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At least 109 records · Page 6

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NASA NTRS1973

Environmental test report for the WX-32335 SEC camera tube

The environmental testing activity on the WX-32335 was carried out to determine if this tube type could withstand the environmental requirements established for the International Ultraviolet Explorer (IUE) camera tube (WX-32224). The results of the tests led to the following conclusions: (1) The WX-32335 as processed with a CsTe photocathode surface can withstand the temperature extremes established for the IUE camera tube without damage to the photocathode surface or without introducing background signal in the tube after one hour of dark integration. (2) The WX-32335 built with a WX-32224 type target support structure can withstand the sinusoidal vibration requirements established for the IUE camera tube. (3) Although the vibration test of the WX-32335 type tubes built with the flat target ring structure could not be completed, there was no indication that these tubes could not withstand the sinusoidal vibration requirements established for the IUE camera tube.

Malanoski, R. J.↗

NASA NTRS1983

Wave propagation in intense flux tubes

The nature of nonadiabatic wave propagation in a slender magnetic flux tube is explored. The results of the theory are compared with the observations of Giovanelli et al. (1978), and found to be in general agreement. Those observations, of tubes in the photosphere-chromosphere, show outwardly propagating waves, with periods of 300 s, which take some 19 s to propagate from one level of line formation to another level higher in the atmosphere. In sharp contrast to this, is the time of 7 s for a similar disturbance outside the tube to propagate between the same two levels of line formation, estimated to be some 600 km apart in the field-free atmosphere. It is argued that the sharply contrasting propagation times for the tube and its environment is principally due to the elasticity of the tube and its subsequent propensity for propagation. A nonadiabatic disturbance may be essentially propagating within the tube but essentially nonpropagating outside, with considerably slower phase speeds thus arising inside the tube. The theory suggests that the observed disturbances are nonadiabatic, acoustic-gravity waves channelled along a magnetic flux tube and modulated by external pressure variations.

Roberts, B.↗

NASA NTRS1985

Alining Heat-Exchanger Tubes for Assembly

Simple support method makes costly jigs and fixtures unnecessary. "Dummy" tubes installed at regular intervals to support "real" tubes before real tubes installed, filled with Cerrobend (or equivalent) material, metallic substance with low melting point, makes dummy tubes rigid so they brace real tubes as installed. When all available spaces for real tubes filled, dummy tubes removed and replaced with real tubes.

Benson, K. A.↗

NASA NTRS1988

Analytical study of graphite-epoxy tube response to thermal loads

The thermally-induced stresses and deformations in graphite-epoxy tubes with aluminum foil bonded to both inner and outer surfaces, and to the outer surface only are computed. Tubes fabricated from three material systems, T300/934, P75s/934, and P75s/BP907, and having a 1 inch inner radius and a lamination sequence of (+15/0 + or - 10/0)sub s are studied. Radial, axial, and circumferential stresses in the various layers of the tube, in the foil, and in the adhesive bonding the foil to the tubes are computed using an elasticity solution. The results indicate that the coatings have no detrimental effect on the stress state in the tube, particularly those stresses that lead to microcracking. The addition of the aluminum foil does, however, significantly influence the axial expansion of the T300/934 tube, the tube with the softer graphite fibers. The addition of foil can change the sign of the axial coefficient of thermal expansion. Twist tendencies of the tubes are only slightly affected by the addition of the coatings, but are of second order compared to the axial response.

Knott, Tamara W.↗

NASA NTRS1991

Finding and utilizing lunar lava tubes

Horz describes the evidence for lava tubes associated with rills in lunar photoimaging. These tubes have terrestrial counterparts as described by Billings, et al., and Gillet. The widths of these tubes range from 10s to 100s of meters. Their roof thickness are at least 0.125 to 0.25 times their widths and stand unsupported on the Moon. To confine one atmosphere of internal pressure, static roof thickness must be at least 16 m. Favorable locations of lava tubes may be surveyed using roving gravity meters on Doodle Bugs, which consist of platforms containing equipment for communication with Earth-based control stations. The stable -20 C temperature of the lava tubes should provide a workable habitat environment. The greater than 16 m of basalt in the roof should give adequate radiation and impact protection. Typically, after clearing entries and grading ramps, habitats might be placed in tubes and inflated. Later, larger habitats might be built by enclosing tube sections with compacted-regolith dams. The interior can then be sealed to hold an atmosphere. The huge lava tubes inferred from the photographs are capable of providing habitats hundreds of meters wide, in lengths of kilometers.

Kuck, David L.↗

NASA NTRS1990

The influence of gas velocity on surface heat pumping for the orifice pulse tube refrigerator

The basic pulse tube refrigerator produces cooling by a mechanism known as surface heat pumping. Cyclical compression and expansion of a gas within an enclosed tube produces large temperature gradients. The purpose of the tube is to act as 'nodal regenerator'. Heat is stored at node positions along the tube wall and is transported between nodes by moving gas parcels. This process gives rise to refrigeration, with hot temperatures at the closed end and cold temperatures at the open end. Unfortunately, much of the available refrigeration is not realized because the closed end of the basic pulse tube restricts gas movement - gas at the extreme temperatures does not come in contact with the heat exchangers. The orifice pulse tube overcomes this limitation by using a valve and surge volume assembly at the warm, closed end. This allows for a residual gas velocity to remain present during the heat transfer process, thereby permitting more gas to exchange heat at the heat exchangers. This paper describes the pulse tube as a nodal regenerator and the effect residual gas velocity has on the heat transfer mechanism of the orifice pulse tube.

Lee, J. M.↗

NASA NTRS1994

Dynamics of flux tubes in accretion disks

The study of magnetized plasmas in astrophysics is complicated by a number of factors, not the least of which is that in considering magnetic fields in stars or accretion disks, we are considering plasmas with densities well above those we can study in the laboratory. In particular, whereas laboratory plasmas are dominated by the confining magnetic field pressure, stars, and probably accretion disks, have magnetic fields whose beta (ratio of gas pressure to magnetic field pressure) is much greater than 1. Observations of the Sun suggest that under such circumstances the magnetic field breaks apart into discrete flux tubes with a small filling factor. On the other hand, theoretical treatments of MHD turbulence in high-beta plasmas tend to assume that the field is more or less homogeneously distributed throughout the plasma. Here we consider a simple model for the distribution of magnetic flux tubes in a turbulent medium. We discuss the mechanism by which small inhomogeneities evolve into discrete flux tubes and the size and distribution of such flux tubes. We then apply the model to accretion disks. We find that the fibrilation of the magnetic field does not enhance magnetic buoyancy. We also note that the evolution of an initially diffuse field in a turbulent medium, e.g., any uniform field in a shearing flow, will initially show exponential growth as the flux tubes form. This growth saturates when the flux tube formation is complete and cannot be used as the basis for a self-sustaining dynamo effect. Since the typical state of the magnetic field is a collection of intense flux tubes, this effect is of limited interest. However, it may be important early in the evolution of the galactic magnetic field, and it will play a large role in numerical simulations. Finally, we note that the formation of flux tubes is an essential ingredient in any successful dynamo model for stars or accretion disks.

Vishniac, E. T.↗

NASA NTRS2001

Modeling of Multi-Tube Pulse Detonation Engine Operation

The present paper explores some preliminary issues concerning the operational characteristics of multiple-tube pulsed detonation engines (PDEs). The study is based on a two-dimensional analysis of the first-pulse operation of two detonation tubes exhausting through a common nozzle. Computations are first performed to assess isolated tube behavior followed by results for multi-tube flow phenomena. The computations are based on an eight-species, finite-rate transient flow-field model. The results serve as an important precursor to understanding appropriate propellant fill procedures and shock wave propagation in multi-tube, multi-dimensional simulations. Differences in behavior between single and multi-tube PDE models are discussed, The influence of multi-tube geometry and the preferred times for injecting the fresh propellant mixture during multi-tube PDE operation are studied.

Ebrahimi, Houshang B.↗

NASA NTRS2004

Lightweight, Low-CTE Tubes Made From Biaxially Oriented LCPs

Tubes made from biaxially oriented liquid-crystal polymers (LCPs) have been developed for use as penetrations on cryogenic tanks. ( Penetrations in this context denotes feed lines, vent lines, and sensor tubes, all of which contribute to the undesired conduction of heat into the tanks.) In comparison with corresponding prior cryogenic-tank penetrations made from stainless steels and nickel alloys, the LCP penetrations offer advantages of less weight and less thermal conduction. An additional major advantage of LCP components is that one can tailor their coefficients of thermal expansion (CTEs). The estimated cost of continuous production of LCP tubes of typical sizes is about $1.27/ft ($4.17/m) [based on 1998 prices]. LCP tubes that are compatible with liquid oxygen and that feature tailored biaxial molecular orientation and quasi-isotropic properties (including quasi-isotropic CTE) have been fabricated by a combination of proprietary and patented techniques that involve the use of counterrotating dies (CRDs). Tailoring of the angle of molecular orientation is what makes it possible to tailor the CTE over a wide range to match the CTEs of adjacent penetrations of other tank components; this, in turn, makes it possible to minimize differential-thermal expansion stresses that arise during thermal cycling. The fabrication of biaxially oriented LCP tubes by use of CRDs is not new in itself. The novelty of the present development lies in tailoring the orientations and thus the CTEs and other mechanical properties of the LCPs for the intended cryogenic applications and in modifications of the CRDs for this purpose. The LCP tubes and the 304-stainless-steel tubes that the LCP tubes were intended to supplant were tested with respect to burst strength, permeability, thermal conductivity, and CTE.

Rubin, Leslie↗

NASA NTRS2015

A Sinuous Tumulus over an Active Lava Tube at Klauea Volcano: Evolution, Analogs, and Hazard Forecasts

Inflation of narrow tube-fed basaltic lava flows (tens of meters across), such as those confined by topography, can be focused predominantly along the roof of a lava tube. This can lead to the development of an unusually long tumulus, its shape matching the sinuosity of the underlying lava tube. Such a situation occurred during Klauea Volcanos (Hawaii, USA) ongoing East Rift Zone eruption on a lava tube active from July through November 2010. Short-lived breakouts from the tube buried the flanks of the sinuous, ridge-like tumulus, while the tumulus crest, its surface composed of lava formed very early in the flows emplacement history, remained poised above the surrounding younger flows. At least several of these breakouts resulted in irrecoverable uplift of the tube roof. Confined sections of the prehistoric Carrizozo and McCartys flows (New Mexico, USA) display similar sinuous, ridge-like features with comparable surface age relationships. We contend that these distinct features formed in a fashion equivalent to that of the sinuous tumulus that formed at Kīlauea in 2010. Moreover, these sinuous tumuli may be analogs for some sinuous ridges evident in orbital images of the Tharsis volcanic province on Mars. The short-lived breakouts from the sinuous tumulus at Kīlauea were caused by surges in discharge through the lava tube, in response to cycles of deflation and inflation (DI events) at Kīlauea's summit. The correlation between DI events and subsequent breakouts aided in lava flow forecasting. Breakouts from the sinuous tumulus advanced repeatedly toward the sparsely populated Kalapana Gardens subdivision, destroying two homes and threatening others. Hazard assessments, including flow occurrence and advance forecasts, were relayed regularly to the Hawaiʻi County Civil Defense to aid their lava flow hazard mitigation efforts while this lava tube was active.

volcanic hazards↗

NASA NTRS2020

Using X-Ray Computed Tomography to Image Apollo Drive Tube 73002

The Apollo missions collected 382 kg of rock, regolith, and core samples from six locations on the nearside of the Moon. Today, just over 84% by mass of the Apollo collection remains in pristine condition within the curation facility at Johnson Space Center. Most Apollo samples have been well characterized, however there are several types of samples that have remained wholly or largely unstudied since their return, and/or that have been curated under special conditions. These sample types are: (1) unopened samples sealed under vacuum on the Moon; (2) unopened (but unsealed) drive tubes; (3) Apollo 17 samples frozen shortly after their return; and (4) Apollo 15 samples opened and stored in a helium atmosphere since their return. Last summer, NASA solicited proposals for the Apollo Next Generation Sample Analysis Program (ANGSA), and 9 teams were selected to study: (1) unsealed, unopened drive tube 73002; (2) sealed, unopened drive tube 73001 (paired with 73002); and (3) a subset of the frozen and He-purged samples [1]. The first sample opened as part of the ANGSA program was drive tube 73002. This is a 30 cm long, 4 cm diameter drive tube collected on a landslide deposit near Lara Crater at the Apollo 17 landing site. It was part of a 60 cm long double drive tube collected, and the bottom half of the tube (73001) was sealed under vacuum on the Moon [2]. Prior to opening sample 73002, the sample was imaged with a high resolution Xray Computed Tomography (XCT) scan of the entire tube. Additional XCT scans have been made of “large” clasts removed from the core as part of the dissection process [3]. Here we present a first look at the XCT data from 73002, and talk about the utility of the scans as part of the curation process, including the potential for future science returns from the high resolutions scans.

Zeigler, R. A.↗

NASA NTRSDate not supplied

Using X-Ray Computed Tomography to Image Apollo Drive Tube 73002

The Apollo missions collected 382 kg of rock, regolith, and core samples from six locations on the Moon. Although most Apollo samples are well characterized, several types of samples remain wholly or largely unstudied since their return: unopened and/or sealed drive tube samples, samples frozen upon return, and samples stored in a He-purged environment. NASA selected nine teams to participate in the Apollo Next Generation Sample Analysis (ANGSA) Program to study representative samples from each of these categories. The first sample studied as part of the ANGSA program is drive tube 73002, a 4 cm diameter unopened (but unsealed) drive tube collected on a landslide deposit near Lara Crater at the Apollo 17 landing site. It was part of a ~60 cm long double drive tube, and the bottom half of the tube (73001)was sealed under vacuum on the Moon (and will be studied next). As part of the preliminary examination of sample 73002, the entire drive tube was imaged with a high resolution X-ray Computed Tomography (XCT) scan prior to opening and dissecting the sample. Additionally, >50 XCT scans have been made of “large” clasts (>4 mm) removed from the core as part of the ongoing dissection process. Here we will present both the whole drive tube XCT data showing the overall structure of sample 73002 prior to dissection, as well as XCT scans of individual clasts that reveal the types and abundance of different lithologies present within the drive tube. We will also discuss the utility of the scans as part of the curation and preliminary examination process, as well as the potential for future science returns from the XCT scans.

Ryan A Zeigler↗

DOE OSTI2023

Experimental investigation on nucleate boiling heat transfer of low GWP refrigerants over metal-foam enhanced tube bundles

The objective of this work is to develop an enhanced tube bundle to improve the nucleate boiling heat transfer for the application of flooded evaporators. The enhanced tube bundle was made by deploying metal foam around the outer surface of aluminum tubes, which provide higher heat transfer area and nucleation site density. The pool boiling experiments for horizontal tube bundles were conducted in a pressure vessel at difference heat fluxes. The heat transfer performance of bare aluminum tube bundle was compared against the metal-foam enhanced tube bundle using low GWP refrigerant, R-1234yf. The experimental results showed that the heat transfer coefficient of the metal-foam enhanced tube bundle was at least two times higher than that of the bare tube bundle, and the enhancement ratio depended on the heat flux condition.

Yang, Cheng-Min↗

DOE OSTI2023

Pool boiling on metal-foam enhanced tube bundle: heat transfer characteristics and flow visualization

A flooded evaporator configuration is common in large central air conditioning or process cooling systems. It is basically a shell and tube heat exchanger, in which a secondary fluid (brine or water) circulates inside the tube bundle and is cooled by the vaporization of the refrigerant on the outside surface of the tubes. The enhanced pool boiling process enables the compact design of flooded evaporators, which substantially reduces the refrigerant charge. High-porosity metal foam, with a large surface-area-to-volume ratio, could provide an extended heat transfer area and a high-density of nucleation sites. This study experimentally investigated the pool boiling heat transfer and flow characteristics on metal-foam enhanced tube bundles. The enhanced bundle consists of four aluminum tubes with aluminum foam brazed around the outer surface, which are horizontally mounted in a staggered arrangement. The results showed that the metal-foam enhanced tube bundles improved the heat transfer coefficient by 100-160% with a lower wall temperature difference of 1-10°C, compared to the baseline. In addition, the tube pitch played a significant role in determining the pool boiling behavior of the tube bundles.

Yang, Cheng-Min↗

DOE OSTI2022

Experimental Investigation of the Heat Transfer between Finned Tubes and a Bubbling Fluidized Bed with Horizontal Sand Mass Flow

The sandTES technology utilizes a fluidized bed counter current heat exchanger for thermal energy storage applications. Its main feature is an imposed horizontal flow of sand (SiO2) particles fluidized by a vertical air flow across a heat exchanger consisting of several horizontal rows of tubes. Past international research on heat transfer in dense fluidized beds has focused on stationary (stirred tank) systems, and there is little to no information available on the impact of longitudinal or helical fins. Previous pilot plant scale experiments at TU Wien led to the conclusion that the currently available correlations for predicting the heat transfer coefficient between the tube surface and the surrounding fluidized bed are insufficient for the horizontal sand flow imposed by the sandTES technology. Therefore, several smaller test rigs were designed in this study to investigate the influence of different tube arrangements and flow conditions on the external convective heat transfer coefficient and possible improvements by using finned tubes. It could be shown that helically finned tubes in a transversal arrangement, where the horizontal sand flow is perpendicular to the tube axes, allows an increase in the heat transfer coefficient per tube length (i.e., the virtual heat transfer coefficient) by a factor of 3.5 to about 1250 W/m2K at ambient temperature. Based on the literature, this heat transfer coefficient is expected to increase at higher temperatures. The new design criteria allow the design of compact, low-cost heat exchangers for thermal energy storage applications, in particular electro-thermal energy storage.

25 ENERGY STORAGE↗

DOE OSTI2020

Visualization of R410A Flow Boiling Inside Horizontal Smooth Tubes under Diabatic Conditions

This article presents a novel approach to visualize the flow boiling in round tubes under “diabatic conditions”. In the visualization test section, a 3D printed round tube is placed inside a glass tube with secondary fluid at a higher temperature flowing in the annulus between the two tubes thus providing diabatic conditions. Experimental work was conducted for evaporating R410A flow in a horizontal smooth round tube with the inner diameter of 6.3 mm. Compared to the traditional adiabatic visualization technique, the more realistic evaporative condition is simulated and the developing evaporation process is captured. New insights for the flow behavior at low vapor quality are brought by this diabatic method. The vapor plug occurs at very low vapor quality, and this is attributed to the coalescence of bubbles generated on the heated tube wall. For the intermittent flow, liquid slug triggered by Kelvin–Helmholtz instability affects the nucleation on the tube wall. It brings the fresh liquid to rewet the dry surface and activate the nucleation sites. Finally, heat flux condition affects the heat transfer mechanisms during the flow boiling, and the heat transfer through the nucleate boiling mechanism increases as the heat flux increases.

3D printed↗

NASA NTRS2016

Optimizing Facility Configurations and Operating Conditions for Improved Performance in the NASA Ames 24 Inch Shock Tube

The Ames Electric Arc Shock Tube (EAST) is a shock tube wherein the driver gas can be heated by an electric arc discharge. The electrical energy is stored in a 1.2 MJ capacitor bank. Four inch and 24 inch diameter driven tubes are available. The facility is described and the need for testing in the 24 inch tube to better simulate low density NASA mission profiles is discussed. Three test entries, 53, 53B and 59, are discussed. Tests are done with air or Mars gas (95.7% CO2/2.7% N2/1.6% Ar) at pressures of 0.01 to 0.14 Torr. Velocities spanned 6.3-9.2 km/s, with a nominal center of 7 km/s. Many facility configurations are studied in an effort to improve data quality. Various driver and driven tube configurations and the use of a buffer section between the driver and the driven tube are studied. Diagnostics include test times, time histories of the shock light pulses and tilts of the shock wave off the plane normal to the tube axis. The report will detail the results of the various trials, give the best configuration/operating conditions found to date and provide recommendations for further improvements. Finally, diaphragm performance is discussed.

Shock Tube↗

DOE OSTI2020

Diabatic visualization shows effects of micro-fins on evaporation of R410A: Smooth, axial micro-fin, and helical micro-fin tubes

A novel approach to visualize the flow boiling inside a clear micro-fin tube under diabatic conditions is presented. Transparent smooth, axial micro-fin, and helical micro-fin tubes are made by 3D printing. The 3D printed tube is placed inside a glass tube and heated by the transparent secondary fluid flowing between the two tubes for providing the evaporation conditions and transparency. R410A flow boiling and the flow patterns in the three geometries captured with a high speed camera are compared. The experimental results show that micro-fin geometry influences flow behavior. Bubbles are mainly generated in the groove region due to a higher superheat than the fin region. Some of the liquid refrigerant is trapped in the grooves of the upper part of the micro-fin tube when the slug flow is present, and bubbles are generated in this thin liquid layer. In addition, the bubbles in the helical micro-fin tube are easier to merge because of the obstacle of the fin geometry for the bubble flowing path. As the two bubble merge, the conversion of surface free energy causes the bubble to travel with a higher velocity.

3D printed↗