Vortex air barrier

Details Vortex air barrier Vortex air barrier

2001-06-29

2003-09-23

Joyce, Harold (Department: 3745)

Ventilation

Having protecting air current

Surrounding protected area

C454S190000, C454S188000, C454S191000

Reexamination Certificate

active

06623352

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates initially, and thus generally, to means of forming “air barriers” that serve to isolate spaces without the use of a conventional physical barrier. The isolated space may be maintained at atmospheric pressure, or at greater or lesser than atmospheric pressure.
BACKGROUND OF THE INVENTION
There are many possible uses of systems that utilize an air barrier to isolate one region from another. Air barriers are unique because they lack bulky physical structures that would normally be associated with any type of conventional barrier system. Air barriers find use in many different fields, including, but not limited to: air curtains, clean rooms, oxygen tents and testing chamber apparatus.
Air Curtains
An air curtain is a device specifically designed to provide a resistance to air flow through an opening, without utilizing a physical barrier. Simply put, an air curtain is a fan that is designed with an air outlet that has a low turbulent air stream (as laminar a flow as possible) that can be angled towards the incoming air stream in such a manner that the inflow of air can be prevented, and thereby creates a seal.
Air curtains can either be of the re-circulating type, or non re-circulating type. Conventional re-circulating air curtains emit air from a discharge grill on one side of the door opening and collect the air on the opposite side. It is then filtered, sometimes heated, and then is returned to the discharge grille. These units are essentially a modified heating system and use large amounts of air. They are usually associated with high initial costs and high operating costs. Also, because the air has to be filtered, the maintenance costs are also quite high. The feature is that they use low velocity air streams, which is desirable in some commercial entrances. They are usually used in supermarkets and store entrances. Thus, the need is apparent to provide an improved re-circulating air curtain.
Non re-circulating air curtains are more widely used. They are commonly characterized by lower initial and operating costs. Since non-recirculating air curtains do not re-use the air, they do not normally have to be filtered and thereby can be made essentially maintenance free.
The non-recirculating air curtain operates by discharging air at a high velocity through a narrow discharge nozzle. The discharged air stream must have the proper angle, usually 20 degrees towards the pressure side, and the air stream must be laminar for highest efficiency.
The non-recirculating air curtain operates on a very simple law of physics. One object will change its direction if it is subjected to a force, or a momentum, from another object. The momentum is found by the product of the air mass and the velocity at which it travels. The force could also be from an air mass that is increasing its velocity. The outside wind has a certain mass and a certain velocity, so does the air curtain stream. If the air curtain force (or momentum of the airflow) is equal and opposed to the force (or momentum of the airflow) from the draft through the door then the draft is prevented from entering, i.e., conservation of momentum. If the draft is much stronger than the air curtain, it will break through and some will enter. However, even in this circumstance, an air curtain will prevent some of the outside wind from entering at all times. If the air curtain is much stronger than the draft some of the air will go outside. The strength of the non-recirculating air curtain follows the formula: mass times the velocity squared. Therefore, an air curtain that blows at twice the speed has four times the wind stopping power at the same air volume.
An air curtain can be mounted above, on one side, or on both sides of a door. The most common way is to mount an air curtain above the door. Mounting the air curtain in this fashion is usually preferred because it keeps the unit out of the way and is less likely to be damaged by, for example, forklifts. It is also the most economical way of installing an air curtain. The drawback is that a small amount of air at the extreme bottom of the doorway may enter due to the height of air curtain.
An air curtain can also be mounted vertically on one side of the door. There are some disadvantages to this, however. If, for example, a truck is parked in the doorway then the entire doorway is unprotected because the truck will break the air stream. Also, with the unit mounted on one side of the door it is more likely to be damaged. Further, if there is no equal force on the other side of the door to stop the stream then the flow will follow the wall for some distance and may disturb people who are standing in the air stream.
The final way of mounting an air curtain is on both sides of the door with the air streams flowing towards each other. This is the most comfortable way of installing an air curtain as it eliminates the above drawbacks, except the possibility of damage.
In order to be able to select a proper air curtain for a given application, there are a few things that have to be considered:
(1) The physical dimensions of the opening and the space available for installation.
(2) Prevailing winds and temperatures for the opening.
(3) If there is any negative pressure in the building (this is usually caused by exhaust fans or stack effect.)
(4) The need for additional heat to be introduced in the air curtain.
(5) The need for additional heat in the areas when the door is closed and/or the need for make up air in the building.
The applications for air curtains are many. They include:
(1) Industrial Climate Control
(2) Air Conditioned Areas
(3) Industrial Oven Openings
(4) Dust and Humidity Control
(5) Mines
(6) Commercial Entrances
(7) Insect Control
(8) Cold Storage
Each of this applications will be briefly described.
Industrial Climate Control
The primary purpose of a climate control air curtain is to prevent the influx of outside air through an opening into a heated or cooled area. Openings where an air curtain would typically be used include exterior shipping and receiving doors to plants and warehouses and interior doors between plant areas of different temperatures (these applications are discussed in further detail infra). In addition, there are special applications such as the control of oven temperature, humidity and dust or the control of fresh air. Other applications include preventing the drifting of over spray from spray paint booths; blowing water off of hot steel after it has been dipped; and blowing scrap paper from a paper cutter into a collecting intake.
In order to control climate, an air curtain emits an air stream with enough velocity at a nozzle having a width commensurate with the width of the opening. For different door sizes and different wind conditions, different air velocities at the nozzle are required.
To prevent the entry of outside winds, the discharge nozzle is angled outward so that the air leaving it meets the wind trying to enter. The wind will meet or strike the air curtain stream in the doorway. When the vector representative the air stream (generated by the air curtain) and the vector representing the wind equalize, they form a resultant which should meet the floor in the door plane for maximum efficiency.
In buildings with high ceilings the air tends to stratify into a warmer layer at the ceiling and a considerably cooler one at the floor. For such buildings it is recommended that the air curtain be mounted across the top of the doorway opening and that it be provided with a top intake connected to a duct extending up to the ceiling. The warm air will then be drawn down into the air curtain and blown to the floor putting otherwise wasted heat to use. This warmer air also helps to reduce the wind chill of the moving air.
Air Conditioned Areas
Air conditioned areas are normally well balanced and seldom have negative pressure. In fact a slight over-pressure is more common where air conditioning systems are bringing fresh air into an area. Air curtains for interior doors need only be sized for the dr

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