An Experimental Study on Cryogenic Spray Quenching of a Circular Metal Disk II. Chilldown Efficiency and Effects of Coating and Flow Pulsing

This is the second part of a two-part series that presents the results of liquid nitrogen spray quenching of a Stainless Steel disc. The results of continuous-flow spray chilldown of a bare surface disc are summarized first that serves as the baseline information for evaluating the effects of disc surface coating and pulse flow. We found that for continuous-flow spray chilldown of a bare surface disc, the chilldown efficiency is mainly a function of the average mass flow rate with the trend of decreasing efficiency with increasing mass flow rate. Additional experiments were performed to evaluate the enhancement of cryogenic spray quenching by three techniques: 1. Using intermittent pulse sprays on SS bare surface, 2. Coating the SS surface with a layer of low thermal conductivity Teflon film, and 3. Spraying liquid nitrogen intermittently on the coated SS surface. In general, the results indicate that all three methods effectively produced higher spray thermal efficiencies and reduced liquid nitrogen mass consumption. However, it was also found that the Teflon coating was more effective than the flow pulsing due to that the Teflon coating induced a large surface temperature drop at the beginning of the chilldown that allowed the quenching to move quickly from poor heat transfer film boiling to efficient heat transfer transition and nucleate boiling regimes. This quick transition shortens the film boiling period, thus facilitates the switch to much higher heat transfer transition boiling and nucleate boiling periods earlier to complete the chilldown process faster.

An Experimental Study On Cryogenic Spray Quenching of a Circular Metal Disk I. Effects of Mass Flux, Spray Fluid Inlet Subcooling, and Gravity

This is the first part of a two-paper series that reports the design, experimentation, and results of a spray quenching experiment of a circular metal disk in terrestrial gravity conditions. The objective of this experiment is to provide experimental data and corresponding analysis on the heat transfer characteristics and chilldown performance of the cryogenic spray quenching process. In this paper, the presented continuous-flow spray quenching results include the spray-cone angle visualization, spray cooling heat transfer characteristics represented by chilldown curves and boiling curves, gravity effects, and Leidenfrost rewet point temperatures. Additionally, detailed discussion is given on the film boiling heat transfer and rewet temperature in terms of various contributing factors such as gravitational acceleration, spray mass flux, and radial position on the plate. Based on experimental data, empirical correlations for film boiling heat transfer coefficient and rewet temperatures are provided. We expect that, the current terrestrial study would offer invaluable information for the design of a robust in-space cryogenic propellant storage tank spray chilldown system.

2020 Max Jacob Memorial Award (P. C. Wayner, Jr.) Review: Change-of-Phase in an Extended Meniscus

The extended meniscus and the intermolecular and capillary forces that govern its behavior and connection to change of phase heat transfer have been the subject of an increasing body of research over the past 50 years. We have been fortunate to be at the forefront of this effort starting from the development of a capillary feeder, in Earth's gravity, to stabilize film boiling to running a series of transparent heat pipe experiments aboard the International Space Station hoping to better understand the role of intermolecular forces in microgravity. The use of ellipsometry and interferometry to highlight the location and state of the vapor-liquid interface have been key to these studies and have helped to uncover many new, interesting, and sometimes unexpected, phenomena associated with fluid flow and change-of-phase heat transfer.

INFLUENCE OF THE POROUS MEDIA ON HEAT EXCHANGE AT FILM BOILING LIQUID

The present work focuses on a study of heat transfer during film boiling of a liquid on a vertical heated wall immersed in a porous medium subject to variation of different parameters of the porous medium and heating conditions at the wall. An analytical solution was obtained for the problem using Darcy-Brinkman-Forchheimer model. It was shown that heat transfer intensity during film boiling in a porous medium is weaker than in a free fluid (without porosity) and decreases with the decreasing permeability of the porous medium. The use of a porous medium model in the Darcy-Brinkman-Forchheimer approximation showed the effect of the Forchheimer parameter on heat transfer during film boiling in a porous medium. An increase in the Forchheimer parameter leads to heat transfer deterioration, which is more significant at small values of the Darcy number. Effects of different thermal boundary conditions on the heated wall on the heat transfer are insignificant.

Boiling of He-II on a cylindrical heater inside a porous shell with constant operation condition

This paper presents new efforts undertaken in the study of boiling in superfluid helium on the surface of a cylindrical heater located along the axis in a cylindrical cavity inside a porous shell. New experimental results are obtained with maintaining constant temperature of the helium-II and helium vapor pressure. The modernization of the experimental setup and vacuum system carried out to obtain a series of longer experiments with maintaining a stationary state are described. The basic experimental configurations are specified. Visualization of helium-II film boiling in constant operation condition is represented.