Convective heat transfer in diverging and converging microchannels

Analysis of two-phase pressure drop fluctuations during micro-channel flow boiling

Separating plasma from blood using a microfluidic platform is favored and beneficial in point-of-care diagnostics. This paper presents a microdevice enabling blood plasma separation. In the present work, the microfluidic channel was innovatively designed in such a way that a combination of effects such as Fahraeus effect, bifurcation law, cell-free region, centrifugal action, and constriction–expansion is utilized together for skimming plasma from human blood. Microdevices were designed and fabricated using PDMS (poly-di-methyl siloxane), which is a bio-compatible material. The results obtained are extremely encouraging in terms of separation efficiency. Separation efficiency of almost 100 % has been achieved at moderate hematocrit contents of around 20 %. The separation efficiency for undiluted blood (hematocrit of 45 %) is around 80 %. This microdevice is free from clogging issues that are usually encountered in blood plasma separation devices.

A novel, compact and efficient microchannel arrangement with multiple hydrodynamic effects for blood plasma separation

An overview of liquid–vapor phase change, flow and heat transfer in mini- and micro-channels

Critical heat flux in a 0.38 mm microchannel and actions for suppression of flow boiling instabilities

This paper focuses on experimentally studying the pressure drop characteristics for two-phase flow in microchannels of hydraulic diameter 109 mum , over a relatively large range of heat flux of (0-30 W/cm2) and mass flow rate values (44-1114 kg/m2-s). Three fluid flow regimes (single-phase, two-phase, and dryout) have been covered in this paper, with deionized water as the working fluid. For a given heat flux, the variation of average pressure drop with flow rate can be classified into three distinct regimes. In the first regime (higher flow rate), the pressure drop decreases linearly with decrease in flow rate. In the second regime (lower flow rate), pressure drop increases with decreasing flow rate and reaches a maximum (with a minimum on either side). Finally, in the very low flow rate regime, pressure drop increases rapidly with decreasing flow rate. The average pressure drop in the two-phase regime is predicted well by the annular flow model. In addition to absolute pressure drop values, we also report pressure fluctuations. The magnitude of pressure fluctuations appears to be correlated to the underlying flow regime, such as bubbly, slug, and annular regimes, which have been identified through the flow visualization. An important outcome of this study is the identification of as many as four operating points with similar pressure drop penalty. This may help to choose the right operating conditions for a microchannel-based heat sink for use in cooling electronics. These detailed experimental results are also expected to be useful for modeling two-phase flow in microchannels.

Two-Phase Flow Pressure Drop Characteristics in Trapezoidal Silicon Microchannels

This paper focuses on experimental determination of onset of nucleate boiling
(ONB) and critical heat flux (CHF) at the microscales, and comparison of these with
available correlations. The working fluid is deionised water and microchannel of four
different hydraulic diameters: 65, 70, 107 and 125 m, have been tested. Effect of
hydraulic diameter (65-125 m), mass flux (60-1410 kg/m2s) and heat flux (0-910
kW/m2) on ONB and CHF has been studied in detail. The heat flux for onset of nucleate
boiling increases with hydraulic diameter and mass flux. The critical heat flux tends to
increase with a decrease in hydraulic diameter and with increasing mass flux. The effect
of surface roughness on CHF has also been tested to a limited extent; no clear change in
the CHF value was observed upon changing the surface roughness by an order of
magnitude. The empirical correlations tested in this study predict the experimental data to
varying extent. These results may help better determine the lower and upper limits of heat
flux while designing heat sink for electronic cooling.

R.R. Bhide

Papers

Two-Phase Flow Pressure Drop Characteristics in Trapezoidal Silicon Microchannels

Onset of Nucleate Boiling and Critical Heat Flux with Boiling Water in Microchannels