WO2013171744A1

WO2013171744A1 - Venturi refrigeration system

Info

Publication number: WO2013171744A1
Application number: PCT/IL2013/050414
Authority: WO
Inventors: Itzhak MERKSAMER
Original assignee: Merksamer Itzhak
Priority date: 2012-05-14
Filing date: 2013-05-13
Publication date: 2013-11-21
Also published as: US20150135741A1; IL235454B

Abstract

Apparatus that primarily includes a narrow tube, through which a gas, preferably air, is forced to flow at a substantially high axial velocity. The gas, which must accelerate to reach that velocity and consequently becomes substantially cooler than the environment, then dissipates heat, through the wall of the tube from whatever is in thermal communication with that wall and thus refrigerates it. The gas does not undergo a change of phase. Preferably the tube forms the middle segment of a continuous tri-segment duct, through which the gas flows; the other two segments have each a tapered passageway, whose diameter varies between that of the tube and a considerably larger diameter at the corresponding end of the duct.

Description

VENTURI REFRIGERATION SYSTEM

TECHNICAL FIELD

The present invention relates in general to refrigeration methods and systems and in particular - to refrigeration using a single-phase gas.

BACKGROUND ART

Most conventional refrigeration systems are based on condensation and evaporation of a bi-phase refrigerant fluid in a closed circulation circuit. This method, while thermodynamically efficient and capable of generating considerable temperature differentials, has several disadvantages:

(a) The refrigeration apparatus is relatively complex and thus is relatively costly to manufacture; particularly costly components include the compressor and the atmospheric heat exchanger (condenser) especially if reasonable longevity is required.

(b) Some types of the bi-phase refrigerant fluid are harmful to the environment, with detrimental effect on the ozone layer; other types are relatively expensive; the consequential need to avoid leaks in the closed circulation circuit also adds to the cost of its manufacturing and/or maintenance.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a method and apparatus for refrigeration that is relatively simple, and thus inexpensive to fabricate and to maintain, and does not require expensive or harmful fluids.

A refrigeration method and system according to the present invention is based on the principle that when a gas (e.g. air) is forced to accelerate to a high speed, the process dissipates heat and thus the gas cools. More specifically, apparatus according to the invention primarily includes a narrow tube, to be referred to as a Venturi tube (or "venturi" for short), through which a gas, preferably air, is forced to flow at a substantially high axial velocity - typically being at approximately half the speed of sound. The gas, which must accelerate to reach that velocity and consequently becomes substantially cooler than the environment, then dissipates heat, through the wall of the venturi tube from whatever is in thermal communication with that wall and thus cools, or refrigerates, it. The flowing gas is therefore referred to herein as a refrigerant gas or, briefly, refrigerant. It is noted that the venturi tube is considered to be narrow, in that it is substantially narrower than any passageway of the gas in which it flows at a low velocity.

Preferably the venturi tube forms the middle segment (also referred to as the venturi segment) of a continuous tri-segment duct, through which the gas flows; the other two segments, referred to as tapered segments, have each a tapered passageway, whose diameter varies between that of the venturi and a considerably larger diameter at the corresponding end of the duct. One of the two tapered segments is termed intake segment and the other tapered segment is termed exhaust segment; the gas is made to flow - generally by means of some external driver - into the wide end of the intake segment, axially through the entire tri-segment duct and out of the wide end of the exhaust segment.

While flowing through the intake segment, the tapered inner diameter causes the axial velocity of the gas to gradually increase, while preferably keeping the flow laminar, until the velocity reaches a maximal value when entering the venturi segment. During, and as a result of, this process, which is endothermic, the gas cools. While flowing through the middle segment, i.e. through the Venturi tube, the gas dissipates heat from the wall of the tube. Finally, while the gas flows through the exhaust segment, its axial velocity gradually decreases, whereby it warms up, as this process is exothermic. The Venturi tube is in thermal communication, possibly through a heat exchanger, with whatever needs to be refrigerated - i.e. some medium (a fluid - liquid or gas - or a solid object). The tri-segment duct as structurally or functionally described herein will be referred to as a refrigeration engine - specifically a venturi refrigeration engine - and its combination with a gas flow driver and a heat exchanger and possibly with additional refrigeration engines and their heat exchanger will be referred to as a (venturi-based) refrigeration system.

More preferably, the gas is air and the tri-segment duct is configured so that air flows into the intake segment from the surrounding atmosphere and out of the exhaust segment - essentially back to the atmosphere. The duct is further preferably configured so that gas or air is drawn into the tri-segment duct by the action of one or more fans or fan assemblies, disposed at the wide end of the exhaust segment or in a duct attached thereto. When the fans operate, air is drawn from the atmosphere through the open end, flows through the intake segment, then through the venturi and finally through the exhaust segment, whence it is returned by the fans into the atmosphere.

The Venturi tube is preferably in thermal contact with a heat exchanger, which, in turn is in thermal contact with the medium to be refrigerated. The medium, if a fluid, may be flowing (e.g. through a pipe) while being thus refrigerated or it may occupy an enclosed space. In one configuration of a system according to the invention, for example, the venturi with its heat exchanger may be disposed inside a closed cabinet and configured to absorb heat from the air therein, the cabinet thus serving as a refrigerator. In another configuration, the venturi with its heat exchanger may be disposed inside a duct, through which air is forced to flow in and out of a refrigerator cabinet, again dissipating heat therefrom. In yet another configuration, the venturi with its heat exchanger may be in thermal contact with a flowing fluid (gas or liquid) that needs to be cooled, again dissipating heat therefrom. In still another configuration the venturi tube with its heat exchanger may be configured to dissipate heat from a solid object, such as an electronic component. In some configurations of a venturi- based refrigeration system according to the invention, a plurality of venturi

refrigeration engines may be deployed to cool a medium - possibly air inside a cabinet.

It is noted, as a basic feature of the invention, that the refrigerant gas does not undergo a change of phase, i.e. it remains in gaseous state (or phase), throughout the process - in contrast to the two phases (gaseous and liquid) that the refrigerant undergoes in conventional refrigeration apparatus.

It is further noted that the thermal energy extracted from the refrigerant gas (thus causing the desired cooling effect) is spent on the increased flow velocity, while the energy exerted (e.g. by a driving fan) on the gas to cause it to flow through the venturi is largely spent in overcoming friction between them and does not substantially affect its thermal state. Consequently the cooling process is thermodynamically efficient. It is further noted that, to the extant that the gas, while cool, has absorbed heat from outside, e.g. through the wall of the venturi (which is the desired effect), it exits warmer than before entering the flow passage; the thus added thermal energy must then be dissipated into the environment. If the refrigerant gas is other than

atmospheric air, it would generally be made to re circulate through the system and thus the dissipation of the added thermal energy need to be effected through a suitable heat exchanger. On the other hand, if atmospheric air is used as the refrigerant, it simply mixes with the surrounding air upon exiting the system.

It will be appreciated that a refrigeration engine and system according to the present invention is considerably simpler in construction than conventional cooling systems and is therefore inherently less expensive to fabricate and to maintain. Moreover, when using air as the flowing refrigerant, no atmospheric heat exchanger is necessary - which further reduces the costs. Additionally, a refrigeration engine and system according to the present invention does not involve expensive or environmentally detrimental fluids.

To Summarize: In one aspect, the invention is of a refrigeration method for

refrigerating a medium, including the steps of -

(a) causing a gas to flow through a tube at a substantially high velocity, whereby its temperature is reduced, and

(b) letting the gas dissipate heat, through the wall of the tube, from the medium;

wherein the gas does not undergo a change of phase throughout the flow.

Preferably the gas is atmospheric air. In another aspect, the invention is of a refrigeration engine , for refrigerating a medium, comprising a duct that includes a venturi segment, formed as a narrow tube, the duct being configured to cause any gas flowing therethrough to flow through the venturi segment at a substantially high velocity and the venturi segment being further configured to be in thermal communication with the medium, wherein the gas does not undergo a change of phase throughout the flow. The gas, prior to entering the venturi segment, cools owing to an endothermic process.

Preferably the duct further includes an intake segment and an exhaust segment, each formed to have a tapered passageway, its narrow end connected to a corresponding end of the venturi segment. More preferably, the gas is air and the duct is configured so that air flows into the intake segment from the surrounding atmosphere and out of the exhaust segment - essentially back to the atmosphere. As an added feature, the engine further includes a fan or a fan assembly, attached to the wide end of the exhaust segment.

In yet another aspect, the invention is of a refrigeration system for cooling a medium, comprising

one or more ducts, each configured to permit gas to flow therethrough and including a venturi segment, formed as a narrow tube,

means to cause flow of a gas through the ducts; and

means for thermal communication between the venturi segment of each duct and the medium,

wherein each duct is further configured to cause any gas flowing therethrough to flow through the venturi segment at a substantially high velocity and the gas does not undergo a change of phase throughout the flow. Rather, the gas, prior to entering the venturi segment, cools owing to an endothermic process and the means for thermal communication enables heat to be dissipated from the medium to the flowing gas.

Preferably each of the ducts further includes an intake segment and an exhaust segment, each formed to have tapered cross- sectional dimensions, its narrow end connected to a corresponding end of the venturi segment; furthermore, the means to cause flow of gas is one or more fans or fan assemblies, in fluid communication with the wide end of the exhaust segment of one or more of the ducts. Also preferably the means for thermal communication is a heat-exchanger, in contact with the venturi tube and configured to be in thermal communication with the medium.

In some configurations of the system the medium is a fluid, flowing through a pipe; in certain configurations both ends of the pipe are inside an enclosure. In other configurations of the system, in which the medium to be cooled is a fluid inside an enclosure, the ducts and the means to cause flow are configured so that all flow through the ducts is only from, and to, atmospheric air outside the enclosure and so that each venturi segment is inside the enclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates, in axial- sectional view, a basic embodiment of a refrigeration engine according to the present invention.

Figure 2 illustrates, in axial- sectional view, an embodiment of one configuration of a system based on the refrigeration engine of Fig. 1, applicable to cooling a flowing fluid.

Figure 3 illustrates in top-sectional view a configuration similar to that of Fig. 2, applied to cooling a closed space.

Figures 4A and 4B illustrate, in side view and in sectional view, respectively, an

embodiment of another configuration of a system based on the refrigeration engine of Fig. 1, applicable to cooling a closed space.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 depicts, in a axial- sectional view, an embodiment of the basic refrigeration engine according to the invention, with air being the refrigerant gas. It is seen to be a shaped hollow duct 10, consisting essentially of three segments - a middle segment 12 (termed the venturi segment) that is formed as a very narrow tube (that is - a tube with a very narrow passageway) and two tapered (or conical) end-segments - an exhaust segment 11 and an intake segment 13. The duct 10 (to be also termed the tri- segment duct) is symmetrical about a length axis (not shown, but lying horizontally in the drawing) and its (inner) passageway preferably has a circular cross-section; however a square or rectangular cross-section may also be practical. The passageway of each of the two end-segments gradually changes in it cross dimensions (e.g. diameter) between that of the middle segment and a much larger open end. In practice, the wall of each segment is of uniform thickness, as represented by the thick black lines in the drawing; thus its outer shape follows that of its inner surface, which forms the passageway.

In operation, air flows into the duct, as indicated by arrows 16, through the intake segment 13 and out through the exhaust segment 11. It is noted that the flow of air through the entire duct 10 is continuous. The manner of driving this flow is discussed below, but generally it is advantageous to do it by drawing the air from the end of the exhaust segment, as this minimizes turbulence in the intake segment, which would cause inefficiencies in the flow and in the cooling effect.

The dimensions of each segment and their mutual proportions are also chosen so as to make the airflow as laminar as possible, as well as to enable the desired rate of heat transfer at a reasonable energetic efficiency. Thus it has been found that the inner diameter of the wide end of each end- segment should be approximately seven times that of the venturi tube (in the middle segment) and thus the ratio of their cross- sectional areas is approximately 50. The latter figure is necessarily also the ratio between the axial airflow velocities through the venturi and through the ends of the duct. It has likewise been found that the length of the exhaust segment 11 should be approximately 2.5 times that of the intake segment 13. The length of the venturi segment is obtained as an optimal balance between the desire to maximize thermal communication with the medium outside the tube (which is to be cooled) - which calls for a long tube - and the desire to minimize resistance to air flow - which calls for a short tube.

For use in a typical small refrigeration system, the dimensions of the duct segments preferably range as follows: The middle (venturi) segment 12 is 20 to 50 cm long and has a diameter of 2 to 4 cm. The length of the intake segment 13 is 20 to 30 cm and that of the exhaust segment 11 is 50 to 70 cm. The diameter of the wide ends of the two conical end segments is 14 to 28 cm, but they need not be identical. It is noted that other dimensions are possible and depend largely on the desired heat dissipation capacity, on the desired low temperature and on the acceptable efficiency of the apparatus; they may also be limited by external geometric constraints. Preferably the inner surface of the venturi tube is lined with a moisture-repelling substance, so as to prevent the buildup of frost inside the tube, which would gradually restrict airflow. Also preferably, the intake end of the duct is covered with a filter, to block out dust and other airborne particles.

In order to maximize thermal communication between the air flow through the venturi tube and its surrounding medium (so as to dissipate heat), the middle segment 12 is in thermal contact with a heat-exchanger 15, which, in turn, thermally communicates with the medium. In Fig. 1 it is depicted schematically as a ring, in contact with the tube 12, and attached thereto - a plurality of disc-like fins, about which a fluid medium may flow. Many of the configurations of heat exchangers known in the art may be deployed, the exact configuration being dependent on the type of the medium to be cooled - whether gaseous, liquid or solid - and on the specific nature of that medium, as well as on the configuration of the system in which the refrigeration engine is deployed. Some of these will be discussed in the sequel.

Turning now to Figure 2, there is shown, by way of example, a refrigeration system according to the invention, configured to refrigerate a flowing fluid - which may be any gas or a liquid. The system comprises a refrigeration engine 10, such as described above in conjunction with Fig. 1, with a heat exchanger 15 in thermal contact with the venturi tube 12. Most of the length of the tube 12 and the heat exchanger 15 are disposed within a pipe (or duct) 22, through which the fluid is made to flow - as indicated by the arrows 23. Only the relevant segment of pipe 22 is shown

schematically in the drawing; the rest of the pipe, as well as the flow driver of the fluid, may be in any configuration, as befitting the application of the system. The heat exchanger 15 may likewise be configured in any manner known in the art and as befitting the nature of the fluid and its rate of flow. Connected to the wide end of the exhaust segment 11, and in fluid communication therewith, there is disposed a fan assembly 14, including a fan 17 that rotates about a shaft 18, which is driven by a motor (not shown). Optionally, the fan assembly may include a plurality of fans; also optionally, the fan assembly may be disposed remotely and connected to the exhaust segment by a duct. The wide end of the intake segment 13 is open to the atmosphere, but may optionally include a filter assembly.

The fan assembly 14 is operative to draw air from the exhaust segment 11 - which causes atmospheric air to be drawn into the intake segment 13 and thence to flow through the venturi tube (middle segment) 12 to the exhaust segment, wherefrom it is exhausted through fan assembly 14 back to the atmosphere. While flowing through the tapered passageway of the intake segment, the axial velocity of the air gradually increases, until reaching a substantially high velocity, at which it subsequently flows through the venturi tube. As explained above, this increased velocity causes a substantial reduction in the temperature of the air. The thus cooled air, while flowing through the venturi tube, dissipates heat, through the wall of the tube and the heat exchanger, from the fluid that flows through the pipe 22.

A particular configuration of a system like that shown in Fig. 2 is one that includes an enclosed space to be cooled - such as a home refrigerator. This is illustrated, for example, in the top- sectional view of Figure 3. In this configuration the pipe (or duct) 22 is formed so that both its ends communicate with the inside of the refrigerator cabinet 20. Air within the cabinet is forced, by means of a fan 27, which is driven by a motor 28, to circulate through the duct 22, as indicated by the arrows. Across the duct 22 there is positioned, in a vertical orientation (i.e. differently than that shown in Fig. 2), a refrigeration engine, such as described above. In this top sectional projection the engine is viewed head-on, showing the venturi tube 12, the heat exchanger 15 (with two fins) and the circular end of the exhaust segment 11. The air flowing through duct 22 (after being drawn from inside the refrigerator cabinet by the driving action of fan 27) passes over the heat-exchanger 15 and is thus cooled, before returning to the cabinet space. Another configuration of a system according to the invention, also aimed at refrigerating an enclosed space, is depicted in Figures 4A and 4B. In this particular configuration there are three refrigeration engines, similar to those shown in Fig. 1, disposed within a cabinet 20 between two opposing walls thereof and near its rear wall. The number of these engines may generally be more or less than three. Fig. 4A shows a side view of the cabinet 20. Each of the three large circles represents the wide end of the corresponding intake segment 13 as viewed head-on through a matching corresponding hole (termed intake hole) in the wall. Each of the three small circles represents the corresponding venturi tube 12, seen, again, head-on. The area between the large and small circles represents the conical inner surface of the intake segment. In the opposite wall of the cabinet (not shown en face) there are similar holes (termed exhaust hole), matching the open wide ends of the corresponding exhaust segments 11.

Fig. 4B shows a sectional view of the cabinet and of the three refrigeration engines in a plane that is denoted by a dash-dot line in Fig. 4A. Here the three refrigeration engines 10 are viewable in axial section, as in Figs. 1 and 2, and are seen to extend between the corresponding holes in the sides of the cabinet 20. In an optional configuration the intake holes and/or the exhaust holed may be placed in the rear wall of the cabinet and connected to the corresponding ends of the refrigeration engines by means of elbow ducts. The conical intake- and exhaust segments of the engines 10 (and of the optional elbow ducts, if included) are preferably covered by a layer of thermally insulating material 25, to avoid thermal communication between them and the air inside the cabinet; alternatively, the cones (and elbows) may themselves by fabricated of thermally insulating material. In contrast, the middle (venturi) segment, with the heat exchanger, is made to be highly heat conductive, so as to dissipate heat from the air inside the cabinet.

A manifold duct 26 is connected to the ends of the three exhaust segments and leads to a fan assembly 24. The latter serves to draw air from all the refrigeration engines, in a manner similar to that described in conjunction with Fig. 2. Alternatively to the manifold duct, individual fan assemblies may be attached to the exhaust holes. In yet another optional configuration of the system of Figs 4, the cabinet may be narrower than the length of the refrigeration engines. The intake- and/or exhaust segments would then extend out of the cabinet - through holes of matching diameters.

As mentioned above, a refrigeration system according to the invention may also be applicable to cooling a solid device, such as an electronic component; the latter may, for example be disposed in a test jig for performance quality-control measurements. In such a system, the heat exchanger that is in contact with the venturi tube is designed for maximum thermal communication with the device. This may be facilitated by the availability of standard test jigs that are already provided each with a base that is made to thermally contact the device; in this case, said heat exchanger is designed for maximum thermal contact with such a base.

Finally we provide some notes about design parameters of the refrigeration device and system described above: The degree of cooling is theoretically proportional to the square of the gas velocity within the venturi. It is known, both theoretically and empirically, that in order to substantially reduce the temperature inside the venturi, say by 20 degrees, relative to the outside air, and before dissipating any heat through the heat exchanger, the air velocity therein should be above 110 meters per second; a good operating value would be half speed of sound, i.e. about 180 m/sec. A value equal to 80% of the speed of sound presents an upper bound on the velocity, since beyond that there may develop detrimental shock waves. The power of the fan and the dimensions of the duct segments are preferably scaled to the desired rate of heat dissipation;

preferably the proportion between the various dimensions are retained, so as to essentially maintain laminar flow and to thus keep high overall power efficiency. The length of the venturi tube segment is also determined so as to maximize overall efficiency, wherein three factors come into play: (a) A shorter tube presents less resistance to refrigerant flow and thus increases efficiency of the fan driving effect; (b) a longer tube permits a longer heat exchanger and thus increases the rate of heat dissipation; (c) the length of the heat exchanger, and thus also of the tube, may be prescribed by the parameters of the outside system components (e.g. the diameter of the fluid flow pipe 22 of Fig. 2). INDUSTRIAL APPLICABILITY

The refrigeration engine disclosed herein is readily manufacturable from available materials and components and by any of a number of techniques known in the art, including, for example, sheet metal forming, machining and injection molding. The three segments of the engine may be fabricated individually and welded together.

The refrigeration engine can be readily integrated with existing refrigeration systems - especially industrial ones, as well as with specially designed systems, exemplified by the configurations described above.

Claims

1. A refrigeration method for refrigerating a medium, comprising

(b) letting said gas dissipate heat, through the wall of said tube, from said space or medium;

wherein said gas does not undergo a change of phase throughout said flow.

2. The method of claim 1 wherein said gas is atmospheric air.

3. A refrigeration engine , for refrigerating a medium, comprising a duct that includes a venturi segment, formed as a narrow tube, the duct being configured to cause any gas flowing therethrough to flow through the venturi segment at a substantially high velocity and the venturi segment being further configured to be in thermal communication with the medium,

wherein said gas does not undergo a change of phase throughout said flow.

4. The engine of claim 3 wherein said gas, prior to entering the venturi segment, cools owing to an endothermic process.

5. The engine of claim 3 wherein said duct further includes an intake segment and an exhaust segment, each formed to have a tapered passageway, its narrow end connected to a corresponding end of the venturi segment.

6. The engine of claim 5 wherein said gas is air and said duct is configured so that air flows into the intake segment from the surrounding atmosphere and out of the exhaust segment - essentially back to the atmosphere.

7. The engine of claim 6 further comprising a fan or a fan assembly, attached to the wide end of said exhaust segment.

8. A refrigeration system for cooling a medium, comprising -

- one or more ducts, each configured to permit gas to flow therethrough and

including a venturi segment, formed as a narrow tube,

- means to cause flow of a gas through said ducts; and

- means for thermal communication between said venturi segment of each duct and said medium

wherein each duct is further configured to cause any gas flowing therethrough to flow through the venturi segment at a substantially high velocity and said gas does not undergo a change of phase throughout said flow.

9. The system of claim 8 wherein said gas, prior to entering the venturi segment, cools owing to an endothermic process and said means for thermal communication enables heat to be dissipated from said medium to said flowing gas.

10. The system of claim 8 wherein each of said ducts further includes an intake segment and an exhaust segment, each formed to have tapered cross-sectional dimensions, its narrow end connected to a corresponding end of the venturi segment.

11. The system of claim 10 wherein said means to cause flow of gas is one or more fans or fan assemblies, in fluid communication with the wide end of the exhaust segment of one or more of said ducts.

12. The system of claim 8 wherein said means for thermal communication is a heat- exchanger, in contact with the venturi tube and configured to be in thermal

communication with said medium.

13. The system of claim 12 wherein said medium is a fluid, flowing through a pipe.

14. The system of claim 13 wherein both ends of said pipe are inside an enclosure.

15. The system of claim 8, said medium to be cooled being a fluid inside an enclosure, wherein said ducts and said means to cause flow are configured so that all flow through the ducts is only from, and to, atmospheric air outside the enclosure and so that each venturi segment is inside the enclosure.