Direct Numerical Simulations of Pool Boiling in Presence of a Uniform Electric Field on Nonideal Surfaces with Contact Angle Hysteresis

Imposing uniform electric field is an effective method to enhance boiling heat transfer with the critical density flux (CHF) or/and heat transfer performance being increased. Contact angle hysteresis (CAH) is an inherently inevitable phenomenon for a nonideal real surface. In this work, we study the coupling effects of a uniform electric field and the contact angle hysteresis on pool boiling in FC-72, exploring the mechanisms that improve the boiling heat transfer of dielectric fluids on nonideal real surfaces in the presence of an electric field force. According to the numerical analysis, the electric field always promotes boiling heat transfer at high wall superheats and suppresses it at low wall superheats. This phenomenon is related to bubble dynamics under various wall superheats. Both the bubble size and nucleation site number reduce under a low wall superheat. At high wall superheats, the electric field prevents bubbles from merging and increases the wetted area. The effect of an electric field on the CHF, however, relies on the properties of the heater surface. The CHF rises as the electric field intensifies on the ideal hydrophilic and hydrophobic surfaces. If the width of the CAH is modest, the CHF grows with the increase in the electric field strength on nonideal hydrophilic surfaces. The relationship among the electric field strength, hysteresis windows, and CHF becomes more complicated in the case of a large hydrophilic hysteresis window and a minimal electric field strength. In addition, the CHF drops as the contact angle hysteresis rises on both the hydrophilic and hydrophobic surfaces.