This study is concerned with the improvement in efficiency of axial flow fans that are being used in numerous fields including outdoor units of air conditioners. The tip leakage flow occurring between a blade tip and shroud is one of the major losses in the axial flow fan. A well-known method used to control such tip leakage flow is locating winglet on the suction side of blade tips. Only a few articles have studied the impact of tip clearance on the flow structure of tip leakage flow of axial flow fans with winglet. In this study, the flow structure occurring on the blade tip due to the location of a winglet was analyzed. We confirm the existence of an optimal tip clearance which results in the maximum efficiency for an axial flow fan with a shroud height measuring 30% of the axial chord length.

Effect of tip clearance, winglets, and shroud height on the tip leakage in axial flow fans.

Novel heat pipe radiator for vertical CPU cooling and its experimental study

Bladeless fan is a novel fan type that has no observable impeller, usually used for domestic applications. Numerical investigation of a Bladeless fan via Finite Volume Method was carried out in this study. The fan was placed in center of a 4×2×2m room and 473 Eppler airfoil profile was used as cross section of the fan. Performance and noise level of the fan by solving continuity and momentum equations as well as noise equations of Broadband Noise Source (BNS) and Ffowcs Williams and Hawkings (FW-H) in both steady state and unsteady conditions were studied. Flow increase ratio of the fan was captured. Furthermore, BNS method could find outlet slit of the air as the main source of the noise generation. In order to validation of aeroacousticcode results, a simulation of noise for NACA 0012 airfoil via FW-H method was compared to experimental results and good agreement was obtained.

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Numerical Aerodynamic Evaluation and Noise Investigation of a Bladeless Fan

The study has focused on outdoor unit noise reduction by fan geometry modification with the refined numerical and experimental approaches. The outlet louver, electric motor and its support are included to refine the flow and acoustic model and a hybrid method incorporating CFD and CAA is used to predict the noise behavior. The fan performance curve is well-predicted; the moderate acoustic power is obtained on the outlet louver, motor support and motor exhibiting a significant contribution to overall noise behavior. The aeroacoustic test is conducted in an anechoic chamber and the obtained results are compared with the semi-anechoic chamber ones, and the unremarkable differences are produced, which indicate the ground floor being of some influence. Both modified fan geometries are effective to reduce the noise but the flanging outer-edge blade is more effective. The noise directivities of three geometry fans are investigated both numerically and experimentally and the produced asymmetric characteristics are analyzed.

Prediction and measurement of axial flow fan aerodynamic and aeroacoustic performance in a split-type air-conditioner outdoor unit

To improve the aerodynamic performance of an up-flow outdoor unit in a split-type air conditioner, experimental and numerical investigations on the propeller fan system of the outdoor unit are performed. Based on the prototype analysis, the propeller fan has a complex vortical flow field near the rotor tip. The vortex structures cause blockage effect on the through flow and have influence on the aerodynamic performance of the outdoor unit. The bell-mouth configuration is redesigned to control the vortex structures. It is shown that the redesigned bell-mouth can weaken the tip vortex and reduce the blockage effect. The redesigned bell-mouth is fabricated and installed on the outdoor unit with 2-blade fan to perform experimental validation. The measured results demonstrate that the aerodynamic efficiency of the outdoor unit is improved by 1.2% with use of the redesigned bell-mouth. The 3-blade fan solution is also attempted to provide more work capacity to enhance the flow rate.

Aerodynamic performance improvement of up-flow outdoor unit of air conditioner by redesigning the bell-mouth profile

In variable-frequency Air Conditioner (AC), sizes of frequency controlling electronic module and its supplemental heat sink are much restrained and they are also tightly packed. Heat removal in such a limited space is difficult, and effective and compact heat sinks are required. The study has focused on heat sink thermal performance with different geometries and configurations. To allow for interaction of heat sink and fan, both numerical and experimental investigations are conducted in a real AC outdoor unit environment. An increase in heat sink base area significantly improves its thermal performance; fin height and pitch influence convective surface and also sweeping stream behavior and a good compromise is needed to enhance convective heat transfer. A proper tuning of heat sink configuration is effective to improve convective stream and subsequently enhance thermal performance. Heat sink geometry and configuration produces insignificant influence on fan aerodynamic and aeroacoustic performance, and AC system performance.

Experimental and numerical study of electronic module-cooling heat sinks used in a variable frequency air-conditioner outdoor unit

To improve aerodynamic performance and reduce noise for a split air conditioner outdoor unit fan, a hybrid method is developed, which combines the Computational Fluid Dynamics (CFD) flow simulation with Computational Aero Acoustics (CAA) noise analysis, where Large Eddy Simulation (LES) model and Ffowcs Williams-Hawkings (FW-H) acoustic analogy model are solved respectively for the unsteady flow characteristics and far field noise solutions. Experimental tests are conducted respectively for fan aerodynamic performance and acoustic behavior, with the aerodynamic performance test rig and semi-anechoic room. Numerical results demonstrates that the main dipole sound sources are located mainly on the blade trailing edge and tip surface, and shroud and casing inner surface, such a distribution is caused by fluctuations in instantaneous pressure associated with rotor-stator interaction. The casing dipole sources contribute largely to the total noise of the fan, and are the main causes for fan noise. It is demonstrated both numerically and experimentally that modifications of impeller blade geometry are effective to reduce the fan noise. Two redesign schemes, the concaved-trailing edge and flanging outer-edge blades, are used, but the latter is more effective in reducing the fan noise as well as shaft power simultaneously. The predicted SPL agrees well with the measured results at the fundamental frequency of the highest intensity, and the hybrid method used in the present study is justified.Copyright © 2011 by ASME

Xifeng Zhao

Papers

Prediction and measurement of axial flow fan aerodynamic and aeroacoustic performance in a split-type air-conditioner outdoor unit

Experimental and numerical study of electronic module-cooling heat sinks used in a variable frequency air-conditioner outdoor unit

Numerical and Experimental Investigation of Flow Behaviour and Aerodynamic Noise in Axial Flow Fan of Air-Conditioner