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At least 829 records · Page 46

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NASA NTRS1989

The use of holographic interferometry for measurements of temperature in a rectangular heat pipe

Holographic interferometry is a nonintrusive method and as such possesses considerable advantages such as not disturbing the velocity and temperature field by creating obstacles which would alter the flow field. These optical methods have disadvantages as well. Holography, as one of the interferometry methods, retains the accuracy of older methods, and at the same time eliminates the system error of participating components. The holographic interferometry consists of comparing the objective beam with the reference beam and observing the difference in lengths of optical paths, which can be observed during the propagation of the light through a medium with locally varying refractive index. Thus, change in refractive index can be observed as a family of nonintersecting surfaces in space (wave fronts). The object of the investigation was a rectangular heat pipe. The goal was to measure temperatures in the heat pipe, which yields data for computer code or model assessment. The results were obtained by calculating the temperatures by means of finite fringes.

Marn, Jure↗

NASA NTRS1991

Verification of the proteus two-dimensional Navier-Stokes code for flat plate and pipe flows

The Proteus Navier-Stokes Code is evaluated for 2-D/axisymmetric, viscous, incompressible, internal, and external flows. The particular cases to be discussed are laminar and turbulent flows over a flat plate, laminar and turbulent developing pipe flows, and turbulent pipe flow with swirl. Results are compared with exact solutions, empirical correlations, and experimental data. A detailed description of the code set-up, including boundary conditions, initial conditions, grid size, and grid packing is given for each case.

Conley, Julianne M.↗

NASA NTRS1990

Large deflection random response of a pipe containing fluid flow subjected to random loading

An analytic approach is developed for beam type pipes undergoing large deflections subjected to random loadings. The influence of fluid velocity on the random response is investigated. The root-mean-square (rms) deflections and frequencies for different sound spectrum level values are determined for pipes with both ends either simply supported or clamped. The required number of modes to achieve accurate rms deflections and strains is also studied. The prediction of fatigue life is then based on obtained rms maximum stress. This analytical investigation will help to broaden the basic understanding of the role of fluid flow within structures subjected to acoustic loading.

Chiang, C. K.↗

NASA NTRS1991

Startup of a frozen heat pipe in one-g and micro-g environments - A proposed shuttle flight experiment

An attempt is made to determine how a heat pipe freezes under various low load and/or no load conditions in both one-g and micro-g environments. Also of interest are the mechanisms that can be used to restart the heat pipe after freezing has occurred. Particular attention is given to step function power reductions and the resulting distribution of the working fluid after freezing has occurred and the effect of noncondensible gases on the frozen configuration and the restart characteristics.

Ochterbeck, J. M.↗

NASA NTRS1990

Perturbation amplification in the entry region of a transitional pipe flow

The forced transition due to the application of large disturbances in the entry region of a pipe flow is considered. The disturbances are not large enough to cause a puff-type transition which is peculiar to a pipe low; they cause a slug-type transition which is akin to a flate turbulence spot. The perturbation amplifications with Reynolds number have been measured at the entrance and also soon after the mean turbulent flow has become fully developed. At the entrance, all dominant frequencies amplify in a nearly universal manner which is exponential in part of the Reynolds number range. Further-more, the nonlinear process undergoes a change at Reynolds numbers of 4930 to 6020, and again at 8120 to 10060. At the downstream station, an almost saturated amplification rate has been reached and, in the background of a higher turbulence level, the trend is qualitatively similar to that in peak-valley splitting.

Bandyopadhyay, Promode R.↗

NASA NTRS1991

Verification of the Proteus two-dimensional Navier-Stokes code for flat plate and pipe flows

The Proteus Navier-Stokes Code is evaluated for two-dimensional/axisymmetric, viscous, incompressible, internal and external flows. The particular cases to be discussed are laminar and turbulent flows over a flat plate, laminar and turbulent dveloping pipe flows and turbulent pipe flow with swirl. Results are compared with exact solutions, empirical correlations and experimental data. A detailed description of the code set-up, including boundary conditions, intitial conditions, grid size and grid packing is given for each case.

Conley, Julianne M.↗

NASA NTRS1991

Computational study of duct and pipe flows using the method of pseudocompressibility

A viscous, three-dimensional, incompressible, Navier-Stokes Computational Fluid Dynamics code employing pseudocompressibility is used for the prediction of laminar primary and secondary flows in two 90-degree bends of constant cross section. Under study are a square cross section duct bend with 2.3 radius ratio and a round cross section pipe bend with 2.8 radius ratio. Sensitivity of predicted primary and secondary flow to inlet boundary conditions, grid resolution, and code convergence is investigated. Contour and velocity versus spanwise coordinate plots comparing prediction to experimental data flow components are shown at several streamwise stations before, within, and after the duct and pipe bends. Discussion includes secondary flow physics, computational method, computational requirements, grid dependence, and convergence rates.

Williams, Robert W.↗

NASA NTRS1991

Low-dispersion finite difference methods for acoustic waves in a pipe

A new algorithm for computing one-dimensional acoustic waves in a pipe is demonstrated by solving the acoustic equations as an initial-boundary-value problem. Conventional dissipation-free second-order finite difference methods suffer severe phase distortion for grids with less that about ten mesh points per wavelength. Using the signal generation by a piston in a duct as an example, transient acoustic computations are presented using a new compact three-point algorithm which allows about 60 percent fewer mesh points per wavelength. Both pulse and harmonic excitation are considered. Coupling of the acoustic signal with the pipe resonant modes is shown to generate a complex transient wave with rich harmonic content.

Davis, Sanford↗

NASA NTRS1992

Experimental investigation of freezing blowby in a copper/water heat pipe

An experimental investigation designed to evaluate and better define the overall characteristics of freezing blowby in a copper/water heat pipe was conducted. The results from various rates of restart heat addition and channel blockage, indicate that upon breakthrough the depressurization of the evaporator may result in an effective heat transport capacity far in excess of the steady-state transport limit. The resulting transient conditions imposed on the heat pipe by the effective increased heat transport capacity can cause a loss of liquid in the evaporator and potential dryout. Evidence is presented which indicates that in order to prevent either temporary or permanent dryout, sufficient liquid inventory must be present in the evaporator wicking structure to accommodate the increased transient thermal load and allow sufficient time for the capillary wicking structure to reprime.

Ochterbeck, J. M.↗

NASA NTRS1993

Mapping Temperatures On Heat Pipes

Paints containing thermochromic liquid crystals (TLC's) used to map temperatures on heat pipes and thermosyphons. Color of thermally sensitive TLC coat changes reversibly upon heating or cooling. Each distinct color indicates particular temperature. Transient and steady-state isotherms become visible as colored bands. Positions and movements of bands yield information about startup transients, steady-state operation, cooler regions containing noncondensible gas, and other phenomena relevant to performance of heat pipe.

Gunnerson, Fred S.↗

NASA NTRS1993

Moving-Temperature-Gradient Heat-Pipe Furnace Element

In improved apparatus, ampoule of material directionally solidified mounted in central hole of annular heat pipe, at suitable axial position between heated and cooled ends. Heated end held in fixed position in single-element furnace; other end left in ambient air or else actively cooled. Gradient of temperature made to move along heat pipe by changing pressure of noncondensable gas. In comparison with prior crystal-growing apparatuses, this one simpler, smaller, and more efficient.

Gillies, Donald C.↗

NASA NTRS1991

Construction and testing of ceramic fabric heat pipe with water working fluid

A prototype ceramic fabric/titanium water heat pipe has been constructed and tested; it transported 25 to 80 W of power at 423 K. Component development and testing is continuing with the aim of providing an improved prototype, with a 38 micron stainless steel liner covered by a biaxially-braided Nextel (trademark) sleeve that is approximately 300 microns thick. This fabric has been tested to 800 K, and its emittance is about 0.5 at that temperature. Advanced versions of the water heat pipe will probably require a coating over the ceramic fabric in order to increase this emittance to the 0.8 to 0.9 range.

Antoniak, Zenen I.↗

NASA NTRS1992

Laminar/turbulent oscillating flow in circular pipes

A two-dimensional oscillating flow analysis was conducted simulating the gas flow inside Stirling engine heat exchangers. Both laminar and turbulent oscillating pipe flow were investigated numerically for Re(max) = 1920 (Va = 80), 10,800 (Va = 272), 19,300 (Va = 272), and 60,800 (Va = 126). The results are compared with experimental results of previous investigators. Predictions of the flow regime are also checked by comparing velocity amplitudes and phase difference with those from laminar theory and quasi-steady profile. A high Reynolds number k-epsilon turbulence model was used for turbulent oscillating pipe flow. Finally, the performance of the k-epsilon model was evaluated to explore the applicability of quasi-steady turbulent models to unsteady oscillating flow analysis.

Ahn, Kyung H.↗

NASA NTRS1993

Acceleration induced depriming and capillary rewetting of external artery heat pipes - Comparison with SHARE-II flight experiment

A combined analytical and numerical model for the analysis of the deprime and reprime/rewetting characteristics of two high-capacity external artery heat pipe designs undergoing externally induced accelerations was developed using several previously derived analytical expressions. Three distinct phases of the deprime and reprime/rewetting process were analyzed: (1) the effect of longitudinal accelerations on the depriming, (2) the time required for repriming of the liquid artery once the longitudinal acceleration has been terminated, and (3) the rewetting characteristics of the circumferential wall grooves. Combining the three processes, a technique was developed allowing the prediction of the effect of external acceleration on the characteristics of the external artery heat pipes. The predictions made with this technique agreed well with the microgravity flight results.

Ochterbeck, J. M.↗

NASA NTRS1992

Performance of the Cryogenic Heat Pipe Experiment

The Cryogenic Heat Pipe (CRYOHP) Experiment has been designed to test two cryogenic heat pipes independently in a micro-gravity environment. The CRYOHP experiment is manifested for flight aboard the shuttle (STS-53) which is scheduled for launch in November, 1992. This paper presents the design of this experiment and the thermal vacuum verification test results. A correlation of the test data and the planned mission operations are also provided.

Brennan, Patrick J.↗

NASA NTRS1991

A finite element large deflection random response of a pipe containing fluid flow

A finite element approach is developed for beam type pipes undergoing large deflections subjected to random loadings. The influence of fluid velocity on the random response is investigated. The root-mean-square (rms) deflections and frequencies for different sound spectrum level values are determined for pipes with both ends either simply supported or clamped. The required number of modes to achieve accurate rms deflections is studied. The prediction of fatigue life is then based on the maximum rms stress. This analytical investigation will help to broaden the basic understanding of the role of fluid flow within structures subjected to random excitations.

Chiang, C. K.↗

NASA NTRS1991

Displacement analysis of the interior walls of a pipe using panoramic holo-interferometry

Standard phase-displacement equations, used for both double exposure and real time holo-interferometry, are combined with the geometrical mapping and optical characteristics of panoramic annular lenses to accurately measure surface displacement on the interior wall of a pipe. In this approach, one panoramic annular lens is used to illuminate the surface with coherent light, and the resulting intensity distribution is holographically recorded through a second panoramic annular lens. Interference fringes are obtained in real-time by comparing holograms recorded before and after the pipe is displaced. The annular images and the holographic fringes are acquired and stored digitally in a computer system. Image transformation algorithms are applied to remove optical distortions in the holographic pattern and fringe loci are compared to those predicted on the basis of theory.

Gilbert, John A.↗

NASA NTRS1950

Altitude Performance and Operational Characteristics of 29-inch-diameter Tail-pipe Burner with Several Fuel Systems and Fuel-cooled Stage-type Flame Holders on J35-A-5 Turbojet Engine / Richard L. Golladay and Harry E. Bloomer

An investigation of tail-pipe burning was conducted in the NACA Lewis altitude wind tunnel with a full-scale turbojet engine and an 29-inch-diameter tail-pipe burner. Effects of fuel distribution and number and arrangement of stages on performance and operational characteristics of several fuel-cooled flame holders are presented and discussed. Operation with a three-stage flame holder having the large stage upstream was the most efficient. Combustion efficiency was slightly increased at high altitudes by injecting fuel upstream of the flame holder.

TURBINES, GAS - AFTERBURNING↗