Flow boiling of halogenated olefins inside a square cross-section microchannel

New experimental heat transfer coefficients measured during flow boiling of HFO-1234ze(E) and HFO-1234yf inside a square cross-section microchannel having a hydraulic diameter of 1.23mm are presented. The test runs have been performed with mass flux ranging between 200 and 500kg m(-2) s(-1) and heat flux between 20 and 170 kW m(-2). The local heat transfer coefficients are compared against the values previously measured using the same refrigerants in a 1mm diameter tube, with the aim of highlighting the effect of the noncircular shape of the cross-section. The experimental data are compared against predicting models available in the literature to suggest possible design methods for evaporators adopting hydrofluoroolefins in microchannels.