Field of invention

The invention relates to improvements in gas detector assemblies. In particular it relates to the use of a gas detector assembly to increase the sampling rate of gas and temperature regulation of detectors. Background to the invention

It is known to provide fixed location gas detectors that are used to detect the presence and concentration of particular gases in the region of gas detectors. The performance of such detectors is dependent on the temperature and other environmental conditions, including pressure and humidity. As these conditions vary, the sensitivity of the gas sensors in the gas detectors may change and have negative effects on them, including reduction of component lifetimes and degradation of the sensors. This leads to increased costs in replacement and maintenance of the detectors. These effects may become more relevant dependent upon the location in which the devices are being used. For example, gas detectors are often used in the Middle or Far East, where conditions are typical relatively high in terms of temperature and/or humidity. The detectors are often placed in environments that are subject to radiation from the sun, which may cause the sensors to become hotter which, depending on the level of heating experienced, may subsequently affect their performance and sensor lifetime.

In addition to external sources of radiation, electrical components used in gas-sensing devices can be a further source of heat that can contribute to increased temperature. In order to sample across an extended area, several detectors are typically placed at different locations in order to sample the gas. The use of multiple detectors increases costs in terms of installation and subsequent maintenance. In order to mitigate for increased heating, the gas sensing device may be actively cooled using, for example, a peltier device, air-conditioning system, etc. However such cooling systems are costly to produce and require power sources, which can result in increased production, running and maintenance costs.

Furthermore, in order to provide fire/explosion protection, the sensors may be placed behind sinter blocks. Such positioning may restrict the natural movement of gas in the environment and impact on the accuracy of the reading received from the gas sensors. In order to mitigate for at least one of problems above, there is provided a gas detector assembly comprising: a housing for a gas sensing device, wherein the housing has a first opening and a second opening distal to the first opening, wherein the first and second opening are in fluid communication; a gas sensing device; and a first pressure altering device locatable at one of the openings, such that in use, the pressure altering device creates a pressure gradient between the first opening and the second opening, and increases the net gas flow from one opening to the other opening, thereby regulating the temperature of the gas sensing device. Preferably the pressure altering device is passive and more preferably wind operated. Further aspects of the invention will be apparent from the description and the appended claims.

Brief description of the figures

Figure 1 is a schematic of a gas detector assembly according to a first aspect of the invention;

Figure 2 is a schematic of a gas detector assembly according to a further aspect of the invention;

Figure 3 is a schematic of a gas detector assembly according to a further aspect of the invention;

Figure 4 is a schematic of a gas detector assembly according to a further aspect of the invention; and Figure 5 is a schematic of a gas detector assembly incorporating a solar chimney according to a further aspect of the invention. Detailed description of an embodiment

According to an aspect of the invention there is provided an improved gas detector assembly that harnesses wind energy, from the atmosphere that is being tested, in order to improve the efficiency and performance of the detector. In particular, gas detectors are only able to sample the gas at the rate which the gas diffuses over the sensor. The rate of diffusions is typically low and accordingly, the gas detector is only able to sample the gas from a small, limited, region. In essence the gas detector functions as a fixed point detector that can only sample the gas from a small fixed point in space. The present invention provides a mechanism which harnesses wind energy in order to create an increased flow of gas over the sensor. The increased flow of gas over the sensor allows the detector to draw air from the surrounding regions, thereby increasing gas flow over the detector, enabling the detector to sample the gas from a much larger region, thus changing the detector from a point sensor to an area sensor. Therefore, the effective area from which a detector may sample the gas is greatly increased.

The invention also creates a flow of gas over the sensor which helps regulate the temperature, and increase, the accuracy of the sensor. Figure 1 is a schematic of a gas detector assembly 10 according to an aspect of the invention.

In Figure 1 there is shown a gas detector assembly 10 comprising a gas sensing device 14 located in a housing 12, wherein the housing 12 has a first opening 18 and a second opening 20 distal to the first opening 18, wherein the first 18 and second 20 opening are in fluid communication, and a pressure altering device 16 at the second opening 20. Preferably the first 18 and second 20 opening are connected by a channel (e.g. a tubing, a funnel or the like), and the gas sensing device 14 is placed in this channel. In use, the detector 10 is placed in situ (i.e. the atmosphere to be sampled) and is naturally subjected to air flow 24 (e.g. wind). The air flow 24 passes over the pressure altering device 16. In an embodiment, the pressure altering device 16 is an aerofoil, which due to its shaping, causes gas flowing over it to do so at different rates, thereby altering the pressure of the gas in the vicinity of the aerofoil. One side of the aerofoil therefore produces a relatively higher localised pressure, whilst the other side produces a relatively lower localised pressure. The orientation of the aerofoil is used to determine how the pressure in the vicinity of the aerofoil is altered. Accordingly, in use, the aerofoil creates a variation in the localised pressure in the vicinity of the opening 18, 20 next to which it is placed. The localised pressure in the region next to the opening 18, 20 adjacent to which the aerofoil is placed deviates from the static localised pressure at the distal opening 20, 18. The pressure at the distal opening may be subject to random natural fluctuations but for the most part remains relatively constant.

Preferably the aerofoil is placed adjacent to the second opening 20 and oriented such that the pressure at the second opening 20 is lowered with respect to the pressure at the first opening 18, which is relatively constant. This causes a pressure gradient to be created between the first 18 and second openings 20, which results in an air flow as the atmosphere seeks to minimise the pressure gradient. The result is that there is a net flow in the gas present within the housing 12, from the end with the relatively higher pressure (in the described embodiment the first opening 18) to the end with the relatively lower pressure (the second opening 20).

The net flow of gas within the housing 12 results in more gas being drawn into the housing 12 from the atmosphere 19 outside the housing 12. The gas that is drawn in from the atmosphere 19 subsequently flows from the first opening 18 of the housing 12 to the second opening 20 of the housing 12, passing the gas sensing device 14. The gas passes out of the housing 12 through the opening 20. The process continues as long as the pressure altering device 16 maintains a pressure gradient between the space 21 inside the housing 12 and the space 23 outside the housing 12. Accordingly, as long as the detector 10 and pressure altering device 16 is exposed to an air flow 24, there will be a pressure gradient between the first 18 and second opening 20 and therefore an increased flow over the gas sensing device 14. The increased air flow provides a cooling flow thereby regulating the temperature of the device 14. In the embodiments in which the openings 18, 20 are connected by a channel the gas sensing device 14 is placed in the channel and therefore is subjected to the increased air flow. Increased air flow passing by the gas sensing device 14 results in temperature regulation of the gas sensing device 14.

Preferably air flow 24 is natural wind in the environment. Therefore, the invention harnesses wind energy to regulate the temperature of the device 14. However, in other examples, the air flow 24 is generated using artificial means, such as an electric fan.

Preferably air flow 24 flows in any direction that facilitates the pressure altering device 16 to generate a pressure gradient between the region outside 23 of the housing 12 and the space inside 21 the housing 12. In further examples, the direction of air flow 24 is limited to generate a pressure gradient between the region outside 23 of the housing 12 and the space inside 21 the housing 12 only when the air flow 24 is in one direction. In the instance that the pressure altering device 16 is a passive device, a variation in localised pressure is generated. The shape of the pressure altering device 16 may be varied in accordance with the requirements of the system. For example if the detector 10 were to be placed in a high temperature environment, and therefore the detector 10 would require an increased rate of cooling the shape of the pressure altering device 16 would be selected so as to create the necessary pressure gradient and cooling flow. As the shape of the pressure altering device 16 determines the extent of the pressure gradient that is created and therefore the shape of the pressure altering device 16 is designed according to the pressure gradient that is required. Furthermore, the pressure altering device 16 optionally includes means to temper the pressure gradient that is generated, for example by altering the path of gas flowing past the pressure altering device 16. In an example this is done by altering the shape of the pressure altering device 16 in response to increased or decreased gas flowing past the pressure altering device 16. Advantageously, this allows for design of pressure altering devices 16 that fit in already existing spaces and/or take advantage of particular prevailing winds, or fixed sources of air flow 24.

In the embodiment shown in Figure 1 there is a first pressure altering device 16 positioned at a first opening 20 in order to generate a net flow of gas past the gas sensing device 14 in the gas housing 12. However, in further examples there is more than one pressure altering device 16, wherein the a first pressure altering device 16 is placed at the first opening 20 and a second pressure altering device 16 is placed at the second opening 18. The configuration of the first and second pressure altering devices 16 is such that a net flow of gas through the housing 12 results. In further examples, any number of pressure altering devices 16 are placed over the openings 18, 20 in order to control gas flow through the housing 12 and over the gas sensing device 14.

Preferably the pressure altering device 16 is an aerofoil that is oriented such that air flow 24 past the aerofoil generates a lower pressure at the second opening of the housing 12 and a higher pressure at the first opening of the housing 12, such that gas flows within the housing 12 from the first opening 18 to the second opening 20. In further examples the aerofoil is oriented such that air flow 24 past the aerofoil generates a higher pressure at the second opening 20 of the housing 12 relative to the pressure at the first opening 18 of the housing 12, such that gas flows within the housing 12 from the second opening 20 to the first opening 18.

In further examples, the pressure altering device 16 is a passive device, such that it does not generate energy to power its action from within itself, rather it draws upon energy from the environment. An aerofoil is an example of a passive device as it does not require any energy to alter the pressure. Other examples of passive pressure altering devices include solar- powered or other shaped devices which alter the pressure of the environment.

Advantageously, the use of such a gas detector assembly 10 allows a flow to be created across a gas sensing device 14. Such a flow of gas allows for the temperature of the gas sensing device 14 to be regulated, thereby avoiding the negative effect that exposure to extreme environments has on the performance and lifetime of a gas sensing device 14. Furthermore, the use of such a gas detector 10 has the beneficial effect of drawing gas from the atmosphere 19 to be sampled across the gas sensing device 14, thereby turning the gas sensing device 14 from effectively a point source sensor to a volume sensor. This reduces the time it takes for a gas leak to be detected since it relies on the active measurement of a volume of atmosphere 19, as opposed to relying on Brownian motion.

Furthermore, by placing a gas sensing device 14 in a housing 12 of the gas detector assembly 10, the gas sensing device 14 is protected from the negative effect of wind in the environment, whilst still harnessing the wind to produce a pressure differential that results in gas being drawn into the gas detector assembly 10. Such a flow of gas further regulates the effect of pressure at the gas sensing device 14 resulting in more accurate detection of gases.

Beneficially, the use of an aerofoil as the pressure altering device 16 means that the effect of producing a pressure differential that results in gas being drawn in through the first opening 18, across the gas sensing device 14 and out of the second opening 20 is generated without the need for using an external power supply. The system operates passively. As such, the cost of maintenance and manufacture of the system may be reduced. Furthermore, by regulating the temperature of the device, the sensor is cooled and the adverse effects of heating of the sensor may be avoided. Thus the invention may improve the lifetime and the performance of a sensor, resulting in further ancillary benefits such as lowering the need for maintenance or servicing of the device.

Figure 2 shows a gas detector assembly 20 in accordance with a further aspect of the invention.

In Figure 2 there is shown a gas detector assembly 20 comprising a gas sensing device 14 located in a housing 12, wherein the housing 12 has a first opening 18 and a second opening 20 distal to the first opening 18, wherein the first 18 and second 20 opening are in fluid communication, and a pressure altering device 32 at the second opening 20.

In use, the functionality of the gas detector assembly 20 is the same as gas detector assembly 10 described above in relation to Figure 1. In this example, the pressure controlling device is a ventilator fan 32. The ventilator fan 32 is driven directly by an external air flow 24. The rotation of the ventilator fan 32 is arranged to produce a pressure differential between the volume inside 21 the housing 12 and outside 23 the housing. In further examples the orientation of the ventilator fan 32 can be reversed in order to reverse the pressure differential and cause a net flow of gas from in through the second opening 20 and out through the first opening 18, passing by the gas sensing device 14.

Preferably the ventilator fan 32 relies on the air flow 24 generated by wind in the environment to cause the rotation of the fan blades that cause a pressure differential to be generated. Advantageously, a wind-powered ventilator fan 32 does not require a power source and therefore is more economical to use compared with an active pressure altering device 32.

In further examples, the ventilator fan 32 is comprises a motor that uses an artificial power source to cause it to rotate. Advantageously, the use of a motor ensures that there is always a pressure gradient when in operation, regardless of wind conditions. Furthermore, the use of a motor means that the pressure gradient can be more easily regulated by controlling the rate of rotation of the motor driving the ventilator fan 32. In further examples, a passive ventilator fan 32 has the facility to use a power-driven motor, such that it can be rotated, for example if the wind reduces below a predetermined threshold, the passive ventilator fan 32 can be switched to an active ventilator fan 32, thereby ensuring that a constant pressure gradient is maintained and also that electric power is only consumed when there is not sufficient wind power to cause the same effect. In further examples, the ventilator fan 32 is connected to a motor that can reverse its direction of rotation, thereby encouraging the net flow of gas through the housing 12 to enter either the first opening and leave through the second opening, or vice versa. Advantageously, this enables different regions of atmosphere to be preferentially sampled at the gas sensing device 14 as well as regulating the temperature of the device.

Figure 3 shows a schematic of a gas detector assembly 40 in accordance with a further aspect of the invention.

In Figure 3 there is shown a gas detector assembly 40 comprising a gas sensing device 14 located in a housing 42, wherein the housing 42 has a first opening 18 and a second opening 20 distal to the first opening 18, wherein the first 18 and second 20 opening are in fluid communication, and a pressure altering device 16 at the second opening 20. The housing 42 further comprises an inner wall 44 thereby reducing the cross-sectional area of the housing 42. The gas sensing device 14 is located in the housing 42 such that the sensing face of the gas sensing device 14 samples the flow 22 within the housing 42.

Preferably, the inner wall 44 is used in combination with the housing 42 to form a Venturi tube. The tube can be used to create an area of low pressure, thereby encouraging deviation in the path of the gas flowing through the housing 42. Advantageously, the gas flow through the housing 42 can be controlled such that it deviates beyond any objects, such as protective sinter blocks, that are placed in the gas sensing device 14. For example, the gas sensing device 14 may be placed behind a sinter block in order to protect it from fires and explosions. The use of a Venturi tube in the housing 42 ensures that gas flow from the region of atmosphere being sampled reaches the gas sensing device 14, even when the gas sensing device 14 would otherwise have been shielded from the gas flow. A more efficient gas detector assembly 40 is achieved.

Advantageously, the reduced cross-sectional area of the housing 42 can be used to increase the speed of gas flow through the housing 42, thereby altering the rate of sampling of gases in the atmosphere and increasing the cooling flow achieved. In further examples, the cross- sectional area of the housing 42 can be altered such that the speed of gas flow through the housing 42 is not as fast when passing the gas sensing device 14 compared with its speed through other parts of the housing 42. This can be achieved by having a variable cross section. Advantageously, the rate of gas flow over the gas sensing device 14 is controlled so that the rate of sampling and detecting certain gases is optimised.

Beneficially, the use of an inner wall 44 in the housing 42 means that the passage of gas through the housing 42 can be controlled such that it preferentially passes over the gas sensing part of the gas sensing device 14, in a controlled manner. Furthermore, the passage of gas can be controlled using the inner wall 44 such that the cooling effect of the gas flowing through the housing 42 acts to reduce the temperature of the gas sensing device 14, removing excess heat generated by the gas sensing device 14 and stabilising the temperature at the gas sensing device 14, thereby resulting in more stable and accurate detection of gases.

Advantageously, the use of an inner wall 44 means that the gas sensing device 14 can be placed remotely from the region of atmosphere 19 that is to be sampled without unnecessarily sampling the gas in the housing 42 that has not originated from the region of atmosphere 19 that is to be sampled in recent time. For example, the gas detector assembly 40 may be located in a room adjacent to the room that is being measured. An inner wall 44 divides gas flow through the gas housing 42 such that air from the room in which the gas detector assembly 40 is located is used to cool the gas sensing device 14 and air from the room that is being measured passes over the gas sensing element of the gas sensing device 14. Figure 4 shows a schematic of a gas detector assembly 50, in accordance with a further aspect of the invention.

In Figure 4 there is shown a gas detector assembly 50 comprising a gas sensing device 14 located in a housing 52, wherein the housing 42 has a first opening 18 and a second opening 20 distal to the first opening 18, wherein the first 18 and second 20 opening are in fluid communication, and a pressure altering device 32 at the second opening 20. The housing 52 further comprises an inner wall 54 thereby varying the cross-sectional area of the housing 42. The gas sensing device 14 is located in the housing 52 such that the sensing face of the gas sensing device 14 samples the flow 22 within the housing 52. The pressure altering device 32 is a ventilator fan 32, however, in further examples, the pressure altering device 32 is an aerofoil 16.

Advantageously, by varying the cross-sectional area of the housing 52, the rate of flow of gas through the housing can be controlled. At narrower cross-sectional areas the rate of flow of gas will increase relative to the rate of flow of gas through the wider cross-sectional regions. Furthermore, the variation in cross-sectional area of the housing 52 can be used to protect and shield the gas sensing device 14 from the environment, ensuring that gas sampling rates are maintained within acceptable limits.

In further examples, an above described gas detector assembly is combined with other apparatus in order to further improve the efficiency of the effects that it produces. In an example, the gas detector assembly is combined with a solar chimney in order to create a passive system that actively boosts the effectiveness of the gas detector.

A solar chimney is a, preferably passively, cooled gas detector, comprising a thermal chimney, having a first heat collecting area in fluid communication with a ventilation area and a gas sensing device placed at least in part in the ventilation area, such that in use, when the first heat collecting area is heated, a convection flow between the heat collecting area and ventilation area is established, and provides a cooling flow over at least part of the gas sensing device. An advantage of this invention is that cooling is provided when it is most needed, i.e. when the detector is exposed to the sun. The invention passively maintains a steady temperature that improves sensor lifetime and reduces calibration and maintenance cycles. In a preferred embodiment the passively cooled gas detector is as defined in PCT/GB2013/050629, in the name of Crowcon Detection Instruments Limited, the contents of which are incorporated by reference.

In an example, a combination of the gas detector assembly with a solar chimney has a pressure altering device 16 positioned at the top of the solar chimney. In use, wind energy creates a flow of gas through the thermal chimney. The effect is supplemented by exposure to the sun, which causes the first heat collecting area increase in temperature, thereby effecting convection flow between the heat collecting area and the ventilation area. Figure 5 is a schematic of an example combination of a solar chimney with a gas detector assembly described above and in previous figures.

There is shown a combination apparatus 60 comprising a gas sensing device 14 and a thermal chimney 61. The thermal chimney 61 comprises: heat collecting walls 62, connected to ventilation area walls 64 and a base 74. There are a plurality of vents 72 in the ventilation area walls 64. The ventilation area walls 64, along with the base 74, define a ventilation area 76. The heat collecting walls 62, along with the chimney exit 73 define a heat collecting area 78. The ventilation area 76 is in fluid communication with the heat collecting area 78. The device 14 is integrated in to the ventilation area 76. A pressure altering device 16, 32 is positioned at the chimney exit 73, which is equivalent to the second opening 20 of the gas detector assembly 10, 30, 40, 50. The thermal chimney 61 is equivalent to the housing 12, 42, 52 of the gas detector assembly 10, 30, 40, 50.

The heat collecting walls 62 are made from a material which preferentially absorbs radiation from an external source such as the sun. In use the sun causes the gas in the heat collecting area 78 to heat. Preferably the ventilation area walls 64 are made from a material which preferentially reflects radiation from the sun, allowing for a temperature differential to be created between the gas in the heat collecting area 78 and the ventilation area 76. The temperature outside of the thermal chimney 61 is preferably cooler than inside the heat collecting area 78. Subsequently, the gas heated in the heat collecting area 78 rises out of the thermal chimney 61 due to the creation of a convection current and is replaced with relatively cooler gas from the ventilation area 76. The gas in the ventilation area 76 is then replaced by a supply of gas from outside of the thermal chimney 61, which enters into the thermal chimney 61 through a plurality of vents 72. The replacement gas in the heat collecting area 78 is then heated and the cycle continues, with fresh gas being drawn through the plurality of vents 72, through the ventilation area 76, into the heat collecting area 78, before being expelled through the chimney exit 73. The process is a continuous one, with the overall effect being that there is a steady flow of gas through the thermal chimney 61. As the gas sensing device 14 is placed within the ventilation area 76 the flow of gas passes over the device 14 causing it to cool. In other embodiments the gas sensing device 14 is placed partly within the ventilation area 76, and the part of the device in the ventilation area 76 experiences the gas flow, thereby cooling the device. In use, the thermal chimney 61 acts as a housing for a gas sensing device 14 and therefore is used as a dual purpose housing to effect gas flow by two means; using a pressure altering device 16, 32 to provide a net flow of gas through the housing and using solar energy to create a convective net flow of gas through the housing. Increased net flow of gas through the housing results in temperature regulation of the gas sensing device 14.

Advantageously, a combination apparatus 60 is used to increase gas flow past a gas sensing device 14. The apparatus takes advantage of wind in the environment and solar energy; it can therefore operate passively, meaning that it is low maintenance and does not require excess energy to power it, thereby rendering it more cost efficient.

In further examples, non-passive elements can be used in combination with passive elements, or alone, in order to create a net flow of gas through a housing 12, in which a gas sensing device 14 is housed. In an embodiment, a Venturi tube is placed in the thermal chimney 61 of the combination apparatus 60, and is used to create a low pressure zone in the thermal chimney 61. In another embodiment, a Venturi tube is placed in the housing 12 of the gas detector assembly, thereby creating a low pressure zone, as for the thermal chimney 61. The low pressure zone created by placing a Venturi tube in the apparatus helps to regulate the flow of gas past the gas sensing device 14. The combination of wind and solar energy may result in significant gas flow past the gas sensing device 14, which may in some instances be detrimental to the efficiency of gas sampling at the gas sensing device 14. Therefore, the gas flow may be moderated by the introduction of a Venturi tube in the apparatus. Furthermore, the internal structure of the housing 12 or thermal chimney 61 may be such that parts of the gas sensing device 14 are exposed or shielded from the prevailing gas flow, in a way which is detrimental to the efficiency of the gas sensing device 14. Therefore, the housing 12 or thermal chimney 61 are designed in order to make sure that the gas flows through them in an optimal way. Accordingly, in further examples, the combination of a thermal chimney 61 with a pressure controlling device 16 allows for optimal design in which the features of the creation of a pressure gradient and convective movement of gas are envisaged. Therefore, the present invention provides an improved apparatus which harnesses wind energy in order to create an increased flow of air through a detector to regulate the temperature of the detector. The increased flow of air generated by the apparatus provides a cooling flow and thus provides an efficient, cost effective, cooling mechanism for the detectors which are typically placed in hot and harsh environments such as those found in the Middle East. The described configurations also effectively turn the detector into an area sensor as the air may be sampled from a wider area than would typically be found in prior art systems. Furthermore, the apparatus provides a shield to protect the detector from any potentially adverse effects of the atmosphere. Advantageously, the use of a passive pressure altering device means that no internal power source is required, thereby reducing the number of components and the required maintenance of the gas detector assembly. Further, such detectors can be used in remote locations without the requirement to attend to them to replace power sources, or indeed to supply them with processed energy in order for them to function. This is an economic and simple solution to a problem of powering gas detector assemblies with pressure altering devices.