Advances in Fan Modeling: Using Multiple Reference Frame (MRF) Approach on Blowers

2011 ◽  
Author(s):  
Gokul Shankaran ◽  
M. Baris Dogruoz
Keyword(s):  
Reference Frame ◽  
Axial Flow ◽  
Flow Region ◽  
Pressure Head ◽  
Thermal Design ◽  
Axial Fan ◽  
Acceptable Error ◽  
Error Margin ◽  
Lumped Models ◽  
Multiple Reference

Forced convection air-cooled electronic systems utilize fans to sustain air flow through the enclosure. These fans are typically axial flow fans, radial impellers, and centrifugal blowers. When computing flow fields in electronic enclosures, axial fans have traditionally been abstracted as lumped fan models which may or may not be able to capture the necessary details. Under certain conditions, such lumped models may also capture some flow characteristics in the case of impellers and centrifugal blowers. These lumped models comprise a significantly simplified fan geometry, i.e. usually a planar (2-D) rectangular or circular surface with/without an inner (hub) concentric no-flow region for an axial fan or a rectangular prism/cylinder with a planar inlet for blowers/impellers, and a “pressure head-flow rate” (P-Q) curve, which may be supplied by the fan vendor or experimentally derived by the thermal designer. Irrespective of the source, the P-Q curve is obtained from laboratory experiments that conform to the test codes published by societies such as ASME and AMCA. Convenience and accuracy of lumped fan models are dependent on the specific application, cooling method and also the acceptable error margin. The acceptable error margin of the thermal design has shrunk significantly in the last decade. This has caused an interest in more accurate and robust fan modeling techniques such as Multiple Reference Frame (MRF) model which has already been commonly and successfully used in many different industries for a while. In this paper, an attempt was made to provide a validation of the MRF fan modeling applied to different types of fans. The computational fluid dynamics (CFD) model of an AMCA standard wind tunnel was used for each of the fans investigated. The P-Q curve obtained from the MRF model is benchmarked against the corresponding experimentally derived P-Q curve. Benefits and limitations of the MRF model are also discussed.

Advances in Fan Modeling: Issues and Effects on Thermal Design of Electronics

2012 ◽  
Author(s):  
M. Baris Dogruoz ◽  
Gokul Shankaran
Keyword(s):  
Axial Flow ◽  
Pressure Head ◽  
Thermal Design ◽  
Electronic Systems ◽  
Acceptable Error ◽  
Modeling Techniques ◽  
Lumped Models ◽  
Axial Fans ◽  
Flow Through ◽  
Multiple Reference

Forced convection air-cooled electronic systems consist of fans to provide fluid flow through the enclosure. Typically axial flow fans, radial impellers, and centrifugal blowers fall into this category. In numerical computations of flow fields in electronic enclosures, axial fans have most commonly been abstracted as planar (2-D) rectangular or circular surfaces. In some cases, these abstract or lumped models may be used to mimic impellers and centrifugal blowers as well. All of these models rely on an experimentally derived “pressure head-flow rate” (P-Q) curve (also called “fan curve”). The experiments to obtain the fan curve should conform to the test codes published by ASME and/or AMCA. Convenience and accuracy of abstract fan models are dependent on the specific application/cooling method and the acceptable error margin. The latter for the thermal design of electronics has recently diminished considerably which led to the need of using more accurate and robust fan modeling techniques such as Multiple Reference Frame (MRF) model. The authors validated this method for different types of fans against relevant experimental data previously [1,2]. As a continuation of this earlier effort, an attempt is made to examine the thermal field computed by various fan modeling techniques including MRF for air-cooled enclosures in the present work. The results show that the temperature values obtained from lumped fan model and the MRF technique differ considerably.

PIV Measurements of the Effects of Geometric Scale on Electronics Cooling Axial Fan Flow

2007 ◽  
Author(s):  
Ronan Grimes ◽  
David Quin ◽  
Edmond Walsh ◽  
Jeff Punch
Keyword(s):  
Velocity Distribution ◽  
Axial Flow ◽  
Electronics Cooling ◽  
Thermal Design ◽  
Small Scale ◽  
Axial Fan ◽  
Flow Angle ◽  
Piv Measurements ◽  
Cooling Fan ◽  
Macro Scale

The emergence of highly functional portable electronic systems in recent times means that passive dissipation of heat in these devices may not be an option in the near future. Micro fan technology is currently being developed to address this emerging need. Past investigations by the current authors indicate that the reduction of scale of conventional electronics cooling fan design to the mini scale does not excessively impair the bulk pressure flow performance of the fan. However, the detailed velocity distribution at the outlet of mini scale axial flow fans is unknown, and so effective thermal design in systems which use mini scale fans may be difficult, as the designer does not know the path taken by the flow emerging from the fan. To address this issue, this paper presents PIV measurements performed at the outlet of a series of geometrically similar axial flow fans, whose diameters range from 120 to 6mm, and whose design is based on that of a commercially available macro scale electronics cooling fan. The measurements show that as fan scale is reduced, there is a significant change in the fan outlet velocity distribution, and a large increase in the outlet radial flow angle. As a result, a designer using a small scale axial flow fan must be aware that the region downstream of the fan, where one would normally expect high velocity flow, will in fact be uncooled. Therefore, components should be mounted radially downstream of the fan, where highest air velocities are shown to exist.

Large-Eddy and Unsteady Reynolds-Averaged Navier-Stokes Simulations of an Axial Flow Pump for Cardiac Support

2017 ◽  
Author(s):  
Benjamin Torner ◽  
Sebastian Hallier ◽  
Matthias Witte ◽  
Frank-Hendrik Wurm
Keyword(s):  
Flow Field ◽  
Axial Flow ◽  
Pressure Head ◽  
Damage Parameter ◽  
Ventricular Assist Devices ◽  
Navier Stokes ◽  
Mean Velocity ◽  
Blood Damage ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

The use of implantable pumps for cardiac support (Ventricular Assist Devices) has proven to be a promising option for the treatment of advanced heart failure. Avoiding blood damage and achieving high efficiencies represent two main challenges in the optimization process. To improve VADs, it is important to understand the turbulent flow field in depth in order to minimize losses and blood damage. The application of the Large-eddy simulation (LES) is an appropriate approach to simulate the flow field because turbulent structures and flow patterns, which are connected to losses and blood damage, are directly resolved. The focus of this paper is the comparison between an LES and an Unsteady Reynolds-Averaged Navier-Stokes simulation (URANS) because the latter one is the most frequently used approach for simulating the flow in VADs. Integral quantities like pressure head and efficiency are in a good agreement between both methods. Additionally, the mean velocity fields show similar tendencies. However, LES and URANS show different results for the turbulent kinetic energy. Deviations of several tens of percent can be also observed for a blood damage parameter, which depend on velocity gradients. Possible reasons for the deviations will be investigated in future works.

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