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Results for “Melt pool control”

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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5 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Magnetic Damping of g-Jitter Driven Flows: 3-D Calculations

A 3-D numerical model is developed to represent the oscillating natural convection induced in a cylindrical cavity filled with Ga-doped germanium with and without the presence of an external magnetic field. The model is developed based on the penalty-finite element solution of the equations describing the transport of momentum, heat and solutal element as well as the electromagnetic field distribution in the melt pool. Automatic time step control is applied to help speed up the calculations. Numerical simulations are conducted to study the convection and magnetic damping effects as a function of frequency, directions and amplitudes of g-jitter and also the direction and magnitudes of the applied magnetic fields. The results show that the g-jitter driven flow is time dependent and exhibits a complex recirculating convection pattern in three dimensions and that an applied magnetic field can be employed to suppress this deleterious convective flow and both magnitude and orientation of the applied field are important in magnetic damping of the g-jitter induced convective flows.

Shang, D. Y.↗
NASA NTRS1987

Rate limits in silicon sheet growth - The connections between vertical and horizontal methods

Meniscus-defined techniques for the growth of thin silicon sheets fall into two categories: vertical and horizontal growth. The interactions of the temperature field and the crystal shape are analyzed for both methods using two-dimensional finite-element models which include heat transfer and capillarity. Heat transfer in vertical growth systems is dominated by conduction in the melt and the crystal, with almost flat melt/crystal interfaces that are perpendicular to the direction of growth. The high axial temperature gradients characteristic of vertical growth lead to high thermal stresses. The maximum growth rate is also limited by capillarity which can restrict the conduction of heat from the melt into the crystal. In horizontal growth the melt/crystal interface stretches across the surface of the melt pool many times the crystal thickness, and low growth rates are achievable with careful temperature control. With a moderate axial temperature gradient in the sheet a substantial portion of the latent heat conducts along the sheet and the surface of the melt pool becomes supercooled, leading to dendritic growth. The thermal supercooling is surpressed by lowering the axial gradient in the crystal; this configuration is the most desirable for the growth of high quality crystals. An expression derived from scaling analysis relating the growth rate and the crucible temperature is shown to be reliable for horizontal growth.

Thomas, Paul D.↗
NASA NTRS1985

Adjustable Lid Aids Silicon-Ribbon Growth

Closely-spaced crucible cover speeds up solidification. Growth rate of dendritic-web silicon ribbon from molten silicon increased by controlling distance between crucible susceptor lid and liquid/solid interface. Lid held in relatively high position when crucible newly filled with chunks of polycrystalline silicon. As silicon melts and forms pool of liquid at lower level, lid gradually lowered.

Mchugh, J. P.↗
NASA NTRS1988

Future MAUS payload and the TWIN-MAUS configuration

The German MAUS project (materials science autonomous experiments in weightlessness) was initiated in 1979 for optimum utilization of NASA's Get Away Special (GAS) program. The standard MAUS system was developed to meet GAS requirements and can accommodate a wide variety of GAS-type experiments. The system offers a range of services to experimenters within the framework of standardized interfaces. Four MAUS payloads being prepared for future space shuttle flight opportunities are described. The experiments include critical Marangoni convection, oscillatory Marangoni convection, pool boiling, and gas bubbles in glass melts. Scientific objectives as well as equipment hardware are presented together with recent improvements to the MAUS standard system, e.g., a new experiment control and data management unit and a semiconductor memory. A promising means of increasing resources in the field of GAS experiments is the interconnection of GAS containers. This important feature has been studied to meet the challenge of future advanced payloads. In the TWIN-MAUS configuration, electrical power and data will be transferred between two containers mounted adjacent to each other.

Staniek, S.↗
NASA NTRS1986

Acoustic-Emission Weld-Penetration Monitor

Weld penetration monitored by detection of high-frequency acoustic emissions produced by advancing weld pool as it melts and solidifies in workpiece. Acoustic emission from TIG butt weld measured with 300-kHz resonant transducer. Rise in emission level coincides with cessation of weld penetration due to sudden reduction in welding current. Such monitoring applied to control of automated and robotic welders.

Maram, J.↗