RU206604U1 - COMPACT UNIT FOR CREATING A FLAT LOCAL CLEAN ZONE - Google Patents

Abstract

The utility model relates to devices for creating gas-dynamic protection of technological areas and can be used in medicine, biology, precision mechanics, radio electronics and other fields of technology. The purpose of this device is to form a flat, overlying air jet to create a zone with a given cleanliness on the working surface. The installation contains a unit for preparing clean air, a flexible air duct, an air jet former and a tripod that allows the former to move vertically and horizontally and to change its angle of inclination. This goal is achieved by the fact that the generated jet of clean air has an optimal velocity profile and degree of turbulence, at which laminar, layered flow and mixing with the environment are minimal, and the length of the laminar section of the jet is maximal. The advantage of this device is that the air jet is made according to the scheme of a device for controlling the velocity profile in a fluid flow (patent RU 2035631 C1, 17.06.1992) and, due to its small size, comparable to the height of the generated jet, is placed on a tripod and is simply positioned ...

Description

The utility model can be used in medicine, biology, precision mechanics, radio electronics and other areas of technology to create flat, laminar air jets that provide a clean area of the required cleanliness class on the working surface.

Currently, in industries requiring high cleanliness, the technology of "clean rooms" is widely used, which allows you to control the composition and parameters of the environment in the premises. Despite the fact that the technology of "clean rooms" is well developed and widely used, it is very expensive. There are also restrictions imposed on the composition and parameters of the environment by the presence of maintenance personnel in the clean rooms. On the one hand, this imposes restrictions on the speed and temperature of a clean environment, and on the other hand, it makes it difficult to obtain ultra-clean environments due to disturbances and pollution introduced by the service personnel. It is very difficult to use "clean rooms" in mobile hospitals and in the field, and in conditions of natural disasters and catastrophes it is simply impossible.

One of the directions for improving the technology of "clean rooms" is the creation of local hydrodynamic protection of both medical and technological facilities. One of the ways to create local clean zones are boxes, where purified air enters through the filter system, and their working space is separated from the environment by impenetrable walls. However, the presence of walls can significantly complicate the manipulations carried out with the protected object, and in some cases the use of laminar boxes is made impossible due to the presence of solid walls (for example, in some experiments with animals or in the field).

Often, to create such zones, turbulent jets of purified air (or the desired gas) are used, the diameter of which significantly exceeds the area of the zone in which it is necessary to ensure sterility or a certain composition of the medium, because the turbulent jet at its edges intensively mixes with the environment. Due to turbulent mixing at the edges, only in the central part of the turbulent jet, near its axis, there is an area where unprepared air does not enter. In fact, the clean zone here is the zone near the jet axis, but not the entire jet. In the case of using a laminar jet to create a local clean zone, the problem of mixing at the edges of a clean gas in a jet with ambient air is solved. a laminar jet in each of its sections is a stream of clean air that is almost immiscible with the environment (mixing at the level of molecular diffusion).

The use of laminar jets for hydrodynamic protection of objects is complicated by the fact that laminar jets under normal conditions are destroyed in the immediate vicinity of the hole from which they flow. The length of the laminar section of the jet is determined by the characteristics of the flow at the outlet into the open space: the velocity profile and the intensity of turbulence.

The problem to be solved by the claimed technical solution consists in the formation of a flat laminar jet of clean air, which provides a covering air zone of a given purity on the working surface, and in expanding the functional properties of the installation due to a tripod that allows the forming device to be installed in a certain direction, at a given height and with the desired slope.

This task determines the composition of the installation. The installation diagram is shown in Fig. 1. The installation consists of a clean air preparation unit 1, which houses a fan or other air supply device and a filter package that purifies the air to the required cleanliness class, a flexible air duct 2, through which air from the preparation unit enters the air jet shaper 3, and a tripod 4, which allows the former to be fixed at a given height with the desired inclination and to make turns in the horizontal plane.

A distinctive part of the utility model is a device that forms an air stream.

The most common and often used in fundamental research method of creating long flat laminar jets is the use of a square or rectangular channel, at the beginning of which devices are installed that reduce the level of turbulence, such as gratings, honeycombs, nets. After that, the height of the channel decreases to the size of the formed jet. This decrease in channel height, causing an increase in the flow rate, leads to an additional decrease in the level of turbulence. The decrease in height, that is, the narrowing of the channel, can be several tens of times. Then the converging channel passes into a channel of constant rectangular cross-section, where the flow is stabilized over a certain length. The height of such a channel in the initial section with a flat jet height of 0.1 m can be measured in meters, so such a compact installation will not work. In order for a flow with a near-parabolic velocity profile to form at the outlet of the flat channel, which is required to delay the transition to turbulence, the length of the outlet section at Reynolds numbers of about 10,000 should be tens of meters. So, in order to obtain a flat air stream 0.1 m high, flowing at an average speed of 2 m / s, a flat channel 40 m long is required, while the channel must be straight. This method of creating a laminar air jet is not possible to use in any production.

A device for creating laminar flows with a low level of initial turbulence (patent RU 73044 U1, 2007.12.12) is known, consisting of a receiver with a relatively cooled medium located at the inlet in front of the vertical outlet channel, at the end of which a set of fine-mesh grids with a variable cross-sectional hydraulic resistance is installed due to the selection of the size and number of mesh cells and attaching to the mesh nodes of the threads stretched along the flow, the lengths of which are inversely proportional to the local velocity of the formed laminar flow, at a distance of about 10 diameters of the channel outlet, a cylindrical channel sucking the formed jet with a nozzle from a series of fine mesh forming the distribution of the suction pressure at the channel inlet, surrounded by a large cylindrical channel with its own nozzle from a row of fine mesh grids, into which, independently of the central channel, the cocurrent flow arising around the formed laminar jet is sucked.

The device is very complicated and, according to its description, allows only a vertical, top-down flow direction without the possibility of its positioning. The dimensions of the unit in relation to the jet diameter are not defined. No research has been found in the scientific literature to confirm the operability of this type of device. Such a multitude of disadvantages does not allow considering this device when solving practical problems.

A device for the formation of laminar jets of a fluid is known (patent RU 2681618 C1, 2018.02.15). The device includes an inlet channel, a cylindrical means for reducing turbulence of the fluid flow and an outlet channel connected to each other along the fluid flow, while the outlet channel is a circular diffuser, the outlet section diameter of which is at least twice its length, and at the outlet the diffuser is equipped with at least one mesh partition. The specially selected geometry of the diffuser and the resistance of the mesh baffle ensure that the flow of the fluid inside the diffuser is laminar. Passing through the mesh partition, the fluid flow is leveled, and large pulsations disappear. Such a device makes it possible to create a circular jet immiscible with the environment, the length of which is from 1.5 to 7 outlet diameters of the diffuser at Reynolds numbers from 1000 to 20,000. The length of the device is 1-3 diameters of the jet that it forms. The claimed characteristics have been experimentally confirmed on a device that forms a laminar jet with a diameter of 0.12 m. This method of formation allows you to create only a round jet, but cannot be used to form a flat spreading jet.

Known device for creating a flat laminar gas jet in the process of coating metal strips (patent RU 2562198 C2, 21.06.2012) Such a device is also commonly known as an air knife. The device contains a tube for equalizing the gas flow, containing a branch pipe on which a nozzle is fixed, a supply branch pipe for introducing compressed gas into the pre-chamber through holes, a first partition with holes and a second partition with holes in the equalizing tube, which are located perpendicular to the curved surface of the tube flow. In this case, the tube is made tapering and provides an optimization of the conversion of the gas flow from a turbulent flow at one end to a laminar flow at the second end of the equalizing tube.

The task of the device is to create a flow uniform over the width of the nozzle to ensure uniformity of the coating applied to the strip. The turbulence intensity in the flow is not lower than 2%, which is clearly not enough for the formation of an extended initial laminar section.

The closest prototype is a method for controlling the velocity profile in a fluid flow and a device for its implementation (patent RU 2035631 C1, 1992.06.17). The essence of the invention lies in the fact that a laminar flow is created at the inlet to the working chamber, accelerated by compression with the liner and a velocity distribution is formed with the subsequent expansion of the flow in the gap between the liner surface and the permeable partition, with the help of which the flow is throttled at the outlet of the chamber after expansion. By influencing the flow by changing the curvature of the flexible surface of the liner, the profile of the outlet flow velocity is formed.

Although the description does not show any results of an experimental study of such a method of forming an air flow, this method is taken as a basis for application in the proposed utility model.

The claimed utility model is implemented as follows. The air preparation unit includes a standard air fan, powered by an alternating current of 220 V, and a package of HEPA filters of the 4th and 14th classes, placed in a movable unit (item 1 in Fig. 1). Through a flexible PVC air duct with a diameter of 100 mm (item 2 in Fig. 1), the purified air through the inlet channel enters the air jet former (item 3 in FIG. 1), made according to the scheme of a device for controlling the velocity profile in a fluid flow ( patent RU 2035631 C1, 1992.06.17), mounted on a tripod (item 4 in Fig. 1), which allows you to move the former vertically and horizontally and change its angle of inclination.

The shaper is a rectangular channel consisting of two sections. At the inlet section of the former, there is a flow laminarizer, which consists of several (two or more) permeable partitions, which are woven fine-pored nets of metal filaments with a thickness of 30-40 μm with cells ranging in size from 40 to 70 μm, installed at a certain distance between them. After the laminarizer, the turbulence intensity in the flow is set at 1%. The outlet section of the former serves to form a predetermined profile of the air flow velocity. On its longer walls, convex bushings are installed that occupy the entire length of the outlet section. At the entrance and exit of the section, the same fine-pored meshes are stretched as in the laminarizer. The liners are installed with the formation of a narrowing section from the side of the entrance and an expansion section in the form of a gap between the partition and the surfaces of the bushings facing it. The shape of the surface of the liners is selected from the condition of the continuity of the air flow. Flowing between the liners, the air flow is first compressed. At the same time, its speed increases and levels out, and the speed pulsations decrease. Experiments have shown that by choosing the shape of the liner surface facing the partition, it is possible not only to ensure uninterrupted flow, but also to form a convex unidirectional velocity profile after the permeable partition.

To measure the field of fluid flow velocity, a DISA 56C01 STA hot-wire anemometer was used, the signal from which was transmitted to an analog-to-digital converter (ADC) and processed. The measurement accuracy was 3-4%.

The velocity profiles in the vertical section of the air flow of 100 mm after the outlet mesh of the air jet former with dimensions of 230 × 100 mm for two speed modes are shown in FIG. 2. The profiles of the turbulence intensity u '/ u (the ratio of the root-mean-square velocity fluctuations to the velocity itself) in the same section of the air jet for the same velocity regimes are shown in Fig. 3. The results of measurements in the mode with a higher speed are indicated on the graphs with round symbols, and with a lower speed - with triangular ones.

The results of experimental measurements of the profiles of the speed and intensity of turbulence behind the shaper at different speed modes show that the formed air jet has a smooth convex profile and practically does not diverge. The intensity of turbulence in the jet core remains at the level of 1.5%.

The tests carried out on the prototype of the claimed utility model confirm the possibility of obtaining, when implementing the utility model, the technical result, which consists in the fact that the claimed utility model - a compact installation for creating a flat local clean zone can be implemented, and at the same time is characterized by ease of implementation.

Claims (1)

A compact installation that forms a laminar air stream to create a flat local clean zone, including a clean air preparation unit, a jet former with a turbulence reduction device, connected downstream by a flexible air duct, and a tripod that allows the former to move in vertical and horizontal directions, characterized in that the output the channel of the former is limited by permeable partitions, between which are installed convex liners, pressing the flow at the beginning of the channel and acting on the flow flowing between the liners and the permeable partition at the end of the channel, providing uninterrupted flow around the liners and the formation of an air flow, while the length of the outlet channel of the former does not exceed two times heights.

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