Ventilation – Workstation ventilator – Covered workbench chamber
Reexamination Certificate
1999-07-16
2002-01-01
Joyce, Harold (Department: 3749)
Ventilation
Workstation ventilator
Covered workbench chamber
Reexamination Certificate
active
06334812
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a process for dynamically separating a contaminating zone and a zone to be protected, communicating between each other through at least one separation zone, by means of a clean air curtain obtained by injecting at least two adjacent clean air jets into the separation zone in the same direction.
The process according to the invention may be used in many industrial sectors.
A first family of industries concerned by this process includes all industries (food processing, medical, biotechnologies, high technologies, etc.), in which it is necessary to prevent the atmosphere in a given working zone from being contaminated by the ambient air carrying thermal, microbial, and/or particular and/or gaseous contamination.
Another family of industries concerned by the process according to the invention includes industries (nuclear, chemical, medical, etc.) in which individuals and their environment must be protected from toxic or dangerous products placed inside a confinement containment.
DISCUSSION OF THE BACKGROUND
At the present time, there are two types of solutions for dynamically separating two zones communicating with each other through one or more separation zones, for example in order to allow objects to be brought in and out, these two types being protection by ventilation and protection by an air curtain.
Protection by ventilation consists of artificially creating a pressure difference between the two zones so that the pressure in the zone to be protected is greater than the pressure inside the contaminating zone. Thus, if the zone to be protected contains a product that could be contaminated by ambient air, a laminar flow is injected into the zone to be protected that blows outwards through the separation zone. In the opposite case in which personnel and the environment outside a contaminated space need to be protected, dynamic confinement is achieved by using extraction ventilation in this contaminated space. In each case, an empirical rule imposes a minimum ventilated air speed of 0.5 m/s in the plane of the separation zone through which the two zones communicate in order to prevent contamination from being transferred into the zone to be protected.
However, the efficiency of this ventilation protection technique is not perfect, particularly in a so-called “infractions” situation, in other words when objects are transferred through the separation zone inserted between the two zones. Furthermore, this type of protection makes it necessary to process and control the entire zone to be protected from the contaminating external atmosphere or the entire contaminated zone. When the zone to be processed and controlled is large, this introduces a particularly high investment in operating cost. Finally, this technique of protection by ventilation only provides protection in one direction, in other words it is only useful when contamination transfers are only possible in one direction.
The air curtain protection technique consists of simultaneously injecting one or several adjacent clean air jets in the same direction into the separation zone between the two zones, which form an immaterial door between the zone to be protected and the contaminating zone.
Note that according to the theory of turbulent plane jets, a plane air jet is composed of two separate zones; a transition zone (or core zone) and a development zone.
The transition zone corresponds to the central part of the jet adjacent to the nozzle in which the speed vector is constant. This zone corresponds to the part of the jet in which there is no mix between the injected air and the air on each side of the jet. Considering a cross-section through a plane perpendicular to the plane of the separation zone, the width of the transition zone gradually decreases as the distance from the nozzle increases. This is why this transition zone is called a “tongue” throughout the rest of the text.
The development zone of the jet is the part of this jet located outside the transition zone. In this jet development zone, outside air is entrained by the jet flow. This results in variations in the speed vector and mixing of air. Air entrainment on both sides of the jet within this development zone is called “induction”. Thus an air jet induces an air flow on each of its faces which depends particularly on the injection flow of the jet considered.
Document JP-B-36 7228 proposes producing an air curtain by simultaneously injecting three adjacent air jets in the separation zone and in the same direction. More precisely, a relatively fast air jet is injected between two relatively slow air jets. This arrangement is supposed to provide more efficient confinement than a single air jet, because the entrained air mixed by the central jet is only slightly contaminated, and originates from relatively slow jets injected on each side of this central air jet.
However, this document does not consider the length of the tongues of each jet, nor their injection flows, such that the confinement efficiency is very uncertain.
Document FR-A-2 530 163 proposes to control confinement in a polluted room with an opening by injecting an air curtain into it consisting of two clean adjacent air jets blowing in the same direction. More precisely, dynamic separation is provided by a first relatively slow jet (called the “slow jet”), for which the tongue entirely covers the opening. The second jet (called the “fast jet”) is faster than the slow jet, and is installed between the slow jet and the zone to be protected. Its function is to stabilize the slow jet by a suction effect which brings this slow jet into contact with the fast jet.
Document FR-A-2 530 163 describes that the slow jet tongue is sufficiently long to cover the entire opening when the width of the injection nozzle for this slow jet is equal to at least one sixth of the height of the opening to be protected. It also states that injection flows of the two air jets must be such that the air flow induced by the surface of the fast jet which is in contact with the slow jet is approximately equal to the injection flow through the slow jet.
Document FR-A-2 652 520 suggests using an air curtain to protect a clean working zone provided with an opening, from the contaminating external environment. The main characteristics of the air curtain are similar to the characteristics described in document FR-A-2 530 163. It is also specified that the injection speed of the slow jet must be of the order of 0.4 m/s or 0.5 m/s. It is also specified that jets should be emitted such that the external surface of the fast jet reaches the limit of the opening plane. Due to the jet expansion angles, this results in an angle of about 12° between the median plane of the jets and the plane of the opening.
Document FR-A-2 652 520 also proposes simultaneously injecting clean ventilation air at a temperature adapted to requirements, inside the working zone to be protected. This document states that this clean ventilation air must be injected at a flow approximately equal to the flow induced by the surface of the fast jet that is in contact with clean ventilation air.
Furthermore, document FR-A-2 652 520 also indicates that the intake grille through which the two jets are recovered is located outside the opening and below the work station, so that the ventilation in the contaminated zone can be controlled. Furthermore, the two side walls which delimit the opening are extended towards the outside over a distance equal to at least the thickness of the air curtain.
Document FR-A-2 659 782 proposes adding a third relatively slow clean air jet to the two clean air jets described in document FR-A-2 530 163, so that the fast air jet is located between the two adjacent slow jets and in the same direction.
With this arrangement, which uses the main characteristics described in documents FR-A-2 530 163 and FR-A-2 652 520, the clean ventilation air injection flow inside the zone to be protected is considerably reduced. Furthermore, dynamic confinement is provided in both directions
Laborde Jean-Claude
Mocho Victor Manuel
Commissariat a l'Energie Atomique
Joyce Harold
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