Experimental and Numerical Investigation Into the Heat Transfer Study of Nanofluids in Microchannel

Abstract

There are very few detailed experimental investigations about the heat transfer behavior of nanofluids in microchannel. The heat transfer behavior of nanofluids in microchannel is investigated. Two microchannels with hydraulic diameters 218 and 303 μm are fabricated by wet etching process on silicon wafer. An experimental set-up having provision of flow in the channel and temperature measurement along with bottom wall temperature is built-up. Alumina nanofluids with concentrations of 0.25 vol. %, 0.5 vol. %, and 1 vol. % with 45 nm are prepared, stabilized, and characterized by standard methods. The thermal conductivity and viscosity used in the study were measured and analyzed. The base fluids used are water and ethylene glycol. The effect of volume fraction, channel size, particle size, and base fluids are presented and analyzed. An important phenomenon of dispersion is observed. In addition, numerical modeling is carried out by using discrete phase approach. Shear induced particle migration is identified to be the reason of difference for dispersion of particles. The Brownian and thermophoretic forces are responsible for major changes in particle concentration and their movement. Also, it was found that better heat transfer characteristics can be obtained by higher concentration of nanofluids and by low viscous base fluids.

Thermally “<italic>Smart</italic>” Characteristics of Nanofluids in Parallel Microchannel Systems to Mitigate Hot Spots in MEMS

“…U has been reported to exhibit worst flow distribution [10] followed by I and the distribution is best in case of Z. Therefore, a detailed study on flow characteristics of water and nanofluid as well as configurations with respect to reported data [10,18] in accordance to protocol reported by the present authors [17]. …”

“…Consequently, the non-homogeneous behavior of nanofluids was also reported [16,17] and this placed a hurdle across modeling thermo hydraulics of nanofluids in small dimensional systems such as microchannels. Singh et al [18] reported the thermal behavior of nanofluid in single microchannel and used DPM (Discrete Phase Model) model for understanding particle migration within the channel but the studies were limited to a single microchannel.…”

Particle and thermohydraulic maldistribution of nanofluids in parallel microchannel systems

“…Uniform heat flux has been applied at the bottom and side walls for heat transfer cases and the top wall has been considered adiabatic. The present numerical model has been validated with respect to the published reports by Siva et al [9] and Singh et al [16]. The former study discusses in details flow maldistribution of water in parallel microchannel systems whereas the later study comprises detailed report on the thermo-hydraulic performance of nanofluids in single microchannel system.…”

“…Overall there are few reports which concentrate on the modeling of flow and heat transfer characteristics of with nanofluids in microchannels but all these consider nanofluids as homogeneous single component fluids for analysis; which has been conclusive reported [16] to be an inefficient and incorrect assumption. Thorough survey of literature reveals there are no reports which try to understand the effects of flow and particle concentration distribution of nanofluids (treated as non-homogeneous twin component fluids) in parallel microchannels and its impact vis-à-vis thermal capabilities and uniformity.…”

“…Later, the attention shifted towards obtaining higher thermal transport by modification of the flow field or the fluid itself so as to bring in the practical implementation aspects, such as enhancement of heat transfer using offset fins or employing nanofluids as the working fluid [15,16]. Nanofluids, which are engineered dilute and stable colloidal suspensions of metallic and/or ceramic nanoparticles in a conventional base fluid, exhibit thermal conductivity values ~ 20-150 % higher than the base fluids [17].…”