Showing papers in "Journal of Thermophysics and Heat Transfer in 2013"
TL;DR: In this article, the deterioration of forced convection heat transfer can affect channel flows of supercritical fluids and therefore has to be taken into consideration when dealing with regenerative cooling of liqu...
Abstract: The deterioration of forced convection heat transfer can affect channel flows of supercritical fluids and therefore has to be taken into consideration when dealing with regenerative cooling of liqu...
77 citations
TL;DR: In this article, the influence of melting heat transfer in stagnation point flow of Powell-Eyring fluid toward a linear stretching sheet is investigated, which is characterized by conservation laws of mass, linear momentum, and energy.
Abstract: This paper looks at the influence of melting heat transfer in stagnation point flow of Powell–Eyring fluid toward a linear stretching sheet. The mathematical modeling is characterized by conservation laws of mass, linear momentum, and energy. Appropriate similarity transformations are employed for the reduction of partial differential systems into the ordinary differential systems. Series solutions to the resulting problems are presented. Variations of embedded parameters into the derived problems are graphically illustrated. The skin-friction coefficient and the Nusselt number are computed and examined.
72 citations
TL;DR: In this paper, the two-dimensional steady laminar boundary-layer free convective flows along an isothermal solid horizontal flat plate located in a porous quiescent medium filled with non-Newtonian power law nanofluids that contain both nanoparticles and gyrotactic microorganisms are investigated numerically.
Abstract: The two-dimensional steady laminar boundary-layer free convective flows along an isothermal solid horizontal flat plate located in a porous quiescent medium filled with non-Newtonian power law nanofluids that contain both nanoparticles and gyrotactic microorganisms are investigated numerically. The horizontal plate has uniform surface temperature, solute, nanoparticle concentrations and density of the motile microorganism. The governing partial differential equations are nondimensionalized, and then similarity transformations are developed using a linear group of transformations. Using similarity transformation, the governing equations are reduced to a system of nonlinear ordinary differential equations, which are solved numerically. The influence of controlling parameters on the dimensionless velocity, temperature, nanoparticle concentration, and density of motile microorganisms, as well as the local Nusselt, Sherwood, and motile microorganism numbers, are studied. It is found that the bioconvection para...
69 citations
TL;DR: In this paper, the effect of nanoparticles on flat-plate collector efficiency was examined and the results showed that the collector efficiency at 0.05% was approximately 24% more than that of the pure base fluids for given conditions.
Abstract: The objectives of this paper are to examine the effect of nanoparticles on flat-plate collector efficiency. Nanofluids are nanotechnology-based colloidal dispersion engineered by stably suspending nanoparticles. This study employed direct synthesis method to prepare Cu–water nanofluid to serve as a working experiment fluid in a solar collector. ASHRAE 93 was used to test the solar collector. According to the experimental results, the collector efficiency was higher when the concentration of nanoparticles was raised and the results show that the efficiency of collector at 0.05 wt% was approximately 24% more than that of the pure base fluids for given conditions. This study confirms that nanofluids will have considerable potential for use in solar collectors.
56 citations
TL;DR: In this paper, the effect of non-Darcy flow and natural convection over a vertical cone embedded in a porous medium saturated with a nanofluid is studied using the Forchheimer-extended Darcy law.
Abstract: In this paper, non-Darcy flow and natural convection over a vertical cone embedded in a porous medium saturated with a nanofluid is studied using the Forchheimer-extended Darcy law. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. An analytical technique, similarity solution method, is used to convert the governing equations into a set of ordinary differential equations, and then numerically solved using the finite difference method. The effect of non-Darcy parameter and nanofluid parameters on the velocity, temperature, and nanoparticles volume fraction profiles, as well as on the two important parameters of heat and mass transfer, i.e., reduced Nusselt and Sherwood numbers, are discussed. The results show that an increase in the non-Darcy parameter decreases the velocity profiles, whereas it would increase the temperature and concentration profiles. Simulation results also show that an increase in the non-Darcy parameter would decrease the reduced Nusselt ...
54 citations
TL;DR: In this article, the effect of thermal nonequilibrium between the electron translational and vibrational-electronic modes on the predicted electron density and electron temperature is quantified at flight conditions characteristic of a slender hypersonic vehicle, as well as at a higher energy, superorbital flight condition of a blunt reentry vehicle.
Abstract: The degree of electron thermal nonequilibrium occurring in continuum, hypersonic, slender body, and blunt body flows is investigated. The effect of thermal nonequilibrium between the electron translational and vibrational-electronic modes on the predicted electron density and electron temperature is quantified at flight conditions characteristic of a slender hypersonic vehicle, as well as at a higher energy, superorbital flight condition of a blunt reentry vehicle. The most significant effect of electron thermal nonequilibrium on the flowfield is through the influence of the electron temperature on the magnitude of the chemical reaction rates in the high density shock layer. A twofold reduction in peak plasma density is predicted in the flow around the slender body when the electron nonequilibrium model is used, and this results in better agreement between the simulation results and the experimental electron density measurements. A change in the shape of the electron density profile with the use of the el...
52 citations
TL;DR: In this article, a methodology is presented for predicting surface heat fluxes based on interior temperature measurements, and a physics-based calibration method is mathematically developed presently in the context of the linear heat equation and experimentally verified (in a later paper), indicating the merit and accuracy of the approach.
Abstract: A transformative methodology is presented for predicting surface heat fluxes based on interior temperature measurements. A physics-based calibration method is mathematically developed presently in the context of the linear heat equation and experimentally verified (in a later paper), indicating the merit and accuracy of the approach. Sensor characterization, sensor positioning, and thermophysical properties are inherently contained without being explicitly expressed in the final mathematical expression, relating the surface heat flux to interior temperature measurements. A unified theoretical basis is presently under development that encompasses one-, two-, and three-dimensional multiregion geometries possessing orthotropic thermophysical properties. Additionally, the mathematical formalism will recover either the local surface heat flux or total surface heat transfer. This paper represents the first presentation of the concept, illustrates its genesis, and presents insight toward developing a comprehensi...
51 citations
TL;DR: In this paper, the effect of using TiO2-water nanofluid (ϕ≤2%) on entropy generation between two corotating cylinders in the presence of magnetohydrodynamic flow is investigated.
Abstract: The flow between two cylinders where one or both of the cylinders rotate has many practical applications such as swirl nozzles, rotating electrical machines, rotating disks, standard commercial rhymesters, and chemical and mechanical mixing equipment. In this paper, the effect of using TiO2-water nanofluid (ϕ≤2%) on entropy generation between two corotating cylinders in the presence of magnetohydrodynamic flow is investigated. An analytical approach is applied to solve the simplified governing equations in the cylindrical coordinate system. To calculate the thermal conductivity and viscosity of the nanofluid, two correlations, which are based on the experimental data, are used. The velocity field is obtained as modified Bessel functions, and then, using the expansions of these Bessel functions with three terms, the temperature field and, subsequently, the entropy generation rate are estimated. The results are presented for various parameters, including the entropy generation number (NS), Bejan number (Be)...
45 citations
TL;DR: In this paper, a new approach for predicting surface heat flux from in-depth temperature measurements is experimentally verified by using a custom nichrome element heater sandwiched between two identical bronze plates creating a symmetry condition.
Abstract: A new approach for predicting surface heat flux from in-depth temperature measurements is experimentally verified herein. Specifically, this paper presents an experimental verification of the theory developed in the companion Part 1 work. In Part 1, a novel, physics-based calibration approach to the inverse heat conduction problem is mathematically developed, and a methodology for resolving surface heat flux is presented. It is significant to note that this new approach does not require knowledge of host material thermophysical properties, sensor depth, lead losses, or sensor characteristics. Regularization of the data is accomplished by way of a robust “future information parameter,” which is determined by examination of the residual. This paper presents an electrical heating experiment that validates the new inverse approach. A custom nichrome element heater is sandwiched between two identical bronze plates creating a symmetry condition. The setup is capable of surface heat fluxes near 12 W/cm2. Two te...
44 citations
TL;DR: In this article, the effects of Brownian motion and thermophoresis on the flow, heat, and mass transfer from a flat plate with prescribed surface heat flux were investigated using the Buongiorno model.
Abstract: The Buongiorno model is used to investigate the effects of Brownian motion and thermophoresis on the flow, heat, and mass transfer from a flat plate with prescribed surface heat flux. The experimental correlations for the effective density, thermal conductivity, and viscosity of nanofluid are incorporated in the governing equations. Governing partial differential equations are transformed into a set of ordinary differential equations by using similarity transformations. These equations are solved numerically using the Runge–Kutta–Fehlberg method, which produces a fifth-order-accurate solution. The results for the dimensionless velocity, temperature, wall shear stress, and Nusselt and Sherwood numbers are presented graphically and compared for water-based nanofluids with ethylene-glycol-based nanofluids.
35 citations
TL;DR: In this paper, an analysis for the magnetohydrodynamic mixed convection flow of thixotropic fluid over a moving surface has been carried out for the heat transfer in the presence of thermophoresis, Joule heating, and radiative effects.
Abstract: An analysis has been carried out for the magnetohydrodynamic mixed convection flow of thixotropic fluid over a moving surface. Heat transfer is considered in the presence of thermophoresis, Joule heating, and radiative effects. Similarity transformations are used for the reduction of partial differential equations into the ordinary differential equations. A dimensionless nonlinear problem is computed with the homotopy analysis method. Convergence analysis of homotopic solutions is ensured graphically and numerically. Graphical results are displayed and analyzed. Numerical values of wall shear stress and heat transfer rate are computed and discussed. Comparison with the previous results in a limiting case is made and excellent agreement is noticed.
TL;DR: The renormalization group k-e model with an enhanced wall function provided the greatest fidelity in representation of turbulent thermal and flow behavior studied in heated tube experiments conducted at supercritical pressure as discussed by the authors.
Abstract: Computational fluid dynamics simulations can be used to simulate the flow, heat transfer, and fuel chemistry within fuel system cooling passageways. The standard k-e turbulence model with the standard wall function, renormalization group k-e model with an enhanced wall function, and the shear stress transport k-ω model were evaluated for their ability to represent turbulent fuel flow and heat transfer under high heat flux and flow rate conditions. The renormalization group k-e model with an enhanced wall function provided the greatest fidelity in representation of turbulent thermal and flow behavior studied in heated tube experiments conducted at supercritical pressure. Moreover, the renormalization group k-e model with an enhanced wall function allowed reasonable simulation of heat transfer deterioration, which was more likely for flow conditions involving a large heat flux with low mass flux rate. As the fuel was heated from the liquid to the supercritical phase, the viscosity temperature dependence was...
TL;DR: In this article, a transpiration cooling coupled with combustion was investigated in an H2/O2 liquid rocket thrust chamber with transpiration-cooled injector plate, and a numerical model was developed using the real gas equation of state.
Abstract: Transpiration cooling coupled with combustion was investigated in an H2/O2 liquid rocket thrust chamber with a transpiration-cooled injector plate. A numerical model was developed using the real gas equation of state. The H2 and O2 combustion process was modeled by the eddy dissipation concept model, which includes the detailed chemical reaction mechanisms in turbulent flows. The permeability and the inertia coefficient of the metal mesh, porous media used for the injector plate were obtained experimentally. The simulation results for the porous plate temperatures and H2 fluxes compare well with hot firing experiments, giving reliable predictions of the combustion, flow, and heat transfer processes in the liquid rocket thrust chamber. The model was also used to investigate the effects of the inlet conditions and the plate material on the transpiration cooling. The results show that locations near the chamber wall and the ignition hole on the plate surface have higher temperatures than other locations. The...
TL;DR: Combined radiation and conduction heat transfer through a high-temperature, high-porosity, rigid multiple-fiber fibrous insulation was modeled using a thermal model previously used to model heat transfer in flexible single-fibrous insulation.
Abstract: Combined radiation and conduction heat transfer through a high-temperature, high-porosity, rigid multiple-fiber fibrous insulation was modeled using a thermal model previously used to model heat transfer in flexible single-fiber fibrous insulation The rigid insulation studied was alumina enhanced thermal barrier (AETB) at densities between 130 and 260 kilograms per cubic meter The model consists of using the diffusion approximation for radiation heat transfer, a semi-empirical solid conduction model, and a standard gas conduction model The relevant parameters needed for the heat transfer model were estimated from steady-state thermal measurements in nitrogen gas at various temperatures and environmental pressures The heat transfer modeling methodology was evaluated by comparison with standard thermal conductivity measurements, and steady-state thermal measurements in helium and carbon dioxide gases The heat transfer model is applicable over the temperature range of 300 to 1360 K, pressure range of 0133 to 1013 x 10(exp 3) Pa, and over the insulation density range of 130 to 260 kilograms per cubic meter in various gaseous environments
TL;DR: In this paper, the authors numerically test a horseshoe plasma actuator for film cooling enhancement on a flat plate, and validate a previously reported film cooling experiment with a single row of round cooling holes issuing at a 35-degree angle on the flat plate.
Abstract: We numerically test a horseshoe plasma actuator for film cooling enhancement on a flat plate. We solve three-dimensional plasma governing equations using the finite element based MIG flow code. The electric force density calculated from the plasma governing equations is then employed as a body force density into a finite volume based Navier–Stokes solver with standard turbulence models for controlling the flow. Such electric force influences attachment of the cold jet to the work surface by actively altering the three-dimensional flowfield in the vicinity of the actuator. We consider two problems related to film cooling. The first problem is to understand the influence of a horseshoe plasma actuator on a flowfield where the cooling jet and the bulk flow speeds are of the same order of the flow induced by plasma itself. The second problem is to validate a previously reported film cooling experiment with a single row of round cooling holes issuing at a 35 deg angle on a flat plate, and then predict any impr...
TL;DR: In this article, the effects of dimple depth, pitch, size, and alignment on the heat transfer coefficient in a rib-dimple channel were experimentally investigated, and it was shown that the dimple configuration improved the Nusselt number ratio and the thermal performance factor compared with the rib-only case.
Abstract: The effects of dimple depth, pitch, size, and alignment on the heat transfer coefficient in a rib–dimple channel were experimentally investigated. The heat transfer coefficient in the rib–dimple channel was measured using the liquid crystal technique, and the friction factor was evaluated. The channel aspect ratio was 4; and three Reynolds numbers of 30,000, 40,000, and 50,000 were tested. For the systematic investigation of the effect of dimple configuration, rib–dimple cases with three dimple depths (0.11 to 0.33 of dimple diameter), three dimple pitches (1.2 to 1.5 of dimple diameter), three dimple sizes (11 to 14.8 mm), and two dimple alignment methods were compared. The rib thickness and height were both 5 mm, and the rib pitch to the rib height ratio was 10 for all cases. Results showed that the rib–dimple cases improved the Nusselt number ratio and the thermal performance factor compared with the rib-only case. For the given channel aspect ratio and the rib configuration, the reference case with th...
TL;DR: In this article, a reduced dynamical model describing temperature stratification effects driven by natural convection in a liquid hydrogen cryogenic fuel tank has been developed, which accounts for cryogenic propellant loading, storage, and unloading in the conditions of normal, increased, and micro-gravity.
Abstract: A reduced dynamical model describing temperature stratification effects driven by natural convection in a liquid hydrogen cryogenic fuel tank has been developed. It accounts for cryogenic propellant loading, storage, and unloading in the conditions of normal, increased, and micro- gravity. The model involves multiple horizontal control volumes in both liquid and ullage spaces. Temperature and velocity boundary layers at the tank walls are taken into account by using correlation relations. Heat exchange involving the tank wall is considered by means of the lumped-parameter method. By employing basic conservation laws, the model takes into consideration the major multi-phase mass and energy exchange processes involved, such as condensation-evaporation of the hydrogen, as well as flows of hydrogen liquid and vapor in the presence of pressurizing helium gas. The model involves a liquid hydrogen feed line and a tank ullage vent valve for pressure control. The temperature stratification effects are investigated, including in the presence of vent valve oscillations. A simulation of temperature stratification effects in a generic cryogenic tank has been implemented in Matlab and results are presented for various tank conditions.
TL;DR: In this paper, a numerical method for solving one-dimensional ablation heat transfer problems is presented, along with detailed derivations of the governing equations, and a simple demonstration of a mechanical erosion (spallation) model is provided to illustrate the unique capabilities of the method.
Abstract: A unique numerical method has been developed for solving one-dimensional ablation heat transfer problems. This paper provides a comprehensive description of the method, along with detailed derivations of the governing equations. This methodology supports solutions for traditional ablation modeling including such effects as heat transfer, material decomposition, pyrolysis gas permeation and heat exchange, and thermochemical surface erosion. The numerical scheme utilizes a control-volume approach with a variable grid to account for surface movement. This method directly supports implementation of nontraditional models such as material swelling and mechanical erosion, extending capabilities for modeling complex ablation phenomena. Verifications of the numerical implementation are provided using analytical solutions, code comparisons, and the method of manufactured solutions. These verifications are used to demonstrate solution accuracy and proper error convergence rates. A simple demonstration of a mechanical erosion (spallation) model is also provided to illustrate the unique capabilities of the method.
TL;DR: In this paper, a transient mathematical model is developed to study the transient response and analyze the distribution of heat load in a loop heat pipe, which is based on the one-dimensional and time-dependent conservation equations for heat and fluid flow.
Abstract: A transient mathematical model is developed to study the transient response and analyze the distribution of heat load in a loop heat pipe The model is based on the one-dimensional and time-dependent conservation equations for heat and fluid flow The momentum and energy conservation equations for each of the loop heat pipe components are solved The model results are compared against the data obtained from two miniature loop heat pipes using polytetrafluoroethylene wicks, ethanol, and acetone as working fluids The mathematical model satisfactorily predicts the dynamic behavior of the loop heat pipe unit It is shown that the percentage of heat leak across the wick decreases and the ratio of latent heat increases with increasing heat load Some temperature overshoots observed in the calculation results are not observed in the experimental data When a new power is applied, no time lag is observed in the loop heat pipe response between the simulation and experimental results
TL;DR: In this paper, the authors compared five common fin configurations (plain, perforated, offset strip, wavy, and pin) on the operation of the plate-fin heat exchanger.
Abstract: Comparative appraisal of five common fin configurations (plain, perforated, offset strip, wavy, and pin) on the operation of the plate-fin heat exchanger is the main purpose of this study. Working fluids with different Prandtl numbers, air, water, oil, and ethylene glycol are considered as coolants. First, the simulation results for the two fins, offset strip and wavy, are validated with available experimental data, which obtained good agreement. Then, the effects of specific geometrical parameters of different fins are investigated on the thermal-hydraulic performance of the plate-fin heat exchanger. Finally, the role of the fin configuration and coolant types is compared using the thermal-hydraulic performance factor JF. Results are presented as the plots of JF factors versus Reynolds number in the laminar flow regime, 100≤Re≤1600. It is found that coolant type has no considerable effect on f factor, pin fin has a better performance with about 64% JF factor value enhancement, and water has superior pres...
TL;DR: In this article, the authors focus on numerical modeling of a steady, laminar natural convection flow in a triangular enclosure partially heated from below and with a cold inclined wall filled with Cu-water nanofluid having variable thermal conductivity and viscosity.
Abstract: This work focuses on the numerical modeling of a steady, laminar natural convection flow in a triangular enclosure partially heated from below and with a cold inclined wall filled with Cu-water nanofluid having variable thermal conductivity and viscosity. The problem is formulated in terms of the vortices stream function formulation and the resulting governing equations are solved numerically using an efficient finite difference method. Various results for the streamline and isotherm contours, as well as the local and average Nusselt numbers, are presented for a wide range of Rayleigh numbers and volume fractions of nanoparticles. Different behaviors (enhancement or deterioration) are predicted in the average Nusselt number as the volume fraction of nanoparticles changes. The placement and length of the heat source along the bottom wall is observed to have significant effects on the behavior of the average Nusselt number.
TL;DR: In this article, a parametric analysis and optimization of double-jet film-cooling holes was performed using three-dimensional Reynolds averaged Navier-Stokes equations with the shear stress transport turbulence model.
Abstract: A parametric analysis and optimization of double-jet film-cooling holes was performed using three-dimensional Reynolds averaged Navier–Stokes equations with the shear stress transport turbulence model. The numerical results for film-cooling effectiveness were validated in comparison with experimental data. The lateral and streamwise distances between the centers of the holes, along with two lateral ejection angles, were chosen as the design variables. The effects of these four variables on the film-cooling effectiveness were evaluated. For optimization of double-jet film-cooling holes, film-cooling effectiveness was considered as the objective function. Latin hypercube sampling was used to determine the design points. A weighted average surrogate model was constructed using the objective function values calculated at the design points. Sequential quadratic programming was used to search for the optimal point from the constructed surrogate. The cooling performance of double-jet film-cooling holes was impro...
TL;DR: In this article, a three-dimensional ray tracing method was used to model an existing scramjet and showed that radiation is highly dependent on chamber size, temperature, pressure and radiative species mole fraction.
Abstract: against a three-dimensional ray tracing method. The radiative species considered are H2O and OH. The radiative heat ux is on the order of 10 kW/m 2 , which is 0.1-0.2% of the total convective wall heat ux. Flow cooling due to radiation is found to be on the order of 2 K. Sensitivity analysis shows that radiation is highly dependent on chamber size, temperature, pressure and radiative species mole fraction. Variations in these factors can explain the dierences between previous analyses in the literature that studied hypothetical engines and the current work that models an existing scramjet.
TL;DR: In this paper, an experimental apparatus was designed and constructed to measure both heat transfer coefficient and pressure drop of flowing nanofluids, and a third parameter named performance index was evaluated to determine the possibility of practically using such a nanoparticles.
Abstract: To improve heat transfer properties of turbine oil, TiO2 nanoparticles were added and a new nanofluid which has not been yet reported in articles was produced. An experimental apparatus was designed and constructed to measure both heat transfer coefficient and pressure drop of flowing nanofluids. Results clearly indicated that adding TiO2 nanoparticles increased both heat transfer coefficient and pressure drop. A third parameter named performance index was evaluated to determine the possibility of practically using such nanofluid. All the obtained performance indexes were greater than 1 which emphasizes that using the TiO2/turbine oil nanofluid with volume concentration less than 0.50% leads to higher quality turbine oil.
TL;DR: In this article, the structure of a normal shock wave in noble gas mixtures (Xe-He and Ar-He) of various compositions using molecular dynamics and direct simulation Monte Carlo was studied.
Abstract: We study the structure of a normal shock wave in noble gas mixtures (Xe-He and Ar-He) of various compositions using molecular dynamics and direct simulation Monte Carlo. The molecular dynamics simulations are first validated against experimental data. Good agreement is found between the molecular dynamics solutions and the experimental measurements, with the exception of the parallel temperature profile in the 24.7% Ar-He mixture, despite the satisfactory agreement between the parallel velocity profiles. Secondly, a validation against direct simulation Monte Carlo solutions obtained with the accurate generalized hard sphere model is presented. As expected, the generalized hard sphere direct simulation Monte Carlo and molecular dynamics solutions are in near-perfect agreement. Finally, molecular dynamics results are compared to those obtained with the lower fidelity variable hard sphere model, which, if inappropriately parametrized, fails to describe the shock wave structure. This work exemplifies how full...
TL;DR: In this paper, a thermal lattice Boltzmann Bhatnagar-Gross-Krook model was implemented to simulate the two-dimensional natural convection and to investigate the effect of the most important parameters, the Rayleigh number 103≤Ra≤106 and thermal conductivity ratio of solid to fluid K=1-100.
Abstract: Analysis of entropy generation due to conjugate natural convection in an enclosure region has been carried out. A thermal lattice Boltzmann Bhatnagar–Gross–Krook model was implemented to simulate the two-dimensional natural convection and to investigate the effect of the most important parameters, the Rayleigh number 103≤Ra≤106 and thermal conductivity ratio of solid to fluid K=1–100. Entropy generation contours due to heat transfer irreversibility, isotherms, streamlines, and Nusselt numbers were obtained and discussed. It was found that dimensionless entropy generation due to heat transfer (Bejan number) decreases with an increasing thermal conductivity ratio. For Ra ranging from 103 to 104, the total entropy generation is mostly due to heat transfer because of relatively low velocities, but for Ra>104, the contribution due to fluid friction becomes more effective.
TL;DR: In this paper, the ribbed rectangular divergent/convergent channels with one-sided ribbed surface were compared with the square straight channel under three constraints: identical mass flow rate, identical pumping power, and identical pressure drop.
Abstract: The local heat transfer and pressure drop of developed turbulent flows in the stationary ribbed rectangular convergent/divergent channels have been investigated experimentally. The rectangular convergent/divergent channels with one-sided ribbed surface only have the inclination angles of 0.72 deg and 1.43 deg at which the ribbed wall is manufactured with a fixed rib height (e)=10 mm and the ratio of rib spacing (p) to height (e)=10. The measurement was conducted within the range of Reynolds numbers from 15,000 to 89,000. Because of the streamwise flow acceleration or deceleration, the local heat transfer characteristics of the rectangular divergent/convergent channels are quite different from those of the square straight channel. Thermal performance of the ribbed rectangular divergent/convergent channels is compared with the ribbed square straight channel under three constraints: identical mass flow rate, identical pumping power, and identical pressure drop. The comparison shows that among the four chann...
TL;DR: In this paper, buoyancy-driven flow is modeled as a mixture of thermally perfect gases in either thermochemical equilibrium or chemical nonequilibrium, assuming steady-state melt and vaporization from a 1mm radius spot at the axis of an axisymmetric chamber.
Abstract: Flow in a pressurized, vapor condensation boron nitride nanotube production rig is modeled A laser provides a thermal energy source to the tip of a boron fiber bundle in a high-pressure nitrogen chamber causing a plume of boron-rich gas to rise The buoyancy-driven flow is modeled as a mixture of thermally perfect gases (B, B2, N, N2, BN) in either thermochemical equilibrium or chemical nonequilibrium, assuming steady-state melt and vaporization from a 1 mm radius spot at the axis of an axisymmetric chamber The simulation is intended to define the macroscopic thermochemical environment from which boron-rich species, including nanotubes, condense out of the plume Simulations indicate a high-temperature environment (T>4400 K) for elevated pressures within 1 mm of the surface, sufficient to dissociate molecular nitrogen and form BN at the base of the plume Modifications to the program LAURA, a finite volume-based solver for hypersonic flows including coupled radiation and ablation, are described to enab
Journal Article•
TL;DR: In this article, an experimental apparatus was designed and constructed to measure both heat transfer coefficient and pressure drop of flowing nanofluids, and a third parameter named performance index was evaluated to determine the possibility of practically using such a nanoparticles.
Abstract: To improve heat transfer properties of turbine oil, TiO2 nanoparticles were added and a new nanofluid which has not been yet reported in articles was produced. An experimental apparatus was designed and constructed to measure both heat transfer coefficient and pressure drop of flowing nanofluids. Results clearly indicated that adding TiO2 nanoparticles increased both heat transfer coefficient and pressure drop. A third parameter named performance index was evaluated to determine the possibility of practically using such nanofluid. All the obtained performance indexes were greater than 1 which emphasizes that using the TiO2/turbine oil nanofluid with volume concentration less than 0.50% leads to higher quality turbine oil.
TL;DR: In this paper, a decentralized inverse approach based on Bayesian inference and Markov Chain Monte Carlo sampling is developed to estimate the location and intensity of building fires, which can be performed in real time due to the combination of those two methods.
Abstract: A decentralized inverse approach based on Bayesian inference and Markov Chain Monte Carlo sampling is developed to estimate the location and intensity of building fires. Compared with the methods based only on sensor data or fire models, this approach has little limits on the complexity of building structures and can be performed in real time due to the combination of those two methods. Additionally, by dividing the building into several zones, each of which is capable of fire inversion based on its local sensor reading and/or together with neighbor sensor readings, the decentralized algorithm is more efficient and robust compared with the centralized model using all sensor data. Three cases are designed to test the model and investigate the influence of sensor data quality and quantity in a multiroom building. The estimation from the fire zone can match the actual values when sufficient sensor data are used. The closer a zone is to the fire source, the more accurate the result is. In addition, this paper...