EP1169605A1

EP1169605A1 - Turboventilator which is operated by the expansion of a diphasic refrigerating fluid

Info

Publication number: EP1169605A1
Application number: EP00918962A
Authority: EP
Inventors: Denis Clodic
Original assignee: Association pour la Recherche et le Developpement des Methodes et Processus Industriels
Current assignee: Association pour la Recherche et le Developpement des Methodes et Processus Industriels
Priority date: 1999-04-12
Filing date: 2000-04-12
Publication date: 2002-01-09
Also published as: AU3973100A; US6604378B2; FR2792063A1; US20020129611A1; WO2000061997A1; CA2370235A1; FR2792063B1

Abstract

The invention relates to refrigerating or air conditioning systems comprising at least one exchanger (2, 3). The system uses a refrigerant fluid according to a thermodynamic cycle comprising at least one liquid-vapor expansion phase. According to the invention, the liquid-vapor phase is created by means of a diphasic turbine (4b) that actuates a ventilator (5b), causing air to circulate on said exchanger (3).

Description

TURBO FAN MOVED BY THE RELAXATION OF A DIPHASIC REFRIGERATION FLUID

The present invention relates in particular to refrigeration systems such as domestic refrigerators or freezers and fixed or mobile air conditioning systems. It concerns equipment whose exchangers work as well in natural convection as in forced convection.

Most models of refrigerators and freezers operate in natural convection both for the diffusion of freshness inside the refrigeration enclosure and outside of this enclosure for the extraction of heat from the system. The corresponding natural convection coefficients are very low. They are between 3 and 5 W / m2.K. To transfer heat, these low convection coefficients imply both large exchange surfaces and temperature differences between the exchanger and the air which are typically 15 to 20 K. For example, for a refrigerator whose average interior temperature is 5 ° C, located in a room with an ambient temperature of 25 ° C, i.e. a temperature difference of 20 K, refrigeration cycles must be carried out with evaporation temperatures of the order of - 15 to - 20 ° C in the evaporator located inside the enclosure and the condensation temperatures from 35 ° C to 40 ° C in the condenser located outside the refrigerator. The cycle therefore operates under a temperature difference of 50 to 60 K to maintain a useful difference of 20 K. It is known to use fans inside the enclosure in order to reduce the exchange surfaces, better control air circulation and limit temperature differences between the evaporator and the air located in the enclosure. Similarly to ventilate the external surface of the condenser, it is known to also use fans to increase the exchange coefficients on the condenser. More generally, for air conditioning systems, fans are used both on the condenser and on the evaporator.

In all cases, for fans of small electrical power (typically between 10 and 200 W), the yields of these motorbikes fans are low, typically electric drive motors have efficiencies of 10 to 15%, which has two sets of consequences.

1. For natural convection exchangers, the introduction of a fan improves the exchange coefficients and makes it possible to reduce the difference between the phase change temperature of the refrigerant and the average temperature of the air circulating on the exchanger. This leads, at equal temperature in the refrigerator, to an increase in the evaporation temperature and, at equal temperature to the outside air, a decrease in the condensation temperature. This reduction in the difference in evaporation and condensation temperatures and therefore in the respective evaporation and condensation pressures results in a reduction in the consumption of the compressor. However, the consumption of the fan is much higher than the gain in consumption induced on the compressor. The total consumption of the system (fans + compressor) is greater than the consumption of the compressor operating with natural convection exchangers alone. 2. For exchangers that are already forced convection, such as air conditioning systems and in particular on-board air conditioning systems, the share of fan consumption in overall energy consumption (compressor + fans) is very significant. For example, in automobile air conditioning, it can constitute up to 35% of overall consumption. The object of the present invention is to improve the overall energy balance

(compressor + fans) of refrigeration or air conditioning systems whose exchangers are natural convection or forced convection. The present invention relates more particularly to systems using a fluid according to a thermodynamic cycle comprising an expansion phase carried out by means of a pressure reducer and a compression phase carried out by means of a compressor.

According to the invention, in such systems, the compression phase during a liquid-vapor expansion phase provided for this purpose, it is possible to recover mechanical energy in the two-phase gas flow or the circulating liquid. According to the invention, the liquid-vapor expansion phase is carried out by means of a two-phase turbine actuating a fan causing air circulation on said exchanger.

Preferably, in the case of a system implementing a chain of devices comprising: a compressor, a first exchanger composing a condenser, a second exchanger composing an evaporator, the system comprises a liquid-vapor expansion phase carried out by means of '' a two-phase turbine operating as a pressure reducer, actuating a fan causing air circulation on the evaporator or on the condenser. Thus, the recovery of mechanical energy is carried out by replacing the regulator, which is usually in the form of an orifice or a capillary, a two-phase expansion turbine operating as a regulator comprising movable elements and directly driving a wheel. fan. The passage of a trigger with external work also improves the overall efficiency of the cycle. In the case of another alternative embodiment, preferably also, in the case of a system implementing a chain of devices comprising: a compressor, a first exchanger composing a condenser, a second exchanger composing an evaporator, the system includes:

- a first turbine actuating a first fan causing air circulation on the condenser,

- a second two-phase turbine operating as a pressure regulator actuating a second fan causing air circulation on the evaporator.

The fan wheel is located either in the enclosure to be cooled, such as the enclosure of a refrigerator or freezer, or outside to ventilate the condenser exchange surfaces of a refrigerator for example or the air conditioning system exchange surfaces. In all cases, the two-phase expansion turbine is located in such a way that it can directly drive a fan wheel transferring the air flow on the exchange surface. Advantageously, the system according to the invention is such that: - the axis of the turbine ensuring the two-phase expansion of the refrigerant passes through the body of the turbine,

- The seal between the axis of the turbine and the body of the turbine is achieved by a seal. Advantageously also, in the case of another alternative embodiment, the turbine ensuring the two-phase expansion of the refrigerant actuates the fan by means of a magnetic drive. Thus, the problem of the seal between the body of the turbine and the axis of the turbine is resolved. The invention also relates, in a method for producing cold or heat using a refrigerant according to a thermodynamic cycle comprising at least one liquid-vapor expansion phase, the characteristic step consisting in carrying out said liquid expansion- steam by means of a two-phase turbine actuating a fan causing air circulation on an exchanger. Other characteristics and advantages will appear on reading the description of variants of the embodiment of the invention, given by way of non-limiting example.

FIG. 1a represents the diagram of a conventional refrigeration system and the thermodynamic cycle of said system is represented in FIG. 1b in an entropy temperature diagram (T-s).

FIG. 2a represents the diagram of a refrigeration circuit using two turbine-fans and FIG. 2b represents the thermodynamic cycle of said system in the same T-s diagram. FIG. 3 represents a detailed view of the direct-drive fan-turbine with sealing joint.

FIG. 4 represents another variant of drive by magnetic coupling allowing a high level of sealing.

The classic refrigeration system is presented to allow comparisons with the system with fan turbines and for calculations typical coefficient of performance, given by way of example and showing the energy savings associated with the use of these fan turbines, object of the invention. The cooling performance coefficient is the ratio of the cooling power produced Qo, on the mechanical work W provided, ie COPf = Qo / W. FIG. 1a represents the four conventional components of a refrigeration system, a compressor 1, a condenser 2, a regulator 7 and an evaporator 3. The thermodynamic diagram of FIG. 1b makes it possible to represent the five characteristic points of the cycle. The point Al is at the outlet of the evaporator 3, the point B 1 at the inlet of the compressor 1, the point Cl at the inlet of the condenser 2, the point Dl at the inlet of the regulator 7 and the point El at the inlet of evaporator 3. These points will be used as references for the calculations presented below. Or a domestic refrigerator whose operating conditions are defined by a cycle with an evaporation temperature of -15 ° C and a condensation temperature of 40 ° C. Inside the refrigerator, the difference between the evaporation temperature and the average air temperature is 20 K, that between the average room temperature and the condensation temperature is 15 K. Table 1 indicates the values of the thermodynamic variables allowing the COP of the system to be calculated with R134a (CH2FCF3, tetra-fluoro-di-hydro-ethane) as refrigerant. This fluid is an HFC (hydro-fluoro-carbide) which is the most used refrigerant in domestic cold and automobile air conditioning.

Table 1

The assumptions allowing the calculations are as follows:

• the refrigerant superheat between the outlet of the evaporator Al and the inlet of the compressor B 1 is 20 K; • the sub-cooling to the condenser in Dl is 5 K;

• the reference compression is isentropic and an isentropic compression efficiency is taken into account in the calculations;

• the relaxation of Dl in El is isenthalpe. The actual unit mechanical work (expressed in kJ / kg) is calculated according to formula (1) from the isentropic unit mechanical work and the isentropic yield. A yield of 0.86 was taken into account in this calculation. W _R = W _is / η _is = (h _cl - h _B1 ) / 0.86 = 48.5 kJ / kg (1) COP = Q ₀ / W _R = 139.5 / 48.5 = 2.87

FIG. 2a shows a first turbine 4a (known per se) which drives a fan 5a. This turbine is located between the compressor 1 and the condenser 2. It drives the fan 5a and makes it possible to circulate air on the condenser 2. A second liquid-vapor expansion turbine 4b is shown in FIG. 2a. This two-phase liquid-vapor expansion turbine is located on the part of the circuit where the liquid phase of the refrigerant circulates at the outlet of the condenser 2. It drives a fan 5b which circulates air on the evaporator 3. FIG. 2b allows you to represent the entry and exit points of each of the system components in Figure 2a. The point A2 is at the outlet of the evaporator 3, the point B 2 is at the inlet of the compressor 1, the point C2is is the theoretical outlet point of the compressor 1, C2 _R is the actual outlet point, D2 _R is the actual exit point of the turbine 4a, E2 is the exit point of the condenser 2 (at this point the fluid is in the cooled state), F2 _R is the actual exit point of the liquid two-phase expansion turbine -vapor 4b. In this example, additional expansion by a possible regulator 7 is not taken into account.

Table 2 presents the thermodynamic variables of these different points making it possible to calculate the coefficient of performance of the system equipped with these two fan turbines. For the system with two fan turbines, the fans reduce the temperature differences. On the one hand, the difference between the evaporation temperature and the average air temperature in the refrigerator enclosure is reduced to 10 K (instead of 20 K) for the conventional cycle. On the other hand, in the condenser the condensation temperature is 35 ° C instead of 40 ° C. The condenser outlet temperature is 32 ° C instead of 35 ° C, the sub-cooling is therefore only 3 K. The thermodynamic variables of the different points corresponding to Figure 2b and calculated with R134a are presented in table 2.

Table 2

In the same way as previously, the actual compression work is calculated by taking into account an isentropic compression efficiency which is here taken equal to

0.82 taking into account the compression ratio.

W _R = W _is / η _is = (h _cl - h _B1 ) / 0.82 = (444.9 - 412.2) / 0.82 = 40 kJ / kg (1)

The COP is also calculated.

Qo = ^Π AI - ^h El

COP = Q ₀ / W _R = (394.3 - 240.6) / 40 = 3.84

The COP is improved by around 34% and this is due to two physical phenomena:

• the fans make it possible to reduce the temperature differences between the fluid phase change temperatures and the average outside air temperatures,

• the isentropic expansion of the two-phase turbine 4b constitutes a recovery of mechanical work available, unlike the isenthalpic expansion of the usual systems. There is a difference between turbines 4a and 4b. The turbine 4a consumes mechanical energy which must be produced by the compressor, but this additional mechanical energy can be compensated for by reducing the difference in the refrigerant / air temperature at the condenser. On the other hand, the turbine 4b does not consume additional mechanical energy, but on the contrary uses available mechanical energy and the COP of the cycle is directly improved. For turbines 4a and 4b and taking expansion yields of 0.7, the unitary mechanical work available is respectively 2.3 kJ / kg and 2.7 kJ / kg. For a cooling power of the order of 60 W typical of many refrigerators, the flow rate of R134a is approximately 0.4 g / s. The mechanical ventilation powers available from the two turbines 4a and 4b are respectively 0.9 W and 1 W, which corresponds entirely to the order of magnitude of the mechanical power of the fans necessary for air circulation. on these exchangers. We now describe Figure 3 which shows a detailed view of a fan turbine 4a or 4b. In this figure we recognize the turbine wheel 9, the diffuser

10, the outlet channel 11. The turbine produces mechanical energy which is directly used for driving the fan wheel 5. The drive is done on the same axis 6 (axis 6a for the turbine 4a, axis 6b for the turbine 4b, FIG. 2a). A seal 12 seals between the interior circuit and the exterior volume. In FIG. 4, the same components are recognized, but for sealing reasons, the fan drive 5 mounted on the axis 14 is magnetic (internal core 16a secured to the axis 13 of the turbine, external crown 16b secured axis 14 of fan 5, air gap 17). This magnetic drive makes it possible to have a completely sealed wall 15. The arrows, such as f, appearing in the drawings indicate the direction of circulation of the fluids.

Claims

claims

1. System, in particular refrigeration or air conditioning system, comprising at least one exchanger-evaporator (3) making up an evaporator (3); said system using a refrigerant according to a thermodynamic cycle (fig 2b) comprising at least one liquid-vapor expansion phase; said system being characterized in that the liquid-vapor expansion phase is carried out by means of a two-phase turbine (4b) operating as an expansion valve actuating a fan (5a, 5b) causing air circulation on said exchanger-evaporator (3 ).

2. System according to claim 1 implementing a chain of devices comprising: a compressor (1), a first exchanger composing a condenser (2), a second exchanger composing an evaporator (3); said system being such that it comprises a liquid-vapor expansion phase carried out by means of a two-phase turbine (4b) operating as a pressure reducer, actuating a fan (5b) causing air circulation on the evaporator (3) and / or on the condenser (2).

3. System according to claim 1 implementing a chain of devices comprising: a compressor (1), a first exchanger composing a condenser (2), a second exchanger composing an evaporator (3); said system being such that it comprises:

- A first turbine (4a), located downstream of the compressor (1), actuating a first fan (5a) causing air circulation on the condenser (2).

- a second two-phase turbine (4b) operating as an expansion valve, located upstream of the expansion valve (7) or in the expansion valve (7), actuating a second fan (5b) causing air circulation on the evaporator (3).

4. System according to any one of claims 1 to 3 such as:

the axis (6) of the turbine ensuring the expansion of the refrigerant passes through the body of the turbine, - The seal between the axis (6) of the turbine and the body of the turbine is achieved by a seal (12).

5. System according to any one of claims 1 to 4 such as:

- the turbine ensuring the expansion of the refrigerant actuates the fan (5) by means of a magnetic drive (16a, 16b, 17),

(so that the problem of sealing between the body (15) of the turbine and the axis (13) of the turbine is advantageously resolved).

6. In a process for producing cold or heat using a refrigerant according to a thermodynamic cycle comprising at least one liquid-vapor expansion phase, the characteristic step consisting in carrying out said liquid-vapor expansion by means of '' a two-phase turbine (4b) actuating a fan (5b) causing air circulation on an exchanger-evaporator (3).