scholarly journals Contactless and spatially structured cooling by directing thermal radiation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Nicola M. Kerschbaumer ◽  
Stefan Niedermaier ◽  
Theobald Lohmüller ◽  
Jochen Feldmann
Keyword(s):  
Thermal Radiation ◽  
Radiative Heat ◽  
Radiative Cooling ◽  
View Factor ◽  
Temperature Pattern ◽  
Thermal Gradients ◽  
Science And Engineering ◽  
Building Management ◽  
Temperature Manipulation ◽  
Novel Concept

AbstractIn recent years, radiative cooling has become a topic of considerable interest for applications in the context of thermal building management and energy saving. The idea to direct thermal radiation in a controlled way to achieve contactless sample cooling for laboratory applications, however, is scarcely explored. Here, we present an approach to obtain spatially structured radiative cooling. By using an elliptical mirror, we are able to enhance the view factor of radiative heat transfer between a room temperature substrate and a cold temperature landscape by a factor of 92. A temperature pattern and confined thermal gradients with a slope of ~ 0.2 °C/mm are created. The experimental applicability of this spatially structured cooling approach is demonstrated by contactless supercooling of hexadecane in a home-built microfluidic sample. This novel concept for structured cooling yields numerous applications in science and engineering as it provides a means of controlled temperature manipulation with minimal physical disturbance.

scholarly journals A Deep Neural Network Model of Particle Thermal Radiation in Packed Bed

2020 ◽  
Vol 34 (01) ◽  
pp. 1029-1036
Author(s):  
Hao Wu ◽  
Shuang Hao
Keyword(s):  
Neural Network ◽  
Heat Transfer ◽  
Thermal Radiation ◽  
Radiative Heat Transfer ◽  
Power Plants ◽  
Deep Neural Network ◽  
Radiative Heat ◽  
Particle Packing ◽  
View Factor ◽  
Pebble Bed

Prediction of particle radiative heat transfer flux is an important task in the large discrete granular systems, such as pebble bed in power plants and industrial fluidized beds. For particle motion and packing, discrete element method (DEM) now is widely accepted as the excellent Lagrangian approach. For thermal radiation, traditional methods focus on calculating the obstructed view factor directly by numerical algorithms. The major challenge for the simulation is that the method is proven to be time-consuming and not feasible to be applied in the practical cases. In this work, we propose an analytical model to calculate macroscopic effective conductivity from particle packing structures Then, we develop a deep neural network (DNN) model used as a predictor of the complex view factor function. The DNN model is trained by a large dataset and the computational speed is greatly improved with good accuracy. It is feasible to perform real-time simulation with DNN model for radiative heat transfer in large pebble bed. The trained model also can be coupled with DEM and used to analyze efficiently the directional radiative conductivity, anisotropic factor and wall effect of the particle thermal radiation.

scholarly journals Radiative heat transfer in nanophotonics: From thermal radiation enhancement theory to radiative cooling applications

2020 ◽  
Vol 69 (3) ◽  
pp. 036501
Author(s):  
Yang Liu ◽  
Deng Pan ◽  
Wen Chen ◽  
Wen-Qiang Wang ◽  
Hao Shen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Radiative Cooling ◽  
Radiation Enhancement

scholarly journals Effects of radiative heat transfer on the structure of turbulent supersonic channel flow

2011 ◽  
Vol 677 ◽  
pp. 417-444 ◽  
Author(s):  
S. GHOSH ◽  
R. FRIEDRICH ◽  
M. PFITZNER ◽  
CHR. STEMMER ◽  
B. CUENOT ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Radiative Heat Transfer ◽  
Radiation Effects ◽  
Radiative Heat ◽  
Pure Water ◽  
Molecular Transport ◽  
Working Fluid ◽  
Mean Flow ◽  
Total Energy Balance

The interaction between turbulence in a minimal supersonic channel and radiative heat transfer is studied using large-eddy simulation. The working fluid is pure water vapour with temperature-dependent specific heats and molecular transport coefficients. Its line spectra properties are represented with a statistical narrow-band correlated-k model. A grey gas model is also tested. The parallel no-slip channel walls are treated as black surfaces concerning thermal radiation and are kept at a constant temperature of 1000 K. Simulations have been performed for different optical thicknesses (based on the Planck mean absorption coefficient) and different Mach numbers. Results for the mean flow variables, Reynolds stresses and certain terms of their transport equations indicate that thermal radiation effects counteract compressibility (Mach number) effects. An analysis of the total energy balance reveals the importance of radiative heat transfer, compared to the turbulent and mean molecular heat transport.

Impact of Soot Radiative Properties, Pressure and Soot Volume Fraction on Radiative Heat Transfer in Turbulent Sooty Flames

2020 ◽  
Author(s):  
Kevin Torres Monclard ◽  
Olivier Gicquel ◽  
Ronan Vicquelin
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Volume Fraction ◽  
Soot Volume Fraction ◽  
Turbulent Flames ◽  
Radiative Properties ◽  
Jet Flame ◽  
Soot Particles

Abstract The effect of soot radiation modeling, pressure, and level of soot volume fraction are investigated in two ethylene-air turbulent flames: a jet flame at atmospheric pressure studied at Sandia, and a confined pressurized flame studied at DLR. Both cases have previously been computed with large-eddy simulations coupled with thermal radiation. The present study aims at determining and analyzing the thermal radiation field for different models from these numerical results. A Monte-Carlo solver based on the Emission Reciprocity Method is used to solve the radiative transfer equation with detailed gas and soot properties in both configurations. The participating gases properties are described by an accurate narrowband ck model. Emission, absorption, and scattering from soot particles are accounted for. Two formulations of the soot refractive index are considered: a constant value and a wavelength formulation dependency. This is combined with different models for soot radiative properties: gray, Rayleigh theory, Rayleigh-Debye-Gans theory for fractal aggregates. The effects of soot radiative scattering is often neglected since their contribution is expected to be small. This contribution is determined quantitatively in different scenarios, showing great sensitivity to the soot particles morphology. For the same soot volume fraction, scattering from larger aggregates is found to modify the radiative heat transfer noticeably. Such a finding outlines the need for detailed information on soot particles. Finally, the role of soot volume fraction and pressure on radiative interactions between both solid and gaseous phases is investigated.

CFD Modeling of Cogeneration Burner Applications and the Significance of Thermal Radiative Heat Transfer Effects

2003 ◽  
Author(s):  
A. F. Tenbusch
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Thermal Radiation ◽  
System Design ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Flow Distribution ◽  
Cfd Modeling ◽  
Large Temperature ◽  
Flow Heat

Industrial burners provide process heat for a wide range of applications including cogeneration power production. In such applications a (typically) natural gas fired stationary turbine powers an electric generator and indirectly powers a heat recover steam generator (HRSG). The HRSG steam cycle operates by reclaiming the residual thermal energy of the gas turbine exhaust (GTE) flow. Burners are used to reheat the GTE and increase plant capacity during peak demand periods. CFD modeling is used in the design of burner systems for HRSG applications. GTE flow exiting the turbine unit is passed through a diffuser and then expanded into ductwork where the steam system heat exchangers are located. The expansion of the GTE flow from the turbine diffuser to the full cross section of the ductwork is usually severe and creates an uneven flow distribution. Flow correcting structure may be needed to distribute the flow depending upon the severity of the duct expansion. CFD modeling is used to predict the flow distribution of the GTE and guide the design of any necessary flow correcting structure. Burners are typically installed in an array upstream of the application heat exchanger inlet. CFD combustion, heat transfer, and flow analysis is employed in the burner system design process to locate the burner array, determine any necessary flow baffling, and to ensure and provide a uniform thermal distribution at the downstream heat exchanger inlet. Excessive thermal variation in the GTE flow entering the heat exchanger results in large temperature gradients that can lead to thermal cracking and fatigue of the heat exchanger surfaces. CFD modeling is used to ensure that the burner system design produces a uniform flow and temperature distribution at the heat exchanger inlet region downstream of the burners. This report presents a case study of a CFD flow, heat-transfer, and combustion analysis for a typical HRSG burner application. Two CFD models were constructed for the analysis. The first model included the coupled effects of flow, heat transfer, and combustion for the entire HRSG model volume, but excluded the effects of thermal radiation. The second model included a sub-domain of the HRSG volume near the burner and included the additional effects of thermal radiation, both surface radiation and the effects of the radiatively participating flue gas. Radiative effects were included in the second model by employing the Discrete Transfer Method. Results of the study showed the significant role thermal radiative heat transfer had on the resulting temperature predictions downstream of the flame zone.

Broadening of the Cloud Droplet Size Distribution due to Thermal Radiative Cooling: Turbulent Parcel Simulations

2020 ◽  
Vol 77 (6) ◽  
pp. 1993-2010
Author(s):  
Mares Barekzai ◽  
Bernhard Mayer
Keyword(s):  
Thermal Radiation ◽  
Droplet Size ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Growth Efficiency ◽  
Droplet Growth ◽  
Radiative Cooling ◽  
Radiative Effect ◽  
Diffusional Growth ◽  
The Impact

Abstract Despite impressive advances in rain forecasts over the past decades, our understanding of rain formation on a microphysical scale is still poor. Droplet growth initially occurs through diffusion and, for sufficiently large radii, through the collision of droplets. However, there is no consensus on the mechanism to bridge the condensation coalescence bottleneck. We extend the analysis of prior methods by including radiatively enhanced diffusional growth (RAD) to a Markovian turbulence parameterization. This addition increases the diffusional growth efficiency by allowing for emission and absorption of thermal radiation. Specifically, we quantify an upper estimate for the radiative effect by focusing on droplets close to the cloud boundary. The strength of this simple model is that it determines growth-rate dependencies on a number of parameters, like updraft speed and the radiative effect, in a deterministic way. Realistic calculations with a cloud-resolving model are sensitive to parameter changes, which may cause completely different cloud realizations and thus it requires considerable computational power to obtain statistically significant results. The simulations suggest that the addition of radiative cooling can lead to a doubling of the droplet size standard deviation. However, the magnitude of the increase depends strongly on the broadening established by turbulence, due to an increase in the maximum droplet size, which accelerates the production of drizzle. Furthermore, the broadening caused by the combination of turbulence and thermal radiation is largest for small updrafts and the impact of radiation increases with time until it becomes dominant for slow synoptic updrafts.

Ignition by Thermal Radiation of Polyethylene and Human Feces Combustible Wastes: Time and Temperature to Ignition

2014 ◽  
Vol 911 ◽  
pp. 373-377 ◽  
Author(s):  
Filipe Arthur Firmino Monhol ◽  
Marcio Ferreira Martins
Keyword(s):  
Heat Flux ◽  
Thermal Radiation ◽  
Radiative Heat ◽  
Combustion Process ◽  
Fixed Bed ◽  
Fixed Bed Reactor ◽  
Radiative Heat Flux ◽  
Human Feces ◽  
Combustible Wastes ◽  
Over The Top

Due to the growing energy demands of the world and the rapid depletion of fossil fuels, it is necessary to study new energy sources. The waste have a great potential to be tapped, as besides being a raw material abundant, their use helps in reducing the level of environmental pollution and curbing the volume of waste in cities. However, one should know well the combustion process these waste before using them as fuel. Thus, Ignition behavior of combustible wastes was studied in a built fixed bed reactor. To provide a controlled thermal radiation for the ignition instant, a radiative heat flux is generated by a metal surface called a cone heater calibrated to establish the radiative heat flux density provided by a thermal resistance of 2 kW. The heat flux was 25 to 30 kWm2 over the top surface of the fuels. To validate the process, experiments with charcoal were performed varying the diameter of particles and air flow. After this, the polyethylene and human feces were analyzed. Their effects were investigated on the ignition time.

scholarly journals Study of radiative heat transfer in Ångström- and nanometre-sized gaps

2017 ◽  
Vol 8 (1) ◽  
Author(s):  
Longji Cui ◽  
Wonho Jeong ◽  
Víctor Fernández-Hurtado ◽  
Johannes Feist ◽  
Francisco J. García-Vidal ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Energy Transfer ◽  
Detection Limit ◽  
Thermal Radiation ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Surface Cleaning ◽  
Computational Results ◽  
Open Questions ◽  
Cleaning Procedures

Abstract Radiative heat transfer in Ångström- and nanometre-sized gaps is of great interest because of both its technological importance and open questions regarding the physics of energy transfer in this regime. Here we report studies of radiative heat transfer in few Å to 5 nm gap sizes, performed under ultrahigh vacuum conditions between a Au-coated probe featuring embedded nanoscale thermocouples and a heated planar Au substrate that were both subjected to various surface-cleaning procedures. By drawing on the apparent tunnelling barrier height as a signature of cleanliness, we found that upon systematically cleaning via a plasma or locally pushing the tip into the substrate by a few nanometres, the observed radiative conductances decreased from unexpectedly large values to extremely small ones—below the detection limit of our probe—as expected from our computational results. Our results show that it is possible to avoid the confounding effects of surface contamination and systematically study thermal radiation in Ångström- and nanometre-sized gaps.

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