Sub-Millimeter-Scale Measurement of Local Convective Heat Transfer Coefficient Exceeding 100 W/(m^2-K) Using an Optical Pump-Probe Method

TL;DR

This paper introduces a novel optical SPS method that measures local convective heat transfer coefficients exceeding 100 W/(m^2-K) with high accuracy, surpassing previous frequency limitations of traditional pump-probe techniques.

Contribution

The study develops and demonstrates an optical SPS method capable of measuring high local convective heat transfer coefficients at lower frequencies, improving measurement accuracy and range.

Findings

Successfully measured h_c > 100 W/(m^2-K) with uncertainties under 10%

Expanded measurement frequency range from 10 MHz to 1 Hz

Provided detailed Nusselt number distribution in impingement heat transfer

Abstract

Conventional methods for measuring the local convective heat transfer coefficient (h_c) often rely on simplifying assumptions that can compromise accuracy. Pump-probe methods like time-domain thermoreflectance (TDTR) avoid these assumptions but are limited to h_c values larger than 30 kW/(m^2-K) due to modulation frequency constraints. This study introduces an optical-based Square-Pulsed Source (SPS) method, expanding the frequency range from 10 MHz to 1 Hz, enabling measurements of h_c values above 100 W/(m^2-K) with uncertainties under 10%. The efficacy of the SPS method is demonstrated through measurements of local h_c in an impingement heat transfer process with a single round gas jet. The local Nusselt number distribution is compared with existing literature correlations, offering insights into convective heat transfer phenomena. This study presents a novel tool for measuring local intrinsic convective heat transfer coefficients, enhancing the understanding of local convective heat transfer.