Effects of initial temperature on autoignition and detonation development in dimethyl ether/air mixtures with temperature gradient

2017 ◽  
Vol 36 (3) ◽  
pp. 3643-3650 ◽  
Author(s):  
Peng Dai ◽  
Chengken Qi ◽  
Zheng Chen
Keyword(s):  
Temperature Gradient ◽  
Dimethyl Ether ◽  
Initial Temperature ◽  
Detonation Development

Phase changes and convection in the Earth’s mantle

1965 ◽  
Vol 258 (1088) ◽  
pp. 276-283 ◽  
Keyword(s):  
Temperature Gradient ◽  
Phase Change ◽  
Initial Temperature ◽  
Phase Changes ◽  
Homogeneous Layer ◽  
Transformation Zone ◽  
Earth’S Mantle ◽  
Transition Level ◽  
Transformation Rates

A phase change may hinder or enhance convection, depending on its characteristics. Univariant transformations such as may occur in the mantle constitute a barrier to convection unless the motion starts at some distance above or below the transition level; an initial temperature gradient in excess of the adiabatic value is also required. Multivariant transformations only require, in the transformation zone, an initial gradient slightly greater than the adiabatic value for a homogeneous layer. The effect on convection of transformation rates is not likely to be serious.

Thermal-Mechanical Study of 3D Printing Technology for Rail Repair

2018 ◽  
Author(s):  
Ershad Mortazavian ◽  
Zhiyong Wang ◽  
Hualiang Teng
Keyword(s):  
Thermal Analysis ◽  
Thermal Expansion ◽  
3D Printing ◽  
Stress Distribution ◽  
Temperature Gradient ◽  
Initial Temperature ◽  
Mechanical Analysis ◽  
Von Mises Stress ◽  
Additive Materials ◽  
Von Mises

The complicated steel wheel and rail interaction on curve causes side wear on rail head. Thus, the cost of maintenance for the track on curve is significantly higher than that for track on a tangent. The objective of this research is to develop 3D printing technology for repairing the side wear. In this paper, the study examines induced residual thermal stresses on a rail during the cooling down process after 3D printing procedure using the coupled finite volume and finite element method for thermal and mechanical analysis respectively. The interface of the railhead and additive materials should conserve high stresses to prevent any crack initiation. Otherwise, the additive layer would likely shear off the rail due to crack propagation at the rail/additive interface. In the numerical analysis, a cut of 75-lb ASCE (American Society of Civil Engineers) worn rail is used as a specimen, for which a three-dimensional model is developed. The applied residual stresses, as a result of temperature gradient and thermal expansion coefficient mismatch between additive and rail materials, are investigated. At the beginning, the worn rail is at room temperature while the additive part is at a high initial temperature. Then, additive materials start to flow thermal energy into the worn rail and the ambient. The thermal distribution results from thermal analysis are then employed as thermal loads in the mechanical analysis to determine the von-Mises stress distribution as the decisive component. Then, the effect of preheating on residual stress distribution is studied. In this way, the thermo-mechanical analysis is repeated with an increase in railhead’s initial temperature. In thermal analysis, the temperature contours at different time steps for both the non-preheated and preheated cases indicate that preheating presents remarkably lower temperature gradient between rail and additive part and also represents a more gradual cooling down process to allow enough time for thermal expansion mismatch alignment. In mechanical analysis, the transversal von-Mises stress distribution at rail/additive interface is developed for all cases for comparison purposes. It is shown that preheating is a key factor to significantly reduce residual stresses by about 40% at all points along transversal direction of interface.

Evaluation of Variable-Temperature Cures

1928 ◽  
Vol 1 (3) ◽  
pp. 423-440
Author(s):  
J. R. Sheppard ◽  
W. B. Wiegand
Keyword(s):  
Temperature Gradient ◽  
Initial Temperature ◽  
Variable Temperature ◽  
Practical Importance ◽  
Direct Reading ◽  
Time Curve ◽  
Constant Temperature Gradient ◽  
Several Variables ◽  
Exact Evaluation ◽  
Effect Time

Abstract Employing the generally accepted empirical rule that intensity of curing action doubles with a rise of 15° F., relations are developed between the several variables of a cure segment with a constant temperature gradient—viz., “intensity of curing action,” “curing effect,” time, and temperature—and the constants of such a cure, initial temperature and temperature gradient. Exact evaluation of cures is extended to schedules involving variable temperatures by the equations showing curing effect as a function of the other properties of a cure. These are the equations of chief practical importance. Curing effect, the measure of the net value of a schedule in effecting vulcanization, may be determined for a given schedule either by calculation from one of the “effect” equations, by direct reading from one of the several herein displayed graphs of effect vs. other properties, or by estimation of the area under an intensity-time curve.

Detonation evolution due to an initial temperature gradient

2000 ◽  
Author(s):  
T. Hawa ◽  
D. Schwendemann ◽  
A. Kapila
Keyword(s):  
Temperature Gradient ◽  
Initial Temperature

scholarly journals Temperature development of cardboard in contact with high-frequency vibrating metal surfaces

BioResources ◽  
2019 ◽  
Vol 14 (2) ◽  
pp. 3975-3990
Author(s):  
Albrecht Löwe ◽  
Marek Hauptmann ◽  
André Hofmann ◽  
Jens-Peter Majschak
Keyword(s):  
Temperature Gradient ◽  
Moisture Content ◽  
Contact Pressure ◽  
High Frequency ◽  
Initial Temperature ◽  
Vertical Vibration ◽  
Maximum Temperature ◽  
Material Surface ◽  
Internal Dissipation ◽  
Temperature Development

The heating of cardboard was studied when it is in contact with ultrasonic sonotrodes, whose vibrations were orientated parallel and perpendicular to the material surface. The parameters that were varied included the contact pressure on the sonotrode, vibration amplitude, and moisture content of the material. It was shown that there was a major decrease in the contact pressure shortly after the beginning of the experiment when the gap between the sonotrode and anvil was kept constant and thus a decrease in the temperature gradient of the material occurred. With parallel vibration, the material heated up from the sonotrode side, whereas heating started from the center of the material in the case of vertical vibration. This suggested that in cases of vertical vibration, heat is mostly generated by internal dissipation, and in cases of parallel vibration, heat is generated by friction losses on the surface. Furthermore, the results revealed the influence of the parameters on the initial temperature gradient, the maximum temperature, and the moisture content of the material.

Temperature gradient induced detonation development inside and outside a hotspot for different fuels

2019 ◽  
Vol 205 ◽  
pp. 269-277 ◽  
Author(s):  
Jiaying Pan ◽  
Sheng Dong ◽  
Haiqiao Wei ◽  
Tao Li ◽  
Gequn Shu ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Detonation Development
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