UDC 536.423 S. P. Aktershev and V. V. Ovchinnikov Steady propagation of the boundary of a vapor cavity in a layer of a metastable liquid along the heater surface is considered. The temperature and velocity of interface propagation are determined from the equations of conservation of mass, momentum, and energy in the neighborhood of the stagnation point of the vapor cavity and the condition of stability of steady motion of the interface. It is shown that a solution of these equations exists only if the liquid is heated above a threshold value. The calculated velocity of interface motion and the threshold value of temperature are in reasonable agreement with available experimental data for various liquids within wide ranges of saturation pressures and temperatures of the superheated liquid.Introduction. The problem of growth of the vapor phase in a superheated liquid is important for understanding the fundamental features of the boiling process. In the general statement, this problem is extremely complicated, because the growth of the vapor phase depends on many interrelated factors: heat-transfer intensity, evaporation kinetics, liquid dynamics, etc. The experiments [1-4] revealed degeneration of the bubble boiling mode, when already the first emergence of the vapor phase led to formation of a stable vapor film, skipping the bubble boiling mode (third crisis of heat transfer). It was demonstrated [4] that there exists a lower boundary of superheating prior to incipience for the third crisis, and the values of heat fluxes in such a situation are lower than the values of the first critical flux. In this case, instability starts to develop in the contact zone between the vapor bubble surface and the heater, and conical vapor cavities propagating along the heater are formed (Fig. 1).It was shown [5, 6] that the stagnation point of a conical vapor cavity (evaporation front) moves with a constant velocity. The velocity of the evaporation front substantially depends on liquid superheating and can reach tens of meters per second. The data on the evaporation front velocity for various organic liquids, water, and liquid nitrogen, were obtained in [5][6][7][8][9][10][11]. The experiments were performed at pressures both below and above the atmospheric value, with the use of a cylindrical heater and a plane heater under conditions of quasi-steady heating and a stepwise increase in power. It should be noted that the character of motion of the evaporation front is considerably different from the character of motion of the incipience wave, when the incipience zone consisting of isolated growing vapor bubbles propagates along the heated surface with an approximately constant velocity [6,8]. In contrast to the incipience wave, the evaporation front is a moving interface. If the superheating is close to the threshold value, either the evaporation front or the incipience front can be observed; a transition from the incipience front to the evaporation front is also possible [8].The evaporation front has some specific features and is ...
536.248 1. Introduction. Despite numerous studies of the physics of boiling, the calculation of the dynamics of transient processes (vapor explosion, explosive boiling, heat-transfer crisis, transition boiling, and flashing) still remains problematic. This is due not only to the difficulties in describing them by a system of hydrodynamics and heat-transfer equations and in solving this system, but also to an incomplete understanding of the physical factors affecting these processes. The latter is largely accounted for by the absence of fundamental experimental studies that could form the basis for creating adequate theoretical models. Transient processes in boiling systems usually occur at high levels of metastability of a liquid. To understand these complex processes, it is necessary to study the dynamics of evaporation at high superheatings of a liquid.In [1], it was first shown that under strong superheatings of the heating surface relative to the saturation temperature, the disintegration of a metastable near-wall liquid proceeds in the form of evaporation fronts spreading along a heater with high constant velocity. Evaporation fronts appear on the surface of a vapor bubble as a result of the loss of interphase-surface stability [2]. The term "evaporation front" is used for the face part of the surface of a vapor formation spreading along the heater. In [3][4][5][6], the effect of the regime parameters (superheating, pressure, and subcooling) on the velocity of an evaporation front in water and organic liquids at subatmospheric pressures was studied experimentally. At low pressures a critical regime of vapor outflow from an evaporation front occurs. To describe the evaporation front under these conditions, a model was created based on a simplified theory of evaporation using the Hertz-Knudsen formula for vapor
The essential properties of the primary structure of regulatory peptides, i.e. amino acid residues and their combinations, which are characteristic of the whole population of regulatory peptides, have been revealed using statistical methodology. These properties are as follows: increased content of certain residues (Gly, Pro. Phe, Arg, Tyr, Met and Trp) as well as an increased rate of occurrence of certain pairs of residue as compared with proteins, a random sequence of residues and "nonregulatory" peptides. By representing regulatory peptides as a sequence of hydrophobic (2 types) and hydrophilic (3 types) segments, the pattern for alternation of these segments in regulatory peptides has been determined. The segments were classified into 5 types according to the peculiarities of mutual localization of hydrophobic and hydrophilic residues within the primary structure of regulatory peptides. As compared with proteins, "nonregulatory" peptides and a random sequence of segments, regulatory peptides were characterized by an increased frequency of 4 particular pairs of segments among 12 theoretically possible pairs. These 4 pairs are fragments of the periodic segment sequence with periods of 4 segments. The revealed pattern indicates that there exists a general principle of the regulatory peptide primary structure organization and possibly a common type of the regulatory peptides flexible peptide chain folding at the ligand-receptor complex formation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.