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Research Papers: Micro/Nanoscale Heat Transfer

Hydrodynamic Effects on Particle Deposition in Microchannel Flows at Elevated Temperatures

[+] Author and Article Information
Zhibin Yan

School of Mechanical and
Aerospace Engineering,
Nanyang Technological University,
50 Nanyang Avenue,
Singapore 639798, Singapore
e-mail: zyan3@e.ntu.edu.sg

Xiaoyang Huang

Mem. ASME
School of Mechanical and
Aerospace Engineering,
Nanyang Technological University,
50 Nanyang Avenue,
Singapore 639798, Singapore
e-mail: mxhuang@ntu.edu.sg

Chun Yang

Mem. ASME
School of Mechanical and
Aerospace Engineering,
Nanyang Technological University,
50 Nanyang Avenue,
Singapore 639798, Singapore
e-mail: mcyang@ntu.edu.sg

1Corresponding author.

Presented at the 5th ASME 2016 Micro/Nanoscale Heat & Mass Transfer International Conference. Paper No. MNHMT2016-6628.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 23, 2016; final manuscript received June 11, 2017; published online August 16, 2017. Assoc. Editor: Robert D. Tzou.

J. Heat Transfer 140(1), 012402 (Aug 16, 2017) (10 pages) Paper No: HT-16-1414; doi: 10.1115/1.4037397 History: Received June 23, 2016; Revised June 11, 2017

Particulate fouling and particle deposition at elevated temperature are crucial issues in microchannel heat exchangers. In this work, a microfluidic system was designed to examine the hydrodynamic effects on the deposition of microparticles in a microchannel flow, which simulate particle deposits in microscale heat exchangers. The deposition rates of microparticles were measured in two typical types of flow, a steady flow and a pulsatile flow. Under a given elevated solution temperature and electrolyte concentration of the particle dispersion in the tested flow rate range, the dimensionless particle deposition rate (Sherwood number) was found to decrease with the Reynolds number of the steady flow and reach a plateau for the Reynolds number beyond 0.091. Based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, a mass transport model was developed with considering temperature dependence of the particle deposition at elevated temperatures. The modeling results can reasonably capture our experimental observations. Moreover, the experimental results of the pulsatile flow revealed that the particle deposition rate in the microchannel can be mitigated by increasing the frequency of pulsation within a low-frequency region. Our findings are expected to provide a better understanding of thermally driven particulate fouling as well as to provide useful information for design and operation of microchannel heat exchangers.

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References

Figures

Grahic Jump Location
Fig. 1

(a) Schematic of the microfluidic system for the direct observation of the particle deposition kinetics in microchannels at elevated temperatures, inset: cross section view of the pulsation generation unit (PGU); (b) and (c) Images of the microchip and PGU fabricated in this study

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Fig. 2

Schematic of microparticle transport in a microchannel. The forces on the particle are the van der Waals force (Fvdw), gravity force (FG), electric double layer (EDL) force (Fedl), thermophoretic force (FT), and hydrodynamic lift force (FL). The particle radius is ap, the minimum separation distance between the particle surface and the bottom surface of the microchannel is h, the flow velocity distribution is U(y), and heat is conducted from the neighboring heating channels to the deposition microchannel (the figure is not drawn to scale).

Grahic Jump Location
Fig. 3

(a) Number of deposited particles per unit area versus time for different sample flow rates in the microchannel (0.01 mL/h, 0.025 mL/h, 0.1 mL/h, 0.5 mL/h, 2 mL/h); (b) Dimensionless deposition rate (Sherwood number) versus the Reynolds number of the sample flow. Solid square (▪) indicates the measured Sherwood number Shexp determined by Eq. (2), and open square (◻) shows the predicted Sherwood number Shnum by Eq. (10) from numerical modeling. The dotted line shows the least-square fitting curve. Inset shows the Reynolds numbers of the sample fluid as a function of sample flow rate. Data are for the fluorescent polystyrene particles dispersed in a NaCl solution (5 × 10−4 M). The solution temperature is kept at 324.85 K.

Grahic Jump Location
Fig. 4

(a) Dimensionless particle–microchannel interaction potential V¯ versus the dimensionless separation distance H for different Reynolds numbers of the sample flow; (b) The energy barrier (shown by -◻-) and the interaction potential at H = 10 (shown by -▪-) as a function of the Reynolds number; data are calculated by using Eq. (12) for the fluorescent polystyrene particles dispersed in a NaCl solution (5 × 10−4 M). The solution temperature is kept at 324.85 K. The right dotted square indicates the secondary energy minimum region, and the left dotted square indicates the PEM region.

Grahic Jump Location
Fig. 5

(a) The amplitude of the volume flow rate of oscillatory flow (Qamp) versus oscillation frequency (f). The dotted line represents the average value for the amplitude of oscillatory flow rate (Qamp). Inset shows that the flow rate of pulsatile flow (Qpul) is equal to the superposition of a steady flow component (Qs) and an oscillatory flow component (Qos). (b) The normalized particle deposition rate Sh/Sh0 versus the flow oscillation frequency of the microchannel flow in a PMMA microchannel. Polystyrene microparticles (diameter: 930 nm) are dispersed in a NaCl solution (5 × 10−4 M). The flow rate of the steady flow is maintained at 1 mL/h, and the solution temperature is kept at 324.85 K. The amplitude of the flow oscillation (Qamp) is 0.09 mL/h. The dotted line represents the least-squares fitting curve.

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