MXPA98005057A - Flow stabilizer for transver fan - Google Patents

Abstract

The present invention relates to an improved transverse fan and the heat exchanger assembly defining a flow path, serially including the heat exchanger and the fan, the fan having an impeller impeller and one fan side. defined suction in the intermediate flow path to the heat exchange and the fan so the impeller blades advance into the air flow inside the impeller by means of the flow path as the blades advance into the suction side, the heat exchanger having a downstream face characterized in that the improvement comprises: a flow stabilizing blade extending from the downstream side of the impeller in such suction side region;

Description

FLOW STABILIZER FOR TRANSVERSE FAN DESCRIPTION OF THE INVENTION Low frequency flow oscillations can arise in air conditioning systems that utilize a transverse fan located downstream of a plate fin heat exchanger. These oscillations are associated with the vortex flow, contrary to the fan rotation, between the downstream side of the heat exchanger and the fan inlet. Such conditions cause angles of incidence of excessive flow over a local sector of the impeller inlet, producing delayed flow, or standing within that sector. The localized nature of the stopped flow makes it unstable and oscillatory, often fs, on the scale of 30 to 80 percent of the fan's rotational frequency, n. The interaction of the blade with the unstable oscillatory strike results in an excess noise with a frequency corresponding to the product of the oscillation frequency of stop fs, the number of blades in the impeller Z and the rotational frequency of the fan n. The product of Z-n is the pass frequency of the BPF blade, and the excess noise is, therefore, the sub-BPF noise frequently on the scale of 30 to 80 percent of GMP.

The present invention relates generally to cross flow or cross flow fans. More particularly, the invention relates to a transverse fan having a stabilizing blade that prevents the creation of an oscillating air flow stop and the sub-blade pitch frequency noise. The present invention employs a flow stabilizer blade that prevents or reduces oscillating blade stop and the resulting noise in a cross fan and heat exchanger assembly that is subject to such a stop phenomenon. The blade is approximately the same width as the face downstream of the heat exchanger and projects from that face. The vane extends to the fan impeller with a small gap between its distal end and the impeller. The blade may be vertical in the lateral cross section although, in a preferred embodiment the cross section is different from the vertical to achieve structural rigidity, and thus prevent vibration, without excessive blade thickness. The description of • *? »The preferred embodiments below, describes the preferred sizing, positioning and orientation of the pallet. It is an object of this invention to prevent the oscillating blade from stopping.

It is another object of this invention to reduce or eliminate the low frequency flow oscillations in the transverse fan coil arrangements. Those objects, and others, will become apparent hereinafter and are achieved by the present invention. Basically, an individual pallet is located on the downstream side of a heat exchanger oriented to impart a rotational flow, in. the region upstream of the narrowest space between the fan and the heat exchanger, and to thereby reduce the localized vortex flow, which would otherwise tend to cause the oscillating blade to stop and the resulting noise. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph of the sound pressure level in decibels against the normalized frequency, f / BPF, where f is the sound frequency in cycles per second and BPF is the frequency of the pitch in cycles per second of a unit of the PREVIOUS TECHNIQUE and one employing the pallet of the present invention; Figure 2 shows the spectrum of sound power measured in A, one third of an octave in a unit of the PREVIOUS TECHNIQUE and for one that uses a palette; Figure 3 is a schematic diagram of a transverse fan of the PREVIOUS TECHNIQUE operating with an unobstructed input; Figure 4 is a schematic diagram of a transverse fan of the PREVIOUS TECHNIQUE operating in adverse aerodynamic conditions caused by its placement with respect to its associated heat exchanger; Figure 5 is a schematic diagram of the air flow vectors entering the cross-fan blade operating under the same conditions as illustrated in Figure 4; Figure 6 is a schematic diagram of a transverse fan operating under the same conditions illustrated in Figure 4 but with the vane of the present invention installed; Figures 7-10 are schematic diagrams of the transverse fan in four different installations and illustrate some dimensional relationships useful in the description of the present invention; and Figure 11 is a view of a transverse fan and the vane of the present invention. Figure 1 shows the sound pressure level measured against the normalized frequency in the presence and absence of the palette of the present invention. AND? While the data is generally tracked with each other, the palette of the present invention substantially reduces the broad sub-BPF peak as compared to a corresponding unit that lacks the palette of the present invention. Figure 2 shows the 1/3 octave sound power spectrum measured at A corresponding to Figure 1. The measurement at A provides a correction to represent the scale of the human ear. The presence of the blade of the present invention significantly reduces low frequency noise. In Figure 3, the cross flow fan or cross fan of the PREVIOUS TECHNIQUE 30 is operating in a clean entry environment. The flow lines show uniform traffic from the suction inlet 32 through the impeller 31 to the discharge outlet 33. The flow line in a closed cycle represents a well-known vortex region within the ventilator. The ventilator of PREVIOUS TECHNIQUE 230, illustrated in Figure 4, is operating in an aerodynamic environment that leads to the production of sub-BPF noise. The fan 230 differs from the fan 30 in the addition of the heat exchanger 220. The heat exchanger 220 is illustrated, formed by two sections 220-1 and 220-2, although it may be made of a single section or more than two sections. The impeller 231 is very recessed from a portion of the downstream face 221 of the heat exchanger 220. In addition, the air that the impeller 231 removes from the top reaches the downstream face 221 and tends to rotate through a large angle to enter and pass through the impeller, as shown by the flow lines, within the discharge outlets 233. In the region S of the suction inlet 232, the periphery or tips of the blades of the impellers 231 are advancing within the flow of the inlet air against the direction of rotation starting at the closest point of proximity between the driver 231 and the face 221 as determined by the line Li which is a line extending from the AR axis of the fan 231 perpendicular to the face 221 of the heat exchanger 220. The region S extends in the direction of rotation from Li to L2 with L2 being 130% of the external diameter Do of the impeller from the AR axis. Figure 5 shows a blade 235 of the impeller 231 having a tip 236 and rotating about an axis AR at a rotational speed of n revolutions per second to produce the vector ratio illustrated between the peripheral tip speed of blade U, the absolute air velocity V and the resulting relative air velocity W in the region S. If the direction of the velocity V is sufficiently close to the direction of the velocity U, the resulting air velocity W can lead to an angle of excessive flow incidence, i, q? e results in shutdown or separation of the air flow on the blade 235. Referring now to Figure 6, the number 100 generally designates a fan coil unit having an envelope 110 having a entrance lattice 111 and outlet ventilation grilles 112. Heat exchanger 120 is located within the envelope 110 in a confrontational relationship with the entrance lattice 111 and includes two sections, 120-1 and 120-2, and having a downstream face 121. The impeller 131 is located in the envelope 110 so as to rotate about its axis AR and coact together with the wall of vortices 134 and the rear wall 115. to divide the interior of the envelope 110 into the suction inlet 132 and the discharge outlet 133 with the fluid communication being through the impeller 131. The vane 151 of the present invention extends outwardly from the downstream side 121 of heat exchanger 120 to the impeller 131. The vane 151 is located in the region of the suction side of the impeller where the blades of the impeller 131 are advancing within the incoming air flow (region S in Figure 4). The vane 151 does not touch the impeller 131 but there is a space g between the vane 151 and the impeller 131. In a preferred embodiment, the space g is between 0.08 and 0.15 times the outer diameter C of the impulse 131. As illustrated, the vane 151, in a lateral cross-section, is curved or bent.The transverse shape is for structural rigidity and for airflow considerations as a straight cross section that may require additional material. to provide sufficient rigidity to avoid oscillation in the air flow that enters in. If the vane 151 is curved, or a combination of straight lines, the vane should be placed to direct the air flow entering in the same direction as the vane. direction of rotation of the impeller 131. Operation of the fan coil unit 100, rotation of the impeller 131 extracts the air within the suction inlet 132 by means of the lattice 111 and the heat exchanger 120. Since the air exits from the heat exchanger 120 on the complete downstream side 121, the air must rotate by varying the amounts as it passes from different portions of the downstream side 121 and enters the impeller 131. The air passes from the impeller 131 into the discharge outlet 133 and by means of ventilation grilles 112 within the space to be conditioned. It will be noted that the impeller 131 is separated from the portions of the heat exchanger 120 by several distances. As described with respect to Figure 4, starting with the point of closest proximity between the impeller 131 and the face 121 which is along the line Li, an element S is defined in the direction of rotation which leads to the oscillatory stop and the production of noise. The presence of the vane 151, according to the teachings of the present invention, provides a reduced opportunity for oscillating stoppage to occur. This is because the vane 151 reduces the angle of incidence of the flow entering the vanes in the S region by imparting a localized prior rotation on the flow, i.e. the rotation in the same direction as the rotation of the fan. The size and placement of the pallet 151 is important to achieve the objectives of reducing noise due to oscillatory arrest. Figures 7-10 serve to illustrate the principles involved. Figures 7-10 show four different arrangements of heat exchanger and transverse fan assembly. In Figure 7, the heat exchanger 520 has a flat downstream side 521. The impeller 531 is located in a separate relation to the face 521. In Figures 8 and 9, the heat exchangers 620 and 720 are "flexed" , according to the heat exchanger 120 of Figure 6, with the relative location of the "bending" and the placement of the impellers 631 and 731, respectively, are different in the two Figures. In Figure 10, the heat exchanger 820 is also flexed and formed of two sections 820-1 and 820-2. However, section 820-2 is curved. "Flexed" heat exchangers are commonly found in applications where the required facial area of the heat exchanger can not be obtained with a vertical side heat exchanger within the envelope dimensions in which the heat exchanger is installed . The internal units of the duct free partial air conditioning systems, for example, commonly have "flexed" heat exchangers. (One skilled in the art understands that a duct-free, partial-stream air conditioning system is a vapor compression air conditioning system that does not have a central internal heat exchanger that channels to supply the conditioned air to the air conditioning system. the rooms or spaces that are going to be conditioned but has one or more internal heat exchangers, each located in a single room or space that will be conditioned). The principles that control the sizing and positioning of the vane 551, however, are the same regardless of the shape of the heat exchanger and the placement of the fan impeller with respect to the heat exchanger. In each of Figures 6 to 11, the line Li passes through the axis of the rotator AR and is perpendicular to the downstream face 121, 521, 621 or 721 and to the nearest point at 821. The line L? passes through the rotary drive shaft AR and a point on the downstream face 121, 520, 620, 721 or 821 that is at the point of maximum free force or at a distance of 1.3 times the external diameter of the impeller D0 from the shaft of rotation AR. The angle a (Figures 4.8 and 11) between the lines L] and L? defines the region S in which oscillating unemployment tends to occur. Returning to Figure 11, the line Li and the axis of rotation AR define a plane that intersects the face 521 on the line L3. The line L2 and the axis of rotation AR define a plane that intersects the faces 20 on the line L. Without being shown in the Figures, although easily visualized, there is the fact that the impeller 531 has a sweep surface that can be defined with the surface of a cylinder generated by the rotation of a line that is parallel to the axis of rotation AR and that passes also through a point that is radially outward above the impellers 531. For the best effectiveness in reducing the oscillating stop noise, the vane 551 must be positioned and dimensioned so that it is contained within the envelope defined by the face downstream 521, the plane defined by the axis of rotation AR and the line Li, the plane defined by the axis of rotation AR and line L2 and the sweep surface of the impeller. There is a gap of 0.08 to 0.15 times the external diameter of the impeller between the impeller 531 and the vane 551 described above. One skilled in the art can appreciate that a pallet constructed and installed in accordance with the teaching of the present invention could be a source of blade pitch frequency noise. This can be avoided or minimized by placing the pallet so that different points of the same impeller blade do not pass the pallet at the same time. The vane 151 in Figure 11 is placed that way. Figure 11 also shows a blade 551 positioned with respect to the impeller 531 to minimize the blade pitch frequency. The vane of the present invention has been tested on split, conduit-free fan coil units that exhibit the sub-BPF noise problems, and which show to reduce the sub-BPF noise by five to eight decibels. Figures 1 and 2 illustrate the results from each case. Although preferred embodiments of the present invention have been illustrated and described, other changes will be made by those skilled in the art. It is therefore intended that the scope of the present invention be limited only to the scope of the appended claims.

Claims (5)

1. CLAIMS 1. An improved transverse fan and heat exchanger assembly that define a flow path, including serially the heat exchanger and the fan, the fan that has a impeller with impeller blade and a defined suction side in the intermediate flow path to the heat exchanger and the fan whereby the impeller blades advance into the air flow within the impeller via the flow path as the impeller blades advance into the suction side, the heat exchanger having a downstream face characterized in that the improvement comprises: a flow stabilizing blade extending from the downstream side towards the impeller in such a suction side region.
2. 2. The transverse fan and the heat exchanger assembly according to claim 1, characterized in that the impeller has an external diameter (Do) and the vane extends from 8 to 15 percent of the outer diameter of the impeller.
3. 3. The transverse fan and the heat exchanger assembly according to claim 1, characterized in that the impeller has an external diameter (Do) and a rotation axis (AR) and the assembly has a first location on the downstream side, the first location that is the intersection of the face and a foreground, the foreground that is defined by the axis of rotation and a line that passes through the axis of rotation and is perpendicular to the face, and a second location on the face downstream, the second location being the intersection of such face and a second plane, the second plane being defined by the axis of rotation and a line passing through the axis of rotation and also passing through a point on the face that is at a distance of approximately 130 percent of the external diameter from the axis of rotation to provide a free space of approximately 80% of the external diameter, and the pallet is extu from the downstream side along a third location on the face between the first location and the second location.
4. 4. The transverse fan and the heat exchanger assembly according to claim 3, characterized in that the impeller has a sweeping surface, the sweeping surface which is the surface of a cylinder generated by the rotation of a line that is parallel to the axis of rotation and which also passes through a radially outermost point on the impeller, and the vane is contained within a shell defined by the face Ib laughing role b.ijo, the foreground, the second plane and the swept surface.
5. 5. The transverse fan and the heat exchanger assembly according to claim 1, characterized in that the vane is configured so that different points along the length of an impeller blade pass the vane on different occasions.