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Experimental and numerical investigation on steady and transient flow in the flat-walled micro-diffuser/nozzle

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Abstract

In this paper, experiments and numerical simulations have been conducted to investigate the flow characteristics in the flat-walled micro-diffuser/nozzle on conditions of angle (0°–60°), Reynolds number (100–1500) and excitation frequency (0–5000 Hz). In steady flow, the diffuser efficiency increases with an increase in Reynolds number as θ ≤ 10°, but the optimal diffuser efficiency is found as 20° ≤ θ ≤ 60°, and the internal flow characteristics at the optimal diffuser efficiency are recorded. Based on statistics, it is concluded that the interaction of adverse pressure gradient and diverging flow results in the optimal angle, and the optimal angle decreases with an increase in Reynolds number. While in transient flow, the excitation frequency has great impacts on the optimal angle, the higher frequency results in the larger optimal angle. As the Reynolds numbers are 100 and 1500, the variations of diffuser efficiency with excitation frequency show the opposite trends. At low Reynolds number, the acceleration term caused by the excitation frequency increases the flow loss and reduces the diffuser efficiency. However, at high Reynolds number, the energy of diverging flow is stored in the vortexes and used to prevent the converging flow, this contributes to the great increase in the diffuser efficiency. Therefore, the influence of excitation frequency on the diffuser efficiency is determined by the location and intensity of the vortexes.

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Abbreviations

A i :

The cross-section i

A e :

The cross-section e

A 1 :

The cross-section of the throat

A 2 :

The cross-section of the big end

H :

The depth of the channel (μm)

L :

The length of the channel (mm)

P :

The pressure of the pump chamber (Pa)

P a :

The atmosphere (Pa)

P i :

The pressure at the cross-section i (Pa)

P e :

The pressure at the cross-section e (Pa)

T :

The period of operation (s)

V dia :

The volume changes in half period (m)3

W :

The width of the throat (mm)

f :

Excitation frequency (s−1)

l :

The characteristic length (mm)

m :

The width of the buffer chamber (mm)

n :

The length of the buffer chamber (mm)

r :

The radius of inlet/outlet (mm)

r t :

The rounding radius (μm)

u m :

The maximum value of the area mean velocity at the throat in a period (m/s)

\( \upsilon \) :

The kinematic viscosity of fluids (m2/s)

Θ :

Angle (°)

ρ :

The fluid density (kg/m3)

η :

The pump efficiency

λ :

The diffuser efficiency

\( \alpha_{i} \) :

The kinetic-energy correction factor at the cross-section i

\( \alpha_{e} \) :

The kinetic-energy correction factor at the cross-section e

\( \overline{u}_{i} \) :

The mean velocity at the cross-section i (m/s)

\( \overline{u}_{e} \) :

The area mean velocity at the cross-section e (m/s)

\( \overline{u}_{d} \) :

The area mean velocity at the throat in the diverging direction (m/s)

\( \overline{u}_{n} \) :

The mean velocity at the throat in the converging direction (m/s)

\( \xi_{n} \) :

The pressure loss coefficient in converging flow

\( \xi_{d} \) :

The pressure loss coefficient in diverging flow

φ n :

The flow rate of micropump through the outlet (m3/s)

φ d :

The flow rate of micropump through the inlet (m3/s)

φ net :

The net flow of micropump (m3/s)

∆P n :

The pressure loss in the converging direction (Pa)

∆P d :

The pressure loss in the diverging direction (Pa)

∆P i–e :

The pressure loss from cross-section i to e (Pa)

∆P i–1 :

The pressure loss from cross-section i to 1 (Pa)

∆P 1–2 :

The pressure loss from cross-section 1–2 (Pa)

∆P 2–e :

The pressure loss from cross-section 2 to e (Pa)

∆P e–i :

The pressure loss from cross-section e to i (Pa)

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Acknowledgements

This work was supported by National Natural Science Foundation of China [Grant Number: 51276082] and Departments of Education and Finance, Jiangsu Province of P. R. China (A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education institutions, PAPD) [Grant Number: SUZHENGBANFA (2014) No. 37].

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Authors and Affiliations

  1. School of Energy and Power Engineering, Jiangsu University, No. 301, Xuefu Road, Zhenjiang, 212013, Jiangsu Province, People’s Republic of China

    Xiuhua He, Nan Lin, Wei Xu & B. B. Uzoejinwa

  2. Agricultural and Bioresources Engineering Department, University of Nigeria, Nsukka, Nigeria

    B. B. Uzoejinwa

  3. Faculty of Science, Jiangsu University, Zhenjiang, People’s Republic of China

    Zhidang Deng

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  1. Xiuhua He
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  2. Nan Lin
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  3. Wei Xu
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  4. B. B. Uzoejinwa
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  5. Zhidang Deng
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Correspondence to Xiuhua He.

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He, X., Lin, N., Xu, W. et al. Experimental and numerical investigation on steady and transient flow in the flat-walled micro-diffuser/nozzle. Microsyst Technol 24, 1853–1861 (2018). https://doi.org/10.1007/s00542-017-3558-7

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  • DOI: https://doi.org/10.1007/s00542-017-3558-7

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