Infrared thermography measurement of two-phase boiling flow heat transfer in a microchannel

• Published in: Applied thermal engineering Vol. 94; pp. 568 - 578
• Main Authors: Liu, Tsung-Lin, Pan, Chin
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 05.02.2016
• Subjects: Boiling; Boiling heat transfer; Fluid flow; Fluids; Heat transfer; Infrared; Infrared technique; Mathematical analysis; Microchannel; Microchannels; Thermography; Two-phase flow patterns; Two-phase flow patterns; Infrared technique; Boiling heat transfer; Microchannel
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2015.10.084

•The IR images can capture the two-phase flow patterns as well as the fluid temperature.•The calibrated process for IR camera to measure the fluid temperature is discussed.•Two-phase local heat transfer coefficients and two-phase flow patterns are discussed.•The heat transfer coefficients are compared with the widely used correlations. In this study, a non-intrusive method to directly measure the fluid temperature and two-phase flow patterns in micro-scale system was developed. To achieve this goal, an adequate calibration process of infrared (IR) thermography measurement and an experimental design of IR transparent convective flow in a microchannel were established. The temperature distribution of the fluid along the microchannel was measured by IR thermography through a germanium window of thickness 5 mm. The transparent germanium window was used to facilitate the transmission of long-wavelength IR rays. The infrared images were obtained at a frame rate of 200 fps, which enabled observation of the transient temperature behavior during flow boiling in the microchannel. A semi-transparent liquid, namely ethanol, was used as the working fluid, with a mass flux of 20.3 kg/m2s and heat flux range of 3.1–244.1 kW/m2. The experimental results confirmed that IR thermography could be used to capture the transient single- and two-phase flow patterns as well as the fluid temperature along the channel. To the best of our knowledge, this paper is the first presentation of IR visualization of two-phase flow patterns in a microchannel. The trends of the local heat transfer coefficients with respect to the two-phase flow patterns are discussed, and the experimentally determined coefficients are compared with those calculated by commonly used equations.