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Ng, Y. S.

Publications and source records attributed to Ng, Y. S..

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Comparison of SIRTF dewar performance in the 900 km and 100,000 km orbits

Feasibility studies showed that the Space Infrared Telescope Facility (SIRTF) can be launched into a 100,000-km high earth orbit (HEO) using a Titan/Centaur launch vehicle. This paper compares the performance of an all-superfluid helium dewar system for SIRTF under conditions of the LEO (900-km) and the HEO missions. Results show that the SIRTF all-superfluid He dewar can achieve a 5-yr lifetime for the 100,000 km HEO mission, with 20 percent margin. Methods to achieve further enhancement of dewar lifetime for the HEO mission are suggested.

Lee, J. H.↗
NASA NTRS1990

Thermal modeling of the NASA-Ames Research Center Cryogenic Optical Test Facility and a single-arch, fused-natural-quartz mirror

A thermal model of the dewar and optical system of the Cryogenic Optical Test Facility at NASA-Ames Research Center was developed using the computer codes SINDA and MONTE CARLO. The model was based on the geometry, boundary conditions, and physical properties of the test facility and was developed to investigate heat transfer mechanisms and temperatures in the facility and in test mirrors during cryogenic optical tests. A single-arch, fused-natural-quartz mirror was the first mirror whose thermal loads and temperature distributions were modeled. From the temperature distribution, the thermal gradients in the mirror were obtained. The model predicted that a small gradient should exist for the single arch mirror. This was later verified by the measurement of mirror temperatures. The temperatures, predicted by the model at various locations within the dewar, were in relatively good agreement with the measured temperatures. The model is applicable to both steady-state and transient cooldown operations.

Ng, Y. S.↗
NASA NTRS1989

Analysis of dewar and transfer line cooldown in Superfluid Helium On-Orbit Transfer Flight Experiment (SHOOT)

The Superfluid Helium On-Orbit Transfer Flight Experiment (SHOOT) is designed to demonstrate the techniques and components required for orbital superfluid (He II) replenishment of observatories and satellites. One of the tasks planned in the experiment is to cool a warm cryogen tank and a warm transfer line to liquid helium temperature. A math model, based on single-phase vapor flow heat transfer, has been developed to predict the cooldown time, component temperature histories, and helium consumption rate, for various initial conditions of the components and for the thermomechanical pump heater powers of 2 W and 0.5 W. This paper discusses the model and the analytical results, which can be used for planning the experiment operations and determining the pump heater power required for the cooldown operation.

Ng, Y. S.↗
NASA NTRS1988

Analytical study of He II flow characteristics in the SHOOT transfer line

Pressure and temperature profiles for He II flow in the transfer line for the Superfluid Helium On-Orbit Transfer (SHOOT) experiment are determined using a finite difference method to solve the one-dimensional two-fluid conservation equations. For practical purposes, forced flow of He II with Re greater than 10 to the 6th can be treated as a classical turbulent flow For a maximum SHOOT transfer rate of 800 cu dm/h, the temperature rise between the pump outlet and the receiver tank is about 80 mk with a 7-W heat load imposed on the 4-m-long transfer line. A pump outlet pressure of 160 torr is required to sustain the 800 cu dm/h flow without causing vapor formation within the transfer line.

Lee, J. H.↗
NASA NTRS1988

Pump performance requirement for the liquid helium orbital resupply tanker

The Liquid Helium Orbital Resupply Tanker (currently renamed to Superfluid Helium Tanker) will greatly enhance the lifetime of the space missions which require superfluid helium. The Superfluid Helium Tanker pump performance requirement is driven by the superfluid helium replenishment needs of the Space Infrared Telescope Facility (SIRTF). SIRTF is one of the space missions which will require on-orbit superfluid helium resupply in the 1990s. The Superfluid Helium Tanker will carry at least 10,000 L of superfluid helium and provide a minimum pump head of 170 torr (0 to 200 L/h) to cool SIRTF from 150 to 2 K. When the SIRTF tank starts to collect liquid, a minimum flow rate of 300 L/h with a pump head of 60 torr is required to fill the 4000-liter tank.

Lee, J. H.↗
NASA NTRS1988

Cryogenic and thermal design for the Superfluid Helium On-Orbit Transfer (SHOOT) experiment

The analysis and trade-offs of the external thermal design of the two 200-liter dewars required in the SHOOT experiment to extend space mission life by superfluid helium replenishment are discussed. Also considered are the support electronics and the optimization and prediction of the performance of the dewar and cryostat assemblies. Particular attention is given to the ground-hold and standby performance of the dewars, along with the temperature of the helium bath during high-flow-rate helium transfers.

Lee, J. H.↗
NASA NTRS1987

Analytical modeling of helium II in forced flow conditions

A numerical model was developed to examine the flow behavior of He II under forced flow conditions. The model basically solves the governing equations in the two-fluid model of He II, and can be used to assess the pump requirement for transferring He II in spaceborne systems. Predictions of liquid temperature and pressure drop agree well with empirical data obtained from small scale tests. At high transfer rates, the model predicts that the forced convection dominates the Gorter-Mellink conduction in heat transfer, and the classical turbulent flow correlation is sufficient for calculating the pressure drop across the transfer line.

Ng, Y. S.↗
NASA NTRS1987

Proposed mechanistic model to simulate transfer line cool-down process using liquid helium

This paper proposes a mathematical model to simulate the cool-down behavior of a warm transfer line using liquid helium (including He II) in a microgravity environment. The thermal-hydraulic characteristics of different possible flow regimes which may occur during the cool-down process are discussed. Correlations for predicting the heat and momentum transfer rates in each flow regime are presented.

Ng, Y. S.↗
NASA NTRS1977

An investigation of accelerating mode and decelerating mode constant-momentum mass spectrometry and their application to a residual gas analyzer

A theoretical analysis of constant momentum mass spectrometry was made. A maximum resolving power for the decelerating mode constant momentum mass spectrometer was shown theoretically to exist for a beam of ions of known energy. A vacuum system and an electron beam ionization source was constructed. Supporting electronics for a residual gas analyzer were built. Experimental investigations of various types of accelerating and decelerating impulsive modes of a constant momentum mass spectrometer as applied to a residual gas analyzer were made. The data indicate that the resolving power for the decelerating mode is comparable to that of the accelerating mode.

Ng, Y. S.↗