Patent Application
20190186431
The invention relates to a tube, in particular a flat tube, for an exhaust gas cooler and an exhaust gas cooler with at least one such tube.
To decrease the emission of harmful substances from internal combustion engines, it is known to recirculate exhaust gas to the fresh air side, wherein, at least under certain operating conditions, the exhaust gas must be cooled. In order to satisfy the continuously stricter requirements with regard to harmful substance emissions, increasingly more efficient exhaust gas coolers are required.
Exhaust gas coolers of prior use are known that comprise numerous flat tubes through which flows the exhaust gas and which include on the inside numerous projections to ensure good heat transfer. However, in particular at the gas inlet, overheating of the coolant that is utilized for cooling the exhaust gas may occur such that air bubble formation may occur in the coolant circulation. Moreover, in the case of such projections it must be noted that they increase the pressure drop and therewith cannot be developed at any desired height or depth, which means they cannot be developed extending far into the tube interior. To overcome said limitations, it is fundamentally conceivable to provide more flat tubes through which the gas must flow which, however, entails the disadvantage of a rise in expenditures and space requirement.
Against this background the invention addresses the problem of specifying a tube for an exhaust gas cooler that represents an improvement with regard to efficiency.
This problem is resolved through the tube described in patent claim 1.
The tube according to the invention, which will be described in the following with reference to the preferred embodiment of a flat tube, comprises conventionally numerous, yet in every case at least two, projections developed on the inside, of which at least one is implemented closer to the gas inlet, in the direction toward the tube axis at a lower level, than at least one projection implemented closer to the gas outlet. Stated differently, the height/depth of the projections or their extent increases in the direction of the interior of the tube and/or in the direction of flow of the gas, such that at the gas inlet overheating of the coolant can be avoided and the heat transfer can be equalized over the course of the tube. This is achieved in particular thereby that the height/depth of the projections increases in the gas flow direction such that a turbulent flow is also maintained in the direction of the gas outlet and consequently the heat transfer and the pressure loss are optimized over the length of the tube. Especially the pressure loss at the gas inlet as well as the heat transfer are decreased since at this site the gas temperature is highest, however, the gas velocity, due to the comparatively flat projections, remains high. The boiling of the coolant in the proximity of the gas inlet can therewith be decreased and an extensive portion of the heat transfer can be shifted in the direction toward the gas outlet. Hereby the efficiency of an exhaust gas cooler equipped with the described tube is overall increased. With regard to the projections, it should be stated that they may be developed flat and advantageously can appear on the outside of the tube in the form of indentations, impressions, dents, pits or dimples. However, critical is the projection in the direction of the tube interior which ensures the described effects. By ‘flat’ projection is understood that the projection has a surface that extends substantially parallel to the tube axis, in other words parallel to the direction of flow.
Preferred further developments of the flat tube according to the invention are described in the further claims.
As stated, it is preferred for the height/depth of the projection in the direction of the tube axis increases continuously, wherein directly adjacent projections, if need be, are developed of the identical height/depth. The described effects can hereby be especially extensively maintained.
In view of the cross section of the flat tube according to the invention it is preferred for the flat tube to comprise at least two parallel side walls in which preferably the projections, or the indentations on the outside of the tube, are developed. In particular, these are preferably provided in both parallel side walls. The “other” walls can be lower and/or rounded.
Further, elongated projections have been found to be especially efficient. Regarding their orientation, it is preferred for them to extend at an angle to the direction of flow. This is especially preferred for high-pressure heat exchangers; however, in particular in low-pressure heat exchangers elongated projections can also extend substantially perpendicularly to the direction of flow.
To maintain turbulent flow, it is in this connection further preferred for the elongated projections of opposing side walls to criss-cross.
Especially good results in view of efficiency are further anticipated if the projections have a height/depth of 1% to 40%, preferably 10% to 30%, of the distance between two (preferably parallel) side walls, in other words of the height of the tube.
Further, a flow cross section for the flat tube according to the invention has been found successful which, apart from the described projections, is implemented uniform over the length of the tube.
Subject matter of the invention is further an exhaust gas cooler, in particular that of an exhaust gas recirculation system, with at least one tube, preferably numerous tubes, described above.
In the following a preferred embodiment example of the invention is described in greater detail with reference to the Figures. In the drawing depict:
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| Number | Date | Country | Kind |
|---|---|---|---|
| 102017222742.7 | Dec 2017 | DE | national |
