The Effects of Diameter and Rotational Speed on the Aerodynamic Performance of Low Profile Miniature Radial Flow Fans

2007 ◽  
Author(s):  
R. Grimes ◽  
P. Walsh ◽  
E. Walsh ◽  
V. Egan
Keyword(s):  
Reynolds Number ◽  
Power Consumption ◽  
Flow Rate ◽  
Radial Flow ◽  
Pressure Rise ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Low Profile ◽  
And Performance ◽  
High Reynolds

Space constraints in many emerging electronic systems mean that there is a growing demand for heat sinks which are low in profile. As a result, small, low profile fans are necessary. In many instances Radial flow fans are best suited. An understanding of the design and performance of these fans is therefore necessary. For radial flow fans little work has been done to quantify the deviation of aerodynamic performance from that predicted by conventional fan laws. This paper aims to address this situation, by performing measurements of pressure rise, flow rate and power consumption for 3.5mm high radial flow fan rotors ranging in diameter from 20 to 35mm over a range of speeds. Measurements presented show variations of pressure rise and flow rate with Reynolds number to be largely in accordance with trends predicted by high Reynolds number theory, with the exception of flow rates at the lower range of Reynolds numbers which fell below the predicted values. Variations in power consumption show a similar trend to those of flow rate, with power consumption obeying the fan laws for the higher Reynolds numbers investigated, but showing a large increase at the lower Reynolds numbers.

The Effects of Reynolds Number on the Aerodynamic Performance of Geometrically Similar Fans

2008 ◽  
Author(s):  
K. Hanly ◽  
R. Grimes ◽  
P. Walsh
Keyword(s):  
Reynolds Number ◽  
Electronic Device ◽  
Flow Characteristics ◽  
Pressure Rise ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Simultaneous Increase ◽  
Maximum Pressure ◽  
Low Profile ◽  
High Reynolds

The cooling of portable electronic devices has become paramount in the last number of years due to the simultaneous increase in power consumption and reduction in package size. This has lead to an increase in the amount of heat that needs to be dissipated by these devices. Passive cooling techniques will no longer provide an adequate solution and therefore active cooling solutions need to be implemented. The use of miniature radial fans in conjunction with heatsinks is a possible solution. These types of fans are especially suited as they can be deployed in a low profile format. However, little is known about the aerodynamic effects of reducing the fan scale and therefore Reynolds number to the extent necessary for use in portable electronic device cooling. This paper looks to quantify deviation of aerodynamic performance with Reynolds number from that predicted by the fan laws. Before tests were carried out experimental facilities were calibrated. Four radial fans with diameters of 80, 40, 18.3 and 10mm were then tested at a number of different rotational speeds with measurements of pressure rise and flow rates recorded for each of these speeds. The measurements presented show the need for a homogonous experimental setup with the exact conditions replicated each time a test is carried out. Results also show that there is good correlation between the experimental results for pressure rise and flow rate at high Reynolds numbers in accordance with trends from high Reynolds number theory. However at the lower Reynolds numbers a fundamental change in flow phenomena emerges which alters the maximum pressure and flow characteristics.

Airfoil Section Characteristics at a Low Reynolds Number

1997 ◽  
Vol 119 (1) ◽  
pp. 129-135 ◽  
Author(s):  
Shigeru Sunada ◽  
Akitoshi Sakaguchi ◽  
Keiji Kawachi
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Performance ◽  
Flight Performance ◽  
High Reynolds ◽  
Shape Characteristics ◽  
Sharp Leading Edge

The aerodynamic characteristics of airfoils operating at Re = 4 × 103 were examined, varying the parameters related to the airfoil shape such as thickness, camber, and roughness. Airfoils with good aerodynamic performance at this Re have the following shape characteristics: (1) they are thinner than airfoils for higher Re numbers, (2) they have a sharp leading edge, and (3) they have a camber of about five percent with its maximum camber at about mid-chord. The characteristics of airfoils are strongly affected by leading edge vortices. The measured two-dimensional airfoil characteristics indicate that the planform, which greatly affects the flight performance of the three-dimensional wing at high Reynolds numbers, has little effect on the flight performance at this Reynolds number.

On the low-Reynolds-number flow in a helical pipe

1981 ◽  
Vol 108 ◽  
pp. 185-194 ◽  
Author(s):  
C. Y. Wang
Keyword(s):  
Reynolds Number ◽  
Flow Rate ◽  
Reynolds Numbers ◽  
Order Unity ◽  
Low Reynolds Number Flow ◽  
Reynolds Number Flow ◽  
Helical Pipe ◽  
Number Flow ◽  
High Reynolds ◽  
Curvature And Torsion

A non-orthogonal helical co-ordinate system is introduced to study the effect of curvature and torsion on the flow in a helical pipe. It is found that both curvature and torsion induce non-negligible effects when the Reynolds number is less than about 40. When the Reynolds number is of order unity, torsion induces a secondary flow consisting of one single recirculating cell while curvature causes an increased flow rate. These effects are quite different from the two recirculating cells and decreased flow rate at high Reynolds numbers.

Scaling of Flow Characteristics and Power Consumption With Profile Height for Miniature Centrifugal Fans

2007 ◽  
Author(s):  
P. A. Walsh ◽  
V. Egan ◽  
R. Grimes ◽  
E. Walsh
Keyword(s):  
Aspect Ratio ◽  
Power Consumption ◽  
Flow Rate ◽  
Scaling Laws ◽  
Flow Characteristics ◽  
Pressure Rise ◽  
Maximum Flow ◽  
Aspect Ratios ◽  
Low Profile ◽  
Centrifugal Fans

This paper addresses issues that relate to downscaling the height of centrifugal fans for application in low profile technologies, such as the cooling of portable power electronics. The parameters studied throughout the paper include flow rate, pressure rise and power consumption characteristics. The former two of these are measured using a fan characterization rig and the latter by directly measuring the power supplied to the fan. These are studied for fans ranging in diameter from 15 to 30mm and with profile heights ranging from 0.3mm to 15mm. It is found that all of the phenomena encountered are best described in terms of fan aspect ratio. Overall, the results show that the conventional scaling laws cannot be accurately applied when the blade profile alone is being scaled. Indeed the only parameter that was observed to be accurately predicted by the scaling laws was the pressure rise attainable but was only accurate for fan aspect ratios greater than 0.17. Below this, the measured pressure rise characteristics fell logarithmically toward zero. The results also showed that there is no advantage to using fans with aspect ratio greater than 0.3. This was because the maximum flow rate was achieved at this aspect ratio and decreased slightly as it was further increased. Overall, the scaling phenomena described throughout this paper are invaluable to designer of efficient low profile cooling solutions that are to incorporate such fans.

scholarly journals Aerodynamics of smooth and rough square-section prisms at incidence in very high Reynolds-number cross-flows

2021 ◽  
Vol 62 (3) ◽  
Author(s):  
Nils Paul van Hinsberg
Keyword(s):  
Reynolds Number ◽  
Cross Sections ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Surface Boundary ◽  
Experimental Proof ◽  
Surface Boundary Layer ◽  
Pitch Moment ◽  
The Mean ◽  
High Reynolds

Abstract The aerodynamics of smooth and slightly rough prisms with square cross-sections and sharp edges is investigated through wind tunnel experiments. Mean and fluctuating forces, the mean pitch moment, Strouhal numbers, the mean surface pressures and the mean wake profiles in the mid-span cross-section of the prism are recorded simultaneously for Reynolds numbers between 1$$\times$$ × 10$$^{5}$$ 5 $$\le$$ ≤ Re$$_{D}$$ D $$\le$$ ≤ 1$$\times$$ × 10$$^{7}$$ 7 . For the smooth prism with $$k_s$$ k s /D = 4$$\times$$ × 10$$^{-5}$$ - 5 , tests were performed at three angles of incidence, i.e. $$\alpha$$ α = 0$$^{\circ }$$ ∘ , −22.5$$^{\circ }$$ ∘ and −45$$^{\circ }$$ ∘ , whereas only both “symmetric” angles were studied for its slightly rough counterpart with $$k_s$$ k s /D = 1$$\times$$ × 10$$^{-3}$$ - 3 . First-time experimental proof is given that, within the accuracy of the data, no significant variation with Reynolds number occurs for all mean and fluctuating aerodynamic coefficients of smooth square prisms up to Reynolds numbers as high as $$\mathcal {O}$$ O (10$$^{7}$$ 7 ). This Reynolds-number independent behaviour applies to the Strouhal number and the wake profile as well. In contrast to what is known from square prisms with rounded edges and circular cylinders, an increase in surface roughness height by a factor 25 on the current sharp-edged square prism does not lead to any notable effects on the surface boundary layer and thus on the prism’s aerodynamics. For both prisms, distinct changes in the aerostatics between the various angles of incidence are seen to take place though. Graphic abstract

Experimental Investigation of Effect of Tip Coolant Ejection on Internal Flow Characteristics Within a Realistic Blade Coolant Channel

2013 ◽  
Author(s):  
Jian Pu ◽  
Zhaoqing Ke ◽  
Jianhua Wang ◽  
Lei Wang ◽  
Hongde You
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Turbine Blade ◽  
Flow Rate ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Flow Ratio ◽  
Lp Turbine ◽  
Mass Flow Ratio

This paper presents an experimental investigation on the characteristics of the fluid flow within an entire coolant channel of a low pressure (LP) turbine blade. The serpentine channel, which keeps realistic blade geometry, consists of three passes connected by a 180° sharp bend and a semi-round bend, 2 tip exits and 25 trailing edge exits. The mean velocity fields within several typical cross sections were captured using a particle image velocimetry (PIV) system. Pressure and flow rate at each exit were determined through the measurements of local static pressure and volume flow rate. To optimize the design of LP turbine blade coolant channels, the effect of tip ejection ratio (ER) from 180° sharp bend on the flow characteristics in the coolant channel were experimentally investigated at a series of inlet Reynolds numbers from 25,000 to 50,000. A complex flow pattern, which is different from the previous investigations conducted by a simplified square or rectangular two-pass U-channel, is exhibited from the PIV results. This experimental investigation indicated that: a) in the main flow direction, the regions of separation bubble and flow impingement increase in size with a decrease of the ER; b) the shape, intensity and position of the secondary vortices are changed by the ER; c) the mass flow ratio of each exit to inlet is not sensitive to the inlet Reynolds number; d) the increase of the ER reduces the mass flow ratio through each trailing edge exit to the extent of about 23–28% of the ER = 0 reference under the condition that the tip exit located at 180° bend is full open; e) the pressure drop through the entire coolant channel decreases with an increase in the ER and inlet Reynolds number, and a reduction about 35–40% of the non-dimensional pressure drop is observed at different inlet Reynolds numbers, under the condition that the tip exit located at 180° bend is full open.

Numerical Simulations of Resonant Heat Transfer Augmentation at Low Reynolds Numbers

2001 ◽  
Author(s):  
Miles Greiner ◽  
Paul F. Fischer ◽  
Henry Tufo
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Natural Frequency ◽  
Flow Rate ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Spectral Element ◽  
Pumping Power ◽  
Number Systems ◽  
Low Reynolds

Abstract The effect of flow rate modulation on low Reynolds number heat transfer enhancement in a transversely grooved passage was numerically simulated using a two-dimensional spectral element technique. Simulations were performed at subcritical Reynolds numbers of Rem = 133 and 267, with 20% and 40% flow rate oscillations. The net pumping power required to modulate the flow was minimized as the forcing frequency approached the predicted natural frequency. However, mixing and heat transfer levels both increased as the natural frequency was approached. Oscillatory forcing in a grooved passage requires two orders of magnitude less pumping power than flat passage systems for the same heat transfer level. Hydrodynamic resonance appears to be an effective method of increasing heat transfer in low Reynolds number systems where pumping power is at a premium, such as micro heat transfer applications.

A Computational Study on Airfoils at a Low Reynolds Number

2000 ◽  
Author(s):  
Ajit Pal Singh ◽  
S. H. Winoto ◽  
D. A. Shah ◽  
K. G. Lim ◽  
Robert E. K. Goh
Keyword(s):  
Reynolds Number ◽  
Computational Analysis ◽  
Computational Study ◽  
Low Reynolds Number ◽  
Micro Air Vehicles ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Low Reynolds Numbers ◽  
Study Results ◽  
Low Reynolds

Abstract Performance characteristics of some low Reynolds number airfoils for the use in micro air vehicles (MAVs) are computationally studied using XFOIL at a Reynolds number of 80,000. XFOIL, which is based on linear-vorticity stream function panel method coupled with a viscous integral formulation, is used for the analysis. In the first part of the study, results obtained from the XFOIL have been compared with available experimental data at low Reynolds numbers. XFOIL is then used to study relative aerodynamic performance of nine different airfoils. The computational analysis has shown that the S1223 airfoil has a relatively better performance than other airfoils considered for the analysis.

The Effect of Reynolds Number on the Aerodynamic Performance of Micro Radial Flow Fans

2005 ◽  
Author(s):  
K. Hanly ◽  
R. Grimes ◽  
E. Walsh ◽  
B. Rodgers ◽  
J. Punch
Keyword(s):  
Reynolds Number ◽  
Heat Dissipation ◽  
Radial Flow ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Performance ◽  
Fundamental Change ◽  
Geometric Similarity ◽  
Flow Phenomena ◽  
Conventional Cooling ◽  
High Degree

Elevated heat dissipation and simultaneous reductions in package sizes are well documented for a range of electronics systems. The problem is heightened in portable systems where the space available for the implementation of an active cooling methodology is limited and conventional cooling products are too large. Using micro scale radial flow fans is a potential solution. However, little is known about the aerodynamic effects of reducing the fan scale and therefore Reynolds number to the extent required for typical portable electronic applications. This paper investigates this issue, by quantifying the reduction in aerodynamic performance which accompanies the reductions in scale. To do this, geometrically similar radial flow fans were fabricated with diameters ranging from 80 to 10mm. Measurements of the rotors’ geometries are presented, showing a high degree of geometric similarity between the fans. The aerodynamic performance of each of the fans was measured. Non-dimensional performance of each of the larger fans were almost identical, while the performance plot of the smallest fan differed significantly from the others. The paper tentatively concludes that a fundamental change in flow phenomena has emerged in the smallest scale fan which has altered its aerodynamic characteristics.

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