KR0126550B1 - Trans-critical vapour compression cycle device - Google Patents

Abstract

No content

Description

[Name of invention]

Capacity adjusting method of steam compression cycle and vehicle air conditioner including the cycle

[Brief Description of Drawings]

1 is a schematic diagram of a conventional (less than critical) steam compression cycle apparatus.

2 is a schematic diagram of a trans-critical vapor compression cycle apparatus constructed in accordance with a preferred embodiment of the present invention. This embodiment is an integral part of the evaporator system and includes a volume for holding the refrigerant in the liquid state.

3 is a schematic diagram of a trans-critical vapor compression cycle apparatus constructed by a second embodiment of the present invention. This embodiment includes an intermediate pressure receiver connected directly to the flow circuit between two valves.

4 is a schematic diagram of a trans-critical vapor compression cycle apparatus constructed in accordance with a third embodiment of the present invention. This embodiment includes a special receiver that keeps the refrigerant in the liquid state or in the supercritical state.

5 is a graph showing the relationship between pressure and enthalpy in the trans-critical vapor compression cycle apparatus of the second, third and fourth degrees under different operating conditions.

6 is a graph showing the control of the freezing capacity by the pressure control method according to the present invention. The results shown are measured in a laboratory experimental system assembled according to a preferred embodiment of the present invention.

7 is a graph showing control of the freezing capacity by controlling the amount of heat exclusion according to the present invention. The results shown are measured in a laboratory experimental system assembled according to a preferred embodiment of the present invention.

FIG. 8 is an experimental result showing the relationship between temperature and enthalpy in the trans-critical vapor compression cycle apparatus of FIG. 2 operating at different high side pressures while using carbon dioxide as a refrigerant.

Detailed description of the invention

[Field of Invention]

FIELD OF THE INVENTION The present invention relates to steam compression cycle devices such as refrigerators, air-conditioning devices and heat pumps using refrigerants operating under trans-critical conditions in a closed circuit, and in particular, to adjust and control the capacity of such devices. It is about how to.

[Background of invention]

1 shows the main part of a conventional steam compression cycle apparatus for the purpose of refrigeration, air conditioning or heat pump. The apparatus consists of a compressor 1, a condensation heat exchanger 2, a throttle valve 3 and an evaporation heat exchanger 4. These components are connected to a flow closed circuit where the refrigerant is circulated. The principle of operation of the steam compression cycle system is as follows. The pressure and temperature of the refrigerant vapor are increased by the compressor 1 before entering the condenser, condenser 2, and then cooled and condensed in the condenser 2, releasing heat to the secondary coolant. Then, the high pressure liquid refrigerant is throttled or throttled to the evaporation pressure and temperature by the expansion valve 3. In the evaporator 4, the refrigerant boils and absorbs heat from its surroundings. At the outlet of the evaporator, steam is drawn into the compressor, completing the cycle.

Conventional steam compression cyclers utilize refrigerants (eg, R-12, CF ₂ Cl ₂ ) that operate entirely at sub-critical pressures, ie below the critical pressure. Many different materials or mixtures of materials may be used as the refrigerant. Since the critical temperature of the fluid sets an upper limit for condensation to occur, the choice of refrigerant is influenced by the condensation temperature along with other factors. In order to maintain reasonable efficiency, it is usually desirable to use a refrigerant whose critical temperature is at least 20-30K higher than the condensation temperature. Typically critical approximate temperatures are avoided in the design and operation of conventional systems.

This technique is described in detail in the literature, for example in the Handbooks of American Society of Heating, Refrigerating and Air Conditioning Engineers Inc., Fundamentals 1989 and Refrigeration 1986. It is described.

The ozone depletion of today's common refrigerants (halocarbons) has led to strong international action to reduce or limit the use of these refrigerants, and as a result, there is an urgent need to find alternatives to current technologies. It is becoming.

The capacity control of a conventional vapor compression cycle apparatus is mainly achieved by adjusting the mass flow rate of the refrigerant passing through the evaporator, which is done, for example, by throttle control or bypass operation of the compressor capacity. These methods include issues such as more complex flow circuits, the need for additional equipment or accessories, reduced partial load efficiency, and other complexity.

A common type of fluid regulator is a thermostatic expansion valve, which is controlled by overheating at the evaporator outlet. Proper valve actuation with variations in operating conditions is achieved by using a substantial portion of the evaporator to overheat the refrigerant, resulting in a lower heat transfer coefficient.

Moreover, since heat rejection in the condenser of the conventional steam compression cycle apparatus is mainly generated at a constant temperature, the thermodynamic loss imparts heat to the secondary coolant by a large temperature increase as in the heat pump application. When or when the useful secondary coolant flow rate is small, it occurs due to a large temperature difference.

In the past, some operations of steam compression cycles under trans-critical conditions were carried out. Until halocarbon became available 40 to 50 years ago, CO ₂ was generally used as a refrigerant in food and cargo ship refrigeration. The system was designed to operate normally below the critical pressure by evaporation and condensation. In general, when a vessel passes through a tropical region, the cooling sea water temperature is too high to condense to normal, so that the device operates in high-side super-critical conditions. There was (critical temperature to 31 ° C. for CO ₂ ). In this state, in order to maintain the refrigeration capacity at a reasonable level, the filling amount of the refrigerant at the high-side was increased to the point where the pressure at the outlet of the compressor is increased to 90 to 100 bar. Refrigeration techniques by CO ₂ are described in classical literature such as "Kalteprozesse" (Springer 1933) by P. Ostertag, or "Refrigeration Engineering" (Hiley 1973) by HJ MacIntire.

A common practice in conventional CO ₂ systems has been to add the special filling required from a separate storage cylinder. In a conventional method, a receiver mounted after the condenser may not provide the functionality intended by the present invention.

Another method of increasing the capacity and efficiency of a given steam compression cycler, operating at supercritical high-side pressures, is known from the specification of German Patent No. 278095 (1912). This method involves two-stage compression with intermediate cooling in the supercritical region. Compared to standard systems, this requires the installation of additional compressors or pumps and heat exchangers.

W.B Gosney's The Principles of Refrigeration (University of Cambridge, 1982) presents some characteristics of critical approximate pressure operation. The implication here is that an increase in the refrigerant charge on the high pressure side can be achieved by temporarily shutting off the expansion valve and transferring some charge from the evaporator. However, this causes a lack of liquid in the evaporator, which causes a decrease in capacity at the most desirable time.

Although it was conceivable to use carbon dioxide as a refrigerant to achieve supercritical pressure at the high side of the vapor compression cycle, no solution could be found for adjusting the refrigeration capacity, and nothing was specified.

[Purpose of invention]

Accordingly, it is an object of the present invention to provide a novel, improved, simple and efficient means capable of adjusting and controlling the capacity of a trans-critical vapor compression cycle apparatus while avoiding the above-mentioned problems and disadvantages in the prior art.

It is a further object of the present invention to provide a vapor compression cycle, which avoids the use of CFC refrigerants and can apply several refrigerants which are good for safety, environmental hazards and cost.

It is still another object of the present invention to provide a novel capacity control method, which mainly includes operation at a constant mass flow rate of refrigerant and simple capacity adjustment by valve operation.

Moreover, another object of the present invention is to provide a cycle for rejecting heat at the gliding temperature, and when the secondary coolant flow rate is small, or when the secondary coolant is heated at a relatively high temperature, heat exchange To reduce the loss.

[Overview of invention]

The above and other objects of the present invention are directed to trans-critical conditions (ie supercritical highside pressure, sub-threshold low) in which thermodynamic properties in the supercritical state are utilized in controlling the refrigeration and heating capacity of the device. By providing a method that is typically operated at low-side pressure.

The present invention involves the adjustment of specific enthalpy at the evaporator inlet by the deliberate use of pressure and / or temperature before throttling for capacity control. The capacity is controlled by varying the enthalpy difference of the refrigerant in the evaporator and by changing the specific enthalpy of the refrigerant before the throttle operation. This can be done by varying the pressure and temperature independently in the supercritical state. In a preferred embodiment, this specific enthalpy is adjusted by changing the pressure before the throttle operation. The refrigerant is cooled by the effective cooling medium as much as possible, and the pressure is adjusted to give the required enthalpy. Another embodiment includes adjusting the enthalpy by changing the refrigerant temperature prior to the throttle operation, which is done by controlling heat removal from the device.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail with reference to FIGS. 1-8.

Detailed description of the invention

The trans-critical steam compression cycle apparatus according to the present invention includes a refrigerant in which the critical temperature is between the heat inlet temperature and the average temperature of the heat outlet and the working fluid closed circuit in which the refrigerant is circulated.

Suitable working fluids include, for example, ethylene (C ₂ H ₄ ), diborane (B ₂ H ₆ ), carbon dioxide (CO ₂ ), ethane (C ₂ H ₆ ), and nitrogen oxides (N ₂ O).

The working fluid closed circuit consists of a refrigerant flow loop with an integral storage segment. 2 shows a preferred embodiment of the invention in which the storage segment is an integral part of the evaporator system. The flow circuit includes a compressor 10 connected in series with the heat exchanger 11, a counter flow heat exchanger 12, and a throttle valve 13. The throttle valve can be replaced with any expansion device. Low compression of the evaporative heat exchanger 14, the liquid separator / receiver 16, and the counterflow heat exchanger 12 is circulated between the throttle valve 13 and the inlet 19 of the compressor 10. It is. The liquid receiver 16 is connected to the evaporator outlet 15 and the gaseous outlet of the receiver 16 is connected to the counterflow heat exchanger 12.

The counterflow heat exchanger 12 is not absolutely necessary to achieve the function of the apparatus, but increases its efficiency, in particular its response to increasing capacity requirements, and also serves to return oil to the compressor. To this end, the liquid line from the receiver 16 (dotted line in FIG. 2) is at point 17 in front of or opposite to the counterflow heat exchanger 12, or any point between these points. In position it is connected to the suction line. The liquid flow rate, i.e., the refrigerant and the oil, is controlled by a suitable conventional liquid flow rate controller (not shown). By introducing a predetermined excess liquid refrigerant into the steam line, a liquid excess at the evaporator outlet is achieved.

3 shows a second embodiment of the invention, wherein the storage segment of the working fluid circuit comprises a receiver 22 integrated in the flow circuit, between the valve 21 and the throttle valve 13. The other components 10-14 of the flow circuit are the same as in the above embodiment, but the heat exchanger 12 can be omitted without producing any significant consequences. The pressure in the receiver 22 is maintained in the middle of the high side pressure and the low side pressure of the flow circuit.

4 shows a third embodiment of the present invention wherein the storage segment of the working fluid circuit comprises a special receiver 25 in which the pressure is maintained between the high side pressure and the low side pressure of the flow circuit. The storage segment also has a valve 23 and a valve 24 connected to the high and low pressure portions of the flow circuit, respectively.

Explain the action. The refrigerant is compressed in the compressor 10 to an appropriate supercritical pressure, and the compressor outlet 20 is shown as state a in FIG. The refrigerant is circulated through the heat exchanger 11 and cooled there to state b, releasing heat into a suitable coolant, such as cooling air or water. If desired, the refrigerant may be further cooled to state c in inward heat exchanger 12 before throttled to state d. Due to the pressure drop in the throttle valve 13, as shown in FIG. 3 as state d, a two-phase mixture of gas / liquid is formed. The refrigerant absorbs heat by evaporation of the liquid phase in the evaporation heat exchanger (14). From the state e at the evaporator outlet, the vapor of the refrigerant may be superheated from the counterflow heat exchanger 12 to the relative f before entering the compressor inlet 19, and the cycle is completed by the inlet to the compressor inlet 19. do. In the preferred embodiment of the present invention, as shown in FIG. 2, the state e of the evaporator outlet is in the two-phase region state due to the excess liquid state at the evaporator outlet.

Adjustment of the capacity of the trans-critical cycler is achieved by changing the state of the refrigerant at the evaporator inlet, i.e. point d in FIG. The freezing capacity per unit mass flow rate of the refrigerant, ie the predetermined freezing capacity, corresponds to the enthalpy difference between states d and e. This enthalpy difference is shown in FIG. 5 as the horizontal length of the enthalpy-pressure plot.

Since the throttle operation is an enthalpy process, the enthalpy at point d is the same as the enthalpy at point c. As a result, the refrigeration capacity kW at a constant refrigerant mass flow rate can be controlled by changing the enthalpy at point c.

Note that in the trans-critical cycle, it should be noted that the refrigerant vapor in the high pressure single phase does not condense, but the temperature drops in the heat exchanger 11. The final temperature of the refrigerant in the heat exchanger (point b) is several degrees higher than the temperature of the inlet cooling air or the water temperature when the counterflow is used. And the high pressure steam can be cooled to a few degrees lower point c in the counterflow heat exchanger 12. However, at a constant cooling air or water inlet temperature, the temperature at point c becomes mostly constant irrespective of the pressure level at the high side.

Therefore, adjustment of the device capacity is achieved by changing the pressure at the high side in a state where the temperature at point c is almost constant. The curvature of the isotherm near the critical point causes a change in enthalpy due to pressure, as shown in FIG. 5 shows a reference cycle (abcdef), reduced capacity cycle (a'-b'-c'-d'-ef) due to lowering the high side pressure, and increased capacity cycle due to high pressure at the high side. (abcdef) is shown. The evaporator pressure is assumed to be constant.

The pressure on the high pressure side (high pressure side) is independent of temperature because the high pressure side is filled with single phase fluid. In order to change the pressure, it is necessary to change the mass of the refrigerant on the high side, that is, to add or remove a predetermined amount of the instantaneous refrigerant charge amount on the high side. These changes must be handled by a buffer to avoid overflow of the liquid or drying of the evaporator.

In the preferred embodiment of the present invention shown in FIG. 2, the refrigerant mass of the high side can be increased by temporarily decreasing the opening degree of the throttle valve 13. Due to the incidentally reduced refrigerant flow rate to the evaporator, the amount of excess liquid at the evaporator outlet 15 is reduced. However, the liquid refrigerant flow rate flowing from the receiver 16 to the suction line is constant. As a result, the balance between the flow rate of the liquid into and out of the receiver is changed, so that the liquid content (inventory amount) of the receiver is reduced, and correspondingly the refrigerant accumulates at the high pressure side of the flow circuit.

Increasing the refrigerant charge on the high side increases the pressure, thus accompanied by an increase in refrigeration capacity. Mass transfer from the low pressure side to the high pressure side of this circuit continues until a balance develops between the refrigeration capacity and the load.

Since the amount of evaporation of the refrigerant is almost constant, the amount of excess liquid at the evaporator outlet 15 is increased by opening the throttle valve 13. The difference between the liquid flow rate flowing into the receiver and the fluid flow rate from the receiver to the suction line is accumulated. As a result, the refrigerant charge amount is transferred from the high side to the low side of the flow circuit, stored in the liquid state at the receiver, and the high side charge amount is reduced. By reducing the high side charge, and thus reducing the pressure, the capacity of the device is reduced until a balance is found.

In addition, some amount of liquid transfer from the receiver to the compressor suction line is necessary to avoid the accumulation of lubricant in the liquid phase of the receiver.

In the second embodiment of the present invention shown in FIG. 3, the refrigerant mass at the high side is controlled by simultaneously shutting off the valve 21 and adjusting the throttle valve 13 to provide a sufficient liquid flow rate to the evaporator. Can be increased. This reduces the flow rate of the refrigerant from the high side to the receiver via the valve 21, in which case the refrigerant mass is transferred from the low side to the high side by the compressor.

Reduction of the high side filling amount is achieved by opening the valve 21 while maintaining a substantially constant flow rate through the throttle valve 13. This transfers the mass from the high side of the flow circuit to the receiver 22.

In the third embodiment of the present invention shown in FIG. 4, the refrigerant mass of the high side can be increased by opening the valve 24 and simultaneously reducing the flow rate through the throttle valve 13. As a result, the refrigerant charge amount is accumulated in the high pressure side by the decrease in the flow rate passing through the throttle valve 13. Sufficient liquid flow to the evaporator is obtained by opening the valve 24.

Reduction of the high side charge amount can be achieved by opening the valve 23 to transfer a predetermined amount of refrigerant charge amount from the high side to the receiver. Thus, capacity control of the device can be achieved by operating the throttle valve 13 while adjusting the valve 23 and the valve 24.

The preferred embodiment of the present invention shown in FIG. 2 has the advantage that the capacity control is simple if the valve alone is operated. Moreover, the trans-critical vapor compression cycle apparatus assembled according to the present embodiment is adapted to adapt to fluctuations in the cooling load by a change in the liquid content of the receiver 16 accompanied by a change in the refrigerant charge amount on the high side, and thus the cooling capacity. Thus, it has a certain self adjusting capacity. Moreover, the desired heat transfer properties are imparted by the operation of having excess liquid at the evaporator outlet.

The second embodiment shown in FIG. 3 has the advantage of simple valve operation. Only the valve 21 adjusts the pressure of the high side of the apparatus, and the throttle valve 13 alone ensures sufficient supply to the evaporator. Thus, conventional thermostatic valves are used for throttle operation. The return of oil to the compressor is easily accomplished by flowing the refrigerant through the receiver. However, this embodiment does not impart a capacity control function at high side pressures lower than the critical pressure. The volume of the receiver 22 only needs to be relatively large since it only runs between the terminal outlet pressure and the liquid line pressure.

Yet another embodiment, shown in FIG. 4, has the advantage that when operated in a steady state, it is operated as a conventional vapor compression cycle apparatus. The valve 23 and the valve 24 connecting the receiver 25 to the flow circuit are only operated during capacity control. This embodiment requires the use of three different valves during capacity change.

The latter two embodiments have the drawback that the pressure of the receiver is high when compared with the first preferred embodiment. However, the differences between the individual systems in terms of design and operating characteristics are not very important.

The trans-critical vapor compression cycle apparatus assembled by the embodiments described so far may be applied to various fields. The technology is well suited for small and medium-sized fixed air conditioning units (air-con units), movable air-conditioning units, small and medium-sized refrigerators / refrigerators, small heat pumps and units. One of the most promising applications is in automotive air conditioners, where there is an urgent need for new, non-CFC, lightweight and efficient alternatives to R12 systems.

The above-described embodiments of the present invention are merely illustrative, and do not limit the present invention. On the other hand, it is possible to control the capacity of the trans-critical cycle apparatus by maintaining the high side pressure mainly constant and adjusting the refrigerant temperature before the throttle operation (state c) by varying the circulation speed of cooling air or water, that is, the flow rate. You can also see that. By reducing the flow rate of the cooling fluid, ie air or water, the temperature before the throttle operation will increase and the capacity will decrease. Increasing the flow rate of the cooling fluid will lower the temperature before the throttle operation, thus increasing the capacity of the device. It is also possible to combine pressure and temperature control.

Examples

Practical application of the present invention to refrigeration or heat pumps has obtained experimental results from a trans-critical vapor compression cycle apparatus assembled with carbon dioxide (CO ₂ ) as a refrigerant and assembled according to the embodiment of the present invention shown in FIG. It will be described in the following embodiments.

The laboratory experimental system uses water as the heat source, ie the water is cooled by heat exchange with boiling CO ₂ in the evaporator 14. Water is also used as coolant and is heated by CO ₂ in heat exchanger (11). The experimental system includes a 61 ccm reciprocating compressor 10 and a receiver 16 with a total volume of 4 liters. The system also includes a counterflow heat exchanger 12 and a liquid line connection from the receiver to point 17, as shown in FIG. The throttle valve 13 is operated manually.

Example 1

This example shows how the refrigeration capacity is controlled by changing the position (openness) of the throttle valve 13 and thereby changing the pressure at the high side of the flow circuit. The change in high side pressure controls the specific enthalpy of the refrigerant at the evaporator inlet and consequently the refrigeration capacity at a constant mass flow rate.

The water inlet temperature for the evaporator 14 is kept constant at 20 ° C and the water inlet temperature for the heat exchanger 11 is kept constant at 35 ° C. The circulation of water is kept constant in both the evaporator 14 and the heat exchanger 11. The compressor runs at a constant speed.

6 shows the fluctuation of the refrigerating capacity Q, the axial load of the compressor, the high side pressure PH and the CO ₂ mass flow rate m when the throttle valve 13 is operated as shown in the upper part of the figure. indicates the liquid level (h) in the CO ₂ temperature (Tb) and the receiver in the CO ₂ temperature (Te), the heat exchanger 11, the outlet of the evaporator outlet. Adjustment of the throttle valve position is by manual operation only.

As shown in the figure, the refrigerating capacity Q is easily controlled by operating the throttle valve 13. It is also clear from the figure that the mass flow rate m of the circulating CO ₂ in the stable state is mainly constant and independent of the cooling capacity. The CO ₂ temperature Tb at the outlet of the heat exchanger 11 is also generally constant. The graphs show that the change in capacity is simply the result of changing the high side pressure (PH).

As can also be seen from the diagram, the increased high side pressure is accompanied by a decrease in the receiver liquid level h due to the transfer of the CO ₂ charge to the high pressure side of the circuit.

Finally, it can be noted that the temporary period during the increase in capacity does not include significant overheating at the evaporator outlet, ie only a small fluctuation in Te.

Example 2

If the water inlet temperature for the heat exchanger 11 is higher (eg higher ambient temperature), it is necessary to increase the high side pressure to maintain a constant freezing capacity. Table 1 shows the test results operated in a state where the water inlet temperature tw for the heat exchanger 11 is different.

The water inlet temperature for the evaporator is kept constant at 20 ° C. and the compressor runs at constant speed.

As shown in Table 1, the refrigeration capacity can be maintained substantially constant by increasing the high side pressure as the ambient temperature rises. As shown, the frozen mass flow rate is generally constant. The increased high side pressure is accompanied by a decrease in the receiver liquid content as indicated in the liquid level column.

TABLE 1

Example 3

This example shows the possibility to control and adjust the capacity of the device by keeping the high side pressure constant and by adjusting the flow rate of the coolant (eg air or water) circulating through the heat exchanger 11.

FIG. 7 shows the change in the freezing capacity Q when the circulation rate of the cooling water, that is, the flow rate m _w , is adjusted as shown in the upper part of the figure. The mass flow rate m of CO ₂ , the high side pressure PH and the water inlet temperature ti for the heat exchanger 11 are kept constant. The compressor operates at a constant speed and the temperature and flow rate of the water entering the evaporator are kept constant.

As shown in the figure, the freezing capacity is easily controlled by varying the flow rate of water and the mass flow rate of CO ₂ is generally constant.

Example 4

8 is a graph showing the trans critical cycle in the entropy / temperature plot. The cycle shown in the diagram is based on measurements in a laboratory experimental system obtained during operation at five different high side pressures. The evaporator pressure is kept constant and the refrigerant is CO ₂ .

The diagram shows that the capacity control principle, which represents the change in specific enthalpy h at the evaporator inlet caused by the change in high side pressure P, is good.

Claims (9)

On the high pressure side of the steam compression cycle, a series-connected compressor 10, cooler 11, throttling means 13 and evaporator 14 are formed to form an integrated closed circuit operated at supercritical pressure. In the capacity adjustment method of the steam compression cycle comprising: the capacity adjustment is performed by changing the instantaneous refrigerant charge amount on the high pressure side of the closed circuit by changing the liquid inventory amount of the refrigerant receiver installed in the closed circuit. To adjust the capacity of a steam compression cycle. The low pressure refrigerant receiver (10) according to claim 1, wherein the capacity adjustment is based on the adjustment of the supercritical pressure, and is arranged between the evaporator (14) and the pressure gauge (10) using only the throttle means (13) as the capacity adjustment means. 16. A capacity adjustment method for a steam compression cycle, characterized by changing the liquid stock amount of 16). The method according to claim 1, wherein the instantaneous change in the refrigerant charge amount on the high pressure side of the circuit is adjusted by the receiver 21 provided in the circuit between the valve 21 and the throttling means 13 by adjusting the valve 21 and the throttle means 13. A method of adjusting the capacity of a steam compression cycle, which is achieved by varying the amount of supercritically pressurized refrigerant charge in a). The method of claim 1, wherein the instantaneous change of refrigerant charge on the high pressure side of the circuit is transferred to a storage device (25) connected to the high and low pressure sides of the circuit by pipes having valves (23, 24). Vapor compression, characterized by continuing to adjust the charging of the refrigerant or removal of the refrigerant from the storage device 25 and by maintaining the pressure in the storage device between the high side pressure and the low side pressure. How to adjust the capacity of the cycle. 5. The heat exchanger according to claim 2, wherein the outlet condition of the evaporator is maintained as a two-phase mixture of vapor and liquid and provides a liquid surplus to the low pressure inlet of a further heat exchanger 12. And the low pressure refrigerant at 12 is evaporated and superheated by heat from the high pressure refrigerant before entering the compressor. The method of any one of claims 1 to 4, wherein the refrigerant is carbon dioxide. In an automotive air conditioning apparatus comprising a compressor 10, a cooler 11, a throttle means 13 and an evaporator 14 connected in series to form an integrated closed circuit, the refrigerant is compressed to supercritical pressure on the high pressure side of the closed circuit. The throttling means 13 adjusts the capacity of the apparatus by causing a change in the supercritical high side pressure by changing the liquid stock of the low pressure refrigerant receiver 16 disposed between the evaporator 14 and the compressor 10. Automotive air conditioning apparatus, characterized in that applied to. 8. The heat exchanger (12) according to claim 7, further comprising a heat exchanger (1) having a low pressure inlet (17) in communication with the receiver (16) and a high pressure inlet in communication with an outlet of the cooler (11). ) Is disposed in the circuit between the receiver (16) and the compressor (10). The vehicle air conditioner according to claim 7 or 8, wherein the refrigerant is carbon dioxide.