WO2015173075A1

WO2015173075A1 - Refrigerant circuit for the recovery of energy from the thermal losses of an internal combustion engine

Info

Publication number: WO2015173075A1
Application number: PCT/EP2015/059847
Authority: WO
Inventors: Laurent Labaste-Mauhe; Yulia GLAVATSKAYA; Bertrand Nicolas; Samy Hammi; Mohamed Yahia; Abdelmajid Taklanti; Régine Haller; Jin-ming LIU
Original assignee: Valeo Systemes Thermiques
Priority date: 2014-05-16
Filing date: 2015-05-05
Publication date: 2015-11-19
Also published as: FR3021070A1; FR3021070B1

Abstract

The invention relates to a refrigerant circuit, in particular for the recovery and transformation of heat discharged from a motor vehicle, which comprises a first heat exchanger (1) forming a boiler, an expansion means (5) capable of producing a mechanical torque from the work of expansion, and a means capable of circulating the refrigerant along at least one loop successively traversing the first heat exchanger (1) and the expansion means (5). The circuit comprises means for feeding (9) liquid refrigerant into the boiler (1) or between the first heat exchanger (1) and the expansion means (5).

Description

Refrigerant circuit for energy recovery from thermal losses of an internal combustion engine

The present invention relates to a refrigerant circuit for recovering and transforming thermal energy produced by a motor vehicle.

As illustrated in FIG. 1, such a circuit conventionally comprises a first heat exchanger 1 forming a boiler, a second heat exchanger 2 forming a condenser, a third heat exchanger 3 forming a subcooler, a pump 4, a relaxing means 5 adapted to transform the relaxation work into a mechanical torque, a refrigerant reservoir 6 and means adapted to circulate the refrigerant according to at least one loop successively passing through the pump 4, the boiler 1, the means 5, the condenser 2, the tank 6 and the subcooler 3.

The expansion means 5 makes it possible, for example, to actuate an electric generator and thus to produce electrical energy. Such a mode of operation corresponds to a Rankine cycle. The boiler 1 is for example able to take calories from the vehicle exhaust. Finally, the condenser 2 is intended to cool and condense the refrigerant by the air arriving at the front of the vehicle.

FIG. 2 is a Mollier diagram schematically illustrating the operation of the circuit of FIG. 1.

In this diagram, the abscissa is formed by the mass enthalpy h and the ordinate is formed by the pressure P of the refrigerant. Points referenced 11 to 15 have been reported both on the Mollier diagram and on the refrigerant circuit illustrated in Figure 1 to facilitate understanding. The phases of the refrigerant (liquid L, diphasic Di, that is to say liquid and vapor, vapor V) are also indicated on the diagram, as well as the different stages of the cycle (evaporation E, condensation CD, compression CP, relaxation D). It is found that the refrigerant from the boiler 1 (point i2) is superheated steam. However, certain expansion means need to be traversed by refrigerant in two-phase form to ensure their proper operation, especially for reasons of lubrication of said expansion means.

The liquid is said to be saturating, when it is on the left on the curve referenced 7 in FIG. 2 and the steam is said to be saturating when it is on the right on the curve referenced 8. These two curves delimit a domain in which the fluid is two-phase, that is to say comprises both a liquid phase and a vapor phase.

In the two-phase domain, the mass vapor mass x of a fluid is defined by the following relationship x = mg / (ml + mg) where:

mg is the saturating vapor mass;

- ml is the mass of saturating liquid.

The title x can also be designated by the relation x = (hm - hl) / (hg-hl), where:

hm is the mass enthalpy of the two-phase fluid;

- hl is the mass enthalpy of the saturating liquid;

hg is the enthalpy of saturating vapor.

The mass titre thus defines the quantity of gas of the two-phase fluid.

A title equal to 1 indicates that the fluid has only vapor (on the curve 8), while a title equal to 0 indicates that the fluid comprises only liquid.

In order to ensure that the fluid passing through the expansion means 5 is in the two-phase state, it is therefore necessary to control the enthalpy of the refrigerant intended to pass through the expansion means 5. For example, it is desired to have a title understood between 0.8 and 0.95, as needed.

The invention aims in particular to provide a simple, effective and economical solution to this problem.

For this purpose, it proposes a refrigerant circuit, in particular for the recovery and transformation of heat discharges. of a motor vehicle, which comprises a first heat exchanger forming a boiler, a means of relaxation capable of producing a mechanical torque from the relaxation work, and means adapted to circulate the refrigerant according to at least one through-loop successively the first heat exchanger and the expansion means, characterized in that it comprises means for supplying liquid refrigerant into the first heat exchanger or between the first heat exchanger and the expansion means.

The refrigerant supply means can bring liquid refrigerant into the first heat exchanger or allow to bring liquid refrigerant between the first heat exchanger and the expansion means.

According to a variant, the refrigerant supply means are located in the first heat exchanger or are located between the first heat exchanger and the expansion means.

The liquid refrigerant has a low enthalpy which makes it possible, when mixed with vapor phase refrigerant, to lower the enthalpy of the mixture. Depending on the fluid flow rate in the vapor phase from the boiler and depending on the liquid phase fluid flow that is injected, it is possible to obtain a two-phase refrigerant, having a title close to the target title for the operation of the means of relaxation, for example a title between 0.8 and 0.95.

According to one characteristic of the invention, the circuit comprises a separation zone capable of separating the liquid phase from the gaseous phase of the refrigerant, an overheating zone able to be traversed by the gaseous phase of the refrigerant coming from the separation zone. , and a mixing zone adapted to receive the gaseous refrigerant from the overheating zone and adapted to receive at least a portion of the liquid phase of the refrigerant from the separation zone.

According to one characteristic of the invention, said separation zone, said overheating zone and / or said mixing zone are located in the first heat exchanger and / or between the first heat exchanger and the expansion means.

Preferably, in this case, the circuit comprises means for measuring pressure and temperature, able to measure the pressure and temperature of the gas phase of the refrigerant from the overheating zone.

According to one characteristic of the invention, the circuit comprises a source of refrigerant.

The refrigerant from the first heat exchanger and the liquid refrigerant from the source are mixed at the mixing zone.

Preferably, the source is a point of the high pressure circuit at which the refrigerant is in the liquid state, preferably at a known or determinable enthalpy.

According to one aspect of the invention, the circuit comprises a bypass channel of the refrigerant connecting the separation zone to the mixing zone.

According to one aspect of the invention, the circuit comprises a pump constituting the means adapted to circulate the refrigerant, the loop successively passing through the pump, the first heat exchanger and the expansion means.

According to one aspect of the invention, the circuit comprises a second heat exchanger forming a condenser, the loop successively passing through the pump, the first heat exchanger, the expansion means and the second heat exchanger.

According to one aspect of the invention, the circuit comprises a third heat exchanger forming a subcooler, the loop successively passing through the pump, the first heat exchanger, the expansion means, the second heat exchanger and the third heat exchanger. heat. According to one aspect of the invention, the circuit comprises a reservoir for containing liquid refrigerant fluid, said reservoir being located between the second heat exchanger and the third heat exchanger.

According to one aspect of the invention, the circuit comprises means for regulating the portion of the flow of liquid refrigerant from the source and entering the mixing zone.

According to one aspect of the invention, these control means may consist of a three-way valve, preferably disposed at the outlet of the pump and which distributes the total flow into two secondary flow rates.

The invention also relates to a method of operating a circuit of the aforementioned type, wherein the refrigerant circulates in a loop through the first heat exchanger and the expansion means, liquid refrigerant being injected at a zone mixture located in the first heat exchanger or between the first heat exchanger and the expansion means, so that the refrigerant from the mixing zone and passing through the expansion means is two-phase.

Preferably, the refrigerant circulates in a loop through the pump, the first heat exchanger, the expansion means, the second heat exchanger, the reservoir and the third heat exchanger.

The invention will be better understood and other details, characteristics and advantages of the invention will appear on reading the following description given by way of non-limiting example with reference to the accompanying drawings in which:

FIG. 1 is a schematic view of a refrigerant circuit of the prior art,

FIG. 2 is a Mollier diagram illustrating the operation of the circuit of FIG. 1, FIGS. 3 and 4 are views respectively corresponding to FIGS. 1 and 2 and illustrating a first embodiment of the invention,

- Figures 5 and 6 are views respectively corresponding to Figures 1 and 2 and illustrating a second embodiment of the invention.

FIG. 3 represents a refrigerant circuit according to a first embodiment of the invention. This comprises a first heat exchanger 1 forming a boiler, a second heat exchanger 2 forming a condenser, a third heat exchanger 3 forming a subcooler, a volumetric pump 4, a trigger means 5 adapted to recover a mechanical torque from the work of relaxation and coupled to an electric generator for example, and a tank 6.

The refrigerant circulates in a loop through successively the pump 4, the boiler 1, the expansion means 5, the condenser 2, the tank 6 and the subcooler 3.

The circuit further comprises a mixing zone 9 at which the refrigerant from the boiler 1 and the liquid refrigerant from a source 10 is mixed. The refrigerant coming from the mixing zone 9 then passes through the cooling medium. relaxation 5.

The source 10 may for example be a point of the high pressure circuit at which the refrigerant is in the liquid state, preferably at a known or determinable enthalpy, as at the output of the pump 4 for example.

The flow rate of the refrigerant at the inlet of the expansion means 5 can be adjusted by varying, for example, the displacement and / or the rotational speed of the pump 4. Means 1 1 making it possible to regulate the portion of the flow of refrigerant liquid from the source 10 and entering the mixing zone 9 may also be provided. FIG. 4 is a Mollier diagram schematically illustrating the operation of the circuit of FIG. 3.

Points referenced 11 to 17 have been reported both on the Mollier diagram and on the refrigerant circuit illustrated in Figure 3 to facilitate understanding. The phases of the refrigerant (liquid L, diphasic Di, that is to say liquid and vapor, vapor V) are also indicated in the diagram.

As shown in Figure 4, the liquid refrigerant from the source 10 (point i3) has an enthalpy referenced h3 and a rate that will be noted Q3. Furthermore, the refrigerant from the boiler 1 is superheated steam (point i2) which has an enthalpy referenced h2 and a rate that will be noted Q2.

As indicated above, it is necessary for the refrigerant entering the expansion means 5 (point 14) to be two-phase, with a given titre x, for example between 0.8 and 0.95.

Remember that the title x satisfies the relation x = (hm-hl) / (hg-hl), where:

hm is the enthalpy of the two-phase fluid;

- hl is the enthalpy of saturating liquid;

hg is the enthalpy of saturating vapor.

In this case, hm = h4, the points h1 and hg are defined by the Mollier diagram and depend on the pressure P1 of the points i2, i3 and i4. In particular, in this example, hl = h3 because the refrigerant from the source is saturating liquid or undercooled if it comes from the pump 4, in this case h4 = h1.

The value of h2 can be easily known by measuring the temperature and pressure of the refrigerant at point i2.

The target value of x being known, the values h1 and hg are also known, it is possible to deduce the value of h4 to obtain.

If Q4 is defined as the flow of refrigerant through point 4, then Q4.h4 = Q2.h2 + Q3.h3. The flow Q4 can be determined easily because it is equal to the flow rate of the pump 4 and is therefore a function of the displacement and the rotational speed of the pump 4, in the case of a positive displacement pump, for example. On the other hand, the flow Q4 checks the relation Q4 = Q2 + Q3.

As seen above, the value of h4 can be calculated from the title x to obtain, the values of h2, Q2 and h3 being determinable. It is therefore possible to deduce the flow rate Q3 of liquid refrigerant to be injected into the mixing zone 9 to obtain the title x target. This flow rate Q3 can be regulated using the corresponding means 1 1, whatever the operating conditions. The means 1 1 may be a three-way valve disposed at the outlet of the pump 4 and which distributes the total flow Q4 in two secondary flow rates Q2 and Q3. This three-way linear function can also be performed electronically with shut-off valves. When the path connected to the boiler 1 is closed, all the refrigerant comes from point i3. Conversely, when the path connected to point i3 is closed, all the refrigerant comes from point i2. By varying the opening and closing times of the different channels, the distribution of the two flows can be adjusted.

Figures 5 and 6 illustrate a second embodiment in which the circuit does not require the use of control means.

This circuit comprises, as before, a first heat exchanger 1 forming a boiler, a second heat exchanger 2 forming a condenser, a third heat exchanger 3 forming a subcooler, a positive displacement pump 4, a means of relaxation 5 fit recovering a mechanical torque from the relaxation work and possibly coupled to an electric generator for example, and a reservoir 6.

The circuit furthermore comprises a separation zone 12 capable of separating the liquid phase from the gaseous phase of the refrigerant, an overheating zone 13 adapted to be traversed by the gaseous phase of the refrigerant coming from the separation zone 12, and a mixing zone 14 adapted to receive the refrigerant in gaseous form from the overheating zone 13 and adapted to receive at least a portion of the liquid phase of the refrigerant from the separation zone 12 and flowing in a bypass channel 15.

The refrigerant circulates in a loop through successively the pump 4, the boiler 1, the separation zone 12, a first portion of the refrigerant (the vapor phase) then passing through the overheating zone 13 before entering the mixing zone 14, while another part of the refrigerant (the liquid phase) is directed directly from the separation zone 12 to the mixing zone 14, the whole of the refrigerant coming from the mixing zone 14 then passing through the means of mixing. 5, the condenser 2, the tank 6 and the subcooler 3.

FIG. 6 is a Mollier diagram schematically illustrating the operation of the circuit of FIG. 5.

As before, points referenced 11 to 19 have been reported both on the Mollier diagram and on the refrigerant circuit illustrated in FIG. 5 to facilitate understanding. The phases of the refrigerant (liquid L, diphasic Di, that is to say liquid and vapor, vapor V) are also indicated in the diagram.

In particular, refrigerant (superheated steam) at an enthalpy h5 (point i5) and refrigerant (saturating liquid) at an enthalpy h3 (point i3) are mixed in the mixing zone 14, so as to produce refrigerant biphasic with an enthalpy h6 (point i6), intended to pass through the expansion means 5.

In this embodiment, the various elements of the circuit are dimensioned so as to ensure that the point i6 is located in the two-phase zone of the Mollier diagram, whatever the operating conditions. The circuit then has no regulating means for adjusting, in an active manner and in real time, the flow of liquid fluid passing through the pipe 15, for example. On the contrary, two-phase character of the refrigerant at point i6 is ensured passively. The cost of such a circuit is therefore reduced, compared with the circuit of FIG.

However, in this embodiment, it is not possible to guarantee a constant and optimal title x of the two-phase fluid passing through the expansion means 5, for all operating conditions.

Claims

1. Refrigerant circuit, in particular for recovering and transforming the thermal discharges of a motor vehicle, which comprises a first heat exchanger (1) forming a boiler, an expansion means (5) capable of producing a mechanical torque at from the relaxation work, and means adapted to circulate the refrigerant according to at least one loop successively passing through the first heat exchanger (1) and the expansion means (5), characterized in that it comprises means for supply (9, 14) of liquid refrigerant in the first heat exchanger (1) or between the first heat exchanger (1) and the expansion means (5).

2. Circuit according to claim 1, characterized in that it comprises a separation zone (12) adapted to separate the liquid phase from the gas phase of the refrigerant, an overheating zone (13) adapted to be traversed by the phase refrigerant gas from the separation zone (12), and a mixing zone (14) adapted to receive the gaseous refrigerant from the overheating zone (13) and adapted to receive at least a portion of the liquid phase of the refrigerant from the separation zone (12).

3. Circuit according to claim 2, characterized in that said separation zone (12), said overheating zone (13) and / or said mixing zone (14) are located in the first heat exchanger (1) and / or between the first heat exchanger (1) and the expansion means (5).

4. Circuit according to one of claims 2 and 3, characterized in that it comprises means for measuring the pressure and temperature, able to measure the pressure and temperature of the gas phase of the refrigerant from the overheating zone (13).

5. Circuit according to one of claims 2 to 4, comprising a bypass channel (15) of the refrigerant connecting the separation zone (12) to the mixing zone (14).

6. Circuit according to one of claims 1 to 5, characterized in that it comprises a pump (4) constituting the means adapted to circulate the refrigerant, the loop through successively the pump (4), the first heat exchanger heat (1) and the relaxing means (5).

7. Circuit according to claim 6, characterized in that it comprises a second heat exchanger (2) forming a condenser, the loop successively passing through the pump (4), the first heat exchanger (1), the expansion means (5) and the second heat exchanger (2).

8. Circuit according to claim 7, characterized in that it comprises a third heat exchanger (3) forming a subcooler, the loop successively passing through the pump (4), the first heat exchanger (1), the means trigger (5), the second heat exchanger (2) and the third heat exchanger (3).

9. Circuit according to claim 8, characterized in that it comprises a reservoir (6) for containing liquid refrigerant fluid, said reservoir (6) being located between the second heat exchanger (2) and the third heat exchanger (3).

10. A method of operating a circuit according to one of claims 1 to 9, wherein the refrigerant circulates in a loop through the first heat exchanger (1) and the expansion means (5), liquid refrigerant being injected at a mixing zone (9, 14) located in the first heat exchanger (1) or between the first heat exchanger (1) and the expansion means (5), so that the refrigerant from the mixing zone (9, 14) and passing through the expansion means (5) is two-phase.

1 1. A method of operating a circuit according to claim 10, wherein the refrigerant circulates in a loop through the pump (4), the first heat exchanger (1), the expansion means (5), the second heat exchanger (2), the tank (6) and the third heat exchanger (3).