Heat Transfer Enhancement in Ferrofluids Flow in Micro and Macro Parallel Plate Channels: A Comparative Numerical Study

Abstract

This paper presents a comparative numerical study of heat transfer enhancement in steady, laminar, hydrodynamically fully developed flow of water-based ferrofluids under no magnetic field in micro and macro parallel plate channels subjected to constant equal heat fluxes on its top and bottom, considering Brownian diffusion and thermophoresis of ferroparticles in the base fluid. While the microchannel results match very well with the experimental data for water in an equivalent microtube (Kurtoglu et al., 2014, “Experimental Study on Convective Heat Transfer Performance of Iron Oxide Based Ferrofluids in Microtubes,” ASME J. Therm. Sci. Eng. Appl., 6(3), p. 034501.), the numerically predicted enhancement factor in ferrofluids is much below that for the same microtube. A detailed parametric study points to possible inaccuracies in the experimental results of Kurtoglu et al. (2014, “Experimental Study on Convective Heat Transfer Performance of Iron Oxide Based Ferrofluids in Microtubes,” ASME J. Therm. Sci. Eng. Appl., 6(3), p. 034501.) for ferrofluids. The nanoparticle concentration profiles in the microchannel flow reveal that (a) the nanoparticle concentration at the wall increases with axial distance, (b) the wall nanoparticle concentration decreases with increasing heat flux, and (c) the concentration profile of nanoparticles is parabolic at the exit. A comparison of thermally developing flow in microchannel and macrochannel of the same length (0.025 m) indicates that the enhancement factor at the microchannel exit is 1.089 which is only marginally higher than that at the macrochannel exit in the heat flux range of 20–80 kW/m2. On the other hand, for the thermally fully developed flow in both microchannel and macrochannel of the same length (0.54 m) the maximum enhancement factor for the macrochannel is 1.7, as compared to 1.1 for the microchannel, in the heat flux range of 1–4 kW/m2.