DA-2393 — Development of an Anechoic Termination Design for an In-Duct Fan Sound Test Facility

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Air handling is a principal function of nearly all packaged air-conditioning and heating products. In these units, centrifugal and propeller fans are installed in conjunction with suitable drives, mounting brackets, etc., to deliver conditioned air to an occupied space, and to develop sufficient pressure to overcome losses in the unit and in the distribution system to which it is connected.

In these products, the space available for the air handling system components is limited, the fans are nearly always applied in close proximity to other system components, cabinet walls, etc., and the airflow entering and leaving the fan is generally far from ideal. The performance of fans under such conditions is of considerable interest to equipment manufacturers.

Traditionally. manufacturers of fans used in packaged air-conditioning products have standardized their testing so that selections might be made from different vendors on a consistent basis, and in order to overcome the difficulty in anticipating the wide variety of ways in which their products were used. Accordingly, data are typically reported for tests in which the fans are operated with a totally unrestricted inlet, and with ideal inlet and discharge airflow conditions. OEM engineers are thus left with the responsibility for selecting these components on the basis of the “ideal” test data. At the present state of the art, little definitive data are available to assist the design engineer in arriving at the best balance of economy and performance; consequently the only recourse is to use experience in selecting candidate components, followed by developmental testing to evolve and qualify a suitable system. There is, except on a comparative basis with prior art, little opportunity to assess the solution in terms of an “optimum” solution since limited engineering and testing time is generally available. This time-consuming and frequently trial and error method of product development may not, in the final analysis, yield the best cost-performance combination for the product.

Optimizing fan applications on the basis of cost and performance requires the analysis of fan performance under applied conditions, and this means valid aerodynamic and acoustic lerformance data. A 10,000 cfm aerodynamic and acoustic fan test facility was projected to conduct such applied fan performance research in the Research Division (RDC) of Carrier Corporation. To be efficient for this research the test facility shou1d permit simultaneous measurement of the aerodynamic an acoustic performance of the fans for various product application configurations.

The peculiarities of sound propagation in ducts requires an anechoic section at the termination of the sound test duct for accurate low-frequency acoustical measurement. The function of this anechoic section, for the RDC fan test facility, is to connect the sound test duct to a 180 deg full radius elbow leading to the airflow metering section of the facility, and to reduce the reflections of the incident sound wave propagating down the duct from the sound source. Satisfactory solution of this end reflection measurement problem is a major step toward achievement of an accurate in-duct sound test facility.

Product Details

Published:

1976

Number of Pages:

12

File Size:

1 file , 1.5 MB

Product Code(s):

D-DA-2393

Note:

This product is unavailable in Russia, Belarus