Abstract
Flow characteristics and heat transfer performances of carboxymethyl cellulose (CMC) aqueous solutions in the microchannels with flow control structures were investigated in this study. The researches were carried out with various flow rates and concentrations of the CMC aqueous solutions. The results reveal that the pin-finned microchannel has the most uniform temperature distribution on the structured walls, and the average temperature on the structured wall reaches the minimum value in cylinder-ribbed microchannels at the same flow rate and CMC concentration. Moreover, the protruded microchannel obtains the minimum relative Fanning friction factor f/f0, while, the maximum f/f0 is observed in the cylinder-ribbed microchannel. Furthermore, the minimum f/f0 is reached at the cases with CMC2000, and also, the relative Nusselt number Nu/Nu0 of CMC2000 cases is larger than that of other cases in the four structured microchannels. Therefore, 2000 ppm is the recommended concentration of CMC aqueous solutions in all the cases with different flow rates and flow control structures. Pin-finned microchannels are preferred in low flow rate cases, while, V-grooved microchannels have the minimum relative entropy generation S’/S0’ and best thermal performance TP at CMC2000 in high flow rates.
Highlights
In microtechnology a microchannel is defined as a channel with a hydraulic diameter smaller than 1 mm [1]
As the heat flux densities increases in the automotive, aerospace, air separation, integrated circuit, biological, power engineering, chemical engineering and cryogenic industries, the heat transfer of fluid flow in the microfluidic devices has gained tremendous attention and the requirement of a flow control structure with large heat removal and lower pressure penalty has become more urgent in recent years
Xie et al [11] studied the heat transfer in channels with protrusions, and the results shows that protrusion structures can effectively enhance the heat and mass transfer of carboxymethyl cellulose (CMC) solutions with low penalty in specific cases
Summary
In microtechnology a microchannel is defined as a channel with a hydraulic diameter smaller than 1 mm [1]. Li and Wang et al [13] investigated the 3-dimensional flow development in curved rectangular ducts with continuously varying curvature using Particle Image Velocimetry (PIV) and numerical simulations, and the results revealed complex changes in the flow pattern with respect to both the flow and geometric parameters All these studies show that flow control structures can effectively enhance or influence heat transfer in microchannels. The previous literatures show that enhanced heat transfer with low pressure penalty can be expected by means of the combination of microchannel heat sinks with different flow control structures and shear-thinning power law fluids. In what follows, the heat transfer and flow characteristics of CMC aqueous solutions of different concentration in microchanneld with four flow control structures under various flow rated are analyzed in detail
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