Considerable improvement of heat transfer efficiency for power-law fluids in flat-plate heat exchangers is obtainable by inserting in parallel an impermeable resistless sheet to divide an open duct into two channels for conducting double-flow operations. The influence of the power-law index on average Nusselt numbers in double-pass parallel-plate heat exchangers under uniform wall fluxes has been investigated theoretically. The complete solution was obtained using an eigenfunction expansion technique in terms of power series for the homogeneous part and an asymptotic solution for the non-homogeneous part. The theoretical predictions show that the effect of double-pass operations for power-law fluids results in the heat-transfer efficiency enhancement as compared with those in an open conduit (without an impermeable resistless sheet inserted). The effects of impermeable-sheet position and power consumption increment for power-law fluids have also been presented.
International Journal of Heat and Mass Transfer 61, pp.464-474