AUTHOR=Wang Li , Liu Qiusheng 

TITLE=Transient Heat Transfer Characteristics of Twisted Structure Heated by Exponential Heat Flux

JOURNAL=Frontiers in Energy Research

VOLUME=9

YEAR=2021

URL=https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2021.771900

DOI=10.3389/fenrg.2021.771900

ISSN=2296-598X

ABSTRACT=<p>This study was conducted to investigate the transient heat transfer characteristics of a twisted structure. The twisted structure was heated according to exponential function (<inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">Q=</mml:mi><mml:msub><mml:mi mathvariant="normal">Q</mml:mi><mml:mi mathvariant="normal">0</mml:mi></mml:msub><mml:mi mathvariant="normal">×exp</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mrow><mml:mi mathvariant="normal">t</mml:mi><mml:mo>/</mml:mo><mml:mi mathvariant="normal">τ</mml:mi></mml:mrow></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math></inline-formula>, where <inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Q</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula> is the initial heat generation rate, W/m<sup>3</sup>; <italic>t</italic> is time, s; and <italic>τ</italic> is the period of heat generation rate). A wide range of τ from 37 ms to 14 s was applied for the experimental study. A platinum plate with five pitches (each was 180° twisted with 20 mm in length) was used in the experiment. Helium gas with inlet temperature of 298 K under 500 kPa was used as the coolant. The heat transfer coefficient is found to increase with the decrease of τ, and the transition point was estimated to be at <inline-formula id="inf3"><mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>τ</mml:mi><mml:mo>≈</mml:mo><mml:mn>1</mml:mn><mml:mi>s</mml:mi></mml:mrow></mml:math></inline-formula>, which means that, when the increasing ratio of heat generation rate satisfies <inline-formula id="inf4"><mml:math id="m4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mfrac><mml:mrow><mml:mi>d</mml:mi><mml:mi>Q</mml:mi></mml:mrow><mml:mrow><mml:mi>d</mml:mi><mml:mi>t</mml:mi></mml:mrow></mml:mfrac><mml:mo>≥</mml:mo><mml:msub><mml:mi>Q</mml:mi><mml:mn>0</mml:mn></mml:msub><mml:mo>⋅</mml:mo><mml:msup><mml:mi>e</mml:mi><mml:mi>t</mml:mi></mml:msup></mml:mrow></mml:math></inline-formula>, the heat transfer enhancement phenomenon will be observed. The response analysis for transient heat transfer at fluid-solid interface was conducted by applying the concept of penetration depth. It is considered that, when the penetration depth is smaller than the thermal boundary thickness, the heat transfer from the interface (wall surface) to the fluid domain is not fully developed during the disturbance.</p>