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A synthetic jet is a zero-net-mass-flux device, which synthesizes stagnant air to form a jet, and is potentially useful for cooling. Due to the inherent suction and ejection processes in a synthetic jet, its utility in a confined enclosure is not obvious. The synthetic jet impingement heat transfer characteristics inside a rectangular duct are studied in this paper. In addition, the effect of cross-flow created using either fans or another synthetic jet on its heat dissipation capability is examined. Experiments are conducted for different jet Reynolds numbers (Re), in the range of 950-4000, at different offset positions of the synthetic jet with respect to a heated block flush mounted on one surface of the duct. The height of the duct is the same (25 mm) for all measurements while the width is varied between 110 mm and 330 mm in order to examine the effect of confinement on the heat transfer coefficient. The change in the width of the duct is found to have a negligible effect on heat transfer. The heat transfer coefficient is found to be more with synthetic jet direct impingement (150 W/m2 · K) than with combined flow (both impingement and cross-flow) (134 W/m2 · K) or with only cross-flow (45 W/m2 · K) in the duct. The offset of the synthetic jet from the center of the heated block is found to drastically reduce the heat transfer. These results are expected to be useful for designing synthetic jet-based cooling solutions.