Heat transfer under conditions of nucleate boiling

New physical concepts are developed in connection with the two fundamental processes resulting in the transfer of heat from a heater to a liquid under conditions of nucleate boiling.     

Transient nucleate boiling of liquid nitrogen with a stepwise change of heat flux

Results of experimental and theoretical investigations of unsteady nucleate boiling of liquid nitrogen are presented. A strip of niobium foil placed along the axis of a tube served simultaneously as a heater and as a resistance thermometer. Noted deviations from correlations for the steady nucleate boiling are explained by a new methematical model, which considers the process of transient nucleate boiling as stochastic.     

Generalization of test results on heat transfer in film boiling under natural convection conditions

Experimental results on heat transfer during film boiling in a large volume are compared for 13 fluids and with the computational dependences of different authors.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 1, pp. 54–58, July, 1977.     

Molecular thermodynamic method of correlating heat transfer in liquid boiling

A correlation is obtained for heat transfer in boiling of various liquids. A classification of materials in similarity groups is proposed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 36, No. 4, pp. 603–613, April, 1979.     

Electric field effects on boiling heat transfer of liquid nitrogen

This paper describes an experimental study into the influence of a d.c. uniform electric field on boiling heat transfer characteristics of liquid nitrogen. The electric field effect on the onset of boiling, nucleate boiling curve, hysteresis phenomenon and critical heat transfer were quantitatively investigated using a mesh-plane electrode system. For this purpose, a novel copper block electrode with temperature measurement and vacuum heat insulation was designed and manufactured. Moreover, a heat transfer model based on this electrode geometry has been developed in order to provide some useful data for the electrode design and assist temperature calculations. Detailed heat transfer processes appearing on the copper surface were observed and monitored using a high-speed camera. The experimental results show that electric fields have an obvious effect on boiling heat transfer of liquid nitrogen.     

Contribution to the static heat transfer to boiling liquid helium

Aluminium is now being used as a stabilizing material for superconducting materials. With regard to its use as a stabilizer, the heat transfer properties to boiling helium of 99.9999% pure aluminium are measured and compared with those of 99.999% pure aluminium and OFHC copper     

Convective heat transfer in a metastable liquid with delayed boiling

An analysis is made of the steady-state heat transfer in a large volume of diethyl ether, npentane, and benzene with a thin wire immersed. A 90°C superheat was produced at the wire surface, while the bulk liquid remained at saturation temperature.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 4, pp. 614–617, April, 1972.     

Forced flow boiling heat transfer of liquid hydrogen for superconductor cooling

Heat transfer from inner side of a heated vertical pipe to liquid hydrogen flowing upward was first measured at the pressure of 0.7 MPa for wide ranges of flow rates and liquid temperatures. The heat transfer coefficients in non-boiling regime for each flow velocity were well in agreement with the Dittus–Boelter equation. The heat fluxes at the inception of boiling and the departure from nucleate boiling (DNB) heat fluxes are higher for higher flow velocity and subcooling. It was found that the trend of dependence of the DNB heat flux on flow velocity was expressed by the correlation derived by Hata et al. based on their data for subcooled flow boiling of water, although it has different propensity to subcooling.     

Heat transfer during boiling of liquid nitrogen at coiled heat exchangers

An experimental study was made of the heat transfer during the boiling of liquid nitrogen at various types of immersed heat exchangers. The values of the heat-transfer rate are given for various temperature differences and heat load levels.Deceased.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 4, pp. 643–649, April, 1973.     

Transient processes in falling films of liquid under conditions of unsteady-state heat release

Results are given of experimental investigation of the dynamics of development of heat transfer and critical phenomena in falling wavy films of nitrogen under conditions of unsteady-state heat release from the surface of a thin-walled heater. The experiments involve the investigation of transient modes with formation of dry spots and development of dryout in the case of stepwise and quasi-steady laws of heat release. It is demonstrated that the disintegration of laminar-wavy film of liquid in the case of low heat flux in critical modes under conditions of stepwise increase involves the emergence of metastable regular structures with jets of liquid and large-scale non-wetted zones between them. The generalization of experimental data is used to demonstrate that the value of characteristic transverse dimension between jets of liquid is more than twice the respective values obtained under conditions of steady-state heat release with boundary condition T _heater ～ const. In the case of high heat flux, the vigorous boiling of liquid leads to a rapid ejection of liquid in the form of droplets and to complete drying (almost simultaneously) of the entire heat-emitting surface. Experimental data are obtained on the times of expectation of boiling of liquid, of development of regular structures, and of drying of the heat-emitting surface as functions of heat flux in the range of variation of Reynolds number Re_in = 90–1690. It follows from analysis of experimental data that, in calculating the time of expectation of boiling of liquid in the case of stepwise heat release in the investigated range of variation of heat flux, one must take into account the development of intense evaporation from the free surface of laminar-wavy film.     

Heat transfer during film boiling of a subcooled liquid under conditions of forced flow through channels

An experimental study of heat transfer during the film boiling of subcooled liquid nitrogen in pipes with the Reynolds number Re=80,000-1,500,000 and=0.20–0.95 is reported.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 4, pp. 610–613, April, 1972.     

Nucleate and film pool boiling heat transfer to saturated liquid helium

Pool boiling heat transfer from a square copper heating surface to liquid helium has been investigated experimentally. The study includes both nucleate and film boiling regimes, the measurements of maximum and minimum heat fluxes and superheats of the heating wall in the pressure region from 0.445 up to 0.98 P/P_c. The results are compared with the available experimental data and correlations.     

The influence of three-dimensional capillary-porous coatings on heat transfer at liquid boiling

The process of heat transfer at pool boiling of liquid (Freon R21) on tubes with three-dimensional plasma-deposited capillary-porous coatings of various thicknesses has been experimentally studied. Comparative analysis of experimental data showed that the heat transfer coefficient for a heater tube with a 500-μm-thick porous coating is more than twice as large as that in liquid boiling on an otherwise similar uncoated tube. At the same time, no intensification of heat exchange in the regime of bubble boiling is observed on a tube with a 100-μm-thick porous coating.     

Experimental study of heat transfer in liquid boiling in high-heat-conductivity capillary structures

Results are presented from an experimental study of heat exchange in the boiling of water in copper capillary structures at low saturation vapor pressures.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 6, pp. 893–898, June, 1982.     

Stochastic resonance in the crisis boiling regime under periodic heat release

The results from experimental study of thermal pulsations on going from the nucleate to film boiling of water on a wire heater with a periodic Joule heat release are given. The intermittency between the nucleate and film boiling regimes was observed at a frequency of the periodic current component of less than 0.1 Hz. In this case, the amplitude of thermal pulsations increased about fourfold. The data obtained are interpreted as a stochastic resonant response of the system when the periodic component of pulsations increases in the presence of noise.     

Experimental study of heat transfer in the boiling of liquids at low pressures under conditions of free motion

The results of an experimental investigation into the boiling of water, ethyl alcohol (96% aqueous solution), and 13% NaCl solution under conditions of free motion at pressures of 0.036–1 bar are presented. The experimentally observed characteristics of the boiling mechanism at low pressures are discussed.Translated from Inzhenerno-Fizichenskii Zhurnal, Vol. 18, No. 4, pp. 624–630, April, 1970.     

Investigation of boiling heat exchange under conditions simulating weak gravitational fields

A method for simulating weak gravitational fields is presented; it is based on compensation of the gravitational force by a force acting on a magnetic liquid in an inhomogeneous magnetic field. Results are reported for an investigation of boiling heat exchange and the first critical heat flux under the conditions of weak gravitational fields.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 2, pp. 201–209, August, 1969.