GB2171329A - Atmospheric monitoring devices - Google Patents

Abstract

An atmospheric monitoring device of liquid impingement type comprising a vessel (10) for the liquid, with gas entry and exit ports (13, 14) above the liquid (24), and a nozzle (22) depending from the entry port into the liquid, is improved by transverse division into two chambers (11, 12) respectively below the ports, the chambers being separately intercommunicated (16, 15) above and below the liquid level, to produce a recirculatory action enhancing collection efficiency. The nozzle preferably extends substantially to the bottom of the entry chamber and below the lower chamber intercommunication. <IMAGE>

Description

SPECIFICATION Atmospheric monitoring devices This invention concerns two aspects of atmospheric monitoring devices.

One aspect of interest is that of such devices for personal use by carriage on the body of an individual to monitor the close environment in respect of a potential health hazard by way of atmospheric contamination. Devices of this kind commonly involve a dry medium selected to collect contaminant of interest from a sample of the relevant atmosphere presented thereto in a controlled manner. Such devices can be of a passive form with contaminant collected by diffusion from a neighbouring static atmospheric zone. However, better results are often obtained with devices of dynamic form through which a sample of the relevant atmosphere is passed for contaminant collection by adsorption and other actions, this form of device resulting from the availability of small bodily-portable battery driven pumps.

The other aspect of interest is that of devices of liquid impingement type involving a liquid contaminant-collecting medium deployed as a trap through which a stream of the atmosphere of interest is passed. This type of device can operate with a higher order of collection efficiency for some contaminants than a comparable device involving a solid contaminant-collecting medium and is therefore superficially attractive for personal use.

However, the higher efficiency of a liquid impingement device is generally associated with the use of a liquid trap volume which is sufficiently large as not to be readily compatible with a device size suited to personal use.

An object of the present invention is to ameliorate this last difficulty.

According to the invention there is provided an atmospheric monitoring device of liquid impingement type comprising a closed vessel holding contaminant-collecting liquid, two ports located at the top of the vessel respectively for entry and exit of an atmospheric stream to be passed through the liquid, and a nozzle depending from the entry port to constrain the ingoing stream to enter the liquid, the vessel being transversely divided into two chambers respectively disposed below the two ports, such chambers being separately intercommunicated in relatively lower and higher regions of the vessel, and the liquid level being between such regions.

Use of this device involves, of course, application of an appropriate pressure differential between the ports, typically by a pump and hose connection with the entry port, to pass a stream of the atmosphere to be monitored into the entry port, through the liquid by way of the nozzle, and out of the exit port. However, in the present case, the resultant collection in the liquid of atmospheric contaminant from the stream is enhanced by the generation of a recirculatory action within the vessel.

This recirculatory action has two facets.

The ingoing atmospheric stream emerges from the nozzle as bubbles which rise through the liquid in the entry chamber. The bubbles do not necessarily all burst at the liquid surface, but can emerge in a free liquid-film-enveloped form which pass to the exit chamber and drop to re-enter the liquid. This clearly enhances collection efficiency by the inherent recirculation of the atmospheric content of the free bubbles into the liquid.

At the same time, bursting of the bubbles, whether at first emergence from the liquid or thereafter, can give rise to the production of liquid droplets which pass to the exit chamber to re-enter the main body of liquid. This will cause recirculation of liquid to the entry chamber in the lower region of the vessel and the liquid movement which this involves will, in turn, act to cause greater fragmentation of the bubbles rising from the nozzle than would otherwise occur. Contaminant collection efficiency is then enhanced by virtue of the increased area of interface between the bubbled atmosphere and liquid.

Given this overall enhancement of collection efficiency, it has been found possible to provide a device of a small size compatible with personal use and which gives operational results at least as good as iarger devices of liquid impingement type and personal-use devices employing dry collection media.

In the presently proposed device the nozzle preferably extends to the lowermost region of the entry chamber to maximise the rising path of the bubbles through the liquid. At the same time the lower region intercommunication between the chambers is preferably above the level of the nozzle tip so that the recirculating liquid flow is directed at the rising bubbles with a significant transverse component of motion to further extend the path as well as to fragment the bubbles.

In order to facilitate a fuller understanding of the invention, the same is further described below, by way of example, with reference to the accompanying drawings, in which: Figures 1 and 2 respectively illustrate in transverse section and side view a presently preferred embodiment of the invention.

The illustrated device comprises a vessel 10 formed from four component parts. These parts can be seen as two different pairs of tubes, with the two tubes of each pair being similar. In one pair the tubes are of larger diameter and longer, and respectively define the entry and exit chambers 11 and 12. These chambers are located in mutually spaced side-by-side disposition, they have one pair of corresponding ends closed, and they have their other ends open to define, in association with other components, entry and exit ports 13 and 14 which are located uppermost in use of the device. The other pair of smaller shorter tubes 15 and 16 are connected between the two chambers respectively towards the closed and open ends of the latter to form lower and upper region intercommunications.

Each of the chambers is provided with an external thread about its open end portion, suitably by heat shrinking a component 17 of plastics material therearound. These threads are each engaged by an individual apertured screw cap 18 to hold, in sealing engagement against the end face of the associated chamber, the outwardly flanged wider end of a respective hollow tapered entry or exit hose connector 19 and 20.

The entry connector 19 is distinguished by continuation into a longitudinally projecting sleeve 21 at its wider end, which sleeve serves to carry in press fit receipt, or other manner, a nozzle 22 extending at its tip to the lowermost region of chamber 11.

The exit connector 20 terminates at its flange and can serve to secure an optional hydrophobic filter membrane 23 across the open end of chamber 12. Such a membrane is particularly appropriate when the atmospheric contaminant of interest involves an aerosol, but the membrane can be useful in any case to obviate loss of contaminant-collecting liquid droplets.

Regarding this last liquid; this is denoted at 24, the vessel being filled to a level between those of the tubes 15 and 16.

The operation of the device has already been described above but is clarified by Figure 1 which indicates the ingoing and outgoing atmospheric stream flow directions, the rising bubbles which emerge from the nozzle and act to elevate the liquid level slightly in the entry chamber relative to the exit chamber, bubbles and liquid droplets passing to the exit chamber to cause recirculation, and the resultant return liquid flow direction.

Figure 2 additionally shows one form of accessory to facilitate personal carriage of the device, such accessory including a back plate 25 of bracket form on which the vessel is seated and held by a C-shaped clip 26 projecting from the plate, the plate having a crocodile clip 27 connected therewith for securement with a user's clothing.

As an indication of suitability for personal use, it is noted that a device similar to that illustrated, with overall dimensions of about 85 > < x 3535 x 15 mm and employing a micro-pipette tip for the nozzle has been satisfactorily tested in relation to monitoring atmospheric contaminants of particulate, gaseous and aerosol form. Moreover it is to be noted that, while accidental liquid spillage is a prospective disadvantage of liquid impingement devices, no such spillage occurred during the lastmentioned tests. This is due to the design of the ports with their tapered hose connectors and screw cap sealed securement with the vessel, which design renders the device effectively spill-proof in use while allowing ready disassembly for replacement and/or cleaning of the nozzle and filter.

While the invention has been described above with reference to a specific embodiment thereof, it is not intended to be limited thereby. Clearly variations in detailed structural form are possible within the ambit of the appended claims.

Claims (7)

1. An atmospheric monitoring device of liquid impingement type comprising a closed vessel holding contaminant-collecting liquid, two ports located at the top of the vessel respectively for entry and exit of an atmospheric stream to be passed through the liquid, and a nozzle depending from the entry port to constrain the ingoing stream to enter the liquid, the vessel being transversely divided into two chambers respectively disposed below the two ports, such chambers being separately intercommunicated in relatively lower and higher regions of the vessel, and the liquid level being between such regions.

2. A device according to Claim 1 wherein the nozzle depends to the lowermost region of the entry chamber.

3. A device according to Claim 1 or 2 wherein the lower region intercommunication between the chambers is above the level of the nozzle tip.

4. A device according to Claim 1, 2 or 3 comprising a hydrophobic filter membrane located across the exit port.

5. A device according to any one of Claims 1 to 4 wherein said ports each comprise a tapered hose connector reieasably sealably secured at its wider end with the vessel by an individual apertured screw cap through which the respective connector projects, the nozzle being held in position by the connector and cap of the entry port.

6. A device according to any preceding claim of sufficiently small overall size to allow personal use by carriage on the body of a user.

7. A device substantially as herein described with reference to the accompanying drawings.