Large Temperature Drop Research Articles

Highly efficient multi-layer flexible heatsink for wearable thermoelectric cooling

Flexible thermoelectric cooler (fTEC), which interfaces well with curved human body surface and provides cooling functions, is an emerging candidate for personal thermal management and non-hospitalized medical treatment. Achieving efficient and long-term cooling performance of TEC requires high thermal conductivity and heat diffusion of the hot side, which has yet to achieve. In this study, we design and fabricate a highly thermally conductive and flexible heatsink with a multi-layered structure especially for wearable TEC wristband, which obtains a large temperature drop (8.8 °C) for imitated on-body test and the maxim 13.1 °C temperature decrease in air. Here, we demonstrate that a well-designed functional composite layer, including phase change material, thermally conductive fillers and metal foam, can establish an effective equilibration among cooling performance, thermal management capacity and mechanical property. Particularly, the heatsink with highly thermal conductive skeleton (k ∼ 2.7 W/mK) and effective heat dissipating fins can significantly improve heat conduction and dissipation, which improve the cooling performance by more than 55 %. With the help of theoretical simulation, we propose a promising strategy for heat management on thermoelectric device through a flexible multi-layered structure, paving the way for achieving practical applications of wearable thermoelectric coolers for personal thermal regulation or cooling therapy.

Tall tower observations of a northward surging gust front in central Amazon and its role in the mesoscale transport of carbon dioxide

AbstractHigh‐frequency measurements obtained at two micrometeorological towers are investigated for a rare northward surging gust front that impacted the Amazon Tall Tower Observatory (ATTO), in central Amazon. The gust front originated from a decaying mesoscale convective system (MCS) during the morning hours of 27 December 2021 near Manaus, Amazonas state, northern Brazil, and surged north‐eastward towards the ATTO site. Large temperature drops and vigorous, persistent winds were observed at the towers which lasted for over 4 h despite the gust front being detached from its parent, decaying MCS. More importantly, the gust front was responsible for drastic increases of CO2 concentrations throughout the tower depths, which suggests that the gust front winds horizontally advected CO2‐rich air from a source upstream from the ATTO site. The CO2‐rich outflow is hypothesized to originate from downward transport and/or biomass burning from forest fires in southeastern Amazon, both ideas that are supported by large increases of aerosol concentrations measured at ATTO following the gust front passage. Our results stress the need for further investigations addressing the role played by mesoscale convective circulations in the redistribution of trace gases and aerosols in the Amazon.

Global Warming Impacts on Southeast Australian Coastally Trapped Southerly Wind Changes

Coastally trapped southerly wind changes are prominent during southeast Australia’s warm season (spring and summer). These abrupt, often gale force, wind changes are known locally as Southerly Busters (SBs) when their wind speeds reach 15 m/s. They move northwards along the coast, often producing very large temperature drops. SBs exceeding 21 m/s are severe SBs (SSBs). SBs have both positive and negative impacts. They bring relief from oppressively hot days but can cause destructive wind damage, worsen existing bushfires, and endanger aviation and marine activities. This study assesses the impacts of global warming (GW) and associated climate change on SBs and SSBs, using observational data from 1970 to 2022. Statistical analyses determine significant trends in annual frequency counts of SBs and SSBs, particularly during the accelerated GW period from the early–mid-1990s. It was found that the annual combined count of SBs and SSBs had increased, with SSBs dominating from 1970 to 1995, but SB frequencies exceeded SSBs from 1996 to 2023. The ascendency of SB frequencies over SSBs since 1996 is explained by the impact of GW on changes in global and local circulation patterns. Case studies exemplify how these circulation changes have increased annual frequencies of SBs, SSBs, and their combined total.

Nanoscale-precipitate-strengthened (Ni,Cu)-rich TiNiCu shape memory alloy with stable superelasticity and elastocaloric performance

This study aimed to enhance the stability of the superelastic and elastocaloric properties of a Ti49Ni41Cu10 shape memory alloy through a synergistic approach combining compositional design and precipitation hardening. The alloy was subjected to a 168-h aging treatment at 400 °C. The aging treatment increased the hardness of the alloy due to the formation of nano-scale C11b Ti(Ni,Cu)2 precipitates. The C11b Ti(Ni,Cu)2 precipitates exhibited a coherent interface with the matrix, contributing to the significant strengthening effect. The thickness of the precipitates was measured to be approximately 2 nm. Additionally, the lattice compatibility between the B2 parent and B19 martensite phases, determined to be 0.997 after aging, indicated a high level of compatibility between the two phases. The high compatibility and precipitate strengthening further contributed to the functional stability of the alloy. The 168-h aged Ti49Ni41Cu10 shape memory alloy showed excellent functional stability during thermal and deformation cycles. The peak temperature of B2 to B19 transformation only decreased by 0.2 °C after 10 thermal cycles and showed limited changes with a decrement of 3.2 °C after 10,000 superelastic cycles. The Ti49Ni41Cu10 SMA showed a large elastocaloric temperature drop of 18 °C at the 1st superelastic cycle and maintained a large temperature drop of 17 °C after 1000 cycles. These findings contribute to a deeper understanding of the microstructural changes and their impact on the functional properties of the Ti49Ni41Cu10 shape memory alloy. This study has demonstrated the potential for developing shape memory alloys with improved stability and performance by utilizing compositional design and precipitation hardening techniques.

Energetic assessment on a dual-temperature evaporation refrigeration system for hydrogen pre-cooling

The rapid, safe, and adequate refueling for hydrogen-based fuel cell vehicles relies on deep pre-cooling on the station side, which brings significant energy consumption. Step cooling is an ideal solution for the occasion with a large temperature drop. In this paper, a novel pre-cooling system is proposed by incorporating two-temperature evaporation to realize step cooling in the hydrogen refueling station. The pre-cooling load, system performance, and energy-saving potential are investigated under variable storage configurations and working conditions. The results show that the integral pre-cooling load increases linearly with the ambient temperature. However, the load share and the system performance are affected by the hydrogen intermediate temperature, the optimal value of which exhibits a nearly linear relationship with the ambient temperature. The novel system can save up to 30.2 % electricity relative to the conventional system with a single evaporator.

Thermophysical evolution during different decompression of N2‐containing S‐CO2 pipelines

AbstractPipelines transporting impure supercritical carbon dioxide in the carbon capture, utilization, and storage (CCUS) chain exhibit varying decompression characteristics due to engineered emissions or accidental leakage, resulting in diverse temperature drops and heat transfer mechanisms in the media and pipe walls. Therefore, studying heat transfer characteristics during slow and instantaneous decompression is crucial to investigating pipeline operational risks. In this work, supercritical CO2 pipeline valve release and rupture disc release experiments were performed with a 1.5% molar ratio of N2 content in an experimental pipeline (16 m long, 100 mm inner diameter). The evolution of the medium and pipe wall's physical properties was measured and discussed. Two methods of depressurization were employed to analyze the phase changes and heat transfer processes in the pipe. The instantaneous decompression process has a shorter decompression time and undergoes fluctuating and stable decompression stages. The slow decompression process has a slower temperature drop rate, but the wall during the process can reach a lower minimum temperature. Both release methods cause a larger temperature drop and Nusselt number at the bottom of the pipe wall due to evaporation heat transfer compared to the middle and top. The slow decompression process demonstrates a higher peak Nusselt number at the bottom, resulting in superior heat transfer efficiency compared to the instantaneous decompression process. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

Thermodynamic and techno-economic analysis of a direct thermal oil vaporization solar power system

A unique direct thermal oil vaporization solar power system employing cascade organic-steam Rankine cycle is proposed. The oil is a mixture of biphenyl and diphenyl oxide, and it is used for heat transfer, storage and power cycle fluid in the novel system. Stable electricity output and prolonged storage capacity can be facilitated. In the rated mode, the oil is vaporized at 390 °C in the collectors and drives a top turbine. The exhaust heat is used for preheating and evaporating water of the bottom cycle. Meanwhile, the hot oil in a high-temperature tank (HTT) superheats and reheats the generated steam. When the irradiation is insufficient, the heat released by the oil from the HTT to a low-temperature tank drives the bottom cycle. Fundamentals, thermodynamic performance and techno-economic feasibility are elaborated. The results indicate that, compared with the mainstream dual-tank solar power systems, the proposed system has a higher thermal efficiency with a lower water evaporation temperature (42.90% at 260 °C vs. 38.06% at 310 °C) and a larger temperature drop between the two tanks (121 °C vs. 100 °C). The equivalent payback time with respect to the top oil cycle is less than 3 years.

Construction of a ceramic coating with low residual stress on C/CA composites for thermal protection at ultra-high temperatures

Carbon fiber reinforced carbon aerogel (C/CA) composites are promising candidates for thermal protection at ultra-high temperatures. However, the poor anti-oxidative performance and difficulties in preparing a dense and crack-free coating without damaging the substrate have limited their use in oxidizing environments. Here, we have prepared a dense SiC coating on C/CA by chemical vapor deposition under the assistance of a SiC gradient layer derived from in-situ ceramization of the CA matrix. By courtesy of the gradual compaction and composition, the SiC bilayer coating with 440 μm thickness is crack-free and has low residual stress. Resultantly, the coating has a high interfacial bonding strength of 6.79 MPa due to the difficult crack initiation and propagation as well as the limited strain localization. The coated C/CA shows good ablation resistance with a linear ablation rate of 0.62 μm/s at 1900 °C for 600 s and remarkable thermal insulation with a large temperature drop of 930 °C in 10 mm thickness. The strategy of a combination of dense CVD and gradient ceramization layers can be extended to other components with excellent high temperature properties such as ZrC, HfC, which will facilitate the improvement of the ablation performance of C/CA in ultra-high temperatures.

The influence of dust aerosols on solar radiation and near-surface temperature during a severe duststorm transport episode

In the west of China, a rarely seen black storm, with a high intensity of dust aerosols and a large area of influence, occurred from April 26–29, 2015, for the first time, after more than 30 years. Based on the regional climate model (RegCM version 4.6), combined with Moderate Resolution Imaging Spectroradiometer (MODIS) satellite retrieval, meteorological, and environmental data, this work presents the pollution situation, weather background, and backward trajectory during the black storm process. In addition, we analyzed the temporal–spatial distribution of aerosol optical depth (AOD) and the impacts of dust aerosols on solar radiation and near-surface temperature under this extreme weather condition. We discovered that this black storm process was caused by the surface cold high pressure and frontal transit under the background of the upper-air circulation of “two troughs and two ridges.” The pollutants primarily from Xinjiang and the Central Asia region, along with the airflow, entered northern Xinjiang almost simultaneously with the southwest airflow, piled up along the Tianshan Mountains, and then crossed the mountains into southern Xinjiang. In addition, the areas with high AOD were mostly in the desert regions and basins, whereas the low-value areas were mountainous areas with relatively high altitudes due to the effect of geographical and climatic conditions. The AOD from RegCM 4.6 was generally lower, unlike the MODIS AOD. Moreover, the dust aerosols from this black storm caused a significant decline in net short-wave radiation (NSR) both at the top of the atmosphere (TOA) and surface. The cooling effect was more significant in the region with high AOD. For the areas where the AOD was higher than 0.7, the net short-wave radiative forcing of dust aerosols (ADRF) at the surface was above −70 W•m−2; on the other hand, the cooling effect at the TOA was not as significant as that at the surface, with the ADRFTOA being only about a quarter of the ADRFSUR. The ADRFSUR could reduce the near-surface temperature, and the region with a large temperature drop corresponded to the high-value areas of ADRFSUR/AOD. During this black storm, the near-surface temperature response to dust aerosols reached 0.40°C–2.9°C with a significant temperature drop because of cold air.

Study of Extreme Cold Surges in Hong Kong

Temperatures over Hong Kong have shown a marked increasing trend since the 1970s due to global warming and urbanization, but outbreaks of intense winter monsoon can bring very low temperatures in Hong Kong at times. This study aims at establishing criteria of extreme cold surges that suit the climatological characteristics of Hong Kong. Surges in this study were selected through percentile ranking of three weather attributes of each cold event: the lowest temperature, the largest temperature drop and the maximum sustained wind speed. Out of 152 cold events in 1991–2020, only four significant cold events in 1991, 1993, 2010 and 2016 met the most extreme 10th percentile of the three attributes concurrently and could be classified operationally as “extreme cold surge”. Very cold temperatures (at or below 7.0 °C), a temperature drop of at least 8.0 °C in two days and gale force wind speed (at or above 17.5 m/s) were recorded in all four surges. The results of classification are illustrated by selected cases. As ensemble products of some numerical weather prediction models tend to have a stable indication of extremity of cold events, the potential applications of cross-referencing the forecast and actual extremity in operational forecasting are also discussed.

Grain boundary and dislocation strengthening of nanocrystalline NiTi for stable elastocaloric cooling

We fabricate a nanocrystalline NiTi with an average grain size of 31 nm and high-density (4.7 × 1015 m−2) dislocations via cold rolling (38% thickness reduction) and annealing (310 ℃, 2 min) for elastocaloric cooling. It is found that the high-density-dislocation nanocrystalline NiTi shows a high yield strength of 2.09 GPa, a large and stable average temperature drop (ΔT) of 17.3 ℃ over 106 phase-transition cycles under the stress of 1.4 GPa at room temperature. The high cyclic stability originates from grain boundary and dislocation strengthening mechanisms, where the grain boundaries and the high-density dislocations suppress the nucleation of transformation-induced dislocations. The simple and effective processing route via cold rolling and low-temperature annealing is applicable to mass production of bulk nanostructured NiTi with stable elastocaloric cooling performances.

Intra-Lid Multi-Core Vapor Chamber Architecture for Heterogeneous Electronic Packages: Technology Concept to Prototype Evaluation

Thermal management of future heterogeneous electronic packages with extreme heat fluxes relies on effective spreading of heat in the package lid. Intra-lid integration of vapor chambers is a promising strategy for simultaneous dissipation of large total heat loads and localized high-flux hot spots. However, conventional vapor chambers comprising a single vapor core require relatively thick evaporator wicks to prevent dry out at high total heat loads, thereby imposing a large temperature drop across the wick at the hot spot location. We recently proposed a cascaded multi-core vapor chamber (CMVC) architecture comprising a single-core vapor chamber stacked on an array of smaller footprint vapor cores having relatively thinner wicks. The multi-core array is designed to spread heat from arbitrarily distributed high-flux hot spots before they enter the top vapor chamber having a thicker wick. Then, the top vapor chamber spreads the high total heat loads to the base of the mounted heat sink. To evaluate the proposed CMVC technology, we make a weighted decision to identify an appropriate minimum viable prototype for subsequent design and testing. A reduced-order model is used to determine the dimensions and properties of the wick and vapor core that minimize the temperature drop across the down-selected multi-core vapor chamber architecture for a given power map, considering manufacturing process constraints. Finite element analysis (FEA) simulations are employed to decide a condenser wall thickness that avoids permanent deformation in the vapor chamber architecture under a mechanical load. A prototype is manufactured by a commercial vendor following these parameters and manufacturing constraints. As predicted by the thermal model, experimental characterization of this first-reported multi-core vapor chamber array prototype offers a notable reduction in temperature drop relative to a benchmark solid copper spreader, owing to attenuation of hot spots at a low temperature difference.

Quantitative investigation of the evaporation and resistance characteristics of inlet jet precooling

Abstract A quantitative study is carried out to explore the air/mist-coupled cooling in the cooling section incorporating a spray device, aiming to conduct a comparative simulation on the effects of two radial spray arrangements (Apparatus A and Apparatus B) on the change of flow field. The results show that an even spray arrangement leads to improved flow performance owing to the large temperature drop in the cooling section. Compared with Apparatus A, Apparatus B enables a 1.60–2.25% higher temperature drop coefficient and a 1.1–3.0% higher water evaporation rate. Six high-altitude conditions are simulated to find that the spray device and water injection are the main factors causing flow loss, whereas the additional mass flow caused by water vapor reduces the amount of loss. The highest temperature drop coefficient is observed for Case 6 (27.3%), in which there is a more uniform nozzle arrangement. A slight difference in terms of total pressure drop coefficient between Apparatus A and Apparatus B is observed. Moreover, the highest total pressure drop coefficient (5.8%) at the location of the spray system is observed for Case 6, which has the largest injection rate and highest inlet air Mach number.

Thermal effects in spintronic materials and devices: An experimentalist’s guide

Research in spintronics often involves generation of heat in nanoscale magnetic systems. This heat generation can be intentional, as when studying effects created by an external applied temperature difference, or unintentional, coming as a consequence of driving relatively large charge currents through tiny structures. Understanding and controlling these thermal gradients can present challenges to experimentalists, which are related at some level to the fact that heat flow is much more difficult to isolate and manipulate than charge flow. This paper aims to provide a simple, intuitive framework to understand the fundamental issues that arise in spintronic materials and devices involving thermal gradients. The first goal is to provide simple tools to demonstrate how thermal gradients arise in systems with thin conducting films on bulk substrates. The main results are that a thermal gradient pointing perpendicular to the plane of a thin film supported on a macroscopic substrate is very common, even while the largest temperature drop in the system will exist across the bulk substrate itself. These results point to the need to understand the range of thermoelectric and magnetothermoelectric effects that can generate voltage signals and other responses to thermal gradients. I provide a brief review of these, along with relevant spin effects. The review concludes with examples and comments on several important ongoing issues in spintronics where thermal gradients play key roles.

Short-term effect of ambient temperature and ambient temperature changes on the risk of warts outpatient visits in Hefei, China: a retrospective time-series study.

Concerns are growing about the adverse health effects of ambient temperature and ambient temperature changes. However, the association between ambient temperature and ambient temperature changes on the risk of warts outpatient visits is poorly understood. Our study used the distributed lag non-linear model (DLNM) aimed to evaluate the association between ambient temperature, ambient temperature changes (including temperature change between neighboring days (TCN) and diurnal temperature range (DTR)), and warts outpatient visits. We also performed subgroup analyses in order to find susceptible populations by gender and age groups. The maximum relative risk (RR) of low ambient temperature (0°C) for warts outpatient visits was 1.117 (95% CI: 1.041-1.198, lag 04days), and the maximum RR of high ambient temperature (32°C) for warts outpatient visits was 1.318 (95% CI: 1.083-1.605, lag 07days). The large temperature drop (TCN = - 3°C) decreased the risk of warts visits, with the lowest RR value at the cumulative exposure of lag 7days (RR = 0.888, 95% CI: 0.822-0.959), and the large temperature rise (TCN = 2°C) increased the risk of warts visits, with the highest RR value at the cumulative exposure of lag 7days (RR = 1.080, 95% CI: 1.022-1.142). Overall, both low and high ambient temperatures and large temperature rise can increase the risk of warts visits, while large temperature drop is a protective factor for warts visits. However, we did not find any association between DTR and warts visits. Furthermore, subgroup analyses showed that males and the young (0-17years old) were more sensitive to low and high ambient temperatures, and the elderly (≥ 65years old) were more susceptible to TCN. The results may provide valuable evidence for reducing the disease burden of warts in the future.

Transient analysis of cryogenic cooling performance for high-power semiconductor lasers using flash-evaporation spray

• Transient phase-change heat transfer analysis was performed in cryogenic regimes. • A heat flux estimation method that considers an imposed heat flux was proposed. • The moderate spurt duration (Δ t = 30 s) produced preferable cooling performance. • Small-orifice-diameter nozzle has low cooling rate but high thermal efficiency. Focusing on the cryogenic cooling for the high-power semiconductor lasers to improve their output performance, this work conducted an experimental investigation on analyzing the transient cooling performance using a single-pulsed flash-evaporation spray with the environmental cryogen R32. A heat flux calculation methodology that considers an imposed heat flux as a boundary condition, was first developed to assist the transient heat transfer analysis. The results provided further insight into phase-change heat transfer on the hot surface from high-temperature to cryogenic regimes through coupling the heat transfer measurements with observations of hydrodynamic liquid film formation and development. The moderate spurt duration (Δ t = 30 s) that produced a large temperature drop (109.5 °C) and high time-averaged cooling rate (24.1 W/cm 2 ) was preferable. The significant losses in droplets’ momentum and mass contributed to the fast decrease in cooling effect as nozzle-to-surface distance ( Z ) increased. Specifically, shortening Z from 50 to 10 mm not only increased the maximum surface heat flux from 19.6 to 73.6 W/cm 2 , but also broadened the temperature region with high heat flux. The nozzle with a smaller orifice diameter (0.5 mm) produced a lower cooling rate. Whereas surprisingly, its lower flow rate resulted in the lesser coolant accumulation and splashing on the hot surface, which elevated its thermal efficiency. The low spray thermal efficiencies (≤16.2%) in the present work attribute to the low liquid utilization and coverage area across the hot spot surface under the spray impact.

Realizing a 10°C Cooling Effect in a Flexible Thermoelectric Cooler Using a Vortex Generator.

In this study, flexible thermoelectric coolers (FTECs) are used to develop an alternative personalized cooling technology to achieve a large temperature drop of 10 °C and cooling capacity of 256 W m-2 . Such an excellent cooling performance is attributed to the innovative design of the quadra-layered Ag2 Se/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate structure in FTECs and the induced air vortices by the vortex generator attached to the hot surface of the device. The applied pulse-width modulation technique guarantees human body comfort at inconsistent ambient temperature by modulating the duty ratio of the power source, which also saves 35% of the power consumption. As a result, the as-prepared FTECs only consume 68.5W so as to maintain a comfortable skin temperature (32±0.5 °C) when the ambient temperature is at 31 °C. This technology provides a reliable and adjustable solution for personalized cooling in environments where comfortable temperatures are exceeded.

Comparison of Temperature and Light Distributions Around Nano-Resistors in SSI-LEDs

A recent optoelectronic device termed the Solid-State Incandescent LED (SSI-LED) was discovered by Kuo’s group in 2013 [1]. The device is made by subjecting a MOS Capacitor of transparent gate material and appropriate high-k properties to dielectric breakdown, which results in the formation of numerous nano-scale conduction paths called nano-resistors (NRs). Due to its extremely small cross-sectional area, NRs display high current densities for relatively small voltages applied across the device. Consequently, the high current densities yield high local temperatures that approach black body radiation and allow NRs to undergo incandescence, where white light is emitted from the top surface through the transparent gate electrode by thermal excitation of electrons. Since the heat generated from Joule heating is contained within the NRs, a large temperature drop occurs over the surrounding volume as the heat flux transitions from nanoscale to microscale, keeping the whole device at a much lower temperature. The light emission from the SSI-LED is similar to that of an incandescent lamp where a spectrum of a wide range of wavelengths is produced in contrast to the narrow band light emitted from the conventional pn junction-structured LED. Therefore, SSI-LEDs are suitable for natural light or white light applications [2].It is desirable to have a direct comparison of emitted light intensity, temperature, and current density profiles of not just single NRs, but of NRs with various layouts to quantify the interaction of these variables. Earlier simulations using COMSOL Multiphysics have produced temperature and current density distributions without any accompanying light intensity study [3]. Using the python simulation framework developed earlier, these variables were studied in COMSOL Multiphysics for 3 NRs arranged as a right-angled triangle, 4 NRs as a square, and 5 NRs in the shape of a '+' sign. The effect of mesh quality on the temperature and current density distributions was also quantified. Since the current density profile is highly dependent on the relative positions of the NRs, the mesh quality has a noticeable effect on the temperature surrounding the NRs. In accordance with theoretical calculations, there is a direct relationship between the current density as well as the temperature and light intensity. The resultant light intensity profiles qualitatively match experimental observations and offers a degree of validation at near screen distances. Near the circumference at the surfaces of the NRs, the current density is high [4].Figure 1(a) shows the arrangement of NRs which are all of 10 nm radius with NR centers separated from adjacent NR centers by 40 nm. Fig. 1(b) shows the light intensity (in log10 scale) of the same patterns at a distance of 1 nm above the gate electrode surface, where the light is emitted from the blackbody radiation with corresponding the CCT to the NR at the top surface. Fig. 1(c) is the temperature of the gate electrode surface for the same set of NR patterns. Blue regions have higher temperature and white regions are close to room temperature. The temperature on the gate electrode surface blends to form a distribution that resembles individual NRs, when in fact, the observed temperature is for the pattern as a whole. The possible reason for this is that temperature is distributed in terms of sinusoidal waves according to the solution of the heat equation and is largely diffused when measured at the gate electrode surface, while the light intensity distribution obtained from the Stefan-Boltzmann law and inverse square law, varies with the 4th power of temperature close to the gate and shows a significantly steeper curve with individual NRs still distinct.More detailed comparisons of the temperature and light distributions will be shown in the presentation.1. Y. Kuo and C.-C. Lin, Appl. Phys. Lett., 102, 031117 (2013).2. Y. Kuo, 2014 IEEE International Electron Devices Meeting, 4.7.1-4.7.4 (2014).3. A. Shukla and Y. Kuo, ECS J. Solid State Sci. Technol., 9, 065017 (2020).4. K. Natarajan and Y. Kuo (To be published). Figure 1

Simulation of Selective Radiation Anti-Reflection Coating for Improvement of Emissivity

The optoelectronic and radiative properties of monolayer ARCs made from five distinct crystalline silicon (c-Si) PV materials (SiO2, Si3N4, Al2O3, TiO2, and HfO2) were simulated in this study. The absorption of c-Si in the range of 300 nm-1200 nm was first determined using the ideal thickness, and then the emissivity and radiant power when the thickness and emission angle were modified. They wanted to see which of the above five materials discharged the most light in the wavelength region of 8 to 13 m, which would improve the absorption of c-Si solar cells. In response to thickness variations from 20 nm to 1000 nm, Si3N4 emits the most in the atmospheric window, increasing from 10 Wm-2 to 161 Wm-2. The absorption ranges from 300 nm to 1200 nm, which is higher than other materials. Single-layer SR-ARCs can produce radiation with wavelengths ranging from 8 to 13 m, however multilayer SR-ARCs are unable to emit as much radiation in order to enhance efficiency and longevity. Temperature decrease was measured. The SR-ARCs were tested in two-layer, three-layer, and four-layer configurations. During the study, the bilayer SR-ARC with the ideal thickness of SiO2/Si3N4 had a temperature drop of around 0.9oC and various absorptions at 300nm-1200nm. The maximum temperature drop was about 0.7°C when the four materials were employed as ARCs at the optimum thickness, which was lower than the bilayer, but all other combinations had the highest absorption in this combination. Compared to all other studied combinations, the largest temperature drop for SiO2/Si3N4/TiO2 is 1.9°C. Lower thicknesses cannot produce a temperature reduction of 5°C or more, according to the research. Physical and optical characteristics were determined and used for SR-ARC investigations using commercially available c-Si solar cells in the study. Solar cells with a wavelength range of 300 nm to 4000 nm absorb about 832 Wm-2 from the sun's spectrum. The overall emission power is increased by a factor of 2.4 over four wavelengths when ARC with a secondary SiO2 layer (2.5 m) is applied to solar cells, but the emissivity is improved. The luminescence was not improved by adding Al2O3 between the bilayer ARCs, however the absorbance was enhanced by 9 Wm -2, which is a minor increase. Simulation findings were used to verify the final bilayer structure. The temperature of the PV module is decreased by 5.6°C when the double-layer SR-ARC is used, and the STC's overall efficiency is raised by 0.22%.

Precursory pressure oscillation in a laboratory geyser system

We conducted laboratory experiments using a setup consisting of a flask and a conduit, which reproduces cyclic eruptions and the time-predictability of natural geysers. We measured pressure and temperature in the flask and the eruptive mass of each eruption, varying three geometric parameters of the experimental system: (i) the flask volume, (ii) the inner diameter of the glass conduit and (iii) the initial water level in the conduit. During the heating stage of each eruption cycle, continuous pressure oscillations were observed in the flask. The pressure measurement and visual observation using normal-speed and high-speed cameras revealed that the pressure oscillations consisted of two components: (i) lower-frequency fluctuation related to the vertical displacements of the water column in the conduit and (ii) superimposing pulses caused by bubble nucleation in the flask. The dominant frequency of the pressure oscillations decreased systematically toward the next eruption. To explain the frequency of pressure oscillations, we present a mathematical model relating the pressure change in the flask to the vertical displacements of the water column in the conduit. The frequency calculated by our model well explained the observed frequency, which suggested that the oscillation frequency was controlled by the three geometric parameters and the effective bulk modulus of the fluid in the flask. The systematic decrease of dominant frequency toward the next eruption was explained by a decrease in the effective bulk modulus of the fluid in the flask due to an increase in gas volume fraction by heating. We also found that the erupted mass of an eruption controlled the initial frequency just after the eruption. The larger erupted mass causes a larger temperature drop in the flask, lowering the initial gas volume fraction to increase the initial oscillation frequency.