scholarly journals Agreed – there is no need to switch the modified Arrhenius function back to the old form

2021 ◽  
Vol 231 (6) ◽  
pp. 2117-2117
Author(s):  
Joseph R. Stinziano ◽  
Bridget K. Murphy
Keyword(s):  
Arrhenius Function

scholarly journals Water vapor transmission properties of acrylic organic coatings

2020 ◽  
Author(s):  
Réka Lilla Kovács ◽  
Lajos Daróczi ◽  
Péter Barkóczy ◽  
Eszter Baradács ◽  
Eszter Bakonyi ◽  
...  
Keyword(s):  
Water Vapor ◽  
Transmission Rate ◽  
Performance Testing ◽  
Preexponential Factor ◽  
Diffusion Activation Energy ◽  
Vapor Permeability ◽  
Coating Materials ◽  
Comparative Performance ◽  
Water Vapor Transmission ◽  
Arrhenius Function

AbstractIn this work, we evaluate the water vapor transmission rate (WVTR), the permeability (P), solubility (S), and diffusion (D) coefficients of Paraloid B44, Paraloid B72, and Incralac coatings in the temperature range of 5–35°C. The Arrhenius function—diffusion activation energy and preexponential factor—has also been determined from the data: $$D_{B44} = 35.2\;{\text{cm}}^{2} \;{\text{s}}^{ - 1} \exp \left( { - 25\;{\text{kJ mol}}^{ - 1} /{\text{RT}}} \right)$$ D B 44 = 35.2 cm 2 s - 1 exp - 25 kJ mol - 1 / RT ; $$D_{B72} = 9.5\;{\text{cm}}^{2} \;{\text{s}}^{ - 1} \exp \left( { - 23\;{\text{kJ mol}}^{ - 1} /{\text{RT}}} \right)$$ D B 72 = 9.5 cm 2 s - 1 exp - 23 kJ mol - 1 / RT ; $$D_{\text{Incralac}} = 622.8\;{\text{cm}}^{2} \;{\text{s}}^{ - 1} { \exp }\left( { - 28\;{\text{kJ mol}}^{ - 1} /{\text{RT}}} \right)$$ D Incralac = 622.8 cm 2 s - 1 exp - 28 kJ mol - 1 / RT . These resins are important coating materials, for example, for conservators to protect metallic artifacts, such as statues, against corrosion. Despite Paraloid B44 and B72 resins being considered as reference materials in conservation practice, that is, new coating materials (either water vapor retarders or transmitters) are often compared to them, there are no comprehensive data for the quantities describing the vapor permeability (P, S, D) of these materials. The measurements are based on the ISO cup-method using substrate/coating composite samples. The strength of this technique is that it can also be used when the coating is non-self-supporting; nevertheless, P, S, and D can be deduced for the coating layer itself, and it seems to be a standardizable procedure for comparative performance testing of coating materials. Paraloid B72 layers exhibited higher WVTRs—from 39 to 315 g m−2 day−1 as the temperature increased from 5 to 35°C—compared to Paraloid B44 and Incralac coatings—from 17 to 190 g m−2 day−1, respectively. The transmission rate parameters were also compared to the results of corrosion tests. Incralac was the most effective corrosion inhibitor, and the performance of the B44 was better than the B72, which is in good agreement with the transmission rate tests.

Temperature profiles in endothermic and exothermic reactions and the interpretation of experimental rate data

1970 ◽  
Vol 320 (1540) ◽  
pp. 71-100 ◽  
Keyword(s):  
Steady State ◽  
Correction Factor ◽  
Exothermic Reaction ◽  
Kinetic Studies ◽  
Activation Energies ◽  
Uniform Temperature ◽  
Exothermic Reactions ◽  
Arrhenius Function ◽  
Point To Point ◽  
Reacting Systems

Any endothermic or exothermic reaction is accompanied by self-cooling or self-heating. In reacting systems in which heat transfer is controlled by conduction, non-uniform temperature-position profiles are established. Examples of this situation are the exothermic decomposition of gaseous diethyl peroxide and the endothermic decomposition of nitrosyl chloride at low pressures (when convection is unimportant). In kinetic studies, allowance must be made for the non-uniform temperature to derive accurate isothermal velocity constants and Arrhenius parameters. In the present paper, the necessary corrections have been derived for a reactant in the steady state whose reaction rate varies exponentially with temperature and in which the temperature excess varies from point to point, being zero at the boundary (Frank-Kamenetskii’s conditions). The geometries considered are the slab, cylinder and sphere. The temperature gradient at the surface in the steady state ( Г ) occupies a key position, and this is exploited to find the correction factor required to convert 'observed’ rate constants to isothermal conditions, and thence to correct ‘observed’ activation energies and pre-exponential factors. The correction factor is found to be simply related to Frank- Kamenetskii’s δ (a dimensionless measure of heat-release rate). A similar analysis is given for systems hotter or cooler than their surroundings but uniform in temperature—such as well stirred fluid systems or small solid crystals (Semenov’s conditions). In these circumstances, systems of arbitrary geometry may be studied, and no approximation need be made to the Arrhenius function. For either type of boundary condition, uncorrected activation energies are overestimates in exothermic reactions and underestimates in endothermic reactions. Explicit relations are derived for making corrections. Boundary conditions intermediate between the two extremes investigated can also be treated though the resulting expressions are more cumbersome. In an appendix, an alternative ‘experimental’ approach is made to the elimination of errors from measured reaction velocities. This approach identifies the measured velocities with a temperature intermediate between those at centre and surface. The optimum choice, which weights the central and surface temperatures in the ratios 2:1 (slab), 1:1 (cylinder) and 2:3 (sphere), gives exactly correct results for the cylinder and acceptable precision for the slab and sphere even to within 5 K of the explosion limit. Other correction methods are also discussed.

scholarly journals Depth perception: the need to report ocean biogeochemical rates as functions of temperature, not depth

2017 ◽  
Vol 375 (2102) ◽  
pp. 20160319 ◽  
Author(s):  
Peter G. Brewer ◽  
Edward T. Peltzer
Keyword(s):  
Oxygen Consumption ◽  
Large Scale ◽  
Climate Change Impacts ◽  
Sargasso Sea ◽  
Ocean Ventilation ◽  
Biogeochemical Models ◽  
Consumption Rates ◽  
Arrhenius Function ◽  
Transient Events ◽  
Warming World

For over 50 years, ocean scientists have oddly represented ocean oxygen consumption rates as a function of depth but not temperature in most biogeochemical models. This unique tradition or tactic inhibits useful discussion of climate change impacts, where specific and fundamental temperature-dependent terms are required. Tracer-based determinations of oxygen consumption rates in the deep sea are nearly universally reported as a function of depth in spite of their well-known microbial basis. In recent work, we have shown that a carefully determined profile of oxygen consumption rates in the Sargasso Sea can be well represented by a classical Arrhenius function with an activation energy of 86.5 kJ mol −1 , leading to a Q 10 of 3.63. This indicates that for 2°C warming, we will have a 29% increase in ocean oxygen consumption rates, and for 3°C warming, a 47% increase, potentially leading to large-scale ocean hypoxia should a sufficient amount of organic matter be available to microbes. Here, we show that the same principles apply to a worldwide collation of tracer-based oxygen consumption rate data and that some 95% of ocean oxygen consumption is driven by temperature, not depth, and thus will have a strong climate dependence. The Arrhenius/Eyring equations are no simple panacea and they require a non-equilibrium steady state to exist. Where transient events are in progress, this stricture is not obeyed and we show one such possible example. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.

scholarly journals Determination of Grain Boundary Diffusion Coefficients in C-Regime by Hwang-Balluffi Method: Silver Diffusion in Pd

2009 ◽  
Vol 289-292 ◽  
pp. 763-767 ◽  
Author(s):  
Z. Balogh ◽  
Z. Erdélyi ◽  
Dezső L. Beke ◽  
Alain Portavoce ◽  
Christophe Girardeaux ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Diffusion Coefficients ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Controlled Processes ◽  
Diffusion Controlled ◽  
Arrhenius Function ◽  
Data Points ◽  
Accumulation Kinetics

Diffusion controlled processes play a crucial role in the degradation of technical materials. At low temperatures the most significant of them is the diffusion along grain boundaries. In thin film geometry one of the best methods for determining the grain boundary (GB) diffusion coefficient of an impurity element is the Hwang-Balluffi method, in which a surface sensitive technique is used to follow the surface accumulation kinetics. Results of grain boundary diffusion measurements, carried out in our laboratory by this method in three different materials systems (Ag/Pd, Ag/Cu and Au/Ni) are reviewed. In case of Ag diffusion along Pd GBs the surface accumulation was followed by AES method. The data points can be well fitted by an Arrhenius function with an activation energy Q=0.99eV

scholarly journals Effect of Temperature and Time on Oxygen Consumption by Olive Fruit: Empirical Study and Simulation in a Non-Ventilated Container

Fermentation ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 200
Author(s):  
Eddy Plasquy ◽  
María C. Florido ◽  
Rafael Rubén Sola-Guirado ◽  
José María García Martos ◽  
Juan Francisco García Martín
Keyword(s):  
Oxygen Consumption ◽  
Anaerobic Respiration ◽  
Co2 Production ◽  
Effect Of Temperature ◽  
Critical Threshold ◽  
Irreversible Damage ◽  
Olive Fruit ◽  
Different Temperatures ◽  
Arrhenius Function

Fermentation processes within olive fruit jeopardize the quality of the extracted oil. Aeration, temperature, and time play a crucial role in attaining the critical threshold at which an aerobic respiration shifts towards anaerobic. In this work, the O2 consumption and CO2 production of olive fruit kept in a closed container at different temperatures (5–45 °C) were measured over 7 h. The data allowed us to describe the relationship between the temperature and the respiration rate as an Arrhenius function and simulate the oxygen consumption in the inner part of a container full of fruit with low aeration, considering the generated respiration heat over time. The simulation revealed that olives risk shifting to anaerobic respiration after 3 h at 25 °C and less than 2 h at 35 °C when kept in a non-ventilated environment. The results underline the irreversible damage that high day temperatures can produce during the time before fruit processing, especially during transport. Lowering, as soon as possible, the field temperature thus comes to the fore as a necessary strategy to guarantee the quality of the olives before their processing, like most of the fruit that is harvested at excessive temperatures.

scholarly journals The Effects of Activation Energy and Thermophoretic Diffusion of Nanoparticles on Steady Micropolar Fluid along with Brownian Motion

2020 ◽  
Vol 2020 ◽  
pp. 1-12 ◽  
Author(s):  
Zulqurnain Sabir ◽  
Assad Ayub ◽  
Juan L. G. Guirao ◽  
Saira Bhatti ◽  
Syed Zahir Hussain Shah
Keyword(s):  
Activation Energy ◽  
Brownian Motion ◽  
Differential Equations ◽  
Concentration Profile ◽  
Micropolar Fluid ◽  
Numerical Solutions ◽  
Nonlinear Partial Differential Equations ◽  
Local Skin ◽  
Arrhenius Function ◽  
Local Skin Friction

The present study is related to the effects of activation energy and thermophoretic diffusion on steady micropolar fluid along with Brownian motion. The activation energy and thermal conductivity of steady micropolar fluid are also discussed. The equation of motion, angular momentum, temperature, concentration, and their boundary conditions are presented for the micropolar fluid. The detail of geometry reveals the effects of several parameters on the parts of the system. The nonlinear partial differential equations are converted into nonlinear ordinary differential equations, and a famous shooting scheme is used to present the numerical solutions. The comparison of the obtained results by the shooting technique and the numerical bvp4c technique is presented. The behavior of local skin friction numbers and couple stress number is tabulated for different parameters, and some figures are plotted to present the different parameters. For uplifting the values of AE for parameter λA, the concentration profile is increased because of the Arrhenius function, and AE increases with the reduction of this function. The increasing values of the parameter of rotation G show the decrement in velocity because of the rotation of the particle of the fluid, so the linear motion decreases. Thermophoresis is responsible for shifting the molecules within the fluid, and due to this, an increment in boundary layer thickness is found, so by a greater value of Nt, the concentration profile decreases and temperature profile goes down.

scholarly journals Peristaltic Blood Flow of Couple Stress Fluid Suspended with Nanoparticles under the Influence of Chemical Reaction and Activation Energy

Symmetry ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 276 ◽  
Author(s):  
Rahmat Ellahi ◽  
Ahmed Zeeshan ◽  
Farooq Hussain ◽  
A. Asadollahi
Keyword(s):  
Activation Energy ◽  
Chemical Reaction ◽  
Couple Stress ◽  
The Body ◽  
Couple Stress Fluid ◽  
Large Molecules ◽  
Arrhenius Function ◽  
Flexible Walls ◽  
Speed Up ◽  
Buongiorno Model

The present study gives a remedy for the malign tissues, cells, or clogged arteries of the heart by means of permeating a slim tube (i.e., catheter) in the body. The tiny size gold particles drift in free space of catheters having flexible walls with couple stress fluid. To improve the efficiency of curing and speed up the process, activation energy has been added to the process. The modified Arrhenius function and Buongiorno model, respectively, moderate the inclusion of activation energy and nanoparticles of gold. The effects of chemical reaction and activation energy on peristaltic transport of nanofluids are also taken into account. It is found that the golden particles encapsulate large molecules to transport essential drugs efficiently to the effected part of the organ.

scholarly journals Hot Deformation Behavior and Strain-Compensated Constitutive Equation of Nano-Sized SiC Particle-Reinforced Al-Si Matrix Composites

Materials ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1812 ◽  
Author(s):  
Zhen Wang ◽  
Aiqin Wang ◽  
Jingpei Xie ◽  
Pei Liu
Keyword(s):  
Activation Energy ◽  
Constitutive Equation ◽  
Hot Deformation ◽  
Deformation Behavior ◽  
Pure Aluminum ◽  
Matrix Composites ◽  
Compression Tests ◽  
Hot Deformation Behavior ◽  
Arrhenius Function ◽  
Sic Particle

The hot deformation behavior of nano-SiCp/Al-Si composites was studied by isothermal compression tests at 470–530 °C and strain rates of 0.01–5 s−1. A strain-compensation constitutive model was developed with a Z parameter and an Arrhenius function, and its accuracy was verified by error analysis. The results show that the flow stress of the composites decreased with the increase in deformation temperature and the decrease in strain rate. The average activation energy for nano-SiC particle-reinforced Al-Si matrix composites was 277 kJ/mol, which was larger than the activation energy for self-diffusion of pure aluminum. The average relative error was calculated as 2.88%, indicating the strain-compensated constitutive equation could accurately predict the hot deformation behavior of nano-SiCp/Al-Si composites.

Cellular Automata Approach to Hydration Heat of Concrete Based on Equivalent Time

2020 ◽  
Vol 982 ◽  
pp. 181-188
Author(s):  
Yi Liu ◽  
Yue Ting Yang ◽  
Ling Chen ◽  
Jing Zeng
Keyword(s):  
Cellular Automata ◽  
Ambient Temperature ◽  
Temperature Rise ◽  
Concrete Slab ◽  
Hydration Heat ◽  
Slab Thickness ◽  
Adiabatic Temperature Rise ◽  
Equivalent Time ◽  
Arrhenius Function ◽  
The Relationship

Cellular automata can be used to analyze a physical system which is satisfying differential equations. A cellular automata program for a thermal analysis of hydration heat was developed. Based on the fundamental theory of cellular automata, the heat conduction equation was deduced for validating the cellular automata approach. By introduction of the concept of equivalent time, the variation of the chemical reaction rate of hydration heat with temperature was studied by use of the Arrhenius function. The relationship between the adiabatic temperature rise and equivalent time was determined by analyzing testing data．A parametric analysis of ambient temperature and concrete slab thickness was also conducted. The temperature rise of concrete increases with increasing ambient temperature and thickness of the slab.

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