Outlet grill for use in an air-blowing device having an axial fan
The present invention relates to an outlet grill, comprising grill elements which extend between a front side of the outlet grill and a rear side of the outlet grill.
Such an outlet grill is well-known, and is designed for use in an air-blowing device comprising a rotatable axial fan for generating an airflow. The terms "front side" and "rear side" are related to such use, wherein a side of the outlet grill which is intended to face the axial fan is defined as the rear side.
The outlet grill mainly serves to protect users from touching the fan when it is rotating. The generated airflow may be used to cool an object. Therefore, an air-blowing device is often applied as a cooling device. In a well-known application, the air-blowing device is used in a computer, where the air-blowing device needs to cool the processor of the computer. In another well-known application, the air-blowing device is used in a projector, where the air-blowing device needs to cool a lamp. In these applications, as well as in many other possible applications, it is important that the air-blowing device is compact and quiet. The noise which is generated by the air-blowing device originates from two main sources. In the first place, noise is caused by the fan cutting through the air. In the second place, noise is caused by the generated airflow passing the outlet grill.
In addition to causing noise to be generated, the outlet grill also affects the cooling capacity of the air-blowing device in a negative way. Since the airflow is interrupted by grill elements of the outlet grill, a pressure drop in the airflow is obtained across the outlet grill.
It is an object of the present invention to provide an outlet grill of the above- described type, i.e. for use in an air-blowing device having an axial fan, and comprising grill elements which extend between a front side of the outlet grill and a rear side of the outlet grill, wherein the generated noise level as well as the pressure drop across the outlet grill is reduced in comparison with an outlet grill according to the state of the art.
The above-mentioned object is achieved in an outlet grill, wherein at least one main body surface of at least one grill element is shaped in such a way that, in case the outlet grill is combined with an axial fan being able to generate an airflow, the main body surface extends substantially parallel to the generated airflow. Each grill element comprises two main body surfaces, which are relatively large in comparison with other surfaces of the grill element, and which extend between the rear side of the outlet grill and the front side of the outlet grill.
The outlet grill according to the state of the art comprises curved grill elements which are coaxially arranged with respect to a central axis of the outlet grill, as well as straight grill elements which extend in an axis plane comprising the central axis of the outlet grill. Considering that an airflow originating from an axial fan is divergent and spiral-shaped, it will be readily understood that this airflow strikes against the main body surfaces of the grill elements of the known outlet grill.
According to the present invention, interruption of the airflow by the outlet grill may be reduced to a mimmum. In a preferred embodiment of the outlet grill according to the present invention, curved grill elements are shaped and arranged in such a way that, in an axis plane comprising the central axis of the outlet grill, the main body surfaces of the grill elements are inclined with respect to the central axis of the outlet grill. In such an arrangement, the inclination of the grill elements may be adapted to the divergent shape of the airflow. In that case, an angle between a grill element and the central axis of the outlet grill is larger when the grill element is located near an outer circumference of the outlet grill than when the grill element is located near the central axis of the outlet grill.
Furthermore, in a preferred embodiment of the outlet grill according to the present invention, grill elements extending from a hub of the outlet grill to the outer circumference of the outlet grill comprise spiral-shaped main body surfaces. In such an arrangement, the shape of the main body surfaces of the grill elements may be adapted to the spiral shape of the air flow.
Since the shape and arrangement of the grill elements of the outlet grill of the present invention are better adapted to the airflow than the shape and arrangement of the grill elements of the outlet grill according to the state of the art, the resistance caused by an outlet grill according to the present invention is relatively low. As a result, the pressure drop across the outlet grill is relatively very small, and the noise level is relatively very low.
The present invention will now be explained in greater detail with reference to the Figures, in which similar parts are indicated by the same reference signs, and in which:
Figure 1 is a front view of a preferred embodiment of an outlet grill according to the present invention;
Figure 2 diagrammatically shows a cross-section A-A of the outlet grill according to Figure 1 as being arranged in an air-blowing device further comprising an axial fan;
Figure 3 shows a first option of the shape of a cross-section of a grill element;
Figure 4 shows a second option of the shape of a cross-section of a grill element;
Figure 5 shows a third option of the shape of a cross-section of a grill element; and Figure 6 shows a fourth option of the shape of a cross-section of a grill element.
Figure 1 shows a preferred embodiment of an outlet grill 1 according to the present invention. Figure 2 shows the outlet grill 1 as being arranged in an air-blowing device 2 further comprising an axial fan 3. The axial fan 3 is shown in a diagrammatical way, and will not be explained in more detail, as the axial fan 3 may be any suitable conventional axial fan.
During operation, the axial fan 3 rotates about a rotation axis 4 and generates an airflow, which is mainly directed towards the outlet grill 1. An important function of the outlet grill 1 is covering the axial fan 3 in such a way that, on the one hand, a user is not able to touch the axial fan 3 and, on the other hand, the generated airflow is allowed to pass the outlet grill 1. The shown outlet grill 1 is rotation-symmetrical about a central grill axis 5, wherein the outlet grill 1 is arranged in such a way with respect to the axial fan 3 that the central grill axis 5 coincides with the rotation axis 4 of the axial fan 3.
A direction in which the rotation axis 4 of the axial fan 3 and the central grill axis 5 extend will hereinafter be referred to as axial direction. According to usual definitions, both a radial direction and a tangential direction are directions in a plane perpendicular to the axial direction.
The outlet grill 1 comprises a number of grill elements 8, 9 extending from a rear side 6 of the outlet grill 1 to a front side 7 of the outlet grill 1. In the shown example, the outlet grill 1 comprises two types of grill elements 8, 9.
Grill elements 8 of a first type are shaped as segments of rings of which a central axis substantially coincides with the central grill axis 5. In a plane perpendicular to the axial direction, these grill elements 8 extend in a tangential direction, and will therefore hereinafter be referred to as tangential grill elements 8. In Figure 1, a rear side 15 of the tangential grill elements 8 is depicted by means of broken lines, whereas a front side 16 of the tangential grill elements 8 is depicted by means of solid lines. Grill elements 9 of a second type extend between a circular hub 10 of the outlet grill 1 and an outer circumference of the outlet grill 1. In a plane perpendicular to the axial direction, these grill elements 9 extend in a radial direction, and will therefore hereinafter be referred to as radial grill elements 9. In Figure 1, a rear side 14 of the radial grill elements 9 is depicted by means of broken lines, whereas a front side 13 of the radial grill elements 9 is depicted by means of fat continuous lines.
In the preferred embodiment as shown in Figures 1 and 2, the outlet grill 1 comprises three radial grill elements 9, wherein all spaces between the radial grill elements 9 have a length of arc of 120°. In said spaces, sets of four tangential grill elements 8 are provided, which extend between two radial grill elements 9. It will be understood that the number of tangential grill elements 8 and radial grill elements 9 is not essential. Furthermore, it will be understood that the tangential grill elements 8 and the radial grill elements 9 may be arranged according to any suitable pattern, which need not necessarily be regular.
The outlet grill 1 may comprise plastic, and may be manufactured by means of injection moulding. The circular hub 10 of the outlet grill 1 serves to cover a central portion of the axial fan 3 comprising a motor. As no airflow is generated at the position of the motor, the hub 10 of the outlet grill 1 may be totally closed, as is the case in the example shown in Figures 1 and 2.
The central portion of the axial fan 3 comprising the motor may be connected to a supporting outer frame by means of radial arms. If that is the case, the positions of the radial grill elements 9 of the outlet grill 1 preferably correspond to the positions of the radial arms, as there is no airflow at these positions.
According to an important aspect of the present invention, the shape of main body surfaces 11 of the tangential grill elements 8 as well as the shape of main body surfaces
12 of the radial grill elements 9 is adapted to the shape of the airflow generated by the axial fan 3. In Figure 2, this airflow is diagrammatically depicted by means of arrows AF. In general, the airflow generated by an axial fan 3 is divergent and spiral-shaped.
In an axis plane comprising the central grill axis 5, a number of tangential grill elements 8 are inclined with respect to the central grill axis 5, in order to be adapted to the divergent shape of the airflow. A grill element angle between a main body surface 11 of a tangential grill element 8 and the central grill axis 5 is different for tangential grill elements 8 being arranged at different radial distances with respect to the central grill axis 5. The relation between the grill element angle and the radial distance with respect to the central grill axis 5 is such that the grill element angle is larger for a tangential grill element 8 being arranged at a larger radial distance with respect to the central grill axis 5 than for a tangential grill element 8 being arranged at a smaller radial distance with respect to the central grill axis 5. In such an arrangement, the directions in which the main body surfaces 11 of the tangential grill elements 8 extend may be fully adapted to local directions of the airflow, such that the grill element angle a of a tangential grill element 8 corresponds to an angle between the rotation axis 4 of the axial fan 3 and the airflow at the location of the tangential grill element 8.
The main body surfaces 12 of the radial grill elements 9 are spiral-shaped so as to be adapted to the spiral shape of the airflow generated by the axial fan 3. In the shown example, an angle β between a straight front side 13 of the radial grill element 9 and a straight rear side 14 of the radial grill element 9 is approximately 10°. It will be understood that the angle β is related to the spiral shape of the airflow, and may have a value which is different from 10°.
If the grill elements 8, 9 are arranged as described in the foregoing, the influence of the outlet grill 1 on the generated airflow passing the outlet grill 1 is relatively very small. Even if the shapes of the main body surfaces 11, 12 of the grill elements 8, 9 are not fully adapted to the airflow, in other words, even if the main body surfaces 11, 12 extend in directions which do not fully correspond to local directions of the airflow, the airflow is not so much interrupted as on application of an outlet grill according to the state of the art. Therefore, on application of the outlet grill 1 according to the present invention, a lower noise level and a lower pressure drop across the outlet grill 1 is obtained.
The shape of the airflow relates to a number of factors, such as the rotational speed of the axial fan 3. Therefore, the design of the outlet grill 1 is preferably adapted to the shape of the airflow at an operating speed which is normally assumed during operation of the axial fan 3. If the axial fan 3 rotates at a different speed than this operating speed, the airflow
strikes against the grill elements 8, 9 of the outlet grill 1. Nevertheless, the airflow is less interrupted than in case of a known outlet grill being applied, as differences between directions in which the grill elements 8, 9 extend and local directions of the generated airflow are smaller. The advantageous effect of the design of the outlet grill 1 according to the present invention on the noise level of the generated airflow as well as on the pressure drop across the outlet grill 1 is already achieved in the case of a slight deviation from the design of the outlet grill according to the state of the art. It is therefore not essential that the shapes of both the main body surfaces 11 of the tangential grill elements 8 and the main body surfaces 12 of the radial grill elements 9 are adapted to the shape of the generated airflow; adaptation of the shape of only one type of main body surface 11, 12 already causes an improvement. It is not even necessary that the shapes of all main body surfaces 11 of the tangential grill elements 8 and/or all main body surfaces 12 of the radial grill elements 9 are adapted to the shape of the generated airflow. Furthermore, the main body surfaces 12 of the radial grill elements 9 do not need to be spiral shaped. A radial grill element 9 having a main body surface 12 which deviates from an axis plane comprising the central grill axis 5 is already better adapted to the generated airflow than a conventional grill element of which both main body surfaces extend in said plane.
The fact that the design of the outlet grill 1 according to the present invention is well-adapted to the shape of the generated airflow may be applied in different advantageous ways. In the first place, both the noise level and the pressure drop across the outlet grill 1 may be reduced, so that the air-blowing device 2 comprising the outlet grill 1 is quieter and has an enhanced capacity. In the second place, the axial fan 3 may rotate at a lower speed if the capacity may remain at a certain level. In that case, the noise level is not only reduced because of the adapted design of the outlet grill 1, but also because of the lower rotational speed of the axial fan 3. In the third place, the sizes of the axial fan 3 and the outlet grill 1 may be reduced if there is no need to reduce the noise level and/or to enhance the capacity of the air-blowing device 2. In that case, a more compact air-blowing device 2 is obtained. Figures 3 to 6 show different options of the shape of a cross-section of a tangential grill element 8. Similarly as in Figure 2, the generated airflow is diagrammatically depicted by means of an arrow AF in each Figure.
According to a first option as shown in Figure 3, the cross-section of the tangential grill element 8 has a rectangular shape. This shape corresponds to the shape of conventional grill elements.
According to a second option as shown in Figure 4, the cross-section of the tangential grill element 8 has a round rear side 15. An advantage of this option is that the airflow is able to pass the tangential grill element 8 in a relatively smooth way, as the airflow does not encounter any sharp edges at the rear side 15.
According to a third option as shown in Figure 5, the cross-section of the tangential grill element 8 has a round rear side 15 as well as a round front side 16. Due to this design of the tangential grill element 8, the airflow is able to pass the tangential grill element 8 without being impeded by any sharp edge, and the interruption of the airflow is reduced.
According to a fourth option as shown in Figure 6, the dimensions of the cross-section of the tangential grill element 8, which are substantially perpendicular to the airflow, are smaller at the rear side 15 of the tangential grill element 8 than at the front side 16 of the tangential grill element 8. An advantage of this option is that a larger portion of the tangential grill element 8 extends at a relatively small angle with respect to the airflow, whereby the resistance caused by the tangential grill element 8 is reduced.
A tangential grill element 8 having a cross-section according to the second, third or fourth option causes less interruption of the airflow than a tangential grill element 8 having a cross-section according to the first option. A round rear side 15 is advantageous in that it offers less resistance to the airflow than a straight side. A further reduction of the resistance is obtained in case the front side 16 is round as well. Less resistance of the tangential grill element 8 to the airflow involves a lower noise level and a smaller pressure drop. It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the present invention as defined in the attached claims.
An outlet grill 1 comprising both tangential grill elements 8 and radial grill elements 9 has been disclosed in the foregoing. Within the scope of the present invention, an embodiment comprising only radial grill elements 9 is also possible.
An embodiment of the outlet grill 1 which is also to be counted as one of the possibilities of the present invention comprises rotatably mounted grill elements, which are automatically put in an optimal position under the influence of an airflow.
The cross-section of the tangential grill elements 8 maybe shaped according to a different option than the options shown in Figures 3 to 6. For example, the cross-section may be shaped like a rectangle having round edges, wherein main portions of the rear side 15 as well as the front side 16 are straight and extend substantially perpendicular to the airflow. Furthermore, cross-sections of grill elements other than the tangential grill elements 8 may be shaped according to the shown options and other possible options.
The shown outlet grill 1 is rotation-symmetrical about the central grill axis 5. However, the outlet grill 1 need not be rotation-symmetrical. If the outlet grill 1 is not rotation symmetrical, the central grill axis 5 is defined by a virtual axis of the outlet grill 1 which is intended to coincide with the rotation-axis 4 of the axial fan 3.
An outlet grill 1 for use in an air-blowing device 2 having an axial fan 3 has been described in the foregoing. The outlet grill 1 comprises grill elements 8, 9 having main body surfaces 11, 12 which are shaped in such a way that, in case the outlet grill 1 is indeed combined with the axial fan 3, the main body surfaces 11, 12 extend substantially parallel to an airflow generated by the axial fan 3.
The outlet grill 1 comprises tangential grill elements 8 being shaped as segments of rings, a central axis of which substantially coincides with a central grill axis 5. In an axis plane comprising the central grill axis 5, the main body surfaces 11, 12 of a number of tangential grill elements 8 are inclined with respect to the central grill axis 5. A grill element angle a between the central grill axis 5 and the direction in which a tangential grill element 8 extends in the axis plane is related to an angle between a rotation axis 4 of the axial fan 3 and the generated airflow at the location of the tangential grill element 8. In this way, the directions in which the tangential grill elements 8 extend are aligned with local directions of the airflow.