Heat Transfer Investigation in an Engine ExhaustType Pulsating Flow

Abstract

In many practical engineering situations, such as in the exhaust pipes of Internal Combustion Engines, heat is transferred under conditions of pulsating flow. In these conditions, the heat transfer mechanism is affected by the pulsating flow parameters. The objective of the present work was to experimentally investigate heat transfers for pulsatile turbulent flows in a pipe. A specific experimental apparatus able to reproduce a pulsating flow representative of the engine exhaust was designed. A stationary turbulent hot air flow with a Reynolds number ranging from 1.8x10 4 to 3.5x10 4 , based on the time averaged velocity, is excited through a pulsating mechanism and exchanges thermal energy with a steel pipe. Pulsation frequency ranges from 10 to 95 Hz. The effects of pulsation frequency and pipe length on the convective heat transfer were evaluated. It was observed that flow pulsation enhances convective heat transfers in comparison with the steady case. The results highlight that, when the flow is excited with a pulsation frequency equal to a resonance mode of the system, a local maximum of the heat transfer rate appears. This behaviour was found to be independent of the pipe length. Instantaneous measurements of air velocity and temperature demonstrated that the increase in the energy axial advection due to the oscillating component of the velocity is the major cause of the heat transfer enhancement.