Vol 27, No 3 (2018)

To describe the motion of the film flowing downward the vertical wall in the mode of condensation or evaporation into the surrounding space, the model proposed in [1] is used. It is reduced to one equation for the film thickness. The model comprises two governing parameters. The first one is proportional to the difference in the wall temperature, assumed to be constant, and the saturation temperature, and the second is proportional to the surface tension coefficient. In a series of publications [1–4] the authors studied solutions of thementioned equation at zero surface tension. Their characteristic feature is the presence of strong and weak discontinuities of layer thickness. In this paper we studied the regularizing effect of surface tension on the film flow structure with phase transitions. Numerical and asymptotic analysis of the resulting structures is carried out. Also, the case where the wall temperature is an arbitrary function of time is considered.

The paper presents results of a computational experiment simulating rapid cooling by falling liquid nitrogen film of an overheated vertical copper plate with a structured capillary-porous coating. A dynamic pattern of the running quench front was obtained, and it correlates satisfactorily with that observed in the experiments. The features of the heat transfer and quench front dynamics in the transient process are studied. The maximum density of the heat flux carried away into the liquid turned out to exceed by far that in quasi-stationary conditions. The presence of capillaryporous coating significantly affects the dynamics of quenching and temperature fields and makes it possible to reduce the total quenching time more than threefold. Initialization of a quench front on a plate with a structured capillary-porous coating occurs at a temperature much higher than the thermodynamic limit of liquid superheat. The reliability of the numerical simulation results was confirmed via direct comparison with experimental data on the variation of the plate temperature, as well as on the velocity and geometry of the quench front.

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.

Thermodynamic analysis of a new adsorption cycle recently suggested for upgrading ambient heat (the so-called “Heat from Cold” or HeCol cycle) was performed. The energy and entropy balances at each cycle stage and in each converter component were calculated for the methanol–AC-35.4 activated carbon working pair under conditions of ideal heat transfer. It is shown that useful heat can be obtained only if the ambient temperature is below a threshold temperature. The threshold temperature was calculated based on the Polanyi principle of temperature invariance and was experimentally validated. The specific useful heat can reach 200–300 J/(g adsorbent), which is of practical interest. The use of adsorbents with an abrupt change in the adsorption uptake between boundary isosters of the cycle may lead to further enhancement of the useful heat. For the HeCol cycle, the exergy losses under the conditions of ideal heat transfer are small. At low ambient temperature, the losses in the evaporator, condenser, and adsorber are comparable, whereas at higher ambient temperature the main exergy losses originate from the adsorber heating and cooling.

Accurate and sensitive nanoscale thermal probing for thermophysical property characterization is appealing but still a challenge to date. Previous studies have revealed that graphene quantum dots (GQDs) are good temperature markers for their small dimension and superior fluorescence excitation. In this work, we show that the thermal response of fluorescence spectrum of GQDs is strongly pH-dependent. Significant decrease (about 56% to 30%) for temperatureinduced intensity reduction within a small range of 75°C under different excitation wavelengths of 370 nm, 390 nm, and 410 nm is observed as pH value increases from pH = 1 to pH = 13. The temperature coefficients of peak wavelength change from positive to negative with the increase of pH value, meaning that the blue shift happens as the condition is changed from acidity to alkalinity. Temperature dependence of peak width is also studied with the largest coefficient of 0.2255nm/°C, which is remarkable. These suggest that when using GQDs in nanoscale thermal probing, the pH value is an important factor that should be considered besides the excitation wavelength. Regarding the superior biocompatibility and low cytotoxicity, GQDs could play an important role in thermal probing or mapping in a complex biology system such as a cell, and help to develop novel treatments and diagnoses.

An experimental study of the process of high-speed acceleration in a ballistic booster complex–reference node pair was carried out as well as mathematical modeling of the distribution of temperature fields in the reference node material. Metallographic study was done to confirm the modeling.