Abstract
An experimental study of pulsatile flow in microchannel is reported in this paper. Such a study is important because time-varying flows are frequently encountered in microdevices. The hydraulic diameter of the microchannel is 144 μm and deionized water is the working fluid. The pressure drop across the microchannel as a function of time is recorded, from which the average and r.m.s. pressure drops are obtained. The experiments have been performed in the quasi-steady flow regime for a wide range of flow rate, frequency of pulsations, and duty cycle. The results suggest that the pressure with pulsations lies between the minimum and maximum steady state pressure values. The average pressure drop with pulsation is approximately linear with respect to the flow rate. The theoretical expression for pressure has also been derived wherever possible and the experimental data is found to lie below the corresponding theoretical values. The difference with respect to the theoretical value increases with an increase in frequency and a decrease in flow rate, with a maximum difference of 32.7%. This is attributed to the small size of the microchannel. An increase in frequency of square waveform leads to a larger reduction in pressure drop as compared to rectangular waveform, irrespective of the duty cycle. The results can be interpreted with the help of a first-order model proposed here; the model results are found to compare well against the experimental results. A correlation for friction factor in terms of the other non-dimensional governing parameters is also proposed. Experimental study of mass-driven pulsatile flow in microchannel is being conducted for the first time at these scales and the results are of both fundamental and practical importance.
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Abbreviations
- A :
-
Area of cross-section of channel (m2)
- C :
-
Capacitance (F)
- D h :
-
Hydraulic diameter of the channel (=4A/perimeter) (m)
- f :
-
Average friction factor \( \left( {{{pD_{\text{h}} } \mathord{\left/ {\vphantom {{pD_{\text{h}} } {{\tfrac{1}{2}}\rho v^{2} L}}} \right. \kern-\nulldelimiterspace} {{\tfrac{1}{2}}\rho v^{2} L}}} \right) \)
- f rms :
-
Friction factor r.m.s \( \left( {{{p_{\text{rms}} D_{\text{h}} } \mathord{\left/ {\vphantom {{p_{\text{rms}} D_{\text{h}} } {{\tfrac{1}{2}}\rho v^{2} L}}} \right. \kern-\nulldelimiterspace} {{\tfrac{1}{2}}\rho v^{2} L}}} \right) \)
- F :
-
Dimensionless form of frequency \( \left( { = {\frac{{D_{\text{h}} }}{{(t_{\text{N}} + t_{\text{F}} )\alpha }}}} \right) \)
- i :
-
Current (A)
- L :
-
Length of the microchannel (m)
- m F :
-
Minimum flow rate (kg/s)
- m N :
-
Maximum flow rate (kg/s)
- \( \tilde{p} \) :
-
Pressure (Pa)
- p :
-
Time-averaged pressure drop (Pa)
- p rms :
-
Root mean square value of the pressure drop (Pa)
- Q :
-
Volumetric flow rate (m3/s)
- R :
-
Resistance (ohm)
- Re :
-
Reynolds number \( \left( { = {\frac{{vD_{\text{h}} }}{\alpha }}} \right) \)
- Re N :
-
On-time Reynolds number \( \left( { = {\frac{{v_{\text{N}} D_{\text{h}} }}{\alpha }}} \right) \)
- t :
-
Time (s)
- t F :
-
Off-time. Time for which minimum flow (m F) occurs (s)
- t N :
-
On time. Time for which maximum flow (m N) occurs (s)
- T :
-
Duty cycle or ratio of on-time to off-time (t N/t F)
- u :
-
Streamwise velocity (m/s)
- v :
-
Time-averaged velocity of the flow over the cross-section (m/s), normalized voltage
- V :
-
Voltage (V)
- v F :
-
Average velocity over the cross-section, during the state of minimum flow (m/s)
- v N :
-
Average velocity over the cross-section, during the state of maximum flow (m/s)
- x :
-
Streamwise coordinate (m)
- α:
-
Kinematic viscosity of the fluid (m2/s)
- β:
-
Womersley parameter \( \left( { = D_{\text{h}} \sqrt {{\frac{\pi }{{2\alpha (t_{\text{N}} + t_{\text{F}} )}}}} } \right) \)
- μ:
-
Dynamic viscosity of the fluid (Pa.s)
- ω′:
-
Dimensionless form of frequency \( \left( { = {\frac{{D_{\text{h}} }}{{4(t_{\text{N}} + t_{\text{F}} )\alpha }}}} \right) \)
- ρ:
-
Fluid density (kg/m3)
- τF :
-
Time constant during the off-phase (s)
- τN :
-
Time constant during the on-phase (s)
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Tikekar, M., Singh, S.G. & Agrawal, A. Measurement and modeling of pulsatile flow in microchannel. Microfluid Nanofluid 9, 1225–1240 (2010). https://doi.org/10.1007/s10404-010-0642-z
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DOI: https://doi.org/10.1007/s10404-010-0642-z