Infrared thermography for convective heat transfer measurements

Abstract

This paper deals with the evolution of infrared (IR) thermography into a powerful optical tool that can be used in complex fluid flows to either evaluate wall convective heat fluxes or investigate the surface flow field behavior. Measurement of convective heat fluxes must be performed by means of a thermal sensor, where temperatures have to be measured with proper transducers. By correctly choosing the thermal sensor, IR thermography can be successfully exploited to resolve convective heat flux distributions with both steady and transient techniques. When comparing it to standard transducers, the IR camera appears very valuable because it is non-intrusive, it has a high sensitivity (down to 20 mK), it has a low response time (down to 20 ls), it is fully two dimensional (from 80 k up to 1 M pixels, at 50 Hz) and, therefore, it allows for better evaluation of errors due to tangential conduction within the sensor. This paper analyses the capability of IR thermography to perform convective heat transfer measurements and surface visualizations in complex fluid flows. In particular, it includes the following: the necessary radiation theory background, a review of the main IR camera features, a description of the pertinent heat flux sensors, an analysis of the IR image processing methods and a report on some applications to complex fluid flows, ranging from natural convection to hypersonic regime.

Evaluating airfoil behaviour such as laminar separation bubbles with visualization and IR thermography methods

“…In the past, many experimental methods and visualization techniques have been used to facilitate the investigation of the boundary layer flow such as pressure tabs, hot films, pressure sensitive paints, particle image velocimetry, SOFV and IT [1][2][3][4][5][6]. Most of these methods are more challenging when dealing with small or complex model sizes, and low Re flows [7].…”

Flow pulsation in the near-wall layer of impinging jets

“…Details, however, were and still remain not completely clear. The character of the flowfield has been inferred indirectly, from the patterns in visualised distributions on the impingement wall mainly of heat transfer using the infrared thermography [26] or thermochromic liquid crystals [27]. A study of the flowfield became available in [28], the drawback there being the validity for only very small Reynolds numbers (Re = 500) .…”

“…23 -taken directly from [25] with the added note taken from [26]. These conjectures are actually somewhat doubtful as they rely upon the separation and flow reversal that were not observed.…”

Comparison of two methods for contactless surface temperature measurement

“…The IR camera is frequently used to analyze complex fluid flows. It is a suitable tool to study convective heat fluxes on the heated wall or the behaviour of the surface flow field [1]. The applications of IRT have been numerous.…”