Numerical investigation of flow boiling characteristics of water in a rectangular microchannel
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Numerical investigation of flow boiling characteristics of water in a rectangular microchannel Thavamani Jeyaraj1 · Kumar Pankaj1 Received: 17 May 2020 / Accepted: 4 September 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract In the case of flow boiling, the prediction of vapour fraction in the horizontal microchannel is a severe issue using the numerical technique. Two-dimensional numerical simulation was carried out for the flow boiling in microchannels with different boiling models (VOF, MM and EM). This study is one of the first studies that report a numerical assessment of these three models. Numerical simulations have done with water as a working fluid. The different mass flow rates (1.586 × 10−6 kg−1, 2.541 × 10−6 kg s−1, 3.112 × 10−6 kg s−1) and different heat fluxes (300 kW m−2, 400 kW m−2, 500 kW m−2) with different flow boiling models are used. The vapour fraction estimation was done by image processing in MATLAB program and compared with various mass flow rate and heat flux. It well validated with the published literature. An onset of nucleate boiling point position is estimated with same time step, and uncertainties of the numerical simulation were less than 2.5% at the lowest mass flow rate. The result shows that the vapour fraction in the microchannel increases with an increase in mass flow rate and heat flux. Similarly, the model’s heat transfer rate compared with the same mass flow rate and heat flux. The mixture model is best to estimate of vapour fraction compared to other models. The estimated vapour fraction values are 0.2950, 0.1848 and 0.1726 for MM, VOF and EM respectively. The heat transfer coefficient value for the mixture model is 20.381 kW m−2. Its value was very higher compared to other models because of the increase in fluid temperature difference at constant heat flux. This comparison can be used to provide design guidelines by selecting proper model for simulation work and minimize the complexity and wastage time.
* Kumar Pankaj [email protected] Thavamani Jeyaraj [email protected] 1
Department of Mechanical Engineering, College of Engineering & Technology, SRM Institute of Science and Technology, Kattankulathur, Chennai, Tamilnadu 603203, India
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T. Jeyaraj, K. Pankaj
Graphic abstract
Keywords Two-phase flow · Microchannel · VOF model · Mixture model · Eulerian mode Abbreviation VOF Volume of fluid MM Mixture model EM Eulerian model PISO Pressure implicit with splitting operations PRESTO Pressure staggering options QUICK Quadratic upstream interpolation for convective kinematics RPI Rensselaer Polytechnical Institute (RPI) wall boiling model ONB Onset of nucleate boiling CHF Critical heat flux
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List of symbols Mqp Mass transfer from phase q to phase p (kg s−1) Mpq Mass transfer from phase p to phase q (kg s−1) Eq Energy of the phase (J s−1) Keff Effective thermal conductivity (W m−1 K−1) Vm Mass averaged velocity (m s−1) F Body force (N) hk Sensible enthalpy for phase (kJ kg−1) E Energy (J s−1) Vdr Drift vel
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