Small channels have been an area of interest since the 1970s owing to their enhanced heat transfer characteristics. However a wide number of studies in literature show inconsistent results. In this work, an experimental set-up has been designed and constructed to investigate pressure drop and heat transfer characteristics of single-phase water flow in rectangular multiport minichannels. Laminar flow inside three minichannels with different hydraulic diameters and different port numbers were examined under a constant heat flux boundary condition. The results are presented in terms of Poiseuille number (Po) and average Nusselt number (Nu). Generally, average Nusselt number results and Poiseuille number results showed good agreement with constant Po theory and constant Nu theory, excluding developing effects and experimental errors. On the other hand, developing effects are found to be increasing as hydraulic diameter decreases. Similarly, constant Nu value showed a decrease with increasing hydraulic diameter. The experimental results are compared with conventional correlations. While the agreement with conventional correlations is satisfactory, the predictions of the correlations overestimated most of the results. No early transition was observed for Reynolds number (Re) smaller than 1800.

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