Numerical investigation of saturated flow boiling on thin walls

Abstract

Boiling heat transfer provides a means of removing high heat fluxes at low temperature differences in many applications in the power and process industries. A strong interest has been also developed for the cooling of silicon-based devices, such as electronic chips. However, a complete model to describe the processes involved has not been developed as yet. This PhD project focused on the study of nucleate pool boiling via numerical simulations for a solid plate horizontally immersed in a saturated liquid with a large number of potential nucleation sites. The simulations were developed by a FORTRAN code based on a hybrid approach, combining the 3-dimensional time-dependent solution for the temperature field on the substrate with semi-empirical models for phenomena occurring on the liquid side. The starting point of the project was the modification of a previous version of the code in order to reduce the computational time (in collaboration with Dr. Nelson at Los Alamos National Laboratory) and improve the modelling of the physics of the processes. One of the key features of the code is the flexibility in adapting to different conditions. In fact the code was used to study bubble growth, site activation frequency and superheat variations, as well as the interactions between nucleation sites. The differences in behaviour between very thin metal foils immersed in water and thicker silicon substrates in FC-72 were studied. The results were compared with experimental results produced at the University of Edinburgh and the University of Ljubljana, both partners of this project. Both the numerical and physical modifications introduced made it possible to have simulations for a large number of sites, of the order of 100, in reasonable times, of the order of days, so that the code can be now used as a tool for the design of new test sections.