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An efficient micromixer combining oscillatory flow and divergent circular chambers

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Abstract

Oscillatory/pulsatile flow is an important approach for mixing enhancement at micro scales. Here we report a micromixer that consists of a microfluidic oscillator and divergent chambers. The oscillator autonomously produces an oscillatory flow, which further causes efficient stretching and folding of the fluids to improve the mixing. Testing results show that the design works well at relatively high flow rates and high viscosities. At around 40 ml/min, the mixing index can reach 0.97 at 8 mPa s, and 0.89 at 12 mPa s, respectively. Efficient mixing can also be achieved at viscosity ratios of up to 10 (20 mPa s:2 mPa s). Application of the micromixer for preparation of nano sized RDX (cyclotrimethylenetrinitramine) is investigated. Using the anti-solvent crystallization method, nano-RDX particles with the size ranging from 150 to 900 nm are obtained. Its thermal decomposition characteristics are tested and compared with the raw RDX.

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Abbreviations

A :

The pre-exponential factor (–)

D :

Diffusion coefficient (m2/s)

E a :

The apparent activation energy (kJ/mol)

f :

Frequency of the oscillatory flow (Hz)

\(I_{i}\) :

Pixel intensity (–)

\(I_{mix}\) :

Pixel intensity after complete mixing (–)

\(I_{unmix}\) :

Pixel intensity before mixing (–)

L :

Characteristic length of fluid channel (mm)

P o :

Operating pressure of the microfluidic oscillator (bar)

Q :

Flow rate (m3/s)

\(\bar{Q}_{1}\) :

Time-averaged flow rate of the oscillatory flow applied at inlet 1 (ml/min)

Q 2 :

Flow rate at inlet 2 (ml/min)

R :

Gas constant (J/(K mol))

Re :

Reynolds number (–)

T :

Oscillation period (s)

t :

Time (s)

T m :

The temperature of molten endothermic peak (°C)

T p :

The temperature of thermal decomposition exothermic peak (°C)

U :

Fluid velocity (m/s)

β :

Heating rate (°C/min)

μ :

Fluid viscosity (Pa s)

ν :

Fluid kinematic viscosity (m2/s)

\(\sigma\) :

Mixing index (–)

τ :

Normalized mixing time, τ = t/T (–)

χ:

Viscosity ratio (–)

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Acknowledgements

This work was supported in part by the National Natural Science Foundation of China (51575282), the Fundamental Research Funds for the Central Universities (30915118803; 30916012101), the Priority Academic Program Development of Jiangsu Higher Education Institutions.

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Correspondence to H. M. Xia.

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Wu, J.W., Xia, H.M., Zhang, Y.Y. et al. An efficient micromixer combining oscillatory flow and divergent circular chambers. Microsyst Technol 25, 2741–2750 (2019). https://doi.org/10.1007/s00542-018-4193-7

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