Abstract:
A vortex generator for accepting high-pressure condensible vapor and separating the condensible vapor into a relatively hot stream of vapor and a relatively cool liquid. 
     The vortex generator includes an inlet at the first end for allowing high pressure vapor to enter, and an outlet at the second end for allowing condensed liquid to exit wherein the outlet communicates with the inlet via a longitudinal chamber. A nozzle located near the inlet having a plurality of equally-spaced tangential inlets along its perimeter for injecting the vapor that is inlet to the vortex generator into the longitudinal chamber as a high-speed vortex vapor stream proximate the longitudinal axis.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a vortex tube and, in particular, a vortex generator for condensing condensible vapor. 
     BACKGROUND OF THE INVENTION 
     Vortex tubes are well known. Typical vortex tubes are designed to operate with non-condensible gas such as air. A typical vortex tube turns compressed air into two air streams, one of relatively hot air and the other of relatively cold air. A common application for current vortex tubes is in air supply lines and other applications that utilize non-condensible gas under a high pressure. 
     A vortex tube does not have any moving parts. A vortex tube operates by imparting a rotational flow motion to the incoming compressed air stream. Directing compressed air into an elongated channel in a tangential direction does this. 
     FIGS. 12A and 12B illustrate vortex tubes of two known designs. FIG. 12A illustrates a counterflow vortex tube  200 A in which a first outlet  202 A is located proximate an inlet  206 A, and a second outlet  204 A (a substantially peripheral opening) is located at the opposite end. 
     FIG. 12B illustrates a uniflow vortex tube  200 B in which both outlets  202 B,  204 B are located at the end opposite the inlet  206 B. The operating principle of the uniflow vortex tube  200 B is similar to the operation of the counterflow vortex tube  200 A. 
     The general flow pattern inside a typical vortex tube  200  is shown. High-pressured or compressed gas enters the vortex tube tangentially at one end at inlet  206  and produces a strong vortex flow in the tube  200 . A nozzle  208  is designed to direct the incoming gas in a tangential direction. One stream of gas is produced along the sidewall while a second stream of gas is produced along the longitudinal axis of the vortex tube  200 A. Referring to FIG. 12A, the second outlet  204 A communicates with the stream of gas that was produced along the outer wall; exiting air is relatively hotter than the compressed air that initially entered the vortex tube  200 A. The first outlet  202 A communicates with the steam of gas that was produced along the longitudinal axis. The air exiting the first outlet  202 A is relatively cooler than the initial compressed air. 
     As the compressed gas enters the vortex tube  200 A at inlet  206 A, the velocity of fluid induces a vertical motion which creates a forced vortex at the center of the tube. This flow produces a pressure distribution along the radial direction. The gas proximate the sidewall of the vortex tube  200  is adiabatically compressed, thereby resulting in an increase in temperature. The work to compress the gas is produced by the gas near the longitudinal axis or centerline of the tube  200 A, which is adiabatically expanded and cooled. 
     The cooler gas is confined to the center of the vortex tube substantially along the longitudinal axis and, in fact, creates a second vortex air stream within the initial vortex air stream but traveling in the opposite direction of the initial air stream. The inner vortex air stream of cooler gas leaves the vortex tube  200 A along the axial direction of the vortex tube from an outlet  202 A located near the first end of the vortex tube  200 . The first or peripheral outlet  202 A is positioned proximate the second end of the vortex tube  200 A. The second or peripheral outlet  204 A outlet provides an exit for the relatively hot gas. Accordingly, two separate air streams are produced at the respective outlets and the vortex tube  200 A effectively separates a single air stream into a cold air stream and a hot air stream. 
     The total discharge (hot and cold) volume from a vortex tube is proportional to the absolute inlet pressure. Valves at the inlet (and in alternate embodiments at one or both outlets) control the air flow and, indirectly, the relative temperature gradients of the exiting gases. 
     SUMMARY OF THE INVENTION 
     In contrast with currently available vortex tubes, the present invention is referred to as a vortex generator in order to indicate that it is designed to operate on condensible vapor such as steam or a refrigerant vapor for use in a refrigeration apparatus. 
     The vortex generator of the present invention separates a high-pressure stream of condensible vapor into a relatively hot vapor component and a relatively cool liquid component. In contrast with current vortex tubes, there is no outlet for a cool stream. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and, together with the description, serve to explain the principles of the invention. 
     In the drawings: 
     FIG. 1 is a diagrammatic cross-sectional view of a vortex generator in accordance with the present invention; 
     FIG. 2 is a graphical representation of the radial flow velocity taken across the vortex generator of FIG. 1; 
     FIGS. 3A and 3B are graphical representations of the pressure and temperature distributions, respectively, with respect to radial distance in the vortex generator; 
     FIGS. 4A and 4B are diagrammatic representations illustrating the principle of phase-changing of the vapor inside the vortex generator of the present invention; 
     FIG. 5 is a representation of the cascade effect produced inside of a vortex generator in accordance with the present invention; 
     FIG. 6 is a graphical representation of the liquid produced by mass with respect to pressure across the subject vortex generator; 
     FIG. 7 is a graphical representation of the efficiency of liquid production with respect to axial length of a subject vortex generator; 
     FIG. 8 is a cross-sectional view of an alternate embodiment of a vortex generator that utilizes a central feed in the nozzle; 
     FIG. 9A is a side view and FIG. 9B is an end view, of a nozzle used in a subject vortex generator; 
     FIG. 10 is a cross-sectional view of an alternate embodiment of a vortex generator illustrated in FIG. 8 that utilizes a branch tube to divert a portion of the incoming vapor; 
     FIG. 11 is an alternate embodiment of a vortex generator in accordance with the present invention; and 
     FIGS. 12A and 12B are simplified cross-sectional views of a counter-flow vortex tube and a uniflow vortex tube, respectively, which generally represent the state of the art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In describing a preferred embodiment of the invention, specific terminology will be selected for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
     The terms “right,” “left,” “top,” “bottom,” “lower,” and “upper” designate relative directions in the drawings to which reference is made. The terms “inward” and “outward” will usually refer to a direction relative to the longitudinal axis of the vortex generator. The terms “inside” and “outside” will usually refer to a volume or region inside or outside, respectively, of the vortex generator. 
     The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings in which a vortex generator is generally indicated at  10 . 
     FIG. 1 is a cross-sectional view of a vortex generator  10  in accordance with the present invention. The vortex generator  10  includes an elongated or longitudinal chamber  20 , an inlet  12 , a nozzle  14 , and an outlet  16 . Although the longitudinal chamber  20  is shown as substantially tubular in shape and is defined by sidewall  13 , it is believed that other designs (e.g., oval) may be utilized. 
     Condensible vapor enters the vortex generator  10  at inlet  12 . The condensible vapor is under a high pressure. The nozzle  14  is fixed with respect to the sidewall  13  of the longitudinal chamber  20 ; there are no moving parts in the vortex generator  12 . The nozzle  14  is designed to direct the incoming vapor in a tangential direction with respect to the sidewall  13  of the longitudinal chamber  20 . 
     As a result of the injection of vapor in a tangential direction, a vortex-shaped vapor stream  25  is produced within the longitudinal chamber  20 . The vortex-shaped vapor stream  25  (sometimes referred to as cyclonic- or spiral-shaped) created by the nozzle  14  is illustrated in FIG.  1 . The operation of the nozzle  14  will be more thoroughly discussed in connection with the description of FIGS. 8,  9 A and  9 B. 
     Referring now to FIG. 2, near the core region  33  (i.e., parallel to the longitudinal axis) of the elongated chamber, a forced vortex flow is generated, where circumferential velocity linearly increases with the radial distance. Outwards from the core region, there is a free vortex, where circumferential velocity exponentially decreases along the radial distance. As indicated previously, the vortex  25  has the general appearance of a spiral. 
     As illustrated in FIG. 2, the highest velocity of the vortex  25  occurs at r o . In a typical embodiment, the maximum flow velocity at r o  reaches approximately 100 m/s. 
     Referring now to FIGS. 3A and 3B, the distributions of both pressure and temperature inside a vortex generator  10  along the radial coordinate are graphically illustrated. The vapor at the core expands due to the centrifugal force, thus reducing its temperature. In comparison, the vapor at the outer region is compressed as the vapor is pushed toward the sidewall by the centrifugal force, thus resulting in an increased temperature. 
     As condensible vapor enters a vortex generator  10 , the vapor at the core of the vortex generator  10  expands due to the vortex flow motion of the vapor, resulting in a localized drop in pressure. Subsequently, its temperature also drops, converting the condensible vapor to liquid (phase change). (Initially, relatively small droplets of liquid are formed.) As the phase change of the condensible vapor occurs, the volume of the condensible vapor shrinks because the volume of liquid is significantly smaller than that of vapor. For example, the volume of liquid water is about 1,000 times smaller than that of water vapor (i.e., steam). For typical refrigerants, such as R-22 and R-134a, the volume of the liquid is approximately 80-100 times smaller than that of the vapor. 
     As a result of the vapor-liquid conversion, the volume of the condensible vapor decreases, prompting a significant drop in the local pressure. This sudden drop in pressure is essentially the same as what happens when the vapor suddenly expands. The sudden drop in the pressure accompanies a corresponding temperature drop, causing additional condensation around the initial condensed droplet. As a result, the condensible vapor is separated into a relatively cool liquid  38  and relatively hot vapor  39  as shown in FIG.  4 . 
     FIGS. 4A and 4B summarize the operating principle of a vortex generator  10 . The condensation of condensible vapor inside a vortex generator  10  may be summarized in three steps. Step One, as illustrated in FIG. 4A, shows the vortex flow created by a nozzle  14  at the inlet of a vortex generator  10 . Step Two, as illustrated in FIG. 4B, shows the vapor-to-liquid phase change and the creation of a vacuum in the core region; Step Three, also illustrated in FIG. 4B, shows the movement of a liquid droplet from the core to the sidewall of the vortex generator, which is the result of centrifugal force. For continuous phase-change of condensible vapor into a liquid in a vortex generator, it is essential to maintain proper vacuum strength. For example, if the vacuum is too strong, the vortex flow motion will be destroyed as the core vacuum pulls the vapor from the perimeter of the vortex generator to the core. This issue will be discussed further herein. 
     Liquid production as a result of a cascade effect inside a vortex generator will now be described. Referring now to FIG. 5, the portion of a condensible vapor is represented by region  1 , having a temperature that reaches (or drops below) its saturation temperature due to the vortex motion near the inlet of the vortex generator. The vapor converts to liquid in region  1 , causing the pressure in the adjacent area (indicated by  2 ) to drop, prompting a temperature drop and subsequent vapor-liquid conversion. Subsequently, the pressure in region  2  suddenly drops, and the vapor around region  2  is affected by the vacuum, prompting further vapor-liquid conversion. This cascade effect accelerates vapor-liquid conversion in the vortex generator. 
     The cascade effect is self-sustaining once the first liquid droplet is produced due to the vortex flow motion. In other words, if the vortex motion cannot be maintained, then cold and hot vapor become mixed, and the cascade effect of self-sustaining vapor-liquid conversion stops. In summary, one has to maintain the vortex flow structure to sustain this cascade process. 
     When the vacuum is too strong, the core of the vacuum pulls vapor in from the perimeter, thus destroying the vortex flow. This happens if the pressure drop is larger than an optimum value which will be discussed herein, in association with FIG.  7 . Therefore, the pressure drop across a vortex generator should be small enough to prevent the core vacuum from destroying the vortex flow inside the vortex generator. 
     Referring now to FIG. 6, test results of the percentage (%) of liquid produced versus pressure drop with R-113 refrigerant in a vortex generator of inside diameter of approximately ⅜ inches are graphically illustrated. As the pressure drop decreased from 1.5 to 0.5 psig, the percentage of liquid produced increased from 7 to 20%. These test results confirm the aforementioned statement on the effect of core vacuum on the continuous phase-change operation of a vortex generator for condensible vapor. Below 0.5 psig, the production of liquid suddenly drops, which can be attributed to insufficient energy to initiate a vortex flow inside a vortex generator. In other words, below 0.5 psig, an adequate vortex flow could not be created inside the vortex generator. Above 0.5 psig, the process of vapor-liquid conversion becomes less effective as the core vacuum becomes so strong that it begins to destroy the vortex flow motion. Hence, the optimum pressure drop for this particular test was 0.5 psig. 
     It is well known that conventional vortex tubes perform better as the inlet pressure or the pressure drop across the vortex tube increases. Indeed, conventional vortex tubes (both counterflow and uniflow types) can separate compressed air into cold and hot air streams most efficiently with a large inlet pressure or a large pressure drop across the vortex tube. In contrast, as demonstrated in FIG. 6, a phase-changing vortex generator does not perform efficiently if the inlet pressure is large because larger pressure drops result in stronger vacuums at the core, which destroy the vortex flow structure. Hence, a phase-changing vortex generator needs a small pressure drop, i.e., just small enough to initiate and sustain vortex flow motion inside the vortex generator. 
     Referring still to FIG. 6, the effects of a pressure drop across the vortex generator are shown. At zero pressure drop, of course there is no flow and no vortex motion. With decreasing pressure drop, the vortex generator performs better until it suddenly stops functioning because the vortex flow motion cannot be created at a very small pressure drop. The optimal value of the pressure drop depends on the properties of the refrigerant (or water) vapor and the dimensions of the vortex generator. The dimensions given in FIG. 8 are optimized for a vortex generator circulating R-113. 
     When the elongated chamber  20  of the vortex generator is too long, liquid can re-evaporate inside. As illustrated in the graph of FIG. 7, test results illustrate the effects of the length of a vortex generator on the performance of a vortex generator using R-113 refrigerant. As shown in FIG. 7, as the length of the vortex generator increased from 1.5 inches to 5 inches, the efficiency of liquid production in the vortex generator decreased from 100% to approximately 10%. 
     The test results illustrated in FIG. 7 indicate that for a vortex generator circulating R-113 with an inside diameter of approximately ⅜ inches, the optimal length is about 1.5 inches. When the vortex generator is longer than the optimal value, liquid may re-evaporate inside the vortex generator, thereby reducing the efficiency of liquid production as shown in FIG.  7 . With a vortex generator shorter than 1.5 inches, the efficiency of liquid production dramatically decreased, indicating that a vortex flow could not develop in such a short vortex generator. 
     A phase-change vortex generator should be designed to maximize the production of liquids. The length of a vortex generator should be relatively short. 
     Referring now to FIG. 8, a cross-sectional view of a phase-changing vortex generator  90  is illustrated, which has one inlet  42  and one outlet  43 . The outlet  43  may be an open end to the longitudinal chamber. Condensible vapor enters the vortex generator at inlet  42  at one end, and both condensed liquid and the remaining vapor exit through the other end. A nozzle  44  is used to guide the condensible vapor into the vortex generator tangentially at the inlet so that the vapor can form a vortex flow in the longitudinal chamber  40  of the vortex generator. 
     The design of the nozzle  44  is shown in FIG. 9. A plurality of guide vanes  48  direct the tangential entry of the vapor into the longitudinal chamber  40  of the vortex generator. 
     In another embodiment of the current invention, a small portion of the vapor (e.g., 5-25%) enters the core of the longitudinal chamber  40  of the vortex generator through a center feed  29 , through a second chamber  47  and through channel  41 , as illustrated in FIGS. 8,  9 A and  9 B. The center feed  29  is positioned on a circumferential rim  45  of the nozzle  44 . The channel  41  is preferably located at the radial center of nozzle  44 , and provides a means for second chamber  47  to communicate with the longitudinal chamber  40 . 
     The center feed  29  directs a portion of the incoming vapor directly into the core of the longitudinal chamber  40  in order to maintain a sufficient vacuum strength inside the vortex generator. The size or diameter of the center feed  29  is determined by the desired percentage of vapor to be directed along the longitudinal axis of the vortex generator. Preferably, the center feed  29  should direct approximately 10% of the vapor to the core of the longitudinal chamber; however, the percentage may vary depending on the type of vapor used and the various dimensions of the vortex generator. 
     In an alternate embodiment illustrated in FIG. 10, a split inlet design is illustrated. A branch tube  50  is used to feed a fraction of the vapor into the core of the longitudinal chamber  40  of the vortex generator. The branch tube may feed the fraction of vapor into a secondary chamber similar to that illustrated in FIG. 8, or directly through the nozzle and into the core of the longitudinal chamber. 
     In another embodiment illustrated in FIG. 11, a vortex generator similar to that illustrated in FIG. 1 is disclosed; but that has one inlet  56  and two outlets  52 ,  54 . First outlet  52  is positioned at the end opposite the inlet  56 , as shown in FIG.  11 . The second outlet  54  is positioned proximate the first outlet  52  but on the sidewall  13  of the longitudinal chamber  20 . Relatively hot vapor exits through the first outlet  52 , while relatively cool liquid exits through the second outlet  54 . 
     The vortex generator disclosed in FIG. 11 utilizes a liquid extractor  55  to separate condensed liquid from vapor. The liquid extractor  55  is a projection (in the illustrated embodiment it is triangular or fin-shaped, but can be almost any shape, e.g., rectangular, circular, etc.) that protrudes slightly into the longitudinal chamber  20 . Since the liquid droplets  68  move in a spiral path along the inner wall  21  of sidewall  13  of the vortex generator, such a liquid extractor  55  can collect almost all of the liquid droplets that are formed. 
     The vortex generator illustrated herein has been tested over a range of refrigerant flow rates between 0.01 and 0.022 kg/s. The dimensions of the vortex generator identified in this application are based primarily on this flow rate range. However, for higher flow rates, the vortex generator will have substantially larger dimensions. 
     Although this invention has been described and illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made which clearly fall within the scope of this invention. For example, the present invention can be utilized with all condensible vapors, including steam, R-12, R-22, R-113 , R-134a, R410a, ammonia, carbon dioxide, natural gas, etc. The present invention is intended to be protected broadly within the spirit and scope of the appended claims.