Optimizing performance of a 10−12 torr thermal vacuum system

Vacuum ◽  
1966 ◽  
Vol 16 (10) ◽  
pp. 555
Keyword(s):  
Vacuum System ◽  
Thermal Vacuum

Numerical Analysis to Predict the Temperature Distribution and Heat Transfer Rate From a Satellite Structure and Experimental Comparison

2012 ◽  
Author(s):  
Daniel T. Schwendtner ◽  
M. Ruhul Amin ◽  
David M. Klumpar
Keyword(s):  
Heat Flux ◽  
Numerical Analysis ◽  
Temperature Increase ◽  
Experimental Results ◽  
Vacuum System ◽  
Experimental Comparison ◽  
Bottom Plate ◽  
Flux Rate ◽  
Thermal Vacuum ◽  
Satellite Structure

Due to their small size and other attractive features, nanosatellites are becoming popular in space applications. Experimental investigation of the thermal behavior of such a satellite can be conducted in a laboratory setup using a thermal vacuum chamber to mimic the conditions of outer space. A small, cost effective thermal vacuum system was desired for performing thermal vacuum testing on nanosatellites. Numerical calculations and laboratory testing were performed as part of the design of this thermal vacuum system. A numerical method using the finite element method was employed to determine the amount of heat flux needed to be applied at the bottom plate of a satellite to achieve a certain rate of temperature increase in the plate. The numerical analysis was performed on a 40.5 kg satellite structure to predict the heat rate per unit area through its bottom surface when it was cycled in the temperature range of −40°C to +80°C with a rate of temperature change from 1°C/min to 5°C/min. A time dependent increase in temperature on the bottom wall was used as a boundary condition. The rest of the satellite walls were assumed to be insulated. Contact resistances between the components of the satellite structure were neglected. Temperature and heat flux distributions on various walls of the satellite were computed and reported in the study. From the numerical results, a maximum heat flux rate of 3,332 W/m2 was calculated on the bottom plate for a temperature increase rate of 1.5°C/min of the plate. A similar experimental setup was tested under similar conditions as a comparison and as a method to validate the thermal system design. Experimental results indicated a heat flux rate of 17,094 W/m2 through a test satellite. The difference between the numerical and experimental results is attributed to geometric differences between the numerical satellite model and the experimental test structure.

Standard thermal vacuum system for measuring the water content of grain products

1984 ◽  
Vol 27 (11) ◽  
pp. 1062-1064
Author(s):  
Yu. A. Kazantsev ◽  
V. P. Ivanov ◽  
N. N. Shubin ◽  
R. I. Isakova
Keyword(s):  
Water Content ◽  
Vacuum System ◽  
Thermal Vacuum ◽  
Grain Products

Analytical and Experimental Study to Predict Radiated Heat Power Between a Satellite and Thermal Shroud

2014 ◽  
Author(s):  
Daniel T. Schwendtner ◽  
M. Ruhul Amin ◽  
David M. Klumpar
Keyword(s):  
Operating Conditions ◽  
Vacuum System ◽  
Maximum Output ◽  
Heat Power ◽  
Thermal Vacuum ◽  
Small Satellites ◽  
Laboratory Setup ◽  
System A ◽  
Concentric Cylinders ◽  
Small Form Factor

Nanosatellites, a class of small satellites, are becoming increasingly popular because of their small form factor and many other attractive features. In the process of qualifying nanosatellites for space readiness, their thermal behavior can be investigated in a laboratory setup using a thermal vacuum system to mimic orbital conditions. For these reasons, a thermal vacuum system suited specifically for nanosatellites was desired for performing thermal vacuum testing. Analytical calculations and laboratory testing were performed as part of the design of this thermal vacuum system. A set of simultaneous equations was solved using the LU Decomposition method to find the radiosities of several surfaces in an enclosure. The radiosities along with their respective view factors were then used to solve for the heat power required to heat and cool the thermal shroud under steady state conditions at the most extreme operating conditions expected. The analysis was performed on a system of three concentric cylinders of varying heights: the outer being the vacuum chamber wall, the middle the thermal shroud inside the chamber, and the inner the satellite. Under the most extreme operating conditions expected, the thermal shroud was cooled to −40°C and the satellite heated to 80°C during satellite cooling and the reverse during satellite heating. All surfaces in the enclosure were assumed to be diffuse, grey, opaque and isothermal. The thermal shroud was separated into two surfaces: the cylindrical shroud body and the shroud top disc. From the analytical results, the expected heating power for the shroud body was found to be 704.0 Watts, and 229.8 Watts for the shroud top. During cooling, where the temperatures were reversed, the expected heat power for the shroud body was calculated as −685.5 Watts, and −220.9 Watts for the shroud top. An experimental setup was tested under similar conditions as a comparison and as a method to validate the thermal shroud design and the analytical calculations. The shroud body and top heaters were selected to output 750 Watts and 230 Watts, respectively, and were driven at their maximum output, with the satellite held at −40°C. The shroud reached 80°C with no difficulty, indicating that the analytical calculations had correctly predicted the required heat power and that the design of the thermal shroud was capable of supporting testing under the most extreme conditions expected.

scholarly journals Modernization of NASA Johnson Space Center’s Chamber A to support Cryogenic Vacuum Optical Testing of the James Webb Space Telescope (JWST)

2021 ◽  
Vol 64 (1) ◽  
pp. 30-41
Author(s):  
Mary Cerimele ◽  
Jonathan Homan ◽  
Sam Garcia ◽  
Jaime Garza ◽  
Gabriel Hirsch ◽  
...  
Keyword(s):  
Vacuum Chamber ◽  
High Vacuum ◽  
Vacuum System ◽  
Thermal Vacuum ◽  
Space Telescope ◽  
James Webb Space Telescope ◽  
Cryogenic Vacuum ◽  
Optical Test ◽  
The World ◽  
Helium Refrigeration

Abstract NASA is the mission lead for the James Webb Space Telescope (JWST), the next of the “Great Observatories,” scheduled for launch in 2021. NASA is directly responsible for the integration and test (I&T) program that culminated in an end-to-end cryo vacuum optical test of the flight telescope and instrument module in Chamber A at NASA Johnson Space Center. Historic Chamber A is the largest thermal vacuum chamber at Johnson Space Center and one of the largest space simulation chambers in the world. Chamber A has undergone a major modernization effort to support the deep cryogenic, vacuum and cleanliness requirements for testing the JWST. This paper describes the upgrades to the Chamber A facility: Thermal Shrouds, Helium Refrigeration, Liquid Nitrogen System, High Vacuum System, Clean Airflow System, and Utilities.

Replication of Wet Objects and Cells

1974 ◽  
Vol 32 ◽  
pp. 102-103
Author(s):  
S. Basu ◽  
D. F. Parsons
Keyword(s):  
Water Vapor Pressure ◽  
High Vacuum ◽  
Polystyrene Latex ◽  
Vacuum System ◽  
Saturated Water Vapor ◽  
Replication Method ◽  
New Methods ◽  
Saturated Water ◽  
Water Vapors ◽  
Intermediate Chamber

We are approaching the invasiveness of cancer cells from the studies of their wet surface morphology which should distinguish them from their normal counterparts. In this report attempts have been made to provide physical basis and background work to a wet replication method with a differentially pumped hydration chamber (Fig. 1) (1,2), to apply this knowledge for obtaining replica of some specimens of known features (e.g. polystyrene latex) and finally to realize more specific problems and to improvize new methods and instrumentation for their rectification. In principle, the evaporant molecules penetrate through a pair of apertures (250, 350μ), through water vapors and is, then, deposited on the specimen. An intermediate chamber between the apertures is pumped independently of the high vacuum system. The size of the apertures is sufficiently small so that full saturated water vapor pressure is maintained near the specimen.

Vacuum System to Minimize the Specimen Contamination of High-Performance EM

1977 ◽  
Vol 35 ◽  
pp. 68-69
Author(s):  
N. Yoshimura ◽  
K. Shirota ◽  
T. Etoh
Keyword(s):  
Electron Microscope ◽  
High Speed ◽  
High Performance ◽  
High Vacuum ◽  
Vacuum System ◽  
Pump System ◽  
Pumping System ◽  
Diffusion Pump ◽  
Almost All ◽  
Cascade Type

One of the most important requirements for a high-performance EM, especially an analytical EM using a fine beam probe, is to prevent specimen contamination by providing a clean high vacuum in the vicinity of the specimen. However, in almost all commercial EMs, the pressure in the vicinity of the specimen under observation is usually more than ten times higher than the pressure measured at the punping line. The EM column inevitably requires the use of greased Viton O-rings for fine movement, and specimens and films need to be exchanged frequently and several attachments may also be exchanged. For these reasons, a high speed pumping system, as well as a clean vacuum system, is now required. A newly developed electron microscope, the JEM-100CX features clean high vacuum in the vicinity of the specimen, realized by the use of a CASCADE type diffusion pump system which has been essentially improved over its predeces- sorD employed on the JEM-100C.

A Superconducting Microscope

1971 ◽  
Vol 29 ◽  
pp. 10-11 ◽  
Author(s):  
R. E. Worsham ◽  
J. E. Mann ◽  
E. G. Richardson
Keyword(s):  
Liquid Helium ◽  
Focal Length ◽  
Vacuum System ◽  
Objective Lens ◽  
Electrical Instability ◽  
Radiation Shields ◽  
And Control ◽  
Thermal Oscillations ◽  
Flux Pump

This superconducting microscope, Figure 1, was first operated in May, 1970. The column, which started life as a Siemens Elmiskop I, was modified by removing the objective and intermediate lenses, the specimen chamber, and the complete vacuum system. The large cryostat contains the objective lens and stage. They are attached to the bottom of the 7-liter helium vessel and are surrounded by two vapor-cooled radiation shields.In the initial operational period 5-mm and 2-mm focal length objective lens pole pieces were used giving magnification up to 45000X. Without a stigmator and precision ground pole pieces, a resolution of about 50-100Å was achieved. The boil-off rate of the liquid helium was reduced to 0.2-0.3ℓ/hour after elimination of thermal oscillations in the cryostat. The calculated boil-off was 0.2ℓ/hour. No effect caused by mechanical or electrical instability was found. Both 4.2°K and 1.7-1.9°K operation were routine. Flux pump excitation and control of the lens were quite smooth, simple, and, apparently highly stable. Alignment of the objective lens proved quite awkward, however, with the long-thin epoxy glass posts used for supporting the lens.

A Freeze Shadow Technique for the Preparation of Soft Paint Latexes for Electron Microscopy

1977 ◽  
Vol 35 ◽  
pp. 314-315
Author(s):  
Earl R. Walter ◽  
Glen H. Bryant
Keyword(s):  
Sample Preparation ◽  
High Vacuum ◽  
Vacuum System ◽  
Latex Particles ◽  
New Methods ◽  
Diffusion Pump ◽  
Film Forming ◽  
Routine Basis ◽  
Distribution Studies ◽  
Preparation Techniques

With the development of soft, film forming latexes for use in paints and other coatings applications, it became desirable to develop new methods of sample preparation for latex particle size distribution studies with the electron microscope. Conventional latex sample preparation techniques were inadequate due to the pronounced tendency of these new soft latex particles to distort, flatten and fuse on the substrate when they dried. In order to avoid these complications and obtain electron micrographs of undistorted latex particles of soft resins, a freeze-dry, cold shadowing technique was developed. The method has now been used in our laboratory on a routine basis for several years.The cold shadowing is done in a specially constructed vacuum system, having a conventional mechanical fore pump and oil diffusion pump supplying vacuum. The system incorporates bellows type high vacuum valves to permit a prepump cycle and opening of the shadowing chamber without shutting down the oil diffusion pump. A baffeled sorption trap isolates the shadowing chamber from the pumps.

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