Correlation Between Wall Heat Transfer And Characteristics Of Pulsating Flow In A Rectangular Tube Toward An Automobile Exhaust System

Abstract

- The objective of this study is to investigate experimentally the effect of pulsation frequency on the heat transfer characteristics and the mechanism of the pulsation flow, which is representative of the operating conditions of the engine exhaust flow. The experimental apparatus consists of a rotating disk with holes that converts steady hot air flow rate into a pulsating flow to exchange heat energy with external air. The fluid temperature is measured by thermocouples, and the wall temperature is measured by thermography. It is found that heat transfer enhancement due to pulsation does not occur at frequencies below 25 Hz, even though the velocity amplitude is large. In order to investigate the cause of this phenomenon, the flow field is measured by PIV(Particle Image Velocimetry) and the turbulent kinetic energy is evaluated. It is clarified that the turbulent kinetic energy near the wall is small at frequencies below 30 Hz, despite the large velocity amplitude. From the time series of velocity data, it was observed that the turbulence is extremely small during the acceleration phase of the fluid. As a result, the turbulent mixing during the acceleration phase is suppressed, and the time-averaged turbulent kinetic energy becomes small, which is thought to have suppressed heat transfer enhancement. This is the first attempt to experimentally link heat transfer and flow structure fluctuations in a pulsating flow, which is achieved by unsteady measurement of the flow field using PIV and calculation of the turbulent kinetic energy.