Numerical study of nucleate boiling. Diffuse interface simulations of steam bubble departures from superheated wall
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Applied mechanics (MPAME), MSc
Publicerad
2023
Författare
Johansson, Adam
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Nucleate boiling is a type of boiling which is characterised by the nucleation, growth
and rise of vapour bubbles at the superheated surface. Because latent heat is typ ically much larger than sensible heat, the heat transfer associated with nucleate
boiling is much larger than that of other forms of liquid cooling. Despite its im portance, the effect of the wall and fluid properties on heat transfer is not yet fully
understood, due to the several mechanisms involved and the many governing param eters. In a field where experiments are cumbersome and hard to realise, numerical
simulations are of out most importance to increase our understanding. Here we in vestigate the effect of contact angle θw, wall superheat temperature ∆T and number
of nucleation sites Nbub on the departure of boiling steam bubbles in quiescent liquid
water by means of a novel Diffuse Interface (DI) algorithm for weakly compressible
flows. More specifically we estimate the time-averaged Nusselt number, quantifying
the non-dimensional wall heat flux. The maximum time averaged Nusselt number
was found for ∆T = 2.5 K, θw = 45° and Nbub = 1, which was the lowest super heat temperature, smallest contact angle and lowest number of nucleation sites that
were tested. However these results are to be taken with reservations since the simu lated bubbles were of several orders of magnitude larger than physical bubble nuclei,
probably underestimating the effect of phase change on heat transfer. More work is
required to obtain an algorithm that is stable enough to simulate a wider range of
parameters.
Beskrivning
Ämne/nyckelord
boiling , phase change , diffuse interface , bubble , heat transfer , nucleate boiling , contact angle