Types Of Thermal Behavior Research Articles

Slippery-sticky transition of interfacial fluid slip

The influence of temperature on interfacial fluid slip, as measured by molecular dynamics simulations of a Couette flow comprising a Lennard–Jones fluid and rigid crystalline walls, is examined as a function of the fluid–solid interaction strength. Two different types of thermal behavior are observed, namely, the slippery and sticky cases. The first is characterized by a steep and unlimited increase in the slip length at low temperatures, while the second presents a vanishing slip length in this regime. As the temperature increases in relation to a characteristic value, both cases converge to finite slip lengths. A recently proposed analytical model is found to well describe both thermal behaviors, also predicting the slippery-sticky transition that occurs at a critical value of the fluid–solid interaction parameter, for which, according to the model, fluid particles experience a smooth average energy landscape at the interface.

Identification and optimization of thermally safe operating conditions for single kinetically controlled reactions with arbitrary orders in isoperibolic liquid-liquid semibatch reactors

To obtain thermally safe operating conditions for kinetically controlled liquid-liquid reactions occurring in isoperibolic semibatch reactors (SBRs), an extreme scenario in which the product (UA) of the overall heat transfer coefficient (U) and the area (A) is equal to its initial value, (UA)0, was studied and combined with the ideal scenario where the UA is proportional to the liquid volume. Under both scenarios, the jacket temperature evolution of the maximum temperature of synthesis reactions (MSTR) after cooling failure and the corresponding time (θMTSR) for isoperibolic liquid-liquid SBRs was thoroughly investigated, and it was found that four types of thermal behaviors, namely IS (inherently safe), NI (non-ignition), TR (thermal runaway) and QFS (quick onset, fair conversion and smooth temperature condition) can be effectively identified by the variations of θMTSR. Then, a thermal behavior identification criterion was proposed. Subsequently, a series of boundary diagrams based on the proposed criterion were developed along with the corresponding novel adiabatic temperature diagrams to directly provide information about the maximum value of MTSR in the case of cooling failure for any operating points in the boundary diagrams. Further, synthesizing the information from the boundary diagrams and the adiabatic temperature diagrams allows for convenient attainment of generalized thermally safe operating conditions with considerable practicability and sufficient thermal safety even in adiabatic situations.

Structural and thermodynamic properties of new pyrazolo[3,4-d]pyridazinones

This work describes the synthesis of new 4-substituted-pyrazolo[3,4-d]pyridazinones (R=C6H5, 4-F-C6H4, benzofur-2-yl, CF3, 4-NO2-C6H4) from the reaction of dicarbonylpyrazoles with hydrazine hydrate. Solid and solution-state NMR were used to unequivocally assign the structure and identification of the byproduct formed when R=4-NO2-C6H4. Geometrical features and the intermolecular interactions of compounds were described using single crystal X-ray diffraction. The thermal behavior of the compounds was studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Kinetic parameters, such as the activation energy (Ea) and pre-exponential factor (A), were determined as a function of the conversion degree for the thermal decomposition of two compounds, by using the isoconversional methods of Friedman and Ozawa–Flynn–Wall (OFW). The results showed that the Ea for thermal decomposition of compound with R=CF3 is always higher than for compound with R=C6H5, independent of the model used (Friedman or OFW), indicating that the former is more stable than the latter. Furthermore, the Ea values for compounds with R=C6H5 and CF3 are practically constant for all α values from 0.1 to 0.9, indicating the existence of a single-step degradation reaction. The kinetics results also reveal the linear dependence of Ea on the pre-exponential factor. In addition, the 4-substituted-pyrazolo[3,4-d]pyridazinones studied have two types of thermal behavior: (i) a compound that passes from the glass to a liquid phase, followed by cold crystallization, and a melting transition (R=C6H5, CF3); (ii) A compound that has no melting or freezing points, only glass-transition temperatures (R=4-NO2-C6H4). Finally, we showed that compounds with R=C6H5 and CF3 undergo amorphization during the heating cycles, reaching 48% and 74% of amorphous content, respectively.

Thermal Analysis and Heat Capacities of 1-Alkyl-3-methylimidazolium Ionic Liquids with NTf2–, TFO–, and DCA– Anions

Ionic liquids are good candidates as replacements for current heat-transfer liquids used in industry. For this use, it is important to know their thermal behavior. The melting, freezing, cold crystallization, and glass transition temperatures, together with heat capacities in the temperature range (293.15 to 333.15) K of the ionic liquids 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [CnMimNTf2 (n = 2,3,4,6)], 1-hexyl-3-methylimidazolium trifluoromethanesulfonate (C6MimTFO), and 1-hexyl-3-methylimidazolium dicyanamide (C6MimDCA), have been determined using differential scanning calorimetry. Three different types of thermal behaviors were found, and in general it was concluded that as the temperature scan rate in the thermal analysis increases, the freezing temperature decreases, and the glass transition and cold crystallization temperatures increase. The heat capacity values of the imidazolium ionic liquids with the bis(trifluoromethylsulfonyl)imide anion increase as the alkyl-side chain o...

Thermal evolution of first-order magnetization processes in the single-ion one-sublattice system with uniaxial anisotropy

The thermal evolution of first-order magnetization processes (FOMP's) is intensively studied within a description of the anisotropy energy of a single-ion one-sublattice system with two or three anisotropy constants. By following the temperature-induced trajectories in the anisotropy-parameter plane, all possible types of thermal evolution of the FOMP are detected by an effective parameter method in the mean-field approximation. Within the two-constant approximation, three types of thermal behavior of the FOMP are found. Within the three-constant approximation, 12 types are found when the zero-temperature second-order anisotropy constant K-1(0) is positive, and 14 types when K-1(0) is negative. Phase diagrams for the existence condition of thermal behavior of the FOMP are given in the zero-temperature anisotropy space in combination with analytical and numerical calculations. For each type of variation of the FOMP, an example is selected to describe the temperature dependence of the normalized amplitude and the critical field of the magnetization jump. The relation between the type of variation of the FOMP and the spin-reorientation transition is discussed in detail.

Sol-Gel transition behavior of pure iota-carrageenan in both salt-free and added salt states.

This paper describes how strongly the gelation process of iota-carrageenan is affected by addition of metallic ions from the creep and creep recovery, dynamic viscoelasticity (DVE) and DSC measurements. Creep results at T = 25 degrees C indicate that below a polymer concentration C of 3.0 wt % the salt-free system behaves as a viscous solution, and it starts to exhibit viscoelasticity as C exceeds 3.0 wt %. In the range C = 5.0-7.0 wt %, the salt-free system shows gellike behavior whereas the added salt system, measured in the low C range 1.0-2.5 wt %, showed gellike behavior at the same temperature. The sol-gel transition temperature T(c) was determined using Winter's criterion as the temperature at which both G'(omega) and G' '(omega) follow power law behavior with the same exponent n. DSC measurements reveal that salt-free and added salt systems take different types of thermal behavior within the same temperature range. The temperature T(c) is quite close to the gelation temperature T(m) determined from DSC measurement. The Eldrige-Ferry plot was performed to estimate activaton enthalpy, which shows that physical cross-links in the salt-free iota-carrageenan is not strong in comparison with those of samples which contains metal ions. We conclude from the data analysis of C dependence of the plateau modulus using the theory developed by Jones and Marques for rigid networks based on the fractal theories that addition of metallic ions gives rise to a rigid fiber like structure even at low C of iota-carrageenan in contrast to the salt-free system for which a flexible structure has been maintained at higher C.

Calorimetric Behaviour of Anhydrous β-Cyclodextrin at Very Low Temperature

Heat capacities of anhydrous β-cyclodextrin were measured between 10 K to 300 K using an adiabatic low-temperature calorimeter. Two distinct types of thermal behaviour were observed in the temperature range 50–130 K, depending on the way the sample was cooled. In the absence of hydration water molecules, we assumed that the two types of thermal behaviour could be attributed to freezing in more or less ordered states of the hydroxyl groups engaged in the intramolecular interglucose flip-flop-type interactions.

Diagnostic probes for fire hazard evaluation based on thermal analysis methodology. An example of use in hot asphalt mixing operations

The ability of thermal analysis techniques such as differential scanning calorimetry (DSC) and thermogravimetry (TGA) to ‘fingerprint’ samples of varying thermal history, is demonstrated in this paper using an asphalt tank as an illustrative test system. The possibility of occurrence of smouldering fires inside such a tank is exemplified by a case study in which excessive heat build-up occurred inside the bitumen-limestone matrix. Samples collected from this tank showed essentially three types of thermal behaviour as probed by DSC and TGA. The first type was characterized by low temperature endothermic transitions and very little exothermic activity at temperatures, > 200 °C. In the second category, samples had a high unburnt (initial) bitumen content; these showed pronounced exothermic response at temperatures > 200 °C. The third type of thermal behaviour was characteristic of samples that had fire hazard potential; these showed strong low temperature exothermic response starting at ≈ 120 °C. A catalytic effect exerted by bitumen and/or limestone components (e.g. pyrophoric iron sulphide) is invoked for this response.