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Results for “FILM BOILING”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Transient-forced convection film boiling on an isothermal flat plate

An approach for the solution of transient-forced convection film boiling on an isothermal flat plate using the boundary layer model is developed. The similarity variables are used to convert the governing partial differential equations to ordinary ones. The results of numerical solutions of these ordinary equations indicate that the transient process can be classified as one-dimensional conduction, intermediate, and the steady state regions. The time required for the one-dimensional conduction and the time necessary to attain a steady state condition are obtained. The influence of interfacial shear is seen to be negligible while the Prandtl Number and the ratio (C sub p delta T divided by h sub fg times Pr) have major influence. The use of local similarity approximations for the intermediate regime facilitates prediction of complete boundary layer growth. Using the ratio of time at any instant to the steady state time as abscissa, the curves representing the boundary layer growth can be merged into a single mean curve within 5 percent. Further, the analysis shows that the average rate of heat transfer during transient is 50 to 100 percent higher than those at steady state. The average rate of vapor convected away is 10 to 15 percent lower than at steady state while the average rate of accumulation to form the vapor layer is 1 to 14 times larger. Further, the total heat transferred during transient increases and the evaporation decreases for increasing values of C sub p delta T divided by h sub fg times Pr

Nagendra, H. R.↗
NASA NTRS1972

Transient-forced convection film boiling on an isothermal flat plate.

Development of a new approach for the solution of transient-forced convection film boiling on an isothermal flat plate using the boundary layer model. The similarity variables are used to convert the governing partial differential equations to ordinary ones. The results of numerical solutions of these ordinary equations indicate that the transient process can be classified as one-dimensional conduction, intermediate, and the steady-state regions. The time required for the one-dimensional conduction and the time necessary to attain a steady-state condition are obtained. The use of local similarity approximations for the intermediate regime facilitates prediction of complete boundary layer growth. Using the ratio of time at any instant to the steady-state time as abscissa, the curves representing the boundary layer growth can be merged into a single mean curve within 5%. Further, the analysis shows that the average rate of heat transfer during transient is 50 to 100% higher than those at steady state. The average rate of vapor convected away is 10 to 15% lower than at steady state while the average rate of accumulation to form the vapor layer is 1 to 14 times larger.

Nagendra, H. R.↗
NASA NTRSDate not supplied

Three-Dimensional CFD Simulations in the Film Boiling Regime During Liquid Nitrogen Chilldown Process

The paper presents a three-dimensional CFD simulation for predicting the liquid nitrogen chilldown process through a SS-304 tube. A dispersed mixture model has been employed to predict the two-phase flow behavior whereas the Lee phase change model has been used to predict the boiling process. Cryogenic chilldown process starts with a pure vapor region and proceeds to film, transition and nucleate boiling regimes before reaching the single phase liquid flow and complete chilldown of the transfer line. The present numerical model predicted the film boiling regime accurately and the slope of the chilldown curve deviates slightly from the experimental curve towards the transition and nucleate boiling regime, which needs further investigation. The contours of liquid volume fraction and temperature profiles has been presented to understand the inverted annular film flows in the film boiling regime in detail. In future, the present CFD model will be extended to a wide range of chilldown conditions and different cryogenic fluids to develop a robust methodology.

CFD↗
NASA NTRS1988

Pool film boiling from rotating and stationary spheres in liquid nitrogen

Results are presented for a preliminary experiment involving a saturated pool boiling at 1 atm from rotating 2 and 3 inch diameter spheres which were immersed in LN2. Additional results are presented for a stationary 2 inch diameter sphere quenched in LN2, which were obtained with a more versatile and complete experimental apparatus. The speed of the rotational tests varied from 0 to 10,000 rpm. The stationary experiments parametrically varied pressure and subcooling levels from 0 to 600 psig and from 0 to 50 F, respectively. During the rotational tests, a high speed photographic analysis was undertaken to measure the thickness of the vapor film surrounding the sphere.

Cuan, Winston M.↗
NASA NTRS1972

Oscillation effects upon film boiling from a sphere.

Heat transfer rates from a silver-plated copper sphere, 0.75 in. in diameter, were studied by high speed photography during oscillations of the sphere in saturated liquid nitrogen and Freon-11. The oscillation frequencies ranged from zero to 13 Hz, and the amplitude-to-diameter ratio varied from zero to 2.67. The sphere was supported by a thin-walled stainless steel tube and carried a thermocouple attached near the lower stagnation point. A Fastax WF-3 16mm movie camera was used at about 2000 frames/sec. The differences in the vapor removal process at lower and higher oscillation frequencies are discussed.

Schmidt, W. E.↗
NASA NTRSDate not supplied

CFD Predictions of Boiling Regime Transitions during Line Chilldown validated against a 1G LN2 Experiment

Introduction Before filling a propellant tank on the ground or in Space, the transfer line between the donor and receiver tanks must be cooled down preferably by sacrificing a minimum amount of the cryogenic fluid. The cryogenic line chill-down process involves a transition between different flow boiling regimes, namely, film boiling, transition film boiling, and nucleate boiling which are complex and may be quite gravity-dependent. Capturing these boiling phenomena and predicting the transition between them in a CFD framework is new and challenging both for 1g and microgravity applications. Materials & Methods The present work addresses this challenge by employing a two-phase Eulerian approach in the context of a homogeneous fluid mixture together with the Lee phase change model to capture the film boiling regime of the chill-down process using ANSYS Fluent®. The nucleate boiling regime is predicted by incorporating an in-house developed sub-grid model that accounts for bubble nucleation, bubble growth, bubble departure diameter, and their shedding frequency. The sub-grid model is encoded and implemented into Fluent via a user-defined function for the wall-fluid heat flux calculations. The mathematical formulation and numerical implementation of the CFD model are described in detail. The coupled CFD-Subgrid model is validated against published experimental data for liquid nitrogen chill-down of a heated stainless-steel pipe in 1g. Results Numerical simulation results show good agreements between the CFD predictions of the wall temperature evolution, rewetting temperature, and transition between film and nucleate boiling, with the experimental measurements published by Darr et al [2] for several different LN2 flowrates in the vertical pipe orientation. The CFD predictions for the wall temperature distribution indicate a rapid quenching of the wall at two upstream and downstream temperature sensing locations as compared to the experimental measurement. The only tuning parameter in the CFD model is the Lee mass transfer coefficient. The CFD Model predicts the Liedenfrost rewetting temperature in close agreement with the experiment. This marks a transition between stable and transitionary flow boiling regimes. The CFD-predicted boiling curve for the downstream sensor location is also compared against its experimental counterpart and indicates that the model is able to predict all the key temperature and heat flux parameters during the transitions from stable to transitionary film boiling to nucleate boiling in close agreement with the experiment. A sequence of predicted volume fraction, and temperature contours depicting these transitions will be presented.

Evaporation Condensation↗