Abstract: Nozzle openings 15a each including a straight duct portion 15s and a tapered portion 15t are situated at an upstream position of an air flow with respect to the straight duct portion. The nozzle openings are formed in a nozzle plate 15 such that the nozzle openings 15a are arranged in grid, and airborne microorganisms passing through the nozzle plate 15 can be effectively collected to form colonies. A degree of cleanness is measured by counting the colonies visually.

Abstract: After supporting a petri dish S having a culture medium K contained therein with a given thickness on a petri dish holder 17 of a housing 14, a nozzle holder 13 is clamped at a top of the housing 14. When a motor 19 is energized to rotate a high static pressure fan 18, air is introduced through nozzle openings 12a, and flows through a space between the nozzle 15 and the culture medium K. By setting a distance between the nozzle and the culture medium to 0.5-1.5 mm, a high collection efficiency can be attained.

Abstract: An air flow visualizing device for introducing clean steam generating by a steam generating device into an insulating chamber in which a refrigerant such as liquid nitrogen or the like is enclosed so as to generate a misty tracer by rapidly cooling down the steam. The generated misty tracer is directly introduced into an air flow to be visually recognized or introduced after controlling the temperature of the misty tracer so as to be easily captured by the air flow.

Abstract: This electrostatic filter dust collector has a dust collecting section which is assembled by using a mini-pleat type filter member having a small width of the fold thereof and a short distance between the adjacent ridge portions thereof, whereby the dust collector is reduced in both its size and thickness. Since a plurality of spacers are inserted into the filter member from the upstream and downstream sides thereof, the percentage of the contacting area of the spacers with respect to the filter member is low, and the percentage of the dust collecting area thereof is high. In addition, it is possible to obtain a sufficiently large insulating distance. Either or both of the upstream and downstream spacers are electrically conductive, and a high voltage is applied between the corresponding conductive spacers, so that a uniform and stable electric field is generated on the filter member as a whole. This enables a high dust collecting efficiency to be obtained.