Engineering topics

Huang, S. C.

Publications and source records attributed to Huang, S. C..

7 records

NASA NTRS1992

HFAST - A harmonic analysis program for Stirling cycles

HFAST is a general-purpose third-order harmonic analysis and design program for predicting the cyclic-steady state thermodynamic performance of Stirling cycles. It represents the state-of-the-art results of years of research efforts at Mechanical Technology Inc. (MTI) in the development of Stirling cycle machines. The code has been extensively used at MTI to support the development of both free-piston and kinematic Stirling cycle machines. Lately, HFAST has undergone many major improvements, both in the analysis method and in the user's interface. This paper presents a brief description of the current analysis method used in HFAST.

Huang, S. C.↗

NASA NTRS1986

Evaluation of Stirling engine appendix gap losses

The efficiency of a Stirling engine can be strongly influenced by the heat transfer losses associated with its appendix gap region. The cyclic energy flows in this region are related to the temperature gradient along the piston and cylinder partition walls, the reciprocating motion of the piston, the pressure variation in the Stirling cycle and the leakage flow across the cold-end seal. This paper outlines a numerical model to simulate these cyclic energy flows and the subsequent effort to correlate it with engine test data. The sensitivity of the appendix gap loss to selected parameters and comparisons with test results are presented.

Huang, S. C.↗

NASA NTRS1985

Rapid solidification characteristics in melt spinning a Ni-base superalloy

The solidification kinetics involved in the process of melt spinning a Ni-base superalloy have been characterized. Through a correlation of ribbon thickness to melt puddle residence time, it was found that the solidification front velocity, V, is typically about 100 mm/sec at the ribbon surface not in contact with the spinning wheel. The rate of solidification varies within the ribbon, increasing with decreasing distance, S, from the wheel-contact surface as V = 3.65/s. Ribbon microstructure and texture characteristics are discussed in light of this kinetics result. The thickness-vs-time correlation was further analyzed to yield information about thermal history during ribbon formation. These thermal results are generally consistent with those deduced from dendrite arm spacing measurements.

Huang, S. C.↗

NASA NTRS1981

Boundary-layer analysis for the convection/diffusion transition in dendritic growth

The supercooling dependence of dendritic growth kinetics under the influence of convective heat transport is investigated theoretically and experimentally with emphasis on theoretical prediction of the supercooling level at which the transition from diffusion-controlled to convection-controlled dendritic growth occurs. It is shown that the crossover between diffusive and convective transport depends on the relative thickness of the Stefan length compared with the thermal boundary layer. These lengths become equal at a supercooling which may be calculated from diffusion theory and fluid mechanics. It is also shown that the crossover supercooling varies weakly with the gravitational acceleration, melt viscosity, and the volumetric expansion coefficient.

Glicksman, M. E.↗

NASA NTRS1979

Convective heat transfer during dendritic growth

Axial growth rate measurements were carried out at 17 levels of supercooling between 0.043 C and 2 C, a temperature range in which convection, instead of diffusion, becomes the controlling mechanism of heat transfer in the dentritic growth process. The growth velocity, normalized to that expected for pure diffusive heat transfer, displays a dependence on orientation. The ratio of the observed growth velocity to that for convection-free growth and the coefficients of supercooling are formulated. The dependence of normalized growth rate in supercooling is described for downward growing dendrites. These experimental correlations can be justified theoretically only to a limited extent.

Glicksman, M. E.↗

NASA NTRS1979

Convective flow during dendritic growth

A review is presented of the major experimental findings obtained from recent ground-based research conducted under the SPAR program. Measurements of dendritic growth at small supercoolings indicate that below approximately 1.5 K a transition occurs from diffusive control to convective control in succinonitrile, a model system chosen for this study. The key theoretical ideas concerning diffusive and convective heat transport during dendritic growth are discussed, and it is shown that a transition in the transport control should occur when the characteristic length for diffusion becomes larger than the characteristic length for convection. The experimental findings and the theoretical ideas discussed suggest that the Fluid Experiment System could provide appropriate experimental diagnostics for flow field visualization and quantification of the fluid dynamical effects presented here.

Glicksman, M. E.↗

NASA NTRS1978

Convective heat transfer during dendritic solidification

Experiments on succinonitrile are described in which the dependence of dendritic growth velocity is studied as a function of orientation with respect to gravity. Growth rate measurements were carried out at a relatively small supercooling, requiring high specimen purity as well as extreme thermal stability and precision temperature measurement. The normalized growth velocity showed a dependence on orientation described by the ratio of observed growth velocity to that expected for convection-free growth being equal to 3.52 times the n-th power of Cos half the orientation angle, where n lies between 0.5 and 0.75.

Glicksman, M. E.↗