Conjugated heat transfer in heat sinks for low-grade waste heat recovery

Purpose This study aims to theoretically and experimentally analyze conjugated conductive–convective heat transfer in laminar flow within rectangular microchannel heat sinks. Design/methodology/approach A three-dimensional steady-state conjugated heat transfer problem was solved using the generalized integral transform technique (GITT), uniquely reformulating the channel and substrate regions as a single domain with variable properties. This single-domain modeling strategy enables seamless treatment of multi-region problems without the complexity of multiple coupled integral transformed domains or mesh-based discretization with interfaces refinement typically required in conventional numerical methods. Experimental data, obtained from a custom-built thermohydraulic circuit using water and water/ethylene glycol (50 Wt.%) as working fluids, were used to validate the model. Findings The GITT solutions achieved a root-mean-square error of at most 10−2 and, upon comparison to experimental measurements, demonstrated good predictive accuracy. Unlike conventional microchannel correlations, the results captured the critical influence of the substrate on heat flux distribution, revealing deviations that arise primarily from lengthwise heat conduction effects. Originality/value This work introduces a novel application of GITT with single-domain modeling to practical heat sink configurations, offering a robust, efficient and accurate hybrid numerical–analytical framework. Compared to traditional discretization-based approaches, this method simplifies the treatment of conjugated problems and significantly reduces computational cost while faithfully capturing substrate conduction effects that are often overlooked in standard simulations and classical correlations.