Single-stage impactor with a rotating petri dish for sampling microbial aerosols

 

The invention relates to analytical instrumentation, namely, devices for sampling aerosols for subsequent microbiological studies. The device includes impactions cascade consisting of a split ring manifold, suction inlet of the impactor is limited by the inner wall of the reservoir upper portion of the axial bore, the bottom outlet with profiled edges also performs the functions of the input manifold of the vacuum source is a centrifugal fan. At the entrance to the impactor installed sectoral confuser, under the confuser close to him pinned disc with slotted nozzles, which is immediately adjacent the nozzle sector confuser. The device provides improved survival of microorganisms in the sample and allows it to be used in sampling of microbial aerosols in different conditions.. 1 C.p. f-crystals, 3 ill.

The invention relates to analytical instrumentation, in particular to devices for sampling aerosols for subsequent microbiological analysis.

The device can be used at carrying out of sanitary-epidemiological the premises of food, the pharmaceutical industry, transportation, cultural institutions, etc.

The purpose of the control is the determination of the number concentration in the air of microorganisms - colony-forming units (CFU m-3). Existing methods include two stages of control: sampling on a nutrient medium under conditions conducive to maintaining the viability of organisms and their physical condition (single cells or aggregates), and the subsequent conduct of microbiological analysis using standard techniques.

Sanitary-epidemiological control of microbial contamination in the vast majority of cases are performed using mnogoshipovyh single-stage impactors.

The impactor includes a ring collector, mnogozubkovoy the grill and placed under it fixed glass Petri dish filled with a dense nutrient medium, on which surface imposterous aerosol microbes (here and hereinafter the term microbes are indicated by different organisms: microbes, bacteria, viruses, fungi, etc); this uses the kinetic energy acquired by the particle when the speed increases the air flow in nozzles. The hcpa is prostranih can be attributed to domestic single-stage impactors PU-1B (see W. Hygiene and sanitation No. 4, 1997, S. 60-61, “flora 100 (TU 6409833).

Much more rarely used foreign instruments SAS-Super -90, MAC -100 (see handouts).

All these designs are made on the modern technical level, the effectiveness of the selection of aerosol particles is quite high: for different models, the value of d50is from 1.4 to 2 μm, d50the diameter of aerosol particles captured with an efficiency of 50%. The devices are small, weighing less than 2 kg, the energy consumption is 8-10 W, which allows, if necessary, to use an independent source of power. Together with these advantages discussed megasplay the impactors share common serious disadvantage of particles, impactively on solid nutrient medium, are continuous throughout the time of sampling the effect of the air nozzle flows, reducing the viability of selected microorganisms that alter the properties of the medium.

Unlike reviewed mnogoshipovyh impactors in the Device for bacteriological analysis air. Model 818 (device Krotov) (see Aerosols in veterinary medicine, M.: Kolos, 1972, S. 72,73) deposition of aerosol particles produced by rotating the Petri dish.

C the suction nozzle. Air promazyvaetsya through the slit nozzle axial fan and aerosol particles imposterous on a nutrient medium. Air flow through small impeller rotates the Petri dish and when sampling slotted air flow impinges on the selected microorganisms and nutrients in ten times less, only in the area directly under the nozzle.

The speed of rotation of the Petri dishes should be minimal: already at about 2·-1dimension of the radial acceleration2r is 6.9 m·-2, i.e. close to the value of the acceleration of gravity 9.8 m·-2dense medium is deformed on its surface can cause cracks. With the increase in the number of revolutions of the deformation increases. The nutrient medium may splash out of the Cup. The speed of rotation of the Cup constantly need to be adjusted. The device Krotov used for this purpose primitive braking device. When this takes place as a stop, and the increase in the number of turns that can lead to significant errors in sampling.

The width of the intake nozzle - shaft varies along the radius, changing the speed of impactive particles and souterraines the rotameter. The volume flow in the device Krotov to 40 l· min-1. The power consumption of 150 watts, weight 8 kg, the device is bulky, noisy loud.

These drawbacks have led to the fact that the device Krotov, developed several decades ago, morally and physically obsolete, now finds very limited application.

Along with this itself is a schematic diagram of the impactor with a rotating Petri dish, ensuring when sampling the protection of selected microorganisms from re - peated exposure slit air flow, protection of the nutrient medium has indisputable advantages.

German industry in recent years has released portable samplers rotary type RCS Plus and Standard RCS, with a volume capacity of up to 1000 l· min-1with high efficiency, sterilized in an autoclave (see Clean rooms, M: Asinkom, 1998, S. 190,191), we Can assume that in these structures the effect of air flow on selected microorganisms is limited. However, the use of these devices instead of Petri dishes imported tapes industrial production significantly limits the prospects for the use of these devices in domestic law is camping before, is the lack of protection from the effects of nozzle air flow selected microorganisms, which can lead to a decrease in their viability.

The device Krotov, a concept which allows to virtually ensure the protection of selected microorganisms from repeatedly repeated exposure slit air flow, protection of the nutrient medium has a number of serious design flaws which restricts the possibility of its use.

The technical result of the present invention is the creation of the impactor protecting selected microorganisms and nutrients from exposure slit air flow that is achieved by introducing the structure of the rotating Petri dishes and disk slot nozzles. Together with this, in the proposed device corrected the deficiencies noted in the review of the device Krotov, provided ease of use, operational conditions sampling of aerosols in different conditions.

The technical result is achieved due to the fact that the device for sampling microbial aerosols, including impactions cascade consisting of a split ring manifold, suction inlet of the impactor is per the new edges also performs the functions of the input manifold of the vacuum source is centrifugal fan according to the invention at the entrance to the impactor installed sectoral confuser, under the confuser close to him pinned disc with slotted nozzles, which is immediately adjacent the nozzle sector confuser. The technical result is achieved due to the fact that under the disc slot nozzles is set filled with a dense nutrient medium rotating the Petri dish, the rotation of which is micro stepper inside impacting cascade.

The effectiveness of sampling aerosols should not be less than the efficiency of the considered single-stage mnogoshipovyh impactors, the value of d50which is 1.4-2 mm.

When designing developing device selecting a size of the slit nozzle, the magnitude of the volumetric flow rate, determining the desired value of d50were made using the formula (1) obtained by solving the equation of motion of particles in the field of air flow in the impactor. The force of air resistance to the motion of particles was taken into account in accordance with the Stokes formula (see Mechanics of aerosols, Moscow, “Nauka”, 1955, S. 173-178):where dc is the width of the slotted nozzle, m; L - total length is p> kg· m-1·with-1;is the density of particles 1· 103kg-3; Q - value of the volume flow m3·with-1. Dimensions of physical quantities in the SI system.

Taking a value of dc=5· 10-4m, L=0,14 m, Q=1,67· 10-3m3·with-1:

The invention is further illustrated by the accompanying drawings and the description of its operation.

In Fig.1 shows a General view of the device of Fig.2 - sector confuser, Fig.3 - disc with slotted nozzles.

The primary site of impactor - impactions cascade (Fig.1), which implements the selection of microbial aerosols, includes an annular collector 1 with the annular groove 2 in the direction of the axial hole.

The upper part of the axial bore 3, bounded by the inner wall of the collector 4, serves as a suction inlet of the impactor. Bottom outlet with profiled edges 5 also performs the functions of the input manifold of the vacuum source is a centrifugal fan. To increase the coefficient of aspiration of aerosol particles at the entrance set the confuser 6 (Fig.2) fixed to the inner wall of the collector; in the confuser is mounted the disc slot with the and rounded, the angle between the walls, obrazuemymi nozzle confuser, given the materials listed in the Handbook of hydraulic resistance (M, "engineering", 1985, 170-172 C., 209-211), is assumed equal to 30° , the width of the nozzle outlet S=1,5 mm

In the disk slot nozzles (Fig.3, the individual elements of the drive are represented in a larger scale) with a diameter of 80 mm made 4 of the nozzle, the angle between them is 90° . The total length of the nozzle L=140 mm disc Thickness 4 mm, opening angle, the width of the nozzle at the exit are the same as those nozzles confuser (30° ; 1.5 mm). The depth of straight pipe nozzle ("work area") with a width of dc=0.5 mm is 2 mm, the end nozzle area rounded.

The Petri dish 8, filled with a dense nutrient medium 9 on which impactites aerosol particles, is placed under the disc slot nozzles on the rotating disk 10 and is fixed flexible springs 11 using elastic strips 12. Shims allow you to adjust the distance between the slit nozzles and the surface of the medium, which should be 1.5-2 mm. Rotating disk is mounted on an axis stepper microelectrodes 13 (FL-15, the number of revolutions 0,2333 about·-1(about 14· min-1),12 V, power consumption 4 watts). Engine research Institute details impacting cascade, must be resistant to disinfection treatment. The engine is enclosed in a tight housing 16, the output shaft also compacted 17.

Impactions cascade is attached to the housing 18. As one of the options can be used case and the main part of the nodes of the impactor PU-1B: the micro 19 of the centrifugal fan 20, an electronic circuit 21 with optocoupler controlling the fan speed and thus the magnitude of the volumetric flow; part of the electronic circuit also includes a control unit stepper motor. On the outer surface of the shell are placed controls 22.

The aerodynamic characteristics of the fan used in the impactor PU-1B, suggests that when working in developed slit impactor performance will be approximately 85-110 l· min-1i.e. will be close to the value adopted in the calculations presented here, the values of d50.

When enabled, the centrifugal fan includes a motor which spins the disk on which you installed it in the Petri dish. The air sucked by the fan from the environment, through the confuser enters the slit nozzle accelerates them and aerosol particles imposterous on the surface of the feeder is the second most small aerosol particles, not caught by the impactor, is released into the atmosphere.

Weight, dimensions, power consumption, finally, the value of d50practically coincide with the corresponding characteristics mnogoplanovo the impactor PU-1B.

During the rotation of the Petri dishes, the contact area of the slot flow with the environment constantly shifting, so impacte is performed on the entire surface of the medium, and the selected microorganisms and the environment are protected to a new contact with slotted threads. The actual time of exposure to air flow is many times smaller duration of sampling.

The area of dense nutrient medium in a Petri dish is 5000 mm2(Dh=80 mm), and the total area of contact of the jets with the medium taking into account mentioned before spreading flow on the deposition surface (Dp=2dwith-600 mm2(mnogozonovaya lattice impactors PU-1B contains 367 nozzle diameter 0.8 mm2), i.e. really works for only a minor part of the environment around 15%. Accordingly, in areas under the nozzles, dramatically increases the load on the environment.

In the developed design with a rotating Petri dish eliminated the main disadvantage of mnogoplatnye nozzle air flow on environment and selected microorganisms. Oxidation, dehydration, change in pH change in the composition of the nutrient medium, impaired osmoregulation biological organisms (see Airborne infection, M, “ Medicine”, 1975, S. 144,145,158,163). The rotation of the Cup can significantly reduce the intensity of the considered inactivating processes, providing reliable protection of the environment and microorganisms and, obviously, will significantly improve the survival rate of the samples.

Noted the quality gap of the impactor allow to speak about the prospects of its application in sampling of microbial contamination in a variety of conditions.

During production of the developed design with the use of technological equipment slot nozzles can be performed directly in the sector confuser. When this disc with slotted nozzles excluded from the product. Production impactors also simplified the number of nodes used in the single-stage mnogoshipovyh the impactors PU-1B, “flora 100”.

Claims

1. Device for sampling microbial aerosols, including impactions cascade consisting of a split ring manifold, suction inlet of the impactor is limited wew what mkami also performs the functions of the input manifold of the vacuum source is centrifugal fan, wherein the inlet impactor installed sectoral confuser; under the confuser close to him pinned disc with slotted nozzles, which is immediately adjacent the nozzle sector confuser.

2. The device under item 1, characterized in that under the disc slot nozzles is set filled with a dense nutrient medium rotating the Petri dish, the rotation of which is provided with an Electromechanical actuator placed inside impacting cascade.



 

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