Impact Of Temperature Gradients Research Articles

Long-term measurement and characterization of boundary layer optical turbulence

The United States Naval Academy long-term scintillation measurement campaign was a multi-year effort to characterize optical turbulence in the near-maritime atmospheric boundary layer (ABL). At its core, the field experiment consists of in situ measurements of bulk atmospheric and oceanographic parameters, as well as path-averaged measurements of the refractive index structure parameter, C n 2, collected using a large-aperture scintillometer. The field experiment ran from January 1st, 2020, through September 26th, 2023, representing the most comprehensive collection of optical turbulence measurements in the near-maritime ABL to date. Long-term measurements enable researchers to evaluate existing theory and develop new models applicable to this environment. The present study characterizes some of the physical relationships that affect optical turbulence. This characterization focuses on the relationship between local optical turbulence and select atmospheric and oceanographic parameters. The impact of temperature gradients on the extent of optical turbulence was analyzed, along with its interactions with relative humidity and wind speed. The diurnal and seasonal variations in measured C n 2 were examined, with comparisons drawn against other environments. Further information and the full dataset are publicly available through the optical turbulence benchmark repository [Jellen et al., GitHub, 2023].

Analysing unbalanced ageing in EV battery Packs using the Low-Cost Lumped Single Particle Model (LSPM): the impact of temperature gradients among parallel-connected cells

Lithium-ion battery cells are widely used in electric vehicles (EVs) due to their high energy density and long lifespan. However, these cells are sensitive to temperature and can age at different rates depending on the temperature they are subjected to. While EV battery packs are equipped with a battery thermal management system (BTMS) to regulate the temperature of the pack, it cannot completely eliminate temperature gradient within the pack due to the limited cooling capabilities. As a result, a maximum temperature gradient of 5°C is allowed in BTMS designs for EVs, which leads to uneven ageing speeds within the pack. Due to practical limitations of battery management system (BMS), it is difficult to directly measure the currents flowing through each parallel-connected cell, making it challenging to actively balance the cells. To investigate the pack-level current distribution and ageing trends caused by temperature gradient, this paper adopts the low computational cost Lumped Single Particle Model (LSPM) coupled with Arrhenius dependency to investigate the influence of temperature on current distribution as well as the resulting unbalanced ageing rates among parallel-connected cells in a 4s6p Panasonic NCR18650PF battery pack.

Reflected shock-initiated ignition probed via simultaneous lateral and endwall high-speed imaging with a transparent, cylindrical test-section

A TRAnsparent cylindrical (TRAC) shock tube test section has been developed to explore the ignition structure behind reflected shockwaves via simultaneous lateral and endwall high-speed imaging using three fuel/oxidizer mixtures: 0.1% n-C7H16/1.10% O2/4.14% N2/94.66% Ar, 0.1% iC8H18/1.25% O2/4.69% N2/93.96% Ar, and 5% CH4/10% O2/85% CO2. During mild ignition, the first exothermic centers were located outside of the observable test section. It is shown that with increasing temperature the far-wall ignition events move closer to the endwall, until a strong ignition is achieved. The temperature gradients that promote mild ignition were quantified and were found to have a slight dependence on fuel with the RMS temperature gradients being 0.80% for n-heptane and 1.07% for isooctane. The impact of temperature gradients on metrics used to improve kinetic models, such as species time histories, is noteworthy. From this temperature gradient, an experimental correlation is provided to estimate the transition temperature from mild to strong ignition for a mixture. The effect of diagnostic location in non-homogeneous reactions is quantified in reference to ignition delay. The unique and insightful perspective on the ignition process under heavy shock bifurcation is also discussed.

Modelling stress evolution and voiding in advanced copper nano-interconnects under thermal gradients

As the chip power densities increase radically with scaling, thermal gradients are predicted to become a major reliability concern in interconnects compatible with the 3 nm technology node and beyond. In this study, the impact of temperature gradients on the reliability of Cu nano-interconnects with highly scaled linewidth of 10 nm is simulated using a Korhonen-type modelling framework previously calibrated for electromigration predictions. ∆T dictates the stress distribution at steady state while dT/dx along the interconnect governs the stress evolution rate. It is shown that a linear temperature profile with a ∆T of >25 °C can generate voiding by thermomigration alone in these narrow lines. The adverse impact of thermal gradients by thermomigration and also by thermally induced flux divergence points are explored, showing a 20% drop of jmax in the presence of a ∆T of 10 °C and secondary nucleation sites along the line depending on temperature distribution. Immortality of Cu nano-interconnects to electromigration in the presence of thermal gradients was assessed whereby a thermally adjusted jLc is found relevant depending on the direction of electron flow with respect to temperature gradient.

Impact of temperature gradients on average bit error rate performance of low-density parity-check-coded multihop underwater wireless optical communication systems over the generalized gamma distribution

The impact of temperature gradients on the average bit error rate (ABER) performance of low-density parity-check (LDPC)-coded underwater wireless optical communication (UWOC) systems is investigated over the generalized gamma fading channels. The effects of absorption and scattering are also taken into account in our computation on the basis of the Monte Carlo (MC) ray-tracing method. The decoded-and-forward multihop communication is applied to extend the viable communication range of UWOC systems. In particular, using the generalized Gauss–Laguerre quadrature rule, the ABER analytical expressions of the multihop UWOC system with binary phase shift keying and multiple phase shift keying modulation schemes are mathematically derived under weak temperature-induced oceanic turbulence condition, respectively, which are also confirmed by MC simulation. In addition, LDPC codes are adopted to improve the UWOC system performance. The results reveal that the ABER performance of this multihop UWOC system degrades with increasing temperature gradients, hop numbers, and modulation orders, while it can be significantly enhanced by LDPC codes and the coding gains increase with the increase of temperature gradients and hop numbers. Our work will benefit the design and development of UWOC system.

Inhomogeneous Degradation of Li-Ion Cells: A Post Mortem Study Using Glow Discharge Optical Emission Spectroscopy (GD-OES)

Commercialization of many Li-ion cell chemistries is hindered by undesirable processes occurring during usage of Li-ion batteries, limiting their lifetime. One such process is the development of temperature gradients, especially in large-format cells, leading to uneven utilization of electrode material.1 Such inhomogeneity could locally accelerate or change the aging phenomena.2 Correlation of the electrochemical data with the post mortem analysis of cell components enables root cause analysis of aging mechanisms under the given conditions.3The present study looks into the applicability of GD-OES as a powerful method in post mortem analysis of Li-ion cell electrodes. GD-OES provides direct depth-resolved elemental analysis of the complete electrode coating (~100µm) within hours.4Sensitivity to light elements (e.g. Li and H), fast analysis, and quantification of the recorded elemental intensity, are among the features of GD-OES that compare with similar analytical methods (SIMS, XPS, and AES). A method is developed using reactive sputtering for investigating aged graphite electrodes. Calibration is performed using homemade reference coatings with systematic variation of Li-containing salt in graphite slurries. GD-OES depth profiling is employed to study SEI formation during the initial charge of a graphite/Li(NixCoyMnz)O2 cell. It is discovered that SEI formation is not limited to the reduction potential of electrolyte components and additives, but continues during Li intercalation at lower cell potentials.5,6 Furthermore, the method is used for quantitative detection of Li plating (Figure 1).7Applying the method to different planar positions of aged graphite electrodes harvested from large-format commercial cells, the impact of temperature gradients on Li distribution across the electrode is studied. Acknowledgement This research has been performed within the MAT4BAT project (http://mat4bat.eu/) and received funding from the European Community's Seventh Framework Program (FP7/2007-2013) under grant agreement n°608931.

Conjugate Analysis of Heat-Species-Charge Transport for Evaluating Effects of the Temperature Gradient on Cell Performance

1. Introduction Management of water in the PEMFC is very important to improve the cell performance. However, the water transport mechanism in the PEMFC is complicated and it is difficult to understand by only experimental methods because of the thinness of the components of the PEMFC. Thus, numerical analyses are very useful methods. The two-dimensional analytical model considering distributions of temperature, spices and reaction in components of the PEMFC is developed to estimate the unsteady performance of the PEMFC. The absolute value of the temperature of the cell impacts on the cell performance. However, the gradient of temperature has also great impacts on the cell performance. Moreover, temperature, chemical reaction and transport phenomena have interaction, for example the phase change and impeding the transport of the reactant gases by liquid water. So, it is important to consider not only temperature but also water transport. MPL was reported to moisturize CL and PEM and at the same time MPL enhances liquid water drainage to Channel. However, the detailed mechanism how MPL works on the cell performance is yet unclear. Finally, in this study, the effects of the gradient of temperature are investigated, and the models with MPL and without MPL are compared to validate the work of MPL. 2. Analytical methods The unsteady cell performance has been studied with two-dimensional analytical model considered heat, species and charge transport in components of the PEMFC, such as GDL, MPL, CL and PEM. The impact of temperature gradients has been investigated by comparison of non-isothermal and isothermal condition at 72 deg. C. 3. Results and discussions In Fig. 1, the distribution of temperature was shown. From this, the temperature of the area nearby CL and PEM was the highest and the value was 72 deg. C. And the temperature around separators was lowest and the value was 70 deg. C. The difference of temperature is only 2 deg. C, however, the current density had more than 5 times difference between non-isothermal and isothermal condition as shown in Fig. 2. The distributions of the liquid water saturation of each condition were shown in Fig. 3 and Fig. 4, respectively. Under isothermal condition, the value of liquid water saturation in CL was about approximately s=1, on the other hand, there is little liquid water in CL under non-isothermal condition. Then, current density drastically decreased from 40 s under isothermal condition with the liquid water accumulation in the CL. Figure 1

Real time, non-intrusive measurement of particle emissivity and gas temperature in coal-fired power plants

We present a novel, remote technique for measuring in situ and in real time (every 2 s) the spectral emissivity of particles at λ = 3.95 µm, in optically thick combustion environments. The novelty lies in the use of spectral information in the mid-IR (the blackbody emission profile of the 4.3 µm CO2 band and the gray emission profile of particles between 3.8 and 4.1 µm) to determine the physical and brightness temperatures of the gas–particle medium, from which particle emissivity can be calculated. The retrieved particle emissivity at 3.95 µm is a reasonable average of total particle emissivity between 1 and 15 µm. Thus, CFD researchers who work with radiation sub-models may use this technique to obtain in situ emissivities at different locations, with a portable, rugged and inexpensive device. A small prototype was built with off-the-shelf components: standard light collection optics, a grating spectrometer and a linear-array pyroelectric detector. The particle emissivity is calculated from the asymptotic solution of the radiative transfer equation for optically thick media with isotropic scatterers. Results from a proof-of-concept test at a full-scale, coal-fired boiler 10 m above the top row of burners showed an average particle emissivity of 0.41 and an average gas temperature of 1533 K. Intrinsic and prototype error as well as the impact of temperature gradients in the line of sight of the instrument are discussed.

Thermal gradient effects on the propagation of nonlinear pressure waves in a gas

A numerical study of wave propagation through gases with nonuniform temperature distributions will be presented. The main objective of this study is to determine the impact of temperature gradients on high-intensity, initially sinusoidal pressure waves. Particular emphasis is paid to wave reflection, transmission, and any influence a high-temperature region may have on nonlinear behavior. Ultimately, the performance of thermal barriers in attenuating nonlinear waves is evaluated. The concept of using regions of hot gas inside an ambient environment has potential in aeroacoustic applications, such as jet screech mitigation. This analysis considers one-dimensional compressible unsteady Euler equations with an ideal gas state equation, applied over a uniform domain. The domain is composed of two regions with uniform and equal gas properties (ambient conditions) separated by a third region with higher gas temperature and, accordingly, lower density. Pressure is uniform throughout the domain. We introduce a high-intensity sinusoidal wave into this medium. The shape and extent of the high-temperature zone is varied to study the effect of this region on wave propagation. Further, wave reflection and transmission are studied for a range of wave and thermal field parameters. Results for nonlinear pressure waves are compared to linear acoustic waves.

Retrieving cloud top structure from infrared satellite data

A new retrieval method to detect steep temperature gradients between the convective overshoots of cumulonimbus clouds and the surrounding cirrus has been applied to determine gradients and their orientation in the image plane of infrared data of the advanced very high resolution radiometer (AVHRR). These orientations are used to derive cloud elevations which are brightened by the Sun or are in shadow, which strongly affects the visible signal. The impact of temperature gradients on the visible radiances is illustrated by two examples that indicate deep convective overshoots. Both examples show that the illuminated side of the overshoots can exceed the cloud top reflectivity by 50%, while the shadows account for <50% of the cloud top reflectance. The shadows usually extend several pixels beyond the base of the overshoots. Here we show that statistical analyses of cloud optical depth are affected by the cloud top structure, based on 1 month of high‐resolution AVHRR satellite data. The contribution of shadow side pixels with steep temperature gradients (≥16 K) can exceed 30% for small optical depths (<3). The contribution of illuminated sides of cloud top structures and cloud sides with steep temperature gradients can exceed 70% for large optical depths (>32).