Cylindrical Thermal Cloak Based on the Path Design of Heat Flux

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Linzhi Wu
Keyword(s):  
Heat Flux ◽  
Thermal Protection ◽  
Transient Behavior ◽  
Large Degree ◽  
Comsol Multiphysics ◽  
Material Parameters ◽  
Path Design ◽  
Transient Thermal ◽  
Blue Print ◽  
Dynamic Diffusion

When heat flux flows in a given medium, its path will solely be determined. This implies that material parameters determined by the predesigned path of heat flux will guide heat to flow along the designed path. Based on this idea, we develop a new method for the design of the cylindrical thermal cloak which can make heat flux detour the cloaked object. For the inhomogeneous anisotropic medium, we derive the relation between the path trajectory of heat flux and material parameters and obtain two differential equations and one boundary condition which are used to determine material parameters in the cylindrical cloak. The transient behavior on the flow of heat flux is simulated by Comsol Multiphysics and the transient thermal protection of the cylindrical cloak for the cloaked object is examined. The effect of the product of density and specific heat on the dynamic diffusion process of heat flux is analyzed. Since one can flexibly design the path of heat flux in the cloak, it has the large degree of freedom to construct thermal cloaks with the specific distributions of material parameters. The present method provides a new blue print for the transient thermal protection of a specific target.

Experimental Evidence of the Thermal Cloak Based on the Path Design of the Heat Flux

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Xiao He ◽  
Tianzhi Yang ◽  
Linzhi Wu
Keyword(s):  
Heat Flux ◽  
Experimental Evidence ◽  
Thermal Protection ◽  
Large Degree ◽  
New Method ◽  
Material Parameters ◽  
Path Design ◽  
New Strategy ◽  
Transient Thermal ◽  
Blue Print

We recently showed theoretically that the infinite singularity of the thermal cloak designed by transformation thermodynamics could be eliminated by a new method—the path design of the heat flux without any approximation. In this paper, we present the experimental evidence of such a new strategy of thermal cloak, that is, a truly singularity-free thermal cloak. We fabricate such a transient thermal cloak device without using extreme material parameters. The experimental results show fully controlled, transient cloaking behavior, which are perfectly consistent with the theoretical derivations and simulated results. Since one can flexibly design the path of heat flux in the cloak, it has the large degree-of-freedom to construct thermal cloaks with the specific distributions of material parameters. The new method provides a new blue print for the transient thermal protection of a specific target.

scholarly journals Effects of operating and material parameters on the thermal characteristics of a wet clutch

2021 ◽  
Vol 13 (7) ◽  
pp. 168781402110341
Author(s):  
Zhigang Zhang ◽  
Ling Zou ◽  
Hang Liu ◽  
Yonglong Chen ◽  
Benzhu Zhang
Keyword(s):  
Heat Flux ◽  
Applied Pressure ◽  
Thermal Characteristics ◽  
Thermal Models ◽  
Material Parameters ◽  
Heat Transfer Theory ◽  
Friction Disk ◽  
Viscous Shear ◽  
Wet Clutch ◽  
Transient Thermal

Based on the frictional mechanism of a wet clutch, frictional models of wet clutch engagement were established using the modified Reynolds equation and the elastic contact model between frictional pairs. Then, the heat flux models for the viscous shear and asperity friction were built, and the two-dimensional transient thermal models for the separator plate, friction disk, and ATF heat convection model were deduced based on the heat transfer theory and conservation law of energy. Finally, the Runge–Kutta numerical method was used to solve the frictional and thermal models. The average temperature of the separator plate, friction disk, and ATF were calculated. The effects of operating and material parameters, such as applied pressure, initial angular velocity, friction lining permeability, surface combined roughness RMS, equivalent elastic modulus, and ATF flow, on the thermal characteristics of friction pairs and ATF during engagement, were studied. The simulation results show that the temperature characteristics of the separator plate, friction disk, and ATF depend mainly on the viscous shear and asperity friction heat flux, and that the operating and material parameters of the wet clutch also have significant impacts on the overall variation trend of the thermal characteristics of the separator plate, friction disk, and ATF.

scholarly journals A Parametrical Study on Convective Heat Transfer between High-Temperature Gas and Regenerative Cooling Panel

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1784
Author(s):  
Jiangyu Hu ◽  
Ning Wang ◽  
Jin Zhou ◽  
Yu Pan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Temperature ◽  
Thermal Protection ◽  
Flow Direction ◽  
Heated Surface ◽  
Heat Transfer Process ◽  
Cocurrent Flow ◽  
Regenerative Cooling ◽  
High Temperature Gas

Thermal protection is still one of the key challenges for successful scramjet operations. In this study, the three-dimensional coupled heat transfer between high-temperature gas and regenerative cooling panel with kerosene of supercritical pressure flowing in the cooling channels was numerically investigated to reveal the fundamental characteristics of regenerative cooling as well as its influencing factors. The SST k-ω turbulence model with low-Reynolds-number correction provided by the pressure-based solver of Fluent 19.2 is adopted for simulation. It was found that the heat flux of the gas heated surface is in the order of 106 W/m2, and it declines along the flow direction of gas due to the development of boundary layer. Compared with cocurrent flow, the temperature peak of the gas heated surface in counter flow is much higher. The temperature and heat flux of the gas heated surface both rises with the static pressure and total temperature of gas. The heat flux of the gas heated surface increases with the mass flow rate of kerosene, and it hardly changes with the pressure of kerosene. Results herein could help to understand the real heat transfer process of regenerative cooling and guide the design of thermal protection systems.

Heat Flux Measurement Method of Two-Phase Flow in SRM

2012 ◽  
Vol 152-154 ◽  
pp. 883-888
Author(s):  
Xiang Yu Zhang ◽  
Guo Qiang He ◽  
Pei Jin Liu ◽  
Jiang Li
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Two Phase Flow ◽  
Thermal Protection ◽  
Flux Measurement ◽  
Combustion Products ◽  
Phase Flow ◽  
Solid Rocket Motor ◽  
Two Phase ◽  
Heat Flux Measurement

Accurate information on heat transfer data of combustion products in the solid rocket motor chamber is a crucial prerequisite for the engine thermal protection. A measurement technique was well developed to acquire steady-state heat flux data of two-phase flow and was used successfully in the hostile environment. Experimental heat flux measurement has been obtained with an innovative designed instrument by simulating the flow field of complex charging configuration. The total heat flux of combustion products in the chamber was brought away by the coolant and calculated by its enthalpy rise in this device. The data could be used to analyze the heat transfer phenomena in SRMs and provide boundary condition for establishing insulation erosion model.

Simulation of Generator with Moving Mesh

2012 ◽  
Vol 522 ◽  
pp. 891-894
Author(s):  
Lu Yang ◽  
Ming Li Sun ◽  
Liang Dao Tang ◽  
Guang Ming Cheng
Keyword(s):  
Permanent Magnets ◽  
Rotation Velocity ◽  
Circular Motion ◽  
Moving Mesh ◽  
Comsol Multiphysics ◽  
Stator Winding ◽  
Material Parameters

This paper shows how the circular motion of a rotor with permanent magnets generates an induced EMF in a stator winding. The generated voltage is calculated with moving mesh in COMSOL Multiphysics as a function of time during the rotation. The model also shows the influence on the voltage from material parameters, rotation velocity, and number of turns in the winding.

scholarly journals Numerical Study Of Thermal Behavior Of Anisotropic Medium In Bidirectional Cylindrical Geometry

2019 ◽  
Vol 286 ◽  
pp. 08009
Author(s):  
Rabiâ Idmoussa ◽  
Nisrine Hanchi ◽  
Hamza Hamza ◽  
Jawad Lahjomri ◽  
Abdelaziz Oubarra
Keyword(s):  
Heat Flux ◽  
Heat Conduction ◽  
Thermal Behavior ◽  
Anisotropic Medium ◽  
Numerical Study ◽  
Heat Conduction Problem ◽  
Inverse Transformation ◽  
Complicated Geometry ◽  
Alternating Directions Method ◽  
Transient Thermal

In this work, we investigate the transient thermal analysis of two-dimensional cylindrical anisotropic medium subjected to a prescribed temperature at the two end sections and to a heat flux over the whole lateral surface. Due to the complexity of analytically solving the anisotropic heat conduction equation, a numerical solution has been developed. It is based on a coordinate transformation that reduces the anisotropic cylinder heat conduction problem to an equivalent isotropic one, without complicating the boundary conditions but with a more complicated geometry. The equation of heat conduction for this virtual medium is solved by the alternating directions method. The inverse transformation makes it possible to determine the thermal behavior of the anisotropic medium as a function of study parameters: diagonal and cross thermal conductivities, heat flux.

scholarly journals Temperature Distribution Near a Crevasse

1961 ◽  
Vol 3 (30) ◽  
pp. 985-996
Author(s):  
C. J. Pings
Keyword(s):  
Heat Flux ◽  
Temperature Distribution ◽  
Thermal Behavior ◽  
Ice Sheet ◽  
Transient Thermal

AbstractDuring the summer of 1955, 53 thermocouples were installed in the ice mass near a crevasse in a glacier in the ice sheet of northern Greenland. Temperatures were observed in 1955 and 1956. The accumulated data were sufficient to prepare a description of the transient thermal behavior of the ice body adjacent to the crevasse. The isotherm maps have provided a base for the computation of heat flux vectors.

scholarly journals Aerothermodynamic Shape Optimization for Re-entry Capsule Using Genetic Algorithms

2019 ◽  
Vol 11 (4) ◽  
pp. 71-79
Author(s):  
Ionut BUNESCU ◽  
Mihai-Victor PRICOP ◽  
Mihaita Gilbert STOICAN ◽  
Adrian Gheorghe DINA
Keyword(s):  
Heat Flux ◽  
Genetic Algorithms ◽  
Thermal Protection ◽  
Outer Space ◽  
Main Task ◽  
Maximum Heat ◽  
Maximum Heat Flux ◽  
Long Time ◽  
Preliminary Study ◽  
New Generation

Space hasn’t been for a long time now the final frontier, in the last years more and more spaceships have accessed outer space for different missions, some of them being required to return. The actual and main task of researchers is to find an optimal geometry for new generation of spacecraft which must be reusable and fit the imposed loads (heat flux, pressure, acceleration). The purpose of this paper is to optimize the design of a re-entry capsule configuration, in order to minimize the maximum heat flux on the thermal protection system and to obtain a wanted imposed drag coefficient. For the optimization process we use genetic algorithms and for the solving process, local inclination methods. Even if the latter are low-fidelity methods and do not offer satisfying results on all conditions, we consider them to be good enough for a preliminary study of an optimal design. Thus, this paper purpose is to describe the procedure to obtain an optimal configuration which can be better analyzed with high-fidelity methods.

Modeling Exposures of a Nylon-Cotton Fabric to High Radiant Heat Flux

2016 ◽  
Vol 11 (3) ◽  
pp. 155892501601100
Author(s):  
Thomas Godfrey ◽  
Margaret Auerbach ◽  
Gary Proulx ◽  
Pearl Yip ◽  
Michael Grady
Keyword(s):  
Heat Flux ◽  
Cone Calorimeter ◽  
Burn Injury ◽  
Thermal Protection ◽  
Transient Heat Conduction ◽  
Radiant Heat ◽  
Heat Fluxes ◽  
Direct Result ◽  
Face Modeling ◽  
Flaming Combustion

American soldiers and marines involved in the recent conflicts in Iraq and Afghanistan have suffered increased incidence of burn injury, often as a direct result of exposure to improvised explosive devices. In this work, a one dimensional numerical pyrolysis model for transient heat conduction, incorporating material transformations described by chemical kinetics, is used to investigate the response of the standard 230 g/m2 Army Combat Uniform (ACU) fabric to high radiant heat fluxes in short duration thermal protection tests and long duration cone calorimeter tests. Thermal protection tests are performed using a Thermal Barrier Test Apparatus–an automated device, incorporating a closed-loop controlled IR radiant heat source, automated water cooled shutter, a fabric sample holder, an adjustable stage with a water cooled Schmidt-Boelter heat flux gauge and a PC based data acquisition system. Cone calorimeter tests are performed on fabric specimens at an exposure heat flux of 25 kW/m2. In thermal protection tests involving exposures of 90 kW/m2 for five seconds and 77 kW/m2 for four seconds, modeling indicated that desorption and evaporation of moisture content has an important effect, but melting of the nylon component and material decomposition had insignificant effects on the heat flux transmitted through the fabric back face. Modeling results for cone testing exhibited good agreement for time to ignition and duration of flaming combustion.

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