Abstract
As electronic devices become smaller and more powerful, the demand for micro-scale thermal management becomes necessary in achieving a more compact design. One way to do that is enhancing the forced convection heat transfer by adding nanoparticles into the base liquid. In this study, the nanofluid forced convection heat transfer coefficient was measured inside stainless-steel microchannels (ID = 210 μm) and heat transfer coefficient as a function of distance was measured to explore the effects of base liquid, crystal phase, nanoparticle material, and size on heat transfer coefficient. It was found that crystal phase, characteristics of nanoparticles, the thermal conductivity and viscosity of nanofluid can play a significant role on heat transfer coefficient. In addition, the effects of man-made and commercial TiO2 on heat transfer coefficient were investigated and it was found that man-made anatase TiO2 nanoparticles were more effective to enhance the heat transfer coefficient, for given conditions. This study also conducted a brief literature review on nanofluid forced convection heat transfer to investigate how nanofluid heat transfer coefficient as a function of distance would be affected by effective parameters such as base liquid, flow regime, concentration, and the characteristics of nanoparticles (material and size).
Highlights
Over the last century, the researchers have tried to enhance the forced convection heat transfer coefficient in the macroscale
The results indicated that: (a) The thermal developing length of nanofluids was greater than that of the base liquid and the thermal developing length of nanofluid increased with an increase of particle concentration. (b) The nanofluid enhanced the heat transfer coefficient significantly, at the entrance region and at higher Reynolds numbers
The forced convection heat transfer coefficient was measured as a function of distance for different base liquids and nanofluids
Summary
The researchers have tried to enhance the forced convection heat transfer coefficient in the macroscale. Power enhancements and the miniaturization of devices have driven researchers to enhance the thermal management of devices in microscale These more compact technologies require the use of smaller channels. The thermal physical properties of working fluids can be modified, by adding nanoparticles into the base liquid which is called nanofluid. It was observed that adding nanoparticles has great potential to enhance the forced convection heat transfer coefficient, because of thermal conductivity enhancement and energy transportation inside the nanofluid [2,3]. It was observed that the forced convection heat transfer coefficient of nanofluids inside microchannels, along with other physical properties, depend on channel geometry, channel size (diameter and length), flow regime, base liquid, surfactant and homogeneity of nanofluids, concentration, and characteristics of nanoparticles such as size, material, shape, and coating. Recent investigations [8] indicated that adding nanoparticles would increase thermal conductivity and viscosity of working fluids, as results optimization of effects of nanoparticles on thermal conductivity and viscosity of nanofluids is necessary
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