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NASA NTRS1993

Calibration of a calorimeter for measuring the performance of thermal control surfaces

The calibration to evaluate the heat leak in terms of the deviation from a perfect calorimeter is described. A thermal vacuum test was carried out to characterize the performance of the calorimeter. The calorimeter was equipped with a heater to control the sample disc temperature and with specific instrumentation to measure the heat leak. The radiation sink temperature of the black cavity target was varied from -192 to +31C, while the heater power was varied from 0 to 311 milliwatts. A steady state thermal model was developed to correlate the results. The calorimeter performance was characterized in terms of the heat leak as a percentage of the ideal heat flow of the calorimeter disc. Large deviations from ideal performance occur at low sink temperatures. The effect of the use of the heater is discussed. The effects of transient conditions during low Earth orbit are discussed. It is concluded that heat leak calibrations are necessary for a wide range of conditions.

Houseman, John↗

NASA NTRS1998

Large Scale Testing of a Foam/Multilayer Insulation Thermal Control System (TCS) for Cryogenic Upper Stages

The development of high energy cryogenic upper stages is essential for the efficient delivery of large payloads to various destinations envisioned in future programs. A key element in such upper stages is cryogenic fluid management (CFM) advanced development/technology. Due to the cost of and limited opportunities for orbital experiments, ground testing must be employed to the fullest extent possible. Therefore, a system level test bed termed the Multipurpose Hydrogen Test Bed (MHTB), which is representative in size and shape (3 meter diameter by 3 meter long with a volume of 18 cubic meters) of a fully integrated space transportation vehicle liquid hydrogen propellant tank has been established. To date, upper stage studies have often baselined the foam/multilayer insulation (FMLI) combination concept; however, hardware experience with the concept is minimal and was therefore selected for the MHTB. The foam element (isofoam SS-1 171 with an average thickness of 3.5 centimeters) is designed to protect against ground hold/ascent flight environments, and allows for the use of a dry nitrogen purge as opposed to the more complex/heavy helium purge subsystem normally required with MLI in cryogenic applications. The MLI (45 layers of Double Aluminized Mylar with Dacron spacers) provides protection in the vacuum environment of space and is designed for an on-orbit storage period of 45 days. Several unique features were incorporated in the MLI concept and included: variable density MLI (reduces weight and radiation losses by changing the layer density), larger but fewer DAM perforations for venting during ascent to orbit (reduces radiation losses), and roll wrap installation of the MLI with a commercially established process to lower assembly man-hours and reduce seam heat leak. Thermal performance testing of the MHTB TCS was conducted during three test series conducted between September 1995 and May 1996. Results for the ground hold portion of the tests were as expected producing an average heat leak of 63 WattS/M2 at an average foam surface temperature of 170 K. The results of the simulated orbit hold test interval produced heat leaks ranging from 0.085 to 0.22 Watts/squareM at warm boundary temperatures of 164K and 305K, respectively. When compared to the performance for a traditional MLI system, a 60% reduction in orbital heat leak or boiloff was measured. Overall, the MHTB TCS demonstrated satisfactory performance for all mission phases required of a cryogenic upper stage.

Hastings, Leon↗

NASA NTRS2015

Comparison of Cryogenic Flow Boiling in Liquid Nitrogen and Liquid Hydrogen Chilldown Experiments

This paper presents a comparison between experimental results from recent liquid hydrogen (LH 2 ) transfer line chilldown experiments at high Reynolds (Re) numbers versus liquid nitrogen (LN 2 ) experiments conducted at low Re numbers. Parasitic heat leak, inner wall temperatures, inner wall heat fluxes, and heat transfer coefficients are computed to compare between the two systems. Analysis of temperature traces and flow visualization indicates that the chilldown process evolves much more rapidly at higher Re numbers due to a quick transition from vapor flow to annular liquid flow and near immediate liquid contact along the pipe walls. The lower kinematic viscosity and surface tension of LH 2 , along with reduced parasitic heat leak and higher Re numbers relative to the LN 2 experiments, causes chilldown to proceed almost immediately into the nucleate boiling regime, in comparison to low Re flows where >75% of the chilldown is spent in vapor film boiling.

Cryogenic Heat Transfer Coefficient↗

NASA NTRS2015

Thermal Design of Vapor Cooling of Flight Vehicle Structures Using LH2 Boil-Off

Using hydrogen boil-off vapor to cool the structure of a flight vehicle cryogenic upper stage can reduce heat loads to the stage and increase the usable propellant in the stage or extend the life of the stage. The hydrogen vapor can be used to absorb incoming heat as it increases in temperature before being vented overboard. In theory, the amount of heat leaking into the hydrogen tank from the structure will be reduced if the structure is cooled using the propellant boil-off vapor. However, the amount of boil-off vapor available to be used for cooling and the reduction in heat leak to the propellant tank are dependent to each other. The amount of heat leak reduction to the LH2 tank also depends on the total heat load on the stage and the vapor cooling configurations.

heat transfer↗

NASA NTRS2017

Investigation of Vapor Cooling Enhancements for Applications on Large Cryogenic Systems

The need to demonstrate and evaluate the effectiveness of heat interception methods for use on a relevant cryogenic propulsion stage at a system level has been identified. Evolvable Cryogenics (eCryo) Structural Heat Intercept, Insulation and Vibration Evaluation Rig (SHIIVER) will be designed with vehicle specific geometries (SLS Exploration Upper Stage (EUS) as guidance) and will be subjected to simulated space environments. One method of reducing structure-born heat leak being investigated utilizes vapor-based heat interception. Vapor-based heat interception could potentially reduce heat leak into liquid hydrogen propulsion tanks, increasing potential mission length or payload capability. Due to the high number of unknowns associated with the heat transfer mechanism and integration of vapor-based heat interception on a realistic large-scale skirt design, a sub-scale investigation was developed. The sub-project effort is known as the Small-scale Laboratory Investigation of Cooling Enhancements (SLICE). The SLICE aims to study, design, and test sub-scale multiple attachments and flow configuration concepts for vapor-based heat interception of structural skirts. SLICE will focus on understanding the efficiency of the heat transfer mechanism to the boil-off hydrogen vapor by varying the fluid network designs and configurations. Various analyses were completed in MATLAB, Excel VBA, and COMSOL Multiphysics to understand the optimum flow pattern for heat transfer and fluid dynamics. Results from these analyses were used to design and fabricate test article subsections of a large forward skirt with vapor cooling applied. The SLICE testing is currently being performed to collect thermal mechanical performance data on multiple skirt heat removal designs while varying inlet vapor conditions necessary to intercept a specified amount of heat for a given system. Initial results suggest that applying vapor-cooling provides a 50 heat reduction in conductive heat transmission along the skirt to the tank. The information obtained by SLICE will be used by the SHIIVER engineering team to design and implement vapor-based heat removal technology into the SHIIVER forward skirt hardware design.

small scale testing↗

NASA NTRS2011

Cryogenic Propellant Feed System Analytical Tool Development

The Propulsion Systems Branch at NASA s Lyndon B. Johnson Space Center (JSC) has developed a parametric analytical tool to address the need to rapidly predict heat leak into propellant distribution lines based on insulation type, installation technique, line supports, penetrations, and instrumentation. The Propellant Feed System Analytical Tool (PFSAT) will also determine the optimum orifice diameter for an optional thermodynamic vent system (TVS) to counteract heat leak into the feed line and ensure temperature constraints at the end of the feed line are met. PFSAT was developed primarily using Fortran 90 code because of its number crunching power and the capability to directly access real fluid property subroutines in the Reference Fluid Thermodynamic and Transport Properties (REFPROP) Database developed by NIST. A Microsoft Excel front end user interface was implemented to provide convenient portability of PFSAT among a wide variety of potential users and its ability to utilize a user-friendly graphical user interface (GUI) developed in Visual Basic for Applications (VBA). The focus of PFSAT is on-orbit reaction control systems and orbital maneuvering systems, but it may be used to predict heat leak into ground-based transfer lines as well. PFSAT is expected to be used for rapid initial design of cryogenic propellant distribution lines and thermodynamic vent systems. Once validated, PFSAT will support concept trades for a variety of cryogenic fluid transfer systems on spacecraft, including planetary landers, transfer vehicles, and propellant depots, as well as surface-based transfer systems. The details of the development of PFSAT, its user interface, and the program structure will be presented.

Lusby, Brian S.↗

NASA NTRS2019

Return to Service of a Liquid Hydrogen Storage Sphere

One, of two, 850,000 gallon liquid hydrogen storage spheres, at NASA's Kennedy Space Center, was decommissioned in 2010. This tank had an abnormally high heat leak that was investigated and determined to be the result of a large void in the perlite insulation. The insulation void was subsequently filled, and the tank was refurbished for its planned use in the Space Launch Systems (SLS) program. Return to service of this tank began in December of 2017 with a partial liquid hydrogen fill. Since that time, routine measurement of the liquid level have been recorded in order to establish a new boiloff rate and associated heat leak. This data shows the perlite top off activities have resulted in a much reduced, and within design specification, heat leak.

air leak↗

NASA NTRS2019

Return to Service of a Liquid Hydrogen Storage Sphere

Krenn, A. G.↗

NASA NTRS1982

Improved multilayer insulation applications

Multilayer insulation blankets used for the attenuation of radiant heat transfer in spacecraft are addressed. Typically, blanket effectiveness is degraded by heat leaks in the joints between adjacent blankets and by heat leaks caused by the blanket fastener system. An approach to blanket design based upon modular sub-blankets with distributed seams and upon an associated fastener system that practically eliminates the through-the-blanket conductive path is described. Test results are discussed providing confirmation of the approach. The specific case of the thermal control system for the optical assembly of the Space Telescope is examined.

Mikk, G.↗

NASA NTRS1993

Liquid oxygen (LO2) propellant conditioning concept testing

Testing of a simplified LO2 propellant conditioning concept for future expendable launch vehicles is discussed. Four different concepts are being investigated: no-bleed, low-bleed, use of a recirculation line, and He bubbling. A full-scale test article, which is a facsimile of a propellant feed duct with an attached section to simulate heat input from an LO2 turbopump, is to be tested at the Cold Flow Facility of the Marshall Space Flight Center West Test Area. Work to date includes: design and fabrication of the test article, design of the test facility and initial fabrication, development of a test matrix and test procedures, initial predictions of test output, and heat leak calibration and heat exchanger tests on the test articles.

Perry, Gretchen L. E.↗

NASA NTRS1993

Liquid Oxygen (LO2) propellant conditioning concept testing

Marshall Space Flight Center (MSFC) and industry contractors have undertaken activities to develop a simplified liquid oxygen (LO2) propellant conditioning concept for future expendable launch vehicles. The objective of these activities is to reduce operations costs and timelines and to improve safety of these vehicles. The approach followed has been to identify novel concepts through system level studies and demonstrate the feasibility of these concepts through small-scale and full-scale testing. Testing will also provide data for design guidelines and validation of analytical models. Four different concepts are being investigated: no-bleed, low-bleed, use of a recirculation line, and helium (He) bubbling. This investigation is being done under a Joint Institutional Research and Development (JIRAD) program currently in effect between MSFC and General Dynamics Space Systems (GDSS). A full-scale test article, which is a facsimile of a propellant feed duct with an attached section to simulate heat input from a LO2 turbopump, will be tested at the Cold Flow Facility at MSFC's West Test Area. Liquid nitrogen (LN2), which has similar properties to LO2, will be used in place of LO2 for safety and budget reasons. Work to date includes design and fabrication of the test article, design of the test facility and initial fabrication, development of a test matrix and test procedures, initial predictions of test output, and heat leak calibration and heat exchanger tests on the test article. The tests for all propellant conditioning concepts will be conducted in the summer of 1993, with the final report completed by October, 1993.

Perry, Gretchen L. E.↗

NASA NTRS2002

Effect of External Pressure Drop on Loop Heat Pipe Operating Temperature

This paper discusses the effect of the pressure drop on the operating temperature in a loop heat pipe (LHP). Because the evaporator and the compensation chamber (CC) both contain two-phase fluid, a thermodynamic constraint exists between the temperature difference and the pressure drop for these two components. As the pressure drop increases, so will the temperature difference. The temperature difference in turn causes an increase of the heat leak from the evaporator to the CC, resulting in a higher CC temperature. Furthermore, the heat leak strongly depends on the vapor void fraction inside the evaporator core. Tests were conducted by installing a valve on the vapor line so as to vary the pressure drop, and by charging the LHP with various amounts of fluid. Test results verify that the LHP operating temperature increases with an increasing differential pressure, and the temperature increase is a strong function of the fluid inventory in the loop.

Jentung, Ku↗

NASA NTRSDate not supplied

Stationary Testing of a Pulse Tube Cryocooler Designed to Rotate at 6800 RPM with the Superconducting Rotor of an Electric Machine

Electrified aircraft are being developed to increase the efficiency and reduce the cost of operating subsonic transport aircraft. Achieving a substantial impact necessitates focusing on single- and twin-aisle aircraft which use propulsion systems with >20 MW ratings. For these aircraft, multi-MW superconducting electric machines are being developed due to their high specific power and high efficiency. Most of these electric machines employ superconductors on their rotor, thereby requiring cryogenic cooling of the rotating system. An attractive solution is to conductively cool the rotor using a cryocooler that rotates with the rotor. NASA has been developing a 50 K pulse tube cryocooler for its High Efficiency Megawatt Motor (HEMM) that can operate while rotating at up to 6,800 rpm. The first non-rotating tests of the fully assembled HEMM cryocooler have been completed, and initial testing has yielded a no-load temperature of 112 K. A small helium leak into the vacuum system has been identified as the major bottleneck to performance, and based on measurements with the motor turned off there is an observed vacuum-side heat leak of approximately 30 W at 115 K. Immediate next steps for testing are to locate and mitigate the apparent helium leaks into the vacuum chamber. Thus far, compressor performance and the apparent heat lift after correcting for the heat leak are on par with expectations.

Electrified Aircraft Propulsion↗

NASA NTRS1957

Experimental study of foam-insulated liquified-gas tanks

Experiments with liquid nitrogen and liquid hydrogen is styrofoam-insulated tanks have indicated good agreement between measured and calculated heat-leak rates when the insulation was formed from a single block of material. In a large tank installation where the insulation was applied in sections without sealing the joints, the measured heat leak was about 2 and 1/2 times the calculated value.

Reynolds, Thaine W↗

NASA NTRS2005

Improving Control in a Joule-Thomson Refrigerator

A report discusses a modified design of a Joule-Thomson (JT) refrigerator under development to be incorporated into scientific instrumentation aboard a spacecraft. In most other JT refrigerators (including common household refrigerators), the temperature of the evaporator (the cold stage) is kept within a desired narrow range by turning a compressor on and off as needed. This mode of control is inadequate for the present refrigerator because a JT-refrigerator compressor performs poorly when the flow from its evaporator varies substantially, and this refrigerator is required to maintain adequate cooling power. The proposed design modifications include changes in the arrangement of heat exchangers, addition of a clamp that would afford a controlled heat leak from a warmer to a cooler stage to smooth out temperature fluctuations in the cooler stage, and incorporation of a proportional + integral + derivative (PID) control system that would regulate the heat leak to maintain the temperature of the evaporator within a desired narrow range while keeping the amount of liquid in the evaporator within a very narrow range in order to optimize the performance of the compressor. Novelty lies in combining the temperature- and cooling-power-regulating controls into a single control system.

Borders, James↗

NASA NTRS2011

Issues of Long-Term Cryogenic Propellant Storage in Microgravity

Modern multi-layer insulation (MLI) allows to sharply reduce the heat leak into cryogenic propellant storage tanks through the tank surface and, as a consequence, significantly extend the storage duration. In this situation the MLI penetrations, such as support struts, feed lines, etc., become one of the most significant challenges of the tanks heat management. This problem is especially acute for liquid hydrogen (LH2) storage, since currently no efficient cryocoolers exist that operate at very low LH2 temperatures (20K). Even small heat leaks under microgravity conditions and over the period of many months give rise to a complex slowly-developing, large-scale spatiotemporal physical phenomena in a multi-phase liquid-vapor mixture. These phenomena are not well-understood nor can be easily controlled. They can be of a potentially hazardous nature for long-term on-orbital cryogenic torage, propellant loading, tank chilldown, engine restart, and other in-space cryogenic fluid management operations. To support the engineering design solutions that would mitigate these effects a detailed physics-based analysis of heat transfer, vapor bubble formation, growth, motion, coalescence and collapse is required in the presence of stirring jets of different configurations and passive cooling devices such as MLI, thermodynamic vent system, and vapor-cooled shield. To develop physics-based models and correlations reliable for microgravity conditions and long-time scales there is a need for new fundamental data to be collected from on-orbit cryogenic storage experiments. Our report discusses some of these physical phenomena and the design requirements and future studies necessary for their mitigation. Special attention is payed to the phenomena occurring near MLI penetrations.

Muratov, C. B.↗

NASA NTRS1993

A two-stage magnetic refrigerator for astronomical applications with reservoir temperatures above 4 K

We propose a novel adiabatic demagnetization refrigerator (ADR) to produce temperatures as low as 100 mK starting from a high temperature reservoir between 4 and 8 K. The high temperature reservoir for the ADR can be provided by a mechanical cooler or an unpumped liquid helium bath. This refrigerator can be used to cool bolometric infrared detectors for low background astronomy from mountain tops, balloons or satellites as well as to cool cryogenic x-ray detectors. The two-stage ADR consists of a single magnet with a paramagnetic chromic-cesium-alum (CCA) salt pill to produce the low temperature and paramagnetic gadolinium-gallium-garnet (GGG) as the first stage to intercept heat from the high temperature reservoir. Thermal contact between the paramagnets and the reservoir during magnetization is made with a mechanical heat switch. The ADR is suspended with Kevlar chords under tension for high mechanical stiffness and low parasitic heat leak. In a single cycle, the ADR maintains a temperature of 100 mK for 10 to 100 hours. This time depends strongly on the magnetic field and reservoir temperature but not on the volume of the paramagnetic material as long as the heat leak is dominated by the suspension.

Hagmann, C.↗

NASA NTRS1974

Study of multilayered insulation pipe penetration. Thermal acoustic oscillation

Tests were conducted to determine the net heat leak to a source of liquid nitrogen caused by a metal penetration through the blanket of multilayer insulation. The conditions under which the tests were conducted are described. A graph of the theoretical and experimental temperature distribution is developed for comparison. The variables involved in the computer program to process the data are defined. A study was conducted to develop analytical methods for predicting the effect and magnitudes of thermoacoustic oscillations on the penetration heat leak to cryogens. The oscillations develop as a result of large thermal gradients imposed on a compressible fluid. The predominant amplitudes and frequencies of the thermal acoustic oscillations were investigated.

Lovin, J. K.↗