Flow Characteristics in Microchannels

Transition from laminar to turbulent flow was observed by Bau and Pfahler [50]. Investigation of turbulent flow in microchannels is limited. 

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Takuto A, Soo KM, Hiroshi I, Kenjiro S (2000) An experimental investigation of gaseous flow characteristics in microchannels. In International conference on heat transfer and transport phenomena in microscale, Banff... 

The effect of channel diameter on adiabatic two-phase flow characteristics in microchannels. Int. J. Multiphase Flow,... 

Accompanied with rapid development of MEMS technologies, micromachining techniques have been increasingly employed in the integration of microfluidic devices. The liquid flow characteristics in microchannels are important in the design and the process control of MEMS and microfluidic devices. 

Chung PM-Y, Kawaji M (2004) The effect of channel diameter on adiabatic two-phase flow characteristics in micro-channels. Int J Multiphase Flow 30 735-761 Colgan E (2005) A practical implementation of silicon microchannel coolers for high power chips. 

Choquette et al. [10] performed analyses to obtain momentum and thermal characteristics in microchannel heat sinks. A computer code was developed to evaluate the performance capabilities, power requirements, efficiencies of heat sinks, and for heat sink optimization. Significant reductions in the total thermal resistance were found not to be achieved by designing for turbulent flows, mainly due to the significantly higher pumping power requirements realized, which offset the slight increase in the thermal performance. 

Kandlikar SG (2006) Nucleation characteristics and stability considerations during flow boiling in microchannels. Exp Thermal Fluid Sci 30 441-447... 

The model described has been applied to compressible air flow with Reynolds numbers in the range of 500 to 1,500. These values were obtained using Eq. 5 that is also valid for shockwave propagation in a narrow channel [2]. Further, based on the analysis of gas flow characteristics in silicon microchannels [6], the friction coefficient/has been found to be approximately 0.04 for a Reynolds number of 500, while for Reynolds numbers greater than 1,000, the friction coefficient becomes less than 0.005. 

Ying-Tao D, Zhao-Hui Y, Meng-Yu S (2002) Gas flow characteristics in straight silicon microchannels. ChinPhys 11(9) 869-875... 

Due to the predominantly laminar flow present in microchannels, mixing in these devices is largely controlled by molecular diffusion. In the scale of dimensions considered here, i.e. channel widths/depths ranging from a few hundred micrometers to a few millimeters, the mixing process by molecular diffusion is extremely slow, since the mixing time is proportional to df/Dm, where di is the characteristic... 

Kim YM, Kim WS, Lee SH, Baek JY (2005) Effects of surface roughness on the flow characteristics in PDMS microchannel 3rd lEEE/EMBS Special Topic Conference on Microtechnology in Medicine and Biology, 292-295... 

A promising device for measuring nanoscale and microscale channel flows is micro PIV, as mentioned in the previous Sect. How Characteristics in Microchannels. Santiego et al. [62] developed a micro PIV for measuring the instantaneous and mean liquid velocities around a circular cylinder of a diameter of 30 p,m placed in a microchannel. The diameter of the tracer particles ranged from 100 to 300 nm. Visualization of flow field in microchannels [63,64] and Brownian motion of a tracer particle [65] can also provide useful insight. Micro PIV is also used for observing the motion of blood cell in a capillary [66,67]. Micro hot-wire anemometer [68] and Doppler velocimetry [69] have also been recently developed for such studies in which bulk carbon nanotube were used as a wire. 

Judy J, Maynes D, Webb BW (2002) Characterization of frictional pressure drop for liquid flows through micro-channels. Int J Heat Mass Transfer 45 3477-3489 Kandlikar SG, Joshi S, Tian S (2003) Effect of surface roughness on heat transfer and fluid flow characteristics at low Reynolds numbers in small diameter tubes. Heat Transfer Eng 24 4-16 Koo J, Kleinstreuer C (2004) Viscous dissipation effects in microtubes and microchannels. Int J Heat Mass Transfer 47 3159-3169... 

The subject of this chapter is single-phase heat transfer in micro-channels. Several aspects of the problem are considered in the frame of a continuum model, corresponding to small Knudsen number. A number of special problems of the theory of heat transfer in micro-channels, such as the effect of viscous energy dissipation, axial heat conduction, heat transfer characteristics of gaseous flows in microchannels, and electro-osmotic heat transfer in micro-channels, are also discussed in this chapter. 

Mala GM, Li D, Werner C (1997b) Flow characteristics of water through a micro-channel between two parallel plates with electro kinetic effects. Int J Heat Fluid Flow 18 491 96 Male van P, Croon de MHJM, Tiggelaar RM, Derg van den A, Schouten JC (2004) Heat and mass transfer in a square micro-channel with asymmetric heating. Int J Heat Mass Transfer 47 87-99 Maranzana G, Perry I, Maillet D (2004) Mini- and micro-channels influence of axial conduction in the walls. Int J Heat Mass Transfer 47 3993 004 Maynes D, Webb BW (2003) Full developed electro-osmotic heat transfer in microchannels. Int J Heat Mass Transfer 46 1359-1369... 

The experimental data obtained in conventional size channels and micro-channels with diameters between 100 pm and 6.0 mm are examined to further elucidate and understand the differences in two-phase flow characteristics between the microchannels and conventional size channels. Since two separate sets of experiments have been conducted using air and water in acrylic channels with diameters between 500 pm and 6.0 mm, and nitrogen gas-water in fused silica channels with diameters between 50 and 500 pm, the authors refer to the former channels as conventional size channels, and the latter channels as micro-channels for convenience. Two different inlet sections were covered in micro-channel experiments, a gradually reducing section and a T-junction. 

Flow is typically laminar in microchannel devices, although not always rigorously so. Correlations for fully developed laminar flow in perfectly rectangular microchannels have been validated in the literature [33-35]. Transition and turbulent flows in a microchannel have no such consistent treatise, and are highly dependent upon channel shape, aspect ratio, and surface characteristics [36, 37]. 

The characteristics of electrokinetically controlled fluid flow in microchannel manifolds has been studied in a systematic way by Harrison and coworkers [28, 30]. An illustrative demonstration of the potential of this approach is shown in Fig. 2 for the controlled dilution of a fluorescein solution under voltage control. In parallel with a stepwise decrease of the potential applied to the fluorescein reservoir, a decrease of fluorescence signal downstream after the junction is visible in Fig. 2. As long as the ionic strength and pH in each supply channel is the same (same jieo), mass balance is automatically fulfilled, and the incoming flows at the intersection will be exactly balanced by the outgoing flow of the mixed components (otherwise, mass balance would be enforced by additional hydrodynamic or secondary internal flows). This way of mixing fluids was also... 

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