GAS DELIVERY APPARATUS
FIELD OF THE IMΗNTION
[0001] This invention relates to a gas delivery apparatus for delivering a mixture of a first gas, preferably oxygen, and a second gas, preferably ambient air, into a neo-natal oxygen hood, or other environments, so as to achieve a desirable concentration of oxygen in the gas mixture.
BACKGROUND TO THE INVENTION
[0002] Known apparatuses for supplying mixtures of air and oxygen involve separate high pressure supplies of air and pure oxygen (O2), and means including diaphragms, cams or the like for adjusting the supply pressure, and flow rates, of the individual gas supplies to achieve desirable concentrations of oxygen. Such apparatuses are often complex to manufacture or operate, and costly.
[0003] It is an object of the present invention to provide a gas delivery apparatus which, at least in preferred embodiments, overcomes or ameliorates disadvantages associated with, or provides an alternative to, the prior art.
SUMMARY OF THE INVENTION
[0004] According to an aspect of the invention there is provided a gas delivery apparatus for delivering a mixture of a first gas and a second gas, the apparatus including: a mixing chamber; connection means for connecting the mixing chamber in fluid flow communication to a supply of the first gas which supply is under a first-gas supply pressure, for supplying the first gas into the chamber at a first volume flow rate; second-gas supply means in fluid flow communication with the mixing chamber for supplying the second gas into the chamber at a second volume flow rate, to establish a mixture therein between the first and second gases; and a gas outlet from the chamber for directing said mixture from the chamber, wherein the apparatus is configured such that, as said first gas supply pressure increases, the second- gas supply means is caused to reduce the second volume flow rate, and the first volume flow rate increases.
[0005] In a preferred embodiment, the second-gas supply means is configured to supply the second gas to the chamber when the second gas is part of a body of gas surrounding the apparatus.
[0006] The second-gas supply means preferably includes a fan.
[0007] In a preferred embodiment, the second-gas supply means is configured to move the second gas from an upstream side of the second-gas supply means to a downstream side of the second-gas supply means and into the mixing chamber, and to reduce the volume flow rate of the second gas into the chamber upon an increase of pressure at the downstream side caused by an increase of said first-gas supply pressure.
[0008] Preferably, said supply of the first gas is a compressed gas supply.
[0009] In a preferred embodiment, the apparatus is configured for the gas outlet to direct said mixture from the chamber at a third volume flow rate which remains substantially constant upon said increasing of said first volume flow rate.
[00010] Preferably, the first gas is of a first gas type and the second gas is a mixture of the first gas type and at least one other gas type. Then, preferably, the first gas type is pure oxygen and the second gas type is air.
[00011] In a preferred embodiment, the apparatus is configured such that, during said increasing of said first volume-flow-rate, the increase of the ratio of said first gas type in said mixture as a relationship to said increase of said first volume-flow-rate is substantially linear.
[00012] In a preferred embodiment, said second-gas supply means is configured such that the second volume-flow-rate is at a maximum, being substantially within a predetermined range, when the first volume-flow-rate is substantially zero; the second volume-flow-rate reduces as the first volume-flow-rate increases; and the second volume-flow-rate is substantially zero when the first volume-flow-rate is at a maximum, being substantially within said predetermined range.
[00013] Preferably, said predetermined range is substantially 7 litres per minute to 9 litres per minute. Then, preferably, each of said second volume-flow-rate maximum and said first volume-flow-rate maximum is substantially 8 litres per minute.
[00014] In a preferred embodiment, the apparatus includes a mixing device which defines said mixing chamber and said gas outlet, and which includes said connection means and which further includes attachment means for attachment to said second-gas supply means.
[00015] In a preferred embodiment, the mixing device includes a substantially straight elongate passage extending in a first direction, the passage defining at least part of said mixing chamber, and the mixing device is configured to direct the second gas through the passage substantially parallel to said first direction, and to direct the first gas into the passage, through a side of the passage, to intersect the second gas at an angle.Preferably, said angle of intersection is any one of substantially a right angle, substantially 180°, an acute angle or an obtuse angle. Most preferably the angle is substantially 90°.
[00016] In a prefen-ed embodiment, said passage is a first passage, the mixing device further including a substantially straight elongate second passage connected to a downstream end of the first passage, the second passage extending in a second direction being at an angle to the first direction, and the gas outlet is located at a downstream end of the second passage. In this case, preferably said angle between the first and second directions is substantially a right angle.
[00017] Where the mixing device includes said substantially straight elongate passage, preferably the mixing device includes an orifice restrictor in said passage, for restricting flow of at least the second gas through the passage. Where the mixing device includes said first and second passages, preferably the mixing device includes an orifice restrictor in one of the first passage and the second passage, for restricting flow of at least the second gas through the passages. In a preferred embodiment, the orifice restrictor is located downstream of the mixing chamber, preferably immediately upstream of the outlet.
[00018] In a preferred embodiment, the gas outlet is constituted by a slotted opening in the apparatus. Preferably, the apparatus includes a length of piping, the piping having a side wall with a slot therein, the slot constituting the gas outlet.
BRIEF DESCRIPTION OF THE DRA WINGS
[00019] Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a schematic side elevation of an apparatus according to an embodiment of the invention, in a condition of use;
Figure 2 is a schematic perspective view of a mixing device forming part of the apparatus of Figure 1 ;
Figure 3 is a schematic partly cut-away side elevation of the mixing device of Figure 2; and Figure 4 is a schematic partly cut-away plan view of the mixing device of Figure 2.
DETAILED DESCRIPTION
[00020] Referring to Figure 1 , there is shown an apparatus 10 in accordance with an embodiment of the invention. The apparatus 10 is shown in use together with a neo-natal oxygen supply hood 12 for supplying suitable concentrations of oxygen to an infant 14 (the hood and infant being shown schematically in broken lines).
[00021] The apparatus 10 includes a mixing device 16 and a gas supply means in the form of a fan 18.
[00022] The appratus 10 includes a frame 20 which defines a frame outlet 22 (see Figure 2), which in turn leads into a transition formation 24. The transition formation 24 opens into the mixing device 16, which includes a short length of piping 26 which defines, therein, a short, but substantially straight, elongate first passage 28. The length of piping 26 joins a further length of piping 30 at right angles, the further length of piping also defining therein, a short, but substantially straight, elongate second passage 32. It will be appreciated that the first passage 28, and the second passage 32 are joined end-to-end at a rounded corner 31 to form, essentially, a single passage.
[00023] In one preferred embodiment, at a position 34 where the transition formation 24 opens into the first passage 28, the internal diameter of the transition formation is 11 mm while the diameter of the first passage is 15 mm.
[00024] The mixing device 16 also includes a connection means in the form of a side leg 36 for connection to a compressed oxygen supply (not shown). The side leg 36 has a first portion 38 having one end connected to the length of piping 26, and a second portion 40 at an opposite end of the first portion, the second portion terminating at a free end 41 of the side leg 36. The first and second portions 38 and 40, respectively, define an internal passage 42 which opens into the first passage 28. Each of the first and second portions, 38 and 40, respectively, is tapered, in a direction from the length of piping 26 to the free end 41, and is thus adapted for being inserted into a supply hose (not shown) of the compressed oxygen supply.
[00025] In a preferred embodiment, the diameter of the internal passage 42 is 3.5 mm at the free end 41 and 11 mm where the internal passage opens into the first passage 28. The further length of piping 30 has a first part 44 and a second part 46 which is of larger internal diameter than the first part, so that there is a step 48 at the transition between the first part and second part.
[00026] At the opposite end of the second part 44, there is provided a slot 50 in the upper part of the wall of the further length of piping 30. Immediately beyond the slot 50 is an end wall 52 of the further length of piping 30.
[00027] Immediately upstream of the slot 50 is an orifice restrictor 53 (see Figure 3) in the form of an annular flange. The orifice restrictor 53 defines a central orifice 53.1, with sharp corners 53.2. While sharp corners are readily manufactured and are preferred, it is expected that a satisfactory result could also be obtained without sharp corners being provided.
[00028] The fan 18 is attached to the frame 20 by means of a pair of diagonally disposed screws 54. The fan 18 is powered by a DC supply (not shown) and when operating, draws air from the space surrounding the apparatus 10, via the frame outlet 22 and the transition formation 24, and into the first passage 28. If desired the screw 54 could be replaced by double sided adhesive tape to attach the fan 18 to the frame 20. This tape can serve the additional purpose of providing some vibration damping and or sound damping, which might otherwise result from the fan 18 contacting the frame 20.
[00029] The oxygen supply (not shown) is a cylinder of compressed oxygen or another form of oxygen supply which is under pressure. Therefore, at the same time as the fan 18 forces air into the first passage 28, oxygen from the oxygen supply is forced by the pressure of the oxygen supply itself through the internal passage 42 of the side leg 36 and into the first passage 28, so that tins oxygen is mixed with the air forced into this passage by the fan 18.
[00030] As the side leg 36 is disposed perpendicularly to the length of piping 26, the internal passage 42 opens into the first passage 28 as a T-junction. This facilitates the mixing in the first passage 28 of the air drawn in by the fan 18 and the oxygen from the oxygen supply. It will be appreciated that the first passage 28, serving as a place where mixing of the oxygen and air occurs, constitutes a mixing chamber.
[00031] The apparatus 10 is used as shown in Figure 1 to provide a mixture of pure oxygen from the oxygen supply, and air from the area surrounding the apparatus 10, into the hood 12
for supplying a desirable concentration of oxygen to the infant 14. To this end, the further length of piping 30 extends through an aperture 55 in the hood 12.
[00032] The combined air and oxygen, after being mixed in the first passage 26, travels into the second passage 32 before passing through the slot 50 into the space 58 below the hood 12. The right angle between the first passage 28 and the second passage 32 at the corner 31 enhances the mixing of the oxygen from the oxygen supply and the air introduced by the fan 18.
[00033] In a preferred embodiment of the invention, the concentration of oxygen in the mixture of oxygen and air that passes through the slot 50 can be adjusted merely by adjusting the supply pressure, and hence the volume flow rate, of the oxygen through the side leg 36. As the oxygen supply pressure at 41 is increased, the flow rate of oxygen through internal passages 42, 28 and 30 increases, and serves to establish a higher back pressure via the transition formation 24 and frame outlet 22, to the fan 18. This back pressure has the effect of reducing the volume flow rate of air supplied by the fan 18.
[00034] The selection of fan 18 and configuration of the mixing device 16 is such that, in a preferred embodiment, the volume flow rate of mixed gas exiting the mixing device via the slot 50 remains substantially constant, this rate preferably being substantially 7 to 9 litres per minute, and more preferably, substantially 8 litres per minute.
[00035] Preferably, the apparatus 10 is configured such that when the supply of oxygen from the oxygen supply via the side leg 36 is switched off, the volume flow rate of air introduced by the fan 18 into the first passage 28 is a maximum. It is also preferably configured such that, as the supply of oxygen from the oxygen supply via the side leg 36 is progressively increased, the supply of air via the fan 18 is progressively decreased until the oxygen supply reaches a predetermined maximum, at which point the supply of air via the fan is substantially nil.
[00036] In a preferred embodiment, the predetermined maximum volume flow rate of oxygen from the oxygen supply via the side leg 36, when the supply of air via the fan 18 is substantially nil, is between 7 litres per minute and 9 litres per minute. Similarly, the maximum volume flow rate of air via the fan 18 when the oxygen supply via the side leg 36 is switched off is also preferably between 7 litres per minute and 9 litres per minute. In one preferred version of this embodiment, the maximum oxygen flow rate from the oxygen supply
(while the flow rate from the fan 18 is nil) is substantially 8.7 litres per minute, while the maximum air flow from the fan 18 (while the flow rate from the oxygen supply is nil) is substantially 7.8 litres per minute. In a more prefened embodiment, each of these maximum flow rates, respectively, is substantially 8 litres per minute. [00037] Also in a prefened embodiment, the apparatus 10 is configured such that there is a constant volume flow rate of mixed gas exiting the mixing device 16 via the slot 50, and the concentration of oxygen in this mixed gas increases linearly in relation to an increase in the volume flow rate of oxygen from the oxygen supply via the side leg 36. [00038] In this regard, it will be appreciated that the air forced into the first passage 28 by the fan 18 includes oxygen together with other gases which are primarily nitrogen. For the purposes of illustration, it will be assumed that the remaining gases in the air are entirely nitrogen with the ratio of oxygen to nitrogen in the air being 25%. To illustrate the linearity, according to a prefened embodiment, of the increasing oxygen concentration relative to the increasing volume flow rate of oxygen supplied via the side leg 36, based on the above assumption, the following table is provided. In the prefened embodiment illustrated in the table, the volume flow rate of the mixed gases exiting via the slot 50 remains at substantially 8 litres per minute.
[00039] Because of the substantial linearity between the increase of the volume flow rate of oxygen via the side leg 36 and the increase of the total percentage of oxygen in the mixed gas
exiting via the slot 50 into the space 58 under the hood 12, a chart (not shown) can be provided to inform an operator of the apparatus 10 as to the required volume flow rate of oxygen through the side leg 36, to achieve a desired percentage of oxygen in the mixed gas for supply to the infant 14.
[00040] The manner of adjusting the oxygen flow rate via the side leg 36 will depend on the nature of the particular supply of oxygen to which the side leg 36 is connected. For example, where the supply is in the form of a cylinder of compressed oxygen, there can be provided a valve for controlling the volume flow rate of oxygen emanating from the cylinder and a flow rate gauge.
[00041] In configuring the apparatus 10 to achieve the desired flow rate and oxygen concentration of the mixed gases exiting through the slot 50, the fan 18 can be selected such that it is suitably matched to the flow characteristics of the mixing device 16. These flow characteristics are determined by the configuration and dimensions of the passages through which the air, introduced by the fan 18, flows. The flow characteristics are especially determined by the construction of the orifice restrictor 53, the discharge slot 50 and end wall 52. In addition, a suitable fan 18 is one that will suitably reduce the volume flow rate of air due to the back pressure caused by the increasing supply of oxygen via the side leg 36 according to the characteristics described in the above table.
[00042] The size of the orifice 53.1 of the orifice restrictor 53 affects the flow rate of the mixed gases and particularly that of the air from the fan 18. Thus, an orifice restrictor 53 can be selected so as to have an orifice 53.1 which is sized to "fine tune" the flow rate to a desired value (such as 8 litres per minute), by compensating for the characteristics or supply voltage of the particular fan 18 used in each case. In one prefened embodiment, the orifice 53.1 has a diameter of 6 mm.
[00043] The configuration of the slot 50 and the end wall 52 is such as to facilitate a desirable movement of the mixed gases within the space 58 under the hood 12, after they exit via the slot. This, in turn, contributes to the effective supply of the mixed gases, and hence the desirable oxygen concentration, to the infant 14.
[00044] In one prefened embodiment, the apparatus 10 is provided with a servo-control means which includes an oxygen analyser 60 (shown schematically in Figure 1).
[00045] The servo-control means is preferably a microprocessor or controller. This device can control the voltage to the fan by, for instance, varying the pulse width modulation of the voltage, to the fan. This variation would control the speed of the fan and hence the amount of air drawn into the mixing device by the fan.
[00046] The oxygen analyser- 60 can be placed inside the oxygen hood 12 to sense the concentration of oxygen within the space 58 and is connected via the servo control means to the fan 18 to control the speed of the fan 18 and hence the amount of air drawn into the mixing device by the fan 18. This allows for a rapid compensation should the concentration of oxygen within the space 58 suddenly change, for example if the doors (not shown) of the hood 12 are opened. In this case, where, for example, the oxygen concentration is suddenly decreased, the servo-control means 60, on sensing this decrease in oxygen concentration, sends a signal to the fan 18 causing the fan speed to reduce and hence the volume flow rate of air also to reduce. The reduction in volume flow rate of the air results in a reduction of flow rate of those components of the air which are not oxygen (that is, nitrogen in the above example), and hence allows for an increase in the relative concentration of oxygen in the mixed gases exiting the mixing device 16 via the slot 50.
[00047] This servo-control can also be used to compensate for any voltage/fan speed variations found in a population of fans during manufacturing. The appropriate pulse width modulation voltage to give a standard fan speed (and hence standard air-flow for instance of 8 litres per minute) can be set for each unit at a preliminary calibration/setup procedure.
[00048] The apparatus 10 can also be provided with an alarm 62, shown schematically in Figure 1 , which is configured to emit a warning (audible and/or visual) should the speed of the fan 18 fall below a predetermined value, or should the volume flow rate of air fall below a predeteπnined value. Such a reduction of the speed of the fan 18 can occur, for example, due to an obstruction of the fan blades, and such a decrease in the volume flow rate of air drawn in by the fan can be caused, for example, due to some form of fan blockage such as a clogging up of the fan filters (not shown ) through which the air is forced by the fan.
[00049] Although the apparatus 10 is shown as supplying the mixed gases via the slot 50 directly into the space 58 under the hood 12, it can instead be used to force these mixed gases into a low-resistance humidifier (not shown) before the humidified mixed gases are passed from the humidifier into the space 58 of the hood 12.
[00050] Although the invention is described above with reference to specific embodiments, it will be appreciated by those skilled in the art that it is not limited to those embodiments, and can be embodied in many other forais.