Results for “ambient loops” — Page 6

NASA NTRS1985

Development status of regenerable solid amine CO2 control systems

The development history of solid amine/water desorbed (SAWD) CO2 control systems is reviewed. The design of the preprototype SAWD I CO2 system on the basis of a three-man metabolic load at the 3.8 mm Hg ambient CO2 level, and the functions of the CO2 removal, CO2 storage/delivery, controller, and life test laboratory support packages are described. The development of a full-scale multiple canister SAWD II preprototype system, which is capable of conducting the CO2 removal/concentration function in a closed-loop atmosphere revitalization system during zero-gravity operation, is examined. The operation of the SAWD II system, including the absorption and desorption cycles, is analyzed. A reduction in the thermal mass of the canister and the system's energy transfer technique result in efficient energy use. The polyether foam, nylon felt, nickel foam, spring retained, and metal bellows bed tests performed to determine the design of the zero-gravity canister are studied; metal bellows are selected for the canister's configuration.

Colling, A. K., Jr.↗

NASA NTRS2005

Evaluation of an Active Clearance Control System Concept

Reducing blade tip clearances through active tip clearance control in the high pressure turbine can lead to significant reductions in emissions and specific fuel consumption as well as dramatic improvements in operating efficiency and increased service life. Current engines employ scheduled cooling of the outer case flanges to reduce high pressure turbine tip clearances during cruise conditions. These systems have relatively slow response and do not use clearance measurement, thereby forcing cold build clearances to set the minimum clearances at extreme operating conditions (e.g., takeoff, reburst) and not allowing cruise clearances to be minimized due to the possibility of throttle transients (e.g., step change in altitude). In an effort to improve upon current thermal methods, a first generation mechanically-actuated active clearance control (ACC) system has been designed and fabricated. The system utilizes independent actuators, a segmented shroud structure, and clearance measurement feedback to provide fast and precise active clearance control throughout engine operation. Ambient temperature performance tests of this first generation ACC system assessed individual seal component leakage rates and both static and dynamic overall system leakage rates. The ability of the nine electric stepper motors to control the position of the seal carriers in both open- and closed-loop control modes for single and multiple cycles was investigated. The ability of the system to follow simulated engine clearance transients in closed-loop mode showed the system was able to track clearances to within a tight tolerance (0.001 in. error).

Steinetz, Bruce M.↗

NASA NTRS2005

Evaluation of an Active Clearance Control System Concept

Reducing blade tip clearances through active tip clearance control in the high pressure turbine can lead to significant reductions in emissions and specific fuel consumption as well as dramatic improvements in operating efficiency and increased service life. Current engines employ scheduled cooling of the outer case flanges to reduce high pressure turbine tip clearances during cruise conditions. These systems have relatively slow response and do not use clearance measurement, thereby forcing cold build clearances to set the minimum clearances at extreme operating conditions (e.g., takeoff, reburst) and not allowing cruise clearances to be minimized due to the possibility of throttle transients (e.g., step change in altitude). In an effort to improve upon current thermal methods, a first generation mechanically-actuated active clearance control (ACC) system has been designed and fabricated. The system utilizes independent actuators, a segmented shroud structure, and clearance measurement feedback to provide fast and precise active clearance control throughout engine operation. Ambient temperature performance tests of this first generation ACC system assessed individual seal component leakage rates and both static and dynamic overall system leakage rates. The ability of the nine electric stepper motors to control the position of the seal carriers in both open- and closed-loop control modes for single and multiple cycles was investigated. The ability of the system to follow simulated engine clearance transients in closed-loop mode showed the system was able to track clearances to within a tight tolerance ( 0.001 in. error).

Steinetz, Bruce M.↗

NASA NTRS1974

Investigation of critical burning of fuel droplets

The steady combustion characteristics of droplets were considered in combustion chamber environments at various pressures, flow conditions, and ambient oxidizer concentrations for a number of hydrocarbon fuels. Using data obtained earlier, predicted gasification rates were within + or - 30% of measurements when the correction for convection was based upon average properties between the liquid surface and the flame around the droplet. Analysis was also completed for the open loop response of monopropellant droplets, based upon earlier strand combustion results. At the limit of large droplets, where the effect of flame curvature is small, the results suggest sufficient response to provide a viable mechanism for combustion instability in the frequency and droplet size range appropriate to practical combustors. Calculations are still in progress for a broader range of droplet sizes, including conditions where active combustion effects are small.

Faeth, G. M.↗

NASA NTRS2012

Future Gamma-Ray Imaging of Solar Eruptive Events

Solar eruptive events, the combination of large solar flares and coronal mass ejections (CMEs), accelerate ions to tens of Gev and electrons to hundreds of MeV. The energy in accelerated particles can be a significant fraction (up to tens of percent) of the released energy and is roughly equipartitioned between ions and electrons. Observations of the gamma-ray signatures produced by these particles interacting with the ambient solar atmosphere probes the distribution and composition of the accelerated population, as well as the atmospheric parameters and abundances of the atmosphere, ultimately revealing information about the underlying physics. Gamma-ray imaging provided by RHESSI showed that the interacting approx.20 MeV/nucleon ions are confined to flare magnetic loops rather than precipitating from a large CME-associated shock. Furthermore, RHESSI images show a surprising, significant spatial separation between the locations where accelerated ions and electrons are interacting, thus indicating a difference in acceleration or transport processes for the two types of particles. Future gamma-ray imaging observations, with higher sensitivity and greater angular resolution, can investigate more deeply the nature of ion acceleration. The technologies being proven on the Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS), a NASA balloon instrument, are possible approaches for future instrumentation. We discuss the GRIPS instrument and the future of studying this aspect of solar eruptive events.

Shih, Albert↗

NASA NTRS1983

Stochastic three-wave interaction in flaring solar loops

A model is proposed for the dynamic structure of high-frequency microwave bursts. The dynamic component is attributed to beams of precipitating electrons which generate electrostatic waves in the upper hybrid branch. Coherent upconversion of the electrostatic waves to electromagnetic waves produces an intrinsically stochastic emission component which is superposed on the gyrosynchrotron continuum generated by stably trapped electron fluxes. The role of the density and temperature of the ambient plasma in the wave growth and the transition of the three wave upconversion to stochastic, despite the stationarity of the energy source, are discussed in detail. The model appears to reproduce the observational features for reasonable parameters of the solar flare plasma.

Vlahos, L.↗

NASA NTRS2016

An Advanced Loop Heat Pipe for Cryogenic Applications

A loop heat pipe (LHP) is a very versatile heat transfer device which can transport a large heat load over a long distance with a small temperature difference. All LHPs currently servicing orbiting spacecraft are designed to operate in the room temperature range. Future space telescopes and space-based Earth resource imaging satellites require passive cryogenic heat transport devices that can thermally couple remote cryocoolers to sensor or instrument of interest while providing the capability of payload vibration/jitter isolation, implementation of redundant coolers, and coupling of multiple sensors to a common heat sink. All of these requirements can be satisfied by using a cryogenic LHP (CLHP). Although the development of CLHPs faces several technical challenges, NASA Goddard Space Flight Center has devoted extensive efforts in developing CLHP technology over the past decade and has made significant progress. In particular, the combination of the innovative ideas of using a secondary capillary pump to manage the parasitic heat gain and using a hot reservoir to reduce the system pressure under the ambient condition has led to the successful development of the CLHP. Several CLHPs charged with nitrogen and hydrogen were built and tested in thermal vacuum chambers. These CLHPs demonstrated reliable start-up and robust operation during power cycle and sink temperature cycle tests.

Loop Heat Pipes↗

NASA NTRS2017

An Advanced Loop Heat Pipe for Cryogenic Applications

A loop heat pipe (LHP) is a very versatile heat transfer device that can transport a large heat load over a long distance with a small temperature difference. All LHPs currently servicing orbiting spacecraft are designed to operate in the room temperature range. Future space telescopes and space-based Earth resource imaging satellites require passive cryogenic heat transport devices that can thermally couple remote cryocoolers to sensor or instrument of interest while providing the capability of payload vibration jitter isolation, implementation of redundant coolers, and coupling of multiple sensors to a common heat sink. All of these requirements can be satisfied by using a cryogenic LHP (CLHP). Although the development of CLHPs faces several technical challenges, NASA Goddard Space Flight Center has devoted extensive efforts in developing CLHP technology over the past decade and has made significant progress. In particular, the combination of the innovative ideas of using a secondary capillary pump to manage the parasitic heat gain and using a hot reservoir to reduce the system pressure under the ambient condition has led to the successful development of the CLHP. Several CLHPs charged with nitrogen and hydrogen were built and tested in thermal vacuum chambers. These CLHPs demonstrated reliable start-up and robust operation during power cycle and sink temperature cycle tests.

Loop Heat Pipes↗

NASA NTRS2017

An Advanced Loop Heat Pipe for Cryogenic Applications

A loop heat pipe (LHP) is a very versatile heat transfer device that can transport a large heat load over a long distance with a small temperature difference. All LHPs currently servicing orbiting spacecraft are designed to operate in the room temperature range. Future space telescopes and space-based Earth resource imaging satellites require passive cryogenic heat transport devices that can thermally couple remote cryocoolers to sensor or instrument of interest while providing the capability of payload vibration jitter isolation, implementation of redundant coolers, and coupling of multiple sensors to a common heat sink. All of these requirements can be satisfied by using a cryogenic LHP (CLHP). Although the development of CLHPs faces several technical challenges, NASA Goddard Space Flight Center has devoted extensive efforts in developing CLHP technology over the past decade and has made significant progress. In particular, the combination of the innovative ideas of using a secondary capillary pump to manage the parasitic heat gain and using a hot reservoir to reduce the system pressure under the ambient condition has led to the successful development of the CLHP. Several CLHPs charged with nitrogen and hydrogen were built and tested in thermal vacuum chambers. These CLHPs demonstrated reliable start-up and robust operation during power cycle and sink temperature cycle tests.

Loop Heat Pipes↗

NASA NTRS1993

Screech tones from free and ducted supersonic jets

The dependence of the instability wave spectrum on azimuthal mode number, the jet to ambient gas temperature ratio, and the jet Mach number is studied. It is shown that the switch of the dominant screech mode (axisymmetric to helical/flapping) as Mach number increases is due to the switch in dominance of the corresponding mode of instability waves. Super-resonance can occur when the feedback loop is powered by the most amplified instability wave. It is suggested that the large amplitude pressure fluctuations and tone in the test cells are generated by super-resonance.

Tam, C. K. W.↗

NASA NTRS1989

Photocatalytic post-treatment in waste water reclamation systems

A photocatalytic water purification process is described which effectively oxidizes organic impurities common to reclaimed waste waters and humidity condensates to carbon dioxide at ambient temperatures. With this process, total organic carbon concentrations below 500 ppb are readily achieved. The temperature dependence of the process is well described by the Arrhenius equation and an activation energy barrier of 3.5 Kcal/mole. The posttreatment approach for waste water reclamation described here shows potential for integration with closed-loop life support systems.

Cooper, Gerald↗

NASA NTRS1985

The propagation of solar flare particles in a turbulent coronal loop

Energetic solar flare particles, both electrons and protons, must survive the turbulent environment of a flaring loop and propogate to the lower corona or chromosphere in order to produce hard X-ray and gamma ray bursts. This plasma turbulence, often observed in soft X-ray line widths to be in excess of 100 km/s, is presumably capable of efficiently scattering the fast flare particles. This prevents to some degree the free streaming of accelerated particles and depending on the amplitude of the turbulence, restricts the particles to diffusive propagation along the length of the loop to the target chromosphere. In addition this turbulence is capable of performing additional acceleration of the fast particles by the second order Fermi mechanism. For compact flares with rise times 10s, the acceleration effect is small and the propagation of the particles is governed by spatial diffusion and energy loss in the ambient medium. The solution of the time dependent diffusion equation with velocity dependent diffusion and energy loss coefficients yields for the case of nonrelativistic protons particle precipitation rates which are necessary for calculating thick target gamma ray emission and also yields the total thin target emissivity.

Ryan, J. M.↗

NASA NTRS2022

Water Quality Contamination Sources and Controls for the Exploration Extra-vehicular Mobility Unit (xEMU)

NASA has been developing a new spacesuit, called the Exploration Extravehicular Mobility Unit (xEMU) for over a decade. This spacesuit is underdevelopment to support missions to the International Space Station (ISS) and also to the Moon. The xEMU uses controlled evaporative cooling through a membrane to reject waste heat from the crewmember, avionics, and environmental in-leak during autonomous operation. Given the unique mass and volume constraints imposed by the spacesuit application and the opportunities presented by the selection of a given membrane, the xEMU does not possess a separate feedwater loop to feed the evaporation process, rather the feedwater for the evaporation process is fed directly from the transport loop which collects heat from the sources within the suit. This has many benefits including mass/volume reductions from a lower component count within the system but does pose some additional potential constraints on water quality within the system in order to provide a working fluid that can be pumped, filtered, and used in contact with the remainder of the system while both avoiding fouling of the membrane as well as other deleterious effects such as creating conditions for corrosion of wetted surfaces within the transport loop. The discussion will seek to address the main sources of contamination and the applied controls. Sources considered will include: self-generated via materials selection and processes applied, influent working fluid, contamination of the influent working fluid via Ground Support Equipment (GSE) or processing equipment, microbial activity, and environmental influences such as elevated ambient CO2.

Colin Campbell↗

NASA NTRS1992

Automated High-Temperature Hall-Effect Apparatus

Automated apparatus takes Hall-effect measurements of specimens of thermoelectric materials at temperatures from ambient to 1,200 K using computer control to obtain better resolution of data and more data points about three times as fast as before. Four-probe electrical-resistance measurements taken in 12 electrical and 2 magnetic orientations to characterize specimens at each temperature. Computer acquires data, and controls apparatus via three feedback loops: one for temperature, one for magnetic field, and one for electrical-potential data.

Parker, James B.↗

NASA NTRS2008

Methods of Controlling the Loop Heat Pipe Operating Temperature

The operating temperature of a loop heat pipe (LHP) is governed by the saturation temperature of its compensation chamber (CC); the latter is in turn determined by the balance among the heat leak from the evaporator to the CC, the amount of subcooling carried by the liquid returning to the CC, and the amount of heat exchanged between the CC and ambient. The LHP operating temperature can be controlled at a desired set point by actively controlling the CC temperature. The most common method is to cold bias the CC and use electric heater power to maintain the CC set point temperature. The required electric heater power can be large when the condenser sink is very cold. Several methods have been developed to reduce the control heater power, including coupling block, heat exchanger and separate subcooler, variable conductance heat pipe, by-pass valve with pressure regulator, secondary evaporator, and thermoelectric converter. The paper discusses the operating principles, advantages and disadvantages of each method.

Ku, Jentung↗

NASA NTRS1981

The Cygnus 'superbubble' - A supernova explosion in a tenuous intercloud medium

Cash et al. (1980) observed an incomplete X-ray shell in the Cygnus region with a temperature of 2 x 10 to the 6th K and a density of 0.02 per cu cm. This feature closely resembles Loop I, a nearby supernova remnant expanding in a tenuous (less than 0.01 per cu cm) medium. A similar origin - remnant expansion in a tenuous intercloud medium with the bulk of the interstellar gas concentrated in clouds - is suggested for the Cygnus X-ray feature. This model greatly reduces the required initial thermal energy. Remnant shock interaction with ambient interstellar clouds produces the observed H-alpha filaments.

Higdon, J. C.↗

NASA NTRS1990

Studies of the local interstellar medium. VIII - Morphology and kinematics of the diffuse interstellar clouds toward Orion

Interstellar clouds in the direction of the Orion association show only positive velocities for target stars within 190 pc of the sun, and both positive and negative velocities for more distant target stars, confirming an earlier prediction by Cowie, Songaila, and York (1979). The nearby positive velocity cloud, designated here as Orion-Lepus 70 (OL 70), is a standard diffuse interstellar cloud: it is subject to the ambient galactic radiation field, with properties consistent with T about equal to 100 K and n about equal to 3/cu cm. Combined with a column density log N(H) = 19.8-20.0/sq cm, these values imply a cloud thickness of about 7 pc. The kinematics of OL 70 are consistent with either an origin as part of the expanding Loop I superbubble shell, or as part of Lindbald's expanding ring, or a synthesis of the two models. The negative velocity interstellar components seen in stars at d not less than 200 pc are caused by interstellar matter accelerated by the expanding Ori-Eri superbubble. Relatively dense interstellar gas at positive LSR velocities is also found within the Orion association, so that it is difficult to pick out OL 70 components in the spectra of the distant stars.

Frisch, P. C.↗

NASA NTRS2026

Dynamic Regulation of Sub-Atmospheric Pressure for Constant and Cyclic Gas Loads During Testing of Spacesuit Components

New iterations of the various subsystems within the spacesuit will benefit from a new sorbent technology. For example, sorbents used in the Trace Contaminant Control (TCC) and the Rapid Cycle Amine (RCA) systems within the Exploration Portable Life Support System (xPLSS), part of the Extra-Vehicular Mobility Unit (xEMU). For proper validation, the sub-atmospheric pressure needs to be maintained within a simulated 2 ft 3 spacesuit volume. The traditional approach, which involves placing the entire vent loop within a hypobaric chamber, is not practical for the widespread testing of components and prototypes, as these specialized chambers are costly and not widely available. A two-stage regulator based sub-atmospheric pressure system is presented in this work. The method regulates the pressure based on pressure differentials between the pressure regulation pump, the test system, and the ambient environment. The performance of this system is demonstrated using data collected during a 150+ hour non-regenerative TCC sorbent evaluation, several 24-hour regenerative TCC sorbent evaluations with different regeneration cycles, and an 8-hour RCA sorbent evaluation, all under xEMU operating conditions. For regulation, the inlet regulator was set to propagate a small leak to increase the stability of the system as the gas load from the testing system changes. It was also found that controlling the input flow rate that replaces the material lost during regeneration is critical for ensuring the stability of the system. This system provided excellent pressure regulation, without adjustments, for constant loads during shorter time evaluations (hours), while longer time evaluations (days) are easily obtainable with periodic regulator adjustments. A second method is under development to address longer-term stability and to automate pressure regulation. It will incorporate flow and pressure measurements to dynamically control a set of electronically controlled proportional valves for adjusting the pumping speed and air bleed supply.

Nicholas F Materer↗