Abstract
The study aims to investigate the characteristics of heat transfer with segmented flow in PDMS microchannel under one side constant wall heat flux thermal boundary condition using temperature sensitive paint (TSP) and Micro Particle Image Velocimetry (Micro-PIV). Detailed Temperature distributions in fluid and wall surface have been acquired by temperature sensitive luminescent sensors in the form of temperature sensitive solution and temperature sensitive paint. Velocity profiles in the microchannel devices with single phase flow and two phase flow (segmented flow) have also been measured by Micro PIV. Additionally, ANSYS simulation has been performed to examine the bulk mean temperature profiles acquired by TSP technique using luminescent intensity measurements. The results show that the depth-averaged temperature profiles acquired by TSP technique agree with the bulk-mean temperature calculated from simulation. TSP technique has the advantages of high spatial resolution (200μm/pixel) and global fluid temperature measurements, and heat flux variation from channel entrance can be calculated and the effect from axial heat conduction has been observed.In single phase heat transfer measurement, the fluid and surface temperature distributions in the microchannel device are close to the temperature distribution in straight microchannel at Re number ranging from 11 to 93. The local Nu number in fully developed region and averaged Nu number of ethanol is 2.61 and 2.95. The local Nu number in fully developed region and averaged Nu number of DI water is 2.7 and 3.1 Micro-PIV technique has also been performed to provide the velocity distribution in two phase segmented flow. The structure of flow circulation in ethanol/air two phase flow was identified. The vortex structure in liquid segment can be enhanced by increasing gas phase flow rate while maintaining liquid phase flow rate. Compared with heat transfer from single phase flow, the two phase segmented flow helps the flow mixing in the liquid segment and the fluid temperature rises more quickly while the wall surface temperature decreases faster in the beginning of heating. When L_b/W_m=7.32,the Nu number of 3.23 has been calculated in the two phase segmented flow which is higher than 2.42 measured from single phase (liquid) flow at the same Reynolds number (〖Re〗_L) in the fully developed region. The averaged Nu number of two phase segmented flow shows about 30% increases compared to the Nu Number measured from single phase flow.Considered the effect with void fraction of gas, the veraged Nu number of two phase segmented flow shows about 200% increases compared to the Nu Number measured from single phase flow