Study into the Pattern of Flashing of Liquid in the Vicinity of the Limit of Its Attainable Superheating

The pattern of flashing of liquid in the vicinity of the limit of its attainable superheating is investigated experimentally. The Skripov criterion is used, according to which, in the case of homogeneous boiling, the product of the mean expectation time for boiling by the magnitude of volume being superheated at preassigned temperature and pressure is a constant quantity. The experiments are performed with n-pentane. Thanks to thorough degassing of the liquid being investigated, the temperature of the previously attained superheating is exceeded by 1.0–1.5°C. The mean lifetime is measured in several glass capillaries of substantially different volumes. The data obtained point to the invalidity of the criterion of homogeneity of boiling of liquid in the vicinity of the limit of its attainable superheating. Also studied is the probability density of the expectation times for boiling with respect to magnitude. It is demonstrated experimentally that the probability density curve has a small empty portion at the beginning, an abrupt rise to a maximum, and a close-to-exponential decrease. This form of the probability density function is typical of unsteady-state random processes.     

Special features of boiling of a slightly subcooled liquid

Slightly subcooled boiling is characterized by the fact that vapor bubbles that form at active sites on the heater surface grow continuously and, having attained a maximum size, separate and float. The frequency of bubble separation, which determines the rate of heat transfer, depends on the degree of subcooling of the boiling liquid. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 6, pp. 993–995, November–December, 1998.     

Characteristic features of the boiling of emulsions having a low-boiling dispersed phase

The results of investigation of heat transfer from thin wires to a boiling emulsion, the dispersed phase of which is formed from a liquid with a boiling temperature much lower than the boiling temperature of the dispersion medium, are presented. Two variants of boiling of such an emulsion are possible: boiling of the dispersed phase alone and simultaneous boiling of the dispersed phase and dispersion medium. In the present work, only the first variant has been studied; it is distinguished by the following most important features: high superheat of the dispersed-phase droplets ΔT_sup of the emulsion and a wide temperature range of bubble boiling (50–200°C). For conventional heat carriers (pure liquids and solutions), the value of ΔT_sup does not exceed 1–10°C, with the bubble-boiling interval lying within the range from 5 to 20°C. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 6, pp. 81–84, November–December, 2006.     

Boiling of liquid in the cell of a jet printer

An approximate calculation of the main parameters of boiling of a liquid in the cell of a jet printer — the ejection velocity of a liquid drop and the limiting permissible (critical) heat flow density supplied to the thermoresistor — is carried out. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 2. pp. 218–221, March–April, 1998.     

Role of drop superheating in the nonsteady drop cooling of a high-temperature wall

The influence of superheating and explosive boiling of a contact layer of drops on the heat transfer in drop cooling of a wall at a temperature exceeding the temperature of achievable heating of the liquid is considered.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 1, pp. 128–136, July, 1986.     

Model of vapor slug growth in the channels of power engineering equipment with sodium coolant

The problem of vapor volume growth in superheated liquid is very important both in practical and in theoretical aspects as the behavior of the solitary bubble governs the general patterns and the proceeding character of the boiling process. On the basis of the analysis of experimental and theoretical works, we create the physical and the numerical model of vapor volume growth in superheated sodium in power engineering equipment channels. On that basis, we implement the program module, making it possible to calculate the sodium boiling process under superheating. We perform a numerical analysis of the dependence of the vapor volume growth rate on the superheating value, the liquid film thickness, and the coefficient of the heat transfer with the wall. The numerical modeling results are compared to experimental data on the boiling of the sodium in the column and with the data on the sodium boiling under a decrease of the mass flow rate in the contour.     

Subcooled liquid boiling heat transfer under conditions of stepwise heat-load release

The results of experimental investigations of the effect of liquid subcooling below the saturation temperature on boiling heat transfer under conditions of an increase in a heating load are presented. Water and TS-1 kerosene were used as heat carriers. The obtained experimental data on subcooled liquid boiling heat transfer has been generalized by an empirical relation. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 1, pp. 136–139, January–February, 2007.     

Heat exchange processes near the boundary of a film boiling nucleus

Results are presented of an experimental investigation of the change in temperature, heat flux to the liquid, and rate of displacement of the isotherms near a film boiling nucleus propagating over a plane surface. The experiment was carried out in a liquid nitrogen bath at atmospheric pressure on the saturation line. The heater was a sapphire plate 1.2 mm thick having a heat transfer surface area of 77×22 mm². The following facts were established: 1) near the boundary of the film boiling nucleus a new heat exchange mechanism takes place caused by the instability of the liquid microlayer; 2) the maximum heat flux to the liquid is considerably greater than the critical heat flux; 3) the vapor film in the film boiling region grows gradually with increasing distance from the boundary, i.e., there is a smooth transition in terms of heat exchange intensity before the equilibrium film boiling level is reached. Pis’ma Zh. Tekh. Fiz. 25, 39–46 (November 12, 1999)     

Transient Processes and Thermoacoustic Effects in Surface Boiling of a Liquid

The results of experimental investigation of the phenomenon of hysteresis and the prehistory of boiling on a cylindrical heater have been given. The transient processes associated with thermoacoustic effects in burnout of a liquid under natural convection have been considered. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 4, pp. 22–26, July–August, 2005.     

Homogeneous and heterogeneous melting behavior of bulk and nanometer-sized Cu systems: a numerical study

Molecular dynamics simulations have been used to investigate the solid–liquid transition of different Cu systems. These consisted of surface-free crystalline bulks and semi-crystals terminating with a free surface as well as of particles and wires with different shape and size in the mesoscale regime. The characteristic melting points of the various systems were attained by gradual heating starting from 300 K. Apart from surface-free bulk systems, where the phase transition at the limit of superheating is homogeneous, melting displays heterogeneous character. This is due to the existence of surface layers with structural and energetic properties different from the ones of bulk-like interior. Simulations point out a significant depression of both the melting point and latent heat of fusion for nanometer-sized systems respect to semi-crystals. Below the characteristic melting point, free surfaces are involved in pre-melting processes determining the formation of a solid–liquid interface. The onset of melting is related to the formation of a critical amount of lattice defects and this provides a common basis for the rationalization of homogeneous and heterogeneous melting processes despite their intrinsic differences.     

Numerical Investigation of a Periodic Heating Thermal-Bubble Actuated Diffuser–Nozzle Valveless Pump

A valveless micropump actuated by thermal bubbles which generated by an electrode heater mounted with a pair of diffuser nozzles has been numerically studied by commercial CFD software FLUENT. The relationship between the net flow rate and the superheating and heat supplying frequency has been investigated. The depth of the diffuser–nozzle micropump used in current numerical simulation model is 200 μm, and the diameter of micropump chamber is 1 mm. The pair of diffuser–nozzles are with gaps expanding from 30 to 274 μm and open angles of 7°. The working fluid is methanol in present study. The results show that the pump has different optimal driving frequency with different superheating. The cycle composed of bubble growth and shrinking costs more time at higher superheating. The maximum volume flow rate and the maximum pump pressure will increase with increasing superheating, simultaneously; and the optimal pulse duty, the maximum volume flow rate and pump pressure decrease with increasing superheating. The maximum volume flow rate and the maximum pump pressure are 29.6 μL/min and 680 Pa at ΔT = 15°C, respectively.     

1/f Fluctuations in Critical Modes of Flow of Superheated Liquid

Experimental studies are performed into the variation of the shape of a jet of boiling liquid flowing out of a high-pressure vessel under conditions of high superheating. The mechanisms of bulk heterogeneous and homogeneous nucleation are identified, and the correlation between these mechanisms and critical modes of outflow is determined. The photometry of transmitted laser radiation is used to investigate the dynamics of photocurrent fluctuations. It is found that, in the case of intensive bulk boiling in a jet of superheated liquid, the fluctuation power spectrum has a low-frequency component (flicker noise) diverging as 1/f. This effect is associated with nonequilibrium phase transitions proceeding in the system.     

Bubble chamber as a trace chemical detector

A novel concept for trace chemical analysis in liquids has been demonstrated. The technique utilizes light absorption in a superheated liquid. Although a superheated liquid is thermodynamically unstable, a high degree of superheating can be dynamically achieved for a short period of time. During this time the superheated liquid is extremely sensitive to boiling at nucleation sites produced by energy deposition. Observation of bubbles in the superheated liquid in some sense provides amplification of the initial energy deposition. Bubble chambers containing superheated liquids have been used to detect energetic particles; now a bubble chamber is used to detect a trace chemical in superheated liquid propane by observing bubble formation initiated by optical absorption. Crystal violet is used as a test case and can be detected at the subpart-per-10(12) level by using a Nd:YAG laser. The mechanism for bubble formation and ideas for further improvement are discussed.     

Residence-time distribution of particles in the post of a circulating boiling bed

The residence-time distributions of particles in the lifting post of a circulating boiling bed were calculated on the basis of a model of longitudinal mixing of particles in this bed. It is shown that this model is well approximated by the standard γ-distribution. The dependence of the residence-time distribution function on the main parameters of the circulating boiling bed has been determined. The calculated and experimental distribution functions were compared. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 3, pp. 164–170, May–June, 2006.     

Calculation of the surface density of nucleation sites in nucleate boiling of a liquid

On the basis of an approximate analysis of flow in a liquid macrofilm on a heating surface the characteristics of nucleate boiling (surface density of nucleation sites, effect of the thermal conductivity of the wall on the averaged heat transfer) are estimated. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 1, pp. 176–181, January, 1998.     

Boiling of sodium in a circular pipe

A single-bubble model for the boiling of a coolant in channels is analyzed. Calculations are reported on the dynamics of the ejection of sodium from a circular pipe during the boiling of sodium as a function of the initial superheating, the heat flux, and the point at which the vapor bubble forms.Translated from Inzhenerno-Fizicheskii Zhurnal. Vol. 27, No. 6, pp. 957–963, December, 1974.     

Isobaric Vapor–Liquid Equilibria of 1-Butanol–p-Xylene System

Isobaric vapor–liquid equilibrium data were obtained for 1-butanol–p-xylene system at 97.3 kPa using a vapor recirculating type (modified Othmer’s) equilibrium still. The activity coefficients were obtained by taking into consideration vapor-phase imperfections. The experimental data for this system were tested for thermodynamic consistency and were correlated by various equations. The system forms a minimum boiling azeotrope.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

Modeling the spatially-uniform heating of liquids

An apparatus for achieving the spatially-uniform heating of a liquid up to 80 liters in volume, with a superheating of up to 3–4°C and a pulsed type of boiling, is described; electrolytic heating is employed, the layers next to the electrodes being insulated by means of ion-exchange membranes.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 19, No. 6, pp. 1125–1128, December, 1970.     

Influence of the Operating Time of a Surface Heated by Electric Current on the Heat-Transfer Coefficient of Kerosene and Water Boiling on It

Results of experimental investigation of the influence of the operating time of a heating surface on the intensity of heat transfer in the kerosene and water boiling on it are presented. The experimental data on the heat transfer in the indicated liquids boiling on unrun heating surfaces have been generalized using different relations. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 3, pp. 134–140, May–June, 2005.