A capillary flow model for discretely graded porous media in two phase heat transfer applications

•Modification to homogenous wick model proposed utilising the product of Kozeny-Carman constant for spherical particles and wick tortuosity squared.•A new analytical model for capillary flow in discretely graded wicks is presented and validated against experimental data, featuring standard error <10%.•Graded wicks of large followed by smaller particles show an average of 9% faster capillary rise times than homogeneous wick counterparts while the reverse orientations show ∼150% slower rise times.•It is shown that appropriately designed graded wicks can substantially enhance imbibition rates by up to 175%.•Graded wicks with a 95:5 length ratio for 250 µm to 70− 100 µm diameter particles, respectively, demonstrated the highest imbibition rates of >11.3 mm/s.