Engineering topics

Ramohalli, K.

Publications and source records attributed to Ramohalli, K..

At least 19 records

NASA NTRS1990

Extraterrestrial resource utilization for economy in space missions

The NASA/University of Arizona Space Engineering Research Center is dedicated to research on the discovery, characterization, mapping, beneficiation, extraction, processing, and fabrication of useful products from extraterrestrial material. Schemes for the automated production of low-technology products that are likely to be desired in large quantities in the early stages of any large-scale space activity are identified and developed. This paper summarizes the research program, concentrating upon the production of (1) propellants, both cryogenic and storable, (2) volatiles such as water, nitrogen, and carbon dioxide for use in life-support systems (3) structural metals, and (4) refractories for use in aerobrakes and furnace linings.

Lewis, J. S.↗

NASA NTRS1990

A figure-of-merit approach to extraterrestrial resource utilization

A concept is developed for interrelated optimizations in space missions that utilize extraterrestrial resources. It is shown that isolated (component) optimizations may not result in the best mission. It is shown that substantial benefits can be had through less than the best propellants, propellant combinations, propulsion hardware, and actually, some waste in the traditional sense. One ready example is the possibility of discarding hydrogen produced extraterrestrially by water splitting and using only the oxygen to burn storable fuels. The gains in refrigeration and leak-proof equipment mass (elimination) outweigh the loss in specific impulse. After a brief discussion of this concept, the synthesis of the four major components of any future space mission is developed. The four components are: orbital mechanics of the transportation; performance of the rocket motor; support systems that include power; thermal and process controls, and instruments; and in situ resource utilization plant equipment. This paper's main aim is to develop the concept of a figure-of-merit for the mission. The Mars Sample Return Mission is used to illustrate the new concept. At this time, a popular spreadsheet is used to quantitatively indicate the interdependent nature of the mission optimization. Future prospects are outlined that promise great economy through extraterrestrial resource utilization and a technique for quickly evaluating the same.

Ramohalli, K.↗

NASA NTRS1989

Interdependent figure-of-merit software development

This program was undertaken in order to understand the complex nature of interdependent performance in space missions. At the first step in a planned sequence of progress, a spread sheet program was developed to evaluate different fuel/oxidizer combinations for a specific Martian mission. This program is to be linked with output attained using sophisticated software produced by Gordon and McBride. The programming to date makes use of 11 independent parameters. Optimization is essential when faced with the incredible magnitude of costs, risks, and benefits involved with space exploration. A system of weights needs to be devised on which to measure the options. It was the goal to devise a Figure of Merit (FoM) on which different choices can be presented and made. The plan was to model typical missions to Mars, identify the parameters, and vary them until the best one is found. Initially, most of the focus was placed on propellant selection.

Ramohalli, K.↗

NASA NTRS1985

Novel extraterrestrial processing for space propulsion

In the present quantitative consideration of space processing concepts for chemicals, theoretical parametric calculations are supplemented by a bench scale experiment. Attention is given to the case of water splitting to generate hydrogen and oxygen for a simple rocket motor that can be used in periodic thrusting. This concept of in situ propellant production is treated in detail and compared with more recent energy and materials technologies.

Ramohalli, K.↗

NASA NTRS1983

Forming Mirrors on Composite Materials

Smooth coatings deposited on hard-to-polish substrates. Lightweight mirror, leaning against conventional glass mirror, consists of metallic relective layer on substrate coated with polyester resin. Smooth surface of polyester resin made by covering freshly applied resin with piece of smooth glass coated with release agent.

Gauldin, R. E.↗

NASA NTRS1983

Thermochemical response of honeycomb sandwich panels

A simple study aimed at predicting the thermochemical response of honeycomb sandwich panels is presented. The overall thermal conductivity coefficient for the panel is obtained through a consideration of the convective gas movement within the cell spaces. The earlier correlations of Catton and Edwards are used. The analytical solution for the one-dimensional approximation is quoted from an earlier study. In comparison with three data points obtained at JPL at heat fluxes of 2.5, 5 and 8 W/sq cm, the char penetration depth is well predicted, especially when the debonding of the face sheet is considered. Re-radiation of incident heat flux from the debonded face sheet plays an important role in this model.

Ramohalli, K.↗

NASA NTRS1983

Acoustic imaging for diagnostics of chemically reacting systems

The concept of local diagnostics, in chemically reacting systems, with acoustic imaging is developed. The elements of acoustic imaging through ellipsoidal mirrors are theoretically discussed. In a general plan of the experimental program, the first system is chosen in these studies to be a simple open jet, non premixed turbulent flame. Methane is the fuel and enriched air is the oxidizer. This simple chemically reacting flow system is established at a Reynolds number (based on cold viscosity) of 50,000. A 1.5 m diameter high resolution acoustic mirror with an f-number of 0.75 is used to map the acoustic source zone along the axis of the flame. The results are presented as acoustic power spectra at various distances from the nozzle exit. It is seen that most of the reaction intensity is localized in a zone within 8 diameters from the exit. The bulk reactions (possibly around the periphery of the larger eddies) are evenly distributed along the length of the flame. Possibilities are seen for locally diagnosing single zones in a multiple cluster of reaction zones that occur frequently in practice. A brief outline is given of the future of this work which will be to apply this technique to chemically reacting flows not limited to combustion.

Ramohalli, K.↗

NASA NTRS1982

Analyses of processing variables in propellant burn rate and modulus. I - Mixing times

The effect of the final mixing time on quality of smokeless AP/HTPB propellant with bimodal AP was examined. Identical ingredients were mixed for various intervals, cast in a circular tube, then fired in a static test. Mechanical properties were measured and initial moduli were calculated from the initial slope of the S-N curves. A theoretical model was developed using the data to quantitatively configure a quality control procedure. A minimum time for mixing fine and coarse AP particles was identified and was approximated to within a factor of two or three using a viscous dispersion time and the surface areas of the particles. The model could be improved by considering settling time and particle size distribution effects.

Ramohalli, K.↗

NASA NTRS1981

Advanced development: Fuels

The solar thermal fuels and chemicals program at Jet Propulsion Laboratory are described. High technology is developed and applied to displace fossil fuel (oil) use in the production/processing of valuable fuels and chemicals. The technical and economic feasibility is demonstrated to extent that enables the industry to participate and commercialize the product. A representative process, namely Furfural production with a bottoming of acetone, butanol and ethanol, is described. Experimental data from all solar production of furfural is discussed. Estimates are given to show the attractiveness of this process, considering its flexibility to be adaptable to dishes, troughs or central receivers. Peat, lignite and low rank coal processing, heavy oil stripping and innovative technologies for process diagnostics and control are mentioned as examples of current projects under intensive development.

Ramohalli, K.↗

NASA NTRS1981

Parametric results for heat transfer across honeycomb sandwich panels

The problem of heat transfer across honeycomb sandwich panels is theoretically investigated. The basic objective is to predict the rear surface temperature as a function of time when the front surface is exposed to a prescribed heat flux; the faces are bounded by planar sheets so that the air circulation in the honeycomb cells is bounded and contained. The influence of the air circulation on convective heat transfer is explicitly included. Drawing upon previous investigators' results that indicated various relations for the Nusselt numbers vs Rayleigh numbers in different regimes of the aspect ratio (defined as the ratio of the cell height to cell width), parametric calculations are performed to predict the rear surface temperatures. Chemical degradation of the material, especially the glue holding the face material on the end, is important but has not yet been included. The results indicate that decreasing the cell width, increasing the cell wall thickness and increasing the cell height all have beneficial effects upon the heat transfer; i.e., all of these variations reduce rear surface temperature for a given time for a prescribed heat flux on the front surface.

Ramohalli, K.↗

NASA NTRS1981

Some fundamental acoustic observations in combusting turbulent jets

A study is presented of the possibility of using the acoustic radiation emitted from turbulent combustion zones to characterize the structure, mechanics and properties of turbulent combustion. Theoretical consideration is given to the acoustic characteristics of a nonpremixed open turbulent jet flame and the response of the acoustic spectrum to changes in combustion conditions. Experimental observations made of the acoustic emissions from a laboratory burner that establishes turbulent flames at the exit of a fully developed pipe flow as well as two commercial burners using methane, ethane and propane fuels are then presented which reveal changes in the acoustic amplitudes in three high-frequency bands associated with changes in the air-fuel ratio. Results suggest a means for combustion diagnostics and demonstrate the possibility of using acoustic measurements in investigations of combustion zone processes.

Ramohalli, K.↗

NASA NTRS1980

Effect of silicone oil on solid propellant combustion in small motors

The feasibility of reducing troublesome nozzle blockage (by condensation deposits) in laboratory-scale solid rockets by addition of a silicone oil as a propellant ingredient was explored experimentally. An aluminized composite propellant and its counterpart with 1% silicone oil replacing part of the binder were fired in a 63.5 mm diameter, end-burning, all-metal burner. Pressure-time histories were recorded for all of the tests by a Taber gauge mounted at the downstream end of the chamber; temperature-time data at the nozzle throat were obtained in some of the runs by thermocouples having junctions positioned at the wall but insulated from the metal. Deposition of condensables on the nozzle walls causing a progressive increase in the chamber pressure with time was noted. The fraction of firings exhibiting practically no condensation was 59% with silicone and 32% without. On the average, temperature readings at the nozzle throat were higher with the silicone propellants. Although various phenomena may contribute to these findings, the results are not understood completely.

Ramohalli, K.↗

NASA NTRS1980

Process modifications for improved carbon fiber composites: Alleviation of the electrical hazards problem

Attempts to alleviate carbon-fiber-composite electrical hazards during airplane crash fires through fiber gasification are described. Thermogravimetric and differential scanning calorimetric experiments found several catalysts that caused fibers to combust when composites were exposed to test fires. Composites were tested in the 'Burn-Bang' apparatus and in high voltage electrical detection grid apparatus. In a standard three minute burn test modified composites released no fibers, while state-of-the-art composites released several hundred fiber fragments. Expected service life with and without catalytic modification was studied and electron microscopy and X-ray microanalysis furnished physical appearance and chemical composition data. An acrylic acid polymer fiber coating was developed that wet the carbon fiber surface uniformly with the catalyst, providing a marked contrast with the uneven coats obtained by solution-dipping.

Ramohalli, K.↗

NASA NTRS1979

Novel approaches for alleviation of electrical hazards of graphite-fiber composites

Four basically different approaches were considered: gasification of fibers, retention in the matrix, clumping to prevent entrainment, and electrical insulation of fibers. The techniques used to achieve them are described in some detail. These involved surface treatment of fibers to improve the wettability of fibers and coating the fibers with the selected substances before laying them up for composite fabrication. Thermogravimetric analyses were performed on the plain and treated fibers in inert (nitrogen, argon) and reactive (air) atmospheres. The treated fibers embedded in epoxy were ignited in a Bunsen flame to determine the efficiency of these treatments. A simple apparatus was assembled to detect the time for the first short circuit (in a typical electrical circuit) when exposed to the combustion products from a graphite fiber composite fire. The state-of-the-art and treated fibers cast in typical epoxy were burned and ranked for potential success. It was inferred that the gasification schemes appear promising when reduction or oxidation is tried. It was also found that some very promising candidates were available for the clumping and for the electrical insulation of fibers.

Ramohalli, K.↗

NASA NTRS1979

Thermochemical modeling

The prediction of smoke behavior of a material using only the thermochemical properties geometry and flow, was investigated to determine economical methods for producing better materials. Spinoff, and honeycomb sandwich structures are discussed.

Ramohalli, K.↗

NASA NTRS1979

Vapour phase details in the oscillatory combustion of propellants A porous plate analogue

A perforated porous plate burner is designed to scale up the vapor phase details in composite propellant combustion. A fuel vapor is passed through the pores and an oxidizer vapor is passed through the discrete perforations drilled in the plate. Discussion of the scale modeling of the vapor phase details in oscillatory combustion of composite propellants leads to the following conclusions: (1) the concept of a perforated porous plate analog for the composite propellant vapor phase combustion appears to be valid during oscillatory combustion as well; (2) the flame standoff distance can be conveniently determined with motion picture photography; (3) the flame standoff distance varies with the flow velocity during oscillatory combustion much the same way as during time-independent combustion; and (4) the overall structure of the combustion zone (flame) does not appear to vary too much from its time-independent structure during oscillatory combustion

Ramohalli, K.↗

NASA NTRS1979

Acoustic diagnostics of the nonpremixed turbulent jet flame

The feasibility of inferring information regarding turbulence and combustion details in turbulent combustion zones through the acoustic field is explored. The well known theoretical formulation of Strahle is used. The real difficulty in prediction of the acoustic field is seen to be the unavailability of an expression for the local, instantaneous reaction rate in a turbulent field. A simplified expression is used to infer the nature of the acoustic field. Based on earlier photographic observations, a model is used as a working hypothesis to extract information regarding the acoustic field. These are seen to be substantiated by experiments as well. More importantly, it is found that changes in the operating conditions of various burners are almost instantly revealed in the acoustic spectra. Several experiments with a laboratory burner using several different gaseous reactants are reported to support this diagnostic information content of the acoustic fields of turbulent combustion zones.

Ramohalli, K.↗

NASA NTRS1979

Thermal performance modification of composite materials

This paper reports on an investigation of the concept of modifying the thermal performance of filled polymers through a minor compositional change (presently by coating the filler). The fire-safety of construction materials and the instability of solid rockets are used as examples. A theory is developed which shows that vast improvements are possible by controlling thermal conductivity. Experiments are described that show the weight loss and smoke density in the NBS smoke-density chamber of fiberglass-reinforced epoxy panels, and the instability trends of an AP-HTPB propellant fired in an L-Star rocket motor. The feasibility of tailoring thermal behavior to suit each particular need is demonstrated.

Ramohalli, K.↗