Thermal Cavity Research Articles

Packaging of semiconductor thermoelectric energy generators with in-plane thermocouples and isolation cavities

With the advent of semiconductor foundry services, thermoelectric energy generator (TEG) by CMOS/BiCMOS process has been preferable for production yield, cost effectiveness, and device scalability. The thermocouples in semiconductor TEG often have thermal isolation cavity to reduce heat loss. Both die- and wafer-packaging are proposed in this work to seal the cavity, prevent moisture/dirt from contamination, and avoid short circuit condition in the thermocouples for TEG applications in wearable devices. For a TEG design by 3P6M (3 polysilicon layers and 6 metal layers) BiCMOS process, the die-level packaging by aluminum film of thickness 50 μm over the TEG is shown to be effective, though there is about 23 % temperature gradient loss by the packaging. The voltage factor is 18.22 V/cm2K, about 77 % of that before packaging. For a TEG design by 1P6M CMOS process, the wafer-level packaging by bonding two identical TEG device wafers is shown to have about 22 % loss in temperature gradient. Yet the TEG performance is increased significantly on the same footprint because of doubling area density, and hence doubling both the power factor and voltage factor. The power factor and voltage factor is 0.164 μW/cm2 K2 and 24.32 V/cm2K, respectively, on the TEG in series circuit after packaging.

Near-field radiative heat transfer in many-body systems

Near-field radiative heat transfer refers to the transport of thermal energy by electromagnetic radiation between objects separated by less than a thermal wavelength. It involves tunneling processes that can lead to large deviations from Planck's law for blackbody radiation. These problems are of interest at a fundamental level and for devices that exploit heat transport on the nanoscale. This review summarizes the current state of this important field.

Blackbody radiation, kappa distribution and superstatistics

In this work we apply superstatistics, in a rather novel way, to derive the blackbody radiation laws in the context of the kappa distribution. Superstatistics incorporates automatically an important aspect of the kappa distribution i.e. the correlations between non-interacting degrees of freedom; this is actually a feature of any stationary non-Boltzmannian distribution derived by superstatistics. The correlations between photons in the same state affect the modified Planck and Wien laws. The correlations between photons of different states affect the fluctuations of the radiated energy, inducing very large fluctuations unless the kappa index is fairly large (i.e. near to the Boltzmannian limit), thereby compromising the very notion of stationarity. It is also shown that the Einstein absorption/emission coefficients are left intact, under the plausible assumption that the system matter-radiation obeys the given non-Boltzmannian distribution. The first-order correction to the Planck’s law near the Boltzmannian limit is deduced, and compared with the residual spectrum of the cosmic microwave background radiation from the FIRAS-COBE project data; the modified law cannot account for the residuals. No thermodynamic/entropic arguments are employed in this work.

Search for invisible axion dark matter of mass ma=43 μeV with the QUAX– aγ experiment

A haloscope of the QUAX--$a\gamma$ experiment composed of an oxygen-free high thermal conductivity-Cu cavity inside an 8.1 T magnet and cooled to $\sim200$ mK is put in operation for the search of galactic axion with mass $m_a\simeq43~\mu\text{eV}$. The power emitted by the resonant cavity is amplified with a Josephson parametric amplifier whose noise fluctuations are at the standard quantum limit. With the data collected in about 1 h at the cavity frequency $\nu_c=10.40176$ GHz, the experiment reaches the sensitivity necessary for the detection of galactic QCD-axion, setting the $90\%$ confidence level limit to the axion-photon coupling $g_{a\gamma\gamma}<0.639\times10^{-13}$ GeV$^{-1}$.

Reactive nitrogen around the Arabian Peninsula and in the Mediterranean Sea during the 2017 AQABA ship campaign

Abstract. We present shipborne measurements of NOx (≡ NO + NO2) and NOy (≡ NOx+ gas- and particle-phase organic and inorganic oxides of nitrogen) in summer 2017 as part of the expedition “Air Quality and climate change in the Arabian BAsin” (AQABA). The NOx and NOz (≡ NOy-NOx) measurements, made with a thermal dissociation cavity ring-down spectrometer (TD-CRDS), were used to examine the chemical mechanisms involved in the processing of primary NOx emissions and their influence on the NOy budget in chemically distinct marine environments, including the Mediterranean Sea, the Red Sea, and the Arabian Gulf, which were influenced to varying extents by emissions from shipping and oil and gas production. Complementing the TD-CRDS measurements, NO and NO2 data sets from a chemiluminescence detector (CLD) were used in the analysis. In all regions, we find that NOx is strongly connected to ship emissions, both via direct emission of NO and via the formation of HONO and its subsequent photolytic conversion to NO. The role of HONO was assessed by calculating the NOx production rate from its photolysis. Mean NO2 lifetimes were 3.9 h in the Mediterranean Sea, 4.0 h in the Arabian Gulf, and 5.0 h in the Red Sea area. The cumulative loss of NO2 during the night (reaction with O3) was more important than daytime losses (reaction with OH) over the Arabian Gulf (by a factor 2.8) and over the Red Sea (factor 2.9), whereas over the Mediterranean Sea, where OH levels were high, daytime losses dominated (factor 2.5). Regional ozone production efficiencies (OPEs; calculated from the correlation between Ox and NOz, where Ox= O3+ NO2) ranged from 10.5 ± 0.9 to 19.1 ± 1.1. This metric quantifies the relative strength of photochemical O3 production from NOx compared to the competing sequestering into NOz species. The largest values were found over the Arabian Gulf, consistent with high levels of O3 found in that region (10–90 percentiles range: 23–108 ppbv). The fractional contribution of individual NOz species to NOy exhibited a large regional variability, with HNO3 generally the dominant component (on average 33 % of NOy) with significant contributions from organic nitrates (11 %) and particulate nitrates in the PM1 size range (8 %).

Magnetic force vectors as a new visualization tool for magnetohydrodynamic convection

In the absence of a proper visualizing tool to present the local intensity of magnetic force during magnetohydrodynamic (MHD) convection, the understanding of the local behavior of the magnetic force interacting with a convective flow is not possible. To address the same, this work presents a new visualization tool to explore the local action of the magnetic force during MHD convection, in-depth. The necessity of this visualization tool is illustrated using three typical thermal cavities undergoing MHD convection over a range of parametric variations. From the fundamentals of mechanics and the coupling between a uniform magnetic field and convective velocity, the distribution of the magnetic force is varied in the cavities, which is visualized as a force vector using vector plots. The coupled transports of fluid flow and heat transfer are investigated using the streamlines, isotherms, heatlines, and this newly developed tool of magnetic force vectors. The study is performed considering an incompressible laminar flow within the validity of the Boussinesq approximation using an indigenous code. The outcomes of the study reveal that the implementation of this visualization technique for the magnetic force can properly explain the inner-dynamics of MHD convection in different regions of the thermal cavities. The local strength of the magnetic force strongly depends upon local flow fields and parametric values. The different patterns of the local behaviors of heat and fluid flow dynamics are reported against the pertinent parameters along with the global behavior of heat transfer. The present concept of magnetic force visualization can meaningfully be implemented in different multiphysical areas of magnetohydrodynamic convection involving ferrofluid, nanofluids, porous media, plasma, electrolytes, heat generation, thermal radiation, hybrid nanofluids, bioconvection, biomedical science, liquid metals, material processing, geophysical or astrophysical plasma process.

Stability and critical spinning speed of a flexible liquid-filled rotor in thermal environment with nonlinear variable-temperature

This paper deals with the stability and critical spinning speed of a liquid-filled rotor in thermal environment with nonlinear variable-temperature. The nonlinear temperature field model of the rotor is developed by using Laplace transform. The thermal axial force exerted on the rotor as a result of the thermal effect is calculated as functions of temperature rise rate and rotor thickness ratio. Spinning Timoshenko beam model is employed to establish the structural dynamics equations of the rotor system. The governing equation of the motion is derived by using the Hamilton principle. The validity of the developed model is confirmed by comparing with the numerical solutions available in the literature. The numerical results based on the obtained analytical solutions are given for a better understanding of the effects of the shear deformation, rotary inertia, filling parameters and thermal effect on the system stability and critical spinning speed. The results show that the system stability is dependent on the thermal axial force and cavity ratio. Moreover, the results also highlight the role of thermal effect, rotary inertia, cavity ratio and mass ratio on the critical spinning speed.

Thermal insulation performance and heat transfer mechanism of C/SiC corrugated lattice core sandwich panel

Due to the excellent mechanical and chemical properties at ultra-high temperature, ceramic matrix composites have been promising candidates for lightweight design of future thermal protection systems (TPSs). In this work, C/SiC composite corrugated lattice core sandwich panels (LCSPs) are fabricated and their thermal insulation performances are measured by a self-developed heating system combined with infrared thermal imaging (ITI) technology. Experimental results show that the thermal insulation effect increases with core inclination angle. A new model for predicting equivalent thermal conductivity (ETC), which considers the thermal conduction, cavity radiation, thermal convection and surface radiation is established to explain why the experimentally measured ETC is lower than the predicted value of previous work. Through theoretical analysis, we find that the cavity radiation plays a dominated role in ETC prediction. To reduce or inhibit the cavity radiation, multilayer LCSPs and one-layer LCSP filled with aerogel are designed. Finite element analysis results show that two-layer LCSP is the best solution for multilayer LCSP, and the maximum ETC of one-layer LCSP filled with aerogel only is 0.226 W/(mK), much lower than that of C/SiC composite. We investigate the heat transfer mechanism and thermal insulation performance of fabricated C/SiC corrugated LCSP using experimental, theoretical and numerical simulated approaches.

What if Planck had known about these calculations?

Here we present some results that would possibly have attracted the attention of the physics community in the early days of quantum mechanics in such a way that its development could have been different from what we see today. We will first present a derivation of Planck's blackbody spectrum radiation without the hypothesis of quantized energy levels of the oscillator, the only additional hypothesis to the classical theory being the existence of zeropoint fluctuations in the electromagnetic field, and this would stand as a nontrivial vacuum which could be inferred by classical means. After doing this, we derive the Unruh-Hawking effect for the electromagnetic field in a purely undulatory context, without dualities and without photons, and one question, among many others, arises after these statements: What would be the development of quantum mechanics if Planck was aware of these possibilities?

NUMERICAL ANALYSIS OF CONJUGATE NATURAL CONVECTION IN A PARTIALLY HEATED LOCAL THERMAL NONEQUILIBRIUM POROUS CAVITY WITH VARIABLE DYNAMIC VISCOSITY

NUMERICAL ANALYSIS OF CONJUGATE NATURAL CONVECTION IN A PARTIALLY HEATED LOCAL THERMAL NONEQUILIBRIUM POROUS CAVITY WITH VARIABLE DYNAMIC VISCOSITY

Topology optimization of the fluid flow layout in a thermal cavity receiver under inhomogeneous heat flux

Topology optimization of the fluid flow layout in a thermal cavity receiver under inhomogeneous heat flux

Hot-carrier enhanced light emission: The origin of above-threshold photons from electrically driven plasmonic tunnel junctions

Understanding the origin of above-threshold photons emitted from electrically driven tunnel junctions (ℏω&amp;gt;eVb with Vb being the applied voltage bias) is of current interest in nano-optics and holds great promise to create novel on-chip optoelectronic and energy conversion technologies. Here, we report experimental observation and theoretical analysis of above-threshold light emission from electromigrated Au tunnel junctions. We compare our proposed hot-carrier enhanced light emission theory with existing models, including blackbody thermal radiation, multi-electron interactions, and an interpretation involving finite temperature effects. Our study highlights the key role of plasmon-induced hot carrier dynamics in emitting above-threshold photons and the need to further explore the underlying mechanisms and optimization of upconversion effects in plasmonically active nanostructures.

Research and application of reanalysis data for radio astronomical site testing

Selecting a good site for ground-based astronomy is very important. Based on the ERA-Interim global reanalysis data, this paper studied the atmospheric conditions of the Qitai Telescope (QTT) site from the aspects of absolute humidity, mixing ratio and precipitable water vapor (PWV). Error estimations of meteorological parameters are also analyzed. These primary results show that the QTT site has obvious advantages in terms of conditions with much less atmospheric water vapor than two well-known existing sites with 100-meter-aperture radio telescopes in the world. In addition, due to the influence of atmospheric water vapor on radio observations, the atmospheric transmittance for each frequency band of the site are simulated, and the atmospheric opacity is also calculated as well as Planck radiation brightness. Based on these results, the effective observational time of different bands is further estimated.

Discrete wavelet structure and discrete energy of classical plane light waves

We find by the wavelet transform that the classical plane light wave of linear polarization can be decomposed into a series of discrete Morlet wavelets. In the theoretical frame, the energy of the classical light wave becomes discrete; interestingly, the discretization is consistent with the energy division of P portions in Planck radiation theory, where P is an integer. It is shown that the changeable energy of a basic plane light wave packet or wave train is H 0k = np 0k ω (n = 1, 2, 3, … k = | k |), with discrete wavelet structure parameter n, wave vector k and idler frequency ω, and a constant p 0k . The wave-particle duality from the Mach--Zehnder interference of single photons is simulated by using random basic plane light wave packets.

High-order nonlinear response correction method for infrared radiation detector

The infrared detector can generate nonlinear response error when the Fourier transform infrared spectrometer is used for implementing the radiometric calibration or observing the high temperature targets. Based on the relationship between the incident radiation intensity and the electron concentration in the optical conduction band, the mechanism of the nonlinear response error caused by the high incident photon flow is analyzed. According to Planck radiation law and interference principle, the effect of nonlinear error on spectrum is studied by simulating blackbody radiation data with nonlinear error. It is found that the nonlinear response with a different order has a different influence region, and the higher-order nonlinear response has a wider influence range and generates a larger nonlinear response error. By the general nonlinear response correction method the nonlinear response coefficient is obtained through constructing the nonlinear response model of the interference data and then the spectral distortion produced by the detector is corrected. According to the convolution iteration method, the polar orbit meteorological satellite CrIS constructs the convolution equation to correct the second-order nonlinear response by taking the low-wave number band of 50－500 cm&lt;sup&gt;–1&lt;/sup&gt; as the characteristic region. The European Meteorological Agency’s Airborne Infrared Interferometer Evaluation System (ARIES) selected two feature areas, 50－500 cm&lt;sup&gt;–1&lt;/sup&gt; and 2000－2500 cm&lt;sup&gt;–1&lt;/sup&gt;, and iteratively corrected the second-order and third-order nonlinear response. The gradient descent method is often used to solve the optimization problems of unconstrained multivariate functions. Based on the gradient descent algorithm, an iterative method suitable for correcting the high-order nonlinear response errors is proposed in this paper. In this method, the information about the iteration point is obtained by constructing the nonlinear response function of the high-order detector and setting the appropriate iteration initialization. According to the initial value of the iteration and the information about the known iteration point, the gradient of the iteration variable is calculated to determine the iteration value of the next unknown variable, thus quickly searching for the global minimum point and determining the nonlinear response coefficient. We use Fourier transform infrared spectrometer to carry out radiometric calibration experiment and compare the effects of three correction methods: convolution, cross iteration and gradient descent method. The results show that the three correction methods can effectively reduce the nonlinear error, and improve the fitting extent by 0.15%, 0.29% and 0.39% respectively. The spectral data corrected by gradient descent method are more accurate.

Optimal performance of solar-driven thermo-electric-radiative coupled devices

Based on the models of vacuum thermoelectric and thermoradiative devices, we established a theoretical model of solar-driven thermo-electric-radiative coupled devices. Using theories of the finite-time thermodynamics, thermionic emission, and Planck radiation, we derived the thermal equilibrium equations and the expression for energy conversion efficiency of the coupled devices. First, we discussed the thermal and electrical properties of the short circuit of the thermoelectric device, open circuit of the thermo-radiative device, and two sub-devices in series and analyzed the parametric characteristics at maximum efficiency. Then, we predicted the maximum efficiency and optimized operating conditions of the system when two sub-devices independently generate electricity and analyzed the effects of the anode’s work function, concentrator’s factor, and optical efficiency on the optimum performance. The results show that the optimum performance of the coupled system is better than that of the other three work states, which can provide theoretical guidance for the design of concentrated solar thermal-to-electricity energy conversion systems.

Energy-saving method of heat transfer enhancement during magneto-thermal convection in typical thermal cavities adopting aspiration

In the area of energy-efficient system development, the paper presents a novel approach aiming to enhance heat transfer during magnetohydrodynamic convection in thermal cavities by implementing a technique of free aspiration. Through two small openings, the proposed free aspiration naturally allows a partial admission of fresh fluid into the cavity (from its immediate surroundings) and eventually vents the admitted fluid out the cavity without any pumping device. The efficacy of aspiration technique, whether viable under different problem conditions, is worked out for various classical configurations like differential heating, corner heating, and split heating. The mathematical formulations are derived by applying the Maxwell model (for magnetic fields) and the Brinkman–Forchheimer–Darcy model (for porous media). The evolved complex and coupled mathematical equations (involving the laws of continuity, momentum, and energy) are solved by an indigenously developed computing code. The study is conducted exhaustively addressing both a porous domain and a clear domain in terms of pertinent design parameters—Hartmann number (Ha = 0–100), porosity (ε = 0.1–1), Darcy number (Da = 10−7–10−3), Darcy–Rayleigh number (Ram = 0.1–103), and Rayleigh number (Ra = 103–106). The obtained results conclusively bring out an improved trend of heat transfer for all three thermal cavities due to the aspiration (without any pumping means). Even with the existence of flow-hindering porous substance and magnetic force, the augmentation in heat transfer could be as high as seven times more compared to their respective non-aspiration cases.

Nonlinear heterodyne photothermal radiometry for emissivity-free pyrometry

This work sets the basis for nonlinear homodyne and heterodyne photothermal radiometry (PTR) as a form of active pyrometry. The intrinsic nonlinearity of thermo-optical conversion described by blackbody radiation laws generates intermodulation harmonics, among which the sum and difference frequencies are easily measured by lock-in amplifiers connected in series or in parallel. Double modulation heterodyne PTR avoids superposition with harmonics generated in nonlinear homodyne PTR by laser modulation distortion. Useful expressions are derived for the determination of temperature variations of the target relative to its absolute temperature, independently of emissivity. In order to determine one or the other temperature, calibration of one of them is necessary. The effects of spectral and temperature dependence of emissivity are also discussed. Local self-heating of a glassy carbon target could be estimated using two superposed laser sources modulated at 30 Hz and 40 Hz. This application opens the path to perform temperature-dependent thermophysical properties’ investigations in a non-contact manner, with a simple setup. Absolute temperature was determined on the surface of a Peltier element modulated at 0.1 Hz, at the location irradiated by a laser beam modulated at 1 Hz. Three data reduction methods (series, parallel, and transient configurations) yielded concordant results.

Investigation of the traditional organic vinegars by UV-VIS spectroscopy and rheology techniques.

Optical, rheological and metabolic properties of the apple, hawthorn, artichoke, grape, rosehip and blackberry organic vinegar produced by deep culture method (handmade traditional method) were analysed using UV-Vis spectroscopy and rheology techniques. Flow behaviours for all samples were analysed in the shear rate range of 10-3 to 103 1/s and in frequency range of 10-3 to 103rad/s, respectively. Absorption spectra for six organic vinegars was observed two peaks around 215 and 285nm due to the presence of phenolic compounds and organic acids such as acetic. The effects of optical transitions of organic molecules on the absorption coefficient values for vinegars were determined. Optical energy band gaps of all samples were found to be consistent with Planck's radiation approach known as Rayleigh-Jeans law and Tauc law. The rheological/flow properties of the all vinegars were found to be relevant with non-Newtonian flow behaviour and Ostwald-de Waele model. From the results of optical and rheological analysis, which determines the quantity and quality characteristics of all organic vinegars, it was concluded that these vinegars are in a level that people can drink easily.

Improvement of Thermal Conductivity and Energy Stored by Paraffin with Different Metallic Additives

Phase change thermal storage is an innovative and promising technology for saving energy. It is one of the new areas of research because it provides the solution to problems related between the provided and the required energies. Paraffin is a common phase change material (PCM) that used in many applications in thermal energy storage (TES) systems. However, the main disadvantage is their low thermal conductivities. However, using metallic additives to improve effective thermal conductivity of PCM can lead to decreasing effective heat capacity and the thermal energy stored. An experimental study is carried out to analyze the thermal behavior of the paraffin melting in a thermal cavity integrating different metals (zamak, aluminum and copper) with different configuration. The originality of study is to try to predict the best duo that respects both the improvement of thermal conductivity and energy stored. The experiments show that adding aluminum perforated plate in paraffin accelerates the melting process by about 19% and increases the energy stored by 5.18%.