Pavel V. Skripov

The Attainable Superheat: From Simple to Polymeric Liquids

The phenomenon of the attainable superheat of a substance and the kinetics of nucleation of a vapor phase have been studied experimentally for liquids with molecular weight from 102 to 104. The values of the temperature of spontaneous boiling-up T* have been measured over a wide range of parameters (pressure, heating rate, CO2 content, molecular weight, and thermal stability of a substance) by the method of controlled pulse heating of a thin wire probe using pulse lengths from 0.01 to 4 ms. The investigation is based on a gradual increase in the molecular weight of a sample. The peculiarities of spontaneous nucleation in polymeric liquids that do not boil without decomposition are discussed. It is shown that this phenomenon is a reproducible relaxation process in a polymeric system, which accompanies the initial stage of its thermal decomposition.

Estimation of the critical constants of long-chain normal alkanes

Correlations between the critical constants of normal alkanes and the number of carbon atoms in a molecule have been considered. In an approximation of a self-consistent field for a polymeric fluid, an equation of state of the van der Waals type has been written, and the dependences of the critical constants of chain molecules on the number of mers have been obtained. It has been found that for an infinitely long alkyl chain, the limiting values of the critical temperature, the critical pressure, and the critical density are equal to, respectively, 1135 K, 0 M Pa, and 0 kg · m−3. A method of pulse heating of a wire probe immersed in the substance under investigation has been used to measure the dependence of the temperature of the attainable superheatT* of low-density polyethylene on the pressure p and the duration of heating pulset*. Extrapolation has been used to obtain an estimation of the attainable-superheat temperature of polyethyleneT*(p=0,t*=0)= 1175 K, which can be treated as the “critical” temperature of polyethylene.

Comparison of thermophysical properties for oil/refrigerant mixtures by use of the pulse heating method

Abstract The method of pulse heating for the study of thermophysical properties for oil/refrigerant solutions in a wide temperature range and for monitoring of an actual state of these systems has been developed. The regimes of linear heating and thermostabilization of the superheated probe are applied for solving our task. The objects of study are as follows: synthetic oils Mobil EAL Arctic 22, PLANETELF ACD22, XMPA, and solutions of carbon dioxide in these oils. The upper boundary, with respect to temperature, of the two-phase equilibrium region including the vicinity of the liquid–vapour critical curve of these systems, gas solubility in oils at various temperatures, short-time thermostability, and thermal conductivity of oils are considered. Inclusion of the thermally unstable states of a substance in investigation allows one to essentially extend the set of compared data.

Apparatus for studying heat transfer in nanofluids under high-power heating

A technique of electronic control of the probe heating power is developed using the method of controlled pulse heating of a wire probe, that is a resistance thermometer, was developed. An apparatus implementing this technique was fabricated. The characteristic parameters of the apparatus are as follows: the heating pulse length, 1 to 10 ms; the heat flux density through the surface of a 20 µm probe, 1 to 10 MW/m2; repeatability of selected power value in a series of pulses is on a level of 0.05%. As an example, the constant heating power mode is applied for comparing the thermal resistance of nanofluids in the region of stable states of liquid and superheated (with respect to the liquid-vapor equilibrium temperature of the base liquid) ones. The parameter was the content of Al2O3 nanoparticles in the base liquid (isopropanol).

A method of controlled pulse heating: Applications

This paper is devoted to the state-of-the-art and technical potentials of the pulse heating method for the thin wire probe created in the Ural thermophysical school for studying the kinetics of spontaneous boiling and the related phenomenon of liquid attainable superheating. Special attention is paid to the search for technical means for controlling the power of the probe heating in a pulse experiment with the thermophysical properties of the substance taken into account. Applications of three particular cases are considered: techniques for the constant heating power, the thermal stabilization of the pulse-heated probe, and cooling of the shock-heated probe for investigating the behavior of multicomponent and high-molecular fluids essentially superheated above the temperature of phase equilibrium and/or temperature of molecule thermodestruction in a quasi-static process. Opportunities for application of the method are presented, in particular, for fast detection of volatile admixtures (including their traces) in high-molecular fluids, e.g., in oils of power equipment.

Bubble Nucleation in Polymeric Liquids Under Shock Processes

AbstractThis paper studies the phenomenon of spontaneous boiling-up of polymeric liquids on heating at rates

Spontaneous boiling up as a specific relaxation process in polymer–solvent systems

(\dot T)

Controlled high-power heat release as a tool to selecting working pressure for supercritical water

up to 107 K·s−1. A model of the thermal equation of state for (polymer + monomer) systems and a procedure for determination of the spontaneous boiling-up temperature T* for polymeric liquids, taking decomposition into account, are proposed. The experimental data on T*