Heat transfer and pressure drop in a reciprocating blind duct with swirls generated by a lateral entry jet

This experimental study simulates the advanced piston cooling passage of a marine propulsive diesel engine to examine the heat transfer performance of a reciprocating square blind duct with swirl induced by injecting a lateral jet. The detailed Nusselt number (Nu) distributions over two opposite walls, namely the jet wall and the back wall, of the reciprocating blind duct at channel (jet) Reynolds numbers Re(Rej) of 1500 (6000), 2000 (8000), 3000 (12,000), 5000 (20,000), 7000 (28,000) and 10,000 (40,000) with reciprocating frequencies of 0, 0.67, 0.83, 1 and 1.17 Hz are measured using the steady-state infrared thermo-graphic method. The jet flows and the jet-induced swirl, which improve heat transfer performance considerably, interact with the reciprocating and buoyancy forces to exhibit synergistic impacts on Nu distributions. This is demonstrated by comparatively examining a set of full-field Nu distributions to illustrate the Nu variations responding to the changes of Rej, pulsating (Pu) and reciprocating Grashof (Grp) numbers. The individual and interdependent channel Reynolds number (Re), Pu and Grp   effects on the area-averaged Nusselt number (Nu¯) are parametrically analyzed to devise Nu¯ correlations. A comparison with reported Nu¯ data for the various reciprocating channels indicates the favorable heat transfer performance for the present jet-swirl system. Due to the combined Re, Pu and Grp   effects, the Nu¯ over the jet wall and back wall are respectively raised to 0.78–1.3 and 0.8–1.51 times of the static heat transfer levels. Nevertheless, the high pressure potentials required to facilitate the lateral jet and to overcome the viscous frictions and the pressure drop through the enlargement of flow passage are observed, leading to significant increases of the pressure drop coefficient (f) from the static smooth pipe flow reference (f∞). The thermal performance factors (η) defined on the basis of constant pumping power consumption for such flow configuration relative to the smooth pipe flow condition and the static jet-swirl condition are evaluated.