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Date of Publication:2013-01-01

Journal:实验流体力学

Issue:4

Page Number:32-39

ISSN No.:1672-9897

Abstract:In the whole working process of combustion engine, heat energy is produced and part of which transfers to combustion chamber. More than half of that energy transfers to the piston. Therefore, piston needs to be cooled efficiently with increase of thermal loading of combustion engine. When the power density of the piston exceeds 0.3 kW/cm2, the piston must be cooled by cooling chamber. In order to reveal the flow and heat transfer characteristic of nanofluids in cooling chamber, experiments about physical properties, friction drag and heat transfer rates with different types of nanofluids were carried out in a straight circular pipe under steady and vibration state. It is found that, in the steady state, the friction factor of low mass concentration nanofluids is slightly increased for laminar flow by adding nanoparticles into purified water, while almost has no change for turbulent flow. However, the coefficient of heat transfer is enhanced. It is also found that the optimal enhancement appears nearby the turning point of laminar-turbulent flow and increases as mass concentration of nanofluids and coefficient of heat conductivity increase. When heat transfer chamber vibrates synchronously with piston, heat transfer enhancement coefficient is proportional to vibrational frequency and inversely to the Reynolds number. Using the nanofluids instead of purified water, heat transfer is significantly enhanced and the type of nanofluid has a major impact on the heat transfer effect.

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