Showing papers in "Journal of Thermophysics and Heat Transfer in 2016"

Hybrid Water-Based Suspension of Al2O3 and Cu Nanoparticles on Laminar Convection Effectiveness

Abstract: A numerical investigation of a laminar forced convection of different working fluids including pure water, various volume concentrations of a nanofluid (Al2O3 nanoparticles dispersed in water), and a hybrid water-based suspension of Al2O3 and Cu nanoparticles (which is a new advanced nanofluid with two kinds of nanoparticle materials) in a uniformly heated circular tube is accomplished. In this paper, the effect of using hybrid water-based suspension on thermal behavior and hydrodynamic performance in a range of Reynolds number in the laminar regime is investigated. Then, a comparison is made between the thermal and hydrodynamics behavior of the hybrid suspension with those of the nanofluid (with the same concentration) and the conventional one. It is observed that, for all Reynolds numbers studied, employing the hybrid suspension improves the heat transfer rate compared to pure water and the nanofluid. Nevertheless, it reveals an adverse effect on the wall shear stress and friction factor due to the pres...

Advanced Models for Vibrational and Chemical Kinetics Applied to Mars Entry Aerothermodynamics

Abstract: The paper presents a comparative study of vibrational-chemical kinetics and heat transfer in carbon dioxide flows under Mars entry conditions for two classes of models: the state-to-state and multitemperature models. The state-to-state approach treats each vibrational state of a molecule as a separate chemical species, thus providing a very detailed flow description. Reduced multitemperature models are based on nonequilibrium quasi-stationary Boltzmann distributions over vibrational energy with vibrational temperatures of different modes. Implementation of multitemperature models requires much less computational effort, making them rather attractive for engineering applications. Simulations have been performed for the upper part of the Mars Pathfinder entry trajectory. Comparisons between different models demonstrate a good agreement for the flowfield variables obtained using the state-to-state and multitemperature approaches, except some discrepancies for the species mole fractions prediction. This concl...

Approximate Analytical Method for Porous Stepped Fins with Temperature-Dependent Heat Transfer Parameters

Abstract: This work presents the thermal investigation of a porous stepped fin made from different ceramic porous materials (Al and SiC) having temperature-dependent internal heat generation. The fin is dissipating heat to the environment by means of convection and radiation modes of heat transfer, which are further considered to be temperature dependent. The approximate analytical Adomian decomposing method is used to solve this nonlinear problem along with the Newton–Raphson method. The results obtained using the Adomian decomposing method are compared with relevant results available in literature. The effect of various thermophysical parameters on the thermal behavior of the fin is critically analyzed. An optimization study to maximize the heat transfer rate for a constant material volume has been also conducted. The performance of the porous stepped fin is compared with a porous straight fin and solid stepped fin, which proves that the porous stepped fin is a better alternative.

Review of Advances in Thermal Spreading Resistance Problems

Abstract: Thermal spreading resistance problems have been studied by many different researchers over the past six decades. In this paper, the literature on thermal spreading resistance from the past 50 years is chronologically presented, and the last decade of advances are specifically described. Focus is given to recent advances since much of the literature was reviewed in a handbook chapter published in 2003. For consistency throughout the paper, the rectangular slab and cylindrical disk heat spreader are referred to as flux channels and flux tubes, respectively. The thermal spreading resistance of compound rectangular flux channels and circular flux tubes with and without contact resistance are presented. The sink plane boundary condition is modeled using convective cooling with constant and/or variable heat transfer coefficient. Furthermore, the effects of discrete cooling in the heat-sink plane, orthotropic properties, and temperature-dependent thermal conductivity are also presented.

Numerical Study of Spallation Phenomenon in an Arc-Jet Environment

Abstract: It is hypothesized that spallation could affect the aerodynamic heating rates of reentry vehicles using ablative heat shields. To investigate spallation effects, a code is developed to compute the dynamics of spalled particles. The code uses a finite-rate chemistry model to study the chemical interactions of the particles with the flow field. The spallation code is one-way coupled to a computational fluid dynamics solver that models the hypersonic flow field around an ablative sample. Spalled particle behavior is numerically studied in both argon and air flow fields.

Prediction of Nonequilibrium Air Plasma Radiation Behind a Shock Wave

Abstract: The absolute radiation measurements obtained in the electric arc-driven shock-tube facility at NASA Ames Research Center were analyzed to test the collisional-radiative model developed at Ecole Centrale Paris. Two conditions representative of Earth reentry at 10.54 and 11.17 km/s were investigated in the vacuum ultraviolet and infrared spectral ranges. For each of the conditions, the corresponding charge-coupled device images were analyzed. The electron number density was inferred from Stark-broadened nitrogen and Hα lines. Comparisons with the predicted electron number density profiles enabled us to validate the ionization rate constant model implemented in the flowfield solver and to accurately locate the shock front. For both freestream conditions and all the spectral ranges, the predictions of the initial intensity rises were improved when the total spatial smearing (due to the shock motion, the optics, and the camera) was taken into account. The nonequilibrium intensities observed in the vacuum ultr...

Master Equation Study of Vibrational and Rotational Relaxations of Oxygen

Abstract: Transition rates in O2–O collisions for each vibrational and rovibrational state are generated by means of the quasi-classical trajectory method using potential energy surfaces of different fidelities. The first potential energy surface, obtained via the double many-body expansion method, is adopted to obtain vibrational transition rates assuming transrotational equilibrium. The trajectory simulation on a simpler potential surface, based on the two-body pairwise interaction, generates a complete set of rates for each internal state. Vibrational and rotational relaxations of oxygen in a heat bath of parent atoms are modeled by a system of master equations at translational temperatures between 1000 and 20,000 K. It is shown that the vibrational relaxation becomes less efficient at high temperatures, in contrast with the conventional equation for relaxation time proposed by Millikan and White (“Systematics of Vibrational Relaxation,” Journal of Chemical Physics, Vol. null, No. null, 1963, Paper 3209). Rotati...

Performance Analysis of a Microchannel Heat Sink with Various Rib Configurations

Abstract: Microchannel heat sinks with ribbed channels in various configurations have been analyzed numerically using the three-dimensional Navier–Stokes equations. Six configurations of ribbed microchannels (i.e., rectangular, semicircular, triangular, rectangular–triangular, rectangular–semicircular, and triangular–circular) were tested with a fixed width and length of ribs, and compared to smooth channels in a Reynolds number range of 100–500. The results indicate that thermal resistance of microchannels is greatly reduced by introducing ribs and that triangular ribs show the lowest thermal resistance throughout the Reynolds number range. However, the pressure drop is also increased greatly because of the ribs, and rectangular ribs induced the largest pressure drop.

Equation for the Thermal Conductivity of Liquids and an Artificial Neural Network

Abstract: This work presents a literature survey of the available experimental data regarding the thermal conductivity of organic liquids. Experimental data are regressed with the most reliable semiempirical correlating methods existing in the literature, and a set of 5010 data are finally selected, belonging to 164 compounds in the following families: bromide derivatives, chlorine derivatives, condensed rings, fluorine+chlorine+bromide derivatives, F-derivatives, hydrocarbon chains, monocyclic compounds, carboxylic acids, cycloalkanes, cycloalkenes, esters, and ketones. A new correlation to represent the thermal conductivity of pure liquids is presented. A factor analysis is performed for the data selected in order to select the physical parameters to adopt. Optimal coefficients and a different version of the recently proposed equation are presented. The correlation is very simple and is able to predict the thermal conductivity with very low deviation for all families studied. The correlation reproduces the select...

Oxygen Vibrational Relaxation Times: Shock Tube/Laser Absorption Measurements

Abstract: The vibrational relaxation times of oxygen were measured using laser absorption spectroscopy behind incident and reflected shocks in a shock tube. The Bethe–Teller equation was used to model the vibrational relaxation, which (along with the shock jump relations) was used to model the gas dynamics conditions throughout the nonequilibrium relaxation process. The absorbance was modeled based on these gas dynamics conditions while adjusting the vibrational relaxation time to fit the model to the measured oxygen absorbance time history at wavelengths 210–230 nm in the Schumann–Runge system. Undiluted oxygen was studied behind incident shocks at initial postshock translational/rotational temperatures from 1000 to 3300 K and pressures from 0.05 to 0.7 atm, while a mixture of 2% oxygen in argon was studied behind incident and reflected shocks at initial translational/rotational temperatures from 1000 to 4000 K and pressures from 0.2 to 1 atm. Good agreement was found with prior experimental work by White and Mill...

Theoretical and Experimental Investigation of the Melting Process of Ice Particles

Abstract: In this study, the melting process of nonspherical and spherical ice particles was investigated. Individual ice particles were suspended in an acoustic levitator placed in a chest freezer. Melting of the particles was initiated by directing a warm stream of air with controlled temperature, flow rate, and relative humidity toward them. Tests were conducted at 13 different flow conditions. The melting process was recorded by a high-speed video camera. Datasets of 222 individual melting events were collected. From the images, the melting time and the cross-sectional area of the ice particles during melting were measured. Furthermore, a method is presented that allows an approximate calculation of the initial mass of the ice particles based on the postmelting evolutions of the cross-sectional area. Theoretical melting times were calculated based on a model for spherical and nonspherical particles and were compared with the experimental melting times. The model was validated with spherical ice particles, and i...

Radiative Heating During Mars Science Laboratory Entry: Simulation, Ground Test, and Flight

Abstract: The heat shield of the Mars Science Laboratory was equipped with thermocouple stacks to measure in-depth heating of the thermal protection system during atmospheric entry. The heat load derived from the thermocouples in the stagnation region was found to be 33% lower than corresponding postflight predictions of convective heating alone. It was hypothesized that this difference could be attributed to radiation from the shock-heated gas, a mechanism not considered in preflight analyses of flowfields. To test the hypothesis and quantify the contribution of shock-layer radiation to total surface heating, ground tests and simulations (both flow and radiation) were performed at several points along the best-estimated entry trajectory of the Mars Science Laboratory. The present paper provides an assessment of the quality of the radiation model and its impact to stagnation point heating. The impact of radiative heating is shown to account for 43% of the heat load discrepancy. Additional possible factors behind th...

Infrared Signature of Aircraft Engine with Choked Converging Nozzle

Abstract: Incorporation of an infrared suppressor is generally accompanied by a compromise in engine performance, which indirectly reduces the effectiveness of infrared signature suppression. This investigation illustrates the percentage increase in the infrared signature level in the 1.9–2.9 μm and 3–5 μm bands resulting from an increase in engine backpressure in a jet engine due to a reduction in the exit area of a choked converging nozzle. The effectiveness of optically blocking the hot engine parts by reducing the choked nozzle-exit area is estimated. Thermodynamic offdesign point analysis of the jet engine is done using GasTurb software to evaluate the percentage reduction in thrust and the net change in infrared signature level for the reduced choked converging nozzle-exit area relative to that for the design point.

Exact Heat-Transfer Solutions to Radial Fins of General Profile

Abstract: In this paper, the heating process in fin problems of engineering interest is revisited with a target to work out analytical solutions representing the thermal diffusion in a variety of radial fin shapes. The difficulty arisen due to the strong nonlinearity when the physical properties are temperature-dependent and given by power laws is tackled, and explicit expressions for the fin base heat-transfer rate, fin tip temperature, and fin efficiency are obtained. Taking into account these three effects, the optimal radial fin shape is decided, which is of most physical interest.

Surface Temperature Measurements in Hypersonic Testing Using Digital Single-Lens Reflex Cameras

Abstract: A newly adapted temperature measurement technique is presented for measuring aerospace relevant high surface temperatures. A comparatively cheap, available digital single-lens reflex camera is used as the imaging system for a two-color ratio pyrometry technique. This provides a highly spatially resolved imaging system that uses the blue, green, and red pixels for the ratio pyrometry measurements. At the Centre for Hypersonics at the University of Queensland, a Canon EOS 400D camera was spectrally calibrated using a tungsten filament lamp and a monochromator. With the knowledge of the spectral response of the pixels, emission ratio calculations determining the temperature can be undertaken for images of any surface, which fulfills the requirement of radiating as a gray body. For this particular camera, the measurable temperature limits were determined to be between approximately 1500 and 3000 K. Two tests cases are presented demonstrating the use of this technique: first, a heated carbon–carbon sample test...

Effects of Water Phase Change on the Material Response of Low-Density Carbon-Phenolic Ablators

Abstract: 1 Research Assistant, Department of Mechanical Engineering; ali.omidy2@uky.edu 2 Post Doctoral Research Associate, Department of Mechanical Engineering; francesco.panerai@uky.edu 3 Scientist, Silicon Valley Initiative. Senior Member AIAA; jlachaud@ucsc.edu 4 Chief Scientist for Modeling and Simulation, TN Division. Associate Fellow AIAA; nagi.n.mansour@nasa.gov 5 Assistant Professor, Department of Mechanical Engineering. Associate Fellow AIAA; alexandre.martin@uky.edu

Kinetic Models of Oxygen Thermochemistry Based on Quasi-Classical Trajectory Analysis

Abstract: Recent progress in state-resolved kinetic models of thermal relaxation and dissociation of oxygen based on high-fidelity transition rate coefficients is presented. Specifically, three types of collisions encountered in high-temperature flows are discussed: O2–O, O2–N, and O2–N2. For these molecular systems, the thermal relaxation times and dissociation rate coefficients, obtained from extensive trajectory simulations, are compared with existing experimental data. A new set of calculations for O2–N2 on an ab-initio potential energy surface is presented. Accuracy of multitemperature models is assessed based on comparison with the solution of master equations. Recommendations for adjustable parameters employed in multitemperature models are provided.

Conjugate Heat Transfer Inside Microchannels Filled with Porous Media: An Exact Solution

Abstract: The conjugate heat transfer inside microchannels filled with porous media in the slip regime is analytically investigated based on the local thermal nonequilibrium model, i.e., assuming independent temperatures for the solid and fluid phases of the porous material. The internal heat generations within both the fluid and solid phases of the porous medium are considered. Effects of the pertinent parameters such as the dimensionless thermal resistance of the wall Rw, heat generation parameter ω, Biot number Bi, fluid-to-solid effective conductivity ratio k, and temperature jump coefficient β on the dimensionless temperature profiles θ of the two phases as well as the Nusselt number Num are investigated. Moreover, the validity of the one-equation model (the local thermal equilibrium assumption) is analyzed by comparing the Nusselt number obtained by the one-equation model (local thermal equilibrium, by assuming identical temperatures for the solid and fluid phases of the porous material) to that obtained by t...

Uncertainty Analysis of Radiative Heating Predictions for Titan Entry

Abstract: The objective of this study was to investigate the uncertainty in shock layer radiative heating predictions on the surface of a hypersonic inflatable aerodynamic decelerator during Titan entry at peak radiative heating conditions. Computational fluid dynamics simulations of planetary entry flows and radiative heating predictions possess a significant amount of uncertainty due to the complexity of the flow physics and the difficulty in obtaining accurate experimental results of molecular-level phenomena. Sources of uncertainty considered include flowfield chemical rate models, molecular band emission, and the excitation/deexcitation rates of molecules modeled with a non-Boltzmann approach. Because of the computational cost of the numerical models, uncertainty quantification was performed with a surrogate modeling approach based on a sparse approximation of the point-collocation nonintrusive polynomial chaos expansion. Accurate uncertainty results were obtained with only 500 evaluations of the computational...

Characterization of a Reentry Plasma Wind-Tunnel Flow with Vacuum-Ultraviolet to Near-Infrared Spectroscopy

Abstract: This paper presents the analysis of optical emission spectroscopic measurements from vacuum ultraviolet (120 nm) to near infrared (960 nm) in a high-enthalpy air plasma flow corresponding to superorbital reentry conditions. The vacuum ultraviolet measurements have been realized with a new experimental setup allowing measurements through a bore hole in the sample. Using the commonly applied optical emission spectroscopy from the side, the radiation transport along the line of sight of the vacuum ultraviolet measurements has been assessed. This allowed the determination of the local ground state densities of atomic oxygen and atomic nitrogen from a branching ratio analysis and the blackbody limiting correction of the vacuum ultraviolet radiation. Through the analysis of the absorption in the borehole, the spectra have been corrected, resulting in a stagnation point radiative heat flux in the vacuum ultraviolet of 235 kW/m2.

Experimental Investigation of Methane Convection and Boiling in Rocket Engine Cooling Channels

Abstract: The steady-state heat transfer characteristics under internal forced convection of liquid methane were experimentally investigated using a rectangular channel with a cross section of 1.8×4.1 mm and square channels with a cross section of 3.2×3.2 mm; three square channels had surface finishes typical of milled channels and another three square channels had internal longitudinal fins. A high heat flux test facility capable of handling cryogenic temperatures, which was developed at the Center for Space Exploration Technology Research for the purpose of simulating the high heat load conditions, representative of regeneratively cooled rocket engines, was used in this study. Subcooled film-boiling phenomena were discovered for all the channels presented in this study. Film-boiling onset at critical heat flux was correlated to the boiling number Bo∼0.1. The convective Nusselt number follows predicted trends for Reynolds number with a wall temperature correction for both the boiling and nonboiling regimes.

Shape-Stabilized Composite Phase-Change Materials Prepared with Stearic Acid and Active Carbon

Abstract: Active carbon is used as an absorbent material because of its porous structure. Stearic acid/active carbon composite phase-change materials were synthesized by physical absorption with stearic acid as the phase-change material and active carbon as the carrier to maintain a stable shape. Thermogravimetric analysis, differential scanning calorimetry, a physical property measurement system, and Fourier transform infrared spectroscopy were used to determine the thermal stability, phase-change temperatures and enthalpies, thermal conductivities, and structures of the samples, respectively. The samples were found to have good thermal stability. The stearic acid and active carbon in the synthesized materials were simply physically combined. The maximum absorption ratio of stearic acid in the samples was 79.48 wt %; the melting and solidifying temperatures were 52.83 and 51.74°C, respectively; and the melting and solidifying enthalpies were 108.2 and 105.3 J·g−1, respectively. The thermal conductivities of the s...

Flight Acceleration Effect on Heat Transfer Deterioration of Actively Cooled Scramjet Engines

Abstract: Heat transfer deterioration produces local wall temperature peaks and may endanger actively cooled scramjet engines. The heat transfer deterioration of supercritical-pressure n-decane at different flight accelerations is simulated to represent accelerating hypersonic vehicles. Two types of heat transfer deterioration are observed. The type 1 heat transfer deterioration, which appears at the initial heated section, is due to the formation of the thermal boundary layer. The type 2 heat transfer deterioration, which can be identified with an M-shaped velocity profile, appears because of the reduction of turbulent diffusion. The heat transfer deterioration onset parameter, which is defined as the ratio of heat flux to mass flux in case of incipient heat transfer deterioration, is obtained at both positive and negative flight accelerations. A positive flight acceleration value indicates that the flow direction and the acceleration direction is the same, and a negative value indicates that the two directions ar...

Polarization Dependence of the Reflectance and Transmittance of Anisotropic Metamaterials

Abstract: Due to the interference effect, the reflectance and transmittance of an arbitrary linearly polarized wave cannot be fully described by the reflectance and transmittance of transverse electric and transverse magnetic waves. In this work, the polarization dependence of reflectance and transmittance for anisotropic metamaterials is examined. The explicit mathematical relationship between the Fresnel coefficients and the reflectance (or transmittance) for a given polarization angle is derived. A method is presented that can be used to obtain the reflectance (or transmittance) for any polarization angle from three other polarizations. Several different anisotropic metamaterials are numerically investigated with the finite-difference time-domain technique to elucidate the polarization dependence of reflectance or transmittance. The reflectance and transmittance obtained from the three-polarization-angle method are in agreement with those from the rigorous numerical simulation.

Diffusion Penetration Time for Transient Heat Conduction

Abstract: The time duration for processes involving transient thermal diffusion can be a critical piece of information related to thermal processes in engineering applications. Analytical solutions must be used to calculate these types of time durations because the boundary conditions in such cases can be effectively like semi-infinite conditions. This research involves an investigation into analytical solutions for six geometries, including one-dimensional cases for Cartesian, cylindrical, and spherical coordinates. The fifth case involves a heated surface on the inside of a hole bored through an infinite body, which is a one-dimensional problem in cylindrical coordinates. The sixth case involves two-dimensional conduction from a point heat source on the surface of a slab subjected to insulated boundary conditions elsewhere. The mathematical modeling for this case is done in cylindrical coordinates. For each geometric configuration, a relationship is developed to determine the time required for a temperature rise ...

Laminar Free Convection in Bingham Plastic Fluids from an Isothermal Elliptic Cylinder

Abstract: Free convection from an isothermal elliptical cylinder in Bingham plastic fluids is studied numerically. This work spans a wide range of aspect ratios of the elliptical cylinder (0.1≤E≤10) to delineate the effect of shape on the flowfield close to the heated cylinder. The influence of the relevant parameters, namely, Rayleigh number (102≤Ra≤105), Prandtl number (10≤Pr≤100), and Bingham number (0.5≤Bn≤107), on the momentum and heat transfer characteristics is studied in terms of the yielded/unyielded regions, streamline, isotherm contours, and local Nusselt number for an elliptical cylinder of constant surface area in blunt (E>1) and slender orientations (E 1) impede it. Using the present numerical results, predictive correl...

Thermal Properties of Metallic Films at Room Conditions by the Heating Slope

Abstract: An analytical model and a methodology for determining the thermal diffusivity and the thermal conductivity of metallic thin films at room conditions are proposed. The analytical model is based on the one-dimensional heat transfer equation, which allows estimation of the thermal conductivity and thermal diffusivity through the initial heating slope value. The thermal conductivity and thermal diffusivity values of gold and aluminum films from 20 to 200 nm thicknesses, determined from the initial slope of the measured heating profiles, and their comparison with the analytical ones are discussed. Results show that thermal diffusivity increases from (30±6)×10−6 m2/s to (127±12)×10−6 m2/s for gold films, and it increases from (15±7)×10−6 m2/s to (95±10)×10−6 m2/s for aluminum films; although thermal conductivity increases from (132±35) to (306±48) W/m·K for gold films and from (58±30) to (243±39) W/m·K for aluminum films, when the film thickness increases.

Local Mass-Specific Enthalpy Measurements with a New Mass Injection Probe

Abstract: The results of local measurements of the mass-specific enthalpy in a high-enthalpy oxygen plasma flow are presented. The sensor measures enthalpy based on stagnation point heat flux measurements and its reduction by mass addition into the boundary layer. The efficiency of this boundary-layer cooling depends on the freestream enthalpy. Thus, an analysis of this heat flux reduction is a measure for enthalpy. The enthalpy probe is described and theoretically analyzed, and measured data are compared to locally resolved enthalpy measurements from optical diagnostic measurements. For the pure oxygen plasma flow, a simplified theoretical model neglecting chemical reactions and diffusion fits comparably well to the measurements based on optical diagnostics. The mass-specific enthalpy at the corresponding plasma condition applying optical diagnostics is h=27.47 MJ/kg, and the probe measures h=27.64 MJ/kg.

Heat Transfer and Friction in a Square Channel with Ribs and Grooves

Abstract: Turbulence promoters have been widely applied to enhance heat transfer in internal flow channels, although they cause pressure loss. This study employed the transient liquid-crystal technique to measure the heat transfer distribution in a square channel with compound turbulence promoters with orthogonal (90 deg), continuous angled (45 deg), discrete angled (45 deg), V-shaped, and inverted-V-shaped rib configurations. The rib height-to-hydraulic diameter ratio (e/Dh) and the rib pitch-to-height ratio (P/e) were 0.1 and 8, respectively. Variations in the Nusselt number were observed after adding grooves between the ribs. The Reynolds number tested in this study ranged from 15,000 to 35,000. Adding grooves between the ribs enhanced the heat transfer. The convective heat transfer coefficient increased by up to 40%, whereas the friction factor ratio increased by less than 30%. The discrete angled configuration of grooved ribs exhibited the maximal heat transfer enhancement and thermal performance, whereas the ...

Comparative Performance Analysis of Microjet Impingement Cooling Models with Different Spent-Flow Schemes

Abstract: Nomenclature As = surface area of the substrate base, m 2 d = diameter of the nozzle, m H = height of the channel, m h = heat transfer coefficient,W · m−2 · K−1 k = thermal conductivity,W · m−1 · K−1 lx, ly, lz = length, width, and height of the silicon substrate, respectively, m N = number of observation for calculating mean value n = number of jets P = pumping power, W p, Δp = pressure and pressure drop, respectively, Pa Q = volume flow rate, m · s−1 q = heat flux, W · m−2 Rth = thermal resistance, K · W −1 T, ΔT = temperature and temperature rise, respectively, K ts = thickness of the substrate base, m V = velocity vector, m · s−1 x, y, z = orthogonal coordinate system ρ = density, kg · m−3 σ = standard deviation, K