.60 mm, the coolant-side pressure drop amount in the tube is rapidly increased so that excessive power is required to circulate the coolant. Thus, Th the height of the tube is set to be preferably 1.60 mm≦Th≦2.10 mm, and more preferably 1.70 mm≦Th≦1.90 mm, as a range where the heat transfer rate is maintained as a sufficiently high value and the pressure loss in the tube is not rapidly increased with reference to the required condition and the characteristic of FIG. 7.
FIG. 8 is a graph illustrating a change in heat transfer rate and pressure drop of the radiator depending on Tth thickness of the tube in the present invention. Tth The thickness of the tube in the radiator of the present invention is set to have a preferred range from the graph of FIG. 8. That is, there is a problem in that, as Th thickness of the tube becomes thick, the weight of the radiator is increased and the coolant-side pressure drop amount is largely increased so that excessive power is required to circulate the coolant. On the other hand, there is problem in that, in a case where Tth thickness of the tube is below 0.15 mm, the material becomes too thin so that the tube may be highly modified when injecting the coolant in a manufacturing process, and the tube may be burst or the stacked fin of the core may be crushed due to a problem of pressure resistance. Thus, Tth thickness of the tube is set to be preferably 0.15 mm≦Tth≦0.24 mm as a range where the heat transfer rate is maintained as a sufficiently high value and the pressure drop in the tube is not rapidly increased with reference to the required condition and the characteristic of FIG. 8.
In the present invention, there is suggested a design condition of preferred tubes and fins, in which requirements of a heat radiation characteristic and a pressure drop amount can be simultaneously met, and the lightweight of radiators can be promoted.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, the radiator of the present invention is a thin radiator for reducing the weight of a heat exchanger, enhancing heat radiation performance and reducing a pressure drop amount, and has advantages such as lightweight of a vehicle, increase of fuel efficiency and setting for a layout of a vehicle.
Particularly, the radiator according to the present invention has an advantage in that heat radiation performance can be enhanced in a driving region of a coolant flow rate from 60 to 80 L/min, which is a critical driving condition of a vehicle including a hill-climbing mode, and a pressure drop amount can be reduced.
Further, the present invention has an advantage in that there is suggested an optimal design range in which the heat radiation characteristic and pressure drop amount of the radiator can be mutually complemented.
Furthermore, there is an advantage in that the thickness of a core is set to be thin in view of a cooling system so that an interval with a cooling fan can be more separated, thereby enhancing air-side efficiency.
Those skilled in the art will appreciate that the conceptions and specific embodiments disclosed in the foregoing description may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present invention. Those skilled in the art will also appreciate that such equivalent embodiments do not depart from the spirit and scope of the invention as set forth in the appended claims.

Claims

1. A cooling system for a vehicle, in which coolant, a blend of an antifreezing solution and water which passed through an engine by a pump flows through a pair of tanks and a radiator including a header at one side coupled with the tank at one side to which the coolant is supplied, heat exchange tubes which is structurally fastened to and communicated with the header at one end portion thereof, a header at the other side coupled with the tank at the other side which is structurally fastened to and communicated with the other end portion of the heat exchange tubes to discharge the coolant to the engine, and fins fixedly brazed between the heat exchange tubes,

wherein the cooling system includes a thermostat for adjusting opening/shutting depending on the temperature of the mixed solution which passed through the engine to prevent overheating of the engine and cause the mixed solution to be flowed into the radiator in a flow rate of 60 to 80 L/min when the engine is operated in a high rpm and in less flow rate when the engine is not operated in the high rpm,

the radiator has a core width of 12 to 15 mm, a distance between outmost tubes of 300 to 600 mm, a tube outer width (Th) of 1.7 to 1.9 mm, and a tube material thickness (Tth) of 0.15 to 0.24 mm, and the tube is made of aluminum material, and

the mixed ratio of the antifreezing solution and water in the coolant is 1:1, and the flow of the coolant is a completely developed turbulent flow region having a Reynolds number of 2,100 or more when the flow rate is 60 to 80 L/min and a transition from laminar flow to turbulent flow at a flow rate of 40 L/min or less.

2. The cooling system as set forth in claim 1, wherein, when the flow rate of the coolant is in the range of to 80 L/min and the temperature thereof is 100° C., the flow of the coolant has a Reynolds number of 2,100 or more, a transition from laminar flow to turbulent flow occurs at a flow rate of 40 L/min or less.

3. The cooling system as set forth in claim 1, wherein Fh the height of the fin is in the range of 5.3 to 5.8 mm.

4. The cooling system as set forth in claim 1, wherein the thickness of the fin is in the range of 0.05 to 0.06 mm.

5. The cooling system as set forth in claim 1, wherein the heat exchange tube is a flat type with no dimple in an interior thereof.

6. The cooling system as set forth in claim 1, wherein the radiator is a cross flow type.