The present invention relates to methods and devices for ventilating and airborne decontamination for the purpose of reducing the quantities of contaminating particles suspended in the air of a room, and of the type operating:
by mixing;
with two Coanda effects;
using a blown primary jet attached to the ceiling; and
a suction flow attached to the floor.
Traditionally, air conditioning methods are technically classified depending on the way in which air is distributed within the treated room. The methods of air conditioning a room can thus be classified as follows:
ventilation by air piston displacement using a one-way flow;
ventilation by air displacement using thermal effect stratification;
ventilation by zone;
ventilation by mixing; and
ventilation by localized jet.
In ventilation vocabulary, a “primary air jet” is air that has previously conditioned (cooled, heated, decontaminated, humidified, dehumidified, . . . ), that is introduced into a room via a blow outlet such as a grille, a perforated panel, a diffusing ceiling, . . . . The term “total air” is used for the mixture between the primary air introduced into the room and the air of the room that is progressively entrained by the primary air and mixed therewith.
In the strategy of ventilation by air piston displacement, also known as one-way flow, or as “laminar flow rooms”, air is moved by a one-way primary air jet occupying the entire section of the room. The entire section of one wall of the room is used, generally the ceiling or sometimes one of the side walls, as a surface for blowing the primary air flow into the room. The air is blown in at a speed that is sufficient to pass through the room in parallel streams heading towards the opposite wall (generally the floor), which is porous so as to act as a suction surface. It is also common practice to take up the air through suction wall grilles installed close to the floor at the bottoms of the walls. Laminar flows operate using the “piston” principle. The primary air flow acts like a syringe to push back the contaminated air which is extracted from the room. “Laminar” flow rooms are used for achieving very low concentrations of contaminants. The air that is removed is taken up by an air treatment unit associated with the building, where it is decontaminated by being filtered and where it is mixed with new air. Thereafter it is blown back into the inside of the room through the flow surface (generally the ceiling) which is fitted with high-efficiency particulate air (HEPA) filters. The flow velocity is substantially uniform over the entire section of the room, reaching a value in the range 0.3 meters per second (m/s) to 0.5 m/s over the entire room that is to be protected. The blow and suction surfaces are situated:
The amount of air blown in a laminar flow represents 10 to 100 times the amount of the air blown by a mixing ventilation device with a turbulent flow or a device for moving air by thermal effect stratification. In addition, the entire ceiling needs to be fitted with a wall of HEPA filters. Devices for ventilation by air piston displacement (laminar flow) present:
an investment cost that is an order of magnitude greater; and
an energy cost that is about 10 times greater than that of mixing ventilation devices (turbulent flow rooms) or devices in which air is displaced by thermal effect stratification.
In addition, their structure comprising an entire blow wall (ceiling or wall) makes it impossible for them to be implemented in the form of a mobile system. Ventilation devices using air piston displacement are used solely in decontamination and ultraclean applications and not at all for air conditioning purposes for which they are much too expensive.
In the ventilation strategy making use of air displacement by thermal effect stratification, one or more diffusers of low-temperature air (cool air) are placed on the floor or close to the floor. This method operates by an air density difference within the room. The level of the “new” cool primary air that is introduced via the bottom, and that is denser than ambient air, acts progressively to push up the ambient air (which is warmer and floats on the cool air). The stratification strategy is less expensive than the piston strategy. Its purpose is mainly to ensure that the occupants of the room are at a comfortable temperature. Unfortunately, it is very sensitive to temperature disturbances, and it is not very effective in providing airborne decontamination (in particular of bacteria or fungi). In addition, the diffusers it uses are bulky and require significant infrastructure work at floor level. They cannot be made in the form of a mobile system. Devices for ventilation by displacing air by thermal effect stratification are used essentially in air conditioning applications.
In the zone ventilation strategy, the principle consists in treating certain zones or volumes of the room while the remainder of the room is left without any particular attention. As a general rule, it is accepted that the effectiveness of zone ventilation is better than that of ventilation by mixing in the ventilated zones. However, the low overall dilution of contaminants generally leads to overall decontamination of the room that is ineffective.
In a strategy of ventilation by mixing, air movement is provided mainly by the energy delivered by one or more primary air jets injected into the room. The theoretical objective of the strategy by mixing is to establish uniform conditions for the air inside the room. To do this, the primary air jet(s) injected into the room mix(es) with a large volume of ambient air. This phenomenon is known as “induction”. Ventilation by mixing is generally preferable for achieving better temperature comfort for the occupants. The term “occupation” zone is used to designate that portion of a room in which occupants are usually to be found. It is normally defined as the space extending from a surface that is 50 centimeters (cm) back from walls containing windows, 20 cm back from other walls, and extending up to 180 cm above the floor. The strategy of ventilation by mixing seeks to mix (as completely and as uniformly as possible) the primary air with the air already in the room, so that the impurities and contaminants in the room are not only attenuated by being diluted, but also, traditionally, are distributed uniformly. In the same way, it is desirable for the temperature in the room to be as uniform as possible in order to avoid discomfort for the occupants. Unfortunately, the dimensions of a room of reasonable size and the number of diffusers generally require the primary air jet(s) (cool air) to be injected at a speed that is faster than the speed acceptable for the occupants to be comfortable if they encounter a jet. Methods of ventilation by mixing can technically be subdivided into two sub-types:
ventilation by mixing using a free primary jet; and
ventilation by mixing by using a primary jet that is attached by the Coanda effect.
In methods of ventilation by mixing with a free primary jet, the primary air jet is injected into the room (usually vertically) through a diffuser that is generally situated in the central portion of a wall of the room (usually the ceiling). The primary air jet passes substantially perpendicularly through the envelope of the occupation zone. The movements of air in the room are almost disordered. The air jet reaches the occupants almost directly prior to any significant mixing with the air in the room. This often leads to temperature discomfort for the occupants.
In methods of ventilation by mixing with a primary jet that is attached using the Coanda effect, the primary air jet is injected into the room through a diffuser situated in a lateral region of a wall of the room (generally close to the ceiling), and in a direction that is substantially parallel and tangential to said wall of the room (generally the ceiling). As a result, the primary jet becomes deployed outside the occupation zone between the envelope of the occupation zone and the wall to which the jet is attached. The primary air jet thus travels along a long path and becomes mixed with a large quantity of ambient air prior to reaching the occupation zone. This disposition has the reputation of being thermally more comfortable for the occupants.
Following experiments performed for aeronautical purposes by the Romanian engineer Coanda in 1910, it has been known that when a jet of air is placed close enough to a surface, such as a ceiling for example, the jet of air tends to become attached to the surface and to continue its movement in contact therewith. This phenomenon is known as the Coanda effect or the surface effect. This is due to the fact that a jet of air tends to suck in ambient air in contact therewith in order to mix therewith (diffusion). However in the vicinity of a surface, no ambient air can be sucked in. This leads to a drop in pressure between the flow of air and the surface, thereby tending to cause the air jet to become attached to the surface.
The invention relates to a method of ventilation of the mixing type using a primary jet attached to the ceiling by the Coanda effect with air being extracted via a suction outlet in the form of a suction flow that is attached to the floor, likewise by the Coanda effect. In ventilation of this type, when the dimensions of the room make this possible, the air jet retains its effectiveness and reaches the wall opposite to the wall to which it was blown in, prior to being “diluted”. The total air flow then continues to move downwards along the opposite wall and then returns towards the suction outlet that is close to the floor. This obtains a kind of “envelopment” of the occupation zone by the flow of air going from the blow surface to the suction surface.
The initial experimental data on ventilation methods by mixing with a primary jet attached by the Coanda effect go back to 1939 when Baturin and Hanzhonkov demonstrated the phenomenon of the “reverse flow” deflected by the ceiling and the opposite wall towards the occupation zone. In their analyses of the shapes of the resulting air flow configurations, Baturin and Hanzhonkov concluded that the shapes of the air movements depended on the location of the blow grille (surface) while being influenced little by the configuration of the suction grille (surface) and the suction conditions. Subsequent theoretical work published by Nelson, Steward, Bromleys, and Gunes, gives information about the distribution of temperatures and velocities in the context of ventilation by mixing using an attached primary jet. Other theoretical work undertaken by Linke shows that there exists a maximum length for a room that can be ventilated properly using this principle. He demonstrated in particular that for linear primary jets “attached” to the ceiling, presenting a Reynolds number lying in the range 1,825 to 12,000, the length of the room must not exceed three times its width, if it is to be possible to establish an “enveloping” flow.
When the length of the room lies below this limit (<about 3 times its width), then a flow is obtained that envelops a single zone. A description of this phenomenon is given below with reference to
Beyond this limit, the room is said to be “long”. The room becomes “partitioned” by the air flow. A first looped movement of air, similar to that obtained in a “short” room is constituted by a total air jet following the ceiling and then coming down vertically through the middle of the occupation zone and returning to the suction surface horizontally in the vicinity of the floor. Other vortexes or “closed” air loops develop between the first loop and the other end of the room, and they penetrate into the inside of the occupation zone. A description of this phenomenon can be seen below with reference to the description of
Those published theoretical and experimental scientific studies show that:
when no particular conditions are imposed (conditions recommended by the invention concerning mean blow velocities and mean suction velocities are given below);
then, from a certain horizontal distance from the action side wall (the wall with the blow and suction surfaces) at a distance of about one height of the room, there appears a “sloping interfering shunt air flow”.
This “sloping interfering shunt air flow” tends to rise from the floor and pass through the occupation zone following an upward slope going towards the blow outlet. A description of this phenomenon is given below with reference to FIGS. 2 to 3.
The theoretical work published on the air flow schemes and air velocities in a room implementing a method of ventilation by mixing with an attached primary jet are concerned solely with thermal applications of ventilation. They seek to ensure that the velocities and temperatures in the occupation zone are as agreeable as possible for the occupants. The effect that is generally looked for in the prior art when implementing the method of ventilation by mixing with an attached primary jet is to lengthen the distance followed by the primary jet through the room prior to penetrating into the occupation zone. The person skilled in the art [represented by the community of scientists who have published the above-cited scientific works] has until now not been interested in the means that need to be implemented in order to optimize methods of ventilation by mixing using an attached primary jet for airborne decontamination, i.e. for reducing the quantity of contaminating particles in suspension within a room ventilated in this way. As mentioned above, the person skilled in the art has concentrated essentially on the thermal effects of ventilation and on the thermal comfort of the occupants, such that the “sloping interfering shunt air flow” tending to rise from the floor in a room ventilated by a primary jet attached to the ceiling by the Coanda effect leads to effects that are perceived as being somewhat “beneficial” in that context. For that person skilled in the art, such a “sloping interfering shunt air flow” enhances mixing and thus enhances the effectiveness of thermal ventilation. It will thus be understood that the person skilled in the art has made no attempt to reduce or eliminate the “sloping interfering shunt air flow”, even though its effects are essentially harmful in terms of airborne decontamination. In the usual frame of mind of the person skilled in the art, the problems of airborne contamination are:
either acute and solved by the strategy of ventilation by moving an air piston using a one-way flow, where the main drawback is expense;
or of minor importance and solved by conventional ventilation using mixing with a free primary jet, or by ventilation using mixing with an attached primary jet, with no account being taken of the “sloping interfering shunt air flow” (i.e. the negative consequences thereof are ignored);
or else very small, in which case conventional air purifiers making use of recycling are implemented, leading to decontamination that is not very effective such that the flows of interfering air loaded with contaminating particles coming from the floor and amplified by the presence of the “sloping interfering shunt air flow” are negligible.
The main object of the present invention is to make it possible:
to benefit from the intrinsic advantages recognized of the method of ventilation by an attached primary air jet and in particular the comfort it secures for the occupants and its costs of provision and operation that are lower than those of ventilation by displacement of an air piston in a one-way flow; and
while also being suitable for use in high-level decontamination and “ultraclean” applications.
To do this, the invention seeks to reduce (or eliminate) the effects of contaminated particles that have already settled on the floor being put back into upward motion, as usually occurs in rooms ventilated by mixing using an attached jet. The main object of the invention is thus to propose means for improving the method of ventilation by a primary jet attached to the ceiling by the Coanda effect, that seeks to reduce or eliminate the presence of the “sloping interfering shunt air flow” that has a tendency to rise from the floor. A secondary object of the invention is to propose a novel architecture for a mobile device for decontaminating air that is independent of the structure of the building, the device implementing a method of ventilation by means of an attached primary jet, but without a “sloping interfering shunt air flow”.
Mobile devices for decontaminating air that are independent of the structure of the building:
operate either on a principle of air dilution that is similar to that of rooms in which there is a turbulent flow;
or else act like purifiers, making use of ventilation of the localized jet type.
The remote technological background of the invention includes mobile air decontamination devices that suck air in and blow it out substantially horizontally at substantially the same height. Amongst this class of device, mention can be made of that described in U.S. Pat. No. 6,425,932 to Huehn, Deros, and Bourque. It can clearly be seen that that type of device cannot deliver a primary jet attached to the ceiling or make use of a sucked-in air flow that is attached to the floor.
In the remote technological background there are also mobile devices for decontaminating air that suck in air high up and blow air out low down.
U.S. Pat. No. 5,240,478 to Messina describes a HEPA filter purifier that sucks in air high up and blows it out low down.
U.S. Pat. No. 5,612,001 to Matschke describes a UV lamp purifier that sucks in air high up and blows it out low down.
U.S. Pat. No. 5,656,242 to Morrow and McLean describes a UV lamp purifier with an electrostatic filter that sucks in air high up and blows it out low down.
It will readily be understood that such purifiers sucking in air high up and blowing it out low down do not establish a primary air jet that is attached to the ceiling, and that because they blow air out low down they actively increase the setting up of contaminating interfering air flows coming from the floor.
Also in the remote prior art, there are mobile devices for decontaminating air that suck air in low down and blow it out high up, but too far away from the ceiling to enable the primary air jet to become attached to the ceiling by the Coanda effect.
U.S. Pat. No. 4,900,344 to Lansing describes a filter purifier provided with an intake nozzle of the bottom suction type at floor level and an upper blow nozzle at a low height without any attachment to the ceiling.
U.S. Pat. No. 5,997,619 to Knuth and Carey describes a UV lamp and filter purifier that sucks air in sideways low down and blows it out higher up at a low height, without attachment to the ceiling.
U.S. Pat. No. 6,001,145 to Hammes describes a filter purifier provided with an intake nozzle of the bottom suction type at floor level, and an upper blow nozzle at a low height, without the primary flow becoming attached to the ceiling.
U.S. Pat. No. 5,453,049 to Tillman and Smith describes a triangular section purifier provided with wide bottom suction through a HEPA filter and vertically-directed top delivery through a small opening at low height without the primary flux becoming attached to the ceiling.
U.S. Pat. No. 4,210,429 to Golstein describes a UV lamp and filter purifier with bottom lateral suction and top lateral blowing out at a low height without the primary flow being attached to the ceiling.
Those purifiers are of the type using a localized jet. None of those documents relate to a device that implements a primary air jet that is attached to the ceiling by the Coanda effect, nor does any of them describe means seeking to reduce or eliminate the “sloping interfering shunt air flow” between the floor and the ceiling.
Finally, there are mobile devices for decontaminating air that suck in air low down and blow out air high up close to the ceiling that could theoretically enable the primary air jet to become attached to the ceiling by the Coanda effect.
U.S. Pat. No. 5,290,330 to Tepper, Suchomski, and Mex describes an independent device for decontaminating air that is in the form of a vertical rectangular block with bottom suction and top delivery, both horizontal. Air is decontaminated by cylindrical filter cartridges disposed vertically inside the device. It is specified in that document that suction and delivery are separated vertically so as to ensure that air moves from the ceiling towards the floor. That document does not describe any attaching of an air jet to the ceiling by the Coanda effect nor does it describe any suction flow attached to the floor by the Coanda effect. Nor does that document describe the existence of a “sloping interfering shunt air flow” that tends to rise in a slope from the floor towards the ceiling. That document does not describe any means for avoiding that phenomenon. Finally, it can be seen from its drawings, that the suction and blow grilles are similar and have the same dimensions. As a result, the blow velocity and the suction velocity are substantially equal.
U.S. Pat. No. 5,225,167 to Wetzel describes an independent device for decontaminating air, which device is substantially in the form of a rectangular block, for mounting on the wall of a room and for decontaminating air by using UV lamps and HEPA filters. Air is sucked in through a grille from close to the floor, but nevertheless at a certain distance therefrom. Air is blown out close to the ceiling through a HEPA filter in the form of one-fourth of a cylinder. That document does not describe in any way ensuring that a jet of air is attached to the ceiling by the Coanda effect, nor does it describe a suction flow attached to the floor by the Coanda effect. The blow outlet of the HEPA filter being shaped in the form of one-fourth of a cylinder tends to cause the blown primary jet to slope towards the floor and is unfavorable to it becoming attached to the ceiling by the Coanda effect. The suction inlet which is deliberately placed at a distance from the floor likewise does not seek to facilitate establishing a suction flow that is attached to the floor by the Coanda effect. That document does not describe in any way the existence of a “sloping interfering shunt air flow” that tends to rise from the floor towards the ceiling. That document does not describe any means for avoiding that phenomenon. Finally, from the drawings, it can be seen that the suction and below grilles are of substantially the same dimensions. As a result, the suction and blow velocities are substantially equal.
U.S. Pat. No. 5,616,172 in Tuckerman, Russel, Knuth, and Carey constitutes the prior art that is closest to the invention. It describes a mobile and independent device for decontaminating air, which device is substantially in the form of an elongate rectangular block, and is placed vertically along a wall of a room that is to be treated. Air is decontaminated by UV lamps and HEPA filters. Air is sucked in from the floor via an intake nozzle of the suction type at floor level formed between the bottom of the device and the floor. The blow outlet is placed at the top on the device and blows vertically towards the ceiling. The shape of the device is described as being deliberately elongate in order to increase the distance between the suction grille and the blow grille so as to avoid “short circuits” between them. Fins are also described for placing on the blow grille in order to incline the primary jet that is blown from the top of the device towards the ceiling so that the primary jet is deployed along the ceiling. Although not stated clearly, it can therefore be assumed that the primary jet becomes attached to the ceiling by the Coanda effect. However, that document considers that the only means for avoiding the “shunt effect” between the suction and blow grilles consists in keeping them as far apart from each other as possible. That disposition is indeed necessary. However, as shown by the scientific documents mentioned above, and as shown by the explanations given below, that is not sufficient. Firstly, the document takes no account of the existence of a “sloping interfering shunt air flow” tending to rise from the floor (in the middle of the room) and pass through the occupation zone following a sloping path going upwards towards the blow outlet. That document is concerned only with the direct “shunt” between suction and blowing, which constitutes another problem.
That document therefore does not recommend any means relating:
to the ratio between suction velocity and blow velocity;
or to the ratio between the effective suction surface and the effective blow surface;
for the purpose of reducing and/or eliminating the “sloping interfering shunt air flow” that tends to rise from the middle of the floor towards the ceiling, in spite of the grilles being spaced apart.
The relative dimensions of the effective suction and blow surfaces are not specified. Unfortunately, without taking these particular precautions concerning shapes and flow velocities, the above-mentioned scientific works and the explanations given below demonstrate that the spacing between the blow and suction grilles is not sufficient for eliminating this phenomenon of the “sloping interfering shunt air flow”.
As mentioned above, the person skilled in the art considers that suction inlets are of little importance in the movement of the air and that they have an influence only on their immediate vicinity. It is shown below that the person skilled in the art is wrong on this point. As a result, the prior art has paid little attention to the influence of the shape and the location of suction inlets. It would appear that no scientific study has yet been undertaken on this topic.
It therefore appears that although the method of ventilation by mixing using a blown primary jet attached to the ceiling and a suction flow attached to the floor both by the Coanda effect is known and in widespread use for its thermal qualities in the field of air conditioning, its use is practically non-existent in the field of airborne decontamination because of the “sloping interfering shunt air flow” effect that it generates has not been solved in the prior art and because that effect degrades its decontamination performance.
The invention relates firstly to a method of ventilating a room by mixing using a blown primary jet attached to the ceiling, and a suction flow attached to the floor, both by the Coanda effect. More specifically, the invention relates to ventilation methods of the type in which a previously treated (heated, cooled, decontaminated, humidified, dehumidified, . . . ) jet of primary air is blown through a blow surface situated in register with a “treatment” side wall, close to the ceiling, and in a blow direction of incidence [average over the blow surface of the mean directions of the portions of the primary jet] oriented towards the ceiling (or parallel thereto) in such a manner as to attach said blown primary jet to the surface of the ceiling by the Coanda effect. Simultaneously, a vitiated air flow is sucked in at a flow rate that is equivalent to that of the primary jet, through a suction surface that is substantially vertical, placed in register with the same treatment side wall, in the vicinity of the floor of the room. In this way, it is ensured that air is sucked in from close to the floor along a suction stream that is substantially horizontal, being parallel and attached to the surface of the floor by the Coanda effect.
Empirical experiments and computer simulations have been performed by the inventors concerning ventilation systems using mixing by means of a blown primary jet attached to the ceiling and a suction flow attached to the floor, and these have shown that in a closed room, this type of ventilation leads to the appearance of a “sloping interfering shunt air flow” that tends to rise from the floor and pass through the occupation zone following an upward sloping path towards the blow outlet. This phenomenon is well described in the prior art and in the scientific papers cited above, and no solution has previously been found for eliminating it.
In its simplest form, the ventilation method of the invention consists in that in addition, the mean blow velocity (Vs) [average of the velocities of the primary air jet portions over the blow surface] is caused to be less than the mean suction velocity (Va) [average of the velocities of the air flow portions sucked in through the suction surface] [Vs<Va]. The inventors have found, by using computer models and by undertaking airflow measurements on independent devices for airborne decontamination of a room by implementing the method, that the said phenomenon of the “sloping interfering shunt air flow” is greatly attenuated or even eliminated, when the means of the invention are implemented.
a is a diagrammatic side view showing the air flow distribution obtained by computer simulation of a ventilation device (of the type shown in
b is a diagrammatic perspective view showing the distribution of air flows obtained by computer stimulation of a ventilation device (of the type shown in
a is a diagrammatic view of a portion of a moving air stream enabling the advantages implemented by the invention to be explained analytically and enabling the “sloping interference shunt air flow” to be eliminated.
b is a diagram showing the numerical simulation conditions for air flow diagrams obtained for a prototype of the independent device of the invention for airborne decontamination.
c is a table of values showing the results obtained by the numerical simulation calculation as shown in
d is a graph illustrating the results obtained as shown in
a and 6b are a section view and a perspective view on a larger scale of the independent decontamination device of the invention.
c is a plan view showing the operation of the
d is a diagrammatic side view on a larger scale of the intake nozzle of the
e is a diagrammatic perspective view showing the device of the invention together with its suction stream.
a and 8b are a section view and a perspective view of the blow nozzle of the
c to 8h are side views showing the influence of adjusting the angle of incidence on the blowing performed by the device of the invention.
a and 9b are side views showing the importance of a recommended variant of the invention relating to adjusting the suction and blow velocities.
a is a perspective view showing a detail of a second embodiment of the blow nozzle that is preferred in the invention.
a and 13b are perspective views showing an embodiment of vertical trunk means of adjustable height that is preferred in the invention.
a and 14b are perspective views showing an embodiment of the
a and 15b are perspective views showing an embodiment of the
When the occupants (1) move about in the room (3), they generate disturbances and turbulence (7) level with the floor (6) producing rising-type disturbance currents (8), that put back into suspension some of the accumulated contaminants (4b) and clinging particles (4c) located at floor level (6) in the bottom portion of the occupation zone (2). A phenomenon similar to that which leads to the development of powerful clouds of the cumulonimbus type in weather systems occurs on a smaller scale in the room (3). Light rays (53) from a light fitting (54) located in the ceiling (20) or coming through the window (51) lead to the floor (6) being heated in non-uniform manner. As a result, strong upward convection movements (57) are generated at floor level, thereby also putting back into suspension large amounts of some of the accumulated contaminating aerosols (4b) and the clinging particles (4c) located on the floor (6). These contaminating aerosols (4b, 4c) rise into the upper portions of the occupation zone (2) so as to reach the mouths of the occupants (1) and the zones (9) in which they breathe. As a result, these contaminating aerosols (4b, 4c) that are put back into suspension by these phenomena increase the concentration of contaminating aerosols (4a) in suspension. They increase the risk of being breathed in by the occupants (1) of the room (3), and consequently they increase the possibility of the occupants (1) suffering biocontamination from airborne biological agents that might develop into various types of disease (Aspergillose, Pneumopathies, . . . ).
The prior art makes widespread use of the method of ventilation by mixing using a blown primary jet (19) attached to the ceiling (20) and a suction flow (21) similarly attached to the floor (6), both by the Coanda effect (C).
a and 4b are diagrams showing the characteristic means implemented by the method of the invention in a “short” room (3a) for the purpose of considerably reducing or even eliminating the “sloping interfering shunt air flow” (Fs) effect shown in
Although simple, these means implemented by the invention nevertheless lead to eliminating the “sloping interfering shunt air flow” (Fs) effect, thus providing considerable advantages in terms of airborne decontamination (not achieved in the prior art), as can be demonstrated analytically, initially with the help of Bernouilli's theorem and with reference to
a is a detail view showing a portion of a moving air stream (vf) that is in continuous motion. For simplification purposes, it is assumed that the air (A) is a perfect incompressible fluid subjected solely to gravity forces. Consideration is given to an infinitesimal portion (da) of the moving air in this moving air stream (vf).
The infinitesimal portion (da) of air belonging to the stream (vf) possesses:
variable section (s);
variable velocity (V);
variable length (dx);
mass (dm); and
local pressure (P).
The density (ρ) of the air is assumed to be constant. The acceleration due to gravity is constant and equal to (g).
To a first approximation, the total mechanical energy Et of the infinitesimal portion (da) of air is constituted by the sum:
of its kinetic energy Ec=½dm×V2;
its pressure potential energy
Epr=P×s×dx=P×dm/ρ
and its gravity potential energy Epe=g×z×dm.
To a first approximation, the total mechanical energy Et of the infinitesimal portion (da) of air is conserved all along the moving fluid stream (vf).
Thus, per unit mass of air moving along the entire moving air stream (vf), the following expression can be derived:
V2/2+P/r+g×z=constant
This is an expression of Bernouilli's theorem, and is valid in the absence of any energy losses (which are taken into consideration below) along the entire moving air stream (vf) in the room (3).
With reference to
If there were no “sloping interfering shunt air flow” (Fs) effect, then all of the streams coming from the blow surface (Ss) would join the suction surface (Sa). If consideration is given to the multitude of moving air streams (vf) that go:
from the blow surface (Ss) where the mean blow velocity of the air is (Vs), the blow pressure is (Ps), and where the height is (h);
to the suction surface (Sa) where the mean suction velocity of the air is (Va), the suction pressure is (Pa), and the height (h) is zero;
then all of the streams would be continuous and none of them would split into a plurality of sub-jets along their length. It would be legitimate to apply Bernouilli's theorem thereto in averaged form over the blow surface (Ss) and the suction surface (Sa) leading to:
Vs2/2+Ps/r+g×h=Va2/2+Pa/ρ(average Bernouilli)
It is important to emphasize that it is the very existence of this non-splitting of the streams (vf) that makes it possible to use Bernouilli's theorem in mean averaged form. It is only under such circumstances that it can be assumed that the entire stream (vf) coming from the blow surface (Ss) reaches the suction surface (Sa), and vice versa. This is not true if there is a “sloping interfering shunt air flow” (Fs).
However, it is obvious that because the air is blown into the room (3) through the blow surface (Ss) and is sucked out through the suction surface (Sa), it is necessary for Ps>Pa.
Now assume that Vs>Va. Under such circumstances, it can be seen that the left-hand side of the above-considered equation (averaged Bernouilli) is necessarily greater than the right-hand side of that equation. It must be concluded that the equation obtained from Bernouilli's theorem is not satisfied. This can be expressed as follows:
[no “sloping interfering shunt air flow” (Fs) effect in the room (3)]
AND [Vs>Va]
=>Bernouilli's theorem averaged over the blow and suction surfaces (Ss, Sa) is not satisfied.
The mathematically logical contraposition of the above expression gives:
Bernouilli's theorem is satisfied=>
[the “sloping interfering shunt air flow” (Fs) effect exists in the room (3)]
OR [Vs<Va]
It is thus shown that the means of the invention, i.e. [Vs<Va], is a necessary condition for there to be no “sloping interfering shunt air flow” (Fs) effect in the room (3).
In fact, the true condition is more severe. In the continuous flow of the moving air stream (vf), a fraction of the total mechanical energy is dissipated under the effect of external forces such as friction against the walls of the room (3), and above all because of the effect of induction between the primary air jet (19) and the air (A) in the room (3). Between the two ends of the moving air stream (vf), there is dissipation, giving a friction head loss ΔH. Bernouilli's theorem as applied to the moving air stream (vf) and corrected for the influence of the head loss then becomes:
Vs2/2+Ps/r+g×h=Va2/2+Pa/ρ+ΔH (Bernouilli with Head Losses)
Thus, in the absence of a “sloping interfering shunt air flow” (Fs) in the room (3), it is necessary that:
(Va2−Vs2)/2=(Ps−Pa)/ρ+g×h−ΔH
Va2−Vs2+2×[(Ps−Pa)/ρ+g×h−ΔH]
i.e.:
Va<(Vs2+2×[(Ps−Pa)/ρ+g×h])1/2
Thus leading to the following condition:
Vs<Va<(Vs2+2×[(Ps−Pa)/ρ+g×h])1/2
If the mean suction velocity (Va) is less than the blow velocity (Vs), then a “sloping interfering shunt air flow” (Fs) is established and Bernouilli's theorem is no longer applicable in its averaged form. If the mean suction velocity (Va) is greater than the blow velocity (Vs), then the “sloping interfering shunt air flow” (Fs) phenomenon weakens, tending progressively towards zero. The greater the extent to which the mean suction velocity (Va) exceeds the blow velocity (Vs), the greater the development of induction phenomena leading to air mixing with the induced primary jet (19) and to increased head loss ΔH. Above this second limit:
Va>(Vs2+2×[(Ps−Pa)/ρ+g×h)]1/2
it can be assumed that Coanda effect (C) flow can no longer be established and the movement present is mainly turbulent.
This is naturally a demonstration based on highly simplifying assumptions, but it makes it possible to understand the importance of adjusting the mean suction velocity (Va) relative to the mean blow velocity (Vs), and thus the importance of these nevertheless simple means [Vs<Va] recommended by the invention.
a shows in highly diagrammatic manner the results obtained by the inventors after performing experiments and also making use of computer tool for simulating air flows. This figure shows the air flow scheme for movements of air (A) in a room (3) similar to the room shown in
b is a perspective view of the dispositions to be implemented in the room (3) in terms of effective blow surface (Sse) and effective suction surface (Sae) for implementing the means of the invention in a built-in ventilation system (65). The wall-mounted blow and suction openings (10 and 11) used in built-in ventilation systems (65) are generally fitted with blow and suction grilles (60, 61) occupying the blow and suction surfaces (Ss, Sa) and partially obstructing the air flows. These grilles (60, 61) are conventionally constituted by metal plates provided with a multitude of holes, or metal frames (81) having a plurality of directional slats (83) and/or any other means that partially obstruct the corresponding opening (10, 11), while still allowing air to pass through. The effective area (Sse, Sae) of a grille (60, 61) means the surface of the empty space that would have the same mean overall air flow behavior for the pair comprising [fluid velocity (Vs, Va) passing therethrough/pressure (Ps, Pa)]. Commercially-available grilles are generally accompanied by specifications giving their effective areas. Otherwise, effective area can be measured empirically. In
b shows the numerical simulation conditions used for air flow diagrams obtained for a prototype of the PLASMAIR™ independent airborne decontamination device (101) operating in application of the invention in a room (3), as a function of different effective blow ratios (RS). The term “blow ratio” (RS) designates the ratio between the effective blow surface (Sse) and the effective suction surface (Sae). Numerical simulations were performed under the following conditions:
room length (L)=4 meters (m);
room width (l)=3 m;
room height (h)=2.5 m; and
air flow rate: Qv=500 cubic meters per hour (m3/h).
The axes (X), (Y), and (Z) and the list of the various points (P=P1, P2, . . . , P8) used in the simulations and located 2 cm above the floor (6) as shown in
Thus, if Yvelocity(P) is positive, that means that the air velocity in the vicinity of the point (P) situated 2 cm above the floor has a mean component that slopes upwards. Under such circumstances, it can be deduced that there are mainly upward currents from the floor in the vicinity of the point (P). It can be concluded therefrom that it is highly likely that a “sloping interfering shunt air flow” (Fs) starts from said point.
In contrast, if Yvelocity(P) is negative, that means that the air velocity in the vicinity of the point (P) has a mean component that slopes downwards. It can be concluded therefrom that there is little chance of a “sloping interfering shunt air flow” (Fs) starting from the point.
The table of
The third column (shaded) corresponds to conditions in which the device (101) is adjusted so that the blow ratio (RS) is equal to 1. This is the limiting configuration for the presence of an “interfering shunt air flow” (Fs) as predicted by the theoretical analysis given above.
The second and third columns are shaded to show more clearly conditions that lie outside the recommendations of the invention.
Finally, the fourth column (not shaded) relates to circumstances in which the device (101) is adjusted so that the blow ratio (RS=1.43) is greater than 1. I.e. these conditions lie within those imposed by the invention.
Under the conditions of column 2 in which (Va=0.57 Vs), i.e. (Va<Vs), it can be seen that the local numerical mean of the vertical component of the air velocity is positive at points (P4 to P7) that are remote from the device (101). This means that there are upward air movements in the portion of the room (3) that is far away from the device (101). It can reasonably be concluded that an “interfering shunt air flow” (Fs) rises from the far portion of the room towards the blow outlet (110). Under such conditions, the use of the device (101) as an airborne decontamination system is highly ineffective because of the presence of rising currents from the floor (6).
Under the conditions of column 3 in which (Va=Vs), it can be likewise be seen that the local numerical mean of the vertical component of the air velocity is positive at points (P5 to P7) that are remote from the device (101). This means, as above, that there are upward movements of air in the portion of the room (3) that is far from the device (101). It can be concluded that an “interfering shunt air flow” (Fs) raises from the far portion of the room (3) heading towards the blow outlet (110). Under such conditions, the use of the device (101) as an airborne decontamination system is likewise highly ineffective because of the presence of upward currents from the floor (6).
In contrast, under the conditions of column 4 in which (Va=1.43 Vs) i.e. (Va>Vs), it can be seen that on the contrary the local numerical mean of the vertical component of the air velocity is always negative at all of the points (P1 to P8). It can be concluded that no “interfering shunt air flow” (Fs) rises in the room (3). Under such conditions, the use of the device (101) as an airborne decontamination system is highly effective because of the absence of upward currents from the floor (6).
The ability of the method of the invention to eliminate the phenomenon of the “sloping interfering shunt air flow” can be seen more clearly from the graph of
The principles of the method of the invention making it possible to deal with the defects of the prior art, can advantageously be implemented within the PLASMAIR™ independent airborne decontamination device (101). A mobile independent airborne decontamination device (101) of the invention is shown in
With reference to
With reference to
With reference to
With reference to
The contaminating aerosols (4a, 4b) situated close to the suction flow (21) and included in the suction steam (55) are continuously directed by the suction induction effect (Ias) towards the suction flow (21) that is attached to the floor (6) in order to be removed via the suction inlet (111) and subjected to the decontamination process.
The device (101) of the invention thus achieves a reduction in the quantity of contaminating particles (4b, 4c) that settle by evacuating the particles continuously.
Consequently, the floor (6) becomes dirtied much more slowly and consequently the room (3) requires cleaning less frequently.
There is also a very significant reduction in the effects whereby contaminating particles that have settled (4b, 4c) are put back into upward movement (as a result of convective effects or of turbulence, . . . applied to said particles).
Furthermore, the effect whereby settled contaminating particles in suspension or that have accumulated (4b, 4c) rise, usually because of the existence of the “sloping interfering shunt air flow” (Fs) phenomenon is practically eliminated.
in the top portion (Cs) of the room;
in the bottom portion (Ci) of the room; and
in the middle portion (Cm) of the room.
The blown primary jet (19) and the suction flow (21) both attached by the Coanda effect (C) cover the entire occupation zone (2) of the short room (3a). All of the contaminating particles (4) present in the air (A) in the short room (3a) are subjected to the decontamination process.
In the top portion of the room (Cs), the contaminating particles (4) in the form of contaminating aerosols in suspension (4a) are sucked continuously upwards by the blow induction effect (Iss) towards the ceiling (20) into the blown primary jet (19). Thereafter they are taken vertically along the opposite wall (50) prior to being entrained in the sucked-in air flow (21).
In the middle portion (Cm), the contaminating particles (4) are essentially those that come from emission associated with the occupants in the occupation zone (2). They are at a very low concentration. In addition, they are continuously entrained towards the bottom portion of the room (Ci) by the gravity settling effect (5).
Finally, in the bottom portion of the room (Ci), the contaminating particles (4) in the form of contaminating aerosols in suspension (4a) are continuously sucked downwards by the suction induction effect (Ias) towards the floor (6) into the sucked-in air flow (21).
The absence of the “sloping interfering shunt air flow” (Fs), together with the bottom suction induction effect (Ias) caused by the primary suction flow (21) avoids accumulated contaminating aerosols (4b) and clinging particles (4c) coming from the fine highly-contaminated bottom layer of air (Cc) rising into the higher portions of the room (Cs, Cm).
As a result, the contaminating particles (4) in each portion of the room (Cs, Cm, Ci) are quickly evacuated into the sucked-in air flow (21) prior to penetrating into the device (101) for elimination under the conditions described with reference to
A first advantageous embodiment recommended by the invention for the independent airborne decontamination device (101) is shown with reference to
A second advantageous embodiment recommended by the invention for an independent airborne decontamination device (101) is shown with reference to
A third advantageous embodiment recommended by the invention of the independent airborne decontamination device (101) is shown with reference to
In contrast,
A second preferred embodiment recommended by the invention of the independent airborne decontamination device (101) is shown with reference to
A particular implementation of this second preferred embodiment is described with reference to
The porous flexible cylindrical blow portions (159) can be made in the form of glove fingers using a reinforced woven textile material. The textile material of the glove finger is covered in a protective adhesive strip extending along a generator line thereof. Then a sealing covering is applied to the outside of the glove finger (e.g. of the oil cloth type). Thereafter, the adhesive protective strip is withdrawn. As a result, the major fraction of the glove finger is covered in a sealing material that is impermeable to air. However a longitudinal surface in each porous flexible cylindrical blow portion (159) is free of the sealing material along a generator line so as to allow air to pass through. As a result, a porous surface (Spa) is formed over a fraction of the surface of the glove finger, said fraction occupying a generator line. The remaining surface (SE) over the other fraction is airtight. This provides a blow surface (Ss) that allows a blown primary jet (19) to be issued along the generator line, i.e. parallel to the ceiling (20) when the porous flexible cylindrical blow portions (159) are deployed. Advantageously, it is possible to use a telescopic stiffener (170) having one end placed inside the porous flexible cylindrical blow portion (159) and having its other end secured to the vertical trunk means (103). The telescopic stiffener means (170) serve to increase the extent to which each porous flexible cylindrical blow portion (159) can project when deployed (161). The telescopic stiffener means (170) is preferably deployed by the pressure inside the device (101). It can be collapsed by means of a spring.
This provides a device (101) that is relatively narrow when inactive. It can easily be passed through a door. In contrast, when in the active position, the blow surface (Ss) can deploy over a width that is substantially equal to the width of the room (3). As a result a blow flow is provided that covers the room (3), being deployed over its entire width. This leads to decontamination that is much more effective.
A third preferred embodiment recommended by the invention of the independent airborne decontamination device (101) is shown with reference to
A fourth preferred embodiment recommended by the invention of the independent airborne decontamination device (101) is shown with reference to
A fifth preferred embodiment recommended by the invention of the independent airborne decontamination device (101) is shown with reference to
A sixth preferred embodiment recommended by the invention of the independent airborne decontamination device (101) is shown with reference to
A seventh preferred embodiment recommended by the invention of the independent airborne decontamination device (101) is shown with reference to
An eighth preferred embodiment recommended by the invention of the independent airborne decontamination device (101) is shown with reference to
The main object and advantage of the invention is to attenuate or even eliminate the “interfering shunt air flow” phenomenon that is considered in the prior art as being necessarily associated with using a ventilation method by mixing using a blown primary jet attached to the ceiling and a suction flow attached to the floor by the Coanda effect.
A second advantage of the invention is to reduce the effects of putting contaminated particles that have settled in a room back into upward movement.
A third advantage of the invention is to suck in aerosols in suspension and aerosols accumulated in the highly contaminated fine layer of air situated close to the floor progressively as they settle.
A fourth advantage of the invention is to reduce the quantity of contaminated particles clinging to the floor, and consequently to reduce the cleaning requirements of the room.
A fifth advantage of the invention is to reduce the concentration of contaminating aerosols in suspension in the occupation zone of the room as occupied by its occupants.
A sixth advantage of the invention is to reduce the occurrence of diseases due to biological contamination of airborne origin in a room.
A seventh advantage of the invention is to provide a ventilation system using attached jet mixing that presents performance close to the performance of a lamellar flow in terms of decontaminating a room, and to do so at a cost that is smaller by about one order of magnitude.
An eighth advantage of the invention is to provide an airborne decontamination system that provides a high degree of cleanliness and that is mobile.
A ninth advantage of the invention is to make it possible to bring means quickly into premises that are not so equipped for combating the occurrence of biological contamination. This is equally applicable to medical applications in the home, to combating epidemics, to providing civil protection, to producing pharmaceuticals and/or foodstuffs, . . . .
A tenth advantage of the invention is to provide a mobile device that is well adapted to capturing and removing airborne contaminating particles close to the floor and to avoiding putting them back into suspension. This is of particular concern to subjects who are hypersensitive (allergies).
An eleventh advantage of the invention is to increase the speed at which a room is ventilated by mixing is decontaminated.
The invention makes it possible at reduced cost to optimize the process of decontaminating a room and of removing the airborne contaminating particles therein. The invention thus possesses industrial applications in any type of closed structure that requires air to be decontaminated. In non-exhaustive manner, this can apply to: health, food industry, research, transport, animal husbandry, pharmacy, schools, . . . .
A particularly suitable application lies in airborne decontamination of health premises for protecting patients and staff in a hospital environment against the risk of cross-contamination. This relates to providing protection in hospitals against risks of contagion of the SRAS (severe acute respiratory syndrome) type . . . .
Another application lies to temporarily combating certain consequences of conventional ventilation in professional, public, and domestic premises leading to risks of infection by airborne contaminants conveyed by an air conditioning system. This relates to local protection in a room of a ventilated building against problems of allergy and/or cross-contamination (sick building syndrome) due to the building being air conditioned.
Mention can be made of an application to transporting passengers by sea or by air.
Mention can also be made of an application to industries that present a local biological risk associated with the production of a contaminating agent. This can apply in the pharmaceutical industry and in the food industry. It also relates to microbiological research laboratories.
Another application applies to protecting high density livestock (chickens, pigs, . . . ) in order to maintain good health, in particular in farms where intrusions are limited (for selective breeding).
Another application lies in civil protection in the event of a biological terrorist attack.
A more widespread application lies in limiting risks of transmission between clients and/or staff in cafeterias and restaurants.
Another application lies in preventing the risks of epidemics in nurseries, schools, and premises of small size but containing large numbers of people.
Finally, an application lies in protecting staff and visitors in the offices of dentists, vets, . . . .
The scope of the invention should be considered with respect to the following claims and legal equivalents thereof, rather than from the examples given above.
Number | Date | Country | Kind |
---|---|---|---|
0310654 | Sep 2003 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/FR04/02309 | 9/10/2004 | WO | 12/7/2006 |