Interfacial Heat Transfer Measurements during Flow Boiling in a PDMS Rectangular Microchannel

Flow boiling heat transfer rates and associated thermal and flow patterns were experimentally investigated using interfacial wall temperature mapping with synchronised high-speed visualisation and pressure measurements from integrated pressure sensors in a Polydimethylsiloxane (PDMS) microchannel. Flow boiling experiments were performed in a single high aspect ratio transparent microchannel of width Wch = 2.26 mm and height Hch = 100 µm giving a hydraulic diameter 퐷ℎ = 192 µm using FC-72. The mass flux values studied were 23.59, 36.87, 73.74 and 101.62 kg m-2 s-1 and heat flux was up to 98 kW m-2. The transient two-dimensional (2D) wall temperature maps
recorded by a high-speed infrared camera were used to calculate the heat transfer coefficient at the inner wall of the microchannel. Then, the local heat transfer coefficients were correlated with simultaneous high-speed video optical images obtained from the channel base. The 2D two-phase heat transfer coefficients h in, (푥, 푦) are reported as a function of time in 3D plots. 3D plots of the local heat transfer coefficient fluctuations are presented for the onset of boiling (ONB), maximum heat transfer co efficient (HTCmax) and critical heat flux (CHF). The heat transfer deterioration that occurred in microchannels was associated with liquid film thinning during annular flow that leads to local and temporal dryout.