|Publication number||USRE43398 E1|
|Application number||US 11/366,986|
|Publication date||May 22, 2012|
|Filing date||Mar 1, 2006|
|Priority date||Jun 16, 1997|
|Publication number||11366986, 366986, US RE43398 E1, US RE43398E1, US-E1-RE43398, USRE43398 E1, USRE43398E1|
|Inventors||Scott C. Honkonen, Theodore B. Hill, Charles C. Hill, Graham Walker|
|Original Assignee||Respironics, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (227), Non-Patent Citations (3), Referenced by (11), Classifications (55), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation-in-part of U.S. patent application Ser. No. 08/876,970, filed Jun. 16, 1997 now U.S. Pat. No. 5,979,440.
The field of this invention relates to using an oxygen concentrator to create a portable supply of supplementary oxygen for ambulatory respiratory patients so that they can lead normal and productive lives—as the typical primary oxygen sources are too bulky to carry or require excessive power to operate.
There is a burgeoning need for home and ambulatory oxygen. Supplemental oxygen is necessary for patients suffering from lung disorders; for example, pulmonary fibrosis, sarcoidosis, or occupational lung disease. For such patients, oxygen therapy is an increasingly beneficial, life-giving development. While not a cure for lung disease, supplemental oxygen increases blood oxygenation, which reverses hypoxemia. This therapy prevents long-term effects of oxygen deficiency on organ systems—in particular, the heart, brain and kidneys. Oxygen treatment is also prescribed for Chronic Obstructive Pulmonary Disease (COPD), which afflicts about 25 million people in the U.S., and for other ailments that weaken the respiratory system, such as heart disease and AIDS. Supplemental oxygen therapy is also prescribed for asthma and emphysema.
The normal prescription for COPD patients requires supplemental oxygen flow via nasal cannula or mask twenty four hours per day. The average patient prescription is two liters per minute of high concentration oxygen to increase the oxygen level of the total air inspired by the patient from the normal 21% to about 40%. While the average oxygen flow requirement is two liters per minute, the average oxygen concentrator has a capacity of four to six liters of oxygen per minute. This extra capacity is occasionally necessary for certain patients who have developed more severe problems but they are not generally able to leave the home (as ambulatory patients) and do not require a portable oxygen supply.
There are currently three modalities for supplemental medical oxygen: high pressure gas cylinders, cryogenic liquid in vacuum insulated containers or thermos bottles commonly called “dewars,” and oxygen concentrators. Some patients require in-home oxygen only while others require in-home as well as ambulatory oxygen depending on their prescription. All three modalities are used for in-home use, although oxygen concentrators are preferred because they do not require dewar refilling or exchange of empty cylinders with full ones.
Only small high pressure gas bottles and small liquid dewars are portable enough to be used for ambulatory needs (outside the home). Either modality may be used for both in-home and ambulatory use or may be combined with an oxygen concentrator which would provide in-home use.
As we describe below, the above-described current methods and apparatus have proven cumbersome and unwieldy and there has been a long-felt need for improved means to supply the demand for portable/ambulatory oxygen.
For people who need to have oxygen but who need to operate away from an oxygen-generating or oxygen-storage source such as a stationary oxygen system (or even a portable system which cannot be easily carried), the two most prescribed options generally available to patients are: (a) to carry with them small cylinders typically in a wheeled stroller; and (b) to carry portable containers typically on a shoulder sling. Both these gaseous oxygen and liquid oxygen options have substantial drawbacks. But from a medical view, both have the ability to increase the productive life of a patient.
The major drawback of the gaseous oxygen option is that the small cylinders of gaseous oxygen can only provide gas for a short duration. Oxygen conserving devices that limit the flow of oxygen to the time of inhalation may be used. However, the conserving devices add to the cost of the service and providers have been reluctant to add it because there often is no health insurance reimbursement. Indeed, the insurance reimbursement for medical oxygen treatment appears to be shrinking.
Another drawback of the gaseous oxygen option is the source of or refill requirement for oxygen once the oxygen has been depleted from the cylinder. These small gas cylinders must be picked up and refilled by the home care provider at a specialized facility. This requires regular visits to a patient's home by a provider and a substantial investment in small cylinders for the provider because so many are left at the patient's home and refilling facility. Although it is technically possible to refill these cylinders in the patient's home using a commercial oxygen concentrator that extracts oxygen from the air, this task would typically require an on-site oxygen compressor to boost the output pressure of the concentrator to a high level in order to fill the cylinders. Additionally, attempting to compress the oxygen in pressurized canisters in the home is dangerous, especially for untrained people. This approach of course presents several safety concerns for in-home use. For example, in order to put enough of this gas in a portable container, it must typically be compressed to high pressure (˜2000 psi). Compressing oxygen from 5 psi (the typical output of an oxygen concentrator) to 2000 psi will produce a large amount of heat. (Enough to raise the temperature 165° C. per stage based on three adiabatic compression stages with intercooling.) This heat, combined with the oxygen which becomes more reactive at higher pressures, sets up a potential combustion hazard in the compressor in the patient's home. Thus, utilizing and storing a high pressure gas system in the patient's home is dangerous and not a practical solution.
The convenience and safety issues are not the only drawbacks of this compressed oxygen approach. Another drawback is that the compressors or pressure boosters needed are costly because they require special care and materials needed for high pressure oxygen compatibility. For example, a Rix Industries, Benicia, Calif., ⅓ hp unit costs about $10,000 while a Haskel International, Burbank, Calif., air-powered booster costs about $2200 in addition to requiring a compressed air supply to drive it. Litton Industries and others also make oxygen pressure boosters.
Turning now to the liquid oxygen storage option, its main drawback is that it requires a base reservoir—a stationary reservoir base unit about the size of a standard beer keg—which has to be refilled about once a week. The liquid oxygen can then be obtained from a base unit and transferred to portable dewars which can be used by ambulatory patients. Also, with the liquid oxygen option, there is substantial waste, as a certain amount of oxygen is lost during the transfer to the portable containers and from evaporation. It is estimated that 20% of the entire contents of the base cylinder will be lost in the course of two weeks because of losses in transfer and normal evaporation. These units will typically boil dry over a period of 30 to 60 days even if no oxygen is withdrawn.
There are other complications. Typically, supplemental oxygen is supplied to the patient by a home care provider, in exchange for which it receives a fixed monetary payment from insurance companies or Medicare regardless of the modality. Oxygen concentrators for use in the home are preferred and are the least expensive option for the home care provider. For outside the home use however, only small high pressure gas bottles and small liquid dewars are portable enough to be used for ambulatory needs. One of these two modalities may be used for both in-home and ambulatory use or may be combined with an oxygen concentrator which would provide in-home use. In either case, the home care provider must make costly weekly or biweekly trips to the patient's home to replenish the oxygen. One of the objects of this invention is to eliminate these costly “milk runs.”
Portable oxygen concentrators are commercially available for providing patients with gaseous oxygen. These devices are “portable” solely in the sense that they can be carried to another point of use such as in an automobile or in an airplane. At present, there are no home oxygen concentrators commercially available that can provide liquid oxygen. One type of medical oxygen concentrator takes in air and passes it through a molecular sieve bed, operating on a pressure swing adsorption cycle, which strips most of the nitrogen out, producing a stream of ˜90% oxygen, for example, as shown in U.S. Pat. Nos. 4,826,510 and 4,971,609 (which are incorporated herein by reference). While, as set out in the Information Disclosure Statement, complex oxygen liquefaction systems have been disclosed for use by the military in jet aircraft, and while large-scale commercial plants have been disclosed, this technology has not yet found its way into the home to help individual patients and to benefit the general public. A truly portable oxygen concentrator has not yet been perfected and this event is unlikely, at least in the near future, because the power requirements are too large to be provided by a lightweight battery pack.
Since liquid oxygen requires periodic delivery and home oxygen concentrators are not commercially available that would create liquid oxygen, there has existed a long-felt need for a device or method having the capability to concentrate oxygen from the air, liquefy it, and transfer it into portable dewars in a home environment, and for a home oxygen concentrator unit which allows excess flow capacity from the concentrator to be stored by either compression or liquefaction for later use.
An aspect of the present invention involves a home liquid oxygen ambulatory system for supplying a portable supply of oxygen, where a portion of the gaseous oxygen output obtained from an oxygen concentrator is condensed into liquid oxygen. The system includes an oxygen concentrator which separates oxygen gas from the ambient air, a condenser in communication with the oxygen concentrator for receiving and liquefying the oxygen gas flow, a cryocooler associated with the condenser, and a first storage dewar in fluid communication with the condenser and adapted to store the oxygen liquefied by the condenser, the first storage dewar including means for transferring liquid oxygen from the first dewar to a second dewar for storing a quantity of oxygen suitable for moveable oxygen treatment.
In an embodiment of the above aspect of the invention, the liquid oxygen transferring means is adapted to increase the pressure in the first dewar.
In a further embodiment of the above aspect of the invention, the liquid transferring means includes a heater immersed within the liquid oxygen in the first dewar.
In a still further embodiment of the above aspect of the invention, the first dewar includes an inner vessel in which the liquid oxygen reside, and liquid transferring means includes a heater attached to the outer surface of inner vessel.
In another embodiment of the above aspect of the invention, the condenser is in communication with the concentrator through a line, and the liquid transferring means includes a compressor located in the line between the condenser and the concentrator.
In an additional embodiment of the above aspect of the invention, the liquid transferring means includes a high-pressure compressor in communication with the concentrator for delivering high-pressure air thereto.
In another embodiment of the above aspect of the invention, the liquid transferring means includes a vaporizer loop associated with the first dewar.
In a further embodiment of the above aspect of the invention, the liquid transferring means includes a controllable heat leak associated with the first dewar.
In a still further embodiment of the above aspect of the invention, the liquid transferring means includes a gravity-assisted dispensing mechanism.
In an additional embodiment of the above aspect of the invention, the system further includes the second storage dewar and the second storage dewar is adapted to be filled at a pressure below 20 psig.
An additional aspect of the invention involves a home liquid oxygen ambulatory system for supplying a portable supply of oxygen, where a portion of the gaseous oxygen output obtained from an oxygen concentrator is condensed into liquid oxygen. The system includes an oxygen concentrator which separates oxygen gas from the ambient air, a condenser in communication with the oxygen concentrator for receiving and liquefying the oxygen gas flow, a cryocooler associated with the condenser, and a portable dewar adapted to interface with the condenser and adapted to store the oxygen liquefied by the condenser.
Another aspect of the present invention involves a method for generating liquid oxygen in a home from a home liquid oxygen ambulatory system having an oxygen concentrator, a condenser, and cryocooler, a storage dewar and means for transferring liquid oxygen from the first dewar to a second dewar. The method includes generating a gaseous supply of oxygen using the oxygen concentrator; splitting off at least a portion of the gaseous supply to be liquefied; cooling the supply of oxygen using the condenser and cryocooler to transform the gaseous oxygen to liquid oxygen; storing the liquid oxygen in the storage dewar; and transferring the liquid oxygen in the storage dewar with the liquid oxygen transferring means to a second dewar for storing a quantity of liquid oxygen from which smaller quantities can be transferred for moveable oxygen treatment.
In an embodiment of the above aspect of the invention, transferring the liquid oxygen includes increasing the pressure in the first dewar.
In an additional embodiment of the above aspect of the invention, the liquid transferring means includes a heater immersed within the liquid oxygen in the first dewar and transferring the liquid oxygen includes heating the liquid oxygen in the first dewar so that the pressure is increased in the first dewar.
In another embodiment of the above aspect of the invention, the first dewar includes an inner vessel in which the liquid oxygen reside, the liquid transferring means includes a heater attached to the outer surface of inner vessel, and transferring the liquid oxygen includes heating the liquid oxygen in the first dewar so that the pressure is increased in the first dewar.
In a further embodiment of the above aspect of the invention, the condenser is in communication with the concentrator through a line, and the liquid transferring means includes a compressor located in the line between the condenser and the concentrator, and transferring the liquid oxygen includes increasing the pressure of gaseous oxygen entering the condenser and the dewar with the compressor.
In a still further embodiment of the above aspect of the invention, the liquid transferring means includes a high-pressure compressor in communication with the concentrator for delivering high-pressure air thereto, and transferring the liquid oxygen includes increasing the pressure of gaseous oxygen entering the condenser and the dewar with the compressor.
In an additional embodiment of the above aspect of the invention, the liquid transferring means includes a vaporizer loop associated with the first dewar, and transferring the liquid oxygen includes heating the liquid oxygen in the first dewar with the vaporizer loop so that the pressure is increased in the first dewar.
In another embodiment of the above aspect of the invention, the liquid transferring means includes a controllable heat leak associated with the first dewar, and transferring the liquid oxygen includes heating the liquid oxygen in the first dewar so that the pressure is increased in the first dewar.
In a further embodiment of the above aspect of the invention, the liquid transferring means includes a gravity-assisted dispensing mechanism.
In a still further embodiment of the above aspect of the invention, the system further includes the second storage dewar, the second storage dewar is adapted to filled at a pressure below 20 psig.
Another aspect of the present invention involves a liquefier for a home liquid oxygen ambulatory system that is resistant to plugging. The home liquid oxygen ambulatory system includes an oxygen concentrator for delivering gaseous flow to the liquefier and a storage dewar having an inner vessel for storing liquid oxygen produced by the liquefier. The liquefier includes a condenser, a refrigerating device associated with the condenser, means for communicating incoming gaseous flow from the oxygen concentrator to the condenser, the communicating means having an inner surface with a dimension D, means for venting gaseous flow not condensed from the inner vessel, the venting means having an outer surface with an dimension d, and whereby the dimension D of the inner surface of the communicating means is significantly larger than the dimension d of the outer surface of the venting means to allow for the build-up of solid contaminants on the outer surface of the venting means without plugging up the communicating means.
In an embodiment of the above aspect of the invention, the venting means includes a recuperator comprised of a helical coil of tubing, the tubing having the outer surface with a diameter of the dimension d, whereby the incoming gas stream flows over the outer surface of the helical coil of tubing and a vent stream flows inside the helical coil of tubing.
In another embodiment of the above aspect of the invention, the outer surface of the helical coil of tubing has a cold surface to freeze out trace impurities of solid contaminants such as H2O, CO2 and hydrocarbons.
In a further embodiment of the above aspect of the invention, the communicating means is comprised of a neck tube having the inner surface with a diameter of the dimension D.
In a still further embodiment of the above aspect of the invention, the liquefier further includes a liquid withdrawal tube located central to the refrigerating device, recuperator and condenser for removing liquid oxygen from the storage dewar.
In an additional embodiment of the above aspect of the invention, the refrigerating device is integral with the condenser.
In another embodiment of the above aspect of the invention, the refrigerating device, condenser and recuperator are integral with the storage dewar.
Another aspect of the invention involves a method for generating liquid oxygen in a home from a home liquid oxygen ambulatory system having an oxygen concentrator, a condenser, a cryocooler, a recuperator and a storage dewar. The method includes generating a gaseous supply of oxygen, which includes some trace impurities, using the oxygen concentrator; splitting off at least a portion of the gaseous supply to be liquefied; cooling the supply of oxygen using the condenser and cryocooler to transform the gaseous oxygen to liquid oxygen; condensing less than all of the gaseous oxygen supply flowing into the condenser; freezing out the trace impurities of the gaseous supply of oxygen and venting the non-condensed nitrogen, argon and oxygen with the recuperator; storing the liquid oxygen in the storage dewar; and periodically removing accumulated frozen impurities on the recuperator by boiling-off any stored liquid oxygen and then flow purging the system until the system has reached room temperature.
Another aspect of the invention involves a generally vertically oriented, gravity assisted condenser for use with a refrigerating device to liquefy gaseous oxygen in a home liquid oxygen ambulatory system. The condenser includes a generally vertically oriented tubular member adapted to conduct heat axially to the refrigerating device, the tubular member having outer and inner surfaces, at least one of the outer and inner surfaces having a plurality of generally vertically oriented flutes and convex fins adapted to increase the condensation rate per unit area by thinning the liquid film and drain the condensate to keep the condensate from flooding the condensation surfaces.
In an embodiment of the above aspect of the invention, the fins have a hyperbolic cosine profile.
In an additional embodiment of the above aspect of the invention, the flutes have a profile selected from the group consisting of concave, generally V-shaped, generally rectilinear.
In another embodiment of the above aspect of the invention, the plurality of generally vertically oriented flutes and convex fins are located on both the outer and inner surfaces.
Another aspect of the invention involves a generally vertically oriented, gravity assisted condenser for use with a refrigerating device to liquefy gaseous oxygen in a home liquid oxygen ambulatory system. The condenser includes a generally vertically oriented tubular member adapted to conduct heat axially to the refrigerating device, the tubular member having outer and inner surfaces, at least one of the outer and inner surfaces includes means for enhancing the condensation rate per unit area by maintaining a small liquid film thickness on the condensation surfaces.
In an embodiment of the above aspect of the invention, the condensation enhancing means includes a plurality of generally vertically oriented flutes and convex fins.
In an additional embodiment of the above aspect of the invention, the fins have a hyperbolic cosine profile.
In a further embodiment of the above aspect of the invention, the flutes have a profile selected from the group consisting of concave, generally V-shaped, generally rectilinear.
In a still further embodiment of the above aspect of the invention, the plurality of generally vertically oriented flutes and convex fins are located on both the outer and inner surfaces.
A flow chart of the preferred embodiment of the invention is set out in
Controller 16 may be equipped with a microprocessor, adequate memory, software and ancillary equipment comprising a computer which can be used to monitor and control the operation of the system. The controller 16 may be provided with signals from liquid level sensor 17, oxygen sensor 18, pressure transducer 9, and temperature sensor 10 via lines 53, 59, 55 and 56, respectively. These signals are sensed and processed by the computer, with the controller operating valve 19, valve 25, heater 21, and cryocooler 12, in accordance with predetermined programs.
The controller also provides output indicators for the patient. The liquid level in the dewar is continuously displayed and the patient is alerted when the oxygen concentration is low and when the system is ready for them to transfer liquid to a portable dewar. A modem or wireless link may be included to enable remote monitoring of the key parameters of the system by the home care provider as well as information which is useful for repair, maintenance, billing, and statistical studies of patients for the medical oxygenation market. Key system parameters of interest include the number of liquid transfers performed, the oxygen concentration history, number of run hours on the cryocooler, and time of the last boil-dry as well as number of boil dries performed. The controller may include a computer and/or a microprocessor located either integrally with the liquefaction system claimed herein or remotely therefrom but in communication therewith using either a modem and telephone lines or with a wireless interface. The computer and/or microprocessor may include memory having a database, or may be remotely connected to a memory or database using a network. An Optimal Liquefaction Schedule for optimal operation of the liquefaction system is set out in
Dewar 14 is equipped with a dip tube 20 and heater 21. Heater 21 is used to build pressure in the dewar in order to expel liquid out the dip tube 20 when so desired. A quick disconnect valve 22 or other flow control means is located on the end of the dip tube. This allows connection of a portable LOX dewar 23, which can then be carried by the patient requiring a mobile/ambulatory supply of oxygen.
In another embodiment of this system shown in
In operation, in the preferred embodiment of
Even though 88% oxygen is adequate as supplemental oxygen therapy, if this was liquefied, as will be described below, the initial revaporized stream may have a reduced oxygen content because of the close boiling points of the components of the mixture. The temperature of the split gas stream entering the recuperator 15 is about room temperature. It is cooled to about 270 K (or colder) by the vent gas from the dewar flowing through the other side of the recuperator via line 52. The recuperator 15 reduces the load on the cryocooler by using the cold vent gas to pre-cool the oxygen-rich gas stream flowing into the condenser 13. From the recuperator 15 the high oxygen concentration stream flows through a line 57 to the condenser 13, which is cooled to ˜90 K by the cryocooler 12.
The condenser 13 provides cold surfaces to further cool and condense the flow. It is important to note that the gas passing through the condenser 13 is a mixture of oxygen, argon, and nitrogen. The normal boiling points of these components are: 90.18 K, 87.28 K, and 77.36 K respectively. Because of the close boiling points of the components of this mixture, there was initial skepticism because of the concern that all the nitrogen and argon would condense along with the oxygen. If this concern was realized, when this liquid mixture was revaporized, the lower boiling point components; i.e., nitrogen and argon, would boil off first, resulting in flow with high concentrations of nitrogen, argon and a much lower oxygen concentration than that which was supplied to the condenser—which would make the process of oxygen treatment ineffective or a failure.
This concern is explained in
Because of the aforementioned mixture problem, it is important and even critical not to let the amount of argon and nitrogen in the liquid become too high or when it is revaporized, the oxygen concentration will initially be much lower than that conventionally used in supplemental oxygen therapy (>85%). This can be accomplished by selecting the proper condenser temperature, which is a function of pressure, and by not condensing all of the incoming flow. If only part of the incoming flow (20-99%) is liquefied, the remainder of the flow will purge the vapor with higher impurity concentration from the system. A condenser temperature of about 90 K (for ˜17 psia) minimizes the amount of argon and nitrogen liquefied without overly diminishing the yield of oxygen. Hence there will be both liquid and vapor leaving the condenser. The liquid will fall into the dewar 14 and collect. The vapor which has not condensed is vented to the atmosphere through line 52 and the recuperator 15.
The amount of incoming flow liquefied is controlled by setting the mass flow rate relative to the cooling capacity of the cryocooler. The parameters of the condenser and/or cryocooler can be stored in the memory of the controller and/or computer and the controller regulating the incoming flow depending on the parameters stored and/or sensed. Having a mass flow rate which exceeds the cooling capacity of the cryocooler/condenser combination, prevents the incoming flow from being completely liquefied. The mass flow rate is controlled by the amount of flow restriction between inlet valve 19 and flow control valve 25. This includes the flow losses of the valves themselves as well as those in the recuperator, condenser, and all of the interconnecting plumbing.
The pressure in the dewar 14 is maintained slightly above ambient pressure while the cryocooler is operating by valve 25. It is desirable to keep the pressure in the condenser as high as possible because this increases the condensation temperature (as shown in
This pressure regulating function of the solenoid on-off valve 25 is accomplished by the pressure transducer 9 and controller 16. Alternately, a back pressure regulating valve (such as a Tescom BB-3 series) or a suitable servomechanism may be used in lieu of the actively controlled solenoid. Liquid keeps accumulating in the dewar 14 until the liquid level sensor 17 signals the controller that the dewar is full or until the oxygen sensor 18 signals that the oxygen concentration of fluid exiting the oxygen concentrator 11 is too low.
In the best mode, operating parameters for optimal operation of the system for the condenser should be that the condenser surface temperature should be in the range from 69.2-109.7 K and pressure should be in the range from 5-65 psia. The gas concentrations into the condenser for medical use should have oxygen in the range of 80-100%, nitrogen from 0-20%, and argon from 0-7%.
In order to transfer liquid from the dewar 14; e.g. to fill a portable LOX dewar 23, the pressure in the dewar 14 must be increased so that liquid can be forced up the dip tube 20. As shown in
With reference to
An alternative means for transferring liquid by raising the pressure in the dewar 14 includes adding a compressor 300 between the oxygen concentrator 11 and the condenser 13. The compressor 300 is preferably added in line 51, either before or after valve 19. The compressor 300 increases the pressure in the storage dewar 14 so that when the portable dewar 23 is engaged, liquid is forced up the dip tube 20 and into the portable dewar 23. An additional benefit of adding a compressor 300 at this location is that it increases the pressure during liquefication in the dewar 14, which increases the saturation temperature. An increased saturation temperature eases the cooling requirements on the cryocooler 12.
A further means for transferring liquid by raising the pressure in the dewar 14 includes using a high-pressure compressor 302 within the oxygen concentrator 11 instead of the typical low-pressure compressor. The high-pressure compressor 302 has the effect of increasing the pressure in the storage dewar 14 so that when the portable dewar 23 is engaged, liquid is forced up the dip tube 20. In addition to easing the cooling requirements on the cryocooler 12, a compressor 302 at this location slightly enhances the PSA cycle.
A still further means for transferring liquid by raising the pressure in the dewar 14 includes using a vaporizer loop 304. In this embodiment, the dewar 14 preferably remains at low pressure while liquid is being produced. When transfer of liquid out of the dewar 14 is desired, a valve 306 is opened to allow some liquid to flow into a coil 308 to be vaporized. This would increase the pressure in the dewar 14 so that liquid could be transferred to the portable dewar 23.
Another means for transferring liquid by raising the pressure in the dewar 14 includes a controllable heat leak such as a conductive strap 310 between ambient and the inner vessel of the dewar 14. When transfer of liquid out of the dewar 14 is desired, the heat leak is controlled so that heat from the ambient is transferred to the liquid, causing it to vaporize. This would increase the pressure in the dewar 14 so that liquid could be transferred to the portable dewar 23.
Another means for transferring liquid by raising the pressure in the dewar 14 includes a controllable pump 312 that is actuated when transfer of liquid out of the dewar 14 is desired.
An additional means for transferring liquid without raising the pressure in the dewar 14 includes incorporating a gravity-assisted dispensing mechanism 314 such as a controllable spigot (analogous to those used to dispense liquids from a large insulated cooler) near the bottom of the dewar 14. Unlike the alternative means for transferring liquid from the storage dewar 14 described above, which expel liquid out of the dip tube 20, the gravity-assisted dispensing mechanism eliminates the need for the dip tube 20. The gravity-assisted dispensing mechanism 314 preferably includes a quick disconnect valve 316 or other flow control means, similar to disconnect valve 22 described above, located on the end of the mechanism 314 to allow for connection of a portable dewar 23.
An additional means for transferring liquid without raising the pressure in the dewar 14 includes incorporating a portable dewar 23 adapted to be filled from a pressure less than 20 psig, which is the standard for currently available home stationary liquid dewars. For example, the portable dewar 23 may be adapted to be filled from a pressure such as 5 psig.
A further means for transferring liquid without raising the pressure in the dewar 14 involves replacing the storage dewar 14 with a specially designed portable dewar 23 such as that described above with respect to
In order to eliminate accumulation of solid water and hydrocarbons which may be supplied in trace amounts from the oxygen concentrator, the dewar 14, recuperator 15, and condenser 13 will be warmed to room temperature periodically (preferably after about 30 fillings of a portable dewar, or every two months). This procedure is accomplished most economically when the inventory of liquid in the storage dewar is low; e.g. shortly after liquid transfer and a portable dewar has been filled. In this “boil-dry” mode, valve 19 will be closed, the cryocooler 12 is turned-off, valve 25 is open, and heater 21 is energized until all the liquid has boiled-off as evidenced by, for example, the temperature sensor 10 being above 125 K. The heater will boil-off the remaining liquid in the dewar 14 and with it any trace amounts of water and hydrocarbons which are condensed and solidified in the liquid oxygen or on the cold surfaces. Once valve 19 is re-opened, the flow of concentrated oxygen gas purges and removes most of the water vapor and hydrocarbons from the liquefier. The heater 21 will remain turned on until the dewar temperature, measured by temperature sensor 10, has warmed to about 300 K. Any remaining water vapor will be flushed out by gaseous oxygen during the subsequent cooldown.
The dewpoint/frostpoint of the gas stream provided by the oxygen concentrator is below −55° C. Although the mass of water flowing into the liquefier is quite small, the ice/frost formed at such a cold temperature has a very low density and hence, can take a appreciable volume of space that can lead to plugging of the liquefier. Therefore, the design of the recuperator 15 and/or condenser 13 must be able to allow for accumulation of frost without plugging.
With reference to
Oxygen from the gaseous flow condenses into liquid oxygen at the condenser 74. The condenser 74 is shown in conjunction with a vapor compression cycle cryocooler 86 (evaporator 88, tube-in-tube heat exchanger 90, compressor 92) as its associated refrigerating mechanism. It will be readily understood by those skilled in the art that other refrigerating mechanisms may be used in conjunction with the condenser such as, but not by way of limitation, pulse tube, Stirling, etc. For example, with reference to
Excess gaseous flow not condensed becomes vent gas that is removed from the liquefier 70 via the recuperator 76. Vent gas enters the recuperator 76 through inlet 112, as shown by the arrows, flows through the helical recuperator 76 (providing the aforementioned pre-cooling) and preferably exits to the atmosphere through outlet 114.
The dewar 14 may include a central liquid withdrawal tube 116 for withdrawing liquid oxygen from the dewar 14. The central liquid withdrawal tube 116 may include an integral liquid level sensor 118 for monitoring the level of the liquid oxygen in the dewar 14. A heater 21 may be attached to the outer surface of the inner vessel of the dewar 14 to assist in transferring liquid oxygen from the dewar 14.
A getter cup 120 such as those used in commercial cryogenic dewars may be attached to the inner vessel of the dewar 14 to maintain a high vacuum in the dewar 14.
At initial start-up or after a periodic boil-dry phase, the dewar, condenser, recuperator, and all associated hardware are at room temperature and must be cooled down. This is accomplished in the “start-up” mode, where valve 19 (see
The higher density gas will have better heat transfer with the dewar walls and associated hardware. It is noted that higher flow rates will enhance the convection heat transfer but may exceed the cooling capacity. Based on the cooling characteristics of the cryocooler between room temperature and 90 K, the flow rate can be changed to minimize the cool-down time.
The dewar 14 is equipped with at least one relief valve 26 as a safety feature. Another relief valve 29 is provided and in communication with the inlet gas stream 51, before flowing into the recuperator 15. This serves as a back-up for relief valve 26 as well as providing a means to eliminate accumulated water from the recuperator 15 during periods when the cryocooler 12 is off, if valve 25 is closed. A check valve 27 is also provided to prevent backflow into the oxygen concentrator in the event of a malfunction.
Once the system attains a cool enough temperature, steady state or normal operational condense mode is used. As shown in
The transfer mode in
The double inlet pulse tube refrigerator as shown in
It is noted that with this type of cryocooler, it may be possible to remove some of the heat from the oxygen stream at a temperature warmer than Tc.
One possible geometry of the generally vertically oriented, gravity assisted condenser 13 in
In an alternative embodiment of the invention, the flutes 114 may have a profile that is other than convex such as, but not by way of limitation, generally rectilinear or generally V-shaped.
In a further embodiment of the invention, the fins 112 and flutes 114 may exist on only the exterior side 116 or interior side 118 of the condenser 110. Alternatively, the condenser 110 may have fins 112 and flutes 114 on the interior and/or the exterior and the condenser 110 is used in conjunction with another condensing device such as another condenser located within the interior 118 and/or around the exterior 116 of the condenser 110.
Prior art (U.S. Pat. Nos. 4,253,519, 4,216,819) has been limited to horizontal externally fluted tubes with purely radial conduction through the tube wall. In contrast, the condenser 110 of the present invention may include fins 112 and flutes 114 on both sides 116, 118. Also, heat is conducted axially in the condenser 110 of the present invention.
Thus, an improved home/ambulatory liquid oxygen system is disclosed. While the embodiments and applications of this invention have been shown and described, and while the best mode contemplated at the present time by the inventors has been described, it should be apparent to those skilled in the art that many more modifications are possible, including with regard to scaled-up industrial applications, without departing from the inventive concepts therein. Both product and process claims have been included and in the process claims it is understood that the sequence of some of the claims can vary and still be within the scope of this invention. The invention therefore can be expanded, and is not to be restricted except as defined in the appended claims and reasonable equivalence departing therefrom.
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|U.S. Classification||128/201.21, 128/200.24, 128/204.17, 128/204.15|
|International Classification||A62B7/00, A62B7/06|
|Cooperative Classification||Y02P70/34, F17C2265/015, F17C2270/0509, F17C2223/0161, F17C2221/011, F17C2227/0353, F25J1/0276, F25J2205/80, F25J2205/40, F25J1/0244, F25J1/0212, F25J2220/50, F25J1/0052, F25J1/0017, F25J1/0225, B01D2257/102, B01D2257/504, B01D2259/40001, B01D5/0039, B01D2259/4533, F17C6/00, F25J2205/60, B01D2257/404, B01D2253/116, B01D2257/80, B01D2259/4525, B01D2257/502, F25B9/145, B01D2259/416, B01D2253/108, B01D53/261, F25J2210/40, Y02C10/08, B01D53/047, B01D2259/455, F25B9/006, B01D2256/12, B01D53/053, B01D2259/40009, B01D2259/4541, F25J2270/90, F25J2270/91|
|European Classification||F25J3/04M, F25J3/04Z4U, F17C6/00, F25J1/02Z4U2, F25J3/04C4, B01D5/00F12, B01D53/047|