This article describes a detailed experimental investigation of heat transfer in a reciprocating square-sectioned duct fitted with transverse ribs. The parametric conditions involved several nominal Reynolds numbers ranging from 2, 700 to 9, 000 with five different reciprocating frequencies, namely, 0, 0.415, 0.83, 1.25, and 1.67 Hz. This resulted in a pulsating number, which represented the ratio of reciprocating force to inertial force effect, varying from 0 to 10.5. Inside the reciprocating ribbed duct the typical effects of flow reciprocation on heat transfer were illustrated by examining the periodic spatial-time distributions of Nusselt number. The amplitude of the timewise variable reciprocating Nusselt number was dependent on the axial location and increased with increases of Reynolds number. The time-averaged heat transfer due to flow reciprocation could be accounted for by the pulsating number and, in general, the heat transfer level increased with increases of the pulsating number. At a pulsating number of 10.5, the spatial-time-averaged Nusselt number value could reach about 165% of the equivalent stationary level, which demonstrated the possibility to further enhance the heat transfer via the use of ribs for reciprocating ducts. This study has been motivated by the need to improve the cooling performance of the internal coolant passages inside the pistons of heavy-duty marine diesel engines and to account for the effect of reciprocating motion on the heat transfer within these coolant channels.
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