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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Comparative experimental study of heat transfer processes in accumulation energy recovery exchangers

In this study, an experimental comparison between three different energy accumulating ceramic heat exchangers for energy recovery in ventilation systems was presented. The units were selected to represent three different approaches on the energy recovery process: honeycomb structure with more accumulation mass (more energy can be stored in one unit)- Unit 1.1, honeycomb structure with lower accumulation mass- Unit 1.2, and a rectangular structure with expanded heat transfer surface- Unit 1.3. The achieved results are useful for the future application of such units in ventilation systems. It was established that all evaluated units demonstrated an acceptable effectiveness of thermal energy recovery from the exhaust air. Their average energy recovery efficiency ranged between 70 % and 80 %, aligning with expected performance benchmarks for regenerative heat exchangers employed in contemporary mechanical ventilation systems. It was also established that the factor which has the highest impact on thermal effectiveness is the heat transfer surface available in the tested heat exchangers. Units with the highest number of channels (i.e., with the highest amount of single channel walls, which can be used for heat transfer) achieve the highest thermal effectiveness. However, higher thermal effectiveness can negatively affect the ventilation potential of the units. Unit 1.3, which was characterized by the highest thermal efficiency, was also characterized by the lowest achievable flow rate. It was also found that the important technical aspect that should be taken into account when analyzing accumulation energy recovery units is also the fluctuation of the supply air temperature. The ability to ensure minimal temperature fluctuations is a significant operational advantage, as it ensures a higher level of safety at lower outside temperatures.

Energy recovery↗
NASA NTRS1978

Pressure and heat-transfer distributions in a simulated wing-elevon cove with variable leakage at a free-stream Mach number of 6.9

A concern that ingestion of hot boundary-layer gas past a small, localized seal failure in the cove between the Space Shuttle wing and elevon might threaten unprotected elevon structures led to wind-tunnel tests to define cove environment as a function of leak area. The tests were conducted in the Langley 8-foot high-temperatures structures tunnel using a full-scale representation of the Space Shuttle wing-elevon juncture on the reentry surface. Pressure and heating rates were obtained for both attached and separated turbulent flows on the wing at the cove entrance. Results indicated that (1) for attached turbulent flow on the wing, cove heating progressively increased in severity independent of leak aspect ratio as leak area increased to 100 percent of cove entrance area and (2), for separated turbulent flow over the wing, cove environment was intolerably severe.

Deveikis, W. D.↗
NASA NTRS1978

Pressure and heat-transfer distributions in a simulated wing-elevon cove with variable leakage at a free-stream Mach number of 6.9

An experimental aerodynamic heating investigation was conducted to determine effects of hot boundary-layer ingestion into the cove on the windward surface between a wing and elevon for cove seal leak areas nominally between 0 and 100 percent of cove entrance area. Pressure and heating-rate distributions were obtained on the wing and elevon surfaces and on the cove walls of a full-scale model that represented a section of the cove region on the space shuttle orbiter. Data were obtained for both attached and separated turbulent boundary layers upstream of the unswept cove entrance. Average free-stream Mach number was 6.9, average free-stream unit Reynolds numbers were 1.31 x 10 to the 6th power and 4.40 x 10 to the 6th power per meter (0.40 x 10 to the 6th power and 1.34 x 10 to the 6th power per foot), and average total temperature was 1888 K (3400 R). Cove pressures and heating rates varied as a function of seal leak area independent of leak aspect ratio. Although cove heating rates for attached flow did not appear intolerable, it was postulated that convective heating in the cove may increase with time. For separated flow, the cove environment was considered too severe for unprotected interior structures of control surfaces.

Deveikis, W. D.↗
NASA NTRS1961

Heat Transfer and Boundary-Layer Transition on a Highly Polished Hemisphere-Cone in Free Flight at Mach Numbers Up to 3.14 and Reynolds Numbers Up to 24 x 10(exp 6)

A highly polished hemisphere-cone having a ratio of nose radius to base radius of 0.74 and a half-angle of 14.5 was flight tested at Mach numbers up to 4.70. Temperature and pressure data were obtained at Mach numbers up to 3.14 and a free-stream Reynolds number of 24 x 10(exp 6) based on body diameter. The nose of the model had a surface roughness of 2 to 5 microinches as measured with an interferometer. The measured Stanton numbers were in good agreement with theory. Transition Reynolds numbers based on the laminar boundary-layer momentum thickness at transition ranged from 2,190 to 794. Comparison with results from previous tests of blunt shapes having a surface roughness of 20 to 40 microinches showed that the high degree of polish was instrumental in delaying the transition from laminar to turbulent flow.

Buglia, James J.↗
NASA NTRS1990

Thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity

Computer simulation of steady-state axisymmetrical heat transfer and fluid flow was conducted to study thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity. The effects of key variables on the extent of thermocapillary flow in the melt zone, the shapes of melt/solid interfaces and the length of the melt zone were discussed. These variables are: (1) the temperature coefficient of surface tension (or the Marangoni number), (2) the pulling speed (or the Peclet number), (3) the feed rod radius, (4) the ambient temperature distribution, (5) the heat transfer coefficient (or the Biot number), and (6) the thermal diffusivity of the material (or the Prandtl number).

Lan, C. W.↗
NASA NTRS1981

A digital Seasat SAR correlation-simulation program

A correlation-simulation program for processing Seasat SAR data is presented, featuring the use of FORTRAN code to allow simple transference to another computer. The highest attainable azimuthal resolution for Seasat SAR experiments and the ability to generate images with varying quality by varying resolution or the number of looks are additional features. A fiber optics link transfers the Seasat data from high intensity digital tapes to an SEL 32/55 computer, and the least significant bits of the 5 bit data samples are truncated, thus the input data have 4 bits per sample. A total 8192 echoes are processed each time and stored on 8 separate data files on the disk. In addition, a program operating on 1-look high resolution images for performance simulations of proposed radar systems and processing schemes has been completed. Finally, the coding is simple, and 8 hours are required to process one image using this program.

Li, F.↗
NASA NTRS1991

A laser-induced heat flux technique for convective heat transfer measurements in high speed flows

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high speed flow fields.

Porro, A. R.↗
NASA NTRS1991

A laser-induced heat flux technique for convective heat transfer measurements in high speed flows

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high-speed flowfields.

Porro, A. R.↗
NASA NTRS2007

Experiments in Transitional Boundary Layers With Emphasis on High Free-Stream Disturbance Level, Surface Concave Curvature and Strong Favorable Streamwise Pressure Gradient Effects

Experiments on boundary layer transition with flat, concave and convex walls and various levels of free-stream disturbance and with zero and strong streamwise acceleration have been conducted. Measurements of both fluid mechanics and heat transfer processes were taken. Examples are profiles of mean velocity and temperature; Reynolds normal and shear stresses; turbulent streamwise and cross-stream heat fluxed; turbulent Prandtl number; and streamwise variations of wall skin friction and heat transfer coefficient values. Free-stream turbulence levels were varied over the range from about 0.3 percent to about 8 percent. The effects of curvature on the onset of transition under low disturbance conditions are clear; concave curvature leads to an earlier and more rapid transition and the opposite is true for convex curvature This was previously known but little documentation of the transport processes in the flow was available

Simon, T. W.↗
DOE OSTI2022

Effect of emitters on quantum state transfer in coupled cavity arrays

Over the last decade, conditions for perfect state transfer in quantum spin chains have been discovered and their experimental realizations addressed, as have their extensions to more complex geometries of coupled cavity-emitter arrays. In this paper we further consider such studies and situations in which quantum state transfer can occur with high fidelity, even when the cavity-cavity coupling rates and cavity-emitter interaction rates are comparable. This is accomplished through the development and use of a Monte Carlo approach to the inverse eigenvalue problem, which allows the determination of coupling rates which optimize quantum state transfer fidelity and subsequent time evolution of the polariton wave function through exact diagonalization of the resulting Jaynes-Cummings-Hubbard Hamiltonian. The effect of inhomogeneous emitter locations is also evaluated. Furthermore, our key results include the demonstration that our methodology can be used successfully to establish Hamiltonian parameters for high-fidelity state transfer in more general lattice geometries and excitation number sectors, and also a determination of the effects of fluctuations in those parameters about their optimal values.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1954

Experimental Investigation of Sublimation of Ice at Subsonic and Supersonic Speeds and Its Relation to Heat Transfer

An experimental investigation was conducted in a 3.84- by 10-inch tunnel to determine the mass transfer by sublimation, heat transfer, and skin friction for an iced surface on a flat plate for Mach numbers of 0.4, 0.6, and 0.8 and pressure altitudes to 30,000 feet. Measurements of rates of sublimation were also made for a Mach number of 1.3 at a pressure altitude of 30,000 feet. The results show that the parameters of sublimation and heat transfer were 40 to 50 percent greater for an iced surface than was the bare-plate heat-transfer parameter. For iced surfaces of equivalent roughness, the ratio of sublimation to heat-transfer parameters was found to be 0.90. The sublimation data obtained at a Mach number of 1.3 showed no appreciable deviation from that obtained at subsonic speeds. The data obtained indicate that sublimation as a means of removing ice formations of appreciable thickness is usually too slow to be of mach value in the de-icing of aircraft at high altitudes.

Coles, Willard D.↗
NASA NTRS1981

Finite element analyses of plane thermal entry-length flows

It is pointed out that the design of actively cooled engine and airframe structures for hypersonic flight requires strong interaction between fluid, thermal, and structural analyses. Research programs are being conducted to develop an integrated thermal-structural analysis capability based upon the finite element method. In connection with these programs, a finite element engineering approach has been developed based upon a number of assumptions customarily used in practical heat transfer analysis. An evaluation is conducted of the finite element engineering approach for entry-length flows. The evaluation makes use of an analysis of plane thermal entry-length flows by a finite element approach utilizing mean fluid temperatures with a convection coefficient. Another analysis is based on a finite element continuum approach, taking into account the rigorous momentum, mass, and energy equations of viscous, incompressible flow. The engineering approach was found to give excellent agreement with the rigorous continuum approach for Peclet number values not less than 100.

Thornton, E. A.↗