Flow Boiling of R-134a in Minichannels With Transverse Ribs

An experimental effort was undertaken to investigate the flow boiling of R-134a in minichannels with transverse ribs. The test channel consisted of two parallel plates; the lower plate was heated while the upper plate was adiabatic and fabricated from a clear material to facilitate the visualization and photography of the boiling process. A number of transverse ribs were deployed along the lower plate to form a meandering flow passage inside the minichannel. The ribs blocked 3/4 of the flow cross-section in the transverse direction and the hydraulic diameter of the channel was 1.93 mm. In these experiments, the range of test parameters were: mass flux 100 to 225 kg/m²s, saturation temperature 15 to 30°C, heat flux 14 kW/m², and average vapor quality 0.12 to 0.86. With these parameters, the Convective and Boiling numbers ranged from 0.04 to 0.90 and 7.49 × 10⁻⁴ to 8.98 × 10⁻⁴, respectively. Of a total of 60 data points recorded, 78% of the data fell in the convective boiling region, while the remaining 22% were in the nucleate boiling region. In an attempt to model and correlate the data, it was found that the Kandlikar’s correlation proposed for augmented tubes was a suitable model for the present minichannel. Using the least-squares procedure, this two-equation model was fit to a total of 60 experimental data, resulting in a correlation that predicted 58 data points to within ±10%.