WO2017060621A1

WO2017060621A1 - Vehicle heat exchanger, and energy recovery installation and method

Info

Publication number: WO2017060621A1
Application number: PCT/FR2016/052560
Authority: WO
Inventors: Bertrand Nicolas; Mohamed Yahia; Régine Haller; Jin-ming LIU; Samy Hammi; Abdelmajid Taklanti; Yulia GLAVATSKAYA
Original assignee: Valeo Systemes Thermiques
Priority date: 2015-10-08
Filing date: 2016-10-05
Publication date: 2017-04-13
Also published as: FR3042261A1

Abstract

The invention relates to a heat exchanger (11) comprising a bundle allowing exchange of heat between a first fluid, referred to as working fluid (3), and a second fluid (5), the said bundle being configured so that: - the said working fluid (5) circulates in at least one upstream pass (21) and in a terminal pass (23) in which the said working fluid (5) is in the vapour phase in at least a part (23b), - the said working fluid (5) circulates in at least one of the said upstream passes (21) countercurrentwise with respect to the said second fluid (3), - the said working fluid (5) circulates in the said terminal pass (23) cocurrentwise with respect to the said second fluid (3). The invention also relates to an installation comprising a circuit for the circulation of a working fluid (5) comprising such a heat exchanger (11) and to a method using such a circuit.

Description

HEAT EXCHANGER FOR VEHICLE, INSTALLATION AND METHOD FOR

ENERGY RECOVERY

The subject of the present invention is a heat exchanger, in particular for a vehicle, and more particularly a heat exchanger allowing a heat exchange between a working fluid and a second fluid, such as exhaust gases. It also relates to an installation and a method of energy recovery using such a heat exchanger. The environmental constraints driven by the new European standards encourage car manufacturers to reduce C0 ₂ emissions from their vehicles. One possible solution is the recovery of lost energy. In particular, it is possible to recover the energy lost in the exhaust via a thermodynamic Rankine cycle. Indeed, the heat of the exhaust gas can be used to heat and then spray a working fluid in the form of high pressure steam that will be expanded in a turbine and converted into energy, including electrical. The fluid is then condensed to regain its liquid form and start the cycle again. In such a system, the evaporation of the working fluid by the exhaust gas is effected by means of a heat exchanger subject to the very high dynamics of the variation of the flow rate and the temperature of the gas. exhaust.

In the case where the working fluid is ethanol, the problem of degradation thereof arises. Indeed, one of the characteristics of ethanol is to degrade from a temperature of about 250 'Ό. The Rankine cycle must therefore be controlled so that the temperature of the working fluid at the outlet of the heat exchanger is not greater than 250 ° C. Conventionally, the exchanger used in such a system is an exchanger in which the working fluid circulates in countercurrent with respect to the exhaust gas. This type of exchanger is known for its good thermal performance. On the other hand, the time required for the refrigerant to reach the maximum temperature, that is to say the acquisition of the temperature of the working fluid output, is very short (for example it is 5 seconds to reach 250 'Ό when passing 100 at 120 km / h in the case of ethanol as a working fluid). Conversely, the exchangers in which the working fluid circulates cocurrently with respect to the exhaust gases have a necessary duration so that the refrigerant reaches the higher maximum temperature (for example it is 14.7 seconds to reach 250 'Ό when passing from 100 to 120 km / h in the case of ethanol as a working fluid) but their thermal performance is low . There is therefore a need for a heat exchanger overcoming the above disadvantages.

The invention aims, for this purpose, a heat exchanger comprising a beam for a heat exchange between a first fluid, said working fluid, and a second fluid, said beam being configured so that:

said working fluid circulates in at least one upstream pass and in one end pass in which said working fluid is in the vapor phase on at least a part,

said working fluid circulates in at least one of said countercurrent upstream passes relative to said second fluid,

said working fluid circulates in said terminal pass co-current with respect to said second fluid.

Thanks to the terminal pass which works in co-current, such an exchanger makes it possible to increase the time constant of the system in order to ensure a sufficient time for the acquisition of the temperature of the working fluid at the outlet of the exchanger or in other words so that the working fluid can reach the maximum temperature. The heat exchanger however retains a good thermal performance by working all or parts of the previous passes in countercurrent. The increase in the temperature of the working fluid is slower which limits the risk of damaging the working fluid by too high temperatures. Such an exchanger configuration makes it possible to have at the output a minimum temperature of the exhaust gas lower than the evaporation temperature. It is thus not necessary to use a working fluid resistant to high temperatures.

According to various embodiments of the invention, which may be taken together or separately:

said terminal pass succeeds a first pass so that said working fluid circulates in two passes in the exchanger,

the exchange surface of the terminal pass represents at most 50% of the total exchange surface of said first pass and terminates,

said exchange surface of the terminal pass represents between 40 and 10% of the total exchange surface of said first pass and terminates,

said exchange surface of the terminal pass represents between 30 and 20% of the total exchange surface of said first pass and terminates, said exchange surface of the first pass represents at least 50% of the total exchange surface of said first pass and terminates,

said exchange surface of the first pass represents between 60 and 90% of the total exchange surface of said first pass and terminates,

said exchange surface of the first pass represents between 70 and 80% of the total exchange surface of said first pass and terminates,

said exchanger is configured so that said working fluid is a coolant,

said exchanger is configured so that said working fluid is ethanol,

said exchanger is configured so that said second fluid is exhaust gas from a vehicle engine,

said exchanger is configured so that said phase change is located at the end of the first pass and / or at the beginning of the terminal pass,

said exchanger has an elongated configuration,

each of said passes has an elongated configuration,

each of said passes is arranged in parallel with each other.

The invention also relates to a plant for recovering energy from the heat of the exhaust gas comprising a circulation loop of a working fluid, said loop comprising a heat exchanger according to any one of the preceding claims for exchanging heat with said exhaust gas. Said loop may in particular be configured to implement a Rankine cycle.

said loop further comprises a pump,

said loop further comprises an expander,

- Said loop further comprises a condenser, specifically a condenser with subcooler and accumulator.

The invention also relates to a method for recovering energy from the heat of the exhaust gases using a circulation loop of a working fluid, said loop comprising a heat exchanger between said working fluid and said exhaust gas, said method comprising a step of separating said exhaust gas, in a first stream and a second stream, downstream of said exchanger so that the working fluid circulates countercurrently with respect to the first flow in at minus one upstream pass and circulates cocurrently with respect to said second flow in a terminal pass in which said working fluid is in vapor phase on at least a portion.

- The exchange surface of the terminal pass represents at most 50% of the total exchange surface of said first pass and passes terminal.

said exchange surface of the terminal pass represents between 30 and 20% of the total exchange surface of said first pass and terminates,

said exchange surface of the first pass represents at least 50% of the total exchange surface of said first pass and terminates,

said working fluid is a coolant,

said working fluid is ethanol,

said phase change is located at the end of the first pass and / or at the beginning of the terminal pass,

said exchanger has an elongated configuration,

each of said passes has an elongated configuration,

each of said passes is arranged in parallel with each other,

said loop further comprises a pump,

said loop further comprises an expander,

said loop further comprises a condenser,

said loop implements a Rankine cycle.

The invention will be better understood, and other objects, details, features and advantages thereof will become more clearly apparent in the following detailed explanatory description of at least one embodiment of the invention given to As a purely illustrative and non-limiting example, with reference to the attached schematic drawings. On these drawings:

FIG. 1 is a schematic view of a circulation loop of a working fluid according to the Rankine cycle comprising a heat exchanger according to the invention,

FIG. 2 is a schematic view of the heat exchanger of FIG. 1; FIG. 3 schematically represents the change of state of a working fluid in the heat exchanger of FIG. 2;

FIG. 4 illustrates a comparison of the change of state of a working fluid in a heat exchanger of the prior art and in a heat exchanger according to FIG. 2 for a vehicle at a constant speed of 100 km / h .

As illustrated in FIG. 1, the invention firstly relates to an installation 1 for recovering energy from a heat source 3. Such an installation here implements a Rankine cycle and comprises a circulation loop. 5. In a conventional manner, such a loop comprises a condenser 7, a pump 9, a heat exchanger 11 and an expansion member 13. In a Rankine cycle, the working fluid 5 is driven by the pump 9 and will undergo different phase changes. At first, the working fluid is cooled to a pressure and a temperature sufficient by the condenser 7 to be fully liquefied. The working fluid in the form of compressed liquid is then vaporized in the heat exchanger 1 1 by heat exchange with a hot source 3. The working fluid 5 in vapor form is finally expanded at the expander 13. The fluid 5 is then again condensed to resume the same cycle. In the example illustrated in Figure 1, the cycle also comprises a secondary cooler 15 placed between the condenser 7 and the pump 9. It reduces the temperature of the working fluid 5 before compression and vaporization.

The condenser 7 and the secondary cooler 15 are supplied with fluid 17 for cooling the working fluid 5. It may be the same fluid flowing in the two elements, or two different fluids. This circulates preferably first in the secondary cooler 15 and then in the condenser 7.

Here, the heat source 3 of the heat exchanger 1 1 is the exhaust gas from a vehicle and the expansion member 13 is a turbine intended to be driven by the expansion of said working fluid 5 in phase gaseous and to produce energy, especially electrical. This cycle thus makes it possible to recover energy from the gases exhaust 3 and transform it into energy to produce, for example, electricity for an element 19 of the vehicle.

As illustrated in FIG. 2, the invention more particularly relates to the heat exchanger 11 of the working fluid circulation loop mentioned above. Said exchanger 11 comprises a beam allowing a heat exchange between a first fluid 5, said working fluid, and a second fluid 3, said beam being configured so that:

said working fluid flows in at least one upstream pass in which said working fluid is in the liquid phase on a first portion and in a liquid / vapor bi-phase state on a second portion and in a terminal pass 23 in which said working fluid 5 is in a two-phase liquid / vapor state on a first part 23a and in a vapor phase on a second part 23b,

said working fluid 5 circulates in at least one of said upstream passes 21 counter-current with respect to said second fluid 3,

said working fluid 5 circulates in said terminal pass 23 co-current with respect to said second fluid 3.

The heat exchanger 1 1 according to the invention preferably comprises two passes and two passes only, namely a first pass 21 and the terminal pass 23. It may also include at least one pass downstream of the first pass 21 in the or which working fluid 5 will be in the liquid phase. It may also comprise at least one intermediate pass in which said working fluid is in a biphasic liquid / vapor state. A pass corresponds to set of tubes defined in the same plane, for example, in the case where there are two passes, the working fluid 5 flows successively in a first direction for the first pass, or within the first set of tubes, then in a reverse direction in the first direction for the second pass or inside the second set of tubes.

The first pass 21 against the current, in which the thermal power exchanged is high, ensures the warming of the working fluid 5 in liquid form and part of the evaporation. The terminal pass 23 co-current ensures the rest of the evaporation and overheating of the working fluid 5. The effect of said overheating will however be limited since it works in co-current. Said second fluid 3 in turn flows in a pass which minimizes the pressure drop. Said heat exchanger 11 may comprise a heat exchange bundle, for example with stacked plates or tubes.

Such a heat exchanger 1 1 makes it possible to implement a method of recovering energy from the heat of a second fluid, here exhaust gas 3, using the circulation loop described above.

Said method comprises a step of separating said exhaust gas 3, in a first stream 3a and in a second stream 3b, downstream of said exchanger January. This separation is done so that the working fluid 5 circulates countercurrently with respect to the first flow 3a in said first pass 21 in which said working fluid 5 is in the liquid phase on the first portion 21a and in the liquid / vapor bi-phase state on the second portion 21b and circulates cocurrently with respect to said second flow 3b in said terminal pass 23 in which said working fluid 5 is in the bi-phasic liquid state / vapor on a first portion 23a and vapor phase on the second portion 23b. The separation is carried out by means of a separation means which comprises any means making it possible to distribute in two streams 3a, 3b as well as a regulation of the flow rates of said exhaust gas streams 3a, 3b. separation members allow a geometrical separation of the exhaust gas 3 and include for example an internal partition within the pipe which carries the exhaust gas 3, thus separating the exhaust gas 3 into two streams 3a, 3b or alternatively a bifurcation of the pipe carrying the exhaust gas 3 in two sub-pipes, thus separating the exhaust gas 3 into two streams 3a, 3b. The separation means may for example separate the exhaust gases so as to have a higher flow rate for a flow 3a than for the other flow 3b.

Said exhaust gas 3 thus exchange heat with said working fluid 5 so that it reaches the liquid / vapor bi-phase state at the outlet of said first pass 21 and that it is in vapor phase but at a temperature limited to the output of said terminal pass 23, that is to say at the outlet of the heat exchange 1 1. These are parts 21b and 23b, respectively.

At the outlet of the heat exchanger January 1, the exhaust gas 3 is cooled and the first and the second stream 3a and 3b are mixed to be subsequently evacuated.

Advantageously, the exchange surface of the end pass 23 represents at most 50%, preferably between 40 and 10%, and more preferably between 30 and 20% of the surface area. total exchange of said first pass 21 and terminal pass 23. Therefore, said exchange surface of the first pass 21 represents at least 50%, preferably between 60 and 90%, and more preferably between 70 and 80% of the total exchange surface of said first pass 21 and end pass 23. In the case of a 1 1 exchanger with two passes, as shown here, the total exchange surface of said first pass 21 and terminal pass 23 corresponds to the surface of exchange of the exchanger 1 1.

In other words, the second fluid 3 flows with a different flow rate in each of the passes. The distribution of the second fluid 3 is such that at most 50%, preferably between 40 and 10%, and more preferably between 30 and 20% of the flow rate of the second fluid 3 circulates in the so-called terminal pass 23. By Therefore, the distribution of the second fluid 3 is such that at least 50%, preferably between 60 and 90%, and more preferably between 70 and 80% of the flow of the second fluid 3 circulates in the first pass 21. The fact of having a small portion of the flow of the second fluid 3 which passes through the terminal pass 23 allows to have a sharp decrease in the temperature of the second fluid 3 during its passage in this pass. In addition, the fact that this pass 23 is in co-current implies that the working fluid 5 at the outlet of the heat exchanger January 1 is in contact with the second fluid 3 at the lowest temperature. This reduces the risks for the working liquid 5 of reaching a temperature too high at the outlet of the exchanger and being damaged.

Advantageously, said working fluid 5 is a coolant, and more particularly ethanol, and said second fluid 3 is the exhaust gas of a vehicle engine. The fluid exchanging heat with the working fluid 5 in the exchangers 7 and 15 may be a coolant.

TEST

Firstly the mechanical power of the detent 13 has been measured when a vehicle is at a static speed of 100 km / h. Then the time taken by the working fluid 5 to reach 250 ° C was measured when a vehicle went from a speed of 100 km / h to a speed of 120 km / h. These tests were carried out in the case of a heat exchanger 1 1 according to the invention wherein said working fluid 5 is ethanol flowing in two passes 21 and 23 and said second fluid 3 is the gases of exhaust of a vehicle engine. These same tests were carried out in the case of a heat exchanger with a countercurrent flow and in the case of a heat exchanger with a co-current pass. 1 pass 2 passes 1 pass counter-co-

90/10 80/20 70/30 50/50 40/60 30/70

current

Power

mechanical (W) 554 530 528 518.7 498 489 476 443 of the regulator

Time (s) for

5 10.1 10.25 10.4 10.7 1 1, 3 12 14.7 reach 250 ° C

Table 1

The countercurrent exchanger makes it possible to obtain maximum mechanical power at the level of the expansion element (554 W), but during the passage from 100 to 120 km / h the temperature of 250 ° C is reached in 5 s. This requires the use of a more expensive temperature sensor and actuator system responding in less than 5 seconds to prevent the working fluid from being damaged.

The co-current exchanger makes it possible to obtain mechanical power at the level of the lower expander of 25% compared to the countercurrent (443 W). On the other hand, when passing from 100 to 120 km / h the temperature of 250 ° C is reached in 14.7 s.

The exchanger 1 1 two countercurrent / co-current passes optimized especially with a fluid distribution of work / second fluid between 80/20 and 70/30 (that is to say that the exchange surface of the terminal pass 23 represents between 20% and 30% of the total exchange surface of said first pass 21 and end pass 23, and therefore the exchange surface of the first pass 21 represents between 80 and 70% of the surface area of total exchange of said first pass 21 and terminal pass 23) allows a moderate reduction of 4% of the power of the expansion member 13 relative to a countercurrent exchanger, while ensuring a time constant of about 10 s twice as high. This gives a heat exchanger 1 1 with a very good thermal performance without having to use an expensive system of temperature sensor and actuator.

Advantageously, said phase change is located at the end of the first pass 21 and / or at the beginning of the end pass 23. In the example illustrated in FIGS. 2 and 3, the working fluid 5 is in liquid form in the first portion 21a. of the first pass 21 and in two-phase liquid / vapor form in the second portion 21b of the first pass 21. In the second pass which is said terminal pass 23, the working fluid 5 is in the form bi-phasic liquid / vapor in the first portion 23a of the terminal pass 23 and in the vapor state in the second portion 23b of the terminal pass 23.

The change of state of a working fluid has been observed in a countercurrent heat exchanger of the prior art and in a heat exchanger January 1 according to Figure 2 with a fluid distribution of work / second fluid of 80/20 for a vehicle at a constant speed of 100 km / h. These measurements appear in the graph of Figure 4.

Thus, the liquid part occupies a very high surface area in the two heat exchangers (70% of the surface area for the counter-current heat exchanger and 60% for the 1 1 two-pass heat exchanger 80/20 according to the invention). This is the part referenced 21a in FIG.

The part allocated to evaporation, that is to say the part or the working fluid is in a two-phase liquid / vapor state, is 25% for the countercurrent exchanger and 17.5 % for the exchanger 1 1 with two passes 80/20 according to the invention. These are the parts referenced 21b and 23a in FIG.

The essential difference between the exchanger of the state of the art and the exchanger 1 1 according to the invention lies in the area allocated for overheating, that is to say the part where the working fluid is under form of steam. This is the portion referenced 23b in Figure 2. Thus, 5% of the countercurrent heat exchanger is in the vapor phase. This exchanger of the prior art is therefore very sensitive to a small variation in the flow rate of the working fluid (ethanol) due to the small surface of the exchanger necessary to achieve the superheating. On the other hand, 22.5% of the exchanger 1 1 with two passes 80/20 according to the invention is in the vapor phase. It therefore requires an exchange area four times larger and is therefore more stable in terms of control than a countercurrent heat exchanger.

Advantageously, the heat exchanger 11 has an elongated configuration. In particular each of said passes 21 and 23 has an elongated configuration and is arranged in parallel with each other. Such a configuration facilitates the integration of the heat exchanger in an exhaust line.

It should be noted that alternative embodiments are of course possible and that the present invention is not limited to energy recovery only from the heat of the exhaust gas. It is conceivable, for example, to recover the heat of any other fluid having the appropriate temperature. Likewise, it is possible to envisage another working fluid than ethanol.

Claims

claims

Heat exchanger (1 1) comprising a beam for exchanging heat between a first fluid, said working fluid (3), and a second fluid (5), said beam being configured so that:

said working fluid (5) circulates in at least one upstream passage (21) and in one end pass (23) in which said working fluid (5) is in the vapor phase on at least part (23b),

said working fluid (5) circulates in at least one of said upstream passes (21) against the current with respect to said second fluid (3),

said working fluid (5) circulates in said terminal pass (23) co-current with respect to said second fluid (3).

Heat exchanger (1 1) according to the preceding claim, wherein said terminal pass (23) succeeds a first pass (21) so that said working fluid flows in two passes in the exchanger.

Heat exchanger (1 1) according to the preceding claim, wherein the exchange surface of the terminal pass (23) represents at most 50% of the total exchange surface of said first pass (21) and passes terminal (23) .

Heat exchanger (1 1) according to any one of claims 2 or 3, wherein said exchanger (1 1) is configured so that a phase change is located at the end of the first pass (21) and / or early terminal password (23).

Heat exchanger (1 1) according to any one of the preceding claims, wherein said exchanger (1 1) is configured so that said working fluid (5) is a coolant and / or ethanol.

Heat exchanger (1 1) according to any one of the preceding claims, wherein said exchanger (1 1) is configured so that said second fluid (3) is exhaust gas from a vehicle engine.

Heat exchanger (1 1) according to any one of the preceding claims, wherein said exchanger (1 1) has an elongated configuration.

8. heat exchanger (1 1) according to any one of the preceding claims, wherein each of said passes (21 and 23) has an elongated configuration and are arranged in parallel with each other. 9. Installation for recovering energy from the heat of the exhaust gas comprising a circulating loop of a working fluid (5), said loop comprising a heat exchanger (1 1) according to any one of preceding claims. 10. Energy recovery plant according to claim 9, wherein said loop further comprises a pump (9), an expander (13) and a condenser (7).

1 1. A method of recovering energy from the heat of the exhaust gas (3) using a circulation loop of a working fluid (5), said loop comprising a heat exchanger (1 1) between said fluid working piece (5) and said exhaust gas (3), said method comprising a step of separating said exhaust gas (3), in a first stream (3a) and in a second stream (3b), downstream of said exchanger (1 1) so that the working fluid (5) circulates countercurrently with respect to the first flow (3a) in at least one upstream passage (21) and flows cocurrently with respect to said second flow (3b) in an end pass (23) wherein said working fluid (5) is in the vapor phase on at least a portion (23b).

12. A method of energy recovery according to the preceding claim, wherein said terminal pass (23) succeeds a first pass (21) so that said working fluid flows in two passes in the heat exchanger (1 1). .

13. Energy recovery method according to the preceding claim, wherein the exchange surface of the terminal pass (23) represents at most 50% of the total exchange surface of said first pass (21) and passes terminal (23). ).

14. Energy recovery method according to any one of claims 12 or

13, wherein said phase change is located at the end of the first pass (21) and / or at the beginning of the end pass (23).

15. Energy recovery method according to any one of claims 1 1 to

14, wherein said working fluid is a coolant and / or ethanol.