Adiabatic Test Research Articles

A thermo-viscoplastic constitutive law for isotropic hardening of metals

A novel empirical constitutive law for thermo-viscoplasticity is proposed, which considers isotropic strain and strain rate hardening as well as thermal softening. The yield stress considers strain rate and thermal effects independently for the initial yield stress and the (strain) hardening stress. To date, most plasticity models consider strain rate and temperature effects only combined for the initial and hardening stress, which is not sufficient for several materials. Seidt and Gilat (Int J Solids Struct 50(2):1781–1790, 2013) presented comprehensive experimental measurements for the aluminum alloy Al2024 including isothermal compression tests at low strain rates and various constant temperatures from room temperature to almost melting temperature as well as adiabatic compression tests at high strain rates (up to 10,900 s $$^{-1}$$ ). In contrast to established thermo-viscoplastic material models, the proposed model is suitable to describe the material behavior of Al2024 accurately over a large range of loading conditions, i.e. from small to large plastic strains, low and high strain rates, and from room temperature to melting temperature, which is validated by the experimental data of Seidt and Gilat (2013). Consequently, with the use of the proposed constitutive law a variety of applications can be modeled, e.g. bulk forming, hot working, chip formation during cutting processes, or crash simulations. It is in particular promising for applications where combined loading conditions occur, like high strain rates and high temperatures at the chip formation.

A Method to Estimate the Error of Adiabatic Temperature Rise Testing Device

The surface temperature of a testing sample should be immediately adjusted to equal to the central point when testing adiabatic temperature rise of concrete. However, due to the insufficient tracking accuracy, there are temperature differences between the environment and the central point temperature. In this paper, the heat loss of the sample is deduced based on thermal balance equation and an assumption that the heat passing through cylindrical surface temperature and through the two ends of the sample do not affect each other, and the total heat losses of the sample can be calculated by adding the heat passing through cylindrical surface and the heat passing through two ends. Then, according to the relationship between heat and temperature, the maximum error caused by the adiabatic temperature rise testing device was deduced, and the proposed measurement accuracy of the adiabatic temperature rise testing device was presented. According to the results of the verification case, a corrective constant should be used to modify the deduction.

Prediction of concrete adiabatic temperature rise characteristic by semi-adiabatic temperature rise test and FEM analysis

Concrete temperature criteria, such as the maximum temperature limit and the maximum temperature difference limit between the interior and exterior of concrete, have become more stringent in recent construction projects. Therefore, the prediction of concrete temperature through thermal analysis is becoming a serious issue. The accuracy of temperature prediction through FEM analysis depends on the input values of concrete thermal properties, and one of the most important properties of concrete is its adiabatic temperature rise characteristic. An adiabatic temperature rise test can determine the most accurate adiabatic temperature rise characteristic of concrete. However, the test equipment is expensive, and not many agencies can perform the test. In this study, a new method that can be easily applied to mass concrete structures and has a high accuracy was developed for predicting concrete adiabatic temperature rise characteristic. Adiabatic temperature rise characteristic were predicted through a combination of a simple semi-adiabatic temperature rise test and a FEM analysis. In order to check its accuracy, the results of the new method were compared with that of a direct adiabatic temperature rise test. The predicted adiabatic temperature rise characteristic were used to numerically analyze the temperature behavior of a concrete structure. Then, a real concrete structure was built, and the temperature of concrete was measured. Finally, the validity of the new method was verified by comparing the results from the thermal analysis with the measurements of the real structure.

High resolution local heat transfer and pressure drop infrared measurements of two-phase flow of R245fa within a compact plate heat exchanger

An experimental study is presented to characterize two-phase thermal and hydraulic performance of a prototype corrugated plate heat exchanger with small pressing depth. In particular, upward flow boiling of low pressure refrigerant R245fa was investigated for a prototype fabricated with two plates of only 1mm pressing depth with a chevron angle of 65°. High spatial and temporal resolution infrared measurements were obtained by self-calibration of the IR camera to measure local (pixel-by-pixel) heat transfer coefficients during diabatic tests and local frictional pressure drops over the entire plate during adiabatic tests. Two-phase experiments were carried out for mass fluxes from 10 to 85kgm−2s−1, heat fluxes from 225 to 4100Wm−2, saturation temperatures from 19 to 35°C and vapor qualities from 0.05 to 0.90. The two-phase frictional pressure drops increased with mass flux and vapor quality while they decreased with increasing saturation temperature. A new correlation for predicting the local frictional pressure gradient through the test section was proposed. The present model captured the entire frictional pressure drop database within a bandwidth of ±30%, providing a mean absolute error of 10% and mean error of 0.2%. The local flow boiling heat transfer coefficients were found to increase with mass flux, heat flux and saturation temperature while rising, leveling off and then decreasing with increasing vapor quality.

Internal short circuit and accelerated rate calorimetry tests of lithium-ion cells: Considerations for methane-air intrinsic safety and explosion proof/flameproof protection methods

Researchers with the National Institute for Occupational Safety and Health (NIOSH) studied the potential for lithium-ion cell thermal runaway from an internal short circuit in equipment for use in underground coal mines. In this third phase of the study, researchers compared plastic wedge crush-induced internal short circuit tests of selected lithium-ion cells within methane (CH4)-air mixtures with accelerated rate calorimetry tests of similar cells. Plastic wedge crush test results with metal oxide lithium-ion cells extracted from intrinsically safe evaluated equipment were mixed, with one cell model igniting the chamber atmosphere while another cell model did not. The two cells models exhibited different internal short circuit behaviors. A lithium iron phosphate (LiFePO4) cell model was tolerant to crush-induced internal short circuits within CH4-air, tested under manufacturer recommended charging conditions. Accelerating rate calorimetry tests with similar cells within a nitrogen purged 353-mL chamber produced ignitions that exceeded explosion proof and flameproof enclosure minimum internal pressure design criteria. Ignition pressures within a 20-L chamber with 6.5% CH4-air were relatively low, with much larger head space volume and less adiabatic test conditions. The literature indicates that sizeable lithium thionyl chloride (LiSOCl2) primary (non rechargeable) cell ignitions can be especially violent and toxic. Because ignition of an explosive atmosphere is expected within explosion proof or flameproof enclosures, there is a need to consider the potential for an internal explosive atmosphere ignition in combination with a lithium or lithium-ion battery thermal runaway process, and the resulting effects on the enclosure.

Design of Pressure Relief Devices for Chemical Reactors on the Basis of Adiabatic Tests – Is this always Conservative?

Is the assumption correct that closed adiabatic tests for the design of pressure relief devices are always conservative? This issue will be investigated in different reaction systems. An effect is postulated, according to which higher temperature rise rates can be reached in adiabatic pressure relief tests in comparison to those in closed adiabatic laboratory tests. This effect can be described as a “distillation effect”. To describe the distillation effect we developed a theoretical number containing the essential characteristics with respect to the energy production by a runaway system and the energy dissipated by the evaporation of solvent during the pressure relief. To investigate the effect, two different reaction systems were examined. Initially, these systems were modified based on predefined criteria.The distillation effect could not be identified by the experimental studies. In principle, the effect is expected when the reaction system has certain properties. Herewith, the reaction must have a high reaction energy and the solvent must have the highest vapor pressure in the system. Furthermore, the reaction heat must be high enough to evaporate the whole solvent and there must be enough energy to accelerate the heating of the reaction system. Overall, it was shown that the effect can be expected only in very few reaction systems.

An Alternative Way to Determine the Self-accelerating Decomposition Temperature by Using the Adiabatic Heat-pressure Accumulation Test

In the paper presented investigations concerning the measuring sensibility of the adiabatic heat-pressure accumulation test are performed by using a well-known decomposition kinetic of a reference substance. The accuracy of the method has been proven by comparison with literature values for different substances.In summary, the Self-Accelerating Decomposition Temperature (hereinafter SADT) values obtained from the adiabatic heat-pressure accumulation are consistent with those of other methods and literature values. Therefore, the adiabatic heat-pressure accumulation can be used for the determination of the SADT.

Adiabatic calorimetry test of the reaction kinetics and self-heating model for 18650 Li-ion cells in various states of charge

Use of adiabatic calorimetry to characterise thermal runaway of Li-ion cells is a crucial technique in battery safety testing. Various states of charge (SoC) of Li-ion cells were investigated to ascertain their thermal runaway features using a Vent Sizing Package 2 (VSP2) adiabatic calorimeter. To evaluate the thermal runaway characteristics, the temperature-pressure-time trajectories of commercial cylindrical cells were tested, and it was found that cells at a SoC of greater than 50% were subject to thermal explosion at elevated temperatures. Calorimetry data from various 18650 Li-ion cells with different SoC were used to calculate the thermal explosion energies and chemical kinetics; furthermore, a novel self-heating model based on a pseudo-zero-order reaction that follows the Arrhenius equation was found to be applicable for studying the exothermic reaction of a charged cell.

Runaway decomposition of dicumyl peroxide by open cell adiabatic testing at different initial conditions

Low-thermal inertia experiments in the open cell configuration were carried out to perform a comprehensive sensitivity analysis of the parameters affecting the runaway self-decomposition of dicumyl peroxide (DCP). This study facilitates a better understanding on how concentration, initial back pressure, and fill level influence DCP runaway severity. The outcome of this experimental study was compared to previous adiabatic closed cell experiments, with the aim of clarifying the discrepancies reported in the literature and contributing to essential knowledge about self-decomposing peroxide systems.Results showed that the detected onset temperature, maximum temperature, maximum pressure, and time to maximum rate are affected by the configuration of the equipment and initial back pressure of the experiments, while the adiabatic temperature rise did not seem to be affected. The roles that the kinetics, fluid dynamics, and thermodynamics play on these observations is addressed and discussed through the manuscript.

단면형상에 따른 초고강도 콘크리트 기둥의 수화열 특성

초고층 빌딩 건설에 있어서 초고강도 콘크리트는 필수적으로 사용되기 때문에 관련연구 또한 증가하고 있다. 이러한 초고강도 콘크리트 배합에는 다량의 시멘트 결합재가 사용되기 때문에 수화열에 의한 온도균열을 평가하고 제어해야만 현장 적용이 가능하다. 본 연구에서는 초고강도 콘크리트의 단열온도상승시험 결과를 이용한 유한요소해석을 통해 초고강도 콘크리트 기둥의 온도균열 분석을 수행하였다. 초고강도 콘크리트 기둥의 형상을 원형과 사각형으로 모델링하여 기둥 형상에 따른 온도, 응력변화 및 온도균열지수를 분석하였다. 그 결과 원형기둥이 사각기둥에 비해 온도균열저항에 더 효과가 있는 것을 확인할 수 있었다. Study on ultra-high-strength concrete(UHSC) has increased since it is essential in skyscraper construction. Since UHSC mixture has a large amount of the cementitious materials, UHSC can be applied on-site only when its thermal crack behavior due to heat of hydration is evaluated and controlled. In this study, finite element analysis using adiabatic temperature rise test data of UHSC was performed to evaluate thermal crack of UHSC columns. By modeling of circular and square UHSC columns, the characteristics of hydration heat, thermal stress, and thermal crack ratio were investigated according to column shape. As a result, it was confirmed that circular columns are more effective in thermal crack resistance than the square column.

Scientific writing seminar to help early-stage investigators publish research

Concrete temperature criteria, such as the maximum temperature limit and the maximum temperature difference limit between the interior and exterior of concrete, have become more stringent in recent construction projects. Therefore, the prediction of concrete temperature through thermal analysis is becoming a serious issue. The accuracy of temperature prediction through FEM analysis depends on the input values of concrete thermal properties, and one of the most important properties of concrete is its adiabatic temperature rise characteristic. An adiabatic temperature rise test can determine the most accurate adiabatic temperature rise characteristic of concrete. However, the test equipment is expensive, and not many agencies can perform the test. In this study, a new method that can be easily applied to mass concrete structures and has a high accuracy was developed for predicting concrete adiabatic temperature rise characteristic. Adiabatic temperature rise characteristic were predicted through a combination of a simple semi-adiabatic temperature rise test and a FEM analysis. In order to check its accuracy, the results of the new method were compared with that of a direct adiabatic temperature rise test. The predicted adiabatic temperature rise characteristic were used to numerically analyze the temperature behavior of a concrete structure. Then, a real concrete structure was built, and the temperature of concrete was measured. Finally, the validity of the new method was verified by comparing the results from the thermal analysis with the measurements of the real structure.

Reaction kinetics of coal oxidation at low temperatures

Adiabatic oven testing of coal to assess the propensity for self-heating produces data on the kinetics of the coal oxidation reaction. Repeat tests on the same coal at different starting temperatures ranging from 20 to 57 °C shows that there is a strong time–temperature effect on the reaction kinetics. At these low temperatures the initial reaction rate is predominantly non-Arrhenius, but converges to Arrhenius behaviour at temperatures above 70 °C. A new rate equation model has been derived that accounts for the change in kinetic behaviour in the low temperature region. This model is based on the concept of reactive site availability.

Implementing ternary supplementary cementing binder for reduction of the heat of hydration of concrete

The purpose of the present study was to examine the high-volume use of by-products as supplementary cementitious materials (SCMs) in order to control the hydration heat of concrete and enhance its sustainability. The prepared ternary binders were composed of varying combinations of fly ash, ground granulated blast-furnace slag, and ordinary Portland cement (OPC). Isothermal hydration tests were conducted on the pastes produced using the prepared ternary binders and OPC under constant temperatures (T) of 13, 23, and 33 °C. Adiabatic hydration tests were also conducted on the concrete mixes at T of 23 °C. The heat production rate curve clearly showed that the induction and acceleratory periods increased with increasing SCM amount, whereas the maximum value of the curve and the decelerator period decreased; as a result, the activation energy of the cementitious pastes tended to increase with increasing SCM amount. The maximum values of total heat production determined from the adiabatic hydration tests also increased with increasing water–to–binder ratio. The relationship between the degree of reaction and the compressive strength development of the concrete was very similar in both the isothermal and the adiabatic hydration tests. The environmental impact assessment demonstrated that the very-high-volume SCM concrete had a reduction in global warming potential of 75–86% and in abiotic depletion of 73–82% as compared with OPC concrete.

Thermal behavior and electrochemical heat generation in a commercial 40 Ah lithium ion pouch cell

Quantitative data on the thermal behavior of lithium ion batteries under charging and discharging conditions are essential for designing thermal management systems and improving battery safety. In this work, commercial 40 Ah lithium ion pouch cells with Li(Ni1/3Mn1/3Co1/3)O2 cathodes were tested under isoperibolic and adiabatic conditions in an Accelerating Rate Calorimeter at different charging/discharging currents from 5 A to 40 A. Adiabatic tests simulate the worst-case scenario of a battery pack without cooling. For charging and discharging an overall exothermic behavior was found and a total temperature increase for one half cycle between 3 and 11 K. Isoperibolic tests simulate a single cell under constant environmental temperature. Here an exothermic behavior for discharging and an endothermic behavior for charging were observed. To transfer the measured temperature changes into heat data, the effective specific heat capacity and the heat transfer coefficient were determined. For the first time the heat generation data for a large format pouch cell have been determined using both isoperibolic and adiabatic conditions. These data were compared with the total heat data calculated as the sum of reversible and irreversible heat that were measured by potentiometric and current interruption techniques respectively. A good agreement was found between all three heat generation determination methods.

The Effect of Specimen Size on the Results of Concrete Adiabatic Temperature Rise Test with Commercially Available Equipment.

In this study, adiabatic temperature rise tests depending on binder type and adiabatic specimen volume were performed, and the maximum adiabatic temperature rises and the reaction factors for each mix proportion were analyzed and suggested. The results indicated that the early strength low heat blended cement mixture had the lowest maximum adiabatic temperature rise (Q∞) and the ternary blended cement mixture had the lowest reaction factor (r). Also, Q and r varied depending on the adiabatic specimen volume even when the tests were conducted with a calorimeter, which satisfies the recommendations for adiabatic conditions. Test results show a correlation: the measurements from the 50 L specimens were consistently higher than those from the 6 L specimens. However, the Q∞ and r values of the 30 L specimen were similar to those of the 50 L specimen. Based on the above correlation, the adiabatic temperature rise of the 50 L specimen could be predicted using the results of the 6 L and 30 L specimens. Therefore, it is thought that this correlation can be used for on-site concrete quality control and basic research.

Cooling of very hot vertical tubes by falling liquid film in presence of countercurrent flow of rising gases

An experimental investigation of cooling a very hot vertical tube by sudden introduction of a falling liquid film in the presence of a countercurrent flow of rising hot gases air is presented. Experiments were carried out for different rising air flow rates, flow rates of falling liquid film, initial tube temperatures and subcooling of the liquid film. Experiments showed that vapor generated during quenching of the tube can produce a countercurrent vapor velocity which exceeds the onset of flooding limit and any addition of rising air can move the situation to be more closer to zero liquid penetration limit. The results showed that the rewetting velocity (velocity of axial rewetting of the tube hot surface with the falling liquid film) increases with the decrease of initial tube temperature and decreases with the increase of air flow rate until zero quenching rate was obtained. However, the rewetting velocity slightly increased with the increase of the liquid film flow rate and liquid subcooling in case of rewetting without rising air, the presence of rising air finishes the effect of inlet liquid film flow rate and liquid subcooling on rewetting velocity. Air flow rate at which the tube cannot be totally rewetted was determined and compared with that obtained during adiabatic flooding test for the same test section and test conditions. Results were compared with previous ones and good agreement was found.

Thermal stress of high volume fly-ash (HVFA) concrete made with limestone aggregate

This paper presents numerical simulation of the thermal stress as well as experimental results establishing thermal and mechanical properties of high volume fly ash (HVFA) concrete of 50% replacement of cement by fly ash. The HVFA concretes are made with fine and coarse aggregates of limestone, so it has a significant low coefficient of thermal expansion (CTE). The low CTE may contribute to reduction of thermal stress in addition to low temperature rise. On the contrary, gradual strength development of HVFA concrete at early age should be considered for possibility of thermal cracking. To examine the crack resistance of the HVFA concrete at early age, a uniaxial tension test using prismatic concrete specimens was performed and tensile properties such as tensile strength and tensile Young’s modulus were quantified for 75 samples. Adiabatic temperature rise and CTE tests were also conducted to provide more evidence of the thermal properties. The thermal properties measurements confirmed that CTEs of the HVFA concrete are approximately 5×10−6/°C. The thermal and mechanical properties of HVFA concrete were adopted in a Finite Element (FE) simulation using a model of T-shaped bridge pier. The numerical simulation confirmed the favorable thermal properties contributing to decrease of thermal stress.

물결합재비를 달리하여 제작한 메타카올린 혼입 콘크리트의 내구성능 평가

본 연구에서는 콘크리트 구조물의 강도 향상을 위하여 혼입하고 있는 메타카올린의 내구성능 향상 효과를 규명하기 위하여 염화물이온 확산계수 및 단열온도상승량을 측정하였다. 그 결과, 메타카올린의 혼입으로 인하여 염화물이온 확산계수가 작아짐이 확인되었으며 플라이 애쉬의 첨가를 통하여 유동성의 저하를 억제할 수 있었다. 따라서 염분침투저항성을 확보하면서 물결합재비를 크게 하는 것이 가능하므로 메타카올린의 혼입으로 발생되는 단열온도상승량을 억제할 수 있어 콘크리트의 내구성능이 향상될 수 있음을 확인하였다. In this study, in order to find the improvement effect of metakaolin for using improvement of strength in concrete structures, it is investigated the diffusion coefficient of chloride ions and adiabatic temperature rise test. As a result, due to the mixing of metakaolin, it has been confirmed reducing diffusion coefficient of chloride ions and could prevent down of slump for use of adding fly ash. Therefore, ensuring resistance to chloride ion penetration into concrete, it is possible to enlarge the W/B ratio and reduce the adiabatic temperature rise by mixing of metakaolin. So, it is confirmed that the durability of concrete structures is increased.

Turbulent penetration in T-junction branch lines with leakage flow

While the study of T-junction mixing with branch velocity ratios of near 1, so called cross flow mixing, is well advanced, to the point of realistic reactor environment fluid–structure interaction experiments and CFD benchmarking, turbulent penetration studies remain an under-researched threat to primary circuit piping. A new facility has been constructed for the express purpose of studying turbulent penetration in branch lines of T-junctions in the context of the high cycle thermal fatigue problem in NPPs. Turbulent penetration, which may be the result of a leaking valve in a branch line or an unisolable branch with heat losses, induces a thermal cycling region which may result in high cycle fatigue damage and failures.Leakage flow experiments have been performed in a perpendicular T-junction in a horizontal orientation with 50mm diameter main pipe and branch pipe at velocity ratios (main/branch) up to 400. Wire mesh sensors are used as a means of measuring the mixing scalar in adiabatic tests with deionized and tap water. The near-wall region of highest scalar fluctuations is seen to vary circumferentially and in depth in the branch a great deal depending on the velocity ratio. The power spectra of the mixing scalar in the region of turbulent penetration are found to be dominated by high amplitude fluctuations at low frequencies, of particular interest to thermal fatigue. Artificial velocity oscillations in the main pipe manifest in the mixing spectra in the branch line in the form of a peak, the magnitude of which grows with increasing local RMS.

Lithium-Ion Cell Safty Experiments Under Adiabatic Conditions: Nail Penetration

We are introducing a new measurement method for nail penetration tests for lithium-ion cells. Nail penetration is a useful abuse test for lithium-ion cells to simulate a catastrophic external caused (e.g. car crash with extensive deformations) internal short circuit. In principle a nail is forced into the cell, leading not only to an immediate short circuit of the electrode layers which is resulting in a fast self-heating of the entire cell but also to a contamination of the electrode material and the electrolyte with oxygen and water.An important safety test guideline for the use of batteries in motor vehicle is the SAND 99-0497 from the US research institute Sandi National Laboratories. Besides a nail penetration test, there is also a thermal abuse test with an accelerating rate calorimeter (ARC) prescribed. The heat generation and pressure development is measured in an ARC under adiabatic conditions. An environment without the possibility of heat dissipation is the worst-case scenario for an abuse test and is simulating the abuse condition of a single cell packed in a larger cell stack of a lithium-ion battery with a defect or not sufficient battery cooling. Measurement Setup– All experiments were carried out in a modified ARC® 254 from Netzsch Gerätebau GmbH (Germany). A schematic view of the ARC measurement setup is provided in Fig. 1. The modifications consist of a pneumatic press and a pneumatic valve to control the speed of the steel nail. The sample holder for an 18650 type lithium-ion cell is keeping the cell in place and providing a possibility to measure the sample temperature on the cell surface.Several research groups investigated the thermal stability of cathode materials for lithium-ion cells in contact with electrolyte. [1-3] Therefore, a 1.1 Ah graphite / lithium-iron-phosphate (LFP) high power cell and a 2.6 Ah graphite / lithium-nickel-manganese-cobalt-dioxide (NMC) and lithium-cobalt-dioxide (LCO) blend, high energy cell at different states of charge (SoC) and states of health (SoH) were used to investigate the influence of different cell types and cathode materials. Results– To the best of our knowledge, there was no literature or experience for this kind of experiments available. To evaluate and classify the results from the here presented tests, an adiabatic nail penetration test was performed on five identical LFP cells at 50 % SoC. In Fig. 2 the temperature and the pressure inside the ARC tube are plotted against the elapsed time for all five experiments. The nail impact into the cell leads to an immediately short circuit of multiple electrode layers and significant damage to the cell body, causing a contamination of the electrodes and electrolytes. This incident is reflected by the fast increase of the temperature (Fig. 2). The peak temperature and pressure (standard deviation of all five tests: ±1.46 K and ±0.01°bar) are a good characteristic of the adiabatic nail penetration experiment.The peak temperature is rising with increasing SoC for the LFP cells (Fig. 3). Furthermore, the measurement parameters e.g. peak temperature, peak pressure, heat rates and press rates are for several experiments with different cell chemistries, SoCs and SoHs compared to each other. The temperature and pressure development for all experiments are carefully analysed and new endothermic reactions are identified. Conclusion– The here presented nail penetration experiment under adiabatic conditions is an advancement in the field of mechanical abuse tests through the selected measurement conditions. This method enables a very detailed and accurate analysis of the nail penetration experiment as tool to analyze worst-case scenarios.