Investigation on heat exchange of iron particle combustion based on simultaneous multi-physics field measurements

Abstract

A study was conducted using a premixed methane/air/oxygen Bunsen flame laden with iron particles to explore the thermal and fluid dynamic characteristics of iron combustion. An integrated diagnostic system was employed to simultaneously capture the characteristics of both gas and solid phases. The temperature of combusted iron particles was measured using pyrometry in conjunction with an RGB camera, while the gas phase temperature near these particles was determined through Background-Oriented Schlieren Tomography (BOST), calibrated by a B-type thermocouple. Velocities of the iron particles and the surrounding gas phase were quantified using Planar Particle Image Velocimetry (PIV), assisted by image segmentation to distinguish between the iron particles and alumina tracers. Synchronisation of all three measurement techniques was achieved, and calibration ensured that data from each method could be accurately correlated within the same coordinate system. Statistical analysis focused on the behaviour of combusted iron particles downstream of the flame region where the convection and radiation heat loss was fully resolved from in-situ measurement, providing insights beneficial for understanding heat transfer phenomena in two-phase flows. The temperature drop of burnt particles contributed from the inert cooling was estimated and compared with the conditional average of particle temperatures, revealing the significant heat production during the phase of reactive cooling. Overall, this study employed a seamlessly integrated multi-physics measurement technique, offering a comprehensive approach to capture all data on combusted iron particles. This methodology holds potential for extension and application to other reacting flows involving particulates.

Novelty and significance statement

A multi-physical measurement was first conducted to capture all thermal characteristics of iron combustion where the heat exchange between the iron combustion and its surrounding environment can be estimated from direct measurement. The temperature evolution of iron particles and their corresponding heat loss was estimated statistically as a function of their residence time, which was started from when they left the flame front of the assisted flame. A good consistency between the modelled and measured iron temperature revealed the reliability of such a measurement technique.