Begell House Inc.
Heat Transfer Research
HTR
1064-2285
38
6
2007
Heat Transfer in Boiling and Ascending Flow Modes in Vertical Rectangular Small-Size Channels
483-493
Vladimir V.
Kuznetsov
The Kutateladze Institute of Thermophysics SB RAS, 1 Lavrentieva Ave., Novosibirsk, 630090, Russia; Novosibirsk State University, 2 Pirogova Str., Novosibirsk 630090, Russia
Alisher S.
Shamirzaev
The Kutateladze Institute of Thermophysics SB RAS, 1 Lavrentieva Ave., Novosibirsk, 630090, Russia
I. N.
Ershov
Novosibirsk State University, Novosibirsk, Russia
In the paper, the data of experimental studies of heat transfer and hydrodynamics of two-phase vapor(gas)-liquid flows in vertical rectangular channels with a gap on the order of the capillary constant are presented. It is shown that boiling of liquid in confined conditions is characterized by a high probability of coalescence of bubbles and appearance of a slug flow, and the velocity of surfacing of slugs in such channels is basically determined by the flow of liquid in the channel corners and the slugs float to the surface even at very small Eotvos numbers. Data on the heat-transfer coefficients are given for Freon R-21 boiling in a plate-and-rib heat exchanger under the conditions of natural liquid circulation.
Computational Study of Nonstationary Modes of Operation of a Solar Sodium Evaporator with Supply of a Nonuniform Heat Flux
495-505
O. E.
Maletskaya
Institute of Technical Thermophysics, National Academy of Sciences, Ukraine
Natalia Mikhailivna
Fialko
Institute of Technical Thermophysics, National Academy of Sciences, Ukraine
E. N.
Shevchuk
Institute of Technical Thermophysics, National Academy of Sciences, Ukraine
V. L.
Yurchuk
Institute of Technical Thermophysics, National Academy of Sciences, Ukraine
Experimental data on superheating during sodium boiling-up in a high-temperature receiver-evaporator, receiving concentrated solar radiation, has been analyzed for the first time. The relationship for calculation of the onset of boiling depending on the saturation temperature (pressure) and the heat-flux density has been obtained. This was used as the basis for evaluating the impact of nonuniformity of a nonstationary heat flux on the temperature field of the evaporator.
On Modeling Heat and Mass Transfer for Vapor Absorption by a Stationary Layer of the Solution with and without Surfactants
507-518
V. E.
Nakoryakov
S. S. Kutateladze Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences, Pr. Ac. Lavrentev, 1, Novosibirsk, 630090, Russia
N. I.
Grigor'eva
S. S. Kutateladze Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk
Simple models of non-isothermal absorption for small and large times have been used to analyze the impact of heat release and heat removal on the intensity of vapor absorption by a motionless layer of solution, not containing surfactants. We consider the models with and without account of displacement of the interface. The results of comparison of calculations with experimental investigations of water vapor absorption by a motionless layer of aqueous solution of lithium bromide are presented. Some problems and contradictions in the existing models, describing heat and mass transfer during absorption of vapors by surfactant-containing solutions are analyzed. A method for determining the gradients of surface tension and the Marangoni criteria in conditions of a heat pump operation is proposed.
Mixed Heat Transfer in a Subcooled Twisted Flow
519-532
Alexander T.
Komov
National Research University "Moscow Power Engineering Institute", Russia, 111250 Moscow, Krasnokazarmennaya str., 14
Alexander N.
Varava
National Research University "Moscow Power Engineering Institute", Russia, 111250 Moscow, Krasnokazarmennaya str., 14
Aleksey V.
Dedov
National Research University "Moscow Power Engineering Institute", Russia, 111250 Moscow, Krasnokazarmennaya str., 14
Victor V.
Yagov
NRU "Moscow Power Engineering Institute", Krasnokazarmennaya Street 14, Moscow 111250, Russia
Characteristics of heat transfer in a flow of water not heated to the saturation temperature in the case of a one-sided heating with a high heat-flux density, exceeding ∼107 W/m2 are presented. Heat is removed from the inner surface of a cylindrical tube. Due to one-sided heating and a high density of heat supplied along the tube perimeter there can simultaneously exist film (in the vicinity of the frontal point), transient, and nucleate boiling modes and a one-phase convection mode.
Experimental Investigations of Heat Transfer in a Subcooled Twisted Flow
533-539
Alexander T.
Komov
National Research University "Moscow Power Engineering Institute", Russia, 111250 Moscow, Krasnokazarmennaya str., 14
Alexander N.
Varava
National Research University "Moscow Power Engineering Institute", Russia, 111250 Moscow, Krasnokazarmennaya str., 14
Aleksey V.
Dedov
National Research University "Moscow Power Engineering Institute", Russia, 111250 Moscow, Krasnokazarmennaya str., 14
R. I.
Kamenskov-Nemynov
Moscow Energy Institute (Technical University), Russia
Methods for conducting experimental investigations of heat transfer to a subcooled twisted flow of water under the conditions of one-sided heating of the working section by a scanning electron beam. The methods allow using measured typical temperatures of the working section to determine temperature and density of the heat flux at the top point of the inner perimeter of the working section, without applying numerical solution of the boundary-value heat-conduction problem.
Heat and Mass Transfer in Processes of Condensation Relaxation of Supersaturated Vapor
541-552
Naum Moiseevich
Kortsenshteyn
G.M. Krzhizhanovsky Power Engineering Institute, 119071 Moscow, Leninsky Prospekt, 19, Russia
E. V.
Samuilow
OJSC G. M. Krzhizhanovsky Energy Institute, Moscow, Russia
The process of volume condensation of vapor from a vapor-gas mixture after a sudden creation of the supersaturated state is analyzed. According to the approach, adopted in physical kinetics, the time of condensation relaxation as a time interval during which the initial supersaturation degree is reduced e-fold has been introduced. Numerical and analytical analysis of the process with due account of release of the phase-transition heat have been used to establish scaling relations, connecting the time of the condensation relaxation and the number density of droplets with the nucleation rate at the initial instant. It is shown that the produced relations give a principal opportunity for experimental determination of the nucleation rate by recording temperature oscillograms in the condensed vapor volume.
Experimental Studies of Heat-Transfer Characteristics of Miniaturized Heat Pipes
553-563
V. Yu.
Kravets
National Technical University of Ukraine, Igor Sikorsky Kyiv Polytechnic Institute, Ukraine
Yu. E.
Nikolaenko
Ministry of Industrial Policy, Ukraine
Ya. V.
Nekrashevich
National Technical University of Ukraine "Kiev Polytechnical Institute", Kiev, Ukraine
Results of studies of heat-transfer characteristics of miniaturized heat pipes with the diameter 2.4 and 6 mm and length from 50 to 250 mm are presented. Pipe shell material is copper. It is shown that decrease of the vapor space dimensions in heat pipes leads to deterioration of their heat-transfer properties (increase of thermal resistance, reduction of transferred heat fluxes, and increase of the temperature difference between the evaporator and the condenser). The thermal resistance value depends on the diameter of miniaturized heat pipes. Physical processes occurring in miniaturized heat pipes are analyzed; heat-transfer coefficients in evaporation and condensation zones are obtained. Dependences of transferred heat loads on the diameter of the vapor space and the total length of miniaturized heat pipes are given. Dependences of the temperature drop between evaporation and condensation zones on the transferred heat flux are presented. Possibilities for increase of heat-transfer characteristics of such heat pipes by application of optimal-structure capillary structures, possessing a high capillary pressure and a high liquid permeability, are analyzed.
On the Paradox about the Propagation of Thermal Energy Speed in a Semi-Infinite Body Heated by a Forced Convective Flow
565-572
Antonio
Campo
Department of Mechanical Engineering, The University of Vermont, Burlington, VT 05405, USA
Salah
Chikh
USTHB, Faculty of Mechanical and Process Engineering, LTPMP, Alger 16111, Algeria
An algebraic evaluation proclaims that the surface heat flux in a semi-infinite body with uniform initial temperature T0 and prescribed uniform temperature TS at the exposed surface ascends to infinity when time approaches zero. This unreasonable behavior responds to a well-known pathology of the phenomenological Fourier's law that translates into an infinite speed of thermal energy propagation in semi-infinite bodies, which is extensive to finite bodies. From thermal physics, it is expected that when the uniform temperature TS at the exposed surface in a semi-infinite body (a Dirichlet boundary condition) is replaced by a generalized convective boundary condition (a Robin boundary condition), the surface heat flux should climb up to infinity also when time approaches zero. Two answers exist. The prevalent abnormal situation happens when the phenomenological Fourier's law is applied at the exposed surface, i.e., from the solid side. On the contrary, the abnormal situation does not occur when the empirical Newton's "equation of cooling" is applied at the exposed surface, i.e., from the fluid side.