Investigation of two-phase boiling heat transfer in microchannels using infrared thermography

• Main Authors: Lin, Chih-Jui, 林芝瑞
• Other Authors: Pan, Chin
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/53558012327138656318

碩士 === 國立清華大學 === 工程與系統科學系 === 102 === The objective of this study is to investigate the boiling two-phase heat transfer in a single rectangular microchannel by using a high thermal sensitivity, non-invasive infrared thermography(IR).The temperature of the working fluid, i.e.enthanol of 95%, in liquid state measured by IR is calibrated by a T-type thermocouple immerse in the bulk liquid. The microchannel is made of aluminum, with a dimension of 0.6 mm in depth, 1.5 mm in width, and 111 mm in length. The test section with the microchannel is adhered on top of a heating module with variable heating power. Five T-type thermocouples are embedded in the test section below the channel bottom surface for the measurement of the local wall temperature. To measure the fluid temperature distribution along the microchannel using an IR thermography, the microchannel is covered with a germanium window with a thickness of 5 mm. The germanium window is transparent for the transmission of long-wavelength (LW) IR. The infrared images of this study are recorded with a frame rate of 200 fps, which facilitates the observation of the transient temperature behavior during flow boiling in the microchannel. The calibrated process for the IR thermography to measure temperature is also discussed. The experimental results show that the infrared images capture the transient two-phase flow patterns as well as the fluid temperature along the channel. Thermal field analysis of slug and liquid slug as well as annular film formed to desiccation are presented and discussed. By observing the flow patterns in the channel, a pair of vortexes with liquid flow forward along the side wall and backward in the center have been identified in the liquid slug between two bubbles. Moreover, the effect of phase change number on the formation of vortexes has also been studied. In addition, the drying out of annular liquid film is also studied based on the isotherms from IR. The average liquid film evaporation rate is 137.8 kW/m2.for the case of qꞌꞌ=104.6kW/m2,G=20.4kg/m2s.