A mechanistic approach to developing two phase flow pattern transition maps for two-phase dielectric fluids subject to high voltage polarization

• Published in: International journal of heat and mass transfer Vol. 127; pp. 1233 - 1247
• Main Authors: Nangle-Smith, S., Cotton, J.S.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.12.2018; Elsevier BV
• Subjects: Boiling; Computational fluid dynamics; Condensation; Convective boiling; Dielectric fluid; Dielectrics; Electric potential; Electrohydrodynamics; Electrostriction; Empirical analysis; Flow mapping; Flow pattern map; Fluid flow; Fluid mechanics; Fluids; Froude number; Heat exchangers; Heat transfer; High voltages; Masuda number; Performance prediction; Phase transitions; Pressure drop; Two phase flow; EHD; ST; Masuda number; KT; Convective boiling; Electrostriction; AM; Dielectric fluid; TD; OD; SSW; IA; Flow pattern map; IB; ID; SWIA; Electrohydrodynamics
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2018.06.076

•A fully, equation-based two-phase flow pattern map for electrohydrodynamic (EHD) convective boiling of dielectric fluids is presented.•A semi-analytical model is developed to determine the interfacial stress due to EHD on the stratified liquid vapour interface to remove the need to numerical model the field strength.•Two-phase flow pattern transition criteria developed by four different researchers were modified to incorporate EHD, compared against experimental data and the Steiner equations were found to be the most accurate when accounting for electric field effects. High voltage electric fields can be used as an active heat transfer enhancement technique for convective boiling or condensing dielectric fluids, with the major component of this enhancement being attributed to phase redistribution and mixing in the system due to electric body forces. Many performance prediction tools for convective boiling and condensation rely on flow pattern maps to identify the flow regime for use with flow pattern specific heat transfer and pressure drop correlations [1,2]. In this paper, a mechanistic approach to developing two phase flow pattern maps for two-phase dielectric fluids subject to high voltage fields using a fully contained, equation-based electric Froude number approach is presented and compared against the experimental flow pattern data for EHD convective boiling & condensation available in the literature and from the current experimental study. Despite the development of newer diabatic, semi-mechanistic flow pattern models for free-field heat exchanger performance analysis, it is recommended that the Steiner equations for flow pattern transition be used as a basis for the mapping when additional physics such as EHD is coupled, as the empirical fits in newer semi-mechanistic maps are unreliable when additional physics is present.