Thermal performance model was developed for a cross-flow aluminum heat exchanger with relatively short passage. Appropriate heat transfer coefficient and friction factor equations for laminar channel flow were obtained considering developing regions. The heat exchanger was analyzed using the unmixed cross-flow ${epsilon}$-NTU relationship considering leak-age between streams. Thermal contact between corrugations and plates was also considered. Tests were separately conducted for two samples - one made of non-treated aluminum sheets, and the other made of varnish-treated ones. The samples were made by stacking corrugations and plates one after another. The model adequately predicted the thermal performance and pressure drop of the non-treated heat exchanger. The thermal performance of the varnish-treated one was $7{sim}12%$ overpredicted, and the pressure drop of the varnished-treated heat exchanger was $5{sim}15%$ underpredicted. The air leakage ratio of the non-treated heat exchanger was $23{sim}26%$. The ratio decreased to less than $10%$ with the varnish treatment.