It is known that heat transfer between two liquid-reservoirs maintained at different temperatures and connected to each other by a capillary bundle is markedly enhanced by oscillatory flow in the bundle. In this paper, first, the effects of physical properties of the working liquid on the enhanced-heat flow rate are investigated. Second, the optimum operating condition maximizing the ratio of the:enhanced heat flow rate to power input is examined. Finally, to increase further the ratio, a novel type with-a-phase shift between oscillatory flows in adjacent tubes is proposed.