A. A. Starostin

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.

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.

Heat transfer in pulse-superheated liquids

Thermophysical properties [thermal conductivity λ(p, T) and thermal diffusivity a(p, T), which depend on pressure p and temperature T] are usually determined for liquids in a stable state. Measurements are carried out with small temperature perturbation δT(t) ! T0 [1]. Reference to the thermostat temperature T0 and long measurement time texp provide the upper limit of the temperature range in a thermophysical experiment ∆T = Ts(p) – T0, where Ts(p) is the temperature of the equilibrium coexistence of a liquid and vapor. The region beyond the line of the absolute stability of the liquid is poorly studied. We aim to experimentally study heat transfer in short-lived liquids superheated with respect to the equilibrium temperature Ts(p) and/or with respect to the onset temperature Td of the thermal destruction of molecules in a quasi-static process. The investigation is distinctive because the system lifetime (T) is limited, and the farther the system is from thermal stability, the more stringent is this limit. The approach under development is aimed at creating short-term quasi-isothermal conditions t (T = const) in a chemically reacting system, texp < ). Singleand multicomponent polymer liquids were studied as typical thermally unstable systems (Td < TO, where TO is the effective critical temperature of a substance). In pulsed processes with characteristic times texp ~ 10–5–10–3 s, a polymer can be substantially superheated with respect to a temperature of Td with negligible thermal destruction [2]. To solve the problem, we developed methods for an automatic choice of the heating function for a thermal probe, determination of the phase stability boundary by using the heat flux density into the substance q(t)T , and calculation of the effective coefficients of thermal conductivity and thermal activity of locally superheated liquids on the basis of pulsed-experiment data and chosen model of the process. Experiments were carried out in a virtually unstudied part of the phase diagram, t

Identification of Heat-Exchange Parameters under Intensive Pulse Heating of a Wire in a Fluid

Complexity of processes running in energy-saturated systems in the thermal shock regime prevents calculating behavior of this type of systems in contingency and emergency situations [1]. It is necessary to study experimentally the specific features of heat exchange in the conditions of fast heating (105– 108 K/s) and also the relaxation of the systems in the case of high-intensity heat generation that is accompanied by penetration into the region of thermal instability of a material [2]. In this connection, we develop versions of the wire pulse heating method [3, 4] and the method of numerical modeling of heatexchange parameters, based on experimental results. The thermophysical properties of a material and the temperature distribution in a thin wall layer govern the heat-exchange intensity, which is controlled by the time dependence of the average wire temperature. While experimenting, one can observe signs of phase or chemical stability loss in the system, whose manifestations are characteristic perturbations of the wire heating curve [2–4]. The method allows one to control the time and temperature changes in the material state and is high sensitive. The wire heating intensity is programmed by computer facilities according to the model representations on behavior of the material, and the observed deviations of the wire heating temperature from modeled dependences show how the system state changes. A classical application of hot wire methods to determining volumetric heat capacity and thermal conductivity by results of one experiment assumes that the experiment goes on to high Fourier numbers Fo 1 because the thermal conductivity is observed in a thermogram in the region of high values of Fo [11]. This circumstance frequently constraints the interval of possible heating intensity values due to premature loss of the material stability [2–6]. However, there have been done many attempts to reduce this interval by dividing the contribution of the main thermophysical characteristics on the interval Fo ∼ 1, which makes it possible to move into the region of overheated states of a material [5, 6]. This approach inevitably requires improving quality of experimental work because the influence of noise and errors in the initial data on the results of calculating the properties grows as much as for the problem of thermogram extrapolation to the region of high Fo. The uncertainty of input data for calculating the properties is connected in many respects with the general approach in traditional unstationary measurement methods. That is, the temperature perturbation value should be done relatively small. Meanwhile, the minimal possible perturbation is frequently determined from the level of experimental setup errors and noise. It is clear that increasing introduced perturbation will positively affect the signal-to-noise ratio, but will lead to necessity to solve the nonlinear nonstationary equation of thermal conductivity because of the temperature-dependent properties of the material and the wire. At the same time, modern methods of numerical experiments have been sufficiently developed for solving direct problems of calculating temperature distribution in unstationary processes. It is possible to construct the procedure of system identification by heat exchange parameters by comparing a numerical solution to the direct problem and the real experiment [7–10]. Estimation or refinement of parameters of a model with a known structure is solved using various optimization procedures, beginning from the leastsquares method to genetic algorithms. Doing so, it is necessary to reduce the influence of systematic and

A method of controllable pulse-heating for investigation of properties of short-lived liquids

AbstractA method of controlled pulse heating of low-inertia thermal probe immersed into the liquid under study with a temperatureT0 is described. The control system provides a “temperature plateau”-type heating mode, which consists in a rapid (t1∼10 μs) increase in the mass-average probe temperature

Development of a self-contained device for rapid detection of volatile impurities in the oil system of a turbine

\bar T

Assessment of the thermal stability of a polymer liquid by the controlled pulsed heating method

to a chosen valueTpl≫T0 and maintains this value for a certain time interval (t2∼103–102 μs) to within 1 K. Thermal effusivity of the substance, in relative units, is determined from the value of its internal heat flux. Sensitivity to changes in the thermal effusivity of a reference substance was 10−4. Due to the short pulse length and fine tuning of theTpl value, the method allows one to conduct step-by-step scanning of “instantaneous” thermal properties of a substance in the region of its short-lived states.

An experimental investigation of heat transfer in thermally unstable polymer systems

The article describes the experimental approach to elucidate the characteristics of the initial spontaneous boiling (spontaneous boiling-up) and the related effect of attainable liquid superheat. Presented is the analysis of the pioneering works on this subject carried out by G.V. Ermakov in the 60ies under the leadership of V.P. Skripov. They were the “healthy stimulus” for the revival of interest to liquid superheat in the scientific community. The article is devoted to the 80ies anniversary of Ermakov (1938–2012), who has been recognized for a series of investigations on thermodynamic properties of superheated liquids and the kinetics of liquid boiling-up [1]. The article presents discussion of the most striking results obtained in Ermakov’s team and also the previously unpublished results. Selection of issues for discussion was dictated by the preferences of the authors who collaborated with Ermakov.