# Water Flow Boiling in Micro/Mini Channels Using Volume of Fluid Model
## 1 Introduction
The working fluid (R141b) entered the horizontal tube and was subcooled at 30 \({}^{\circ}\)C. The results agreed well with the experimental data. Through their research on the FB of water in vertical vapor-vented micro-channels, using the VOF model in Fluent, [PERSON] et al. [46] showed that vapor-vented micro-channels had a lower pressure drop than non-vapor-vented channels up to the critical value (defined as the value where vapor generation exceeds vapor venting rate). [PERSON] et al. [47] numerically investigated CHF during subcooled FB inside vertical mini-channels and proposed that as the length of the dry patch generated by CHF increased, the heat transfer deteriorated. [PERSON] et al. [48] separately used CFD to study the onset of nucleate boiling (ONB) in vertical mini-channels and proposed correlations to better predict ONB that are valid for a range of flow conditions. [PERSON] et al. [49] proposed a one-dimensional numerical to incorporate the effect of pressure fluctuations on HTC for FB inside rectangular microchannels. Additionally, heat transfer under flow reversals and instability caused by pressure fluctuations are also considered. [PERSON] et al. [50] elucidated the microlayer evaporation phenomenon for FB inside mini-channels and demonstrated various heat transfer modes during microlayer evaporation. [PERSON] et al. [51] carried out a numerical study of a two-phase system consisting of oil-water emulsion and superposed both electric field and flow to study the effect of electric field on oil-water separation. Similarly, [PERSON] et al. [52] employed a numerical approach to study two-phase oil-water separation in oilfield production. [PERSON] et al. [53] performed Fb experiments on 12 working fluids for a range of flow conditions and then employed a machine learning approach to predict HTC in micro/mini-channels. [PERSON] et al. [54] performed an experimental study on the thermal hydraulics of straight mini-channels and micro-channels chemically etched on brass plates. The brass plate was heated by cartridge heaters, and thermos-couples were used to find steam temperatures. The HTC was plotted against local quality for both channel sizes. The results showed that micro-channels had a higher HTC than mini-channels for constant mass flow rate and heat flux. Experimentation for the occurrence of three types of instabilities in micro-channels: Ledinbegg instability, pressure-drop oscillation, and density-wave oscillation, was carried out by [PERSON] et al. [55]. They proposed that the instability occurrence could be minimized by increasing the form loss coefficient K at the inlet. There is a lack of research literature on FB of water, and few researchers have investigated FB of water in mini-channels. A computational study for FB of water using parallel mini-channels under a wide range of mass flux and heat flux has not yet been reported. The results from experimental data have to extrapolate temperature at the solid-liquid interface, while the numerical study could cater to the lack of data at the interface, thus providing designers with greater flexibility. Therefore, this paper presents a computational study of FB in parallel mini-channels using the VOF model coupled with the Lee phase change model in the commercial CFD software ANSYS Fluent 15. The computational model consisted of a single rectangular mini-channel of 1 mm \(\times\) 1.5 mm \(\times\) 52 mm. The effect of parallel channels was incorporated by using periodic boundary conditions on side walls; other boundary conditions included mass flow inlet, pressure outlet, adiabatic wall at the top surface, and constant wall heat flux at the bottom surface. A mesh independence study was carried out for the proposed model, and simulations were validated against the results of heat transfer versus vapor quality, as reported by [PERSON] et al. [54], for an extensive range of mass and heat fluxes. The numerical results demonstrated good agreement with the experimental study, and the maximum error was within \(\pm\)16%.