scholarly journals Structural Transition in Supercritical Fluids

2011 ◽  
Vol 2011 ◽  
pp. 1-5 ◽  
Author(s):  
Boris I. Sedunov
Keyword(s):  
Supercritical Fluids ◽  
Thermophysical Properties ◽  
Structural Transition ◽  
Heat Capacities ◽  
Saturation Curve ◽  
Physical Sense ◽  
Supercritical Region

The extension of the saturation curve on the PT diagram in the supercritical region for a number of monocomponent supercritical fluids by peak values for different thermophysical properties, such as heat capacities and and compressibility has been studied. These peaks signal about some sort of fluid structural transition in the supercritical region. Different methods give similar but progressively diverging curves for this transition. The zone of temperatures and pressures near these curves can be named as the zone of the fluid structural transition. The outstanding properties of supercritical fluids in this zone help to understand the physical sense of the fluid structural transition.

scholarly journals EQUATIONS OF AVERAGE ISOBARIC HEAT CAPACITY OF AIR AND COMBUSTION GASES WITH INFLUENCE OF PRESSURE AND EFFECT OF THERMAL DISSOCIATION

2019 ◽  
pp. 18-29
Author(s):  
Maya Vladimirovna Ambrozhevich ◽  
Mikhail Anatol'evich Shevchenko
Keyword(s):  
Heat Capacity ◽  
Thermophysical Properties ◽  
Thermal Dissociation ◽  
Heat Capacities ◽  
Isobaric Heat Capacity ◽  
Information Storage ◽  
Working Fluid ◽  
Saturation Curve ◽  
Functional Dependencies ◽  
Temperature And Pressure

All properties of thermomechanical systems working substance are two-parameter that is determined by two parameters, the most often they are temperature and pressure which are easily measured by experiment. Representing the isobaric heat capacity as a function of temperature cp = f(T) become a thing of the past. Analytical and tabular ways are used to represent dependencies as a function of temperature and pressure. The tabular method is convenient for single calculations, but the analytical one is more convenient for a series of calculations. The advantages of an analytical description in comparison with a tabular one are obvious, namely, compactness of information storage without reference to node points, the ability to integrate and differentiate, dependencies can be embedded directly in the program body and don’t require special subroutines to access to the tables. Developers of the programs for calculating thermophysical properties, as a rule, use functional dependencies which may have a different appearance for temperature and pressure intervals of the same substance. This is explained by the fact that in the region close to the saturation curve, there is a steep change in all the thermophysical properties of substances including the isobaric heat capacity. In thermogasdynamic calculations of heat machines, the main physical parameter of the working fluid is its heat capacity, both true and average. The article presents the analytical dependencies of the average specific isobaric heat capacities of the main components of air and combustion products of hydrocarbon fuels which are united throughout the specified range of pressures and temperatures (nitrogen: p = 1 ... 200 bar, T = 150 ... 2870 K, oxygen: p = 1 ... 200 bar, T = 210 ... 2870 K, argon: p = 1 ... 200 bar, T = 190 ... 1300 K, the water vapor: p = 0,1 ... 200 bar, T = 700 ... 2600 K, carbon dioxide: p = 1 ... 200 bar, T = 390 ... 2600 K). The analytical dependencies were derived on the basis of previously obtained analytical expressions for the specific isobaric heat capacities of these gases. The average specific isobaric heat capacities of gases are also functions of temperature and pressure cp = f(T, P) and take into account the effect of thermal dissociation. Formulas for average specific isobaric heat capacities are obtained by integrating expressions for specific isobaric heat capacities. Verification of the obtained dependencies for different temperature ranges was done.

Experimental Study on the Identification of the Saturation of a Porous Media through Thermal Analysis

2014 ◽  
Vol 611-612 ◽  
pp. 1576-1583
Author(s):  
Maxime Villière ◽  
Sébastien Guéroult ◽  
Vincent Sobotka ◽  
Nicolas Boyard ◽  
Joel Breard ◽  
...  
Keyword(s):  
Thermal Analysis ◽  
Heat Flux ◽  
Porous Medium ◽  
Thermophysical Properties ◽  
Saturated Porous Medium ◽  
Homogenization Method ◽  
Saturation Curve ◽  
Mechanisms Of Formation ◽  
Mechanical Performances ◽  
The One

Resin Transfer Molding (RTM) is among the most commonly used fabrication processes for producing high quality and complex composite structural parts. RTM process consists of placing a dry fibrous preform into a mold cavity. A liquid resin is subsequently injected into that cavity. The consolidation of the part is then obtained by crosslinking in case of a thermosetting resin or by crystallization in case of thermoplastic one. Voids can be created in the porous medium during the flow of the resin. Presence of residual voids in the composite part at the end of the filling drastically affect mechanical performances. Even if several authors have contributed to a better understanding and modeling of the mechanisms of formation and transport of voids during injection, few experimental approaches allowed a direct measurement of the saturation curve. The aim of this study is then to identify the saturation of a fibrous preform by a liquid through thermal analysis. To address this issue, an experimental bench that allows the injection of a fluid into a textile preform has been used. This apparatus combines the measurement of temperatures and wall heat flux densities at several locations. A simplified modeling of the filling front has been performed with FEM using Comsol Multiphysics™. The saturation curve is modeled using several geometric parameters. Saturation is taken into account through the evolution of thermophysical properties. Effective thermophysical properties of the dry and completely-saturated porous medium in transverse and longitudinal directions have been measured by several methods, and their results have been then cross-checked and compared with good accuracy. The evolution between these two states has been modeled. A particular attention has been paid for the modeling of the transverse thermal conductivity. This parameter has been modeled using a periodic homogenization method as a function of the micro- and macro-saturation. The saturation curve parameters are determined by minimizing the cost function defined as the square difference between the measured and computed heat flux. The obtained saturation curve is finally compared with the one measured by a conductometric sensor.

scholarly journals A corresponding-state framework for the structural transition of supercritical fluids across the Widom delta

2019 ◽  
Vol 150 (15) ◽  
pp. 154503 ◽  
Author(s):  
Tae Jun Yoon ◽  
Min Young Ha ◽  
Won Bo Lee ◽  
Youn-Woo Lee
Keyword(s):  
Supercritical Fluids ◽  
Structural Transition
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