Journal of Thermophysics and Heat Transfer, Ahead of Print.

The subcritical cycle performances of eco-friendly pure refrigerants and zeotropic mixtures for heat pump water heater systems were performed by MATLAB programs. The results indicated that pure refrigerants are often restricted in meeting criteria such as environmental protection, efficiency, and flammability. The optimal compositions of R13I1/R161/R32, R13I1/R290/R32, and R13I1/R152a/R32 zeotropic

Continuity, momentum, and energy equations have been solved to predict the natural convection heat transfer from an upward, downward, and sideward solid or hollow hemisphere either suspended in air or placed on the ground. The results have been plotted in terms of average surface Nusselt number Nu as a function of Rayleigh number Ra spanning from 104 to 107 in the laminar flow regime. The behavior

The knowledge of surface heat flux over aerodynamic surfaces is highly desirable for high-speed applications. Impulse test facilities like shock tubes and shock tunnels are invariantly employed for this where the aerodynamic test models experience step/ramp heat loads. Contrary to conventional methods, the usage of an advanced soft computing technique through an adaptive neuro-fuzzy inference system

Transient thermochromic liquid crystal (TLC) experiments can provide high-fidelity spatially resolved heat transfer data for complex geometries, particularly where infrared techniques cannot be applied. One challenge when applying transient methods to internal geometries is the local definition of the driving gas temperature. The transient nature of the streamwise driving gas temperature profile has

Emission spectroscopy was conducted in a miniature arc heater in China Aerodynamics Research and Development Center to study the erosion of water-cooled copper electrode due to the high-temperature environment. With a 2-mm-diam viewpoint, emission signal of plasma torch at the exit of the nozzle was collected. Three tests were implemented under different conditions with arc currents of 400, 600, and

In the present study, the effect of conical obstacles on heat transfer and flow characteristics in a circular tube was investigated. In most previous studies, stationary obstacles were used to stimulate the flow and to investigate heat transfer and pressure drop. In the present paper, in addition to investigating the effect of a stationary obstacle, the effect of using moving obstacles was studied

On 7 September 2017, the U.S. Air Force Research Laboratory launched the second Advanced Structurally Embedded Thermal Spreader (ASETS-II) flight experiment on the fifth flight [Orbital Test Vehicle 5 (OTV-5)] of the Air Force’s X-37B spaceplane. OTV-5 landed on 27 October 2019 after 780 days on orbit. The ASETS-II flight experiment accomplished its mission to demonstrate functionality, characterize

Journal of Thermophysics and Heat Transfer, Ahead of Print.

This study numerically investigates the effects of the geometrical and operational parameters of an air channel, with an inclined baffle mounted opposite the heating plate, on its thermohydraulic performance and entropy generation. The Reynolds number (Re) was examined in the range from 1000 to 20,000 and the baffle angle α from 0 to 60°, and the clearance ratio C/H was studied in the range from 0

Metal effectiveness measurements (or overall cooling effectiveness measurements) are becoming increasingly used to understand complex coupled systems in gas turbine experimental research. Unlike traditional techniques in which individual boundary conditions are measured in isolation and superposed using a thermal model, metal effectiveness measurements give the final result of a complex coupled system

Nonintrusive laser diagnostics are used for the measurements of metastable nitrogen molecules in the lowest excited electronic state, N2(A3Σu+), in a nonequilibrium flow, blowdown supersonic wind tunnel. The tunnel is operated with nitrogen at plenum pressures of P0=200–250 Torr, with the flow expanding through a two-dimensional contoured nozzle to the Mach number of M=3.6–4.6. The steady-state run

Radiative heat transfer in a concentric cylinder system with a participating medium is demonstrated to be inherently two-dimensional, even for the consideration of heat transfer to the total inner or outer surface with uniform boundary conditions. For the evaluation of two-dimensional nongray radiative heat transfer, the zonal exchange factor, together with the concept of point mean beam length, is

High-speed flow problems of practical interest require a solution of nonequilibrium aerothermochemistry to accurately predict important flow phenomena, including surface heat transfer and stresses. The complex coupling of nonequilibrium effects on the aerothermal load remains a challenging aspect of hypersonic flow modeling. As a majority of these flow problems are in the continuum regime, computational

Thermal diffusion and wave phenomena in a two-dimensional solid subjected to convective cooling and an internal exponential heat source are investigated. Both diffusion and Cattaneo–Vernotte (C–V) heat conduction models are solved using the superposition principle in conjunction with the solution structure theorems. For comparison purposes, both models are solved to demonstrate the flexibility of the

The effect of gravity on two-phase flow phenomena depends on the relative magnitude of the gravity force to inertia, viscous, and surface tension forces. Two-phase flow research has investigated heat transfer coefficients, critical heat flux, and flow regimes at different gravity levels and inclination angles, and several researchers proposed threshold flow velocities above which two-phase flow would

A numerical study was undertaken on the laminar convective heat transfer from vertical polygonal cylinders with an uncovered top surface for a relatively small polygons area. The polygonal cylinders were perpendicularly placed on a flat adiabatic base plate, and uniform wall temperature boundary conditions were assumed. The governing equations for geometrical evaluation were solved numerically in terms

Thermohydromagnetic performances of alumina–water nanofluid in a trapezoidal vessel that considered the inclined magnetic field were investigated numerically. The bottom wall of the enclosure is heated uniformly, whereas the upper wall is adiabatic. The remaining walls are kept cold. The mathematical problem was tackled through the Galerkin finite element method. The simulated results were verified

In the framework of large eddy simulation, a supercritical GN2/GH2 jet has been modeled by using the extended corresponding states (ECS) method, the cubic Peng–Robinson (PR) equation of state, as well as the ideal gas law. The accuracy of ECS and PR was first verified for a binary N2/H2 mixture against the standard data. A zone-adaptive hybrid ECS/ideal method was developed to efficiently model the

A novel flexible fuel thermal management architecture with a switched mode control strategy is proposed that provides a framework for increasing the thermal endurance of aircraft that use fuel as a heat sink. Multiple flow topologies within this architecture can be realized by using two valves to provide a range of fuel recycling configurations. The flexible thermal management system uses multiple

This study deals with the influence of a rotating cylinder inside the square cavity and multiwalled carbon nanotube–iron oxide (Fe3O4) hybrid nanofluid with water. A two-dimensional system of partial differential equations has been discretized by employing Galerkin finite element method. A finite element method involving the cubic polynomials (P3) has been implemented to compute for velocity, temperature

In cooling microchannels of advanced flight engines, the fuel temperature rapidly increases to facilitate endothermic cracking reactions. A cooling channel can be divided into noncracking and cracking zones. In this study, various aspect ratios were investigated via numerical simulations to determine the effects of microchannel geometry on the cooling effect. A nine-species surrogate fuel is introduced

A three-dimensional double-sided delta-wing (D-T-W) shape design problem is studied in the present work to estimate the optimal wing-width ratio w/W, height-pitch ratio c/P, and attack angle α of D-T-Ws in a double-pipe heat exchanger for the target thermal performance factor using the Levenberg–Marquardt method and CFD-ACE+ software package. Our solutions indicate that a reasonable discrepancy exists

This paper presents an ultrasonic method for tracking the decomposition front in ablating silica-phenolic thermal protection system material. The method exploits diffuse ultrasonic backscatter from the material microstructure to account for the temperature-dependent change of the speed of sound. The method is demonstrated in a series of ablation tests performed at a heat flux of 1350 W/cm2 provided

This paper presents a new method for modeling rarefied gas flows based on hybridization of direct simulation Monte Carlo (DSMC) and discrete velocity method (DVM)-based quasi-particle representations of the velocity distribution function. It is aimed at improving the resolution of the tails of the distribution function (compared with DSMC) and computational efficiency (compared with DVM). Details of

Journal of Thermophysics and Heat Transfer, Ahead of Print.

The accelerator driven system (ADS) is a nuclear reactor that can burn spent nuclear fuel with inherent safety features and operational flexibility. China is developing an ADS research device named China Initiative Accelerator Driven System (CiADS). The steam generator is one of the most important parts in the primary circuit of CiADS. The rupture of steam generator tubes may cause a significant impact

We study numerically the conjugate heat transfer between the walls of a parallel plate microchannel and a homogeneous porous medium fully saturated with a liquid that is found in motion due to an external pressure gradient. The origin of this problem is caused by a uniform heat flux imposed at the external surfaces of the walls of the microchannel that have a finite thermal conductivity. In this manner

Three of the key associative ionization reactions that lead to plasma formation around hypersonic vehicles are studied in detail. For production of NO+, O2+, and CO+, cross sections derived from experimental measurements for the interactions of atoms in low-lying electronic states are compared to cross sections derived from the overall rates widely used to model these processes. The experimentally

To analyze the thermal performance of longitudinal fins made of functionally graded materials, this article studies the transient heat transfer in a longitudinally graded fin with power-law thermal conductivity in a convective ambiance using a fractional heat conduction model. This model has an advantage over the Fourier heat conduction in describing the anomalous heat diffusion and non-Fourier effect

This work investigates atomic recombination of gas species impinging on high-temperature materials used for thermal protection system of spacecraft entering Earth’s atmosphere. Heterogeneous catalysis models of pre-oxidized PM1000, an oxide dispersion-strengthened Ni-Cr superalloy, and silicon-carbide-coated (SiC-coated) carbon-fiber-reinforced SiC used on the European eXPErimental Re-entry Testbed

Solid–liquid phase change has been widely used in practice, but most of the existing literature focuses on Newtonian phase change materials, and there are few studies on power-law phase change materials (PLPCM). To study the heat transfer problem of PLPCM in the process of solid–liquid phase change, this paper combines the enthalpy method with Lattice Boltzmann method to study the melting process of

Based on a new type of elastic scroll tube bundle (ESTB) heat exchanger, the influence of shell-side fluid inlet velocity and tube bundle constraint condition on the enhanced heat transfer performances are researched by a two-way fluid–solid coupling calculation method. Numerical results show that the average heat transfer coefficient (HTC) increases with the shell-side fluid inlet velocity increases

Pulsed plasma discharges are investigated here as a means of reducing the power necessary for a thermal probe to penetrate an ice sheet. When a high-energy plasma discharge occurs in ice, the ensuing shockwave fractures the ice field and reduces its thermal conductivity. If this reduction is sufficient in both magnitude and geometric extension, it can decrease the heating power necessary to keep the

A compact icing facility is developed to allow the measurement of ice adhesion tensile stress and fracture energy of aerospace impact ice, in coordination with thermal measurements, to ensure a well-characterized thermal environment. The facility was 1.5 m wide, 1.5 m long, and 2.1 m tall, and the tunnel is equipped with a single MOD-1 spray nozzle to produce a cloud of supercooled droplets at the

This is a study on the enhancement of the thermal performance of a thermosyphon heat pipe (THP) using the Al2O3 nanoparticle in a mixture of water and Triton X-100 (TX-100) surfactant. The effects of nanoparticle concentration, surfactant concentration, input power, inclination angle, and filling ratio on the thermal efficiency of THP is evaluated experimentally. Experiments were designed by the Taguchi

Heat removal capacity of catalytically cracked supercritical n-dodecane as a jet fuel analogue in a cylindrical packed-bed reactor is examined. Fuel cracking is endothermic, and can be used in designing a potential hypersonic vehicle thermal management system. In this work, n-dodecane endotherm and product distributions were examined using a platinum catalyst on a ceramic support matrix. Although many

The present paper determined the water recovery potential of a scaled crossflow cooling tower, where finned thermosyphons were used to drive heat from the hot, moist air flowing through the cooling tower toward the ambient. This process, which uses the tower’s outer environment as a heat sink, partially condenses the water vapor present in the flowing air, creating an entirely passive water recovery

The application of combined electric and magnetic fields is proposed for better heat transfer enhancement in a porous fin system. An inverse estimation technique is established to simultaneously determine the interior thermal energy production and strengths of electrical and magnetic fields, by solely using the surface temperature field. At first, verified direct solutions based on the fourth-order

An improved Monte Carlo method (IMCM) is developed to solve radiative heat transfer in participating media in this work. Monte Carlo method (MCM) as a high-precision method has good applicability for the calculation of radiative heat transfer in a complex-shape medium. However, it is highly time-consuming for a large number of energy beams tracing, which limits its application in practical engineering

Journal of Thermophysics and Heat Transfer, Ahead of Print.

As electronics get smaller and faster, novel thermal management systems are needed that are capable of dissipating higher heat fluxes. Additive manufacturing and advanced materials, such as liquid metals and synthetic ceramic, offer new opportunities to realize thermal systems. This paper investigates the use of additive manufacturing to develop thermal structures designed around liquid metals to provide

In the present work, the analysis of natural convection and entropy generation in a square porous cavity, having either a flat or a wavy vertical wall, filled with a non-Newtonian nanofluid is reported. The effect of Rayleigh number (105–106), non-Newtonian power-law index (0.6–1.4), Darcy number (0.0001–0.01), Hartmann number (0–90), and volume fraction of CuO nanoparticles (0–0.12) on heat transfer

The most important point in electricity generation with thermoelectric generators (TEG) is to create a temperature difference between its surfaces. The cooling process is usually carried out by liquid coolers or heat sinks. This study aims to examine experimentally and numerically the cooling and electrical conversion performance of TEG with a heat sink having flat fins at different hot surface temperatures

This paper uses a multi-objective topology optimization method for thermal-fluid problems applied to the design of fins for primary use in plate-fin heat exchangers. The presented method was derived to obtain optimal fin topology for a wide range of design parameters and constraints, with the primary focus on aerospace applications. The performance of obtained fin topologies is evaluated based on the

In a space mission design, the goal of the thermal control subsystem is to ensure that all components of the satellite stay within their operating temperature ranges. The problem becomes more critical if the mission involves nanosatellites with an astrophysics payload requiring a dedicated thermal design to keep it at low temperature, as in the case of the High Energy Rapid Modular Ensemble of Satellites

This paper presents a numerical study of the hydrothermal air-side performance of a tubular heat exchanger fitted with flower baffles (FBs). The investigation was done by testing in-line and staggered FB arrangements for various baffles’ pitch ratios (PR=1, 1.5, 2, 2.5, and 3) with Reynolds number Re ranging from 3000 to 15,000. The results indicate that the use of the FBs leads to stirring the stagnated

Journal of Thermophysics and Heat Transfer, Ahead of Print.

Journal of Thermophysics and Heat Transfer, Ahead of Print.

The zonal method is combined with the Monte Carlo (MC) method to yield the zonal-MC method, a new numerical approach for the analysis of radiative heat transfer in multidimensional absorbing/scattering media. The method is shown to have computational advantages over the stand-alone zonal method. The zonal-MC method can also be combined with ray-tracing to simulate the penetration of a collimated beam

Laminar convective heat transfer for the thermally developing flow in elliptical minichannels is numerically investigated under constant heat flux with high thermal conductivity materials (H1) and low thermal conductivity materials (H2) boundary conditions. The effects of the Peclet number and the aspect ratio on both the local Nusselt number and the thermal entrance length are presented graphically

The fluid-induced vibration heat transfer enhancement technology has great potential, because it can effectively improve the heat transfer efficiency without consuming additional energy. A reasonable design of the elastic heat exchange tube bundle structure is the key to the engineering application of this technology. In this paper, the effects of flow velocity and the center distance L on the characteristics

Journal of Thermophysics and Heat Transfer, Ahead of Print.

Metallic lattice-frame materials, due to excellent heat transfer performance under high heat flux and mechanical property, are regarded as the potential candidates for a vehicle leading edge. This paper presents a new-style lattice-frame sandwich panel with active heat transfer wall-plate. The heat transfer performance and thermal–structural responses are numerically studied, considering the temperature-dependent

Molten calcium–magnesium–alumino–silicate (CMAS) infiltration into thermal barrier coatings (TBCs) of gas turbines causes loss of strain tolerance and delamination of the ceramic topcoat. To develop efficient mitigation strategies, it is crucial to understand CMAS infiltration dynamics into the porous topcoat. This study introduces an integrated model, incorporating liquid flow in unsaturated porous

Journal of Thermophysics and Heat Transfer, Ahead of Print.

A computational fluid dynamics (CFD) laminar-to-turbulence transition model was developed for the NASA Ames Research Center’s 20 MW Panel Test Facility (PTF). Surface pressure, heat flux to a water-cooled plate, and surface temperature on a tile plate coated with reaction-cured glass were measured across several conditions in the facility and compared with laminar and fully turbulent CFD simulations

The magnetron sputtering has been used to prepare metal foam wicks for heat pipes by coating the surface of copper foam with zinc oxide (ZnO) nanoparticles. The main properties, including microscopic appearance, contact angle, and capillary performance, as well as the boiling heat transfer performance of the metal foam wicks, are characterized and tested. The results indicate that, compared with the

This work describes numerical and experimental research in the Indian Hypersonic Shock Tunnel 3 on a blunt cone model and related computation of the facility parameters: nozzle reservoir conditions, nozzle transit time, and freestream conditions. Specialized codes accounting for real gas effects and nonequilibrium are used to obtain facility parameters. Starting at freestream conditions, a physicochemical

Journal of Thermophysics and Heat Transfer, Ahead of Print.