Instantaneous Temperature Changes Research Articles

Observation and analysis of the ultra-rapid cooling effect of cryoprotectant droplets on a sapphire surface

Cryopreservation has emerged as a promising technology to realize semipermanent storage of biomaterials widely used in assisted reproduction and cell therapy. A large portion of successful cryopreservation requires the combination of ultra-rapid cooling and appropriate low-toxicity cryoprotectant agents, which inhibits the formation of ice crystals that damages the cells lethally. Conventional approaches are not competent in accurately capturing high enough cooling rate and more importantly, not able to simultaneously track the instant appearance of the sample at a microscale level during the momentary cooling process. A rapid freezing device for the droplet sample study purpose was designed and developed, which is capable of visualization of the sample on a sapphire surface at a vitrification cooling rate over 104 K/min. The instantaneous temperature changes and the appearance of the cooling samples were recorded at the speed of 10 kHz and 2000 frames. Typical vitrification and crystallization processes were observed and analysed. Low concentrations of the CPA solution inhibited the formation and growth of the crystals, and resulted in the formation of layered ice, punctate ice and scattered small ice. The experimental results could contribute to a better understanding of the ultra-rapid cooling mechanism on cryoprotectant droplets.

Ignition mechanism of near α high temperature titanium alloy

The risk of titanium fire increases significantly with the development of future aero-engine, however, the burning mechanisms of titanium alloys remain uncertain. Therefore, the ignition behavior and mechanism of near α high-temperature titanium alloy are studied in this work by an integrated experiment method, including laser-oxygen concentration ignition method, infrared temperature measurement and observation of molten metal by high-speed camera. Based on this, the ignition boundary curve is determined and the ignition temperature of the alloy is found to decrease from 1595 to 1527 ℃ with the laser power increasing from 200 to 325 W and oxygen concentration increasing from 21% to 60%. The ignition microstructure is characterized by FIB and TEM to study the evolution of reaction products. Pores are found to form beneath the TiO<sub>2</sub> surface layer, which can be attributed to the instablity of TiO. The failure mechanism of protective oxide layer is further analyzed according to the thermal stress caused oxide layer damage model. When the temperature approaches the ignition temperature, which is below the melting point, the high vapor pressure of TiO leads to the formation of porous defects beneath the TiO<sub>2</sub> surface, thus accelerating the fracture and failure of the TiO<sub>2</sub> layer under thermal stress. It is revealed that critical conditions of temperature and instantaneous temperature change rate are needed to realize ignition. Based on this, an ignition model is further constructed to discuss the relationship among ignition temperature, laser power and oxgyen concentration. According to the experimental data fitting, the reaction activation energy of TA19 alloy during the ignition stage is calculated to be about 280 kJ/mol, and the function for calculating ignition temperature is given as follows: <inline-formula><tex-math id="M2">\begin{document}$ 1.2 \times {10^{10}}{{\mathrm{e}}^{\frac{{ - 280000}}{{R{T_{{\text{ig}}}}}}}}{c^{\frac{1}{2}}} + $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2.png"/></alternatives></inline-formula><inline-formula><tex-math id="M2-1">\begin{document}$ 0.52{P_{\mathrm{L}}} - 315 = 0 $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2-1.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2-1.png"/></alternatives></inline-formula>. This provides a theoretical reference for predicting the ignition temperatures of near α high temperature titanium alloy and other types of titanium alloys under complex airflow conditions in aircraft engines.

Thermal-Hydraulic Modeling of Oil-Immersed Motor Pump

The integrated design of the motor and axial piston pump eliminates the coupling structure, resulting in a compact and lightweight motor-pump structure. The challenge of motors overheating has always been a major concern. To address this issue, the hydraulic oil throughout the motor pump is utilized for cooling the high-speed motor, effectively improving the power density and heat dissipation capability of the hydraulic power unit. This integrated design approach has successfully resolved the significant issue of overheating motors, leading to enhanced performance of the hydraulic power unit. To address this concern, the entire motor pump’s oil is utilized to cool the high-speed motor. Consequently, the thermodynamic prediction of high-speed motor pumps has become increasingly important. In this study, the impact of motor heat generation on hydrodynamics is analyzed, and the heat transfer of the motor pump is investigated using the control volume method. Furthermore, thermodynamic models of hysteresis loss, eddy current loss, alternating current loss, churning loss, and throttling loss are established for the oil-immersed motor pump. The change in oil viscosity is also considered. The instantaneous temperature change rule of the oil within the oil-immersed motor pump is derived. Additionally, the influence of various working conditions such as pressure and speed on the temperature of the motor pump’s key node is examined. The experimental results indicate the accuracy of the thermodynamic calculation, and the significant effect of motor loss on the leakage temperature.

Fractional Dual-Phase-Lag Non-Fourier Heat Transfer in a Bimaterial with a Circular Interface Insulator

The transient temperature response of a bimaterial with a circular insulated interface region is studied under sudden heating or cooling. The time-fractional dual-phase-lag heat conduction model is adopted to simulate the non-Fourier effect. The problem is reduced to an initial-boundary value problem. The Laplace transform is applied to convert the problem to a mixed boundary value problem, and then the Hankel transform reduces it to a Fredholm integral equation. Special situations for asymptotic thermal behavior near the insulated circular edge and for the steady-state cases are discussed, respectively. The dynamic intensity factors of heat flux and temperature gradient near the insulated circular edge are computed numerically through Stehfest’s Laplace inversion transform technique. The influences of fractional order and relaxation times on the instantaneous temperature change are analyzed. The exact solution of temperature fields for the steady-state case is derived and displayed graphically. The wave-like diffusion behavior of the fractional dual-phase-lag model is interpreted.

Experimental-numerical method for evaluation of energy consumption in percussive drilling of granite

Most geothermal energy is found in hot and dry rock (HDR), and the total resources distributed at depths of 3-10 km are 20.9×106 EJ. Most HDR projects are developed in granite formations and understanding and control of the energy consumption in percussive drilling of granite is essential. Thus, the impact energy is dissipated in various processes including fracture of the granite, kinetic energy of the particles, and heat. This study presents a numerical-experimental method to evaluate the energy consumption in percussive drilling process. The method uses particle flow code (PFC2D) and experiments using a modified Hopkinson pressure bar system. Optical high-speed and infrared cameras were used to record the impact process during the dynamic drilling process. The velocity of fragments was estimated by the high-speed images and the instantaneous temperature change during the impact was observed from infrared images. Preliminary results are given in this study indicating that the proposed numerical and experimental methodologies can be used to investigate the energy consumption during percussive drilling. The preliminary results presented in this paper are part of a larger work in progress, and more work needs be carried out to obtain the energy consumption of the drilling process under different loading and boundary conditions.

Higher dose rate effect of 500-keV EB irradiation favoring free radical annealing and pre-oxidation of polyacrylonitrile fibers

In this study, free radicals in polyacrylonitrile (PAN) fibers induced by irradiation of 500-keV electron beam (EB) accelerator were investigated via electron spin resonance (ESR). Alkyl radicals and polyimine radicals were formed in PAN fibers after irradiation, and the relative content of the two free radicals changed with respect to the absorbed dose and dose rate. The effect of temperature on the relative content of the two radicals was investigated via analyzing the ESR spectra of alkyl radicals and polyimine radicals, and two parameters (PHR and δPHR) were set for evaluation. The value of δPHR was related to the temperature. The instantaneous temperature change in the PAN fibers during the irradiation process was inferred via analyzing the change in δPHR. Changes in the free radicals in irradiated PAN fibers during the stabilization process were also understood by ESR. Irradiation induced cross-linking and decreased the temperature of pre-oxidation for the PAN fibers. Increases in the dose rate of EB irradiation efficiently induced cross-linking and also led to pre-oxidation of the PAN fiber due to heat accumulation by EB irradiation. Radiation crosslinking significantly reduced the temperature required for peroxidation, and the trend was more evident at higher dose rates. For example, the PAN fiber irradiated to 400 kGy at a dose rate of 2 kGy/s was pre-oxidized at approximately 150 °C while the PAN fiber irradiated to 400 kGy at a dose rate of 13 kGy/s exhibited a darker color and was pre-oxidized at approximately 130 °C.

Marine heatwaves and optimal temperatures for microbial assemblage activity.

The response of microbial assemblages to instantaneous temperature change was measured in a seasonal study of the coastal waters of the western English Channel. On 18 occasions between November 1999 and December 2000, bacterial abundance was assessed and temperature responses determined from the incorporation of 3H leucine, measured in a temperature gradient from 5°C to 38°C. Q10 values varied, being close to 2 in spring and summer but were >3 in autumn. There was a seasonal pattern in the assemblage optimum temperature (Topt), which was out of phase with sea surface temperature. In July, highest 3H-leucine incorporation rates were measured at temperatures that were only 2.8°C greater than ambient sea surface temperature but in winter, Topt was ∼20°C higher than the ambient sea surface temperature. Sea surface temperatures for the adjacent English Channel and Celtic Sea for 1982-2014 have periodically been >3°C higher than climatological mean temperatures. This suggests that discrete periods of anomalously high temperatures might be close to, or exceed, temperatures at which maximum microbial assemblage activity occurs. The frequency and magnitude of marine heatwaves are likely to increase as a consequence of anthropogenic climate change and extreme temperatures may influence the role of bacterial assemblages in biogeochemical processes.

Photosynthetic responses to temperature of two tropical rainforest tree species from Costa Rica

Annual mean temperature increases will cause alterations in many ecosystem processes, which affect plants given their physiological sensitivity to temperature. That is closely related with plant growing conditions, genotype and plasticity. We studied the photosynthetic responses to instantaneous temperature changes and functional leaf traits in two tropical tree species associated with different successional positions, Zygia longifolia (early successional) and Dipteryx oleifera (late successional), in the northern lowlands of Costa Rica. We found that D. oleifera had thicker leaves and lower stomatal density, but similar specific leaf area to Z. longifolia. Maximum photosynthetic rate (Amax) and maximum RuBP saturate rate of carboxylation were higher in Z. longifolia than in D. oleifera. At 37 °C, only Z. longifolia reduced Amax and water use efficiency (WUE). But D. panamensis presented more severe effects on the quantum yield, respiration and light compensation points. The temperature response curves showed a similar optimum temperature near 27 °C for both species. On the other hand, the low and high temperature compensation points were different, with D. oleifera showing a narrower range than Z. longifolia. As a whole, we found two different strategies to avoid temperature stress: one reducing WUE (Z. longifolia), and the other one increasing metabolic rates (D. oleifera). However, the ability to withstand stressful situations may, in a larger context, negatively affect ecosystem water and carbon fluxes. Also, functional plasticity in response to temperature changes may relatively affect the ecosystem by causing long-term variations in their representation within the complex diversity mosaic of their forest habitats.

Dually tunable inverse opal hydrogel colorimetric sensor with fast and reversible color changes

Through opal-templated photopolymerization of copolymeric hydrogel consisting of 2-hydroxyethyl methacrylate, N-isopropylacrylamide, acrylic acid, and N,N′-methylenebis(acrylamide), a dually tunable inverse opal sensor by temperature and pH has been successfully synthesized. Temperature drop or pH increase induced hydrogel swelling and subsequent color changes of the sensor respectively due to lower critical solution temperature behavior of N-isopropylacrylamide and the altered Donnan potential by acrylic acid units. The color change driven by hydrogel swelling could be quantitatively measured by reflectance spectra. Increased content of N-isopropylacrylamide in the hydrogel resulted in a larger volume change under the same T-drop experiment. On the contrary, higher crosslinker content led to a less swollen hydrogel. From the kinetic investigations, response time for temperature change was measured to be much faster than that for pH variation (0.5s vs. 28s). An exceptionally rapid temperature response could be explained by fast water influx to the thin layers at the top of inverse opal hydrogel after an instantaneous temperature change. A cyclic pH/temperature changes (pH jump–temperature-drop–pH drop–temperature-jump) on a dually tunable sensor showed a perfect restoration of diffraction wavelength as well as the rapid response times for all stimuli. This work facilitates the fabrication of a variety of multi-responsive inverse opal sensors exhibiting rapid response kinetics by simply copolymerizing the individual sensing monomers using the optimized photo-polymerization and the colloidal templating route.

Calcium carbonate phase transformations during the carbonation reaction of calcium heavy alkylbenzene sulfonate overbased nanodetergents preparation

The preparation and application of overbased nanodetergents with excess alkaline calcium carbonate is a good example of nanotechnology in practice. The phase transformation of calcium carbonate is of extensive concern since CaCO3 serves both as an important industrial filling material and as the most abundant biomineral in nature. Industrially valuable overbased nanodetergents have been prepared based on calcium salts of heavy alkylbenzene sulfonate by a one-step process under ambient pressure, the carbonation reaction has been monitored by the instantaneous temperature changes and total base number (TBN). A number of analytical techniques such as TGA, DLS, SLS, TEM, FTIR, and XRD have been utilized to explore the carbonation reaction process and phase transformation mechanism of calcium carbonate. An enhanced understanding on the phase transformation of calcium carbonate involved in calcium sulfonate nanodetergents has been achieved and it has been unambiguously demonstrated that amorphous calcium carbonate (ACC) transforms into the vaterite polymorph rather than calcite, which would be of crucial importance for the preparation and quality control of lubricant additives and greases. Our results also show that a certain amount of residual Ca(OH)2 prevents the phase transformation from ACC to crystalline polymorphs. Moreover, a vaterite nanodetergent has been prepared for the first time with low viscosity, high base number, and uniform particle size, nevertheless a notable improvement on its thermal stability is required for potential applications.

Simulation of transient thermal states in layered electronic microstructures

The analysis of dynamic temperature changes in microelectronic layered circuit (especially made in thick-film technology) has been presented in the paper. Such transient states are caused by electric pulse with high energy and short time of duration. It leads to short but the very violent temperature increase and – as result – defects or parameter changes of active layer. The mathematical function which describes the instantaneous temperature changes was presented in this paper in order to provide more accurate analysis of reliability and thermal properties measurement problems. The two-layer structures (with different thermo-physical properties) were the subject of conducted research, especially one of them, namely heat source excited by electric pulse. Such configuration is typical for microcircuits made in hybrid technology such as LTCC (low temperature co-fired ceramic), HTCC (high temperature co-fired ceramic) as well as thick – film technology in which polymer and photoimageable (photosensitive) materials are used.

Computer simulations of the effects of temperature change on defect accumulation in copper during neutron irradiation

Kinetic Monte Carlo (kMC) computer simulations were used to study the effects of temperature change during low-dose 14-MeV fusion neutron irradiations on defect accumulation in copper. Instantaneous temperature changes from 300 to 473 K, from 300 to 673 K and from 373 to 573 K were simulated. All the high temperatures are above the Stage-V annealing temperature for copper, approximately 400 K. The total simulated dose was 0.01 dpa for all temperature-change simulations, at a dose rate of 10−6 dpa/s. In general, the concentrations of both self-interstitial atom (SIA) clusters and vacancy clusters decrease when the temperature is changed from low to high. The relative decrease in concentration of defect clusters when the temperature is increased is determined by the level of accumulation of vacancy clusters in the initial low-temperature part of the irradiation as well as by the specific temperatures involved. If the vacancy clusters are small and their concentration is high, the decrease of cluster density is prominent when the temperature increases, and the higher the second temperature, the easier it is for defect clusters to dissolve.

Thermal residual stress analysis for in situ and post-consolidated composite rings

The thermoelastic response of a thick, multilayered composite ring subjected to the sequential addition of layers which undergo instantaneous temperature change and corresponding thermal deformation is modelled. The analysis considers ply-by-ply variations of material properties and fibre orientations. The resulting residual stress field is examined as a function of important physical parameters such as ring geometry, layer material properties, fibre orientation and layer sequence.

Thermal effects associated with stress-induced martensitic transformation in a TiNi alloy

Stress-induced martensitic transformation in a polycrystalline TiNi alloy (Ti-50.1 at.%Ni) has been investigated by following the instantaneous temperature change during deformation, the effects of strain rate on the kinetics of transformation and the calorimetric effects associated with the thermally induced transformation. Two separate stages of transformation strain and temperature increment are observed during stress-induced martensitic transformation in this alloy. Differential scanning calorimetry results show two exothermic peaks during cooling. The sum of the enthalpy changes for these two events is exactly equal to the single enthalpy change during martensite-to-parent transformation. It is proposed that the two stages of transformation strain and temperature rise during stress-induced transformation are related to the two calorimetric events in thermally induced transformation. It is shown that the stress-strain hysteresis loop as well as the two stages of temperature rise are influenced by the strain rate.

The influence of finite rates of temperature change in the creepT-jump experiment

General equations for nonisothermal creep of a linear viscoelastic solid are presented. Both the time dependent strain and strain rate are predicted for an arbitrary temperature history. The creepT-jump experiment (imposition of a sudden temperature change on a creeping specimen) is analyzed using these equations in order to understand the influence of non-instantaneous temperature changes on the experimental observations. It is shown that an increase in the time required to impose the temperature change causes an increase in the activation energy,ΔHexp, determined via creepT-jump. This effect is most pronounced for materials with large activation energies. Appropriate extrapolation techniques can be used to obtain the result expected for an instantaneous temperature change. Verification of the theoretical prediction was obtained from isothermal and nonisothermal creep experiments on polymethylmethacrylate in the linear viscoelastic region. The activation energy for a nearly instantaneous temperature change was 43 ± 2 kcal/mol. As the rise time of the temperature change was increased to 600 seconds,ΔHexp increased to 70 ± 2 kcal/mol. The effects of the rate of temperature change on other aspects of the creepT-jump experiment were also found to be in keeping with the predictions of the nonisothermal linear theory.

Thermal tolerance of zooplankton

Abstract First immature instar Daphnia pulex Leydig acclimated at 5, 10, 15, 20, 25 and 30°C, and Daphnia magna Straus acclimated at 10, 15, 20, 25 and 30°C, were instantaneously immersed at the specified temperatures which differed from acclimation temperatures by 10°C or more. Observations for mortality were made at regular intervals for 48 h or longer until at least one molting had occurred. Organisms acclimated at the same temperatures were also instantaneously immersed at 35°C, an ultimately lethal temperature, and followed to 95% mortality. Daphnia pulex acclimated at 20°C were stepped over varying rates of temperature change to 35°C and observed for mortality over a 48-h period. Thirty first immature instar organisms were used in each test, and tests were carried out in temperature controlled water baths and incubators. Filtered pond water was used for culture and testing. Both species survived instantaneous temperature changes over the entire normal tolerance ranges tested. Animals succumbed more rapidly upon instantaneous immersion at 35°C as the temperature at which they were acclimated decreased, with D. magna succumbing more rapidly than D. pulex from all acclimation temperatures. Daphnia pulex acclimated at 20°C and stepped to 35°C at varying rates of temperature change exhibited a decreasing 48-h mortality percentage as rates decreased from 6°C h −1 to 1.33°C h −1 . Shortcomings in methodologies of previous thermal tolerance studies on zooplankton were discussed, and recommendations were made as to how these methods can be improved.

Effectiveness factors and instability in non-catalytic gas—solid reactions: the effect of solid heat capacity

Non-isothermal non-catalytic gas—solid reactions of the general type aA gas + B solid ⇌ gG gas + sS solid are discussed, the theoretical treatment being based on the well-known pseudo-steady-state ‘sharp interface’ or ‘shell progressive’ mechanism. Reaction rates and rates of mass and heat transfer are developed in terms of the rate of production of product gas at the reaction interface in a sphere of reaction solid. Solution of the dimensionless equations is achieved by finite difference computation. Corresponding equations for the infinite cylinder and the slab are presented. White steady-state mass balances are assumed, a simple transient term is introduced into the energy balance to avoid instantaneous temperature changes, and to rationalise the analysis of instability. The importance of this transient term is illustrated.

ホットストリップミル作業ロールの稼動中の温度

Temperature of a bottom working roll of the first stand of a hot strip finishing mill during rolling was measured by means of thermocouples embedded in the surface layer of the roll. Instantaneous temperature change was detected and led to the recorder through slip rings. Maximum temperature rise measured was about 100 degrees C at about 1 mm from surface. Characteristics of periodical change in temperature in various zones in the roll were examined. In the zone II, 0.5 to 5mm from surface, temperature depended solely on the angle of rotation. In the zone II, 0.5 to 5mm from surface, temperature depended both on angle of rotation and on the number of rotations during one rolling. In the zone III, 5 to 30mm from it, temperature depended both on number of rotations and on the number of rollings. In the zone IV, 30mm to center, temperature depended solely on the number of rollings. Temperature at center approached a constant value after about 30 rollings. Dependence of temperature rise on rolling variables was examined. Amount of cooling water was found the most critical in determining the temperature in the roll and the reduction rate of plate was the second most so, while the interval of rolling was even less critical.