Thermal characterization of microscale heat convection in rare-gas environment by a steady-state “hot wire” method

Abstract

As power electronics shrinks down to sub-micron scale, the thermal transport from a solid surface to environment becomes significant. Under circumstances when the device works in rare gas environment, the scale for thermal transport is comparable to the mean free path of molecules, and is difficult to characterize. In this work, we present an experimental study about thermal transport around a microwire in rare gas environment by using a steady state "hot wire" method.Unlike conventional hot wire technique of using transient heat transfer process, this method considers both the heat conduction along the wire and convection effect from wire surface to surroundings. Convection heat transfer coefficient from a platinum wire in diameter 25 m to air is characterized under different heating power and air pressures to comprehend the effect of temperature and density of gas molecules. It is observed that convection heat transfer coefficient varies from 14 W/m 2 K at 7 Pa to 629 W/m 2 K at atmosphere pressure. In free molecule regime, Nusselt number has a linear relationship with inverse Knudsen number and the slope of 0.274 is employed to determined equivalent thermal dissipation boundary as 7.03×10 -4 m. In transition regime, the equivalent thermal dissipation boundary is obtained as 5.02×10 -4 m. Under a constant pressure, convection heat transfer coefficient decreases with increasing temperature, and this correlation is more sensitive to larger pressure. This work provides a pathway for studying both heat conduction and heat convection effect at micro/nanoscale under rare gas environment, the knowledge of which is essential for regulating heat dissipation in various industrial applications.

Thermal Exchange of Glass Micro-Fibers Measured by the 3ω Technique

“…by Gao et al where a coefficient of 600 W.m −2 .K −1 has been measured on suspended platinum wire [25]; values even much higher have been found in the case of carbon nanotubes [46]. The difference could originate from the fact that the different micro or nano-structures do not have the same surface roughness and dimensions, but also because Gao and coworkers, for instance, have used an experiment involving much higher ∆T along with different data treatment techniques.…”

“…Most of the previous works are dedicated to the measurement of thermal conductivity of the liquid or sensing the amount of a specific liquid or gas. Recently in 2018, Gao and coworkers have reported on the thermal transport around a micro-wire based on a steady-state hot-wire method [25]. They used a platinum (Pt) wire with a diameter of 25 µm acting as thermometer and heater.…”

Determinación experimental de la transferencia de calor por convección en hilos finos en atmósferas enrarecidas

“…INTRODUCCIÓN Hoy en día tiene gran interés el modelado de la transferencia de calor entre un sistema y una atmósfera enrarecida, debido principalmente al incremento del número de aplicaciones. Los gases enrarecidos pueden encontrarse en las atmósferas de otros planetas (las misiones robóticas de exploración a Marte tienen que enfrentarse a estas condiciones (Gómez-Elvira et al, 2012)), o en las capas más altas de la atmósfera terrestre donde operan los globos estratosféricos (Fernández-Soler et al, 2020;González-Bárcena et al, 2020;Pérez-Grande et al, 2011) así como en aplicaciones científicas en tierra en atmósferas controladas (Gao et al, 2018;Mahajan & Gebhart, 1980;Mahon et al, 2020;Seo et al, 2019).…”

“…Sin embargo, cuando se revisa la literatura relacionada no hay consenso en la estimación de la convección en gases enrarecidos. Además, para presiones muy bajas en el régimen de transición no se encuentran correlaciones para hilos verticales y la disponible para hilos horizontales no es de fácil aplicación (Gao et al, 2018).…”

“…Gao et al (Gao et al, 2018) realizaron experimentos para la caracterización de la convección natural en hilos de 25 µm de diámetro y longitud 19.44 mm. Estos experimentos se realizaron en atmósfera enrarecida de aire con presiones de 0.07 mbar hasta presión ambiente con incrementos de temperatura en el hilo entre 20 y 80 ºC.…”