Reference Temperature Research Articles

Geleneksel bitümlü sıcak karışım üstyapı tabakalarının dinamik rijitlik modülünün tahmini ve marshall dizayn yöntemi verileriyle karşılaştırılması

The mechanistic and empirical design method of bituminous hot mixes, which is tried to be applied in our country, is allowed to estimate the dynamic stiffness modulus for second and third level projects. It is thought that examining the relationship between the dynamic stiffness module, which is one of the most important mechanical properties of bituminous hot mix, and Marshall design data, which is widely used in our country, will contribute to the designers' analysis of coating performance and life cycle costs. In this study, the relationship of the dynamic stiffness modules estimated by the 1999 Witczak Model with the design data of the aggregate produced from the limestone quarry and the bituminous base, binder, abrasion mixtures at the temperatures and frequencies determined according to the bitumen change of Marshall design was evaluated. In order to determine the change of dynamic modulus of the mixtures according to the loading time, the master curves of the layer mixtures were drawn at the optimum bitumen reference temperature of 21.1 oC. It has been determined that the maximum grain size and temperature change are more effective in the estimated dynamic stiffness modules of the mixtures, changes can be made in the superstructure layer thicknesses according to the change in loading time within the project, and the dynamic modulus estimated in the optimum bitumen is approached with some bitumen reduction in bituminous foundation and binder mixtures.

Closed-form modeling of matric suction in unsaturated soils under undrained heating

Matric suction is an important parameter controlling the hydro-mechanical behavior of unsaturated soils. Several emerging geotechnical and geoenvironmental applications involve unsaturated soils subject to undrained heating. This study presents a closed-form model to determine the matric suction in unsaturated soils under undrained heating. The final expression is derived based upon the Young–Laplace capillary principle and only needs the enthalpy of immersion at the reference temperature and as primary input parameters. Under undrained (constant water) conditions, the closed-form model incorporates the impact of temperature on matric suction by considering the temperature dependency of the liquid–gas interfacial tension, the contact angle of the solid–liquid–gas interface, and the enthalpy of immersion. The model is validated against six sets of experimental data for clay, silt, and sand, reported in the literature. The results show a very good agreement between measured and predicted values for all soil types over a wide range of temperatures. The matric suction monotonically decreases with temperature under undrained heating. The proposed closed-form model can readily be employed in numerical and analytical analyses to simulate the undrained behavior of unsaturated soils under elevated temperatures.

Heat traveling waves in rigid thermal conductors with phase lag and stability analysis

Recently, a model equation that describes nonlinear heat waves in a rigid thermal conductor has been derived. The system of the governing equations for temperature and heat flux is nonlinear. The objective of the present work is to find a variety of traveling wave solutions of this system of equations in the whole space. This is achieved by implementing the unified method. The obtained solutions are evaluated numerically and represented graphically. The behavior of these solutions is investigated, where it is shown that the temperature and the heat flux attain steady states in space, but increase with time. The effects of the characteristic length, time, heat flux, and reference temperature are studied via some material data. It is shown that the solutions may have the form of solitary wave, soliton, or soliton with double kinks. It is observed that the heat flux in the material is negative, this reflects the fact that heat flux is in the opposite direction of the normal vector to the material surface on which it is evaluated. The steady state solution of the considered model equation is studied. It is found that the stability of the solutions depends significantly on the wave number.

Dynamic snap-through of functionally graded shallow arches under rapid surface heating

In this paper, dynamic buckling response of a shallow arch constructed from functionally graded materials under thermal shock is investigated. It is assumed that one surface of the beam is subjected to sudden temperature elevation while the other surface is kept at reference temperature. To solve the one-dimensional Fourier heat transfer equation, Crank–Nicolson numerical method along with the central finite difference method are employed. In order to obtain the strain–deflection relations, Donnell theory of shallow arches with von Kármán simplifications are used. The governing equations are acquired based on well-known Hamilton’s principle that are converted to a set of non-linear algebraic equations using the Ritz method. Since the governing equations are non-linear equations, the Newton–Raphson method is applied and after that temporal evolution of displacements are obtained employing the Newmark time marching scheme. In the final stage, a theory to estimate the buckling load is required, which is the Bodiansky–Roth criterion in this research. To validate the formulation and solution method of this project, this work is compared with previous studies and good agreement is obtained. In addition, impacts of power law index, arch thickness, geometrical parameters, and temperature dependency on the dynamic buckling temperature are reported in this study.

Non-optimum ambient temperature may decrease pulmonary function: A longitudinal study with intensively repeated measurements among asthmatic adult patients in 25 Chinese cities.

Non-optimum ambient temperature has not been widely perceived as an important environmental risk factor for asthma, and the association between ambient temperature and pulmonary function is rarely explored. Our study aimed to investigate the associations between non-optimum ambient temperature and pulmonary function among asthmatic adult patients. We performed a longitudinal study among 4,992 eligible adult asthmatic patients in 25 cities of China from 2017 to 2020. The patients were required to complete pulmonary function test every day in the morning and evening. Linear mixed-effects models and distributed lag non-linear models were used to evaluate the associations between ambient temperature and pulmonary function. We evaluated 298,396 records of pulmonary function tests. We found inversely J-shaped exposure-response relationship curves for ambient temperature and pulmonary function. The effects of extreme low temperature occurred at lag 0h and vanished at lag 72h (almost 3days). Compared with referent temperature (29.5 °C), extreme low temperature (-9.4 °C) was associated with decreases of 60.4mL in FEV1, 299.7mL/s in PEF, and 101.5mL in FVC. Extreme high temperature (34.2 °C) was associated with decreases of 26.0mL in FEV1, 35.8mL/s in PEF, and 23.4mL in FVC. Patients of male, overweight, and elder ages were vulnerable populations, and cold effects were more prominent in the south and in areas without central heating. Both extreme low and high ambient temperatures were associated with decreased pulmonary function in adult asthmatic patients. The effect could last for almost 3days and low temperature was more harmful.

The performance evaluation for thermal protection of turbine vane with film cooling and thermal barrier coating

• An expression of temperature-independent overall cooling effectiveness is obtained. • The external convective heat transfer is effected by the internal cooling flow. • Increasing convective heat transfer can increase overall cooling effectiveness. • Four parameters need to be similar when conducting heat transfer experiments. When conducting wind tunnel heat transfer test to evaluate the cooling performance of the turbine, it is difficult and costly to simulate the extremely high temperature gas of the real working conditions, and small temperature difference and room temperature test is usually used instead. In order to evaluate the cooling performance under real working conditions from the experimental results at room temperature, the corresponding evaluation method needs to be studied. In this paper, a turbine vane with film cooling and thermal barrier coating (TBC) is used as the study object. By introducing an improved driving temperature and adopting one-dimensional heat transfer analysis, an improved analytical expression of overall cooling effectiveness, which is independent of temperature, is derived and analyzed. Through numerical calculation, the overall cooling effectiveness defined by different reference temperatures are compared. The results show that the heat transfer of the turbine vane with film cooling and TBC is complicated. The influence of the internal cooling should be considered when calculating the external convective heat transfer. The temperature-independent overall cooling effectiveness on the TBC surface and the superalloy surface are obtained, respectively. The improved overall cooling effectiveness is more sensitive to the thermal resistance of the superalloy compared with the thermal resistance of the TBC. The overall cooling effectiveness can be improved by increasing the internal or external convective heat transfer coefficient. In order to obtain an accurate overall cooling effectiveness (dimensionless wall temperatures), it is necessary to satisfy similarities of four dimensionless parameters, including the Biot numbers ( B i TBC , B i w ), the ratio of external and internal convective heat transfer coefficients ( h e / h i ) and the ratio of gained convective heat transfer coefficient and external convective heat transfer coefficient ( h e , i / h e ).

Structural analysis of solid rocket motor with effects of viscoelastic Poisson's ratio

The new measured viscoelastic Poisson's ratio (VPR) is introduced to investigate the effect of its variation on structure integrity analysis of solid rocket motor. A developed relaxation constitutive model considering VPR is utilized to implement in the finite element code MSC.Marc. Cooling analysis and ignition pressure loading case are designed to analyze the effects along the inner surface of propellant grains. Results show that the little change of the VPR including equilibrium Poisson's ratio (ePR) and reference temperature will affect the output of simulation, and the same up variation of the VPR has relatively less effect on the analysis than the elastic one. Furthermore, the up variation of viscoelastic Poisson ratio will disturb the distribution of strain and stress along the inner surface of propellant grains seriously while the elastic one won’t.

Solving transient coupled conductive and radiative transfers in porous media with a Monte Carlo Method: Characterization of thermal conductivity of foams using a numerical Flash Method

This paper presents a single Monte-Carlo algorithm used to solve transient conductive and radiative heat transfers in three-dimensional porous media. The complete methodology presented step by step herein enables practical and efficient study of geometrical and multiphysical complexities. The code was validated against results obtained by commercial software, analytical and semi-analytical solutions. Computation times were found to be greatly reduced when radiative transfer is predominant compared with those obtained using a deterministic solver. This kind of approach allows a probe calculation in the frame of linear thermal transfers and is well suited for the numerical characterization of heterogeneous media. In this work a numerical flash method was reproduced and enabled us to evaluate the effective total conductivity of the equivalent homogenized medium. The influence of various parameters such as porosity, size of the unit cell, bulk conductivity of the solid phase, reference temperature and emissivity was studied for a stack of Kelvin cells. This tool enables the parametric investigation of geometric and thermal properties. The results are in good agreement with those of the literature.

Fluid-thermo-structural response of actively cooled scramjet combustor in hypersonic accelerating-cruise flight

This paper presents a three-dimensional transient fluid-thermo-structural study of an actively cooled sandwich panel under hypersonic accelerating-cruise flight conditions. The thermo-structural loads are estimated using a high-speed gas-dynamic flow model combined with Eckert's reference temperature method. The thermal safeguard capacity with endothermic fuel-based active cooling shows design optimization scope compared to the passive system. A passive system has to survive excessively high temperatures with a less severe thermal gradient over the panel thickness and a high heat leakage into the structural interior or back wall. The actively cooled system with fuel develops significant panel bending due to a through-thickness thermal gradient in the cooling channels. For a Mach 7 flight, an actively cooled system reduces the bending deformation by 90% and improves the thermal safeguard capacity by 70% compared to a passive approach. Active cooling can effectively control the excessive thermo-structural deformation and fuel heating below its cracking temperature to improve combustion. Our parametric design study indicates the influence of fuel as a coolant for increasing combustion efficiency and the associated complexity and trade-off in the heat transfer and thermo-structural deformation behavior. This transient response under hypersonic accelerating-cruise flight conditions requires a careful review of the scramjet engine thermo-structural design philosophy. The design approach has applications in bodies encountering highly transient thermo-structural loads with differently purposed fuels/coolants.

Contributions of ambient temperature and relative humidity to the risk of tuberculosis admissions: A multicity study in Central China

BackgroundAs a communicable disease and major public health issue, many studies have quantified the associations between tuberculosis (TB) and meteorological factors with inconsistent results. The purpose of this multicenter study was to characterize the associations between ambient temperature, humidity and the risk of TB hospitalizations and to investigate potential heterogeneity. MethodData on daily hospitalizations for TB, meteorological factors and ambient air pollutants for 16 cities in Anhui Province were collected from 2015 to 2020. A distributed lag nonlinear model (DLNM) was performed to obtain the estimates of meteorological-TB relationships by cities. Then, we used the multivariate meta-regression model to pool the city-specific estimates with air pollution, demographic indicators, medical resource and latitude as potential modifiers to explore the sources of heterogeneity. Finally, we divided the whole province into three regions to validate the meteorological-TB relationships by regions. ResultsThe overall pooled temperature-TB association presented an approximate S-shaped curve, with relative risk (RR) peaking at 5 °C (RR = 1.536, 95% CI: 1.303–1.811) compared to the reference temperature (27 °C). Lag-response curve suggested that low temperature exposure increased the risk of TB hospitalizations at lag 0 and 1 day (lag0 day: RR = 1.136, 95% CI: 1.048–1.231, lag1 day: RR = 1.052, 95% CI: 1.023–1.082). However, the overall exposure-response curve between relative humidity and TB showed almost horizontal line with reference relative humidity to 78%. The residual heterogeneity ranged from 27.1% to 36.9%, with air pollution, latitude and medical resource explained the largest proportion. ConclusionWe found that low temperature exposure is associated with an acute increased risk of TB hospitalizations in Anhui Province. The association between temperature and TB admission varies depending on air pollution, latitude, and medical resources. Since the effect of short-term exposure to humidity is not significant, further studies are supposed to focus on the long-term effect of humidity.

Temperature-dependent creep aging behavior of 2A14 aluminum alloy

The creep deformation behavior, aging hardening response and microstructure evolution of 2A14 aluminum alloy (Al-4.81wt%Cu-0.66wt%Mg-0.97wt%Si) at different temperatures have been systematically investigated by creep test, tensile test, transmission electron microscopy and differential scanning calorimetry. The results show that the total creep strain and steady-state creep rate significantly increase with increasing temperature in the range of 408 K–458 K, while the creep behaviors at the optimum aging temperature of 433 K have shortest primary creep stage and lowest stress sensitivity. Pinning of dislocations by the dense and fine Q′ and θ′ phases precipitated in the alloy creep-aged at 433 K, which contributes to obtaining the best mechanical properties. Also, the primary creep deformation mechanism at different aging temperatures has been discussed. A reference temperature describing the degree of the interaction between aging precipitates and dislocations is introduced into the hyperbolic-sine creep model. The creep strain predicted through the temperature-dependent creep model is in good agreement with the experimental data. The research can provide theoretical support for the temperature-varying creep age forming application in the 2A14 aluminum alloy components.

Adaptive thermal comfort model based on field studies in five climate zones across India

Indian residences are vulnerable to heat-driven discomfort amid the mounting prevalence of weather extremes, residential design and construction practices, and densifying urbanscapes. Therefore, it is vital to understand the thermal comfort characteristics of nationwide residences. This study proposes an adaptive thermal comfort model based on yearlong field surveys in eight cities located across five climate zones of India – the India Model for Adaptive Comfort - Residential (IMAC-R). The model prescribes the operative temperature bands for 80% and 90% thermal acceptability in correlation with the outdoor reference temperature, applicable to mixed-mode (MM) and naturally ventilated (NV) residences.More than 80% of the Indian residential occupants experienced a neutral thermal sensation in the indoor operative range of 16.3–35 °C in response to a 5.5–33 °C variation in the 30-day outdoor running mean temperature. Comparing the proposed model with the PMV model revealed that the latter underpredicts the thermal adaptivity of Indian occupants. The model was also compared against its predecessor – India Model for Adaptive Comfort for Commercial Buildings (IMAC MM and NV), along with relevant global and regional thermal comfort models. On average, the neutral temperature prescribed by IMAC-R was warmer than the temperatures prescribed by IMAC MM and NV by 2.9 °C and 2.1 °C, respectively; it was also warmer than the temperature prescribed by the recent ASHRAE-55 and EN 16798-1 models by 2 °C and 0.3 °C, respectively. IMAC-R reserves the prospect of addressing the thermal comfort needs of the national population while paving the way for long-term energy savings and climate action.

Predicting Solute Diffusivity in Polymers Using Time-Temperature Superposition.

We demonstrate a novel application of the time-temperature superposition (TTS) principle to predict solute diffusivity D in glassy polymers using atomistic molecular dynamics simulations. Our TTS approach incorporates the Debye-Waller factor ⟨u2⟩, a measure of solute caging, along with concepts from thermodynamic scaling methods, allowing us to balance contributions to the dynamics from temperature and ⟨u2⟩ using adjustable parameters. Our approach rescales the solute mean-squared displacement curves at several temperatures into a master curve that approximates the diffusive dynamics at a reference temperature, effectively extending the simulation time scale from nanoseconds to seconds and beyond. With a set of "universal" parameters, this TTS approach predicts D with reasonable accuracy in a broad range of polymer/solute systems. Using TTS greatly reduces the computational cost compared to standard MD simulations. Thus, our method offers a means to rapidly and routinely provide order-of-magnitude estimates of D using simulations.

Reference temperature correction and dimensionless number analysis for heat transfer of supercritical CO2 in horizontal tubes

Researchers have extensively studied convective heat transfer of variable property fluids in tubes because of their different heat transfer characteristics to constant property fluids. However, the heat transfer correlations are often limited to small or large tubes or other limited conditions when the properties of fluids change dramatically, which may be due to inaccuracy definition of the reference temperature in average heat transfer coefficient (HTC) and incorrect understanding of dimensionless parameters in Nusselt correlation.As a typical case, this study numerically investigates the cooling heat transfer of sCO2 in horizontal tubes near the pseudo-critical point. Eight numerical models are compared with experimental results in the literature, and the Realizable k–ε model with enhanced wall treatment is best for predicting cooling HTC. A new definition of reference temperature for average HTC is proposed, which is more accurate than the traditional arithmetical average of inlet and outlet bulk temperature. Sensitivity analysis of HTC is carried out for heat transfer mechanisms. In addition, the definitions of dimensionless numbers in Nusselt correlation are analyzed, and more accurate definitions are proposed. Based on the conclusions, a newly developed Nusselt correlation with concise form shows excellent results with a Root Mean Square (RMS) error of 2.9% for 6.22 and 9.40 mm tubes. It can still maintain high accuracy when it is extrapolated to 4.15 and 14 mm tubes. The numerically derived correlation agrees well with the experimental results for 2–6 mm tubes in literature and can also be extrapolated to constant property cases.

Nonlinear dynamic thermometry: Temperature measurement using immobilized magnetic nanoparticles

We present a new method for measuring the temperature of magnetic nanoparticles that can also be adapted to immobilized particles. The Néel relaxation mechanism, which dominates the dynamic magnetization process of immobilized magnetic nanoparticles, can be used as an intermediate parameter in a sensing model to obtain temperature information. In this paper, we use the nonlinear response properties of magnetic nanoparticles to derive an analytical expression for the relationship between the phase of cubic susceptibility and temperature. We also consider dipole–dipole interactions and the dependence on field amplitude. Under experimental conditions at selected frequencies and field amplitudes, we compare temperature measurements of magnetic nanoparticles obtained with the proposed thermometry model with those obtained from existing nonlinear dielectric relaxation models. The results show that the temperature measurements obtained from the proposed model are closer to the reference temperatures in the temperature range of 308–353 K, with a standard deviation of less than 0.1 K in the temperature measurement. This new method successfully applies the nonlinear properties of magnetic nanoparticles to high-precision dynamic temperature measurements. It extends the applicability range of temperature measurement methods to conditions with strong interactions or large ac field amplitudes. This new method is expected to be applicable in anti-magnetic environments, for example, in biochemical temperature measurements of magnetically labeled cells in vivo.

On Residual Stresses and Reference Temperatures in Thermomechanical Simulations of Photovoltaic Modules Using the Finite Element Method

Thermomechanical simulation of photovoltaic (PV) modules using the finite element method (FEM) is a useful tool to evaluate module design features in terms of structural integrity, reliability, and durability. One of the main challenges in the numerical modeling of a PV module is the incorporation of residual stresses induced by the manufacturing process. Modeling assumptions and abstractions are necessary to limit the model complexity and reduce the computational time. However, oversimplifications and incorrect assumptions can lead to erroneous numerical results. Unfortunately, much simulation work still neglects process-induced stresses. This can lead to incorrect predictions of the stress–strain history and erroneous conclusions during the design process. Here, we review current modeling practices for incorporating process-induced stresses, and contrast numerical models that consider residual stresses with those that neglect them. We find that the simulation objective and available material properties dictate which process steps need to be modeled, and explore in depth the modeling of residual stresses induced by the lamination process. We demonstrate that a simplified cooldown procedure at the beginning of the simulation can increase the model accuracy and discuss appropriate choices for starting and reference temperatures in the finite element model.

Middle to Late Jurassic stable isotopes and element ratios of fossils from western India: Developing a reference temperature curve for northeastern Gondwana

The stable isotope (δ13C, δ18O) and element (Mg/Ca, Sr/Ca) composition of 374 well-preserved belemnites, bivalves, and brachiopods of the Kachchh and Jaisalmer basins in western India were used to reconstruct climatic changes in the Middle and Late Jurassic time interval. Absolute water temperatures reconstructed from δ18Oshell values depend on the used δ18Osea value and equation, but indicate a long-term temperature decrease of around 8–9 °C in the study area from the Bajocian to the Tithonian. Measured Mg/Ca ratios also point to decreasing temperatures, but additionally reflect species-specific factors and a lower Mg/Ca ratio of Jurassic seawater compared to today. The recorded cooling in western India agrees with previous results from neighbouring Madagascar and the Indian Himalayas and can be connected to a drift of Eastern Gondwana into higher latitudes. This palaeogeographic shift is accompanied by changes in sedimentation indicating an increasingly humid climate and in the composition of ecosystems reflecting increasingly cooler water temperatures. High-resolution stable oxygen isotope analyses of three oyster shells point to seasonal temperature changes of 4–5 °C in the Kimmeridgian. The recorded δ13C values reflect sea-level changes with a positive excursion in the Oxfordian connected to a major transgressive event. Sr/Ca ratios are observed to follow changes in global ocean chemistry.

Experimental Study of Mechatronic System On Control of Air Flow Temperature

In this work, an experimental study of a mechatronic system on control of airflow temperature has been conducted to identify the characteristics of the system. The system is tested by several reference temperatures from the monitor panel that programmed on the computer. The measurement of the output temperature by the sensor that is expected to be the same as the reference temperature is also displayed on the same monitor panel. While the measurement of AC power consumption by an actuator in the form of a heater is carried out by measuring the AC voltage on the heater during control. This voltage is measured with a computer-based oscilloscope. Based on the test results, with the initial temperature around the room temperature and reference temperature, the system time constant can be identified. This time constant value is obtained based on the output temperature graph which is identical to the first-order system response. Thus, this experimental study succeeded in identifying the characteristics of the system in the form of a time constant and the system was identified as identical to the first order system.

Adaptive Neural Network Global Nonsingular Fast Terminal Sliding Mode Control for a Real Time Ground Simulation of Aerodynamic Heating Produced by Hypersonic Vehicles

This paper presents a strategy for a thermal-structural test with quartz lamp heaters (TSTQLH), combined with an ultra-local model, a closed-loop controller, a linear extended state observer (LESO), and an auxiliary controller. The TSTQLH is a real time ground simulation of aerodynamic heating for hypersonic vehicles to optimize their thermal protection systems (TPS). However, lack of a system dynamic model for the TSTQLH results in inaccurate tracking of aerodynamic heating. In addition, during the control process, the TSTQLH has internal uncertainties of resistance and external disturbances. Therefore, it is necessary to establish a mathematical model between controllable α(t) and measurable T1(t). An ultra-local model of model-free control plays a crucial role in simplifying system complexity and reducing high-order terms due to high nonlinearities and strong couplings in the system dynamic model, and a global nonsingular fast terminal sliding mode control (GNFTSMC) is added to an ultra-local model, which is used to guarantee great tracking performance in the sliding phase and fast convergence to the equilibrium state in finite time. Moreover, the LESO is used mainly to estimate all disturbances in real time, and an adaptive neural network (ANN) shows a good approximation property in compensation for estimation errors by using a cubic B-spline function. The fitted curve of the wall temperature in the time sequence represents a reference temperature trajectory from the surface contour of an X-43A’s wing. The comparative results validate that the proposed control strategy possesses strong robustness to track the reference temperature trajectory.

Does cerebrospinal fluid pulsation affect diffusion-weighted imaging thermometry? A study in healthy volunteers.

Diffusion-weighted imaging (DWI)-based thermometry offers potential as a noninvasive method for measuring temperatures deep inside the human brain. However, DWI might be influenced by the pulsatile flow of cerebrospinal fluid (CSF). This study aimed to investigate the influence of such pulsations on DWI thermometry in healthy individuals. A total of 104 participants (50 men, 54 women; mean [± standard deviation] age, 44.2 ± 14.3years; range 21-69 years) were investigated. DWI-based brain temperature (TDWI ) was acquired at three speeds (maximum and minimum speeds of ascending flow and random timing at the cerebral aqueduct) of CSF pulsation using a 3-T magnetic resonance imaging scanner. Magnetic resonance spectroscopy (MRS)-based temperature (TMRS ) at the thalamus was also obtained as a reference standard for brain temperature. The three different CSF pulsatile flows were monitored by heart rate during the scan. The difference between reference temperature and brain temperature (ΔT = TDWI - TMRS ) along with the three CSF speeds were statistically compared using Student's matched pair t-test. No significant difference in ΔT was evident among CSF speeds (p>0.05). No significant linear correlation between ΔT and CSF flow speed at the cerebral aqueduct was observed. Using DWI thermometry with clinical acquisition settings, which utilizes mean values within thresholds, no effect of CSF pulsation speed was observed in the estimation of ΔT.