Apparatus including a clean mini environment

Abstract

An apparatus (10), including a gas recirculation circuit comprising a mini environment chamber (14), a gas pump (16), a filter assembly (22) which are connected by a recirculation channel (20). The apparatus additionally includes an air supply conduit (18) for supplying air to the gas recirculation circuit and having an air supply conduit inlet (18a) which opens into the ambient air and an air supply conduit outlet (18b) which opens in the recirculation circuit. In use, a mini environment chamber pressure (P.sub.me) is maintained higher than the ambient pressure (P.sub.am). The gas recirculation channel (20) includes a substantially frictionless recirculation restriction embodied as a throat (30). At downstream end of the throat which forms the narrow part of the throat, in use, the static pressure is below the ambient pressure. The air supply conduit outlet opens at the downstream end (30a) of the throat.

Claims

1. An apparatus, including a gas recirculation circuit comprising: a mini environment chamber, provided with a chamber inlet and a chamber outlet; a recirculation channel connecting the chamber outlet with the chamber inlet; a gas pump having a pump outlet and a pump inlet and being positioned in the recirculation channel; and a filter assembly positioned in the recirculation channel downstream of the pump and upstream of the mini environment chamber inlet, wherein the apparatus additionally includes: a pressure release provision configured and arranged to limit a pressure (P.sub.me) in the mini environment chamber; an air supply conduit for supplying air to the gas recirculation circuit and having an air supply conduit inlet which opens into the ambient air and an air supply conduit outlet which opens in the recirculation circuit, wherein, in use, the gas pump circulates the gas from the pump outlet through the filter assembly, the chamber inlet, the mini environment chamber, the chamber outlet and back to the pump inlet thereby maintaining the pressure (P.sub.me) in the mini environment chamber higher than the ambient pressure (P.sub.am), wherein the gas recirculation channel includes a recirculation restriction embodied as a throat in the gas recirculation channel, wherein the throat defines a flow path in the direction of a throat inlet to a downstream end of the throat with a diminishing cross sectional surface area relative to the cross sectional surface area of the gas recirculation channel directly upstream of the throat, wherein the downstream end of the throat defines a minimum cross sectional surface area of the throat, wherein the throat defines the pump inlet, wherein the air supply conduit outlet opens at, or slightly downstream of the downstream end of the throat which defines the minimum cross sectional surface area of the throat, wherein the air supply conduit outlet introduces air in the direction of the flow path at, or slightly downstream of the downstream end of the throat, and wherein the throat has a truncated cone shaped inner surface that is circular symmetric around a central axis, wherein a downstream part of the air supply conduit extends along a central axis and opens in the central part of the downstream end of the throat.

2. The apparatus according to claim 1, wherein the cross sectional surface area (A.sub.sc) of the air supply conduit is smaller than the cross sectional surface area (A.sub.t) of the downstream end of the throat.

3. The apparatus according to claim 1, wherein the air supply conduit comprises an air inlet filter.

4. The apparatus according to claim 1, wherein the pressure release provision comprises a pressure release valve.

5. The apparatus according to claim 1, wherein the pressure release provision comprises a small gap in the mini environment chamber which opens into the ambient environment.

6. The apparatus according to claim 1, comprising a housing defined by external walls, wherein the external walls at least partly bound the mini environment chamber and the recirculation channel, wherein an internal wall forms a boundary between the mini environment chamber and the recirculation channel, wherein the chamber outlet is formed by a gap between an end of the internal wall and an external wall.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is schematically shows an example of an apparatus including a mini environment chamber which is known from practice; and

(2) FIG. 2 shows an example of an apparatus including a mini environment chamber according to the invention.

DETAILED DESCRIPTION OF THE FIGURES

(3) In this application similar or corresponding features are denoted by similar or corresponding reference signs. The description of the various embodiments is not limited to the example shown in FIG. 2 and the reference numbers used in the detailed description and the claims are not intended to limit the description of the embodiments, but are included to elucidate the embodiments by referring to the example shown in FIG. 2.

(4) In the most general terms, the invention relates to an apparatus 10, including a gas recirculation circuit comprising: a mini environment chamber 14, provided with a chamber inlet 24 and a chamber outlet 26; a recirculation channel 20 connecting the chamber outlet 26 with the chamber inlet 24; a gas pump 16 having a pump outlet and a pump inlet and being positioned in the recirculation channel 20; and a filter assembly 22 positioned in the recirculation channel 20 downstream of the pump (16) and upstream of the mini environment chamber inlet 24.

(5) The apparatus additionally includes: a pressure release provision 28 configured and arranged to limit a pressure P.sub.me in the mini environment chamber 14; and an air supply conduit 18 for supplying air to the gas recirculation circuit and having an air supply conduit inlet 18a which opens into the ambient air and an air supply conduit outlet 18b which opens in the recirculation circuit.

(6) In use, the gas pump 16 circulates the gas from the pump outlet through the filter assembly 22, the chamber inlet 24, the mini environment chamber 14, the chamber outlet 26 and back to the pump inlet thereby maintaining the pressure P.sub.me in the mini environment chamber 14 higher than the ambient pressure P.sub.am.

(7) According to the invention, of which an example is shown in FIG. 2, the apparatus 10 is characterized in that the gas recirculation channel 20 includes a recirculation restriction embodied as a throat 30 in the gas recirculation channel 20. The throat 30 defines a flow path with a diminishing cross sectional surface area relative to the cross sectional surface area of the gas recirculation channel 20 directly upstream of the throat 30. A downstream end 30a of the throat 30 defines a minimum cross sectional surface area of the throat 30. The throat 30 defines the pump inlet. The air supply conduit outlet opens at, or slightly downstream of the downstream end 30a of the throat 30 which defines the minimum cross sectional surface area of the throat.

(8) The cross sectional surface area of the throat 30 is smaller than the area of the cross-section of the gas recirculation channel 20. As a consequence, the gas velocity of the circulated gas increases when flowing through the throat 30 up to a maximum velocity at the downstream end 30a of the throat 30 where the cross sectional surface area of the throat is smallest. When the gas velocity increases the dynamic pressure (½ ρv.sup.2) will increase and the static pressure will decrease. The difference between the static pressure at the air supply conduit outlet 18b and the ambient pressure P.sub.am will determine the flow of air within the air supply conduit 18. By positioning the air supply conduit outlet 18b in a region where the static pressure of the gas flow is below the ambient pressure P.sub.am a pressure gradient will be created within the air supply conduit which will drive the ambient gas into the gas recirculation circuit. By using a substantially frictionless recirculation restriction which is embodied as a throat 30, energy losses may be minimized. Thus air may be supplied to the recirculation circuit without the necessity to invest in an additional air supply pump or a high pressure gas source and substantially without energy losses so that the gas pump 16 capacity and/or power consumption is almost the same as in a situation wherein no air is supplied to the gas recirculation system and the pump is only used for pumping the gas through the gas recirculation circuit.

(9) In order to provide the mini environment chamber 14 with clean gas, the gas supplied by the gas pump 16 may be filtered by the filter assembly 22 before it enters the mini environment chamber 14. This may be done at the chamber inlet 24 where the gas enters the mini environment chamber 14.

(10) In an embodiment, the throat 30 may have a truncated cone shaped inner surface that is circular symmetric around a central axis, wherein a downstream part of the air supply conduit 18 extends along the central axis and opens in the central part of the downstream end 30a of the throat 30.

(11) In the center of the throat 30 at the downstream end 30a thereof, where the cross sectional surface area is minimal, the gas velocity may be highest and thus, the static pressure is at its lowest value. Consequently, that position may be the most optimal position for positioning the air supply conduit outlet 18b because the air is sucked most effectively.

(12) In an embodiment of the invention, the cross sectional surface area A.sub.sc of the air supply conduit 18 may be small compared to the cross sectional surface area A.sub.t of the downstream end 30a of the throat 30.

(13) An air supply conduit 18 with a small cross sectional surface area A.sub.sc compared to the cross sectional surface area A.sub.t of the downstream end 30a of the throat 30 may not, or virtually not disturb the flow of the recirculating gas in the recirculation channel 20 and the throat 30 which is beneficial from an efficiency point.

(14) In an embodiment of the invention, the air supply conduit 18 further comprises an air inlet filter 32.

(15) In order to keep the gas in the gas recirculation circuit as clean as possible, it is best to filter the ambient air before supplying it to the gas recirculation circuit. The apparatus could do without such filter, but an air inlet filter 32 may relieve the load of the filter assembly 22 at the mini environment chamber inlet 24.

(16) In an embodiment, the pressure release provision may comprise a pressure release valve 34.

(17) With the pressure release valve 34 the leakage of gas from the mini environment chamber 14 can be controlled in such a way that a constant overpressure can be maintained in the mini environment chamber 14 with respect to the surrounding environment. A pressure release valve 34 may be a simple yet effective way to realize a constant overpressure in the mini environment chamber 14.

(18) In an alternative embodiment, the pressure release provision may comprise a small gap in the mini environment chamber which opens into the ambient environment. Such a small gap is, of course, of a very simple construction and also provides a means to limit the raise of pressure in the mini environment chamber 14.

(19) In an embodiment, the apparatus may comprise a housing defined by external walls 38, wherein the external walls at least partly bound the mini environment chamber 14 and the recirculation channel 20. An internal wall 36 forms a boundary between the mini environment chamber 14 and the recirculation channel 20. The chamber outlet 26 is formed by a gap between an end of the internal wall 36 and an external wall 38.

(20) Such an embodiment is relatively simple from a manufacturing point of view.

(21) The various embodiments which are described above may be used implemented independently from one another and may be combined with one another in various ways. The reference numbers used in the detailed description and the claims do not limit the description of the embodiments nor do they limit the claims. The reference numbers are solely used to clarify.

LEGEND

(22) 10—the apparatus 12—housing 14—mini environment chamber 16—gas pump 18—air supply conduit 18a—air supply conduit inlet 18b—air supply conduit outlet 20—recirculation channel 22—filter assembly 24—chamber inlet 26—chamber outlet 28—pressure release provision 30—throat 30a—downstream end of the throat 32—air inlet filter 34—pressure release valve 36—internal wall 38—external walls P.sub.me—mini environment chamber pressure P.sub.am—ambient pressure A.sub.sc—cross section surface area of the air supply conduit A.sub.t—cross section surface area of the throat at the downstream end A.sub.r—cross sectional surface area of the recirculation channel upstream of the throat