International Journal of Thermofluids (Mar 2025)
Nusselt number and friction factor in zig-zag microchannels subjected to constant heat flux
Abstract
This study quantifies the heat transfer coefficient, pressure drop, Nusselt number and friction factor associated with flow of water in zig-zag microchannels, with square cross-section and sharp edges, when subjected to constant heat flux boundary condition on two sidewalls and bottom wall. Studies are done for Reynolds number ranging from 50 to 500. The heat transfer coefficient, pressure drop, Nusselt number, and friction factor of zig-zag microchannels are higher than that of straight microchannel of similar dimensions irrespective of the Reynolds number. The thermal parameters of the zig-zag microchannel are higher than that of the straight microchannel by ∼ 1.03, at Reynolds number of 50, and ∼ 1.57, at Reynolds number of 500. The hydraulic parameters of the zig-zag microchannel are higher than that of the straight microchannel by ∼ 1.3 and ∼ 1.49 at the lowest and highest Reynolds number, respectively. The thermal enhancement factor of the zig-zag microchannel is greater than unity irrespective of the Reynolds number and it increased with increase in Reynolds number which indicates that the benefits, i.e. enhancement of thermal parameters, outweigh the cost, i.e. increase in hydraulic parameters. The thermal enhancement factor is as high as ∼ 1.38 at the highest Reynolds number. Increase in hydraulic diameter, for a specific Reynolds number, decreases and increases heat transfer coefficient and pressure drop of the zig-zag microchannel, respectively. Increase in hydraulic diameter increases the Nusselt number and decreases friction factor for a specific Reynolds number. For a specific Reynolds number, all thermohydraulic parameters increased with increase in orientation and number of units. Irrespective of the dimensions, increase in Reynolds number leads to increase in heat transfer coefficient, pressure drop, and Nusselt number as well as decrease in friction factor. In addition, this work presents Nusselt number and friction factor correlations associated with flow of water in the zig-zag microchannel when subjected to constant heat flux on three walls; the correlations are unique to this study and beneficial for practising engineers.
