Heat exchanger

Abstract

A heat exchanger may include a gas conduit flowable through by a predetermined gas and a heat conduit flowable through by a predetermined fluid compound working fluid. The heat conduit may be in thermal communication with the gas conduit. The heat exchanger may include a first section having a first section length, a second section having a second section length, and a third section having a third section length. The gas conduit may span, in a direction of flow of the gas, the first section, the second section, and the third section. The heat conduit may span, in a direction of flow of the working fluid, the third section, the first section, and the second section. The first section may include a gas inlet and the third section may include a working fluid inlet and a gas outlet. The section may include a working fluid outlet.

Claims

1. A heat exchanger, comprising: a gas conduit flowable through by a predetermined gas, a heat conduit flowable through by a predetermined fluid compound working fluid, the heat conduit in thermal communication with the gas conduit, a first section having a first section length, a second section having a second section length, and a third section having a third section length, wherein the gas conduit spans, in a direction of flow of the gas, the first section, the second section, and the third section, and the heat conduit spans, in a direction of flow of the working fluid, the third section, the first section, and the second section, the first section including a gas inlet for inletting the gas and the third section including a working fluid inlet for inletting the working fluid, the third section including a gas outlet for discharging the gas and the second section including a working fluid outlet for discharging the working fluid, wherein the gas conduit is passable by the gas from the gas inlet to the gas outlet, and the heat conduit is passable by the working fluid from the working fluid inlet to the working fluid outlet, wherein the first section length is selected such that the gas, when entering the gas inlet at a gas entry temperature of up to 700 C., exits the first section at a gas exit temperature no more than 50 K above a decomposition temperature of the working fluid, provided that the working fluid enters the first section in a liquid state of aggregation, and wherein the first section length ranges between 80 mm and 300 mm, and the third section length is greater than the second section length.

2. A heat exchanger, comprising: a gas conduit for conducting a gas, a heat conduit in thermal communication with the gas conduit for conducting a fluid compound working fluid, a first section having a first section length, a second section having a second section length, and a third section having a third section length, wherein the gas conduit spans, in a direction of flow of the gas, the first section, the second section, and the third section, and the heat conduit spans, in a direction of flow of the working fluid, the third section, the first section, and the second section, wherein the first section includes a gas inlet for inletting the gas and the third section includes a working fluid inlet for inletting the working fluid, and the third section includes a gas outlet for discharging the gas and the second section includes a working fluid outlet for discharging the working fluid, wherein the gas conduit is passable by the gas from the gas inlet to the gas outlet, the heat conduit is passable by the working fluid from the working fluid inlet to the working fluid outlet, wherein the first section length is selected such that the gas, when entering the gas inlet at a gas entry temperature of up to 700 C., exits the first section at a gas exit temperature no more than 50 K above a decomposition temperature of the working fluid, and wherein the first section length ranges between 80 mm and 300 mm, and the third section length is greater than the second section length.

3. The heat exchanger as in claim 1, wherein the first section length enables the gas to exit the first section below the decomposition temperature by up to 50 K.

4. The heat exchanger as in claim 1, wherein the second section length ranges between 80 mm and 300 mm and the third section length ranges between 100 mm and 400 mm.

5. The heat exchanger as in claim 1, wherein the first section length, the second section length, and the third section length are selected such that the gas, upon entering the gas inlet, exits through the gas outlet at an exit temperature between 100 C. and 150 C., provided that the working fluid enters through the working fluid inlet at a working fluid entry temperature between 60 C. and 80 C. and an entry pressure between 20 bar and 50 bar.

6. The heat exchanger as in claim 1, wherein the decomposition temperature ranges between 250 C. and 350 C.

7. The heat exchanger as in claim 2, wherein the first section length enables the gas to exit the first section below the decomposition temperature by up to 50 K.

8. The heat exchanger as in claim 2, wherein the second section length ranges between 80 mm and 300 mm, and the third section length ranges between 100 mm and 400 mm.

9. The heat exchanger as in claim 2, wherein the first section length, the second section length, and the third section length are determined such that the gas, upon entering the gas inlet, exits through the gas outlet at an exit temperature between 100 C. and 150 C., provided that the working fluid enters through the working fluid inlet at a working fluid entry temperature between 60 C. and 80 C. and an entry pressure between 20 bar and 50 bar.

10. The heat exchanger as in claim 2, wherein the decomposition temperature ranges between 250 C. and 350 C.

11. The heat exchanger as in claim 3, wherein the second section length ranges between 80 mm and 300 mm, and the third section length ranges between 100 mm and 400 mm.

12. The heat exchanger as in claim 4, wherein the first section length, the second section length, and the third section length are determined such that the gas, upon entering the gas inlet, exits through the gas outlet at an exit temperature between 100 C. and 150 C., provided that the working fluid enters through the working fluid inlet at a working fluid entry temperature between 60 C. and 80 C. and an entry pressure between 20 bar and 50 bar.

13. The heat exchanger as in claim 12, wherein the decomposition temperature ranges between 250 C. and 350 C.

14. The heat exchanger as in claim 5, wherein the decomposition temperature ranges between 250 C. and 350 C.

15. A heat exchanger for an internal combustion engine, comprising: a gas conduit flowable through by a predetermined gas; a heat conduit flowable through by a predetermined fluid compound working fluid, the heat conduit in thermal communication with the gas conduit; a first section having a first section length, a second section having a second section length, and a third section have a third section length, wherein the gas conduit spans, in a direction of flow of the gas, the first section, the second section, and the third section, and the heat conduit spans, in a direction of flow of the working fluid, the third section, the first section, and the second section; the first section including a gas inlet for inletting the gas and the third section including a working fluid inlet for inletting the working fluid; the third section including a gas outlet for discharging the gas and the second section including a working fluid outlet for discharging the working fluid; wherein the gas conduit is passable by the gas from the gas inlet to the gas outlet, and the heat conduit is passable by the working fluid from the working fluid inlet to the working fluid outlet; wherein the first section length ranges between 80 mm and 300 mm, the second section length ranges between 80 mm and 300 mm, and the third section length is greater than the second section length and ranges between 100 mm and 400 mm, the first section length being determined at least in part such that the gas, when entering the gas inlet at a gas entry temperature of up to 700 C., exceeds a decomposition temperature of the working fluid by up to 50 K upon exiting the first section, provided that the working fluid enters the first section in a liquid state of aggregation; and wherein the first section length, the second section length, and the third section length are determined such that the gas, upon entering the gas inlet, exits through the gas outlet at an exit temperature between 100 C. and 150 C., provided that the working fluid enters through the working fluid inlet at a working fluid entry temperature between 60 C. and 80 C. and an entry pressure between 20 bar and 50 bar.

16. The heat exchanger as in claim 4, wherein the second section length enables the working fluid to overheat in the second section, and the third section length enables the working fluid to temporarily evaporate within the heat conduit.

17. The heat exchanger as in claim 8, wherein the second section length enables the working fluid to overheat in the second section, and the third section length enables the working fluid to temporarily evaporate within the heat conduit.

18. The heat exchanger as in claim 15, wherein the second section length enables the working fluid to overheat in the second section, and the third section length enables the working fluid to temporarily evaporate within the heat conduit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, embodiments of the invention will be described with reference to the accompanying drawings, wherein

(2) FIG. 1 shows a highly simplified illustration of an internal combustion engine with a system for utilizing waste heat of the engine,

(3) FIG. 2 shows an evaporator heat exchanger in its disassembled state,

(4) FIG. 3 shows a plan view of a single slice of the exchanger according to FIG. 2,

(5) FIG. 4 shows a perspective view of the exchanger according to FIG. 2 in its assembled state,

(6) FIG. 5 shows a housing of the exchanger according to FIG. 2,

(7) FIG. 6 shows the flow scheme of a heat exchanger according to an embodiment of the invention, and

(8) FIG. 7 shows a diagram with the gradients of the working fluid's temperature, the gas temperature and the steam content in the respective section of the exchanger according to FIG. 6.

DETAILED DESCRIPTION

(9) Referencing FIG. 1, an internal combustion engine 8 in the form of a reciprocating piston engine 9 for driving a motor vehicle, especially a heavy-goods vehicle, includes a system 1 for recovering waste heat of the internal combustion engine 8 by means of the Rankine cycle. The internal combustion engine 8 comprises an exhaust-gas turbocharger 17. This turbocharger 17 compresses fresh air 16 into a charge-air conduit 13, which is cooled by means of an intercooler 14 before being supplied to the internal combustion engine 8. Through an exhaust pipe 10, part of the exhaust gas 18 resulting from the combustion is discharged from the internal combustion engine 8, again cooled by a heat exchanger 4 serving as an exhaust gas recirculation cooler, and fed back through a gas recirculation line 15 of the internal combustion engine 8 into the charge-air conduit 13. A further part of the exhaust gas 18 is used to drive the turbocharger 17 before being discharged into the surrounding atmosphere.

(10) In addition to such apparatus, a second evaporator heat exchanger (not depicted in FIG. 1) may be employed for cooling the exhaust gas 18 before discharging it into the environment, thus recovering its heat as well. The system 1 comprises a duct 2 filled with a predetermined fluid compound, e.g. Ethanol or Chlorofluorocarbon, serving as a working fluid. An expansion unit 5, a capacitor 6, a reservoir 7, and a pump 3 are embedded into the circuitry thus formed. From the pump 3, the liquid working fluid passing through the circuit is compressed to an elevated pressure level, evaporated by the heat exchanger 4, and passed in its gaseous form to the expansion unit 5 to perform mechanical work, consequently dropping back to its regular pressure. Inside the capacitor 6, the gaseous working fluid is again liquefied and finally returned to its reservoir 7.

(11) FIGS. 2 to 4 illustrate a constructional assembly 35 of the heat exchanger 4, 12. The assembly 35 shown comprises a working fluid inlet 32 and a working fluid inlet zone 41 for inletting the working fluid and a working fluid outlet 33 and a working fluid outlet zone 42 for discharging the working fluid from the heat exchanger 4 and the assembly 35. A heat conduit 19 (not depicted in FIG. 2) is formed between a plurality of plate pairs 29, each pair 29 comprising an upper plate 30 and a lower plate 31, mutually separated by a suitably sized spacer 37. Furthermore, a channel 20 meandering through the lower plate 31 forms a heat conduit 19 (FIG. 3), guiding the working fluid from its working fluid inlet 32 and working fluid inlet zone 41 to the working fluid outlet 33 and working fluid outlet zone 42. Though not discernible in the figures at hand, the upper and lower plates 30, 31 are mutually bonded by means of brazing. The plate pairs 29 of the assembly 35 are stacked above another, holding a corresponding number of pipes 28 between them. FIGS. 2 and 3 illustrate this stacking configuration only partially.

(12) The upper and lower plates 30, 31 further include through holes 36 constituting the working fluid inlet 32 and outlet 33 and their respective working fluid inlet and outlet zones 41, 42, the through holes 36 touching the spacers 37 between each plate pair 29 (FIG. 2) and thus allowing the working fluid to pass through each plate pair 29 to the neighboring plate pairs 29 located above and below. The through holes 36 consequently extend through the spacers 37. Between each plate pair 29, four pipes 28 of rectangular cross section are arranged. These pipes 28 form a gas conduit 21 for conducting the exhaust gas 18, allowing heat to be transferred to the working fluid from said exhaust gas 18 while evaporating the working fluid on its way through the heat exchanger 4.

(13) A base plate 27 (FIG. 2) comprises diffusor ports 38 rectangular in cross section and is again connected integrally to the pipes 28 by brazing. The base 27 holds a gas diffusor 26 (indicated in FIG. 2 by means of a dotted line) comprising a gas inlet 11 and a gas inlet zone 43 for inletting the exhaust gas 18. For illustrative purposes, the exploded view of FIG. 2 shows the base 27 detached from the pipes 28.

(14) The components of the heat exchanger 4for instance, the plate pairs 29, gas diffusor 26, and spacers 37are manufactured from stainless steel or aluminum and cohesively connected by brazing or gluing.

(15) FIG. 3 shows the plates 30, 31 of the assembly 35 in detail. The upper and lower plates 30, 31 comprise the two through holes 36, allowing the working fluid to pass through each of them. Furthermore, the channel 20 forming the heat conduit 19 is worked into the lower plate 31, connecting the through holes 36 end-to-end. Thus, the working fluid is guided from the upper (inlet) through hole 36 through the channel 20 on to the lower (outlet) through hole 36. As indicated above, the spacers 37 arranged between two adjacent plate pairs 29 (FIG. 2) are traversed by the through holes 36 as well. Expansion gaps 22 formed by expansion slots 23 prevent thermal stress.

(16) FIG. 4 shows a perspective view of the heat exchanger 4, 12. At the two through holes 36 of the top plate 30, a socket 24 is arranged. The socket 24 serves to access the working fluid inlet 32 and inlet zone 41 as well as the working fluid outlet 33 and outlet zone 42. The exhaust gas 18 passes through the gas conduit 21 formed between the plate pairs 29. Thus, the exhaust gas 18 enters in an inflow 39 and the assembly 35 of the heat exchanger 4, 12 in an outflow 40. Preferably, several assemblies 35 and/or the entire heat exchanger 4, 12 are encased by means of a suitably dimensioned housing (not depicted), guiding the exhaust gas 18 from one assembly 35 to the next.

(17) FIG. 5 shows a housing of the heat exchanger 4, 12. The plates are stacked up and brazed and the housing around the core guides the exhaust gas through the core.

(18) FIG. 6 shows an embodiment of the inventive heat exchanger 4, 12 comprising three assemblies 35 as shown in FIGS. 2 to 4. In FIG. 5, these assemblies 35 are simplified for illustrative purposes. The three assemblies 35 are successively traversed from left to right by exhaust gas 18, thus forming first, second, and third sections 45, 46, 48 of the heat exchanger 4, 12.

(19) As can be gathered from the figure, the assembly 35 forming the first section 45 of the heat exchanger 4, 12 is substantially smaller than the assemblies 35 forming the second and third sections 46, 48. Specifically, in the embodiment shown in FIG. 5, the first section 45 measures 10 cm whereas the second and third sections 46, 48 each measure 30 cm in length. The exhaust gas 18 enters the first section 45 through the gas inlet 11 at a gas entry temperature of up to 700 C. and is passed on to a gas outlet zone 44 of the first section 45 to enter the second section 46 through a gas inlet zone 43. Mutatis mutandis, this flow scheme spans the second section 46 and third section 48 until the exhaust gas 18 finally exits the heat exchanger 4, 12 through the gas outlet 25, ultimately tempered between 100 C. and 150 C. Upon exiting the first section 45, the exhaust gas 18 has dropped to a temperature level that exceeds the working fluid's decomposition temperature by no more than 50 K. At an exemplary decomposition temperature of 300 C. to 350 C., the working fluid configuration thus causes the exhaust gas 18 to drop below a level of, at maximum, 400 C.

(20) The working fluid, still liquid at a relatively low temperature of between 60 C. and 80 C. and pressurized to between 20 bar and 50 bar, enters the third section 48 of the heat exchanger 4, 12 from the reservoir 7 through the working fluid inlet 32 (FIG. 1) and, due to the geometry of heat transfer surfaces, is only slightly heated to a temperature level of about 200 C., thus staying short of its specific decomposition temperature.

(21) The working fluid enters the third section 48 through the working fluid inlet 32, passes into the first section 45 and further into the second section 46, where it is finally discharged from the heat exchanger 4, 12. In traversing the third section 48, the exhaust gas 18 is cooled down significantly. The working fluid passes through the first section 45 in a co-current flow to avoid decomposing.

(22) FIG. 7 shows a diagram illustrating the gradient of the working fluid's temperature, the gas temperature and the steam content in the first section 45, second section 46 and third section 48 of the embodiment of the inventive heat exchanger 4, 12.