Heat transfer in a subcooled evaporating liquid film

An investigation is performed of heat transfer in films of water and FC-72 liquid falling down a 60×120 mm heater. Heat transfer mode maps are constructed. Zones of structure formation and regions of emergence of breakdown of liquid film are identified, as well as regions of boiling in jets. An averaged coefficient of heat transfer was used in analyzing the experimental data. It is demonstrated that thermocapillary forces have a complex and ambiguous effect on heat transfer. The emergence of extensive stable dry spots causes a decrease in the average coefficient of heat transfer. On the other hand, an increase in the path length of film and in the amplitude of wave motion leads to the washing out of the dry spots and to an increase in the relative intensity of heat transfer. The regularities of heat transfer in the region of flow of film with breakdowns for weakly and intensely evaporating liquids differ significantly. An enhancement of heat transfer is observed under conditions of significant evaporation during structure formation in the thermocapillary mode.     

Phase transformations in a stream of evaporating liquid

An equation is derived describing the kinetics of phase transformations, in dimensionless variables, for the adiabatic nonequilibrium flow of an evaporating liquid.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 23, No. 1, pp. 59–62, July, 1972.     

Slip effect on shear-driven evaporating liquid film in microchannel

The development of compact, advanced cooling technology leads to problems involving two-phase flows at micro-scales. We investigate the effect of slip on heated liquid film driven by its own vapor in microchannel. The macroscopic interface shape is found to be sensitive to slip length comparable with the initial film thickness. The slip at the wall tends to elongate the transition film, and can have an effect on the mass flow rate. Calculations reveal that the maximum of the slip velocity is located in the transition region. The present work is a part of the preparation of the SAFIR experiment of the European Space Agency onboard the International Space Station.     

Marangoni-induced deformation of evaporating liquid films on composite substrates

Marangoni convection plays an important role in hydrodynamics of evaporating liquid films and sessile drops. Evaporation of liquid films induces unsteady nonuniform temperature distribution across the liquid layer and in a substrate. If the substrate is composed of parts with different thermal properties, the interface temperature distribution becomes non-uniform, leading to appearance of Marangoni stresses, convective vortices, and film deformation. In this article, a model describing evaporation, Marangoni effect and interface dynamics of liquid films on composite substrates is developed. The film dynamics is described in the framework of long-wave theory. The unsteady heat conduction in the substrate is described using the Laplace transform method for semi-infinite substrates and using the separation of variables technique for substrates of finite thickness. The non-uniformity of substrate thermal properties has a pronounced effect on film dynamics.     

Study of Marangoni instability of an evaporating liquid layer

Abstract

The onset of Marangoni instability of an evaporating liquid layer is studied theoretically. By assuming the surface regression of the liquid layer is negligibly small and the surrounding gas phase is asymptotically steady, similarity solutions are obtained prior to the onset of instability. Linear stability analysis is then applied to obtain the critical Marangoni number for the onset of instability. The results indicate that : (1) The onset condition is a strong function of the initial temperature of the liquid layer with which the critical Marangoni number decreases. (2) As time proceeds, the thermal boundary layer thickness near the free surface becomes larger, and the liquid layer becomes more unstable. (3) For a liquid layer with a higher initial temperature (closer to the boiling point) the most unstable mode of the disturbance shifts from a lower wave number to a higher wave number.     

Critical discharge of a spontaneously evaporating liquid from cylindrical channels

A method is proposed for the calculated determination of the critical pressure in the discharge of a spontaneously evaporating saturated liquid through cylindrical channels. The results of the calculation are compared with experimental data.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 1, pp. 30–33, January, 1977.     

Undular flow of an evaporating viscous liquid film under uniform injection

The wave profile on the free surface of a thin viscous liquid film flowing along a porous surface under uniform injection is established here by the asymptotic method which has been developed in [1, 2].Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 3, pp. 434–439, March, 1973.     

Diffusion and thermal relaxation at the plane surface of an evaporating liquid

Nonstationary evaporation and diffusion of vapor is considered in conjunction with the associated heat conduction processes. An exact solution of the problem for a plane evaporation surface is obtained with allowance for temperature and concentration discontinuities.     

Temperature field in a heat-transfer wall with a thin liquid film evaporating periodically from its surface

Using an approximate method of analysis developed earlier for studying heat-exchange processes occurring with a periodic intensity, the problem of periodic evaporation of a liquid film from the surface of a heat-transfer wall is considered. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 3, pp. 473–476, May–June, 1998.     

Thermal conductivity of liquid tetrachlorides

The thermal conductivity of liquid carbon, silicon, titanium, germanium, and tin tetrachlorides overthe-20 to +60°C temperature range was measured by the transient relative null method with a hot wire.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 23, No. 5, pp. 835–841, November, 1972.     

Thermal entry length in falling liquid film

The variation in thermal entry length (TEL) in a heated liquid film flowing down a vertical plate has been experimentally studied for high Reynolds numbers of the flow. Even at low heat fluxes, zones with a temperature exceeding the initial temperature of the film are formed at a distance of ∼7 mm from the upper edge of the heater in the region between rivulets, which is formed between the crests of developed three-dimensional synchronous waves. In rivulets passing along the crests of these waves, the TEL is greater, but it rapidly decreases with increasing heat flux density.     

Thermal conductivity of liquid n-alkanes

The thermal conductivity of liquids has been shown in the past to be difficult to predict with a reasonable accuracy, due to the lack of accurate experimental data and reliable prediction schemes. However, data of a high accuracy, and covering wide density ranges, obtained recently in laboratories in Boulder, Lisbon, and London with the transient hot-wire technique, can be used to revise an existing correlation scheme and to develop a new universal predictive technique for the thermal conductivity of liquid normal alkanes. The proposed correlation scheme is constructed on a theoretically based treatment of the van der Waals model of a liquid, which permits the prediction of the density dependence and the thermal conductivity of liquid n-alkanes, methane to tridecane, for temperatures between 110 and 370 K and pressures up to 0.6 MPa, i.e., for 0.3T/T _c0.7 and 2.4P/P _c3.7, with an accuracy of ±1%, given a known value of the thermal conductivity of the fluid at the desired temperature. A generalization of the hard-core volumes obtained, as a function of the number of carbon atoms, showed that it was possible to predict the thermal conductivity of pentane to tetradecane±2%, without the necessity of available experimental measurements.     

Thermal conductivity of liquid mixtures

This paper adopts a phenomenological approach and presents a new model of a mixture of nonreacting liquids as a mixture of two interpenetrating continuous media. An analytical relationship for calculating the effective thermal conductivity of a mixture of liquids is given and the results are compared with experimental data.     

Thermal control over X-ray diffraction patterns

The effect of inhomogeneous light-beam-induced heating of a potassium dihydrophosphate (KDP) crystal on the positions of maxima in the patterns of X-ray diffraction has been studied using the characteristic K _{α1, α2} radiation. This phenomenon can be used in order to decrease aberrations in optical systems.     

Nanoliter liquid metering in microchannels using hydrophobic patterns

Nanoliter-sized liquid drops can be accurately metered inside hydrophilic microchannels using a combination of hydrophobic surface treatment and air pressure. The technique involves spontaneously filling the microchannels up to a hydrophobic region and splitting a liquid drop by injecting air through a hydrophobic side channel. The hydrophobic regions are fabricated by using a patterned metal mask on a substrate. The patterned substrate is immersed in an isooctane solution containing 1H,1H,2H,2H-per-fluorodecyltrichlorosilane to form hydrophobic patches on the exposed surface. Stripping the metal mask leaves the hydrophobic patches and restores the hydrophilic substrate surface. Precise and accurate liquid volumes, ranging from 0.5 to 125 nanoliters, have been metered using this technique. Theoretical predictions of the pressure needed to meter drops compare well with the experimental values.     

An investigation into the heat and mass transfer of a liquid evaporating from a capillary-porous body

A theoretical analysis is presented for the process of heat and mass transfer in the case of a liquid evaporating from a capillary-porous body into an approaching gas stream. The method of the experimental investigation into this process is described. The excellent agreement between the experimental and theoretical data makes it possible to use the resulting quantitative relationships to calculate the heattransfer coefficients in the case of intermittent cooling.     

Thermal conductivity of subcooled liquid oxygen

The thermal conductivity of liquid oxygen below 80 K and pressures up to 1 MPa has been measured using a horizontal, guarded, flat-plate calorimeter. The working equation of the calorimeter is based on the one-dimensional Fourier’s law. The gap between the calorimeter plates was measured in situ from a capacitance measurement. The cooling power to the calorimeter is provided by a two-stage Gifford-McMahan cryocooler. The absolute temperatures are measured using platinum resistance thermometers. The results are compared to existing data and analytical models.     

The relation of steady evaporating drops fed by an influx and freely evaporating drops

We discuss a thin film evolution equation for a wetting evaporating liquid on a smooth solid substrate. The model is valid for slowly evaporating small sessile droplets when thermal effects are insignificant, while wettability and capillarity play a major role. The model is first employed to study steady evaporating drops that are fed locally through the substrate. An asymptotic analysis focuses on the precursor film and the transition region towards the bulk drop and a numerical continuation of steady drops determines their fully non-linear profiles. Following this, we study the time evolution of freely evaporating drops without influx for several initial drop shapes. As a result we find that drops initially spread if their initial contact angle is larger than the apparent contact angle of large steady evaporating drops with influx. Otherwise they recede right from the beginning.     

Thermal conductivity of alternative refrigerants in the liquid phase

Measurements ofthe thermal conductivity of five alternative refrigerants. namely, difluoromethane HFC-321. pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichloropentafluoropropanes (HCFC-225ca and HCFC-225cb). are carried out in the liquid phase, The range of temperature is 253–324 K for HFC-32, 257–305 K for HFC-125, 268–314 K for HFC-134a. 267–325 K for HCFC-225ca, and 286–345 K for HCFC-225cb, The pressure rank is from saturation to 30 MPa, The reproducibility of the data is better than 0.5% and the accuracy of the data is estimated to be of the order of 1%. The experimental results for the thermal conductivity ofeach substance are correlated by an equation which is a function of temperature and pressure. A short discussion is given to the comparison of the present results with literature values for HFC-125, The saturated liquid thermal conductivity values of HFC-32. HFC-125, and HFC-143a are compared with those of chlorodifluoromethane (HCFC-22) and tetrafluoroethane (HFC-134a) and it is shown that the value of HFC-32 is highest, while that of HFC-125 is lowest, among these substances, The dependence of thermal conductivity on number of fluorine atoms among the refrigerants with the same number of carbon and hydrogen atoms is discussed.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994. Boulder, Colorado. U.S.A.     

Thermal acoustic oscillations in triple point liquid hydrogen systems

Thermal acoustic oscillations are often observed in tubes which penetrate a cryogenic system and are closed at the warm end and open at the cold end. Such tubes are genrally used for filling or vetning the tank, providing relief pressure or inserting instruments taps. Large amounts of heat (of the order of ten to a thousand times more than by normal heat conduction) can be transferred into a cryogenic system when such thermaloscillations occur. A number of studies examining thermal acoustic oscillations in liquid helium systems have been performed by Rott et al. However, only minimal consideration has been given to such oscillationsin liquid and sluch hydrogen systems. This study extends Rott's theory to the stability aspects of thermal acoustic oscillations for a straight tube closed at the warm end and inserted into a Dewar flask filled with triple point liquid hydrogen when the cold open end is located above the liquid surface. These results can also be applied to a slush hydrogen when the pressure in the Dewar flask is reduced to the triple point pressure of hydrogen. Numerical results have been obtained in this study for developing stability curves, establishing oscillation frequency characteristics and identifying critical configurations for initiating such oscillation. The mechanisms associated with the two branches of the stability curves for thermal acoustic oscillations have also been investigated.