Microscale heat-flux meter for low-dimensional thermal measurement and its application in heat-loss modified Angstrom method

Abstract

A microscale heat-flux meter is designed based on micro-hotwire and infrared thermal microscopy. Its feasibility in low-dimensional thermal measurement is verified by its application in heat-loss modified Angstrom method for simultaneous measurement of thermal diffusivity, thermal conductivity and specific heat. The hotwire and the sample under test are placed in a vacuum chamber. Through an observation window, the infrared microscopy can capture the thermal image including the hotwire and the sample. When the hotwire is heated, the temperature distribution along the wire is acquired by the readings extracted from the thermal image, which enables the determination of nonlinear and local temperature gradient. This gradient, according to Fourier's Law, can be used to calculate the local heat flux. When a sample is attached to the middle of the hotwire, the attached point is appeared to be a singularity in the temperature distribution along the hotwire, which poses a rigorous challenge to calculate the heat flux flowing into the sample. Here we tried some approaching strategies and verified that the local heat flux at second derivative minima around the singularity is a good enough approximation. The mathematical and physical origins for this approximating strategy are also discussed. This microscale heat-flux meter is a general technique, which is promising for an extension to other thermal measurements.