Oxygen concentrating apparatus

An oxygen concentrating apparatus (10) has an oxygen concentrating unit (12), a compressor (26) for supplying compressed air to the oxygen concentrating unit (12) and a compressor housing (28) for accommodating the compressor (26). The compressor housing (28) includes a plurality of air inlet ports (28a) for introducing the air into the compressor housing (28) and an air outlet opening (28b) for discharging the air from the compressor housing (28). A cooling fan (30) is mounted on the compressor housing (28) at the air outlet opening (28b) for drawing the air from the compressor housing (28). The air inlet ports (28a) are disposed adjacent to the side wall of the compressor (26) to direct the air flow induced by the cooling fan perpendicularly to the side wall of the compressor (26). The capacity of the cooling fan (30) and the diameter of the air inlet ports (28a) are selected to ensure the velocity of the air flow through the air inlet ports (28a) is equal to or lower than 15 m/sec.

TECHNICAL FIELD

The present invention relates to an oxygen concentrating apparatus including a cooling device for a compressor which supplies compressed air to a plurality of adsorption columns filled with an adsorbent such as zeolite.

BACKGROUND ART

Oxygen inhalation therapy has been employed as a most effective method of treatment for respiratory system diseases such as asthma, pulmonary emphysema or chronic bronchitis. In oxygen inhalation therapy, an oxygen concentrated gas is supplied to the patient. For this purpose, package-type oxygen concentrating apparatuses have been developed for use in the home. The package-type oxygen concentrating apparatus includes an oxygen concentrating unit for producing oxygen gas by separating nitrogen gas from the air, a compressor for supplying compressed air to the oxygen concentrating unit and a case for accommodating the oxygen concentrating unit and the compressor in order to insulate the noise. Japanese Unexamined Patent Publications (Kokai) No. 62-140619 and No. 63-218502 disclose examples of such apparatuses.

DISCLOSURE OF THE INVENTION

Recently, some oxygen concentrating apparatus further include a compressor housing, disposed in the case, for accommodating the compressor in order to minimize the noise emission from the apparatus. However, the compressor housing prevents the compressor, disposed therein, from being cooled.

Therefore, the objective of the invention is to provide an oxygen concentrating apparatus improved to efficiently cool the compressor disposed in the compressor housing while an increase in the weight of the apparatus is minimized.

According to the invention, there is provided an oxygen concentrating apparatus which comprises an oxygen concentrating unit, including an adsorption column filed with an adsorbent material which selectively adsorbs nitrogen gas more than oxygen gas, a compressor for supplying compressed air to the oxygen concentrating unit, a compressor housing for accommodating the compressor, the compressor housing including a plurality of air inlet ports for introducing the air into the compressor housing and an air outlet opening for discharging the air from the compressor housing, a cooling fan mounted on the compressor housing at the air outlet opening for drawing the air from the compressor housing and the air inlet ports being disposed adjacent the side wall of the compressor to direct the air flow induced by the cooling fan perpendicularly to the side wall of the compressor. The capacity of the cooling fan and the diameter of the air inlet ports are selected to ensure that a velocity of the air flow through the air inlet ports is equal to or lower than 15 m/sec.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference toFIGS. 1 and 2, a preferred embodiment of the present invention will be described below.

An oxygen concentrating apparatus10according to the embodiment of the invention includes an oxygen concentrating unit12, a compressor unit14for supplying the compressed air to the oxygen concentrating unit12, a tank16for containing the oxygen concentrated gas from the oxygen concentrating unit12, a battery as an electric power source18for the oxygen concentrating unit12and the compressor unit14, electric circuit boards20and22for controlling the oxygen concentrating unit12and the compressor unit14, and a case24accommodating all of the above elements12-22. The oxygen concentrating apparatus10further includes a plurality of conduits or pipes (not shown) for fluidly connecting the oxygen concentrating unit12, the compressor unit14and the tank16. The case24includes an air inlet opening24a, through which the air is introduced into the case24, and a gas outlet opening24bthrough which the nitrogen gas, separated from the air by the oxygen concentrating unit12, is exhausted.

Preferably, the oxygen concentrating unit12may comprise a pressure swing type gas separator. In this particular embodiment, the oxygen concentrating unit12includes a plurality of adsorption columns12afilled with an adsorbent such as zeolite which selectively adsorbs nitrogen gas more than oxygen gas. The oxygen concentrating unit12further includes switching mechanisms12band12cfor sequentially selectively switching the adsorption columns to which the air is supplied from the compressor unit14, and the adsorption columns from which the absorbed nitrogen is released, for regeneration of the adsorbent so that the respective adsorption columns repeatedly absorb nitrogen gas and release the absorbed nitrogen gas according to an absorption-regeneration cycle.

With reference toFIG. 2, the compressor unit14includes a compressor26, a compressor housing28, made of a suitable material, for example, a synthetic resin, such as NBR (acrylonitrile-butadiene rubber), to accommodate the compressor26and to provide noise insulation, and a cooling fan30. The housing28has a foamed polyurethane linear attached to the inner surface thereof as a noise insulating material. The compressor26may comprise any type of compressor, such as a reciprocating compressor and a rotary compressor. In the embodiment ofFIG. 2, the compressor26is a reciprocating compressor and is, for example, a Horizon Model 2250 pressure/vacuum pump, available from Rietschle Thomas, 7222-T Parkway Dr., Hanover, Md. The compressor has cylinders26awithin which pistons (not shown) are slidably disposed, cylinder heads26battached to the ends of the cylinders26aand a diving motor26c. The output shaft of the driving motor26cis connected to a crank shaft (not shown) to which the pistons are connected through connection rods so that the rotation of the driving motor26cis transformed to the reciprocation of the pistons.

The compressor housing28preferably has a configuration similar to the exterior configuration of the compressor26to efficiently pass the air along the surface of the compressor26. The compressor housing28includes a plurality of air inlet ports28a, an air outlet opening28band at least side walls facing the cylindrical side walls of the cylinders26aand defining the inlet ports28a. A cooling fan30is mounted on the compressor housing28at the air outlet opening28b. In this particular embodiment, the housing28includes twenty-eight (28) air inlet port28ahaving diameter of 6 mm. The air inlet ports28aare disposed around the cylinders26ato direct the air flow, induced by the cooling fan30, through the air inlet ports28aperpendicularly to the outer surfaces of the cylinders26aadjacent the ends thereof where the temperature of the air in the cylinders26ais increased by the compression of the air and the friction between the pistons and the inner surfaces of the cylinders26a. This configuration allows the air flow to impinge against the outer surfaces of the cylinders26aand to increase the cooling effect of the air flows. The air introduced into the compressor housing28through the air inlet ports28ais exhausted into the case24through the air outlet opening28b.

With reference toFIGS. 3-7, the effect of the present invention will be described below.

FIGS. 4-7are graphs showing experimental results obtained by using the apparatus ofFIG. 3. InFIG. 3, an experimental apparatus100has a dummy compressor unit110and a vacuum pump120fluidly connected to the dummy compressor unit110through a conduit122. The dummy compressor unit110includes a heater unit112, having a cylindrical exterior configuration and thermal output of 75 W, for demonstrating the heat generation in the compressor26, a hollow cylindrical housing for accommodating the heater unit112and a pressure gauge118for detecting the pressure in the housing. A plurality of air nozzles116, in particular twenty-eight (28) nozzles116, for directing cooling air perpendicularly to the outer surface of the heater unit112, are disposed in the side wall of the housing114.

In the conduit112between the dummy heater unit110and the vacuum pump120, a valve124and a flowmeter126, for controlling and measuring the flow rate of the air through the conduit122, are provided. The experimental apparatus100further includes temperature sensors (not shown) for detecting the temperature difference between the outer surface of the heater unit112and the room temperature. When the vacuum pump120draws the air in the housing114, the air flow through the nozzles116impinges perpendicularly on the outer surface of the heater unit112to cool it.

FIG. 4shows the changes in the temperature of the outer surface of the heater unit112and the pressure loss through the nozzles116relative to the changes in the air flow rate. In this connection, please note that temperature of the outer surface of the heater unit112is indicated by the temperature difference ΔT between the outer surface of the heater unit112and the room temperature. As shown inFIG. 4, the larger the air flow, the more the heater unit112is cooled, and the greater the pressure loss through the nozzles116.

FIG. 5shows the changes in the temperature of the outer surface of the heater unit112and the pressure loss through the nozzles116relative to the diameter of the nozzles116. The detailed experimental data in relation to the graph ofFIG. 5are shown in Table 1 below.

As shown inFIG. 5and Table 1, when the flow velocity of the air is larger than 15 m/sec, the pressure loss through the nozzles116rapidly and extremely increases. Therefore, according to the invention, diameter of the air inlet ports28aand the flow rate of the cooling air therethrough are selected so that the flow velocity of the air flow through the air inlet ports28ais lower than 15 m/sec. If the air inlet ports28acomprise different size ports, the diameter is estimated by the average of the size of each of the ports.

The compressor26is cooled by the air induced by the cooling fan30. The cooling air flow is selected so that the temperature difference ΔT between the temperature Ts of the outer surfaces of the cylinders26aof the compressor26and the room temperature Tr is kept lower than 30° C. As is well known in the art, the higher the power of the compressor, the larger the required flow rate of the cooling air.

FIG. 6shows that there are linear relations between the changes in the power of the compressor and the changes in the flow rate of the cooling air required to maintain the temperature difference ΔT lower than a predetermined value. Two particular cases are shown inFIG. 6, one being a case of a temperature difference ΔT lower than 30° C., indicated by line-and-triangle mark, and the other being a case of a temperature difference ΔT lower than 20° C., indicated by line-and-square mark.

FIG. 7shows that there are linear relations between the changes in the power of the compressor and the changes in the flow velocity of the cooling air through the nozzles 116 required to maintain the temperature difference ΔT lower than a predetermined value. Two particular cases are shown inFIG. 7, one being a case of a temperature difference ΔT lower than 30° C., indicated by line-and-diamond mark, and the other being a case of a temperature difference ΔT lower than 20° C., indicated by line-and-square mark.

With reference toFIG. 7, the cooling air at 15 m/sec maintains the temperature difference ΔT at 30° C., with a compressor of 280 W, and at 20° C., with a compressor of 140 W, and therefore, can sufficiently cool a compressor which is commonly used for an oxygen concentrating apparatus. These experimental results provide parameters of 0.05 m/sec W (ΔT=30° C.) and 0.1 m/sec W (ΔT=20° C.), the flow velocity of the cooling air relative to the power of the compressor.

As described above, the pressure loss becomes excessively high when the velocity of air flow through the nozzles116is higher than 15 m/sec. On the other hand, sufficient cooling of the compressor allows it to operate for long time. Further, in order to provide a large amount of cooling air, a large cooling fan is required, which will result in increase in the volume, weight, noise and power consumption of the apparatus. Therefore, in order fulfill these conditions, according to the invention, the velocity of the cooling air relative to the power of the compressor is selected to be, or to be larger than, 0.05 m/sec W, preferably in a range of 0.05 m/sec W-0.1 m/sec W. When a 100 W compressor is used, the diameter of the air inlet ports28is selected so that the velocity of the cooling air through the air inlet port28falls in a range of 5-15 m/sec and, preferably, in a range of 5-10 m/sec.