In the absence of dispersants, surfactants or other deposition inhibiting techniques, nanoparticles contained in a base fluid could potentially deposit on channel walls. Nanoparticle layering has been shown to impact heat transfer coefficient, alter hydrodynamic characteristics including viscosity and flow regime, and influence the onset of boundary layers. The rate of deposition is a function of nanoparticle size, heat flux, microchannel hydraulic diameter, fluid velocity, temperature, adhesion properties and volume fraction. This paper presents an analytical investigation of nanoparticle deposition in microchannel heat exchanger systems. The objective of this study is to correlate the rate of deposition with nanoparticle size, microchannel hydraulic diameter, heat flux and volume fraction for transient flow conditions in which Brownian diffusion and thermophoresis are appreciable slip mechanisms of nanoparticle transport. A two-component four-equation nonhomogeneous thermal equilibrium model for mass, momentum and energy in nanofluids that includes nanoparticle mass transport into the channel walls is used in this analysis. An analytical model representing the transient distribution of nanoparticles in a channel is proposed.

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