Mechanistic method to predicting minimum heat flux point wall temperature in saturated pool boiling. (August 2020)

• Record Type: Journal Article
• Authors: Cai, Chang; Mudawar, Issam; Liu, Hong
• Is Part Of: International journal of heat and mass transfer. Volume 156(2020)
• Publication Date: 2020-08
• Subjects: Minimum heat flux point -- Pool boiling -- Interfacial instability -- Minimum film boiling temperature; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2020.119854
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: A new mechanistic approach is presented for prediction of wall temperature corresponding to the minimum heat flux. The model incorporates the effects of all forces acting on a unit cell of the interface. The model clearly identifies a 'trigger event' for minimum heat flux. Very good accuracy is realized in predicting data for many fluids and over a broad range of pressures. Abstract: This study details the development of a new mechanistic approach to predicting heating wall temperature corresponding to the minimum heat flux (MHF) point for saturated pool boiling from a horizontal flat surface. The model is constructed by performing a force balance on a unit cell of the wavy liquid-vapor interface, incorporating the effects of pressure difference across the interface, surface tension, gravity and stagnation pressure. It is shown how, in the film boiling regime, where a continuous vapor film insulates the heating surface, a decrease in wall heat flux towards the MHF point causes the liquid to approach the surface but without yielding any contact. A further decrease in heat flux triggers the MHF condition once the downward forces pushing the interface towards the wall overcome the upward forces lifting the interface away from the wall. This causes the wavy liquid-vapor interface to contact and wet the heating surface; vigorous bubble nucleation and vapor production ensue, signaling onset of the transition boiling regime. To achieve closure, the model adopts a previous relation for film boiling heat transfer coefficient, which is used to determine the wall temperature . The new model is shown to provide good agreement with MHF-point wall temperature data for many liquids and a broad range of pressures, evidenced by a mean absolute error of 9.35%. This study also includes an assessment of previous thermodynamic and hydrodynamic MHF models.