This invention relates to fan blades within evaporator blowers, and to acoustic performance of evaporators in vapor cycle cooling systems.
Centrifugal fans are inherently noisy machines, due to the design and airflow interaction of the fan wheel and blower outlet. Air is drawn in at an inlet by a motor-driven rotating impeller. The impeller includes a number of passages arranged in a spiral. Air accelerates through these passages and emerges at an outlet. A cut-off area between the impeller housing and the outlet causes a sudden change of radial and tangential airflow at the outlet. The change in airflow, which is proportional to the blower speed, causes a pressure pulse that results in noise generation.
Conventional efforts to reduce noise generated by centrifugal fans include insulating the fan housing and ducts, both upstream and downstream. Alternately, sound reducing equipment may be installed at the fan inlet or at the fan discharge. For example, U.S. Pat. No. 3,191,851 to Wood describes a two-part system including a square sheet of metal that extends towards and slightly over a small portion of the fan, plus a perforated fairing to decrease size of the fan outlet. U.S. Pat. No. 5,340,275 to Eisinger discloses a rotating cutoff device that is attached within a fan casing. Resonating chambers in the cutoff device are meant to absorb sound. U.S. Pat. No. 6,463,230 to Wargo describes a noise reduction device for smoothing airflow transition at a pinch point of a fan. Wargo focuses on reducing air stagnation at the point where the fan scroll is tangent to the scroll case. The noise reduction device has an airfoil cross section shape, and extends linearly over the fan opening. U.S. Pat. No. 6,575,696 to Lyons et al. combines a sound attenuating cavity, formed as part of the blower housing, with an angled cut off for disrupting pressure fluctuation near the intersection of the exhaust section and the fan scroll.
In another example, U.S. Pat. No. 5,536,140 to Wagner et al. discloses a furnace blower with a flat plate that is inserted parallel to a blower exhaust port. Notches cut in a specified pattern vary the quantity of airflow and reduce pulsing tones. U.S. Pat. No. 5,584,653 to Frank et al. discloses a device for reducing noise in a side channel fan, which appears to include notches or spikes cut into fan outlets and pointing into the intake/discharge, to reduce noise.
U.S. Pat. No. 3,034,702 to Larsson et al. is not concerned with noise suppression, but rather is directed towards a fan having great axial length and dual air inlets, one at each end. Larsson relies upon a series of baffles to provide uniform flow throughout the entire cross-section of the fan discharge opening.
U.S. Pat. No. 6,935,835 to Della Mora discloses various anti-noise stabilizers for centrifugal fans. In particular, Della Mora seeks to homogenize airflow and reduce vortices, in order to reduce noise and improve efficiency of the centrifugal fan. The stabilizers extend for the width of the discharge opening and include dual appendages that face the inlet cone of the fan, one on either side of the discharge opening. U.S. Pat. No. 6,039,532 to McConnell also discloses a device at a fan discharge opening. In particular, McConnell places a baffle in the outlet of a squirrel cage fan. The baffle either tapers continuously from one side of the fan outlet to the other side of the outlet, or is a rectangular insert with a plurality of holes that increase in size from one end to the other end of the baffle.
U.S. Pat. No. 3,687,360 also provides a noise suppressing baffle in a discharge duct. Prew's triangular baffle is inserted within the duct, proximate a chamber housing rotating blades (i.e., a centrifuge chamber). The baffle changes the effective shape of the opening between the duct and the chamber to a trapezoid., and further provides a gradual increase in cross-sectional area of the duct. This change in cross-section decreases velocity of material being discharged into the duct, in order to reduce tendency of the material to build up on walls of the duct.
In an embodiment, an acoustic baffle for reducing noise of a centrifugal fan includes a base for mounting with a fan outlet. A projection extends from the length of the base at a back side of the base, and curves away from a top surface of the base. The projection continuously tapers from the base to an apex that aligns with a center line of the base. When the acoustic baffle is installed in the outlet, the projection extends over the fan wheel and tapers from left and right sides of the outlet to a fan tangency point at a midpoint of the outlet.
In an embodiment, an acoustic baffle for reducing noise of a centrifugal fan includes a base for mounting with a fan outlet. A projection extends from the length of the base at a back side of the base and curves away from a top surface of the base. The projection includes opposing left and right sides that are parallel to or aligned with left and right sides of the base, and an internal cutout forming a trough. A center point of the trough aligns with a center line of the base. Ends of the left and right sides opposite the base form left and right apices of the internal cutout. Opposing inner sides of the projection defining the cutout continually taper from the trough to the apices. When the acoustic baffle is installed in the outlet, the projection extends over the fan wheel and the left and right sides of the projection continually widen from left and right fan tangency points to the trough.
In an embodiment, an acoustic baffle for reducing noise of a centrifugal fan includes a base for mounting with a fan outlet. A projection extends from the length of the base at a back side of the base and curves away from a top surface of the base. The projection continuously tapers along at least one side, from an area proximate the base to an apex. The apex aligns with a fan tangency point, and the apex or a trough of the projection aligns with a midpoint of the outlet, when the acoustic baffle is installed in the outlet.
At least one sidewall 114 provides an attachment point for bolting or otherwise fastening baffle 100 in the fan outlet. Base 102 may include a terminal lip 116 for extending over a bottom edge or end of the fan outlet, to facilitate positioning of baffle 100 with the outlet. Although not shown, base 102, sidewall 114 and/or lip 116 may form openings for hardware to secure baffle 100 in place. An optional joiner 117 may be included to reinforce or stiffen the junction of sidewall 114 with base 102 and spike extension 104.
A fan case extension 118 may be included on a bottom surface 119 of base 102, for filling a gap between the fan impeller and the fan scroll cut off/blower case. Fan case extension 118 may include a longitudinal ridge 120 for fitting with the fan scroll cut off, to facilitate proper positioning of baffle 100 within the blower outlet. Fan case extension 118 tapers from bottom surface 119 to an end 121, for example forming a roughly triangular shape, although shape of fan case extension 118 may vary depending on geometry of a gap to be filled.
In one aspect, a back side 122 of fan case extension 118 continues the curvature of back side 106 of spike extension 104. In another aspect, back side 122 essentially forms an obtuse angle with back side 106. When baffle 100 is secured with a fan outlet, fan case extension 118 fills in gaps that could otherwise remain between baffle 100 and the fan scroll cut off, thus enhancing acoustic performance of baffle 100. A front side 123 of fan case extension 118 is curved or otherwise shaped for fitting with a blower case proximate the cut off, as shown in
It will be appreciated that geometry of back side 106 and back side 122, as well as length and width of baffle 100 and dimensions of fin 108 may vary depending upon dimensions of the fan to be outfitted with baffle 100. It will also be appreciated that geometry of fan case extension 118 may vary depending upon dimensions of the fan to be outfitted with baffle 100. For example, an angle between back side 106 and back side 122 may be determined based upon dimensions of an existing fan case, such that apex 112 is a minimal distance from the fan scroll without interfering with the fan scroll during service or use. Base 102 may also include a cutout 124, dimensions and placement of which may also vary to accommodate preexisting features of the fan outlet.
Left and right sides 128 and 130 of spike extension 104 may taper from base 102 to apex 112 in a linear manner, as shown in
Fins/sidewalls 208 and 209 taper in height from base 202 to opposing left and right apices 212 and 213 of vee extension 204. Sidewalls 208 and 209 may be formed with vee extension 204, for example where baffle 200/250 is molded from plastic or other flowable material), or sidewalls 208 and 209 may be formed as separate parts and attached with vee extension 204 and/or base 202. The junction of sidewall 208 or 209 with base 202 and a respective sidewall 214 of base 202 may be reinforced or stiffened with an additional joiner 217. In one aspect, sidewall 214 and sidewall 208 or 209 form a continuous sidewall, for example where baffle 200/250 is formed as a unitary piece. Joiner(s) 217 may be added if stiffening or reinforcement is desired. Like spike extension 104 and fm 108 (
Sidewall(s) 214 extend from base 202 and provide an attachment point for bolting or otherwise fastening baffle 200/250 in the fan outlet. Base 202 may also include a terminal lip 216 for extending over a bottom edge or end of the fan outlet, to facilitate positioning of baffle 200 with the outlet. Although not shown, base 202, sidewall 214, one or both of sidewalls 208 and 209 and/or lip 216 may form openings for hardware to secure baffle 200/250 in place.
A fan case extension 218 extends from a bottom surface 219 of base 202, for filling a gap between the fan impeller and the fan scroll cut off/blower case, when baffle 200/250 is installed in a centrifugal fan. Fan case extension 218 may include a longitudinal ridge 220 for fitting with the fan scroll cut off, to facilitate positioning of baffle 100 within the blower outlet. Fan case extension 218 tapers from bottom surface 219 to an end 221, for example forming a roughly triangular shape, although shape of fan case extension 218 may vary depending on geometry of a gap to be filled.
In one aspect, a back side 222 of fan case extension 218 continues curvature of back side 206 of vee extension 204. In another aspect, back side 222 essentially forms an obtuse angle with back side 206. When baffle 200/250 is secured with a fan outlet, fan case extension 218 fills a gap that could otherwise remain between baffle 200/250 and the fan scroll cut off, thus enhancing acoustic performance. A front side 223 of fan case extension 218 is curved or otherwise shaped for fitting with a blower case proximate the cut off (see, e.g., baffle 150 in housing 314,
It will be appreciated that geometry of back side 206 and back side 222, as well as length and width of baffle 200/250 and dimensions of sidewalls 208 and 209 may vary depending upon dimensions of the fan to be outfitted with baffle 200/250. It will also be appreciated that geometry of fan case extension 218 may vary depending upon dimensions of the fan to be outfitted with baffle 200/250. For example, an angle between back side 206 and back side 222 may be determined based upon dimensions of an existing fan case, such that left and right apices 212, 213 are a minimal distance from the fan scroll without interfering with the fan scroll during service or use. Base 202 may also include a cutout 224, dimensions and placement of which may also vary to accommodate preexisting features of the fan outlet.
Vee extension 204 of baffle 200 (
Baffles 100, 150, 200 and 250 may be made of any material or materials that are compatible with the fan to be outfitted. In one aspect, baffles 100-250 are made of plastic, such as a thermoformed plastic. Fan case extensions 118, 218 may be integral to baffles 100, 150 and 200, 250, respectively, or fan case extensions 118, 218 may be formed of the same or another material and attached with their respective acoustic baffles.
Base 102 of baffle 150 is sized to span a width w0 of the outlet, for example fitting over or with a cut off of fan 300 (shown in
In
Fan blade passage tone (objectionable fan noise) is dependent upon the quantity of fan blades in the fan impeller, and the speed of the fan. The fan blade passage frequency, which generates the objectionable noise, can be calculated as follows:
Once the fan blade passage frequency is known, it may be isolated during acoustic surveys of the fan, and overall effectiveness of an acoustic baffle may be measured.
As shown, at 1500 Hz, a non-baffled fan produced a fan blade passage tone of about 100 dB. In contrast, a fan outfitted with baffle 200/250 produced about 89 dB of noise. A fan outfitted with baffle 100 produced about 83 dB fan blade passage tone, and a fan outfitted with baffle 150 produced about 81 dB.
Experimental results suggest that overall, “spike” style acoustic baffles such as baffles 100 and 150 have better noise reduction in the 1,200-1,700 Hz fan blade passage frequency, while “vee” style baffles 200 and 250 have better noise reduction in the 2,100-2,600 Hz fan blade passage frequency.
Inclusion of baffle 100, 150, 200 or 250 in the blower outlet of a centrifugal fan (i.e., outlet 302 of fan 300) results in minimal reduction of flow into the distribution duct (e.g., a duct attached at outlet 302). Impact on blower flow rate was calculated by measuring the static pressure at multiple flow rates for a baseline configuration, and with the acoustic baffles installed.
Certain changes may be made in the above systems and methods without departing from the scope hereof. For example, features and use shown or described with respect to one of baffles 100-250 may be incorporated into or pertain to another of baffles 100-250. Thus, it is intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are to cover generic and specific features described herein, and all statements of the scope of the invention which, as a matter of language, might be said to fall there between.
This application is a divisional of U.S. patent application Ser. No. 13/436,093, filed 30 Mar. 2012.
Number | Date | Country | |
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Parent | 13436093 | Mar 2012 | US |
Child | 14181330 | US |