Effect on heat transfer of particle migration in suspensions of nanoparticles flowing through minichannels

Thermal management is one of the greatest challenges in maintaining the functionality and reliability of high-speed micro-electronic systems such as MEMS and NEMS. This requires development of high performance heat transfer media, which can not only flow through micro- and nano-channels under local operating conditions, but also carry as more heat as possible out of the system. Recent work has shown that suspensions of nanoparticles with a size considerably smaller that 100nm but with thermal conductivity orders of magnitudes higher that the base liquids have a greater potential as a high energy carrier for the micro- and nano-systems. However, it is also known that particles in a suspension undergoing a shearing action may migrate, hence lead to non-uniformity. This indicates that the efficiency of heat transfer in the micro- and nano-channels may not be as superior as expected, which bears significance to the system design and operation. This work aims at addressing this issue by examine the effect of particle migration on heat transfer in small channels. This involves development of both flow and heat transfer models, and numerical solution to the models. The flow model takes into account the effects of the shear-induced and viscosity gradient-induced particle migrations, as well as selfdiffusion due to the Brownian motion, which is coupled with an energy equation. The results show that particle migration leads to concentration of particles in the wall region can be much lower than that in the core region. Particle migration is also shown to increase the Nusselt number under both constant temperature and constant heat flux conditions.