Showing papers in "Journal of Thermophysics and Heat Transfer in 1999"

Thermal Conductivity of Nanoparticle -Fluid Mixture

Abstract: Effective thermal conductivity of mixtures of e uids and nanometer-size particles is measured by a steady-state parallel-plate method. The tested e uids contain two types of nanoparticles, Al 2O3 and CuO, dispersed in water, vacuum pump e uid, engine oil, and ethylene glycol. Experimental results show that the thermal conductivities of nanoparticle ‐e uid mixtures are higher than those of the base e uids. Using theoretical models of effective thermal conductivity of a mixture, we have demonstrated that the predicted thermal conductivities of nanoparticle ‐e uid mixtures are much lower than our measured data, indicating the dee ciency in the existing models when used for nanoparticle ‐e uid mixtures. Possible mechanisms contributing to enhancement of the thermal conductivity of the mixtures are discussed. A more comprehensive theory is needed to fully explain the behavior of nanoparticle ‐e uid mixtures. Nomenclature cp = specie c heat k = thermal conductivity L = thickness Pe = Peclet number P q = input power to heater 1 r = radius of particle S = cross-sectional area T = temperature U = velocity of particles relative to that of base e uids ® = ratio of thermal conductivity of particle to that of base liquid ¯ = .® i 1/=.® i 2/ ° = shear rate of e ow Ω = density A = volume fraction of particles in e uids Subscripts

Spreading Resistance of Isoflux Rectangles and Strips on Compound Flux Channels

Abstract: The general expression for the spreading resistance of an isoe ux, rectangular heat source on a two-layer rectangular e ux channel with convective or conductive cooling at one boundary is presented. The general expression depends on several dimensionless geometric and thermal parameters. Expressions are given for some two- and three-dimensional spreading resistances for two-layer and isotropic e nite and semi-ine nite systems. The effect of heat e ux distribution over strip sources on two-dimensional spreading resistances is discussed. Tabulated values are presented for three e ux distributions, the true isothermal strip, and a related nonisoe ux, nonisothermal problem. For narrow strips, the effect of the e ux distribution becomes relatively small. The dimensionless spreading resistance for an isoe ux square source on an isotropic square e ux tube is discussed, and a correlation equation is reported. The closed-form expression for the dimensionless spreading resistance for an isoe ux rectangular source on an isotropic half-space is given.

Mathematical Modeling of Loop Heat Pipes and Experimental Validation

Abstract: A mathematical model to calculate the steady-state performance of a loop heat pipe (LHP) is presented. The mathematical model is based on the steady-state energy conservation equations and the pressure drop calculations along the fluid path in the LHP. The LHP operating temperature is calculated as a function of the applied power at a given LHP condition. The beat exchange between each component of the LHP and the surroundings is taken into account. Both convection and radiation environments are modeled. Experimental validation of the model is attempted by using two different LHP designs. The validity of the mathematical model is investigated for different sink temperatures and elevations. The comparison of the calculations and experimental results showed good agreement (within 5% ). The proposed method proved to be a useful tool for reliable prediction of the steady-state performance characteristics of the LHP.

Viscous Shock-Layer Simulation of Airflow past Ablating Blunt Body with Carbon Surface

Abstract: A kinetic model for air-carbon surface interaction is suggested. The model is based on the langmuir approach to the kinetics of catalytic reactions. It yields a reasonable agreement with published experimental data on graphite oxidation. A viscous shock-layer code has been developed to simulate hypersonic flows of the 19-species mixture containing air and carbon products. Numerical analysis of ablation and strong ionization processes is carried out with different ablation and ionization models. Calculations show that 1) the maximal drop of the heat flux because of ablation, compared with that obtained for the fully catalytic (chemical-equilibrium) wall in the 11-species air, is within 26% under the conditions discussed; 2) mass loss rate strongly depends on the adsorption type (mobile/immobile); 3) ionization model may have a substantial influence on the shock thickness in the case of re-entry with a hyperbolic velocity; and 4) the effect of the wall catalycity with respect to charged particles on the heating rate is small

Eley-Rideal and Langmuir-Hinshelwood Recombination Coefficients for Oxygen on Silica Surfaces

Abstract: The energetics and dynamics of the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) recombination reaction of oxygen atoms on β cristobalite have been studied within a semiclassical collisional model. The calculated recombination coefficient γ for the E-R reaction at T s = 1000 K is in satisfactory agreement with the experimental value, whereas at T s = 600 K a satisfactory agreement is found between the L-H γ value and the experimental one. Results on the energy exchanges between the formed O 2 molecules and the silica surface are reported. Site-specific effects as well as the influence of the top layer surface structure are also pointed out and discussed.

Thermodynamic and Transport Properties for Inductive Plasma Modeling

Abstract: A review is given of models for the thermodynamic and transport properties of inductive plasmas under conditions of local thermodynamic equilibrium The thermodynamic properties of individual species are computed using a statistical mechanics formulation based upon the rigid rotator and harmonic oscillator model Complex cut-off criteria for the electronic levels and anharmonicity corrections are not needed for practical equilibrium calculations An efficient iterative technique is proposed for the calculation of the equilibrium mixture thermodynamics properties Through a Schur-complement approach the number of unknowns in the nonlinear system, which determines the equilibrium chemical composition, may be reduced to the number of basic elements The method is demonstrated for equilibrium air computations The plasma transport properties are computed with the method of Chapman and Enskog Accurate formulas for the heavy particle and electron transport properties are discussed Through a straightforward argument the result of Butler and Brokaw for the reactive thermal conductivity is shown to be valid for ionized equilibrium mixtures Computed results for the thermodynamic and transport properties of air are compared with numerical and experimental results of other researchers

Effect of Surface Radiation on Natural Convection in a Square Enclosure

Abstract: Results of an experimental study of heat transfer by natural convection and surface radiation in an air-e lled squareenclosureusingadifferentialinterferometerarereported.Theenclosurecomprisestwodifferentiallyheated vertical walls and two horizontal adiabatic walls. The suppression of natural convection in the presence of surface radiation has been demonstrated experimentally. For the case of an enclosure with highly emissive walls, mean Nusselt number correlations for convection and radiation, as well as combined convection and radiation, are also presented in terms of Grashof number in the laminar range. Nomenclature d = width of the enclosure, m Gr = Grashof number, gb (Th i Tc)d 3 /m 2 h = local heat transfer coefe cient along the hot wall, W/m 2 K N h = average heat transfer coefe cient along the hot wall, W/m 2 K km = thermal conductivity of air at Tm, W/m K N Nuc = Nusselt number (mean) due to convection, [(qcd)]/[(Th i Tc)km] N Nur = Nusselt number (mean) due to radiation, [(qrd)]/[(Th i Tc)km] N Nur qc = convective heat e ux entering the enclosure from the hot wall, W/m 2 qr = radiative heat e ux entering the enclosure from the hot wall, W/m 2 qt = total heat e ux entering the enclosure, (qc C qr), W/m 2

Operational Behavior of Inductively Heated Plasma Source IPG3 for Entry Simulations

Abstract: Thedesignoftheplasmawindtunnel (PWK3),itsinductivelyheatedplasmagenerator (IPG3),andexperimental results using O 2 and CO2 as operational gases are described. Various operational conditions (mass e ow rate, frequency) were applied. The thermal plasma powers measured with a calorimeter in the chamber of PWK3 are presented, leading to thepossibility to determineefe ciencies. When thepowerwas varied, two discrete operational transitions were observed. The simultaneous differences in the discharge behavior of IPG3 are represented by sudden changes of parameters such as calorimetric powers and local heat e uxes measured with a stationary heat e ux probeinthechamberofthefacility. Additionally,thecoolingpoweroftheIPG3plasmatubeispresented.Here, a plasma stabilization effect appearing with the second operational transition was observed when the tube cooling power decreased suddenly despite the simultaneous increase of the plasma power in the chamber. An imaging spectrometer measuring the radial intensity of the plasma through an axial optical window of IPG3 was used. Both the operational behavior, in particular the stabilization effect, and the heat e ux measurements show that PWK3 enables high-enthalpy tests for both basic thermal protection material tests and atmospheric entry simulation of spacecrafts.

Stagnation-point heat transfer rates for pioneer-venus probes

Abstract: Summary The convective and radiative heat transfer rates are calculated for the stagnation region of the Pioneer- Venus Probe vehicles during their entry flights into the planet Venus. The nonequilibrium thermochemical state of the flow is calculated using a viscous shock layer method accounting for oxidation of heatshield surface by atomic oxygen and for pyrolysis-gas injection. Radiative transport along the stagnation streamline is calculated using a lineby-line technique and tangent-slab approximation. For both radiative and convective heating rates, the present results are substantially smaller than the earlier values obtained assuming equilibrium.

Impingement Heat Transfer on a Target Plate with Film Cooling Holes

Abstract: Detailedheat-transferdistributionsarepresentedforanarray ofjetsimpinging onatargetplatewithastaggered array of e lm cooling holes. The e ow impinges on the target plate through a row of impingement holes and exits the channel from the sides and through the e lm holes. The top plate has 12 rows of impingement holes, and the target platehas11 rows ofe lm holes. Theimpingementholes and the e lm holes have thesame diameterandarestaggered such that the air from the impingement hole does not exit directly through the e lm hole. The setup is typical of an impingement/transpiration cooled gas turbine airfoil. Additional to the e ow exiting through the e lm holes, there is an exit for crosse ow after impingement. The exit opening of the impingement channel is changed to provide three different spent air exit directions. The detailed heat-transfer coefe cient distributions were measured using a transient liquid crystal technique. Results are presented for a range of jet Reynolds numbers between 0.4 ££ 10 3 and 2.0 ££ 10 4 with different exit e ow orientations. Heat-transfer results for the target plate with e lm holes are compared with those without e lm holes under the same e ow conditions. Film extraction reduces crosse ow effects on jet impingement heat transfer. However, overall averaged heat-transfer rates on the target surface appear less affected by presence of e lm hole for cases where the crosse ow is generated in only one direction.

Spectral Radiative Properties of Open-Cell Foam Insulation

Abstract: A method to determine radiative properties of open-cell foam insulation is described. The spectral volumetric absorption and scattering coefficients and the spectral phase function are predicted from the dimensions and hemispherical reflectivity of particles that constitute the solid structure by applying to these particles a combination of geometric optics laws and diffraction theory. Three types of carbon foam of different porosities are studied. Particle dimensions and porosity can be obtained from microscopic analysis, but solid hemispherical spectral reflectivity is very difficult to obtain directly. It is determined by the Gauss method of linearization, applied to bidirectional spectral transmittance data obtained from an experimental device using Fourier-transform infrared spectroscopy. Results obtained from this approach are consistent. Good agreement is observed between the experimental results of transmittance and reflectance and the theoretically predicted values computed from the identified values of particle hemispherical reflectivity.

Coupled Ordinates Method for Multigrid Acceleration of Radiation Calculations

Abstract: The finite volume and discrete ordinates metbods are known to converge increasingly slowly as the optical thickness is increased. This is a result of the sequential nature of the solution procedure; the equations for energy and the directional intensities are solved one by one, assuming prevailing values for other variables. The coupled ordinates method is proposed whereby the discrete energy and intensity equations at each cell are solved simultaneously, assuming spatial neighbors to be known. The point-coupled procedure is used as a relaxation sweep in a multigrid scheme. The formulation of coarse-level discrete equations admits arbitrary nonconvex polyhedra, making the scheme suitable for use with arbitrary unstructured polyhedral meshes. The scheme is shown to substantially accelerate convergence over a range of optical thicknesses

Experimental and computational study of high enthalpy double-wedge flows

Abstract: A series of experiments designed to study reacting nitrogen flow over double-wedge geometries was conducted in the T5 shock tunnel at the California Institute of Technology. These experiments were designed using computational fluid dynamics to test nonequilibrium chemistry models. Surface heat transfer rate measurements were made, and holographic Mach-Zehnder interferometry was used to visualize the flow. Analysis of the data shows that computations using standard thermochemical models cannot reproduce the experimental results. The computed separation zones are smaller than the experiments indicate. However, the computed heat transfer values match the experimental data in the separation zone, and on the second wedge the computed heat transfer distribution matches the shape and heights of the experimental distribution but is shifted due to the difference in the size of the separation zones

Evaporative Heat Transfer in a Capillary Structure Heated by a Grooved Block

Abstract: Experimental results of capillary-driven heat and mass transfer in a vertical rectangular capillary porous structure heated from a grooved block placed on the top are reported in this paper. The formation of the liquid-vapor menisci in the vicinity of the downward-facing heated surface provided the capillary-force for the upflow of water in the porous structure. The temperature distributions in both the heating block and the porous structure as well as the induced mass flow rate of water were measured under different heat flux conditions. The experimental results show that with an increase of the imposed heat flux, the heat transfer coefficient increases to a maximum value and then decreases afterwards. It is also found that the liquid-vapor interface moved towards the downward-facing heated surface as the imposed heat flux was increased. The heat transfer mechanisms leading to the maximum heat transfer coefficient and the critical heat flux are explained based on the visual observation of the phasechange behavior and the measured temperature distributions within the porous structure. The effects of particle sizes, the inlet temperature of the subcooled liquid, and the adverse gravity force on the heat transfer characteristics are also examined.

Experimental investigation of surface reactions in carbon monoxide and oxygen mixtures

Abstract: During hypersonic entry into the CO 2 atmosphere of Mars, competing exothermic chemical reactions may oceur on a spacecraft heatshield surface. Two possible surface reactions are O+O → O 2 and CO+O → CO 2 . The relative importance of these reactions on quartz is investigated using a diffusion tube side-arm reactor together with two-photon laser-induced fluorescence for both O and CO species detection. The experiments show 1) that the presence of CO in the gas phase does not -significantly affect the oxygen recombination reaction on quartz and 2) that the gas-phase CO concentration is not significantly altered by the presence of atomic oxygen. These results indicate that for our experimental conditions the dominant surface reaction on quartz in oxygen-carbon monoxide mixtures is O+O → O 2 . Current heating computations for Martian entries assume CO oxidation to be fully catalytic. The resulting entry heating values are significantly higher than those computed using the assumption of fully catalytic oxygen recombination. The data presented here indicate that the assumption of fully catalytic CO oxidation may be overly conservative for heatshleld sizing purposes

Spectra and critical Grashof numbers for turbulent transition in a thermal plume

Abstract: Turbulent transition and turbulence characteristics of the thermal plume above a line heat source in unstratified air are elucidated by visualizing the plume, measuring the temperature, and analyzing the spectrum of the measured temperature. Large-scale vortices occur in the turbulent region, and they have the same frequency as the laminar swaying motion. Spectra S(s) can be approximated by 0.130f (Hz) -5/3 in the inertia-convective subrange and 0.275f (Hz) -3.0 in the inertia-diffusive subrange. The spectrum enables us to exactly determine the local state of flow, i.e., laminar, transitional, or turbulent. Grashof numbers for the beginning and end of a transition are Gr = 2.0 × 10 8 and Gr = 2.0 × 10 9 . The transitional region is divided into the initial and final stages at Gr b = 7.52 × 10 8

Heat Transfer in Natural Convection of Magnetic Fluids

Abstract: The natural convection of a magnetic e uid in a two-dimensional rectangular cavity with an imposition of an even vertical magnetic e eld was studied experimentally and numerically. Results obtained from the numerical analysis showed good agreement with experimental heat transfer data. From both experiment and numerical analysis, it was revealed that the vertically imposed magnetic e eld has a destabilizing ine uence, and at the super critical state the e ow mode becomes substantially different from that with no magnetic e eld. A prediction from the numerical analysis indicates that the imposition of the magnetic e eld causes thee ow to a higher transition e ow mode, enhancing the heat transfer.

Impingement Cooling in Rotating Two-Pass Rectangular Channels with Ribbed Walls

Abstract: Impingementcooling wasstudiedonribbed wallsinrotatingtwo-passrectangularchannelswith asharp 180-deg turn. Two rows of circular jets impinged opposite to the direction of rotation in one channel and in the same direction of rotation in the other channel. Square cross-sectioned ribs were periodically attached to the target walls and inclined at a 45-deg angle to the direction of spent aire ow. Rib pitch to height and rib height to channel hydraulicdiameterratiosweree xed at10 and0.125,respectively. Afterimpingement,spent air (crosseow)traveled radially outward and inward in the e rst and the second impingement channel, respectively. Jet Reynolds numbers and rotation numbers varied from 4 £ 10 3 to 1 £ 10 4 and 0 to 0.0133, respectively. As the jet Reynolds number increased from 4 ££ 10 3 to 1 £ 10 4 , the ratios of channel-averaged ribbed to smooth surface Nusselt numbers increased from 13 to 47% for the nonrotating test. For the rotating test, however, these ratios changed from 9 to 44% as the jet Reynolds number increased. Rotation-induced Coriolis and centrifugal forces altered the pressure distribution, but the jet velocity distribution was not signie cantly affected. However, those rotation-induced forces decreased the Nusselt number values up to 20% in the ribbed impingement channels.

Behavior of Two-Temperature Model in Intermediate Hypersonic Regime

Abstract: Shock standoffdistancefora sphereis calculated to examine thebehavioroftheexisting two-temperature model in theintermediate hypersonic e ow regime. Calculations are carried outforthreebinary scaling parametervalues, corresponding to nearly frozen, nonequilibrium, and nearly equilibrium e ows, respectively. The obtained shock standoff distances are compared with the experimental data obtained in a ballistic range. It is shown that the two-temperature model reproduces the shock standoff distances in the intermediate hypersonic e ows fairly well but tends to lose its accuracy where vibrational excitation occurs but chemical reactions are nearly frozen. Nomenclature M = collision partner in dissociation/recombination reactions p1 = static pressure in the test section, Pa q = power on the vibrational temperature in the dee nition of Ta, 0

Geometric Optics Applied to Rough Surfaces Coated with an Absorbing Thin Film

Abstract: The geometric optics approximation in which the interference effects are neglected has been shown to accurately predict surface reflection from random rough surfaces over a large domain of geometric parameters. In this work, the geometric optics approximation is extended to rough surfaces coated with an absorbing thin film. Multiple reflections and the effects of interference within the thin film are considered. The thin film model predictions are compared with the experimental findings for an aluminum surface coated with a thin aluminum-oxide composite film. Such comparisons made at a variety of incident angles and wavelengths indicate that the geometric optics thin film model is accurate. The approximate solutions also indicate that a significant amount of energy is absorbed by the thin film, leading to a decrease in the reflected energy. The model is used to demonstrate the strong influence of optical constants and film thickness on the reflection distribution.

Interaction of Spalled Particles with Shock Layer Flow

Abstract: The influence of the solid particles injected into the shock layer by the spaliation of a carbonaceous ablating heatshield on the shock layer flow is investigated theoretically. The equation of motion of a solid particle is integrated using a polynomial expansion. Assuming a Gaussian distribution for the initial masses and velocities of the particles, the rates of production of CO, CN, C 3 , and turbulence energy are calculated by integrating those production rates for one particle over the mass and velocity distributions. The results for the environment of Stardust Earth reentry show that these production rates decay approximately exponentially in the normal direction from the ablating wall. Correlation formulas for the magnitudes and slopes of this decay pattern are derived. The lower limits of particle size and initial velocity are estimated for a carbon-phenolic material from a spectroscopic result obtained in an arcjet wind-tunnel test

Gas Permeability of Lightweight Ceramic Ablators

Abstract: Many lightweight thermal protection system (TPS) materials have a large degree of open porosity, which can make them highly permeable to gas flow Recently, a permeability measurement apparatus was constructed to test rigid, porous TPS materials This note presents further gas permeability, made with this apparatus, on two lightweight ceramic ablator materials; viz, phenolic impregnated carbon ablator and silicone impregnated reusable ceramic ablator

Influence of Nonequilibrium Kinetics on Heat Transfer and Diffusion near Re-Entering Body

Abstract: The heat transfer and diffusion near the surface of a space vehicle under re-entry conditions are studied on the basis of the kinetic theory of gases. The influence of the nonequilibrium kinetics in an (N 2 , N) mixture on the transport properties of the flow is investigated. The nonequilibrium vibrational distributions in the boundary layer near the surface of the re-entering body have been obtained in the state-to-state approach and Inserted in the transport kinetic theory code. As a result, the total heat flux, thermal conductivity, and all diffusion coefficients are calculated under different conditions in the freestream and on the surface. The effects of various energy exchanges, vibrational nonequilibrium, dissociation, and recombination on the heat transfer and diffusion are examined

Characterization of Thin-Film Heat-Flux Gauges

Abstract: c D 0 curve is from Eq. (6) by setting r D 0. We see Tm increases dramatically as ® ! ®m . Next consider the interaction between adjacent cuffs. We shall illustrate with the case ® D 0:5, ̄ D 1. Figure 4 shows, for large b, interaction is negligible and Tm approaches the single cuff values shown in Fig. 3. For givencuff width c; Tm becomes inŽ nite as b » c, i.e., when the cuffs are close and prevents most of the surface heat loss. Increased cuff length c increases the interaction and thus the maximum temperature. For a given wire and a given temperature limit, the allowable length and placement of the cuff can be found. Although other values of ® and ̄ are not presented in this Note, graphs similar to Fig. 4 can be generated easily by the method outlined here. It has been known that thermal failure (local melting) of electric heating elements in household or industrial heating is often at the hot spots because of the supports. For electric overhead power lines, thermal failure is deŽ ned as an unacceptabledecrease in tensile strength because of annealing. The maximum allowable temperature9 is set at less than 100±C. Typical values for a power line are as follows. Consider a bare copper wire of diameter 1.17 cm, carrying 200 A at 130,000 V. The resistance per centimeter is 0.000126 Ä. The power lost to Joule heating is 5.05 W/cm. Thus q0 is 4.71 W/cm.3 Because copper ± D 0:004=±C and k D 3:86 W/cm/±C we Ž nd ® D 0:41. On the other hand, the Nusselt number for forcedconvectionin crosswindis experimentally9 O(1) to (100), giving a value for ̄ from 10¡2 to 1. The present Note provides a method to compute the maximum temperature,which may increase severalfold because of the cuffs. Last, we mention that our analysis also applies to the internal heat generated by chemical reactions.

Effective Thermal Conductivity of Graphite -Metallic Salt Complex for Chemical Heat Pumps

Abstract: An experimental procedure was developed for measuring the effective thermal conductivities of graphite-CaCl 2 -nNH 3 (n = 8, 4, 2), MnCl 2 -nNH 3 (n = 6, 2), and BaCl 2 -8NH 3 complex for chemical heat pumps. Graphite-metallic salt complex was manufactured tbrougb the impregnation of metallic salt Into a porous graphite matrix. Experimental conditions of pressure and temperature were directly established by the thermodynamic equilibrium lines of salt-ammonia systems obtained by the calorimetric method. Afterward, effective thermal conductivities were measured using a transient one-dimensional heat flow technique at a fixed pressure and temperature under an ammonia atmosphere. Effective thermal conductivities of the graphite-metallic salt complex were in the range of 10-49 W/mK, which are significant higher values than powder beds of 0.1-0.5 W/mK. Results showed that the effective thermal conductivity of a graphite-metallic salt complex has a strong dependency on the bulk density, the weight fraction of graphite, and the ammoniated state of salt

Spectroscopic Measurements of Shock-Layer Flows in an Arcjet Facility

Abstract: Under two different test conditions, radiation emanating from the freestream and shock-layer flow over a 15.24-cm-diam blunt-body test article as measured in NASA Ames Research Center's 20 MW Aerodynamic Heating Facility Arcjet. The test gas was a mixture of air and argon. Spatially resolved emission spectra were obtained over a 2000-8900 A wavelength range using a charge-coupled device camera (1024 × 256 array) attached to a spectrograph. The optical system was calibrated using tungsten and deuterium radiation sources. Previously developed analytical tools were used to determine the following line-of-sight-averaged thermodynamic properties from the calibrated spectra: 1) rotational temperature of the freestream and 2) rotational and vibrational temperatures within the shock layer. Based on the variation in intensity of emission spectra along the stagnation streamline, shock standoff distance was determined. Two sets of data for each test condition were compared to evaluate the repeatability of measurements. Considering likely sources of errors, an uncertainty analysis was performed to estimate the error bounds of the determined properties

Kinetics of Free Radicals Behind Strong Shock Waves

Abstract: A spectroscopic study of the spontaneous emission of free radicals behind strong shocks propagating in the simulated atmospheres of Titan and Mars and in pure CO gas has been carried out in the hypersonic facility of Marseille. A streak camera has been used to obtain time-resolved spectra of tbe Δv = 0 sequence of the B 2 Σ + ↔ X 2 Σ + electronic transition of CN, which is the main emitter in these mixtures. The Swan system of C 2 has also been measured in CO gas. The effect of different initial test gas pressures in the shock tube on the emission of CN in the Titan mixture has been investigated. The comparison between experimental and synthetic spectra shows very high nonequilibrium phenomena in the shock layer. Evidence of non-Boltzmann distribution of the vibrational population of CN has been observed, particularly in high initial pressure conditions.

Transient Thermal Analysis of Parallel Translucent Layers by Using Green's Functions

Abstract: An analysis is developed for computing transient thermal behavior in a composite of two parallel translucent layers with a space between them. The radiative two-flux equation is coupled with the transient energy equation, and both equations are solved by using Green's functions. Illustrative results are provided for transient heating of two parallel translucent layers that exchange radiation. The external boundaries of the two-layer combination are each exposed to a radiative environment, and all boundaries can be convectively heated or cooled. The layer refractive indices are larger than one, and internal reflections are included with boundaries assumed diffuse. The analysis includes internal emission, absorption, isotropic scattering, and heat conduction. Transient results from the present method are verified for a single gray layer by comparison with a finite difference solution that incorporates a numerical solution of the exact radiative transfer equations for the radiative heat source. Illustrative transient temperature distributions show the effects of an insulating gap between layers, when one side of the twolayer composite is subjected to heating by radiation and convection, while the other side is being cooled.