Ho Sung Lee

Spherical vapor bubble growth in uniformly superheated liquids

A numerical procedure is presented for the solution of vapor bubble growth with radial symmetry from the thermodynamic critical size in an initially uniformly superheated liquid, which includes the influences of surface tension, liquid inertia and heat diffusion. Results are presented in the form of time varying interface radius, velocity, acceleration and temperature, with particular emphasis on how circumstances during the very early growth periods affect the later growth. The effect on the solution of the disturbance required to initiate the growth is examined in some detail. Comprehensive comparisons are made with previous experiments, analyses and numerical results.

Pool Boiling Curve in Microgravity

Pool boiling experiments using R-113 were conducted in the microgravity of space on a flat heater, consisting of a semitransparent gold film sputtered on quartz substrate, 19.05 x 38.1 mm (0.75 x 1.50 in.). Transient measurements of both the mean heater surface temperature and input heat flux are used to compute the mean heat transfer coefficient at the heater wall. Steady-state pool boiling is achieved in microgravity under conditions in which a large vapor bubble somewhat removed from the heater surface is formed, which acts as a reservoir for the nucleating bubbles. The steady nucleate boiling heat transfer is enhanced materially in microgravity relative to that in Earth gravity, whereas the heat flux at which dryout occurs is considerably less. Using quasisteady data obtained during periods in which some significant portions of the heater surface were dried out, it was possible to construct two distinct composite approximate microgravity pool boiling curves for R-113, one for the higher level of subcooling and one for the lower level of subcooling. These are compared with a reference curve for pool boiling at a/g = +1, constructed from available data and correlations deemed to reasonably represent the circumstances present.

Hemispherical vapor bubble growth in microgravity : experiments and model

Abstract Measurements of vapor bubble growth were made in microgravity using R-113 with transient heating at a flat surface, and comparisons made with a combination of two one-dimensional spherical models; an initially uniform superheat model, using the highest temperature at nucleation, denoted as the upper bound of growth, while the second model uses the non-uniform temperature distribution at nucleation as the initial condition surrounding the critical size vapor bubble, denoted as the lower bound. A bubble growth fraction is introduced, related to the upper and lower bounds, and provides a simple index to describe the vapor bubble growth.

The Origin of the Dynamic Growth of Vapor Bubbles Related to Vapor Explosions

An explosive type of vapor bubble growth was observed during pool boiling experiments in microgravity using R-113. Photographs reveal that the liquid-vapor interface of the explosive bubbles are wrinkled and corrugated, leading to the conclusion that some type of instability mechanism is acting. The classical hydrodynamic instability theories of Landau and Rayleigh-Taylor do not consider the effect of heat transfer at the interface, which is believed to be responsible for the observed instability of the evaporating surface. This was confirmed by the mechanisms proposed by Prosperetti and Plesset, combined with a model of the early growth of spherical vapor bubbles

Quasi-homogeneous nucleation in microgravity at low heat flux : Experiments and theory

Experiments were conducted in the microgravity of space in which a pool of liquid (R-113), initially at a defined pressure and temperature, was subjected to a step imposed heat flux from a semitransparent thin-film heater forming part of one wall of the container such that boiling is initiated and maintained for a defined period of time at a constant pressure level. Measurements of the transient heater surface and fluid temperatures near the surface were made, noting in particular the conditions at the onset of boiling, along with motion photography of the boiling process in two simultaneous views, from beneath the heating surface and from the side. A total of nine tests were conducted at three levels of heat flux and three levels of subcooling. They were repeated under essentially identical circumstances in each of three space experiments. The absence of buoyancy resulted in the onset of boiling at low heat flux levels, with what is defined as quasi-homogeneous nucleation taking place. The influence of these low levels of heat flux and the pressure effect used to produce the bulk liquid subcooling are accounted for by a modification of classical homogeneous nucleation theory.

The pool boiling curve in microgravity

Pool boiling experiments using R-113 were conducted in the microgravity of space on a flat heater, consisting of a semitransparent gold film sputtered on quartz substrate, 19.05 x 38.1 mm (0.75 x 1.50 in.). Transient measurements of both the mean heater surface temperature and input heat flux are used to compute the mean heat transfer coefficient at the heater wall. Steady-state pool boiling is achieved in microgravity under conditions in which a large vapor bubble somewhat removed from the heater surface is formed, which acts as a reservoir for the nucleating bubbles. The steady nucleate boiling heat transfer is enhanced materially in microgravity relative to that in Earth gravity, whereas the heat flux at which dryout occurs is considerably less. Using quasisteady data obtained during periods in which some significant portions of the heater surface were dried out, it was possible to construct two distinct composite approximate microgravity pool boiling curves for R-113, one for the higher level of subcooling and one for the lower level of subcooling. These are compared with a reference curve for pool boiling at a/g = +1, constructed from available data and correlations deemed to reasonably represent the circumstances present.

Quasi-homogeneous boiling nucleation on a small spherical heater in microgravity

Pool boiling experiments were conducted in the European Space Agency (ESA) multi-user facility, the bubble, drop, particle unit (BDPU) in the microgravity environment of space. A part of the study involved the heating of a small sphere immersed in R-123 to the onset of nucleate boiling. An analysis of the nucleation process is presented, based on a prior work for so-called quasi-homogeneous nucleation with a flat heater surface in microgravity. Reasonably good qualitative agreement exists between the analysis and measurements.