WO2001057454A1

WO2001057454A1 - Refrigerating apparatus

Info

Publication number: WO2001057454A1
Application number: PCT/PL2001/000011
Authority: WO
Inventors: Andrzej Sokulski
Original assignee: Andrzej Sokulski
Priority date: 2000-02-07
Filing date: 2001-02-07
Publication date: 2001-08-09
Also published as: AU3250001A; PL338281A1

Abstract

Refrigerating apparatus comprising a compressor (1), a condenser (2), a receiver (2a), a controllable-throttling element (5), an evaporator (3), connecting tubes (10, 11, 12, 13) and also an internal regenerative heat exchanger (8), built of tube segment (14, 15) in which wet refrigerant vapour from the evaporator (3) flows through the tube segment (14) from an inlet (10i) to an outlet (11o) and changes to dry vapour by exchanging heat with liquid refrigerant from the receiver (2a) which flows through the tube segment (15) from an inlet (12i) to an outlet (13o). A sensor (6) of the the controllable-throttling element (5) is attached to the tube (11) connecting the said heat exchanger (8) and the compressor (1) near to the common contact of the tube segments (14, 15). Several examples for the configuration of the heat exchanger (8) are described.

Description

Refrigerating apparatus

This invention relates to a refrigerating apparatus that comprises a compressor, a condenser, a controllable-throttling element, especially a thermostatic expansion valve, an evaporator and tubes connecting in sequence the said assemblies into a close circuit, which inside a refπgerant flows. Moreover there may be provided a liquid receiver placed between the condenser and the throttling element.

The refrigerating apparatus comprises also an additional separated evaporator section, which is called an internal regenerative heat exchanger, used for overheating of vapor returning to the compressor necessary from the point of view to avoid unsafe operation when wet vapor reaches the compressor. The refrigerating apparatus is characterized by higher efficiency and better performance in wide range of applied temperatures.

The present invention is described in details with reference to conventional refrigerating apparatus, but it is obvious that it may be used much wider. For example, it is possible to take advantage of the new idea in air-conditioning systems, heat pumps and others operating according to Carnot cycles.

The refrigerating apparatus is based on principle of heat absorbing by its low temperature side and heat release by high temperature side. The needed for such operation energy is provided to an engine, which powers the compressor. The compressor draws in the refrigerant vapor and compress to a higher pressure. The compressed refrigerant vapor is directed to the condenser where vapor is condensed and the condensation heat is withdrawn. Then the liquid refrigerant is collected, especially in the liquid receiver and whence it flows via expansion means to the evaporator. The heat is delivered to the evaporator from outer medium and in this way the refrigerant may evaporate. As a result the outer medium is cooled. The compressor for recirculating in the close circuit draws in the evaporated refrigerant in vapor phase.

A heat amount absorbed in the evaporator from the outer medium is equal to a heat amount necessary for phase change of the refrigerant from liquid or mixed to vapor at estimated, almost constant evaporation temperature plus some additional heat amount, which rises up its temperature above the said evaporation temperature. And this difference of temperatures is the said overheating and is measured in degrees. In commonly used refrigerating apparatuses the evaporators are built of coils, which are numerous sometimes. The coils are connected parallel in the purpose to gain significant amount of heat absorbed by the evaporator without unnecessary increase of their elongation, which normally leads to large pressure drops, effecting in decrease of the apparatus performance. The coils are supplied with the refrigerant by means of a common expansion valve followed by a liquid distributor that is provided to possibly equally distribute the refrigerant to the inlets of the said coils. The coil outlets are connected to a header directing flow through tubes to the compressor.

Independently from efforts to achieve equal distribution of the refrigerant to each coil by the distributor provided with proper geometric sizes and proper flow pressure drops there are significant differences in the refrigerant amount evaporated in each coil due to distinct heat transfer condition and some irregularities in flow pressure drops in each coil.

As a result, the coils that absorb smaller amount of heat allow to the refrigerant flow in liquid phase along longer segment of the coil. Since the built-in controllable-throttling element, with its sensor, that is responsible to the temperature assuring evaporation of the refrigerant in full before it reaches the mentioned compressor, is situated on the tube leading to the compressor, the said element may control the feeding operation with the refrigerant of the evaporator with respect to that coil, which absorbs the smallest amount of heat. When at the outlet of that coil there will show up some liquid amounts, that is wet vapor, the valve will close or reduce the flow. In the situation, other coils would not receive enough of the refrigerant comparing to possibility of its evaporation or possible heat amount absorbed. There are usually more coils that are fed insufficiently, and then in other words, there is significant reduction in heat performance of the evaporator. Some experiments and some publication, as well show there is around 30 % performance drop, especially when the evaporators work with small temperature differences between evaporation and that of outer medium. But on other hand, the said small temperature differences are substantial when good performance of the refrigerating apparatus is to be obtained.

To achieve good heat transfer and maximum performance of the refrigerating apparatus the coils should be wetted inside by the liquid refrigerant along their whole length. But due to necessity of the overheating there is always some part of the coil dried inside. And that is usually up to 25 % of its length when the evaporator operates with the said small temperature differences and this refers to that coil which is fed with sufficient amount of liquid. However, this length in the case of insufficiently fed coils is even greater. The heat transfer when the vapor overheating takes place is less intensive when compared to evaporation of the liquid, then the heat amount usually absorbed is smaller than it could be, especially when evaporation would take place along the whole length of all coils.

If there are in use simple thermostatic expansion valves, then conditions of operation of the evaporator are subject to fluctuation in consequence of long time necessary for respond and some instabilities of its operation, when the overheating is set at too small value. Then in the case, the said small temperature difference has to be estimated on higher level but this reduce the refrigerating apparatus performance. There are some partial solutions to the problem when electronic expansion valve are employed, but this leads to high prices of components which result in no sense to provide such equipment in smaller refrigerating apparatuses. Moreover, the said thermostatic expansion valves have features of narrow control range for narrow flow range then they have to suit to the evaporator very well and to set at properly estimated values of the overheating, which is a time consuming job.

Efficient utilization of evaporator surface means that sufficiently large amount of liquid must be supplied via the expansion valve, which may be evaporated at the said small temperature difference. But the vapor has to be overheated before it reaches the compressor.

It is known in the art that commonly used thermostatic expansion valve operates stably no till then overheating is set at higher value that it is necessary to prevent from drawing into the compressor wet vapor and that further decreases the apparatus performance. The other reason of the said instability is in fact that there is a flow of non-sub cooled liquid with vapor bubbles in directly before the expansion valve. To avoid this additional problem there is provided between the expansion valve and the condenser or the liquid receiver, if such is employed, an internal heat regenerative exchanger. Available on market examples may be characterized as having significant flow resistance for the refrigerant and complex structure guiding to high prices. The high pressure drops eliminate the opportunity to include this additional exchanger into range of control of the valve, and then level of further overheating would be out of the control. If the value of the overheating is high, a temperature of the operating compressor will rise up significantly leading to rarefaction of lubricating oil and in consequence, deterioration of lubrication and that may cause premature wear of the compressor or even its breakage. If the value of the overheating is set at lower level and the flow resistance is low, as well, when for example, there are employed internal heat regenerative exchangers of tank type, then except their high prices they have another fault which is tendency to stop of oil flow returning from the circuit to the compressor. To keep the apparatus running safe a need of oil separator in the system is very serious.

In conclusion, there is advantageously to obtain a minimal overheating with sub cooling of the liquid before the expansion valve at the same time, whereas to maintain this overheating a source of heat is preferred at higher temperature than that of the outer medium, especially if the last flows around the evaporator and that is proposed by this invention.

The aim of this invention is to provide modified refrigerating apparatus, in which final evaporation and the said overheating take place outside the evaporator employed to cool the outer medium and this process is intensify. The evaporator without overheating zone is more effective. Also shortened coil lengths of about 25 to 30 % lead to decrease in pressure drops not only inside that of the refrigerant flow but of the outer medium flow, as well. When the outer medium flow is with lower pressure drop then with the same energy- applied to cause that flow, so speed of the flow is higher and that rises up heat transfer, in general. The exchanger is of smaller sizes then if frost shows up, necessary defrost operation is improved. Also the system performance is improved.

The following goal is to achieve the said overheating with exchanger of simple structure, which range of operation would be wide enough, so that a selection of sizes for estimated heat loads would be easier. And on other hand the outer sizes of the new exchanger would be small enough, so that without any additional effort it could be placed in traditional housing of the evaporator, without any enlargement of that, as well.

The next aim is to assure very equal and stable flow of the lubricating oil returning to the compressor without any fear that any small size holes usually provided in tank type heat regenerative exchangers would be blocked.

The next purpose of the invention is to increase a range of stable operation of the evaporator when small overheating is requested and to limit influences of unequally fed with the liquid refrigerant coils on the evaporator heat performance.

These aims are achieved with the novel refrigerating apparatus made upon this invention with the internal heat regenerative exchanger made in a shape of arc of two tubes which are in thermal contact along at least some of their length and in one of tubes the refrigerant vapor from the said evaporator header of the coils outlets flows to the compressor and in the other tube the liquid refrigerant from the condenser or the liquid receiver flows to the expansion valve.

The vapor leaving coils at their outlet is substantially wet and flows to the coil header being in a shape of a tube of larger diameter than that of the coils and when the tube is arranged horizontally the wet vapor falls quickly into layers of vapor and of liquid rich with oil. The vapor stream flows in upper part of the tube and the liquid with oil stream in the lower part. When these streams get into horizontally arc bent tube segment the liquid is getting dissipated over the most of the internal tube circumference leaving its lower part position. As a result, it is achieve pretty good wetting of inner tube surface with small amount of liquid in the flow. Since the inner tube surface is large then the heat transfer may be much intensified in short distance of the tube and the final vaporization may last short. On the other hand, in second tube in opposite direction from condenser liquid flows which temperature is much higher than that of the outer medium being cooled. Because the second tube is in direct thermal contact with the first one, then there is a heat exchange between the flows and this heat exchange is much intensify due to higher temperature differences than in the case when the said small temperature difference of the evaporator operation condition is applied.

The dissipated liquid stream evaporates fast and changes into vapor and a slower oil flow of film type whereas the last one without any obstructions moves to the outlet from the arc. On the one hand, this oil stream is heated to temperature much higher than that of the very slightly overheated vapor, so in consequence of small mass flux density of oil and its small value of specific heat the oil may be further cooled down by the vapor flow. On the other hand, the film flow of oil insulates partially the vapor flow from getting overheated, what when the length of the arc of the heat exchanger is short provides very slight overheating of the vapor.

When the exchanger is in form of the arc, it is easier to place it inside an evaporator housing and it may be used a regular thermostatic expansion valve with standard sensor, which may be situated at the exchanger end in a way. So it will measure the tube wall temperature, which is close to the temperature of oil. This oil temperature is higher than the temperature of vapor flow and this way when small overheating is achieved the level of signals from the valve sensor is in the range of its very stable operation.

More positive features flowing out of application of the novel refrigerating apparatus will be apparent from detail description of embodiments of the invention, which are introduce in drawings: fig. 1 presents prior art on the scheme of the refrigerating apparatus, fig. 2 shows the novel refrigerating apparatus, fig. 3 illustrates the first embodiment of the internal heat regeneration exchanger applied in the refrigerating apparatus, a side view, fig. 4 is a top view of the exchanger from fig. 3, fig. 5 is the second embodiment of exchanger upon the invention, fig. 6 is the third embodiment of the exchanger upon the invention, fig. 7 is the forth embodiment of the exchanger upon the invention, fig. 8 is the fifth embodiment of the exchanger upon the invention, fig. 9 is the sixth embodiment of the exchanger upon the invention.

In fig.1 there is illustrated example of prior art refrigerating apparatus in a scheme. The apparatus consists of a compressor 1, a condenser 2, a liquid receiver 2a, which is optional, an evaporator 3 and a controllable-throttling element 5. The evaporator is made of a single heat exchanger 4, placed usually in a housing 9. For better understanding, there is shown an internal heat regenerative exchanger 8 situated outside the evaporator housing and away from place where a sensor 6 of a thermostatic expansion valve is attached to tube 10 leading to the compressor. The exchanger 8 is connected by tube 11 to a suction port of the compressor. The exchanger of this kind of operation is usually omitted and for this reason, the connection 9f, 9g in points a, b, c and d, respectively for the vapor and liquid lines are used.

In turn the exchanger 4 is built of at least one coil 4a, which inside an evaporation of the refrigerant takes place. The part of the coil shown as 4b is used to overheat the refrigerant vapor above saturation temperature and is structured basically in the same manner as the part serving for the evaporation.

Fig. 2 shows the novel refrigerating apparatus. The apparatus consists of the compressor 1, the condenser 2, the liquid receiver 2a, which is here optional, the evaporator 3 and the controllable-throttling element 5 which all are connected by means of the tubes 10, 11, 12 and 13, respectively, in a close refrigerating circuit. The evaporator is built of two exchangers 4 and 8, profitably placed in the common housing 9. The sensor 6 of the valve 5 is situated on the tube 11, profitably close to the exchanger 8 and it reacts to the temperature, which assures full liquid refrigerant evaporation before it reaches the compressor. The exchanger 8 is insulated thermally by means of cover 7. In sequence, the exchanger 4 is built of at least one coil 4a, which does not serve any more even partially for overheating of vapor. The wet vapor via the tube 10 flows to the exchanger 8 where the final evaporation with slight overheating takes place.

Fig. 3 presents first embodiment of the heat exchanger upon the invention applied in the refrigerating apparatus in a side view, while fig. 4 is the same exchanger in the top view. This exchanger is built in a shape of arc, profitably a spiral 16, formed of two tube segments 14 and 15, being in direct contact. Both flows of the refrigerant are from their inlets lOi and 12i to their outlets 1 lo and 13o, respectively, preferable in the counter- current. The exchanger 8 is built of a basically cylindrical section 16a and section 16b, which is in a shape of spiral, especially similar to Archimedean spiral, whereas the tube segments are persistently connected together along their length. The following convolutions of the same tube segment are without common thermal contact. The section 16a has its axle y, which is approximately perpendicular to plane, profitably horizontal formed by the flat section 16b. The outlet 11 o of the vapor to the compressor is in a place where the sensor 6 is attached to and is next to the part of the spiral where the said tube segments start to contact, preferable in a distance no larger than twenty times an inner diameter of the tube 14.

In fig. 5 the exchanger is built in a shape of spiral 16 of two tube segments 14 and 15, connected commonly by means of wrapping with a strip 17, which is a good conductive material. At least one of the ends 17a and/or 17b of the strip are attached to at least one tube, profitable durably. The length of the straight part of the tube segments may be here the shortest possible one and advantageously it does not exceed more than thirty times the inner diameter of the tube 14.

In fig. 6 the tube segment 14 with the inlet lOi of the refrigerant being in a phase of wet vapor and the outlet 1 lo of the dry vapor, profitably overheated, is placed, especially approximately along its full length, inside the circumference of the tube 15 with its inlet of liquid from condenser 12i and its outlet 13o situated at opposite ends of the exchanger 8. The sensor 6 of the controllable-throttling element 5 is placed on the tube connecting the said exchanger 8 and the compressor, next to the curvilinear segment 14 in a place close to common contact of the tube, but no more than twenty times of the inner diameter of this tube.

In fig. 7 the tube segment 14 is curvilinear, especially with a shape of spiral bent around the tube 15 and connected to that tube. The sensor 6 of the valve is situated next to the place of common contact of the said tubes.

In fig. 8 the curvilinear segment of the tube 14 is placed inside the straight tube 15. It may be some different configuration of the tube like multilevel flat spiral or multi segmented spiral made of cylindrical segments with different diameters situated concentric or a mixed configuration with the aim to reduce sizes of the exchanger.

In fig. 9 the curvilinear shape of the tube segment 14 is obtained by bending it into arcs with an angle of approximately 180 degrees and there is shown possibility to change the position of the arc into opposite direction. The straight parts of the tube segments are shorter than the curvilinear parts and no longer than thirty times the inner diameter of the tube 14. Three-dimensional configuration of the tube is optional, but the end part comprising at least one arc of an angle of at least 180 degrees is approximately horizontal. The tubes 14 and 15 are persistently connected along their common contact 18, next to which is attached sensor 6. The place where the sensor is situated is a tube part bent into arc with a radius directed similar to that of the last arc of the exchanger 8, profitably it is straight lined and tangent to the end part of the arc.

In the drawings, especially in fig. 1 and 2 there is illustrated the evaporator placed inside the air cooler, but it is obvious that this invention is applicable to all kinds of evaporator that operates with the said small temperature difference. It is applicable for the evaporators with one or numerous coils. The outer medium may mean an environment that has a lack of a flow feature, like in the case of grounded heat pumps.

There are possible some other modifications of the presented embodiments, especially when saying about shape, flows, way the tubes are connected, direction of the spiral but for the persons skilled in the art they are cover by the invention scope and the attached claims.

Claims

1. A refrigerating apparatus characterized in that it comprises a compressor (1), a condenser (2), especially provided with a liquid receiver (2a), a controllable-throttling element (5) and an evaporator (3) and moreover tube connectors connecting in sequence mentioned assemblies into a close circuit, which inside a refrigerant flows, whereas the evaporator comprises a heat exchanger (4) built of at least one coil (4a), which through the refrigerant flows and evaporates partially, taking away heat from an outer medium and an additional heat exchanger (8) built of two tube segments (14) and (15), especially with circular cross-section, being in direct contact, of which at least tube segment (14) connected by means of tube (10) to the exchanger (4) is at least partially curvilinear, but the second tube segment (15) with liquid inside flowing from the condenser is situated outside circumference of tube segment (14), whereas in the exchanger (8) there is heat exchange between the refrigerant leaving the exchanger (4) and next evaporating, profitably to condition of an overheated vapor, and the refrigerant flowing to the evaporator before the mentioned controllable-throttling element (5), especially a thermostatic expansion valve, with its sensor (6), that is responsible to the temperature assuring evaporation of the refrigerant before it reaches the mentioned compressor, situated on the tube (11) connecting the mentioned exchanger (8) and the compressor (1) in the closest proximity of the mentioned curvilinear segment at place next to the common contact of the said tube segments, profitably at a distance no longer than twenty times an inner diameter of the tube.

2. A refrigerating apparatus as set forth in claim 1 characterized in that the exchanger (4) and the exchanger (8) are situated inside a housing (9) of the evaporator (3).

3. A refrigerating apparatus as set forth in claim 2 characterized in that the exchanger (4) is thermally insulated from outer influences by means of insulation (7).

4. A refrigerating apparatus as set forth in claim 1 characterized in that flows of the refrigerant in the exchanger (8) are directed counter-currently, so inlet (12i) of the refπgerant from condenser (2), especially from liquid receiver (2a), and the outlet (1 lo) of the refrigerant leaving the exchanger (4) are placed at the same end of the exchanger (8).

5. A refrigerating apparatus as set forth in claim 1 characterized in that the exchanger (8) is built of two tube segments (14) and (15) joint together, profitably permanently.

6. A refrigerating apparatus as set forth in claim 5 characterized in that the tubes (14) and (15) are joint together by means of a wrapping strip (17) of the material, which is a good thermal conductor, whereas at least one of ends (17a) and/or (17b) of the strip is fixed to an outer surface of at least one of the said tube segments, profitably persistently.

7. A refrigerating apparatus as set forth in claim 1 characterized in that the length of straight parts of the tube segments between the curvilinear ones of the tube (14) of the exchanger (8), which through the refrigerant leaving the exchanger (4) flows, is no longer than thirty times an inner diameter of the tube.

8. A refrigerating apparatus as set forth in claim 1 characterized in that the place of contact of the sensor (6) is on the tube (11) at a part without a curve which radius may be directed on opposite site than that of the last curve of the exchanger (8).

9. A refrigerating apparatus as set forth in claim 8 characterized in that at least the tube (14) is bent into arc no smaller than 180 degrees, profitably of a shape close to spiral (16).

10. A refrigerating apparatus as set forth in claim 9 characterized in that the spiral (16) consists of at least a part (16a), which is cylindrical approximately, and/or at least another part (16b), which is flat approximately.

11. A refrigerating apparatus as set forth in claim 10 characterized in that an axle (y) of the part (16a) is approximately perpendicular to a plane (x) on which the part (16b) is situated.

12. A refrigerating apparatus as set forth in claim 10 characterized in that the flat part (16b) is in a shape of Archimedean spiral placed horizontally, and following coils of the same tube are without common direct thermal contact.