Sudden Temperature Changes Research Articles

Numerical modelling and transient analysis of a printed circuit heat exchanger used as recuperator for supercritical CO2 heat to power conversion systems

The paper presents a modelling methodology for Printed Circuit Heat Exchangers (PCHEs) in supercritical CO2 (sCO2) power systems. The PCHE model can be embedded in models of the full sCO2 power unit for optimisation, transient simulation and control purposes. In particular, the purpose of the study is to assess the potential and limitations of lower order models in predicting the overall heat transfer performance of PCHEs. The heat transfer processes in the channels of the PCHE recuperator are modelled in 1-D and 3-D using commercial software platforms. The results show that predictions from the two modelling approaches are in good agreement, confirming that the 1-D approach can be used with confidence for fast simulation and analysis of PCHEs. Using the 1-D approach, the model was validated against manufacturer’s data for a 630 kW PCHE recuperator, and subsequently used to simulate the performance of the heat exchanger at design and off-design operating conditions. Performance maps produced from the simulations, enable visualization of the influence of operating conditions on the heat transfer performance and pressure drops in the heat exchanger. Dynamic simulations under transient operating conditions show that the thermal expansion of the working fluid caused by a fast reduction in density and increase in pressure in the system, can be a concern, requiring careful management of the start-up process to avoid sudden changes in temperature and thermal stresses.

Evolutionary Dynamics in the RNA Bacteriophage Qβ Depends on the Pattern of Change in Selective Pressures.

The rate of change in selective pressures is one of the main factors that determines the likelihood that populations can adapt to stress conditions. Generally, the reduction in the population size that accompanies abrupt environmental changes makes it difficult to generate and select adaptive mutations. However, in systems with high genetic diversity, as happens in RNA viruses, mutations with beneficial effects under new conditions can already be present in the population, facilitating adaptation. In this work, we have propagated an RNA bacteriophage (Qβ) at temperatures higher than the optimum, following different patterns of change. We have determined the fitness values and the consensus sequences of all lineages throughout the evolutionary process in order to establish correspondences between fitness variations and adaptive pathways. Our results show that populations subjected to a sudden temperature change gain fitness and fix mutations faster than those subjected to gradual changes, differing also in the particular selected mutations. The life-history of populations prior to the environmental change has great importance in the dynamics of adaptation. The conclusion is that in the bacteriophage Qβ, the standing genetic diversity together with the rate of temperature change determine both the rapidity of adaptation and the followed evolutionary pathways.

ANALYSIS OF THE POSSIBILITY OF REPLACING THE ВНІІНП -286M LUBRI-CANT ON THE AERO SHELL GREASE 33 IN THE HIGH LIFT DEVICES OF THE WING OF THE AN-FAMILY AIRCRAFT

The problem of ensuring the lubrication of gearboxes of high lift devices in aircraft of the AN family is considered. Modern aircraft are equipped with a large number of electromechanical elements with the possibility of remote control. In all these cases, there is a mechanical component, and accordingly, the relative movement of one element relative to another, all this causes the presence of friction processes in these mechanical systems. To ensure reliable, continuous, long-term operation of friction pairs using lubricants. In the work of aeronautical engineering is a special feature - work in different operating conditions. These can be critical conditions associated with node overloading, sudden changes in temperature, the use of low-quality lubricant. In modern conditions, the issue of the quality of materials for the production and maintenance of aeronautical engineering is not at a high level. First of all, this is due to improper transportation, storage, reloading and refilling of lubricant. Under these conditions, lubricants are able to accumulate moisture. This phenomenon leads to watering of the lubricant, and, accordingly, changes in the physicochemical properties of lubricants due to their watering. All this leads to increased wear of parts of the units, as well as to an early replacement of the lubricant when it is flooded, which significantly increases operating costs. In turn, analysis of the effect of different water concentrations on anti-wear and anti-friction properties of lubricants considered in the work, showed that the use of Aero Shell Grease 33 lubricant reduces wear of 30ХГСА steel (leading and lagging surfaces), regardless of water concentration ЕРА ВНІІНП -286M. The state of use of the lubricant is analyzed to ensure reliable operation of the wing mechanization gearbox. The correct approach when choosing a lubricant is quite complicated and important. It is proposed to replace the ВНІІНП -286M lithium grease with Aero Shell Grease 33. The effect of different water concentrations on the antiwear and antifriction properties of lithium greases is analyzed.

Experimental and numerical study of water spray system for a fire event in a confined and mechanically ventilated compartment

SummaryThe present work addresses the application of a water spray system in case of a fire event in large‐scale experiments for nuclear safety issues. It focuses on the interaction between a water spray system and a stratified smoke layer due to a pool fire in a mechanically ventilated enclosure. This study is supported by a set of four large‐scale tests and one numerical simulation with a 3D CFD software, named CALIF3S/ISIS, and developed by the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN). The modelling used in this paper is based on an Eulerian‐Lagrangian approach. The fire tests are performed in a 165 −m3 mechanically ventilated single room. The fire is a lubricant oil pool fire of about 400 kW. The ventilation flow rate is 2550 m3.h−1 and corresponds to a renewal rate of 15.5 h−1. The spray nozzles are deluge and sprinkler type. The test parameters are the water flow rate, the time of activation, and the duration of activation. Based on the large‐scale experiments and the numerical simulation, four typical physical mechanisms have been enlightened. The first one corresponds to the cooling of the gas phase that is the straightforward consequence of the heat transfer exchange between the water droplets and the surrounding gas. The second effect is the process of gas mixing and homogenization induced by the water spraying system. The gas concentrations (O2, CO2) in the upper and lower parts of the room tend to the same level. The third effect is the significant increase of the fire heat release rate (HRR), up to 25 %, when the water spray is activated. Then, the last noteworthy effect is the occurrence of gas pressure peaks when the water spray is activated or shut off, consequence of the sudden change of the gas temperature. The processes of gas cooling and fire HRR increase are showed to be the main causes of these variations of gas pressure.

THE INFLUENCE OF HYPOTHERMIA ON THE PARAMETERS OF THE ELECTROMYOGRAM AT LOW MUSCLE TONE STATE

Effects of sudden changes in temperature on the general state of functional systems of the body can be assessed by the effects of local cold expesure on the neuromuscular system. Aim: to study electromyograms of the retracting muscle flexor of the little finger with weak static muscle tension (F1 = 50 N) during cold exposure. Methods. Altogether, 15 men aged 20-27 years participated in the study. We used one of the stochastic methods in the form of calculation of matrices of paired comparisons of electromyogram samples as an indicator of k pairs of matches of samples. Matrices of paired comparisons of samples were calculated for each test subject at a static voltage F1 = 50 N before and after local cold exposure. At the same time built a quasi-attractor dynamics, the behavior of x(t) and determined area of the quasi-attractor. In the end, the analysis of the state of the muscles of the subjects in the development of static force F was carried out on the basis of a comparison of the area of quasi-attractors in the form of S. Results. With weak (F1 = 50 N) static force after cold exposure, the area of quasi-attractor increased by 2.5 times, while in the matrices of paired comparisons of samples after local cold exposure, the number of matches of pairs of samples increased from 8 to 14. Conclusion: the regularities of changes in the number of matches of pairs of samples k in the matrices of paired comparisons with changes in the static force and under the influence of local cold exposure were revealed; statistically significant differences were found for such samples k and S before and after hypothermia.

Characterization of temperature difference between the neighbouring days in China and its potential driving factors

Understanding the temperature difference between neighbouring days (TDN) is beneficial for reducing the harmful impacts of sudden temperature changes on human health and establishing adaptation policies considering global TDN characteristics. This study analyses the spatiotemporal characteristics of TDN in Mainland China on the basis of the daily observation data from 839 stations in 1961–2017. Results show that the TDN increases with the latitude from south to north. Meanwhile, TDN in winter is higher but lower in summer. These characteristics potentially arise from the variations in solar elevation angle, that is, a decreased TDN corresponds to an increased solar elevation angle in most parts of China. Areas with high solar elevation angle are usually characterized by low TDN, which implies that temperature is stable for neighbouring days in areas with high solar elevation angle. Moreover, the variation rate of the annual mean TDN is negative in most parts of China, especially in the north. These findings are expected to provide an overview of the spatiotemporal characteristics of TDN and support future studies on the impacts of TDN variations on regional environmental changes.

Effect on horizontal pressure in steel silos evoked by a sudden change in the ambient temperature

The Eurocode EN 1991-4 includes provisions which refer to the stress increase in structural members evoked by the temperature differential between the silo wall and the stored material. This Eurocode presents in the clause 5.6 the formula on increase of horizontal pressure as a result of the temperature differential between the silo wall and the stored material. The derivation of this formula by two different approaches was presented in this work. Theoretical considerations were exemplified by chosen examples showing the effort increase of the silo wall as a result of a sudden cooling of the silo wall. Silos of different slenderness and of different coefficients of wall friction were considered. The performed analysis has revealed that in every case the formula based on the plane strain assumption gave higher values of the horizontal pressure increase. Calculations have revealed that the sudden temperature drop of the silo wall by 20 °C can lead even to the 35 % increase of horizontal pressure. Results of analytical solutions were supplemented by numerical simulations which have confirmed correctness of the formulae derived in this work. The alternative formula based on the plane strain assumption should replace the recommended in Eurocode formula based on the plane stress case.

COMPUTATIONAL SIMULATION OF HYGROTHERMAL PERFORMANCE OF PLASTERS WITH ENHANCED MOISTURE ACCUMULATION CAPABILITY

Series of computational simulations are performed within this paper in order to investigate the hygrothermal response of several plasters with enhanced accumulation properties. The newly developed plasters are modified from the reference sample by adding various amounts of super absorbent polymers. Then, the basic physical, thermal and hygric properties are determined in the laboratory conditions and subsequently used as an input parameter in the computational simulations. The simulation output showed that even a thin layer of exterior and interior plaster may significantly affect the hygrothermal performance of the entire building envelope due to increased moisture and thermal buffering of the surface layers. Differences in relative humidity distribution across the studied construction were generally up to 10 % between individual plasters, differences of temperature distribution were mostly negligible, except for the cases when sudden changes of surface temperature were observed. Then, the thermal buffering was evident and the differences of temperature in surface layers were up to 4°C among studied plasters.

What Makes the Wood? Exploring the Molecular Mechanisms of Xylem Acclimation in Hardwoods to an Ever-Changing Environment

Wood, also designated as secondary xylem, is the major structure that gives trees and other woody plants stability for upright growth and maintains the water supply from the roots to all other plant tissues. Over recent decades, our understanding of the cellular processes of wood formation (xylogenesis) has substantially increased. Plants as sessile organisms face a multitude of abiotic stresses, e.g., heat, drought, salinity and limiting nutrient availability that require them to adjust their wood structure to maintain stability and water conductivity. Because of global climate change, more drastic and sudden changes in temperature and longer periods without precipitation are expected to impact tree productivity in the near future. Thus, it is essential to understand the process of wood formation in trees under stress. Many traits, such as vessel frequency and size, fiber thickness and density change in response to different environmental stimuli. Here, we provide an overview of our current understanding of how abiotic stress factors affect wood formation on the molecular level focussing on the genes that have been identified in these processes.

Mathematical Modeling for Hospitalization due to Temperature Variations

Sudden changes in temperature occur due to ecological disturbances which results into global warming, volcanic eruption, depletion of ozone layer etc. This has become a crucial environmental and social issue all over the world. Changes in temperature influences transmission pattern for several diseases which leads to increase in the death rate. This research focusses on hospitalization due to temperature variations. Here, class of exposed individuals are divided into two types: asymptomatic individuals who do not show any symptoms and symptomatic individuals which shows symptoms. The indoor or outdoor medications are the remedial steps to get cured. Severe dehydration, blood pressure fluctuations etc. need hospitalization. The rate at which the individual gets hospitalized is scrutinized using SEIRS - model. The system of non-linear ordinary differential equations is formulated for the given model and the reproduction number is then computed using next generation matrix method which connotes the recovery rate of an individual. Stability and numerical simulations are carried out.

Greenhouse Farming using IoT

The most frequent problems faced in Greenhouse Agriculture is pH changes, Watering and Temperature. Plants need light, carbon dioxide and mineral nutrients in order to produce food and grow. Water is supplied through substrate, and it contains dissolved mineral elements. The mobility of these nutrients is determined by pH. A pH reading is measurement of the acidity or basicity of solution. The goal of a greenhouse grower is to maintain stable pH over the life of crop. In greenhouses, in case of insufficient or poor ventilation of greenhouse, the crops may be attacked by diseases. There may be extreme and sudden temperature changes. Moreover, it is not good to have regular watering routine for crops in the greenhouse, but neither it is not good to let plants dry. Hence sunlight, moisture and pH of soil plays vital role in greenhouse agriculture. To overcome these problems an IoT device which can give suggestions about when to water, adjust pH and change lighting for plants in greenhouse to improve the production. The goal is to increase the yield and reduce the complexities in organic farming for the farmers.

Identification of groundwater exfiltration, interflow discharge, and hyporheic exchange flows by fibre optic distributed temperature sensing supported by electromagnetic induction geophysics

AbstractWater exchange across the sediment–water interface of streams impresses a characteristic thermal pattern at the interface. The use of fibre optic distributed temperature sensing at the sediment–water interface in a small sand‐bed stream identifies such temperature patterns. Groundwater and interflow can be differentiated based on the temporal evolution of temperature patterns. Additionally, sudden temperature changes at the sediment–water interface observed during the transit of floods enable spatial identification of local up and downwelling. Electromagnetic induction geophysics can detect subsurface texture structures that support groundwater–surface water exchange. Our results show that areas of permanent temperature anomalies observed with fibre optic distributed temperature sensing match areas of comparatively homogeneous electrical conductivity. This indicates groundwater discharge and enables differentiating groundwater discharge from interflow and local downwelling.

Phytoplankton adaptation in ecosystem models

We compare two different approaches to model adaptation of phytoplankton through trait value changes. Both consider mutation and selection (MuSe) but differ with respect to the underlying conceptual framework. The first one (MuSe-IBM) explicitly considers a population of individuals that are subject to random mutation during cell division. The second is a deterministic multi-compartment model (MuSe-MCM) that considers numerous genotypes of the population and where mutations are treated as a transfer of biomass between neighboring genotypes (i.e., a diffusion of characteristics in trait space). Focusing on the adaptation of optimal temperature, we show model results for different scenarios: a sudden change in environmental temperature, a seasonal variation and high frequency fluctuations. In addition, we investigate the effect of different shapes of thermal reaction norms as well as the role of alternating growth and resting phases on the adaptation process. For all cases, the differences between MuSe-IBM and MuSe-MCM are found to be negligible. Both models produce a number of well-known and plausible features. While the IBM has the advantage of including more mechanistic (i.e., probabilistic) processes, the MCM is much less computationally demanding and therefore suitable for implementation in three-dimensional ecosystem models.

Extended Microprestress-Solidification Theory for Long-Term Creep with Diffusion Size Effect in Concrete at Variable Environment

The solidification theory has been accepted as a thermodynamically sound way to describe the creep reduction due to deposition of hydrated material in the pores of concrete. The concept of self-equilibrated nanoscale microprestress has been accepted as a viable model for marked multi-decade decline of creep viscosity after the hydration effect became too feeble, and for increase of creep viscosity after any sudden change of pore humidity or temperature. Recently, though, it appeared that the original microprestress-solidification theory (MPS) predicts incorrectly the diffusion size effect on drying creep and the delay of drying creep behind drying shrinkage. Presented here is an extension (XMPS) that overcomes both problems and also improves a few other features of the model response. To this end, different nano- and macro-scale viscosities are distinguished. The aforementioned incorrect predictions are overcome by a dependence of the macro-scale viscosity on the rate of pore humidity change, which is a new feature inspired by previous molecular dynamics (MD) simulations of a molecular layer of water moving between two parallel sliding C-S-H sheets. The aging is based on calculating the hydration degree, and the temperature change effect on pore relative humidity is taken into account. Empirical formula for estimating the parameters of permeability dependence on pore humidity from concrete mix composition are also developed. Extensive validations by pertinent test data from the literature are demonstrated.

Time-Resolved Temperature-Jump Measurements and Theoretical Simulations of Nanoscale Heat Transfer Using NaYF4:Yb3+:Er3+ Upconverting Nanoparticles

We introduce for the first time a time-resolved temperature measurement technique which relies on temperature-jump luminescence thermometry using NaYF4:Yb3+:Er3+ upconverting nanocrystals. This new time-resolved technique is based on optical thermometry using upconverting nanoparticles (UCNPs) and does not have to infer temperature from changes in the optical properties of the heater or surrounding local environment. We have prepared gold-decorated UCNPs that function as a dual single-heater thermometer system. We measure the time-resolved temperature jump from nanocrystal clusters and compare our results to simulated thermal transfer data generated using finite element methods. The simulated data show that temperature dissipation follows a power law where the temperature change is inversely related to time. This result agrees with a thermal diffusion model where a semi-infinite medium is exposed to a sudden temperature change at its surface, but the simulated results do not agree that the heat transfer p...

A fractal derivative model for snow’s thermal insulation property

Snow is of porous structure and good thermal insulation property. A fractal derivative model is established to reveal its thermal property, it is extremely high thermal-stable, the whole snow will not be affected much by the sudden environmental temperature change. A simple experiment is carried out to verify the theoretical finding, and the result is helpful to design advanced materials mimicking the snow structure.

Experimental investigation on a loop thermosyphon with three evaporators: Unique startup and oscillation phenomena

Loop thermosyphon with multiple evaporators has tremendous potential in applications that involve multiple heat sources. In this paper, a loop thermosyphon with three evaporators is investigated experimentally. Unique phenomena of startup and oscillation compared with common loop thermosyphons are reported. In the startup process, a unique phenomenon called “sudden temperature change” is found. This phenomenon occurs in a temporary state in the startup, when the temperature differences between the evaporators without heating power and with heating power reach certain range (−2.6 °C to 0.8 °C in this experiment). In the quasi-steady state, an oscillation map which shows the range when oscillation occurs is obtained. Compared with only one evaporator with heating power, simultaneous heating on multiple evaporators reduces the oscillation frequency, enhances the oscillation amplitude and sometimes makes it irregular, due to the interaction between the evaporators. Also, for every two adjacent evaporators, the phases of oscillation are almost opposite.

Temperature-driven response reversibility and short-term quasi-acclimation of Daphnia magna.

Analysing the effect water temperature has on Daphnia magna is essential in anticipating the impact climate change will have on this freshwater zooplanktonic keystone species. While many authors have followed this line of research, few have covered an extensive temperature range or complex temperature change scenarios. Global warming is mostly associated with increased extreme temperature events, such as heat waves, as well as earlier and more intense thermal stratification. Both of these events may directly influence D. magna fitness, especially in those populations performing diel vertical migration (DVM). We analysed the effect water temperatures, ranging from 11 to 29°C, have on the filtration capacity (FC) of D. magna, to anticipate the effects of acclimation, temperature change rate (TCR) and potential reversibility of responses to such conditions. Results show that sudden temperature changes have an immediate negative impact on the FC of D. magna and is more severe at higher temperatures and higher TCRs. However, D. magna individuals have shown themselves to be capable of quasi-acclimating to temperatures ranging from 11 to 25°C in around a week and achieving much higher FCs; albeit never reaching the optimal FC achieved at 20°C. That said, 29°C is lethal for D. magna individuals within approximately five days. Finally, non-optimal temperature acclimated individuals can recover maximal FC within 2–4 days of the optimal long-term acclimation temperature (20°C) being re-established, thus proving temperature responses to be reversible.

De novo transcriptome analysis of differentially expressed genes in the liver of pampus argenteus under temperature stress

Pampus argenteus is an aquatic cold-blooded animal, and its growth and survival are greatly affected by ambient temperature. During aquaculture, a sudden change in water temperature may be caused by climate change or other human factors, resulting in acute temperature stress. In this study, de novo transcriptome sequencing technology was used to analyze changes in the gene expressions in the liver of P. argenteus under temperature stress to understand the mechanisms of temperature regulation in P. argenteus. The results showed that 72447398, 69534310, 63698204, 78876728 and 53969050 clean reads were obtained from four cDNA libraries (A: 27°C (control group), B: 22°C and 6 h, C: 32°C and 6 h, D: 22°C and 12 h, E: 32°C and 12 h) of the P. argenteus by Illumina sequencing technology. In A\B, A\C, A\D and A\E pairwise comparison, 353, 431, 1303 and 343 differentially expressed genes (DEGs) were detected, respectively. Of these genes, 67 genes were identified among all the pairwise comparisons as the common DEGs. Four genes related to metabolic adaption to temperature were randomly selected to validate the DEGs results by real time PCR. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis indicated some vital genes and pathways associated with metabolism in response to temperature challenge. These results will help us to understand the molecular mechanism underlying temperature regulation in P. argenteus and provide a theoretical basis for the study of related molecular mechanisms in fish under temperature stress.

Interface Separation Detection of Concrete-Filled Steel Tube Using a Distributed Temperature Measuring System

In recent years, concrete-filled steel tubular (CFST) bridges have been widely used in bridge construction. However, interface disengaging is one of the bridges’ most common defects. It affects not only the confinement of the steel tube to the core concrete, but also the bearing capacity and the structure durability. In order to solve the problem of disengaging at the interface of steel tube-confined concrete and ensure the integrity of the structure, a new method based on a distributed temperature detection system is proposed to identify disengaging at the interface between steel tube and concrete. Through the analysis of experiments and numerical simulation, it was found that when the structure surface was heated, the temperature of the void area was higher than that of the solid area. The temperature of the maximum void height was the highest, the temperature increase rate was the fastest, and the cooling rate was the slowest. The boundary of the void suffered from sudden changes in temperature. The more serious the void, the greater was the temperature difference between the void and the solid. After changing the heating direction, the temperature distribution could still be identified. This study achieved simplicity and efficiency with respect to the detection of interface separation.