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Performance characterization of a miniature spiral-channel viscous pump
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Sensors and Actuators A 142 (2008) 256–262
Performance characterization of a miniature spiral-channel viscous pump A.T. Al-Halhouli a,∗ , S. Demming a , M. Feldmann a , S. B¨uttgenbach a , M.I. Kilani b , A. Al-Salaymeh c a
Institute for Microtechnology, Technical University of Braunschweig, Alte Salzdahlumer Strasse 203, 38124 Braunschweig, Germany b Mechatronics Engineering Department, University of Jordan, Amman 11942, Jordan c Mechanical Engineering Department, University of Jordan, Amman 11942, Jordan Received 29 September 2006; received in revised form 25 January 2007; accepted 24 February 2007 Available online 7 March 2007
Abstract This work describes the development and testing of a miniature spiral-channel viscous pump. The pump consists of a 12 mm diameter spiral disk on which a spiral-channel is machined with heights of 1 or 2 mm, a width of 1 mm and a spiral length (angular span) of 2.5π or 3.5π. The spiral-channel forms a fluid passage through which fluid is dragged due to the rotation of the spiral-channel under a stationary plate. Fluid inlet and outlet ports are located at the ends of the spiral-channel. Experimental flow rates and pressure rise data are obtained for rotational speeds from 1000 to 5000 rpm for pumping glycerin, where a maximum flow rate and pressure difference of 3.05 ml/min and 353 mbar is achieved at channel design parameters: w/h = 1.0, and θ = 3π. The flow rate of the pump was found to increase nearly linearly with rotational speed and decrease linearly with the pressure head imposed on the pump. Advantages of spiral pump include simplicity in fabrication, ability to pump particle-laden fluids, and can operate with no valves. © 2007 Elsevier B.V. All rights reserved. Keywords: Spiral pump; Microfluidics; Viscous flow
1. Introduction Micropumps are vital miniature devices required in micro fluidic systems, microelectronics cooling, and chemical analysis systems [1]. Micropumps have been implemented into the market and are used in ink jet printers and fuel injection applications [2,3]. A variety of micropumps are available to meet these applications including non-mechanical micropumps such as the electro-hydrodynamic pumps (EHD), magnet-hydro-dynamic and electroosmotic pumps. These devices have no moving parts and are thus more reliable; however, they are generally limited by low flow rate and pressure rise capabilities, the need for high supply voltage, and the physical characteristics of the working fluids. Mechanical micropumps like centrifugal pumps, diaphragm pumps, rotary pumps, phase change pumps, and several other types of pumps [2,4] have a wide variety of
∗
Corresponding author. Tel.: +49 531 3919741; fax: +49 531 3919751. E-mail address: [email protected] (A.T. Al-Halhouli).
0924-4247/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2007.02.035
possible working fluids and applications [5]. Different viscous micropumps or pumps for pumping viscous fluids have been investigated recently [5–9]. Among these is the spiral-channel micropump illustrated in Fig. 1. The pump works by rotating a disk with a spiral shaped channel below a flat plate covering the channel. The inlet and outlet of the pump are located at the spiral-channel ends, and the pump works due to the drag force generated by the moving action of the rotating channel with respect to the stationary disk. A macroscale prototype of the spiral-channel concept was recently reported [6]. The present experiments were performed on a miniaturized model with a 12 mm spiral disk diameter, which represent 80% miniaturization of the macro scaled prototype tested previously [6]. This allowed achieving a better understanding of the expected performance of a microscale spiral pump, and explodes the effect of viscous dissipation and cross-channel leakage, which will cause deviation between the analytical model, and the experimental performance of the pump. In this work the miniaturized spiral-channel viscous pump was investigated and tested at different boundary conditions and geometrical parameters,
A.T. Al-Halhouli et al. / Sensors and Actuators A 142 (2008) 256–262
Fig. 1. The spiral pump concept.
where maximum flow rate and pressure difference of 3 ml/min and 350 mbar were achieved. 2. Spiral pump configuration and operation The spiral-channel viscous pump is comprised of a stationary flat cover and a spinning spiral-channel disk that forms the pump chamber, with a fluid inlet and outlet ports located at either end of the spiral-channel. Fig. 2 shows a scheme of the spiral-channel pump components. The stationary flat cover is brought to close proximity with the upper walls of the spiral-channel creating a small gap with the objective of minimizing leakage from the pump chamber. The height of the pump chamber is the distance between the disk surface and the bottom of the spiral-channel, which constitutes the flow passage height of the pump. The flow passage heights used for testing are 1 and 2 mm, respectively.
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In a typical viscous micropump, a rotating element on the form of a spinning disk, or a spinning cylinder rotates continuously tangent to the flow field. As the element spins, it drags fluid in a direction tangent to the element’s motion creating a Couette-type flow in the pump chamber between the rotating element and the stationary surfaces of the chamber. If an external pressure gradient is imposed between the inlet and outlet in the fluid chamber, a Poiseuille-type flow takes place, which opposes the motion induced by the element’s rotation. If the opposing external pressure is large enough, some of the fluid between the spinning element and the fixed surfaces of the fluid chamber will re-circulate in the opposite direction of the disk rotation. The Couette and Poiseuille flow patterns appear in the spiral pump geometry and also appear in the single disk and double disk geometry [5,9]. In fact both of these pump concepts produce pumping by generating a flow against an imposed external pressure by utilizing the viscous drag effect resulting from the rotation of a disk tangent to the flow field. The difference in flow performance between these two concepts arises in the maximum pressure head and the maximum flow rate that can be achieved from a pump disk of a given radius. The spiral pump geometry is capable of resisting a larger pressure head than that obtained from the single-disk and double disk pump with the same dimension. This is due to the fact that the spiral pump’s channel has a longer effective length than that of the single disk and double disk pump. The upper limit on the effective channel length in the single disk pump is limited is 2πr, where r is the mean radius of the channel. In a spiral-channel pump, the effective channel length is rm θ, and θ is 2πn where n is the number of turns in the spiral coil. On the other hand, the channel width in the single disk and double disk pumps if the pressure head is low, the single disk and double disk pumps could deliver a larger flow rates than that obtained by a spiral pump because the channel width in these pump geometries could be made larger. 3. Pump component fabrication
Fig. 2. A photograph of the spiral pump components.
The spiral pump assembly consists of three main components: the rotating spiral disk with its shaft, the stationary flat cover, and the pump housing as illustrated in Fig. 2. The spiral disk surface must be flat so that it is aligned with the bottom surface of the stationary flat cover. Any misalignment of the spiral disk will result in leakage due to increased gap height above the channel. The disk is constructed from using precision machining techniques from an aluminum stock with its shaft. The spiral groove forming the spiral-channel was obtained using a CNC milling machine, with an inner radius of the spiral-channel of 2.5 mm and the outer radius of 4.5 mm. The spiral disk was set in the pump housing, which is made using Teflon material. An O-ring groove, bolts borings and a cylindrical protrusion with the dimensions of the spiral disk, 12 mm diameter and 5 and 6 mm heights were machined at its upper face. While another cylindrical protrusion for the bearing with 8 mm diameter and 3 mm height were machined at the back face of the housing, where the inner diameter of the used bearing is 4 mm and equal to the diameter of the spiral disk shaft. The housing was then covered by a visible flat cover, which was
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A.T. Al-Halhouli et al. / Sensors and Actuators A 142 (2008) 256–262 Table 1 Spiral pump design parameters Parameters
Initial radius (m) Gap height (m) Channel width, w (m) Channel height, h (m) Angular span, θ
Fig. 3. A photograph of the spiral-channel pump experimental setup during operation.
manufactured using Plexiglas, and allows the visualization of the flow and ensures that there are no air bubbles during testing. A hole in the centre of the cover, which represents the inlet to the pump is created with 1.35 mm diameter. 4. Pump setup and testing As illustrated in Fig. 1, the spiral pump idea has the advantage of utilizing the effect of high viscous forces of the fluid at small scales, where the fluid presented in the spiral-channel can be dragged along the channel axis by rotating the spiralchannel against a stationary flat cover (moving situation), where a net tangential viscous stress on the boundaries is built up and produces a positive pressure gradient in the direction of flow. A photograph for the spiral pump test setup is shown in Fig. 3. Fluid enters at the center of the spiral disk and leaves tangentially to the spiral-channel from the outlet port. The pressure difference between the inlet and the outlet is measured using a SCX30 DN precision compensated pressure sensor, which was calibrated with the pressure of a water column. The spiral disk shaft is coupled with a Faulhaber 3257G 012CR DC micromotor, and guided in a Teflon sealed bearing, which also forms a seal to reduce the leakage. The rotational speed is determined by attaching a tachometer to the coupling between the motor and the disk shaft. Because of its high viscous property, glycerin with a viscosity of 1412 mPa s, and density of 1261 kg/m3 was used as the working fluid. Several spiral pump designs with different design parameters have been investigated as summarized in Table 1. The range of speed investigated in this study is between 1000 and 5000 rpm. The inlet and outlet tubes are 240 mm long and have an inner diameter of 4.5 mm. The inlet tube is connected to the fluid reservoir, which is large enough to avoid level changes during operation, and the outlet tube is connected to the collection reservoir, which is set above digital balance used to read the mass of the pumped fluid during fixed intervals of time. The tube diameter is larger than that of the inlet and outlet ports, because an expansion of the fluid in the tubes will occur, which yields
Moving situation
Flat plate
Design (A)
Design (B)
Design (C)
Design (D)
2500 100 1000 2000 3π
2500 100 1000 1000 3π
3500 100 1000 1000 2π
– 400 – – –
reduction in the flow velocity and the major losses through the test loop. The assembly of the experimental setup begins by fixing the bearing to the back face of the housing, and setting the spiral disk with it is shaft into the housing. The external motor is fixed to the base, and the coupling is fixed to the motor shaft. The pump is then coupled with the motor, fixed to the base, and the inlet and outlet tubes are connected. Before turning on the power supply and adjusting the tachometer, the air is bled from the test loop, and then the motor is activated to the desired speed. The readings are taken after ensuring steady state flow conditions, where the pumped fluid is collected for fixed interval of times and the flow rate is estimated. While, for the maximum pressure difference values, the digital pressure sensor is mounted such as the pressure difference values at steady state conditions across the pump are measured directly after closing a ball valve completely at the far end of the outlet tube, and recording the maximum reachable value. Fluid leakage is noticed from the pump while reaching the maximum pressure values. 5. Results and discussion The performance of the spiral pump was investigated experimentally by plotting the flow rates against the disk rotational speed. Results showed that the flow rates increase nearly linearly with rotational speed, which supports the influence of the viscous forces in small scales induced in the spiral-channel and the validity of the linear lubrication model for this problem [10]. The microscale flow field of an incompressible Newtonian fluid in the thin narrow gap of the spiral pump geometry is a classical example of flow situation governed by the simplified version of the Navier–Stokes equations known as the lubrication model [11]. The assumptions commonly made in the application of the lubrication model are (i) the fluid film is so thin that derivatives of velocity across the film thickness are far more important than any other velocity derivative, (ii) inertia effects are negligible compared to viscosity, and (iii) channel curvature introduces second-order negligible effects. Under the foregoing assumptions, the equation expressing mass conservation is: ∂u ∂v ∂w + + =0 ∂x ∂y ∂z
(1)
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259
Fig. 4. Flow rates vs. rotational speeds at different aspect ratios.
while the equations of motion reduce to: ∂p ∂ ∂u ∂p ∂ ∂v = μ , = μ , ∂x ∂z ∂z ∂y ∂z ∂z
Fig. 6. Maximum pressure rises vs. rotational speeds for different design parameters.
∂p =0 ∂z
(2)
where u, v, w are the velocity components, x, y, z are the Cartesian coordinates, p the pressure, and μ is the fluid dynamic viscosity. The effect of channel width (w) to channel height (h), or in other words channel aspect ratio (w/ h) on the flow rate is presented in Fig. 4. The flow rates were found to be larger for the higher aspect ratio condition at the same rotational speed. Maximum flow rates of 3.05 and 1.92 ml/min are achieved for rotational speed of 4285 rpm at channel aspect ratios of 1 and 0.5, respectively. Other tests were performed for different spiral lengths (i.e. angular spans = θ) at constant aspect ratio, and under the same conditions. Results are presented in Fig. 5 and showed that the effect of spiral length on the flow rates is noticeable at low rotational speeds (ω < 1400 rpm). Increasing the rotational speed
Fig. 5. Flow rates vs. rotational speeds at different angular spans.
reduce this effect due to the small difference between the channel lengths. The maximum pressure rises for the spiral pump and the flat plate pump are also investigated at different rotational speeds ranging from 1000 to 4500 rpm as shown in Fig. 6. A maximum pressure rise of 353 mbar is achieved for (w/ h = 1.0, θ = 3π) at a rotational speed of 4138 rpm. The maximum pressure rise increases nearly linearly with increasing the rotational speed for all designs. For the purpose of comparison between the effect of viscous forces and centrifugal forces in small scales, a flat plate pump was tested. The idea of this pump is to rotate a flat disk without any protrusion: spiral or C-shaped, as shown in Fig. 7 below the stationary flat cover instead of the spiral-channel disk, which produces centrifugal forces on the fluid and a pumping effect through the ends is obtained. The pump chamber volume is determined from the disk diameter and the gap between the disks, which is 400 m. This pump was designed to have the same pumping volume as in the case of moving and stationary flat disks in design (A). The flow rate results as shown in Fig. 8 and the pressure difference values as in Fig. 6 showed that the spiral-channel pump produces higher flow rate and pressure values for the same operating conditions than that for the flat plate pump. This supports the effect of surface area to volume ratio, in parallel to the dominant effect of viscous stresses over centrifugal forces in microscales. Further, the flow rates were plotted against the pressure difference values. A sample of the results for spiral pump at w/ h = 0.5, θ = 2 is shown in Fig. 9. Results showed that the flow rates decrease linearly with increasing pressure difference. This is consistent with the lubrication flow model and supports also the high influence of viscous stresses in low scales. The miniaturized model described in this work highlights the effect of viscous dissipation and cross-channel leakage on the pump performance. These two effects will cause the flow
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Fig. 7. A photograph of the spiral-channel and flat plate disks.
Fig. 8. Flow rates vs. rotational speeds using spiral disk and flat plate as a rotating disks.
Fig. 9. Flow rates vs. pressure difference at w/ h = 0.5, θ = 2π.
rate to drop significantly from the analytical predictions. As seen in Fig. 10, which shows the experimental, and analytical flow rates at spiral-channel aspect ratio w/ h = 3.2. A close agreement between the experimental and the theoretical results is observed for low values of Re Eu, where reduced Reynolds ¯ 2 /μl), and Euler number number can be defined as Re = (ρUh
is Eu = (Δp/ρU¯ 2 ). ρ is the fluid density, l the spiral-channel length and U¯ is the average channel velocity. At high values of Re Eu, a large deviation between the experimental and the theoretical results is observed. This deviation can be attributed to the effect of viscous dissipation and the effect of cross flow in the gap below the spiral wall in the scaled up
Table 2 Maximum flow rates and pressure rises of different micropumps Pump type
Fluid
Channel width (mm)
Disk diameter (mm)
ω (rpm)
Qmax (ml/min)
Pmax (kPa)
Spiral-channel Micro gear [7] Single disk [5] Double disk [5] Single disk [9]
Glycerin Oil Water Water Water
1 – 1.19 1.19 1.19
12 1.192 2.38 2.38 2.38
4285 – 5000 5000 5000
3.05 1 1 2.1 4.75
35.3 120 0.643 1.19 31.1
A.T. Al-Halhouli et al. / Sensors and Actuators A 142 (2008) 256–262
Fig. 10. Experimental and analytical flow rate vs. pressure head at channel aspect ratio w/ h = 3.2 [10].
model, which is increased with increasing pressure difference. In the experiments presented in this work, Re Eu is in between 6 and 11 and a large deviation between the experimental data, and the analytical predictions are expected. Further, a list of maximum flow rates (Qmax ) and pressure rises (Pmax ) for different viscous micropumps and micro gear pump used for pumping viscous fluids is shown in Table 2. Tests were carried out using different geometrical parameters, working fluids and operating speeds. High flow rates and pressure rises were obtained by the spiral-channel miniaturized pump. 6. Conclusions This paper has presented an experimental investigation of the effect of the design parameters: channel aspect ratio and length on the flow performance of spiral-channel viscous pump. The advantages of this pump are its simplicity in fabrication and the ability to pump particle-laden fluids. The experimental results showed that the flow rates are changed nearly linearly either with the rotational speed or pressure difference, which is consistent with the lubrication model and support the dominant influence of viscous forces in small scales. Acknowledgements The authors wish to acknowledge the support received from the Technical University of Braunschweig and the Deanship for Scientific Research in the University of Jordan. The scholarship for the first author by the German Academic Exchange Service (DAAD) is gratefully appreciated. References [1] B. Van Der Schot, J. Jeanneret, A. Van Den Berg, N. De Rooij, Microsystems for flow injection analysis, Anal. Meth. Instrum. 1 (1993) 38–42. [2] D.J. Laser, J.G. Santiago, A review of micropumps, J. Micromech. Microeng. 14 (2004) 35–64.
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[3] M. Abdelgawad, I. Hassan, N. Esmail, Transient behavior of the viscous micropump, Microscale Thermophys. Eng. 8 (2004) 361– 381. [4] P. Woias, Micropumps-past, progress and future prospects, Sens. Actuators B 105 (2005) 28–38. [5] D. Blanchard, P. Ligrani, B. Gale, Single-disk and double-disk viscous micropumps, Sens. Actuators A 122 (2005) 149–158. [6] M. Kilani, P.C. Galambos, Y.S. Haik, C. Chen, Design and analysis of a surface micromachined spiral-channel viscous pump, J. Fluids Eng. 125 (2003) 339–344. [7] J. D¨opper, M. Clemens, W. Ehrfeld, S. Jung, K.-P. K¨amper, H. Lehr, Micro gear pumps for dosing of viscous fluids, J. Micromech. Microeng. 7 (1997) 230–232. [8] M. Sen, D. Wajerski, M. Gad-el-Hak, A novel pump for MEMS applications, J. Fluids Eng. 118 (1996) 624–627. [9] D. Blanchard, P. Ligrani, B. Gale, Miniature single-disk viscous pump (single-DVP), performance characterization, J. Fluids Eng. 128 (2006) 602–610. [10] M.I. Kilani, A. Al-Salaymeh, A. Al-Halhouli, Effect of channel aspect ratio on the flow performance of a spiral-channel viscous micropump, J. Fluids Eng. 128 (2006) 618–627. [11] H. Schlichting, Boundary Layer Theory, McGraw-Hill, New York, 1951.
Biographies Ala’aldeen Al-Halhouli was born in Alkarak/Jordan in 1976. Al-Halhouli received a B.Sc. degree in Mechanical Engineering from Mu’tah University, Jordan in 1999 and an M.Sc. degree from the University of Jordan in 2001. He is currently a Ph.D. student at the Mechanical Engineering Department of the University of Jordan. In 2005, he received a DAAD scholarship to conduct his Ph.D. research experiments in the area of viscous micropumps at the Institute for Microtechnology in the Technical University Braunschweig. He has special interest in mechanical engineering systems modeling and design, micropumps design and testing, MEMS, microfluidics, and computational fluid dynamics (CFD). Stefanie Demming is a Ph.D. student at the Institute for Microtechnology at the Technical University of Braunschweig, Germany. In 2005 she obtained a double Diploma from the TU Braunschweig and the Centro Polit´ecnico Superior de Zaragoza (Spain) in Bioengineering and Chemical Engineering, respectively. Her research interest is in microfluidics related to Lab-on-a-Chip and BioMEMS. Marco Feldmann received his diploma in mechanical engineering (Dipl.-Ing.) from the Technical University of Braunschweig, Germany, in 2000. He is currently working towards the Ph.D. degree at the Institute for Microtechnology of the Technical University of Braunschweig. His main research interests are in the areas of micro sensors, micro fluidics and micro actuators. ¨ Prof. Dr. Stephanus Buttgenbach obtained the Diploma and Ph.D. degrees in physics from the University of Bonn in 1970 and 1973, respectively. From 1974 to 1985, he was with the Institute of Applied Physics of the University of Bonn, working on atomic and laser spectroscopy. In 1983 he was promoted to Professor of Physics. From 1977 to 1985 he was also a Scientific Associate at CERN. In 1985 he joined the Hahn-Schickard-Society of Applied Research at Stuttgart working on micro system technologies.1988 he was appointed Scientific Director of the Institute of Micro and Information Technology of the Hahn-Schickard-Society at Villingen-Schwenningen. Since 1991 he holds the chair of Microtechnology at the Technical University of Braunschweig, where his research centres on the development and application of micro sensors, actuators and systems. Currently, he is the coordinator of the collaborative research center Design and Manufacturing of Active Micro Systems. Dr. Mohammad Kilani is currently an Associate Professor in the Mechatronics Engineering Department at the University of Jordan, Jordan. His research interest includes development of pumps and micropumps for stress-sensitive microparticles, MEMS and microfluidics. Dr. Ahmed Al-Salaymeh is an associate professor at the Mechanical Engineering Department, Faculty of engineering and Technology, University of Jordan.
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Dr. Al-Salaymeh got his Ph.D. (Dr.-Ing.) degree with honor from the Institute of Fluid Mechanics, Friedrich Alexander Universit¨at Erlangen-N¨urnberg, Erlangen, Germany in April, 2001. He joined the Mechanical Engineering Department at the University of Jordan in August, 2001 as assistant professor. He finished his B.Sc. degree at 1993 and M.Sc. degree at 1995 with
honor from Mechanical Engineer Department at the University of Jordan. Dr. Al-Salaymeh has special interest in Fluid Mechanics, MEMS, CFD, Thermal flow Sensors and Measurements Technique such as HWA and LDA. He has about 50 scientific papers in the international Journals and the international conferences.
Sensors and Actuators A 142 (2008) 256–262
Performance characterization of a miniature spiral-channel viscous pump A.T. Al-Halhouli a,∗ , S. Demming a , M. Feldmann a , S. B¨uttgenbach a , M.I. Kilani b , A. Al-Salaymeh c a
Institute for Microtechnology, Technical University of Braunschweig, Alte Salzdahlumer Strasse 203, 38124 Braunschweig, Germany b Mechatronics Engineering Department, University of Jordan, Amman 11942, Jordan c Mechanical Engineering Department, University of Jordan, Amman 11942, Jordan Received 29 September 2006; received in revised form 25 January 2007; accepted 24 February 2007 Available online 7 March 2007
Abstract This work describes the development and testing of a miniature spiral-channel viscous pump. The pump consists of a 12 mm diameter spiral disk on which a spiral-channel is machined with heights of 1 or 2 mm, a width of 1 mm and a spiral length (angular span) of 2.5π or 3.5π. The spiral-channel forms a fluid passage through which fluid is dragged due to the rotation of the spiral-channel under a stationary plate. Fluid inlet and outlet ports are located at the ends of the spiral-channel. Experimental flow rates and pressure rise data are obtained for rotational speeds from 1000 to 5000 rpm for pumping glycerin, where a maximum flow rate and pressure difference of 3.05 ml/min and 353 mbar is achieved at channel design parameters: w/h = 1.0, and θ = 3π. The flow rate of the pump was found to increase nearly linearly with rotational speed and decrease linearly with the pressure head imposed on the pump. Advantages of spiral pump include simplicity in fabrication, ability to pump particle-laden fluids, and can operate with no valves. © 2007 Elsevier B.V. All rights reserved. Keywords: Spiral pump; Microfluidics; Viscous flow
1. Introduction Micropumps are vital miniature devices required in micro fluidic systems, microelectronics cooling, and chemical analysis systems [1]. Micropumps have been implemented into the market and are used in ink jet printers and fuel injection applications [2,3]. A variety of micropumps are available to meet these applications including non-mechanical micropumps such as the electro-hydrodynamic pumps (EHD), magnet-hydro-dynamic and electroosmotic pumps. These devices have no moving parts and are thus more reliable; however, they are generally limited by low flow rate and pressure rise capabilities, the need for high supply voltage, and the physical characteristics of the working fluids. Mechanical micropumps like centrifugal pumps, diaphragm pumps, rotary pumps, phase change pumps, and several other types of pumps [2,4] have a wide variety of
∗
Corresponding author. Tel.: +49 531 3919741; fax: +49 531 3919751. E-mail address: [email protected] (A.T. Al-Halhouli).
0924-4247/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2007.02.035
possible working fluids and applications [5]. Different viscous micropumps or pumps for pumping viscous fluids have been investigated recently [5–9]. Among these is the spiral-channel micropump illustrated in Fig. 1. The pump works by rotating a disk with a spiral shaped channel below a flat plate covering the channel. The inlet and outlet of the pump are located at the spiral-channel ends, and the pump works due to the drag force generated by the moving action of the rotating channel with respect to the stationary disk. A macroscale prototype of the spiral-channel concept was recently reported [6]. The present experiments were performed on a miniaturized model with a 12 mm spiral disk diameter, which represent 80% miniaturization of the macro scaled prototype tested previously [6]. This allowed achieving a better understanding of the expected performance of a microscale spiral pump, and explodes the effect of viscous dissipation and cross-channel leakage, which will cause deviation between the analytical model, and the experimental performance of the pump. In this work the miniaturized spiral-channel viscous pump was investigated and tested at different boundary conditions and geometrical parameters,
A.T. Al-Halhouli et al. / Sensors and Actuators A 142 (2008) 256–262
Fig. 1. The spiral pump concept.
where maximum flow rate and pressure difference of 3 ml/min and 350 mbar were achieved. 2. Spiral pump configuration and operation The spiral-channel viscous pump is comprised of a stationary flat cover and a spinning spiral-channel disk that forms the pump chamber, with a fluid inlet and outlet ports located at either end of the spiral-channel. Fig. 2 shows a scheme of the spiral-channel pump components. The stationary flat cover is brought to close proximity with the upper walls of the spiral-channel creating a small gap with the objective of minimizing leakage from the pump chamber. The height of the pump chamber is the distance between the disk surface and the bottom of the spiral-channel, which constitutes the flow passage height of the pump. The flow passage heights used for testing are 1 and 2 mm, respectively.
257
In a typical viscous micropump, a rotating element on the form of a spinning disk, or a spinning cylinder rotates continuously tangent to the flow field. As the element spins, it drags fluid in a direction tangent to the element’s motion creating a Couette-type flow in the pump chamber between the rotating element and the stationary surfaces of the chamber. If an external pressure gradient is imposed between the inlet and outlet in the fluid chamber, a Poiseuille-type flow takes place, which opposes the motion induced by the element’s rotation. If the opposing external pressure is large enough, some of the fluid between the spinning element and the fixed surfaces of the fluid chamber will re-circulate in the opposite direction of the disk rotation. The Couette and Poiseuille flow patterns appear in the spiral pump geometry and also appear in the single disk and double disk geometry [5,9]. In fact both of these pump concepts produce pumping by generating a flow against an imposed external pressure by utilizing the viscous drag effect resulting from the rotation of a disk tangent to the flow field. The difference in flow performance between these two concepts arises in the maximum pressure head and the maximum flow rate that can be achieved from a pump disk of a given radius. The spiral pump geometry is capable of resisting a larger pressure head than that obtained from the single-disk and double disk pump with the same dimension. This is due to the fact that the spiral pump’s channel has a longer effective length than that of the single disk and double disk pump. The upper limit on the effective channel length in the single disk pump is limited is 2πr, where r is the mean radius of the channel. In a spiral-channel pump, the effective channel length is rm θ, and θ is 2πn where n is the number of turns in the spiral coil. On the other hand, the channel width in the single disk and double disk pumps if the pressure head is low, the single disk and double disk pumps could deliver a larger flow rates than that obtained by a spiral pump because the channel width in these pump geometries could be made larger. 3. Pump component fabrication
Fig. 2. A photograph of the spiral pump components.
The spiral pump assembly consists of three main components: the rotating spiral disk with its shaft, the stationary flat cover, and the pump housing as illustrated in Fig. 2. The spiral disk surface must be flat so that it is aligned with the bottom surface of the stationary flat cover. Any misalignment of the spiral disk will result in leakage due to increased gap height above the channel. The disk is constructed from using precision machining techniques from an aluminum stock with its shaft. The spiral groove forming the spiral-channel was obtained using a CNC milling machine, with an inner radius of the spiral-channel of 2.5 mm and the outer radius of 4.5 mm. The spiral disk was set in the pump housing, which is made using Teflon material. An O-ring groove, bolts borings and a cylindrical protrusion with the dimensions of the spiral disk, 12 mm diameter and 5 and 6 mm heights were machined at its upper face. While another cylindrical protrusion for the bearing with 8 mm diameter and 3 mm height were machined at the back face of the housing, where the inner diameter of the used bearing is 4 mm and equal to the diameter of the spiral disk shaft. The housing was then covered by a visible flat cover, which was
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A.T. Al-Halhouli et al. / Sensors and Actuators A 142 (2008) 256–262 Table 1 Spiral pump design parameters Parameters
Initial radius (m) Gap height (m) Channel width, w (m) Channel height, h (m) Angular span, θ
Fig. 3. A photograph of the spiral-channel pump experimental setup during operation.
manufactured using Plexiglas, and allows the visualization of the flow and ensures that there are no air bubbles during testing. A hole in the centre of the cover, which represents the inlet to the pump is created with 1.35 mm diameter. 4. Pump setup and testing As illustrated in Fig. 1, the spiral pump idea has the advantage of utilizing the effect of high viscous forces of the fluid at small scales, where the fluid presented in the spiral-channel can be dragged along the channel axis by rotating the spiralchannel against a stationary flat cover (moving situation), where a net tangential viscous stress on the boundaries is built up and produces a positive pressure gradient in the direction of flow. A photograph for the spiral pump test setup is shown in Fig. 3. Fluid enters at the center of the spiral disk and leaves tangentially to the spiral-channel from the outlet port. The pressure difference between the inlet and the outlet is measured using a SCX30 DN precision compensated pressure sensor, which was calibrated with the pressure of a water column. The spiral disk shaft is coupled with a Faulhaber 3257G 012CR DC micromotor, and guided in a Teflon sealed bearing, which also forms a seal to reduce the leakage. The rotational speed is determined by attaching a tachometer to the coupling between the motor and the disk shaft. Because of its high viscous property, glycerin with a viscosity of 1412 mPa s, and density of 1261 kg/m3 was used as the working fluid. Several spiral pump designs with different design parameters have been investigated as summarized in Table 1. The range of speed investigated in this study is between 1000 and 5000 rpm. The inlet and outlet tubes are 240 mm long and have an inner diameter of 4.5 mm. The inlet tube is connected to the fluid reservoir, which is large enough to avoid level changes during operation, and the outlet tube is connected to the collection reservoir, which is set above digital balance used to read the mass of the pumped fluid during fixed intervals of time. The tube diameter is larger than that of the inlet and outlet ports, because an expansion of the fluid in the tubes will occur, which yields
Moving situation
Flat plate
Design (A)
Design (B)
Design (C)
Design (D)
2500 100 1000 2000 3π
2500 100 1000 1000 3π
3500 100 1000 1000 2π
– 400 – – –
reduction in the flow velocity and the major losses through the test loop. The assembly of the experimental setup begins by fixing the bearing to the back face of the housing, and setting the spiral disk with it is shaft into the housing. The external motor is fixed to the base, and the coupling is fixed to the motor shaft. The pump is then coupled with the motor, fixed to the base, and the inlet and outlet tubes are connected. Before turning on the power supply and adjusting the tachometer, the air is bled from the test loop, and then the motor is activated to the desired speed. The readings are taken after ensuring steady state flow conditions, where the pumped fluid is collected for fixed interval of times and the flow rate is estimated. While, for the maximum pressure difference values, the digital pressure sensor is mounted such as the pressure difference values at steady state conditions across the pump are measured directly after closing a ball valve completely at the far end of the outlet tube, and recording the maximum reachable value. Fluid leakage is noticed from the pump while reaching the maximum pressure values. 5. Results and discussion The performance of the spiral pump was investigated experimentally by plotting the flow rates against the disk rotational speed. Results showed that the flow rates increase nearly linearly with rotational speed, which supports the influence of the viscous forces in small scales induced in the spiral-channel and the validity of the linear lubrication model for this problem [10]. The microscale flow field of an incompressible Newtonian fluid in the thin narrow gap of the spiral pump geometry is a classical example of flow situation governed by the simplified version of the Navier–Stokes equations known as the lubrication model [11]. The assumptions commonly made in the application of the lubrication model are (i) the fluid film is so thin that derivatives of velocity across the film thickness are far more important than any other velocity derivative, (ii) inertia effects are negligible compared to viscosity, and (iii) channel curvature introduces second-order negligible effects. Under the foregoing assumptions, the equation expressing mass conservation is: ∂u ∂v ∂w + + =0 ∂x ∂y ∂z
(1)
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Fig. 4. Flow rates vs. rotational speeds at different aspect ratios.
while the equations of motion reduce to: ∂p ∂ ∂u ∂p ∂ ∂v = μ , = μ , ∂x ∂z ∂z ∂y ∂z ∂z
Fig. 6. Maximum pressure rises vs. rotational speeds for different design parameters.
∂p =0 ∂z
(2)
where u, v, w are the velocity components, x, y, z are the Cartesian coordinates, p the pressure, and μ is the fluid dynamic viscosity. The effect of channel width (w) to channel height (h), or in other words channel aspect ratio (w/ h) on the flow rate is presented in Fig. 4. The flow rates were found to be larger for the higher aspect ratio condition at the same rotational speed. Maximum flow rates of 3.05 and 1.92 ml/min are achieved for rotational speed of 4285 rpm at channel aspect ratios of 1 and 0.5, respectively. Other tests were performed for different spiral lengths (i.e. angular spans = θ) at constant aspect ratio, and under the same conditions. Results are presented in Fig. 5 and showed that the effect of spiral length on the flow rates is noticeable at low rotational speeds (ω < 1400 rpm). Increasing the rotational speed
Fig. 5. Flow rates vs. rotational speeds at different angular spans.
reduce this effect due to the small difference between the channel lengths. The maximum pressure rises for the spiral pump and the flat plate pump are also investigated at different rotational speeds ranging from 1000 to 4500 rpm as shown in Fig. 6. A maximum pressure rise of 353 mbar is achieved for (w/ h = 1.0, θ = 3π) at a rotational speed of 4138 rpm. The maximum pressure rise increases nearly linearly with increasing the rotational speed for all designs. For the purpose of comparison between the effect of viscous forces and centrifugal forces in small scales, a flat plate pump was tested. The idea of this pump is to rotate a flat disk without any protrusion: spiral or C-shaped, as shown in Fig. 7 below the stationary flat cover instead of the spiral-channel disk, which produces centrifugal forces on the fluid and a pumping effect through the ends is obtained. The pump chamber volume is determined from the disk diameter and the gap between the disks, which is 400 m. This pump was designed to have the same pumping volume as in the case of moving and stationary flat disks in design (A). The flow rate results as shown in Fig. 8 and the pressure difference values as in Fig. 6 showed that the spiral-channel pump produces higher flow rate and pressure values for the same operating conditions than that for the flat plate pump. This supports the effect of surface area to volume ratio, in parallel to the dominant effect of viscous stresses over centrifugal forces in microscales. Further, the flow rates were plotted against the pressure difference values. A sample of the results for spiral pump at w/ h = 0.5, θ = 2 is shown in Fig. 9. Results showed that the flow rates decrease linearly with increasing pressure difference. This is consistent with the lubrication flow model and supports also the high influence of viscous stresses in low scales. The miniaturized model described in this work highlights the effect of viscous dissipation and cross-channel leakage on the pump performance. These two effects will cause the flow
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Fig. 7. A photograph of the spiral-channel and flat plate disks.
Fig. 8. Flow rates vs. rotational speeds using spiral disk and flat plate as a rotating disks.
Fig. 9. Flow rates vs. pressure difference at w/ h = 0.5, θ = 2π.
rate to drop significantly from the analytical predictions. As seen in Fig. 10, which shows the experimental, and analytical flow rates at spiral-channel aspect ratio w/ h = 3.2. A close agreement between the experimental and the theoretical results is observed for low values of Re Eu, where reduced Reynolds ¯ 2 /μl), and Euler number number can be defined as Re = (ρUh
is Eu = (Δp/ρU¯ 2 ). ρ is the fluid density, l the spiral-channel length and U¯ is the average channel velocity. At high values of Re Eu, a large deviation between the experimental and the theoretical results is observed. This deviation can be attributed to the effect of viscous dissipation and the effect of cross flow in the gap below the spiral wall in the scaled up
Table 2 Maximum flow rates and pressure rises of different micropumps Pump type
Fluid
Channel width (mm)
Disk diameter (mm)
ω (rpm)
Qmax (ml/min)
Pmax (kPa)
Spiral-channel Micro gear [7] Single disk [5] Double disk [5] Single disk [9]
Glycerin Oil Water Water Water
1 – 1.19 1.19 1.19
12 1.192 2.38 2.38 2.38
4285 – 5000 5000 5000
3.05 1 1 2.1 4.75
35.3 120 0.643 1.19 31.1
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Fig. 10. Experimental and analytical flow rate vs. pressure head at channel aspect ratio w/ h = 3.2 [10].
model, which is increased with increasing pressure difference. In the experiments presented in this work, Re Eu is in between 6 and 11 and a large deviation between the experimental data, and the analytical predictions are expected. Further, a list of maximum flow rates (Qmax ) and pressure rises (Pmax ) for different viscous micropumps and micro gear pump used for pumping viscous fluids is shown in Table 2. Tests were carried out using different geometrical parameters, working fluids and operating speeds. High flow rates and pressure rises were obtained by the spiral-channel miniaturized pump. 6. Conclusions This paper has presented an experimental investigation of the effect of the design parameters: channel aspect ratio and length on the flow performance of spiral-channel viscous pump. The advantages of this pump are its simplicity in fabrication and the ability to pump particle-laden fluids. The experimental results showed that the flow rates are changed nearly linearly either with the rotational speed or pressure difference, which is consistent with the lubrication model and support the dominant influence of viscous forces in small scales. Acknowledgements The authors wish to acknowledge the support received from the Technical University of Braunschweig and the Deanship for Scientific Research in the University of Jordan. The scholarship for the first author by the German Academic Exchange Service (DAAD) is gratefully appreciated. References [1] B. Van Der Schot, J. Jeanneret, A. Van Den Berg, N. De Rooij, Microsystems for flow injection analysis, Anal. Meth. Instrum. 1 (1993) 38–42. [2] D.J. Laser, J.G. Santiago, A review of micropumps, J. Micromech. Microeng. 14 (2004) 35–64.
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[3] M. Abdelgawad, I. Hassan, N. Esmail, Transient behavior of the viscous micropump, Microscale Thermophys. Eng. 8 (2004) 361– 381. [4] P. Woias, Micropumps-past, progress and future prospects, Sens. Actuators B 105 (2005) 28–38. [5] D. Blanchard, P. Ligrani, B. Gale, Single-disk and double-disk viscous micropumps, Sens. Actuators A 122 (2005) 149–158. [6] M. Kilani, P.C. Galambos, Y.S. Haik, C. Chen, Design and analysis of a surface micromachined spiral-channel viscous pump, J. Fluids Eng. 125 (2003) 339–344. [7] J. D¨opper, M. Clemens, W. Ehrfeld, S. Jung, K.-P. K¨amper, H. Lehr, Micro gear pumps for dosing of viscous fluids, J. Micromech. Microeng. 7 (1997) 230–232. [8] M. Sen, D. Wajerski, M. Gad-el-Hak, A novel pump for MEMS applications, J. Fluids Eng. 118 (1996) 624–627. [9] D. Blanchard, P. Ligrani, B. Gale, Miniature single-disk viscous pump (single-DVP), performance characterization, J. Fluids Eng. 128 (2006) 602–610. [10] M.I. Kilani, A. Al-Salaymeh, A. Al-Halhouli, Effect of channel aspect ratio on the flow performance of a spiral-channel viscous micropump, J. Fluids Eng. 128 (2006) 618–627. [11] H. Schlichting, Boundary Layer Theory, McGraw-Hill, New York, 1951.
Biographies Ala’aldeen Al-Halhouli was born in Alkarak/Jordan in 1976. Al-Halhouli received a B.Sc. degree in Mechanical Engineering from Mu’tah University, Jordan in 1999 and an M.Sc. degree from the University of Jordan in 2001. He is currently a Ph.D. student at the Mechanical Engineering Department of the University of Jordan. In 2005, he received a DAAD scholarship to conduct his Ph.D. research experiments in the area of viscous micropumps at the Institute for Microtechnology in the Technical University Braunschweig. He has special interest in mechanical engineering systems modeling and design, micropumps design and testing, MEMS, microfluidics, and computational fluid dynamics (CFD). Stefanie Demming is a Ph.D. student at the Institute for Microtechnology at the Technical University of Braunschweig, Germany. In 2005 she obtained a double Diploma from the TU Braunschweig and the Centro Polit´ecnico Superior de Zaragoza (Spain) in Bioengineering and Chemical Engineering, respectively. Her research interest is in microfluidics related to Lab-on-a-Chip and BioMEMS. Marco Feldmann received his diploma in mechanical engineering (Dipl.-Ing.) from the Technical University of Braunschweig, Germany, in 2000. He is currently working towards the Ph.D. degree at the Institute for Microtechnology of the Technical University of Braunschweig. His main research interests are in the areas of micro sensors, micro fluidics and micro actuators. ¨ Prof. Dr. Stephanus Buttgenbach obtained the Diploma and Ph.D. degrees in physics from the University of Bonn in 1970 and 1973, respectively. From 1974 to 1985, he was with the Institute of Applied Physics of the University of Bonn, working on atomic and laser spectroscopy. In 1983 he was promoted to Professor of Physics. From 1977 to 1985 he was also a Scientific Associate at CERN. In 1985 he joined the Hahn-Schickard-Society of Applied Research at Stuttgart working on micro system technologies.1988 he was appointed Scientific Director of the Institute of Micro and Information Technology of the Hahn-Schickard-Society at Villingen-Schwenningen. Since 1991 he holds the chair of Microtechnology at the Technical University of Braunschweig, where his research centres on the development and application of micro sensors, actuators and systems. Currently, he is the coordinator of the collaborative research center Design and Manufacturing of Active Micro Systems. Dr. Mohammad Kilani is currently an Associate Professor in the Mechatronics Engineering Department at the University of Jordan, Jordan. His research interest includes development of pumps and micropumps for stress-sensitive microparticles, MEMS and microfluidics. Dr. Ahmed Al-Salaymeh is an associate professor at the Mechanical Engineering Department, Faculty of engineering and Technology, University of Jordan.
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Dr. Al-Salaymeh got his Ph.D. (Dr.-Ing.) degree with honor from the Institute of Fluid Mechanics, Friedrich Alexander Universit¨at Erlangen-N¨urnberg, Erlangen, Germany in April, 2001. He joined the Mechanical Engineering Department at the University of Jordan in August, 2001 as assistant professor. He finished his B.Sc. degree at 1993 and M.Sc. degree at 1995 with
honor from Mechanical Engineer Department at the University of Jordan. Dr. Al-Salaymeh has special interest in Fluid Mechanics, MEMS, CFD, Thermal flow Sensors and Measurements Technique such as HWA and LDA. He has about 50 scientific papers in the international Journals and the international conferences.