Air movement apparatus

Abstract

An air movement apparatus for installation adjacent a wall 4 in an internal space, to provide ventilation, comprises a fan 6, an inlet nozzle 8 for drawing air through the fan and generating an outflo

Description

The present invention relates to air movement apparatus particularly, but not exclusively, for ventilating a space such as a tunnel or a car park which may be an underground car park or a multi-storey car park. It is known to provide air movement apparatus in the form of longitudinal ventilation by jet fans located in such spaces to improve the air quality during normal use as well as for controlling smoke during a fire, the apparatus having a fan with an inlet nozzle for drawing ventilation air through the space being ventilated and an outlet nozzle for directing the air as a jet through the space, the nozzles and the fan lying generally along a common longitudinal axis and is generally cylindrical in cross-section For practical reasons such as minimising the intrusion of the apparatus when installed in a tunnel or a car park, the apparatus is generally located close to the tunnel lining above the heads of people or vehicles using the tunnel or car park. This has the disadvantage that the jet of air leaving the apparatus is subject to the Coanda effect in which the outer part of the air jet attaches itself to the wall of the tunnel and follows the line of the wall and also spreads laterally in a relatively uncontrolled manner. This leads to increased frictional losses between the air and the wall of the tunnel and to increased turbulence between the outer part of the air jet and the main body of the air jet which further reduces the ventilating force generated by the air jet and hence reduces the efficiency of the ventilation apparatus. At the same time, the increased turbulence creates an unacceptable increase in noise. One known proposal is to direct the output from the outlet nozzle away from the wall and towards the centre of the air jet. Typically, the outlet nozzle is directed at an angle of up to 10° from the axis of the fan, which reduces the Coanda effect but does reduce the force of the air jet and reduces the head space in the tunnel . Another proposal is to incline the nozzle trailing edge at an angle to the axis of the fan jet but this results in a non-circular trailing edge which increases the complexity and of the cost of producing the nozzle. The present invention seeks to improve the efficiency of the ventilation of the apparatus. According to the present invention there is provided air movement apparatus for installing adjacent a wall in an internal space to provide ventilation to the space, the apparatus comprising a fan for generating a ventilating flow, an inlet nozzle for drawing air through the fan and generating an outflow jet of air, and an outlet nozzle for directing the outflow jet of air, the axes of the inlet nozzle, the fan and the outlet nozzle lying generally on a common longitudinal axis, and the outlet from the outlet nozzle has a trailing edge and comprising a bellmouth, wherein the trailing edge of the outlet nozzle has an insert providing an inclined surface reducing the outlet area of the trailing edge over a predetermined part of the periphery of the trailing edge, to direct the part of the air jet passing over the insert away from the wall. Preferably, the insert extends over 30-40% of the periphery of the outlet nozzle. The insert may be a separate body secured in a standard outlet nozzle but may be incorporated in the outlet nozzle itself to provide a bespoke solution. In an alternative arrangement the insert is formed by inclining the axis of the insert relative to the longitudinal axis so that the reduction in size of the outlet area of the trailing edge in the installed condition is at a maximum adjacent the wall gradually reducing to a minimum to a point radially opposite said maximum amount. Preferably, the bellmouth is shaped to be aligned with the profile of the trailing edge. Preferred embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 shows a longitudinal cross-section through part of an outlet nozzle incorporating insert, Figure 2 shows a radial cross-section through the nozzle of Figure 1, Figure 3 shows a longitudinal cross-section through part of an outlet nozzle in which an outlet bellmouth is attached to the trailing edge of the nozzle the profile of the bellmouth being aligned with the trailing edge, Figure 4 shows a radial cross-section through the nozzle of Figure 3, Figure 5 shows an alternative embodiment with a bellmouth aligned with the trailing edge of the outlet nozzle, Figure 6 shows an axial end view of Figure 5, Figure 7 shows a perspective view of the embodiment of Figures 5 and 6, and Figure 8 shows a schematic side view of a fan assembly in the installed position. Referring now to Figure 8, there is shown a fan jet assembly 2 is secured to a wall 4 of a tunnel for example of a road or an underground train tunnel, or an underground or multistorey car park, the assembly comprises a central fan unit 6 in the form of an axial fan (not shown in detail), an inlet nozzle 8 and outlet nozzle 10, the two nozzles and the fan unit are aligned on a common longitudinal axis 12. The inlet nozzle 8 incorporates a bellmouth 14 for guiding air into the inlet nozzle. The length of the nozzles, 8 and 10, is determined by design requirements and is typically based on the diameter of the fan assembly and the whole fan assembly may have a longitudinal length between 1 to 3 times the diameter of the fan but may be up to 10 times the length. The inlet edge16 of the inlet nozzle 8 incorporates a bellmouth 14 designed to assist in improving the airflow characteristics into and through the fan. The interior of both the inlet and outlet nozzles is lined with attenuating material such as fibreglass to dampen noise from the airflow. The outlet nozzle 10 has a trailing edge18 with a bellmouth 20 which will be described with reference to the embodiments shown in Figures 1 -7. Referring now to Figures 1 and 2, these figures show a sectional view through part of the outlet nozzle and comprises an outer casing 22 lined with an attenuating material 24 such as fibreglass to dampen noise passing through the assembly. The attenuating material is retained in position by an inner lining 26 formed of a perforated material such as steel or a plastics material. An insert 28 is incorporated adjacent the peripheral trailing edge 18 and as shown in Figure 1 this embodiment is of triangular cross-section to form an inclined surface 30 designed to deflect part of the outgoing air jet away from the tunnel surface thus reducing the Coanda effect. The insert extends over about 30-40 percent of the periphery of the trailing edge 18 The insert 28 may be a separate component inserted in and secured to the interior surface of a standard design of an off-the-shelf outlet nozzle but equally may be integrally incorporated in the attenuating material of the outer nozzle 24 itself. This embodiment has a bellmouth 20 aligned with the trailing edge 18 of the main body of the outlet nozzle in which case increased turbulence is created in the air jet passing over the insert thereby altering the Coanda effect. This arrangement has the advantage that the bellmouth itself can be formed by a simple spinning operation in view of its annular shape matching the shape of the outlet nozzle. When the insert is a separate body it may incorporate attenuating material prior to being secured to the nozzle. Referring now to Figures 3 and 4, there is shown an embodiment incorporating an alternative design 20a of the bellmouth 20 in which the bellmouth profile is aligned with that of the trailing edge 18 of the insert thereby improving the flow through the outlet of the nozzle in the region of the insert 28. Figures 5, 6 and 7 show an alternative arrangement in which the attenuating material is shaped to provide the outlet end at the trailing edge 18 with a slightly smaller diameter than the cross-section of the main part of the outlet nozzle 10. The attenuating material is shaped in a frusto-conical form whose axis of rotation 32 is inclined at an angle of up to 10° relative to the longitudinal axis 12 of the outlet nozzlel 0 to direct the airflow at this point away from the wall of the tunnel 4 thereby to reduce the Coanda effect. The frusto-conical part of the outlet nozzle 10 may be formed by an insert secured to the inner surface of the attenuating material 24 of the nozzle 10 but in an alternative form the first part of the outlet nozzle may be formed as a separate component which is secured by being bolted to the distal end of the main part of the outlet nozzle 10. Although described as being part of a unidirectional fan assembly, it will be appreciated that the invention is equally applicable to a bidirectional fan assembly. Depending upon the intended use of the bidirectional arrangement use, design changes may be incorporated to maximise the efficiency of the assembly in the direction in which the use is predominant such as a one-way railway tunnel. In such an application, the bidirectional use may be only in exceptional circumstances such as dealing with smoke in a fire. On the other hand, if the application is for a road tunnel regularly having two directions of travel a slightly reduced efficiency in both directions may be acceptable.

Claims

1. Air movement apparatus for installation adjacent a wall in an internal space to provide ventilation to the space, the apparatus comprising a fan for generating a ventilating flow, an inlet nozzle for drawing air through the fan and generating an outflow jet of air, and an outlet nozzle for directing the outflow jet of air, the axes of the inlet nozzle, the fan and the outlet nozzle lying generally on a common longitudinal axis, and the outlet from the outlet nozzle has a trailing edge and comprising a bellmouth, wherein the trailing edge of the outlet nozzle has an insert providing an inclined surface reducing the outlet area of the trailing edge over a predetermined part of the periphery of the trailing edge, to direct the part of the air jet passing over the insert away from the wall.

2. Air movement apparatus according to claim 1, wherein the insert extends over 30-40% of the periphery of the outlet nozzle.

3. Air movement apparatus according to claim 1 or 2 wherein the insert is a separate body secured in a standard outlet nozzle.

4. Air movement apparatus according to claim 1 or 2, wherein the insert is integrally incorporated in the outlet nozzle itself to provide a bespoke solution.

5. Air movement apparatus according to any one of claims 1 to 3 wherein the insert incorporates attenuating material prior to being secured to the outlet nozzle.

6. Air movement apparatus according any one of claims 1 to 5 wherein the insert is formed by inclining the axis of the insert relative to the longitudinal axis so that the reduction in size of the outlet area of the trailing edge in the installed condition is at a maximum adjacent the wall gradually reducing to a minimum at a point radially opposite said maximum amount.

7. Air movement apparatus according to any one of claims 1 to 6 wherein the bellmouth is shaped to be aligned with the profile of the trailing edge.

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