Pumps – With condition responsive pumped fluid control – Plural paths having individual condition responsive control...
Patent
1981-01-13
1983-08-09
Tapolcai, William E.
Pumps
With condition responsive pumped fluid control
Plural paths having individual condition responsive control...
98 38R, 417174, F24F 1100
Patent
active
043972268
DESCRIPTION:
BRIEF SUMMARY
The present invention relates generally to a method of extracting contaminated air by suction, and to an extractor for carrying out the method. Extractors for this purpose find a wide field of use. For example, they can be used in domestic kitchens, in field kitchens and industrial kitchens; in laboratories, and in different industrial applications, such as for extracting impure air from spray booths, and from the vicinity of work benches at which harmful substances are given off; in plants where dust-laden goods are transported and handled; and in connection with metal baths which give off harmful vapours; and within the process industry etc.
Previously known extractors normally comprise a hood which permits effective capture of the contaminated air. Normally, the air is conveyed from the extractor through a system of passages, by means of an extractor fan.
When the air contaminants have the form of particles or aerosols, it is desirable, and in many cases necessary, to filter the air after extraction, in order to prevent clogging of the said passage system and to prevent said contaminants from being discharged to atmosphere.
In extractors of the aforementioned kind, the speed at which the air is captured decreases inversely proportional to the square of the distance to the suction opening. At a distance of one diameter from a circular suction opening, the speed of the air seen in an axial direction will have fallen to about 8% of the speed of said air at the suction opening.
In the case of processes which result in the contamination of the surrounding air and which, at the same time, produce heat, the extractors may include so-called overhead hoods which are located above the source of contamination, whereat the thermal lifting force of the air is utilized to facilitate the extraction thereof. Since the surrounding air is admixed with the upwardly approaching contaminating air, the cross-sectional area of the air flow will increase with an increase in distance from the contaminating source.
An empirical formula often used in these connections states that the overhang of the hood above the contaminating source shall correspond to approximately 1/3 the distance from said source. Known extractors which include overhead hoods therefore require a lot of space.
A further, serious problem connected with overhead hoods is that the contaminated air often passes the breathing zone of a person present in the vicinity of the contaminating source, before the air reaches the suction opening.
One example of a known suction extractor comprising a large and bulky overhead hood is described and illustrated in the U.S. Pat. No. 3,221,635 (Hill). This patent can be said to describe a method of removing contaminated air by suction, in which the impure air is drawn tangentially into a cylinder via an inlet gap or slot. In the interior of the cylinder, the air stream is caused to rotate and, by applying an underpressure, is given an axially directed movement and led away from the cylinder. The effective use of this apparatus also relies on the thermal lifting force of the heated air, i.e. the apparatus can not, for example, be used for extracting contaminated gases by suction from a spray booth or the like where no rising air currents occur.
The Swedish published specification 76 11472-7 (publication number 409.178) describes an air extractor which operates on the suction principle but in which the contaminated air is not caused to pass an inlet gap and, as a rule, is not imparted a rotary movement having an axial movement component. The extractor according to this patent, however, requires a relatively large installation space.
The object of the present invention is to provide a method and an extractor for removing contaminated air by suction, which reduces or eliminates the disadvantages of known methods and extractors.
In its widest aspect the method according to the invention is mainly characterised in that ejector air is blown towards the inlet gap or slot in a manner such as to entrain impurified air therewith and to adm
REFERENCES:
patent: 3221635 (1965-12-01), Hill, Jr.
patent: 3621104 (1971-11-01), Sofia et al.
patent: 3994210 (1976-11-01), Davis
patent: 4002110 (1977-01-01), Teodorescu et al.
patent: 4038912 (1977-08-01), Kuechler
patent: 4085736 (1978-04-01), Kuechler
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