Heat Exchanger

Abstract

The invention relates to a heat exchanger for transferring heat between two media, having a casing tube which has an inlet and an outlet for a medium to be cooled, having an inner tube which is arranged within the casing tube and is closed off at the side facing toward the inlet, is connected at the side facing toward the outlet to a coolant inlet, and has a coolant outlet which leads to that side of the inner tube which faces toward the outlet, and merges into a spiral line which winds from there in the direction of the inlet around the inner tube, which spiral line finally opens out into a coolant outflow.

Description

The invention relates to a heat exchanger for transferring heat between two separate media.

Heat exchangers are often used in technology in order to provide a transfer of heat between two media. Media which are to be treated are either warmed or cooled using heat exchangers in this way.

One field of use for heat exchangers is cooling hot gases. For example, in the field of internal combustion engines, exhaust gases at temperatures of 1000° C. and more are discharged from the combustion chambers. In some cases, it is desirable to cool said hot gases to temperatures of 50° C. and less. Heat exchangers are typically used here. In certain situations in which space is restricted or else in which it is necessary for other reasons to provide the exchange of heat over as short a path as possible, heat exchangers of smaller or shorter design are desirable.

No heat exchangers are known from the prior art which are particularly suitable for generating a high temperature gradient over an extremely short distance (for example cooling hot gases from an inlet temperature of 1000° C. and more to an outlet temperature of below 80° C., preferably below 50° C., over an installation length of approximately 30 cm).

It is therefore an object of the invention to specify a heat exchanger which, with a compact design, makes it possible to obtain a high heat transfer efficiency.

Said object is achieved with a heat exchanger having the features of claim 1. Further advantageous design embodiments of the heat exchanger are specified in claims 2 to 7. Claim 8 specifies a preferred use of the heat exchanger according to the invention, which however does not constitute the only possible use.

The heat exchanger according to the invention is characterized by an inner tube which is situated within a casing tube and which is closed off at one side. The closed-off end of the inner tube is situated at the inlet side of the casing tube, into which flow for example hot gases or other hot media to be cooled. A coolant is initially guided into the inner tube and cools the medium to be cooled, which is flowing past, both on the closed-off end side and on the tube wall. From the inner tube, the cooling medium then passes into a spiral line which is wound around the inner tube, and also leads there to a further cooling action before leaving the heat exchanger.

This firstly results in a considerably increased contact surface in relation to conventional heat exchangers at which contact takes place, separated by means of the walls of the inner tube or of the spiral line, between the cooling medium and the medium to be cooled. In addition, this design embodiment, in which the medium to be cooled initially flows against the single-sidedly closed-off end of the inner tube and then flows laterally past the inner tube along the wound spiral lines, causes turbulence of the medium to be cooled, with said medium also partially running counter to the actual main flow in vortices. This results in a particularly long residence time or a long migration path of the medium to be cooled in the heat exchanger, such that, over a short installation extent of the heat exchanger, intimate contact is generated between the medium to be cooled and the elements, the inner tube and the spiral line, which are to be traversed by the medium. This fact finally has the result that considerable cooling can be obtained over a short longitudinal extent of the heat exchanger.

The heat exchanger according to the invention is of course however also conversely suitable for heating a cool medium, which flows into the casing tube, by means of a heating medium flowing into the “coolant” inflow. In this respect, the terms “coolant inlet”, “coolant outlet” and “coolant outflow” are not to be interpreted to be restricted to a coolant, but can likewise be used for a medium which is used for heating a medium flowing through the casing tube, consequently a “heating medium”.

An outlet tube which, according to claim 2, is to be provided in the interior of the inner tube has the advantage that the coolant flowing into the inner tube must be distributed in the entire inner tube before it can pass into the spiral line through the outlet tube. The cooling action obtained at the wall of the inner tube is intensified in this way, which leads to an overall better cooling capacity or heat transfer capacity of the heat exchanger. Similar considerations of course apply to operation of the heat exchanger for heating a medium.

The formation of the closed-off side of the inner tube as an impact plate leads to a first generation of turbulence of the inflowing medium taking place already at said geometry, which turbulence contributes overall to the long residence time of the inflowing medium in the heat exchanger and to the thereby obtained high heat exchanger efficiency of the heat exchanger.

The refinement as per claim 4, that the spiral line is guided at least along the entire length of the inner tube so as to surround the latter, likewise contributes to a high heat exchanger efficiency. The individual windings of the spiral line are preferably wound tightly but without coming into contact. A spacing must remain between the individual windings of the spiral line in order that there can also be contact there between the medium to be cooled or to be heated and the surface of the spiral line which is traversed by the coolant or heating medium.

A design as specified in claim 5, wherein the spiral line is arranged with a radial spacing to the wall of the inner tube and to the wall of the casing tube, assists the desired turbulence of the medium flowing through the casing tube, and the associated increased heat transfer efficiency. It has been proven here that a radial spacing of the spiral line to the wall of the inner tube which is approximately identical to the radial spacing of the spiral line to the wall of the casing tube provides particularly good results (claim 6).

According to claim 7, it is finally advantageous if at least the spiral line of the heat exchanger is composed of a material with good heat conducting properties. Here, copper is preferably used, though other materials with good heat conducting properties are also conceivable, such as for example silver.

The heat exchanger according to the invention is preferably used to cool combustion exhaust gases from internal combustion engines, in particular combustion exhaust gases from motor vehicle engines. Specifically in motor vehicle engines or in the exhaust system of motor vehicle engines, a heat exchanger of said type must on the one hand provide a high cooling capacity in order to cool the hot exhaust gases, which exit the combustion chamber at approximately 1000° C. and more, to a temperature of 80° C. and less, preferably below 50° C. The heat exchanger must however also be of compact design since the space in the exhaust system of the motor vehicle is restricted. The heat exchanger according to the invention is particularly suitable here.

Further advantages and features of the heat exchanger according to the invention can be gathered from the following description on the basis of the appended FIGURE, in which:

FIG. 1 schematically shows a cross section through a heat exchanger according to the invention.

The FIGURE schematically illustrates a heat exchanger 12 according to the invention in cross section. The heat exchanger 12 according to the invention has a casing tube 8 which opens out via radial narrowed portions into an inlet 1 (illustrated at the top in the drawing) and an outlet 2 (illustrated at the bottom in the drawing). This exemplary embodiment of the heat exchanger 12 is preferably designed for cooling hot gases. The heat exchanger according to the invention can however be used in all possible variants, for example also for cooling liquids, for heating gases or liquids or other heat transfers.

Arranged in the interior of the casing tube 8 and concentrically with respect thereto is an inner tube 3 which is closed off at its end side (illustrated at the top in the drawing) facing toward the inlet 1. The closed-off end side of the inner tube 3 forms an impact plate 11 for a medium, in particular gas, flowing into the heat exchanger 12 via the inlet 1. On that side of the inner tube 3 which faces toward the outlet 2, said inner tube 3 has a coolant inlet 5 which extends through the casing tube 8 and is connected to a coolant inflow 9. Situated in the interior of the inner tube 3 is an outlet tube 6 which extends up to just in front of the impact plate 11 and has an opening there. Said opening is situated approximately centrally on the central axis of the inner tube 3. The outlet tube 6 leads out of the inner tube 3 and merges into a spiral line 7 which is guided, with narrow windings but while maintaining a spacing between the windings, at least along the entire length of the inner tube 3 so as to surround the latter. At the end of the spiral line, the latter merges into a coolant outflow 10 which extends through the casing tube 8.

In a preferred mode of operation for cooling hot exhaust gases of internal combustion engines, the hot exhaust gases pass via the inlet 1 into the casing tube 8. There, said exhaust gases impinge on the impact plate 11, with the flow being separated and first turbulence being generated. This is illustrated schematically in the FIGURE by means of corresponding arrows. A first direct contact with the cooling medium flowing in the inner tube 3 takes place there at the impact plate 11, such that an initial cooling action is already brought about. After the inflowing hot medium, preferably the gas, is deflected by the impact plate 11, said medium passes into the annular space formed between the casing tube 8 and the inner tube 3. Situated in said annular space is the spiral line which, in this exemplary embodiment, is arranged in the radial direction approximately centrally between the wall of the inner tube 3 and the wall of the outer tube 8. As a result of the flow resistance formed by the spiral line 7 on the one hand and also as a result of the convection occurring between the comparatively cold wall of the inner tube 3, on account of the fresh inflowing coolant, and the warmer walls of the spiral line 7 which has already been traversed by heated coolant, the medium, preferably the gas, flowing into the casing tube 8 is forced to become turbulent. This is indicated in the FIGURE at the top right at the upper two windings of the spiral line 7 by corresponding arrows. As a result of said turbulence, the inflowing medium, preferably gas, runs over a considerably longer path within the casing tube 8 and comes into intensive contact with the surfaces of the elements, inner tube 3 and spiral line 7, which are traversed by the cooling medium. After passing through the entire length of the casing tube 8 or of the spiral line 7, and after undergoing intense turbulence in doing so, the cooled medium, preferably gas, passes out through the outlet 2.

The flow of the coolant from the coolant inflow 9 through the inner tube 3 and the spiral line 7 to the coolant outflow 10 is likewise indicated by arrows.

In the exemplary embodiment shown for a heat exchanger according to the invention, the inner tube 3 has a diameter d of 60 mm, the diameter of the spiral line d_s, measured from outer wall to outer wall, is 110 mm, the diameter D of the casing tube is 150 mm, the length L of the casing tube is 200 to 300 mm, and the diameter of the inlet 1 and of the outlet 2 (not denoted in the figures) is approximately 50 to 60 mm. A copper line with a circular cross section and a diameter of 15 mm is used as the spiral line 7.

This heat exchanger is used to cool exhaust gases, which exit an internal combustion engine at approximately 1000° C., to temperatures of approximately 50° C. For this purpose, n-butane at room temperature (approximately 25° C.) is fed into the coolant inlet; the n-butane then left the coolant outlet at a temperature of approximately 120° C. A 30 bar pump was used to feed the coolant n-butane. Instead of n-butane, water or another liquid or liquid mixture can alternatively also be used as coolant.

On account of its dimensions, the heat exchanger according to the invention could be integrated into the exhaust system of a motor vehicle, for example as a replacement for a catalytic converter or silencer.

A positive effect of the drastic cooling of the exhaust gases was found to be that pollutants contained in the exhaust gas, which must otherwise be extracted from the exhaust gas flow by means of complex catalytic converter technology, were precipitated in the heat exchanger. This can be explained in that water is formed as a result of the fast cooling of the exhaust gases from the temperatures at which they exit the internal combustion engine to the dew point of water. Said water almost completely elutriates the further harmful constituents contained in the exhaust gas flow. As a result of the water generated during the cooling of the exhaust gases to the dew point of water, an additional cooling effect is generated, since water can also dissipate a proportion of heat.

In addition, since all gases expand by 1/126 when heated by 1° C. and contract in the event of a reduction in temperature, the gas will assume a smaller volume in the case of a temperature difference of several hundred degrees Celsius. This has the result that the use of the heat exchanger according to the invention for cooling the exhaust gases generated in an internal combustion engine of a motor vehicle the noise emissions can be almost completely dissipated and conventional silencers can be dispensed with with the exception of a final silencer.

The heat exchanger according to the invention is not restricted to the use described in this exemplary embodiment, but can be used for cooling or heating various media. It is for example conceivable to use a corresponding heat exchanger, which is of larger dimensions but similar proportions, for cooling exhaust gases from power plants or industrial plants, with it also being possible here for a purification effect to be obtained as a result of the abrupt cooling of the gases.

The heat exchanger can however also be used only for heat transfer without a purification effect.

In this respect, with regard to the importance and scope of the invention, reference is made to the following claims, which alone restrict the scope of the invention.

List of Reference Symbols

• 1 Inlet
• 2 Outlet
• 3 Inner tube
• 4 Lower tube end
• 5 Coolant inlet
• 6 Outlet tube
• 7 Spiral line
• 8 Casing tube
• 9 Coolant inflow
• 10 Coolant outflow
• 11 Impact plate
• 12 Heat exchanger
• D Diameter
• d Diameter
• d_s Diameter
• L Length

Claims

1. A heat exchanger for transferring heat between two media, comprising a casing tube which has an inlet and an outlet for a medium to be cooled, having an inner tube which is arranged within the casing tube and is closed off at a side facing toward the inlet, is connected at the side facing toward the outlet to a coolant inlet, and has a coolant outlet which leads to a side of the inner tube which faces toward the outlet, and merges into a spiral line which winds from there in the direction of the inlet around the inner tube, which spiral line out into a coolant outflow.

2. The heat exchanger as claimed in claim 1, wherein the coolant outlet of the inner tube is connected to an outlet tube which is guided in the interior of the inner tube up to a side of the inner tube which faces toward the inlet.

3. The heat exchanger as claimed in claim 1, wherein the closed-off side of the inner tube forms an impact plate for medium to be cooled which medium is capable of flowing into the casing tube via the inlet.

4. The heat exchanger as claimed in claim 1, wherein the spiral line is guided at least along the entire length of the inner tube so as to surround the inner tube.

5. The heat exchanger as claimed in claim 1, wherein the spiral line is arranged with a radial spacing to a wall of the inner tube and to a wall of the casing tube.

6. The heat exchanger as claimed in claim 5, wherein the radial spacing of the spiral line to the wall of the inner tube is approximately identical to the radial spacing of the spiral line to the wall of the casing tube.

7. The heat exchanger as claimed in claim 1, wherein at least the spiral line is composed of copper.

8. A method for cooling combustion exhaust gases from an internal combustion engine which comprises providing the heat exchanger of claim 1 and directing combustion exhaust gases from an internal combustion engine through the inlet.

9. The heat exchanger as claimed in claim 2, wherein the closed-off side of the inner tube forms an impact plate for medium to be cooled which medium is capable of flowing into the casing tube via the inlet.

10. The heat exchanger as claimed in claim 2 wherein the spiral line is guided at least along the entire length of the inner tube so as to surround the inner tube.

11. The heat exchanger as claimed in claim 3 wherein the spiral line is guided at least along the entire length of the inner tube so as to surround the inner tube.

12. The heat exchanger as claimed in claim 9 wherein the spiral line is guided at least along the entire length of the inner tube so as to surround the inner tube.

13. The heat exchanger as claimed in claim 2, wherein the spiral line is arranged with a radial spacing to a wall of the inner tube and to a wall of the casing tube.

14. The heat exchanger as claimed in claim 3, wherein the spiral line is arranged with a radial spacing to a wall of the inner tube and to a wall of the casing tube.

15. The heat exchanger as claimed in claim 9, wherein the spiral line is arranged with a radial spacing to a wall of the inner tube and to a wall of the casing tube.

16. The heat exchanger as claimed in claim 10, wherein the spiral line is arranged with a radial spacing to a wall of the inner tube and to a wall of the casing tube.

17. The heat exchanger as claimed in claim 11, wherein the spiral line is arranged with a radial spacing to a wall of the inner tube and to a wall of the casing tube.

18. The heat exchanger as claimed in claim 12, wherein the spiral line is arranged with a radial spacing to a wall of the inner tube and to a wall of the casing tube.

19. The heat exchanger as claimed in claim 13, wherein the radial spacing of the spiral line to the wall of the inner tube is approximately identical to the radial spacing of the spiral line to the wall of the casing tube.

20. The heat exchanger as claimed in claim 14, wherein the radial spacing of the spiral line to the wall of the inner tube is approximately identical to the radial spacing of the spiral line to the wall of the casing tube.