Coupling Enhancement Effect of the Magnetic Field and Wall Superheat on Boiling Heat Transfer Characteristics of Magnetic Nanofluid (MNF) under Reduced Gravity

How to reduce or even eliminate the influence of gravity on boiling heat transfer, how to restrain the emergence of abnormally large bubbles and how to prevent the large decrease of critical heat flux (CHF) are the key to enhancing boiling heat transfer under reduced gravity. Magnetic nanofluid (MNF) boiling is one of the effective methods to solve the above problem. Under reduced gravity, the wall superheat has a crucial influence on the dynamics of the bubbles and boiling heat transfer. However, it has been unsolved whether the application of an external magnetic field can enhance the influence of wall superheat on boiling thermal dynamics or not. Based on the author's previous research, the influence of wall superheat on the enhanced heat transfer of MNF boiling under reduced gravity is further studied by using the computational model of MNF boiling heat transfer under external magnetic field. In this paper, the phase interface dynamics evolution and heat transfer characteristics of MNF boiling under the dual influence of wall superheat and magnetic field are described for the first time. The results show that the application of the magnetic field retards the flow state development of MNF film boiling compared with the results without the magnetic field. As the wall superheat increases, whether magnetic field is applied or not, the heat flux enhancement ratio with respect to wall superheat of 2 K under the various gravity level is almost the same. The effect of the wall superheat on boiling heat transfer characteristics under reduced gravity is enhanced by the application of external magnetic field. When the magnetic field of H = 20 kA/m is applied and the wall superheat is 6 K, under the three gravity levels of g / g e = 1.0, g / g e = 0.44 and g / g e = 0.11, the heat flux with respect to wall superheat of 2 K can be enhanced up to 22.7%, 53.9% and 150.1%, furthermore, the heat flux enhancement rate can be enhanced up to 10%, 18.7% and 12.6%, respectively.