Rapid Temperature Fluctuations Research Articles

A Preliminary Numerical Investigation of Thermal Mixing Efficiency in T-Junctions with Different Flow Configurations

When hot and cold fluids flow through a converging T-junction, rapid temperature fluctuations occur in the mixing region due to the thermal mixing of fluids. This temperature fluctuation causes thermal fatigue, which is responsible for the shortening of service life in a T-junction. Hence, the design of T-junction for thermal mixing requires not only superior mixing performance but minimize thermal fluctuation during mixing is also desirable. The objective of the present paper is to determine the thermal mixing performance at the mixing region of T-junction with two different flow configurations. Water, at different inlet temperatures, is used as a working medium and is assumed incompressible. Two types of flow configurations, namely intersecting and colliding regular T-junction with a sidearm pointing at 12 o’clock position have been evaluated in this paper. Realizable k-epsilon turbulence model was assumed, and its validity benchmarked against RANS and RSM-EB turbulence models. The thermal mixing efficiency of both flow configurations is calculated and compared. The results show that the thermal mixing efficiency of both intersecting and colliding mixing tee increases with the increase of distance and time. Intersecting tee shows higher temperature fluctuation than colliding tee at the mixing outlet, but colliding tee shows higher thermal mixing efficiency than intersecting mixing tee.

Effect of geometrical design on the latent heat cooling properties of a lightweight two-phase composite

Latent heat storage materials undergo phase changes to maintain a constant temperature environment and are fast emerging as a passive “green” technology for thermal management. Phase-change materials (PCMs) typically have poor thermal conductivities; however, their response to rapid fluctuations in temperature can be sluggish. Here, we explore the feasibility of adding various aluminum alloy (AlSi10Mg) structures to speed up the thermal response. The cooling performance of various geometries with the same mass density was first investigated, and the best performing geometries were then further optimized to investigate the possible weight savings. Our results indicate that, for unidirectional heat flux, designs with 3D periodicity, such as triply periodic minimal surfaces, do not perform as well as those with 1D (parallel plates) and 2D (honeycombs) periodicity. Furthermore, a strong correlation was found between the cooling performance and the interfacial area density. An expanding melt front, which leads to an increase in the interfacial area for heat transfer over time, and even heat distribution were also observed to be advantageous. After optimization, the honeycomb design with tapered triangular rods surrounded by the PCM matrix was able to achieve greatest weight savings for a given performance requirement. Compared to a thermal management panel consisting solely of the PCM, it was able to keep a heated surface cooler by 90% and also outperformed a pure Al panel despite being more than 40% lighter.

Bioinspired Radiative Cooling Structure with Randomly Stacked Fibers for Efficient All-Day Passive Cooling.

Without the help of compression-based cooling systems, natural creatures have to make use of other things to decrease their body temperature to survive under thermally harsh conditions. This work finds that the silkworm cocoon of Bombyx mori protects pupae from the rapid temperature fluctuations via the randomly stacked silk fibers, which possess high solar reflectance and thermal emittance for thermal regulation. Inspired by this microstructure, the melt-blown polypropylene (MB-PP) with randomly stacked fibers is fabricated by a large-scale melt-blown fabrication method. For enhancing the thermal emittance of MB-PP, the surface-modified MB-PP (SMB-PP) is obtained by constructing the poly(dimethylsiloxane) film on the MB-PP. As the reason for its high solar reflectance (∼95%) and thermal emittance (∼0.82), the SMB-PP displays subambient temperature drops of 4 °C in the daytime and 5 °C in the nighttime, respectively. Moreover, building energy simulation indicates that the SMB-PP could save ∼132 GJ (∼58.1% of the baseline energy consumption) for 1 year in the contiguous United States. Overall, the bioinspired structures offer a novel pathway out of cooling buildings, showing great promising application prospects in zero-energy buildings.

Athermal silicon photonic wavemeter for broadband and high-accuracy wavelength measurements

We propose and demonstrate an integrated wavemeter capable of accurate and broadband measurements without control or knowledge of the temperature. In our design, interferometers composed of silicon and silicon nitride waveguides enable accurate measurements of an input optical wavelength despite large and rapid temperature fluctuations of 20°C by leveraging the disparity in thermo-optic properties of the waveguides. We derive formulas which resolve the wavelength and temperature ambiguity of the interferometers. The fabricated wavemeter chip is found to have a mean accuracy of 11 pm over an 80 nm range near 1550 nm. To our knowledge, this is the first demonstration of an athermal silicon wavemeter and the lowest measurement error across such a broad wavelength range using silicon photonics. This result may reduce the cost and size of wavemeters used in combination with integrated lasers for optical communications, sensing, and other applications.

High Precision Human Skin Temperature Fluctuations Measuring Instrument.

This paper describes the experimental results of testing a prototype of a high precision human skin rapid temperature fluctuations measuring instrument. Based on the author’s work, an original circuit solution on a miniature semiconductor diode sensor has been designed. The proposed circuitry provides operation in the full voltage range with automatic setting and holding the operating point, as well as the necessary slope of the conversion coefficient (up to 2300 mV/°C), which makes it possible to register fast temperature oscillations from the surface of the human body and other biological objects. Simulation results in the Microcap 12 software and laboratory tests have confirmed all declared design specifications: temperature resolution of 0.01 °C, transducer thermal time constant of 0.05 s. An original thermostat and an experimental setup for the simultaneous registration of the electrocardiogram, pulse wave signals from the Biopac polygraph MP36 and a signal of temperature oscillations from the prototype thermometer have been designed for further investigations. The preliminary test results indicates that using the designed measuring instrument gives a possibility to provide an in-depth study of the relationship between micro- and macro-blood circulations manifested in skin temperature fluctuations.

Plasticity in thermal hardening of the invasive Asian house gecko

The Asian house gecko (Hemidactylus frenatus) is a tropical invasive species that has established and spread throughout several temperate regions around the world. In some invasive species, rapid thermal acclimation (thermal hardening) may contribute to their success in occupying a wide range of climates. In this study, we investigated whether invasive house geckos from southeastern Australia show differing thermal hardening responses than individuals from the native range in Thailand. In the laboratory, we measured the basal heat tolerance (CTmax) of the geckos and their heat hardening response after being subjected to the second thermal stress after 1, 3, 5, 7, 9, or 11 h. When geckos had recovered, we measured their basal cold tolerance (CTmin) and cold hardening response over the same time intervals. We then explored whether hardening responses differed between populations or among time intervals. We found that basal heat tolerances did not differ between populations, but geckos from Australia had lower cold tolerance than geckos from Thailand. The magnitude of the heat hardening was similar between populations, but the introduced geckos had a higher magnitude of cold hardening. The native geckos could maximize their cold tolerance capacity for only 0.6 °C, versus 0.9 °C for the introduced geckos. Also, geckos from Australia exhibited faster responses to thermal stress than did geckos from Thailand. Maximum thermal tolerances as a result of hardening responses peaked within three hours after thermal stress in Australian geckos (adjusted means = 44.0 °C for CTmax and 9.9 °C for CTmin) and at five hours after thermal stress in Thailand geckos (adjusted means = 44.2 °C and 10.2 °C, respectively). The plasticity in the thermal hardening of the invasive gecko should enable it to survive rapid temperature fluctuations, especially winter cold snaps that occur in temperate regions.

Adaptive time offset compensation for TDMA industrial wireless networks

Wireless network nodes working in industrial environment or mounted on mobile machines are exposed to frequent and unpredictable temperature changes, which impact local clock accuracy resulting in synchronization problems (time offset). These issues have to be taken into account when optimizing the network to avoid higher energy consumption and traffic congestion. The time offset problem can be alleviated using temperature driven compensation. In the paper we propose an efficient algorithm to resolve this problem taking into account slow and rapid temperature fluctuations. It combines the physical model of the node oscillator with an original prediction method based on the linear regression. It can be embedded in low cost microcontrollers with limited resources. Our approach needed some experimental studies of oscillator features and microcontroller capabilities. The implemented prototype nodes and performed tests proved high clock resilience for industrial environment as compared with other approaches.

Skeletal deformities and meristic trait variations are common in the intertidal fish Bathygobius cocosensis (Perciformes-Gobiidae).

Extreme environmental conditions, such as temperature, can lead to meristic trait variation and skeletal deformities, which may have major impacts on individual fitness. As intertidal ecosystems experience rapid temperature and physicochemical fluctuations, intertidal fish living and reproducing in these environmental conditions may have phenotypes influenced by such variable environments. The impact of intertidal variability on fish development, however, has not been previously investigated. Skeletal deformities and meristic traits were assessed for Bathygobius cocosensis, a common intertidal fish living across the Indo-Pacific region, using a clearing and staining method on 72 individuals. Over 87% of individuals presented meristic variation and over 70% exhibited at least one type of skeletal deformity, mostly recorded in the caudal fin area. The unexpected prevalence of skeletal deformities among this intertidal fish population suggests that such deformities may be suitable markers to evaluate an individual's stress exposure during development and the subsequent fitness effects.

Broad Thermal Tolerance in the Cold-Water Coral Lophelia pertusa From Arctic and Boreal Reefs.

Along the Norwegian coasts and margins, extensive reefs of the stony coral Lophelia pertusa act as hotspots for local biodiversity. Climate models project that the temperature of Atlantic deep waters could rise by 1–3°C by 2100. In this context, understanding the effects of temperature on the physiology of cold-water species will help in evaluating their resilience to future oceanic changes. We investigated the response of L. pertusa to stepwise short-term increases in temperature. We sampled corals from four reefs, two located north of the Arctic circle and two at the mid-Norwegian shelf (boreal). In on-board experiments (one per reef), the sampled fragments were exposed to increasing temperatures from 5 to 15°C over 58 h. Respiration increased linearly by threefold for a 10°C increase. The short-term temperature increase did not induce mortality, cellular (neutral red assay for lysosome membrane stability; but one exception) or oxidative stress (lipid peroxidation assay) – to a few exceptions. However, the variability of the respiration responses depended on the experiment (i.e., reef location), possibly linked to the genetic structure of the individuals that we sampled (e.g., clones or siblings). The corals from the Arctic and boreal regions appear to have a high tolerance to the rapid temperature fluctuations they experience in the field. Over extended periods of time however, an increased metabolism could deplete the energy stored by the corals, if not met by an increased food availability and/or uptake. Empirical data on organisms’ thermal performance curves, such as the one presented in this study for L. pertusa, will be useful to implement predictive models on the responses of species and populations to climate change.

Development of a SiPM-based CsI(Tl) spectrometer with gain stabilization designs for rapid temperature variations

Abstract A spectrometer employing a silicon photomultiplier (SiPM) based scintillation detector has spectrum drift issues under temperature variations. Although some temperature-dependent compensation methods are reported, spectrum distortions under rapid temperature fluctuations have received little attention. We have developed a SiPM-based CsI(Tl) spectrometer and proposed gain stabilization designs to settle this problem. A temperature sensor was coupled to the SiPM in the detector and wrapped with a thermal insulation foam material to acquire the temperature of the SiPM. Meanwhile, a temperature correction module was applied in the field-programmable gate array (FPGA) within a custom multichannel analyzer (MCA). The effectiveness of the temperature correction module in the FPGA and a specialized detector design were studied and verified under slow and rapid temperature variations. The results prove that the spectrum drifts of the SiPM-based CsI(Tl) spectrometer under rapid temperature variations can be significantly constrained with the proposed gain stabilization designs.

Calculation of specific heat of polymers using molecular dynamics simulations

Precise evaluation of the heat capacity at constant pressure (Cp) of polymers during rapid heating and cooling is required to predict and optimize the performance of polymer products after laser-assisted manufacturing processes. However, currently available experimental methods are not capable of determining Cp at rapid temperature fluctuations. Molecular Dynamics (MD) simulations could be useful to evaluate Cp under such conditions. In order to determine the efficacy of MD simulation, Cp at the room temperature of various well-studied polymers (polyethylene, polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride, and polytetrafluoroethylene) were computed with the MD simulations using General Amber Force Field (GAFF) potentials. The simulated Cp values for these polymers were found to be higher than experimental values. Possible reasons for the disparity in Cp values are discussed, and suggestions for extracting accurate Cp values are provided.

Post rapid freezing growth of Antarctic strain of Heterococcus sp. monitored by cell viability and chlorophyll fluorescence

The soil microalgae of the genus Heterococcus are found in cold environments and have been reported for the terrestrial ecosystems of several Sub-Antarctic and Antarctic Islands. This study focused on resistance of Heterococcus sp. to sub-zero temperature. Heterococcus sp. was isolated from soil samples from James Ross Island, Antarctica. Culture of Heterococcus sp. grown in liquid medium were used to study ribitol effects at sub-zero temperatures on the species resistance to rapid freezing (RF, immersion of a sample into liquid nitrogen) and consequent cultivation on agar. Before the experiment, Heterococcus sp. was cultured in liquid medium for 11 months and then treated in ribitol concentrations of 32 or 50 mM for 2 h. Then, 1 ml samples were frozen to −196 °C in liquid nitrogen (day 0) and inoculated on BBM agar after thawing. Number of living and dead cells was evaluated and the cell viability (Pν) was calculated repeatedly using the optical microscopy approach. The addition of ribitol caused a noticable increase in Pν on days 9, 12, 14 (with a Pν of 25–45% in ribitol-treated samples compared to 10% in the untreated control). In the following period (d 16–19), the positive effect of ribitol on Pν was less pronounced but still statistically significant. To evaluate the negative effects of RF on chlorophyll fluorescence parameters, the potential yield of photochemical reactions in PS II (FV/FM), and the effective quantum yield of photochemical reactions in PS II (ФPSII) were measured immediately before and after RF. Consequently, FV/FM and ФPSII of agar inoculates were measured repeatedly for 30 d cultivation in 3 d interval. Both the 32 and the 50 mM addition of ribitol caused earlier detection of the parameters (d 16) compared to the control measurements (d 23) as well as reaching the maximum values of the chlorophyll fluorescence parameters earlier (d 23 in ribitol-treated samples compared to d 25 in control samples). Heterococcus sp. proved to be a species resistant to rapid freezing. The ability may help the species to survive in harsh Antarctic environments typified by rapid fluctuations in temperature that may bring a rapid freezing of the alga.

Determination of the water gap and the germination ecology of Adenanthera pavonina (Fabaceae, Mimosoideae); the adaptive role of physical dormancy in mimetic seeds.

Dormancy caused by impermeable seed coats, i.e. physical dormancy (PY), regulates the timing of seed germination in species of several genera belonging to 18 angiosperm families. Physical dormancy also occurs in some mimetic species whose seeds mimic brightly coloured, fleshy fruits or arilled seeds. However, the conditions that break dormancy, as well as the location of water gaps in mimetic seeds, remain unclear. Here, we investigated the adaptive role of impermeable coats in the mimetic seeds of Adenanthera pavonina (Fabaceae: Mimosoideae). Specifically, we explored: (i) the conditions that break PY; (ii) the location of the primary water gap that forms during dormancy break; and (iii) the effect of seasonal temperature regimes on seed germination. Seeds were subjected to hot-water treatment, rapid temperature fluctuations and storage at temperatures mimicking summer and autumn conditions. Seed coat anatomy and water-gap regions were characterized using scanning electron microscopy (SEM) and light microscopy. Seeds were artificially buried in the field at 3 and 7 cm depths and exhumed every 6 months for 2 years to monitor germination. Adenanthera pavonina had impermeable seed coats, and thus PY. Seeds treated with hot water and exposed to summer–autumn temperature regimes broke dormancy. Water entered only through the lens (Type-II simple) due to dislodgement of the palisade layer. Seeds buried at 3 cm depth had significantly higher germination than those buried at 7 cm depth, with germination primarily occurring in autumn. Seeds required high summer temperatures followed by moderate autumn temperatures to become permeable to water and germinate in the field during the wet season. We conclude that the impermeable seed coat of A. pavonina is an adaptation that synchronizes germination with the growing season.

A Phenomenological Model of the Screen-Printed, Silver Paste Contact to Si Substrate

A phenomenological model of screen-printed silver contact to an n-doped, p-type multi-crystalline Si wafer, based on extensive electrical, morphological, and compositional evaluations, has been developed. Rapid and quasi steady state heating configurations over broad (150–925°C) temperature ranges were investigated. Conventional rapid thermal annealing (RTA) with a conveyor belt was used for a rapid and custom-designed three-zone quartz tube furnace (QTF) for slow temperature variations. Lowest contact resistivity at 0.15 mΩ cm2 was observed in RTA horizontal configuration which was 25 times smaller than the same in QTF. RTA contact resistivity measurements revealed a minimum at 870°C while linear reduction in contact resistance was observed for the QTF configuration. The silver/silicon contact was based on three physical mechanisms: (1) migration of Si into glass and silver regions of the paste, (2) intermixing of silver and silicon (nano- and micrometer scale), and (3) epitaxial growth of silver/silicon crystallites. Experimental evidence of silicon migration was supported through extensive phosphorous concentration measurements from silicon and silver/silicon regions. The glass film with a colloidal distribution of randomly-distributed silver/silicon crystallites leads to lower contact resistance. Rapid temperature fluctuations facilitate development of Ag/Si crystallites. The higher contact resistance in quasi steady state thermal configuration was attributed to glass films with reduced density of Ag/Si crystallites. This disadvantage may be eliminated through post-contact, forming gas annealing at lower temperatures.

Life-history traits buffer against heat wave effects on predator-prey dynamics in zooplankton.

In addition to an increase in mean temperature, extreme climatic events, such as heat waves, are predicted to increase in frequency and intensity with climate change, which are likely to affect organism interactions, seasonal succession, and resting stage recruitment patterns in terrestrial as well as in aquatic ecosystems. For example, freshwater zooplankton with different life-history strategies, such as sexual or parthenogenetic reproduction, may respond differently to increased mean temperatures and rapid temperature fluctuations. Therefore, we conducted a long-term (18months) mesocosm experiment where we evaluated the effects of increased mean temperature (4°C) and an identical energy input but delivered through temperature fluctuations, i.e., as heat waves. We show that different rotifer prey species have specific temperature requirements and use limited and species-specific temperature windows for recruiting from the sediment. On the contrary, co-occurring predatory cyclopoid copepods recruit from adult or subadult resting stages and are therefore able to respond to short-term temperature fluctuations. Hence, these different life-history strategies affect the interactions between cyclopoid copepods and rotifers by reducing the risk of a temporal mismatch in predator-prey dynamics in a climate change scenario. Thus, we conclude that predatory cyclopoid copepods with long generation time are likely to benefit from heat waves since they rapidly "wake up" even at short temperature elevations and thereby suppress fast reproducing prey populations, such as rotifers. In a broader perspective, our findings suggest that differences in life-history traits will affect predator-prey interactions, and thereby alter community dynamics, in a future climate change scenario.

A hybrid strain and thermal energy harvester based on an infra-red sensitive Er3+ modified poly(vinylidene fluoride) ferroelectret structure

In this paper, a novel infra-red (IR) sensitive Er3+ modified poly(vinylidene fluoride) (PVDF) (Er-PVDF) film is developed for converting both mechanical and thermal energies into useful electrical power. The addition of Er3+ to PVDF is shown to improve piezoelectric properties due to the formation of a self-polarized ferroelectric β-phase and the creation of an electret-like porous structure. In addition, we demonstrate that Er3+ acts to enhance heat transfer into the Er-PVDF film due to its excellent infrared absorbance, which, leads to rapid and large temperature fluctuations and improved pyroelectric energy transformation. We demonstrate the potential of this novel material for mechanical energy harvesting by creating a durable ferroelectret energy harvester/nanogenerator (FTNG). The high thermal stability of the β-phase enables the FTNG to harvest large temperature fluctuations (ΔT ~ 24 K). Moreover, the superior mechanosensitivity, SM ~ 3.4 VPa−1 of the FTNG enables the design of a wearable self-powered health-care monitoring system by human-machine integration. The combination of rare-earth ion, Er3+ with the ferroelectricity of PVDF provides a new and robust approach for delivering smart materials and structures for self-powered wireless technologies, sensors and Internet of Things (IoT) devices.

The influence of temperature differences in moist environments on surface discharges on solid insulation

The electric breakdown strength of insulating surfaces in HV systems is known to be greatly affected by moisture deposited on the surface. This has been known for decades in relation to HV outdoor insulation. Another application range, where breakdown voltages as a function of moisture and temperature are relevant is the offshore industry. Subsea applications of high voltages systems can mean harsh temperature conditions in connection with moist environments, such that electrical breakdown conditions in these environments need special focus.For gas insulated systems the moisture level is normally kept at a preferred minimum to avoid accumulation of condensation on the insulating surfaces, in particular on highly stressed areas.In this paper has been investigated the correlation between the electric flashover voltage of an insulating surface in moist environments and the condensation process on the insulating surface, as dependent on the dynamic moisture/temperature conditions.Under extreme environmental conditions, rapid temperature fluctuations can occur and cause accumulation of water droplets on surfaces. A series of tests were conducted on an insulation sample in air, showing the flashover voltage as a function of the temperature difference between gas and insulating surface.The breakdown field was, as expected, dependent on the formation of condensation on the surface. At high moisture content in the gas no relation between temperature gradient and flashover voltage was found, at moderate moisture the dependency did not give a clear picture.

Lack of a weathering signal with increased Cenozoic erosion?

AbstractThe Late Cenozoic has been marked by large and rapid fluctuations in temperature. This cooling has been attributed to accelerated erosion, with concomitant increased chemical‐weathering rates and CO2 drawdown from the atmosphere. At the same time, much of the supporting evidence appears to be affected by a sampling bias, implying that global erosion and weathering have remained largely constant over the past millions of years. We suggest that sedimentary archives of geomorphic activity, such as grain size and the ratio of terrestrial to oceanic sedimentation, which show accelerated erosion are not subject to these biases. Furthermore, the active tectonic settings where these erosion increases were likely to have taken place are exactly those locations where chemical‐weathering signals are least likely to faithfully follow physical erosion rates. A lack of evidence for an increase in chemical weathering does not necessarily preclude an increase in physical erosion. In this contribution, we suggest an alternative interpretation in which erosion rates have increased in the Late Cenozoic but without significantly increased silicate weathering, which can explain the meagre response of chemical‐weathering proxies.

A fluid–structure interaction approach to investigate the quenching characteristics of a steel tube with temperature dependent properties

Quenching is commonly used for improving material properties of steel tubes because of their numerous applications. However, quenching generates some residual stress and deformation in the material due to rapid temperature fluctuations. The properties of the steel are strong functions of these variable temperatures and therefore, the estimated stress and deformation by constant property or static quenching analysis are not very realistic. This study describes the first extensive study of the quenching process of a steel tube including temperature dependent properties by three liquid quenchants using the dynamic fluid–structure interaction quench model. The cooling characteristics of the three liquid quenchants are compared to each other along with the transient temperature distributions in the steel tube. The time-varying nodal, axial, and radial residual stress and deformation of the tube are studied. It is found that, the effectiveness of quenching does not depend only on a particular quenchant, but also on the temperature-varying properties of the steel and the uniformity of the cooling which ultimately determine the criteria for selecting a suitable quenchant for a specific purpose.

Temperature-Robust Neural Function from Activity-Dependent Ion Channel Regulation

Many species of cold-blooded animals experience substantial and rapid fluctuations in body temperature. Because biological processes are differentially temperature dependent, it is difficult to understand how physiological processes in such animals can be temperature robust [1-8]. Experiments have shown that core neural circuits, such as the pyloric circuit of the crab stomatogastric ganglion (STG), exhibit robust neural activity in spite of large (20°C) temperature fluctuations [3, 5, 7, 8]. This robustness is surprising because (1) each neuron has many different kinds of ion channels with different temperature dependencies (Q10s) that interact in a highly nonlinear way to produce firing patterns and (2) across animals there is substantial variability in conductance densities that nonetheless produce almost identical firing properties. The high variability in conductance densities in these neurons [9, 10] appears to contradict the possibility that robustnessis achieved through precise tuning of key temperature-dependent processes. In this paper, we develop a theoretical explanation for how temperature robustness can emerge from a simple regulatory control mechanism that is compatible with highly variable conductance densities [11-13]. The resulting model suggests a general mechanism for how nervous systems and excitable tissues can exploit degenerate relationships among temperature-sensitive processes to achieve robust function.