Isothermal process

About: Isothermal process is a research topic. Over the lifetime, 14370 publications have been published within this topic receiving 248245 citations. The topic is also known as: isothermal process.

Variation of Peak Temperature With Heating Rate in Differential Thermal Analysis

Abstract: In differential thermal analysis, the temperature at which the maximum deflection is observed varies with heating rate for certain types of reactions. An expression can be derived relating this variation with the kinetics of the reaction. By making a number of differential thermal patterns at different heating rates, the kinetic constants can be obtained directly from the differential thermal data. Measurements of the variation of peak temperature with heating rate have been made for several minerals of the kaolin group, the values of the kinetic constants determined, and these values compared with corresponding values obtained for both the same samples and similar material by conventional isothermal techniques. Some factors affecting the results are discussed. The method of differential thermal analysis (DTA) has been universally accepted by mineralogical laboratories as a rapid and convenient means for recording the thermal effects that occur as a sample is heated. Changes in heat content of the active sample are indicated by deflections shown by a line representing the differential temperature. It is conventional to represent an endothermic effect by a negative deflection and an exothermic effect by a positive deflection. The deflections, whether positive or negative, are called peaks.

Effect of Strain Rate Upon Plastic Flow of Steel

Abstract: An experiment has been designed to check a previously proposed equivalence of the effects of changes in strain rate and in temperature upon the stress‐strain relation in metals. It is found that this equivalence is valid for the typical steels investigated. The behavior of these steels at very high rates of deformation may, therefore, be obtained by tests at moderate rates of deformation performed at low temperatures. The results of such tests are described. Aside from changing the isothermal stress‐strain relation, an increase of strain rate tends to change the conditions from isothermal to adiabatic. It is found that at low temperatures, the adiabatic stress‐strain relation in the plastic range is radically different from the isothermal, having an initial negative rather than a positive slope. This initial negative slope renders unstable homogeneous plastic deformation.

Enthalpy-porosity technique for modeling convection-diffusion phase change: application to the melting of a pure metal

Abstract: The melting of pure gallium in a rectangular cavity has been numerically investigated using the enthalpy-porosity approach for modeling combined convection-diffusion phase change. The major advantage of this technique is that it allows a fixed-grid solution of the coupled momentum and energy equations to be undertaken without resorting to variable transformations. In this work, a two-dimensional dynamic model is used and the influence of laminar natural-convection flow on the melting process is considered. Excellent agreement exists between the numerical predictions and experimental results available in the literature. The enthalpy-porosity approach has been found to converge rapidly, and is capable of producing accurate results for both the position and morphology of the melt front at different times with relatively modest computational requirements. These results may be taken to be a sound validation of this technique for modeling isothermal phase changes in metallurgical systems.

Simulation of nonideal gases and liquid-gas phase transitions by the lattice Boltzmann equation.

Abstract: We describe in detail a recently proposed lattice-Boltzmann model [X. Shan and H. Chen, Phys. Rev. E 47, 1815 (1993)] for simulating flows with multiple phases and components. In particular, the focus is on the modeling of one-component fluid systems which obey nonideal gas equations of state and can undergo a liquid-gas-type phase transition. The model is shown to be momentum conserving. From the microscopic mechanical stability condition, the densities in bulk liquid and gas phases are obtained as functions of a temperaturelike parameter. Comparisons with the thermodynamic theory of phase transitions show that the lattice-Boltzmann-equation model can be made to correspond exactly to an isothermal process. The density profile in the liquid-gas interface is also obtained as a function of the temperaturelike parameter and is shown to be isotropic. The surface tension, which can be changed independently, is calculated. The analytical conclusions are verified by numerical simulations.