Thermal Cavity Research Articles

Comparison of simulated and measured light emission spectra from solid state incandescent light emitting devices

In this paper, the light emission phenomena over solid-state incandescent light emitting devices have been modelled based on Planck’s law of blackbody radiation. The emission spectra from the thermal excitation of nano-resistors with and without inclusion of an Indium Tin Oxide (ITO) or amorphous silicon (a-Si) thin film filter is simulated and compared with those measured from actual devices. The simulated emission spectra are further utilized to study the light characteristics for SSI-LED with ITO, a-Si and polycrystalline silicon (poly-Si) thin film filters.

Photoelectron distribution on sunlit surface of the Moon: A formalism

An analytical formulation describing the characteristic energy distribution of photoelectrons over the sunlit regolith of the Moon has been presented. In deriving the distribution function, Fowler's approach based on fermionic lattice electrons for photoemission has been coupled with observed solar spectra, photoelectric quantum yield, and latitude dependent surface temperature. It is noticed that the dominant contribution in the photoelectron distribution function comes from extreme ultraviolet photons (3 eV–300 eV) of the solar spectra. The analysis also illustrates that the photoelectron distribution for the observed solar spectra is significantly different from the spectrum based on Planck's radiation law. In results, the photoelectron distribution is found to be a significant function of the lunar surface potential—the photoelectron distribution in the steady state considerably differs from that of the uncharged surface. In calculations, the variation in the photoelectron distribution function with the lunar latitude, quantum yield, and work function of the surface material has been parametrically analyzed, and it is found to be sensitive to the constituent parameters.

Cooperation of quadruple cylinder-wound coil and insulation cavities for suppressing the thermal-induced bias drift of FOG

The thermal-induced rate error of the fiber optic gyroscope (FOG) caused by external thermal disturbances is related to the spatial distribution of the temperature field and the winding process of the fiber coil. In order to compensate for the length asymmetry of the fiber center point in the quadrupolar winding (QAD) method, this paper proposes a method based on the cooperation between a quadruple cylinder-wound coil (Q-CYL) and quadruple thermal insulation cavities to suppress the thermal-induced bias drift of the FOG. The bias drift error model is established based on the Shupe error and thermal stress error, and the accuracy of this model is verified by experiment and simulation results of the QAD coil with a single insulation cavity. The drift suppression ability of the Q-CYL with quadruple insulation cavities under different thermal disturbance spatial positions is analyzed through comparisons with three other typical methods using the finite element method (FEM). The results show that the Q-CYL with quadruple insulation cavities can better homogenize the temperature field of the fiber coil and reduces the drift error caused by thermal stress, thereby more effectively suppressing the thermal-induced rate error of the FOG.

Multidimensional microscopic investigation of oxidation-induced hollow cavities in a Co–Al–W–Ti–Ta alloy nanotip by electron tomography

Spallation of thermal oxidation-induced cavities is the main failure mode in CoAl-based alloys, and the γ/γ′ phase structure in Co–Al–W–Ti–Ta alloys has a propensity to form oxide cavities. Multidimensional investigations were carried out herein on irregular oxide cavities by analytical microscopy, including electron tomography and energy dispersive X-ray spectroscopy techniques, to disclose the time-resolved three-dimensional morphological structure and elemental distributions. The alloy nanotip was exposed isothermally in air at 350 °C, and its oxidation evolution was characterized and analysed. The size and quantities of cavities in the γ phase were larger than those in the γ′ phase, which was attributed to the higher content of cobalt in the γ phase than in the γ′ phase. Different migration rates between cobalt outward and aluminium inward prompted the formation of cavities between the outer and inner layers.

Tunable Infrared Metamaterial Emitter for Gas Sensing Application.

We present an on-chip tunable infrared (IR) metamaterial emitter for gas sensing applications. The proposed emitter exhibits high electrical-thermal-optical efficiency, which can be realized by the integration of microelectromechanical system (MEMS) microheaters and IR metamaterials. According to the blackbody radiation law, high-efficiency IR radiation can be generated by driving a Direct Current (DC) bias voltage on a microheater. The MEMS microheater has a Peano-shaped microstructure, which exhibits great heating uniformity and high energy conversion efficiency. The implantation of a top metamaterial layer can narrow the bandwidth of the radiation spectrum from the microheater to perform wavelength-selective and narrow-band IR emission. A linear relationship between emission wavelengths and deformation ratios provides an effective approach to meet the requirement at different IR wavelengths by tailoring the suitable metamaterial pattern. The maximum radiated power of the proposed IR emitter is 85.0 µW. Furthermore, a tunable emission is achieved at a wavelength around 2.44 µm with a full-width at half-maximum of 0.38 µm, which is suitable for high-sensitivity gas sensing applications. This work provides a strategy for electro-thermal-optical devices to be used as sensors, emitters, and switches in the IR wavelength range.

Quantification of Non-refractory Aerosol Nitrate in Ambient Air by Thermal Dissociation Cavity Ring-Down Spectroscopy.

A thermal dissociation cavity ring-down spectrometer (TD-CRDS) for real-time quantification of non-refractory aerosol nitrate in ambient air is described. The instrument uses four parallel detection channels and heated quartz inlets to convert particulate organic nitrate (pON) (at 350 °C) and ammonium nitrate (NH4NO3) aerosol (at 540 °C) to nitrogen dioxide (NO2), whose mixing ratio is monitored via its absorption at 405 nm. Concentrations of aerosol nitrate are determined by difference relative to a parallel TD-CRDS channel in which aerosol is removed by in-line filtering. The method was validated by sampling gas streams containing laboratory-generated NH4NO3 aerosol in parallel to a scanning mobility particle sizer (SMPS). Scatter plots of TD-CRDS and SMPS data correlated (r2 > 0.9) with slopes near unity, confirming quantitative TD-CRDS response to NH4NO3 aerosol. In contrast, no response was observed when sampling (NH4)2SO4 aerosol. Instrument limits of detection (LOD; 2σ, 10 s) were 120 parts per trillion by volume (10-12, pptv) for NO2 and 148 pptv for ammonium nitrate. Partial and unsustained conversion of refractory sodium nitrate (NaNO3) was observed at the inlet temperature used for complete dissociation of HNO3 and NH4NO3, suggesting that this channel may not constitute a robust measurement of total odd nitrogen (NOy) in environments where NaNO3 particles may be present (e.g., the polluted marine boundary layer). A potential application of the TD-CRDS is the calibration of particle counters, for which convenient methods are not currently available. Sample ambient air measurements of pON and total aerosol nitrate in Calgary are presented.

Thermal entanglement in a double Jaynes–Cummings model

In this paper, we have investigated the entanglement dynamics between two initially entangled qubits interacting with two independent thermal cavities modes in the framework of resonant double Jaynes–Cummings model. We obtain the exact solution for the model under consideration and derive the time dependence of the atom-atom negativity. Results reveal that for entangled atoms the initial atomic quantum correlations can partially restore its original values for a finite interval of time, even for relatively high cavity temperatures.

An improved mathematical prediction of the time evolution of the Covid-19 pandemic in Italy, with a Monte Carlo simulation and error analyses

We present an improved mathematical analysis of the time evolution of the Covid-19 pandemic in Italy and a statistical error analyses of its evolution, including a Monte Carlo simulation with a very large number of runs to evaluate the uncertainties in its evolution. A previous analysis was based on the assumption that the number of nasopharyngeal swabs would be constant. However, the number of daily swabs is now more than five times what it was when we did our previous analysis. Therefore, here we consider the time evolution of the ratio of the new daily cases to number of swabs, which is more representative of the evolution of the pandemic when the number of swabs is increasing or changing in time. We consider a number of possible distributions representing the evolution of the pandemic in Italy, and we test their prediction capability over a period of up to 6 weeks. The results show that a distribution of the type of Planck black body radiation law provides very good forecasting. The use of different distributions provides an independent possible estimate of the uncertainty. We then consider five possible trajectories for the number of daily swabs and we estimate the potential dates of a substantial reduction in the number of new daily cases. We then estimate the spread in a substantial reduction, below a certain threshold, of the daily cases per swab among the Italian regions. We finally perform a Monte Carlo simulation with 25,000 runs to evaluate a random uncertainty in the prediction of the date of a substantial reduction in the number of diagnosed daily cases per swab.

Fermionic Analogue of High Temperature Hawking Radiation in Black Phosphorus**Supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0300902 and 2016YFA0202300), the National Basic Research Program of China (Grant No. 2015CB921001), the National Natural Science Foundation of China (Grant Nos. 11774396, 91850120 and 11974045), and the Strategic Priority Research Program (B) of CAS (Grant Nos. XDB30000000

Time-periodic laser driving can create nonequilibrium states not accessible in equilibrium, opening new regimes in materials engineering and topological phase transitions. We report that black phosphorus (BP) exhibits spatially nonuniform topological Floquet–Dirac states under laser illumination, mimicking the “gravity” felt by fermionic quasiparticles in the same way as that for a Schwarzschild black hole (SBH). Quantum tunneling of electrons from a type-II Dirac cone (inside BH) to a type-I Dirac cone (outside BH) emits an SBH-like Planck radiation spectrum. The Hawking temperature TH obtained for a fermionic analog of BH in the bilayer BP is approximately 3 K, which is several orders of magnitude higher than that in previous works. Our work sheds light on increasing TH from the perspective of engineering 2D materials by time-periodic light illumination. The predicted SBH-like Hawking radiation, accessible in BP thin films, provides clues to probe analogous astrophysical phenomena in solids.

Modeling the damping mechanism of MEMS oscillators in the transitional flow regime with thermal waves

This paper investigates the damping behavior of a vibrating micro-oscillator caused by a surrounding gas in the transitional flow regime (0.01 < Kn < 0.1). In this regime, neither the continuum theory given by the Navier-Stokes equations nor the Boltzmann equation for the molecular flow regime can be applied to describe the damping effects correctly. We propose that the well-known Zener formalism developed for describing thermoelastic damping in solid oscillators can be adapted to include thermoacoustic effects in gases. In this newly proposed model, the damping is caused by thermal waves traveling from the micro-oscillator to a neighboring plate which is placed with a gap width ranging from 150 to 750 μm. This theoretical approach can be brought to a nearly perfect fit with the experimental data, including the observed concave zone of the quality factor plot within the transitional flow regime. The resonance frequency of thermal waves of gas within the gap is derived from standard wave theory, verifying the proportionalities extracted from the experimental results. Consequently, the theory in the transitional flow regime can be expanded by the thermal wave concept and the usage of MEMS oscillators for the thermal wave resonator cavity method (TWRC) is feasible.

Impact of convection and radiation on direct/hybrid heating stability of field assisted sintering

Field assisted sintering (FAST) processes allow a direct transmission of the heating energy to the specimen (through the electric, magnetic fields or the electrical current). FAST allows higher heating rates, faster sintering response and a better control of the sintered microstructures. However, FAST suffers high heating instability in direct heating configurations which generally takes the form of a hot spot. The origin of these hot spots is well known and is correlated to the convective/radiative cooling at the specimen surfaces and the thermal dissipation in the specimen. Nevertheless, the impact of these cooling fluxes evolves with the sample dimensions, thermal insulation, heating rate and hybrid heating conditions and there is not clear quantification of the relative importance of these fluxes in regards to the previous cited heating conditions. In this work we develop a finite element (FE) tool which can easily explore the heating stability of an “Equivalent Thermal Cavity” (ETC). We illustrate the ETC concept by the case study of the microwave sintering of zirconia. We show that the dominant heat transfer is radiative, but the convective fluxes have a high importance for the temperatures homogenization, in particular in the case of a hybrid heating configuration.

Characterization of a micro thermal cavity receiver – Experimental and analytical investigation

The objective of this work is to characterize the optical and thermal performance of a micro-scale cylindrical cavity solar receiver for the Brayton gas power cycle at various solar radiation levels through experimental and analytical investigation. A thermal receiver consisting of a 300 mm deep and 200 mm diameter cylindrical cavity equipped with an 8 mm diameter helical copper tube was studied. An advanced ray-tracing technique using OptisWorks software was used to predict the distribution of solar radiation inside the cavity. Also, computational fluid dynamics simulations were carried out using ANSYS CFD software to predict the temperature distributions of the coil surface and the compressed air outlet temperature. Having satisfying conformity between the numerical and the experimental results, the current results demonstrated that a competent flux and temperature distributions were directed on the receiver’s tube. Moreover, an outlet temperature up to 70 °C, based on the available compressed air flow rate. This point leads to the probability of operating a micro-scale dish concentrator for Concentrated Solar Power in a domestic application. The results of a parametric study indicated that a cavity’s receiver depth and width of 180 mm and 240 mm give the best thermal operation.

3D Rayleigh‐Bénard‐type natural convection in MWCNT‐nanofluid‐filled L‐shaped enclosures with consideration of aggregation effect

Rayleigh‐Bénard type convective heat transfer in a 3D L‐shaped enclosure filled with multiwalled carbon nanotube (MWCNT)‐water nanofluids has been studied. The governing equations have been written using the vorticity‐vector potential formalism and solved based on the finite volume method (FVM). The simulations were performed for various values of Rayleigh number, aspect ratio, and MWCNT volume fraction. The aggregation effect was considered, and the viscosity and thermal cavity were evaluated accordingly to fit with the experimental properties. The heat transfer is enhanced by increasing MWCNT volume fraction. The aspect ratio is found to be an optimization parameter of heat transfer especially for low Ra values. The aspect ratio equal to 0.4 provides the highest heat transfer for fraction nanofluid less than 3% and Ra number less than 105. Increasing the aspect ratio and fraction nanofluid enhances of the 3D character.

Monte Carlo Ray Tracing-Coupled Computational Fluid Dynamic Modeling and Experimental Testing of a 1-kW Solar Cavity Receiver Radiated via 7-kW HFSS

Abstract Current state-of-the-art development of concentrated solar power (CSP) applications targets cost-effective and highly efficient processes in order to establish commercialization of these technologies. The design of solar receivers/reactors and their respective flow configuration have a direct impact on the operational performance of the solar thermochemical processes. Thermal efficiencies, reaction kinetics, and other key output metrics are the intrinsic result of the chosen configuration. Therefore, reactor design optimization plays a crucial role in the development of solar thermochemical applications. In this study, a computational fluid dynamics (CFD) model of a directly-irradiated cavity receiver has been developed. The CFD-domain is coupled with incoming radiation that is obtained by using Monte Carlo ray tracing (MCRT). Experimental campaigns of the cavity receiver were carried out using a 7-kW high flux solar simulator (HFSS) as a radiative source. Temperature readings were obtained at different locations inside the cavity receiver for both wall and gas temperatures. In order to mimic naturally changing insolation conditions, the HFSS was run at different power levels. Heat flux at the aperture of the solar receiver was experimentally characterized. The acquired heat flux maps validated the intermediate results obtained with the MCRT method. The coupled computational model was validated against the measured temperatures at different locations inside the receiver. Computed temperature contours inside the receiver confirmed the experimentally observed non-uniformity of the axial temperature distribution. The validated analysis presented in this paper was then used as a baseline case for a parametric study. Design optimization efforts were undertaken toward obtaining temperature uniformity and achieving efficient heat transfer within the fluid domain. Enhanced flow circulation was achieved which yielded temperature uniformity of the receiver at steady-state conditions. The outcome of this parametric analysis provided valuable insights into the development of thermal efficient solar cavity receivers. Hence, findings of this study will serve as a starting point for the future solar reactor design. For example, it was found that reversing flow direction has an adverse effect on the temperature uniformity inside the receiver. Similarly, increasing the inlet angle does not positively affect the temperature distribution and hence should be chosen carefully when designing a solar reactor.

The Marvel and the Mystery of Quantum Mechanics — Some Reflections

The creation of quantum mechanics is one of the most dramatic developments in the physics of the 20th century. After the period 1900–1924, during which the Law of Black Body Radiation, wave particle duality for light and for matter, the general quantisation of energy and stability of matter and the laws of spectroscopy had begun to be understood, the mathematical structure of quantum mechanics was discovered amazingly rapidly in just under two years, 1925–1927. On the other hand, the physical interpretation and meaning of this structure required an enormous effort, in which the uncertainty and complementarity principles, the Born probability interpretation and rule and the wave function collapse idea, all played important roles. While quantum mechanics has all along been amazingly successful in numerous applications, many puzzling questions about interpretation remain and continue to be pursued till today, though the focus has shifted from wave particle duality to entanglement and its signatures and consequences. This article gives an impressionistic account of these developments, accompanied by comments on the origins of human intuition and the meaning of human understanding of nature [1].

Design and analysis of thermal stable regenerative cavity with multiple laser heads using 4f system

Regenerative amplifiers containing multiple diverse laser heads have the ability of scaling up output power as well as broadening spectral bandwidth. However, the thermal lensing effect will be more complicated. A method using a 4f system to simplify the thermal lensing effect in a multidisk condition is proposed. Two kinds of Yb-dropped sesquioxide materials are chosen as an example. On the basis of calculating the thermal lensing parameters of the thin-disk laser heads, a feasible cavity design that can minimize the fluctuation of beam size when changing the pump power is given out. The 4f system consisting of concave mirrors will introduce astigmatism in the cavity. The influence of astigmatism and the compensation method are discussed. Astigmatism can be compensated by adding extra convex mirrors and controlling the angle of incidence at each mirror.

Comparative Study on Radiation Properties of Blackbody Cavity Model Based on Monte Carlo Method

In order to improve the absorption of stray radiation traps and thermal radiation detectors of blackbody radiators and enhance the thermal radiation transmission, large aperture and high-emissivity blackbody radiators or compact space-borne blackbody sources can be developed. The design of blackbody cavity with V-grooves is a method to change the effective emissivity of blackbody radiation source. At the design stage, the most important work is to evaluate its radiation characteristics in order to verify the effectiveness of this method. Two kinds of blackbody cavity models are designed in this paper. One is a cylindrical–conical blackbody cavity with a 2-mm deep 50° angle V-grooves (the cavity is 300 mm long and 80 mm in diameter, with a depth of 277 mm the cone part of the cavity is 23.09 mm long, the top angle of the cone is 120°, the wall thickness is 2 mm, and the surface will be painted with 0.95 emissivity coating). The other is the blackbody cavity model with the same structure and smooth inner wall. Using the special software based on Monte Carlo method, the radiation characteristics of the two blackbody cavity models are simulated under isothermal conditions. The average normal effective emissivity and right-conical effective emissivity of the blackbody cavity with different observation radius are obtained, respectively. The results show that the average normal effective emissivity and right-conical effective emissivity of the blackbody cavity with V-grooves on the inner wall are increased. In addition, the experimental results of radiative properties of the blackbody radiator having the V-grooved cavity measured by thermal cavity reflectometry method agree with the theoretical simulation results. Therefore, it is proved that the blackbody cavity with V-grooves on the inner wall (except for special angles) can be an effective way to improve the emissivity of the blackbody source.

Committed Warming Due to Earth’s Radiative Imbalance Using a Simple 5-Factor Energy Balance Model

The concept of committed warming has been neglected or understated in the climate change conversation, although climate scientists acknowledge that some additional global warming is “baked in” no matter how quickly the world switches to a clean-energy economy. The Earth’s climate is not equilibrated with anthropogenic climate forcing. Ignoring thermal inertia of the oceans, this study shows that stabilizing CO2 concentrations at today’s levels would still commit the earth to at least 0.5oC of additional warming in the next century. Due to past anthropogenic emissions the earth currently absorbs more heat than it emits, which induces a yet unrealized commitment. Even if the CO2 levels stopped increasing, the planet would have to warm further in order to balance solar energy absorbed with energy radiated back to space. This study incorporates a simplified, five-factor model (5FEBM) that uses only known or well-understood factors that drive global warming. These five key factors come close to accounting for the earth’s current radiative imbalance, as well as future temperatures predicted by global climate models. The factors include human greenhouse gas emissions, human generated aerosol emissions, human caused land surface alteration, water vapor feedback, and Planck radiation feedback. Published research on the topic of committed warming mostly corroborates the results of the 5FEBM model. Multiple sources predict a committed warming on the order of 1.5oC relative to pre-industrial conditions. This is particularly relevant to the IPCC’s recent call for more aggressive emission reduction targets to keep total warming below 1.5oC by the end of the 21st century. The evidence herein suggests that may not be possible. Ignoring other feedbacks that will surely worsen, the five factors listed above commit the earth to a global mean surface temperature (GMST) anomaly slightly more than 1.5oC in 2100. A numerical method is developed from the 5FEBM to estimate committed warming under constant concentration conditions. The method is validated by integrating a differential equation involving temperature and time at constant CO2 concentration. The effect of this warming commitment on the year-to-year GMST anomaly is graphed. A sensitivity analysis demonstrates the solution is robust with respect to assumed initial conditions. There is some divergence among estimates of committed warming based partly on assumptions about emissions. Most studies assume constant composition commitment (CCC), but some envision zero emissions. Others assume continued emissions from current fossil fuel investments that would persist through the end of the investments’ useful life. Another scenario admits to an ongoing emissions commitment due to certain energy technologies for which there is currently no commercially available replacement. Presumably, the rationale for estimating committed warming is to portray an idealized but still reasonable picture of the current climate crisis. Calling attention to committed warming seeks to motivate prompt action on climate change by showing both the possibilities and the urgency of mitigating its impacts. The CCC scenario balances these two objectives.

Statistical theory of photon gas in plasma

The thermodynamical properties of the photon-plasma system have been studied using statistical physics approach. Photons develop an effective mass in the medium thus—as a result of the finite chemical potential—a photon Bose–Einstein condensation can be achieved by adjusting one of the relevant parameters (temperature, photon density and plasma density) to criticality. Due to the presence of the plasma, Planck’s law of blackbody radiation is also modified with the appearance of a gap below the plasma frequency where a condensation peak of coherent radiation arises for the critical system. This is in accordance with recent optical microcavity experiments which are aiming to develop such photon condensate based coherent light sources. The present study is also expected to have applications in other fields of physics such as astronomy and plasma physics.

Heat transfer enhancement by localised time varying thermal perturbations at hot and cold walls in a rectangular differentially heated cavity

The objective of this work it is to determine the optimal properties of a thermal disturbance to enhance the heat transfer in a rectangular differentially heated cavity of aspect ratio 4. So, we study numerically the effect on the heat transfer of one or two small thermal actuators (5% of active plate surface) applied at the active walls of this kind of cavity. Thermal disturbances are sine or square waves. Influences of wave characteristics (amplitude, frequency, phase shift) and the vertical location of the disturbance area are investigated for various Rayleigh numbers below its first critical value (RaH=1.02×108). Only a fluid with Prandtl number equal to 0.71 (air) is considered. Flows are calculated solving the 2D unsteady Boussinesq–Navier–Stokes equations using the Spectral Element Method programmed in the Nek5000 opencode. A detailed description of the coupling between one or two thermal disturbances and cavity flow is presented. The main contribution of this work is that the best position to enhance the heat transfer is 70% of the hot plate height or 30% of the cold plate height, and not 0.1 for the hot plate (0.9 for the cold one) which is generally admitted. At this position this increase reaches 5.5% by disturbing at both active walls with local synchronised square waves of amplitude ε=1, of frequency f=0.403 and at a state slightly below the first critical Rayleigh number.