Review Review on flow boiling of refrigerants R236fa and R245fa in mini and micro channels Stanislawa Sandler ⇑ , Bartosz Zajaczkowski, Zbigniew Krolicki Wroclaw University of Science and Technology, Faculty of Mechanical and Power Engineering, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland article info Article history: Received 27 April 2018 Received in revised form 9 May 2018 Accepted 9 May 2018 Keywords: Small-scale flow boiling Mini channels Micro channels Thermal modeling abstract Flow boiling in mini and micro channels is considered to be one of the most efficient cooling solutions for mobile devices and electronic components. Cooling systems relying on flow boiling should be able to work efficiently in a wide range of operating conditions including saturation temperature. Employing refrigerants characterized by low saturation pressures assure lightweight structure of the cooling system even at high operating temperatures. Therefore, this article focuses on two low-pressure refrigerants R236fa and R245fa (refrigerants which are characterized by low saturation pressures corresponding to high saturation temperatures) with special emphasis on the influence of saturation temperature on flow boiling characteristics. It presents a detailed review on the most recognized heat transfer models during flow boiling and an experimental database on R236fa and R245fa covering channel hydraulic diameters ranging from 0.1 to 3 mm, mass fluxes from 42 to 2500 kg/m 2 /s, and wall heat fluxes varying between 6.5 and 422.7 kW/m 2 . The covered vapor qualities range from 0.09 to 1.14 (which translates into subcooled, saturated and superheated flows) and reference saturation temperatures vary between 14 and 120 °C. Subcooling at the heat exchanger inlet changes from 0 to 19 K. The amassed experimental data are com- pared with the results obtained from 24 theoretical models on flow boiling. The models follow additive, asymptotic, Nusselt-type and phenomenological approaches. The accuracy of the models is assessed on the basis of Mean Absolute Percentage Error MAPE and standard deviation r SD . The additive models of Saitoh et al. with MAPE ¼ 27:4% and r SD ¼ 43:8%, Chen with MAPE ¼ 28:6% and r SD ¼ 35:8% and an Nusselt-type correlation of Sun and Mishima with MAPE ¼ 28:4% and r SD ¼ 43:4% exhibit the best accu- racy. The amassed database allowed determination of the range of experimental conditions that need fur- ther scientific investigation. Review on heat transfer models together with results of comparison between the models and experimental data allowed identification of the most problematic aspects of modeling flow boiling in mini and micro channels. Ó 2018 Elsevier Ltd. All rights reserved. Contents 1. Introduction ......................................................................................................... 593 2. Flow boiling in small-scale channels ..................................................................................... 593 2.1. Flow patterns ................................................................................................... 593 2.2. Heat transfer mechanisms ........................................................................................ 594 3. Review of the available models .......................................................................................... 595 3.1. Additive approach ............................................................................................... 595 3.1.1. Chen’s approach ......................................................................................... 595 3.1.2. Gungor and Winterton’s approach .......................................................................... 595 3.1.3. Model of Lee and Lee ..................................................................................... 597 3.1.4. Zhang et al.’s model ...................................................................................... 597 3.1.5. Model of Saitoh et al...................................................................................... 598 3.1.6. Choi et al.’s approach ..................................................................................... 598 https://doi.org/10.1016/j.ijheatmasstransfer.2018.05.048 0017-9310/Ó 2018 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: stanislawa.sandler@pwr.edu.pl (S. Sandler). International Journal of Heat and Mass Transfer 126 (2018) 591–617 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt