This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Non-Newtonian fluid flow in microchannels has significant applications in science and engineering. The effects of temperature and PAM solution concentrations on rheological parameters are analyzed by measuring them with rotating cylinder viscometer. Flow characteristics for deionized water and PAM solutions in fused silica microtubes with diameters ranging from 50 to 320μm, fused silica square microchannels with diameters 75 and 100μm, and stainless steel microtubes with diameters from 120 to 362μm, are studied experimentally. The test results for deionized water in microchannels are in good agreement with theoretical predictions for conventional-size channels. Friction factors of PAM solutions are much higher than theoretical predictions. With the PAM concentration reduced, the deviation is more, which is possibly caused by the significant electroviscous effect on PAM solutions flow in microchannels

3rd Micro and Nano Flows Conference (MNF2011)

Lu, YB

Tang, GH

Tao, WQ

Wang, FF

Zhang, SX

English

Brunel University Research Archive

3rd Micro and Nano Flows Conference Thessaloniki, Greece, 22-24 August 2011 - 1 -  Experimental Study of Non-Newtonian Fluid Flow in Microchannels   G. H. TANG*, F. F. WANG, S. X. ZHANG, Y. B. LU, W. Q. TAO  * Corresponding author: Tel.: ++86 (0)29 82665319; Fax: ++86 (0)29 82669106; Email: ghtang@mail.xjtu.edu.cn MOE Key Laboratory of Thermo-Fluid Science and Engineering, Xi’an Jiaotong University, China  Abstract Non-Newtonian fluid flow in microchannels has significant applications in science and engineering. The effects of temperature and PAM solution concentrations on rheological parameters are analyzed by measuring them with rotating cylinder viscometer. Flow characteristics for deionized water and PAM solutions in fused silica microtubes with diameters ranging from 50 to 320μm, fused silica square microchannels with diameters 75 and 100μm, and stainless steel microtubes with diameters from 120 to 362μm, are studied experimentally. The test results for deionized water in microchannels are in good agreement with theoretical predictions for conventional-size channels. Friction factors of PAM solutions are much higher than theoretical predictions. With the PAM concentration reduced, the deviation is more, which is possibly caused by the significant electroviscous effect on PAM solutions flow in microchannels.  Keywords: Non-Newtonian Fluid, Microchannels, PAM Solution, Electroviscous Effect   1. Introduction In recent years, scientific research on microflow has get great attentions due to the rapid development of MEMS and micro processing technology. Microsystems have been widely used in industry, biological medicine, such as the DNA microarray and sorting, sample pretreatment and analysis, cell separation and detection, environmental monitoring and so on (Whitesides, 2006; Stone et al., 2004; Balagadde et al., 2005; Chen et al., 2005; Vilkner et al., 2004). Many scholars have made experiments on microchannel flow (Brutin and Tadrist, 2003; Celata et al., 2002; Ren et al, 2001; Wu and Cheng, 2003; Ren et al, 2001; Judy et al., 2003; Li, 2001; Li et al., 2007; Tang et al., 2007a and 2007b), but most are limited to Newtonian fluids. Few experimental researches on non-Newtonian fluid flow in microchannels have been conducted. Non-Newtonian fluid flow has broad applications in both our daily life and industry. The research of non-Newtonian flow is of important practical significance in science and engineering. 2. Experimental Setup The experimental test system is depicted schematically in Fig. 1. The detailed descriptions for components and measurement apparatus are listed in Table 1.  Fig. 1 Schematic of the experimental loop Table 1 Flow loop components 3rd Micro and Nano Flows Conference Thessaloniki, Greece, 22-24 August 2011 - 2 - Label Description Manufacturer/model Range Accuracy 1 Gas tank MESSER 15MPa  2 Pressure regulator Shanghai regulator factory/YQD-6   3 Three-way valve SS-43XS4   4 Liquid storage tanks    5 Filter Swagelok /SS-4F-05  0.5 mμ  6 Precision regulator Swagelok /SS-SS4   7 Connection adapter for test section    8 Plug valve Swagelok /SS-4P4T   9 Absolute pressure transducer 1151DP622 0~300Kpa 0.25% 10 Absolute pressure transducer 1151DP722 0~2068Kpa 0.25% 11 Volumetric flow meter Cole-parmer/3291601 0-1ml/min 2% 12 Volumetric flow meter Cole-parmer/3291602 0-5ml/min 2% 13 Volumetric flow meter Cole-parmer/3291606 0-50ml/min 2% 14 High precision electronic balance Mettler Toledo/ AL204 0-210g 0.1mg 15 Data acquisition system    16 Computer    17 Test section SST/FSC/FST    To ensure that the whole experiment system is in single phase flow, gas exhaust is an important step to get valid experimental data. Before each test, we should ensure that the connecting pipe, absolute pressure transducer and the whole experiment system exhaust completely. To avoid gas dissolving in the experimental solution, we choose purity nitrogen insoluble in water as a driving force. Three types of microchannels, fused silica tubes (FST), fused silica square channels (FSC), stainless steel tubes (SST), listed in Table 2, are tested in the experiment. The lengths of the tested twelve microchannels are all fixed at 100mm.Table 2 Dimensions of the test microchannels Test channel Hydraulic diameter D± 1 mμ  Test channel Hydraulic diameter D± 1 mμ  FST_D320 320.10 FST_D250 250.00 FST_D200 201.44 FST_D100 102.74 FST_D75 74.36 FST_D50 50.55 FSC_D100 98.30 FSC_D75 72.00 SST_D362 362.48 SST_D260 260.00 SST_D170 170.80 SST_D120 120.63 The typical photos of cross-section and longitudinal-section by a scanning electron microscope (SEM) are shown in Fig. 2. By using light-section microscope, we can see that the inner surface of stainless steel tube has much irregular convex. But the inner surface of 3rd Micro and Nano Flows Conference Thessaloniki, Greece, 22-24 August 2011 - 3 - fused silica tube and square channel is quite smooth with relative roughness far less than 1%. However, the surface relative roughness of stainless steel tube is measured at 1.9%, 2.7%, 4.1%, and 5.9% for SST_D362, SST_D260, SST_D170, and SST_D120, respectively, which are significantly larger than those for fused silica tubes and square channels.     Fig. 2 SEM images of three typical tested tubes  3. The Viscosity Measurement of Non-Newtonian Fluid  Deionized water and three concentrations (1000wppm, 3000wppm, and 5000wppm) of polyacrylamide (PAM) solutions are used as the working fluid in the experiment. The deionized water as a typical Newtonian fluid, are carried out to check the reliability of experimental system. PAM is a water-soluble polymer, a type of typical shear thinning power-law fluid.  For non-Newtonian fluid, rheological parameters are needed to evaluate the 3rd Micro and Nano Flows Conference Thessaloniki, Greece, 22-24 August 2011 - 4 - rheological characteristics. We use rotating cylinder viscometer of American Brookfield R/S plus series to measure the viscosity of PAM solutions. The constitutive equations of non-Newtonian fluid can be written as, τ ηγ=                             (1) where τ  is the shear force; η  is the apparent viscosity; γ  is the shear rate. The rheological properties of power law fluid are relevant to rheological index n  and consistency coefficient k . And the power law fluid can be written as, nkτ γ=                            (2) with shear thinning fluid 1n < , and shearing thickening fluid 1n > . The power-law equation recovers the constitutive equation of Newtonian fluid with 1n =  and k μ= .  Fig. 3 shows the influence of PAM concentration on the flow rheological characteristics, at different temperatures of 20℃, and 40 . ℃ The k and n of PAM solutions at different temperatures and concentrations are listed in Table 3 and the fitted are presented in Fig. 3 with solid lines. We can see that the shear thinning characteristics of PAM solution concentration has a consistent trend at different temperatures. In the same shear rate, with the rise of PAM solution concentration, shear force increases, and apparent viscosity augments, and thus non-Newtonian features are enhanced.    0 1000 2000 3000 4000 500005101520251000wppm3000wppm5000wppm   T=20οCτγ(a) 0 1000 2000 3000 4000 5000024681012141618201000wppm3000wppm5000wppm   T=40οCτγ(b) Fig. 3 The influence of PAM concentrations on viscosity measurement   Table 3 The values of k and n of PAM solutions at different temperatures and concentrations Temperature  Concentration  k n 1000wppm 0.003069 0.88757 3000wppm 0.19771 0.50715 T=20℃ 5000wppm 0.40332 0.45917 1000wppm 0.006256 0.78277 3000wppm 0.153745 0.50723 T=40℃ 5000wppm 0.39485 0.43141  4. Results and Discussion  Deionized water and three concentrations (1000wppm, 3000wppm, and 5000wppm) of polyacrylamide (PAM) solutions are tested in the experiment. The main research purpose is to obtain friction factor for PAM solutions in different microchannels. Reynolds numbers for deionized water and power-low fluid are defined as Eq.(3) and Eq.(4) (Manglik and 3rd Micro and Nano Flows Conference Thessaloniki, Greece, 22-24 August 2011 - 5 - Ding, 1997), respectively. Equations (5) and (6) show the definitions of average velocity and friction factor, respectively. 4Re uD mDν ρπ ν= =                  (3) 2* 14Re 81 3nn nnD u nK nρ − −⎛ ⎞= ⋅⎜ ⎟+⎝ ⎠         (4) 24m muA Dρ ρπ= =                   (5) 2 52 228D p Df pL u m LρπρΔ ⋅= Δ ⋅ ⋅ =       (6) Where ρ  is density of deionized water;ν  is coefficient of kinematic viscosity; u  is the average velocity; A  is the cross-sectional area of test channels; D  is the equivalent diameter of channels; L  is the length of test channels; m  is mass flow rate; pΔ  is pressure difference.0.1 1 10 100 10000.1110100100010000       3000wppmFST_D320 FST_D250FST_D200FST_D100FST_D75FST_D50y=64/xfRe, Re*(a) 10 100 10000.1110100        5000wppmFST_D320 FST_D250FST_D200FST_D100FST_D75FST_D50y=64/xfRe, Re*(b) Fig. 4 Experimental friction factors for PAM solutions in test fused silica microtubes Figure 4 depicts friction factors for two concentrations of PAM solutions in FST (50-320μm). It presents that friction factor of PAM solution is all greater than theoretical value 64f Re=  in each concentration. It is different from the conventional channels, the friction reduction characteristics of the shear thinning fluid. With the decrease of pipe diameter, deviation from the theoretical value is larger.  Fig.5 describes the influence of PAM concentrations and deionized water (DI water) on friction factors. For the deionized water, the friction factor is accord with theoretical value in FST and FSC test channels. Owing to the relatively large roughness on the inner surfaces of stainless steel tubes, the friction factors of DI water depart from theoretical values and the deviation gets larger as the tube diameter decreases, as seen from Figs. 5(i)-5(l). For PAM solutions, the maximum of friction factor is about 328% higher than the theoretical value. And with the PAM concentration reduced, the deviation becomes much larger. WE declare that it is caused by the electroviscous effect on liquid flow in microchannels. Due to the presence of the EDL, the pressure driven flow induces an electrokinetic potential and the streaming potential which generates a conduction electrical current and hence liquid flowing opposite to the streamwise flow. Experimental results are consistent with numerical analysis (Tang et al., 2010). However, the experimental results for DI water are different from previous experimental results by Ren et al. who argued that the electroviscous effect is obvious even for DI water flow. From Fig.5, we can also see that the solution f~Re curve is not parallel to the theoretical one, and the greater of Re, the larger 3rd Micro and Nano Flows Conference Thessaloniki, Greece, 22-24 August 2011 - 6 - of deviation. If we use Eq. (7) (Poole and Ridley, 2007) to assess the developing length of shear thinning laminar flow, the developing length DX  is 17.9% of the total test length for FST_320 at Re=986.8 and n=0.459. ( ) ( ) 1/1.61.6 1.62/ 0.246 0.675 1.03 0.0567 ReDX D n n ∗⎡ ⎤= − + +⎢ ⎥⎣ ⎦   (7) Therefore the test channel length is not long enough to be assumed as a fully developed flow, especially for fluids with smaller power-law index. 0.1 1 10 10011010010001000wppm3000wppm5000wppmDI watery=64/xfRe, Re*(a) FST_D50 1 10 1001101001000wppm3000wppm5000wppmDI watery=64/xfRe, Re*  (b) FST_D75 1 10 1000.1110100 1000wppm3000wppm5000wppmDI watery=64/xfRe, Re*  (c) FST_D100 1 10 100 10000.010.111010010001000wppm3000wppm5000wppmDI watery=64/xfRe, Re*(d) FST_D200 1 10 100 10001E-30.010.111010010001000wppm3000wppm5000wppmDI watery=64/xfRe, Re*(e) FST_D250 1 10 100 10000.010.111010010001000wppm3000wppm5000wppmDI watery=64/xfRe, Re*  (f) FST_D320 3rd Micro and Nano Flows Conference Thessaloniki, Greece, 22-24 August 2011 - 7 - 1 10 1000.1110100 1000wppm3000wppm5000wppmDI watery=56/xfRe, Re*(g) FSC_D100 1 10 1000.1110100 1000wppm3000wppm5000wppmDI watery=56/xfRe, Re*(h) FSC_D75 1 10 1000.111010010001000wppm3000wppm5000wppmDI watery=64/xfRe, Re*  (i) SST_D120 10 100 10000.111010010001000wppm3000wppm5000wppmDI watery=64/xfRe, Re*(j) SST_D170 1 10 100 10000.010.111010010001000wppm3000wppm5000wppmDI watery=64/xfRe, Re*  (k) SST_D260 100 10000.11101000wppm5000wppmDI watery=64/xfRe, Re*  (l) SST_D362 Fig.5 The influence of PAM concentrations on friction factor for test channels  5. Conclusions  This work reports experimental results of non-Newtonian fluid flow in microchannels. We have used a rotating cylinder viscometer to measure the viscosity of PAM solutions. The measured results reveal the effects of temperature and solution concentration on rheological parameters. The friction factors for deionized water and PAM solution in fused silica microtubes, fused silica square microchannels, and stainless steel microtubes are studied experimentally. The friction factors for deionized water in microchannels are in good agreement with conventional theoretical predictions. But the friction factors of PAM 3rd Micro and Nano Flows Conference Thessaloniki, Greece, 22-24 August 2011 - 8 - solutions are all larger than theoretical values of *64=f Re for circular tubes and of *56 / Re=f  for square channels, and the smaller diameter, the larger deviation from the theoretical value. The possible reasons are discussed and analyzed.  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Characterization of frictional pressure drop for liquid flows through microchannels.

Developmentlength requirements for fully developed laminar pipe flow of inelastic nonNewtonian liquids.

Electro-viscous effects on pressure-driven liquid flow in microchannels.

Electroviscous effect on non-Newtonian fluid flow in microchannels.

Electroviscous effects on liquid flow in microchannels.

Engineering flows in small devices.

Experimental and numerical studies of liquid flow and heat transfer in microtubes.

Experimental friction factor of a liquid flow in microtubes.

Experimental investigation of hydraulic and singlephase heat transfer in 0.130-mm capillary tube. Nanoscale Microscale Thermophys.

Experimental observations and lattice Boltzmann method study of the electroviscous effect for liquid flow in microchannels.

Experimental study of compressibility, roughness and rarefaction influences on microchannel flow.

Friction factors in smooth trapezoidal silicon microchannels with different aspect ratios.

Interfacial electrokinetic effects on liquid flow in microchannels.

Long-term monitoring of bacteria undergoing programmed population control in a microchemostat.

Micro total analysis systems. Recent developments.

Microfluidic chip-based liquid-liquid extraction and preconcentration using a subnanoliter-droplet trapping technique.

The origins and the future of microfluidics.

Experimental study of non-Newtonian fluid flow in microchannels

Experimental study of non-Newtonian fluid flow in microchannels

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