Begell House Inc.
Heat Transfer Research
HTR
1064-2285
39
6
2008
Structure of a Free-Convective Flow Near a Vertical Surface with Stepwise Heating
469-478
Yu. M.
Volodina
St. Petersburg State Polytechnic University, 29 Politekhnicheskaya Str., St. Petersburg, 195251, Russia
Yu. S.
Chumakov
State Technical University, St. Petersburg, Russia
A free-convective flow formed near a vertical heated surface is investigated in the work. Two versions of surface heating are analyzed: a regime of constant temperature over the height of the surface and stepwise heating. The results of measurements of averaged and pulsation components of local temperature fields are presented.
Mathematical Simulation of Mesoscopic Processes of Heat Dissipation and Heat Transfer in a Two-Phase Porous Material Subjected to Shock Compression
479-487
A. V.
Attetkov
N. E. Bauman Moscow State Technical University, 2nd Baumanskaya Str., Moscow, 105005, Russia
E. V.
Golovina
N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygin Str., Moscow, 117977, Russia
B. S.
Ermolaev
N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygin Str., Moscow, 117977, Russia
A mathematical model has been developed and, using the methods of mathematical simulation, the characteristic features of the mesoscopic processes of heat dissipation and heat transfer in a viscoelastic porous material containing spherical pores with a thermally thin coating (a thin layer of plastifier) on their surface subjected low-amplitude dynamic effects have been investigated.
Flow of He-II in a Horizontal Capillary in the Presence of a Longitudinal Heat Flux and in a Superfluid Vortex Flow Regime
489-498
P. V.
Korolev
Moscow Power Engineering Institute (Technical University), 14 Krasnokazarmennaya Str., Moscow, 111250, Russia
The results of computational investigations of a steady-state super-fluid helium (He-II) flow in a horizontal cylindrical capillary in the presence of a longitudinal heat flux and in a superfluid vortex flow regime are presented. To describe the He-II flow, the equations of the Landau two-velocity hydrodynamics and the Gorter−Mellink mutual friction theory are used. Analytical solutions of the problem are obtained. An analysis of the solutions shows that the direction of the He-II flow depends on the capillary diameter and heat flux density. The conditions of the He-II flow to a heat source have been determined.
Distribution of Temperatures over a Spherical Heater Placed in He-II
499-508
A. F.
Mednikov
Moscow Power Engineering Institute (Technical University), 14 Krasnokazarmennaya Str., Moscow, 111250, Russia
Alexei P.
Kryukov
Moscow Power Engineering Institute, Moscow, Krasnokazarmennaya 14, 111250, Russia
The results of calculations of the distribution of temperatures in a spherical heater, which is intended for studying film boiling of He-II [1], and the corresponding experimental data are presented. The construction of the spherical heater is described, and the method to calculate characteristic temperatures in it for both boiling of helium II and direct contact of He-II and the heater surface is given. Based on experimentally measured dependences of temperatures and data of video recording, a comparison with the temperature values calculated by the proposed method is carried out. In analyzing heat transfer through the vapor film, relations are used that take into account the nonequilibrium state of transfer processes on interphase surfaces.
Breakdown of a Falling Wave Liquid Film during Nonstationary Heat Release
509-517
Aleksandr N.
Pavlenko
Kutateladze Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences,
Novosibirsk, Russia
Anton S.
Surtaev
Novosibirsk State University, Novosibirsk, Russia; Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
A. N.
Chernyavskii
S. S. Kutateladze Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences, 1 Lavrent'ev Str., Novosibirsk, 630090, Russia
The results of an experimental investigation of the dynamics of development of heat transfer and crisis phenomena in falling wave nitrogen films during nonstationary heat release from the surface of a thin-wall heater are given. It is shown that at small values of the heat flux density in crisis regimes under the conditions of stepwise increase in loading, the breakdown of a laminar-wave liquid film occurs with the appearance of metastable regular structures with liquid jets and large-scale unwetted zones between them. Experimental data are obtained on the times of expectation of liquid boiling up, development of regular structures, and drying out of heat-releasing surface depending on the heat flux within the range of Reynolds numbers Rein = 907−1690. From the analysis of experimental data it follows that in calculating the time of expectation of liquid boiling up in the case of stepwise heat release in the investigated range of heat flux values it is necessary to taken into account the influence of the convective component of heat transfer and the development of intensive evaporation from the free surface of the wave film. The charts of transient regimes for various Reynolds numbers are constructed; they isolate the region with a basically different character of the breakdown of a film at high heat fluxes with rapid expulsion of a liquid in the form of droplets and complete drying of virtually the entire surface.
Spectral Characteristics of Fluctuations in Ultrasonic Cavitation of Water and Glycerin
519-527
Andrey V.
Vinogradov
Institute of Thermal Physics, Ural Branch of the Russian Academy of Sciences, Ekaterinburg,
620016, Russian Federation
The results of experimental investigation of the dynamics of fluctuations in acoustic cavitation of water and glycerin are presented. Near the radiator surface the structures in interacting vapor-gas bubbles having the form of fractal clusters were formed. Using the method of photometric scanning of transmitted laser radiation, the dynamics of fluctuations was investigated. In the transient regime the range of the power of fluctuations changed inversely proportional to frequency. The distributions of local fluctuations differ from Gaussian ones and reveal the properties of scale invariance. The qualitative behavior of the frequency dependence of the spectral density of fluctuations on change in the power of an ultrasonic radiator was investigated. It is shown that the raise of the high-frequency boundary of the flicker behavior point to the buildup of instability and may serve as a precursor of possible large-scale overshoots.
Characteristic Features of Boiling in Annular Channels with Flow Twisting
529-538
A. B.
Yakovlev
Federal State Government-Funded Educational Institution of Higher Professional Education "Kazan National Research Technical University named after A. N. Tupolev" (KAI), 10 Karl Marx Str., Kazan, Republic of Tatarstan, 420111, Russia
S. V.
Kostenko
A. N. Tupolev Kazan State Technical University, 10 K. Marx Str., Kazan, 420111, Russia
Stanislav E.
Tarasevich
Federal State Government-Funded Educational Institution of Higher Professional Education "Kazan National Research Technical University
named after A. N. Tupolev" (KAI), 10 Karl Marx Str., Kazan, Republic of Tatarstan, 420111, Russia
E. A.
Boltenko
Elektrogorsk Scientific Research Center of Safety of Nuclear Power Stations, Elektrogorsk, Russia
The results of experimental investigation of the boiling of water at a pressure of P = (98−103)·105 Pa in annular channels with a wire spiral and two-sided heat supply are presented. The problems of determining the temperature of the boiling inception and of boiling heat transfer intensity on a convex and concave surfaces of the annular channel with flow twisting are considered.
Optimization of the Parameters of an Emitting Finned Tube
539-548
V. S.
Zarubin
N. E. Bauman Moscow State Technical University, 5 2nd Bauman Str., Moscow, 105005, Russia
M. A.
Peshkova
N. E. Bauman Moscow State Technical University, 5 2nd Bauman Str., Moscow, 105005, Russia
A mathematical model of an emitting finned tube with an arbitrary number of rectangular fins and nonblack emitting surfaces is considered. Optimization of the structure has been done to obtain a maximum of the emitted heat flux and a minimum of the over-all mass of fins. It is shown that for the geometric parameters that satisfy the requirements of a maximum heat flux the requirement of a minimum mass is also met, as well as the optimal configuration of a rib at a fixed mass is preserved, which makes it possible to find the best parameters of the structure without resorting to optimization.
Numerical Comparison of the Effect of Concave and Convex Curvatures over the Rate of Heat Transfer from a Vertical Wall in Natural Convection Flow
549-558
O. Nourani
Zonouz
Mechanical Engineering Department, Marvdasht Islamic Azad University, Fars, Iran
Mehdi
Salmanpour
Department of Mechanical Engineering, Azad Islamic University, Marvdasht Branch, Fars, Iran
The main aim of this article is determination of optimum geometric conditions that help the rate of heat transfer from isothermal vertical walls to be increased. The basic shape is a vertical flat plate. In order to understand the effect of curvature on the heat transfer rate, two different conditions were considered. In both of these cases, the length of the wall is divided into three parts. The first and third parts are completely flat; in the second part, a defining curvature was induced. In the first case, the curvature has a convex shape and, in the second one, the shape is concave. To fully consider the role of curvature, in each case the computation was repeated for 10 different radii. To make a proper domain for solving the governing equations, the physical domain and related governing equations of interest are transferred to the computational domain. To discretize the equations the finite difference scheme is used. The distribution of the Nusselt number and the total heat transfer rate were computed. For covering different Prandtl numbers, air and water were selected for the ambient fluid. The results show that the rate of heat transfer is decreased with making the concave shape and will be increased by using the convex shape. This increase in the magnitude of heat transfer is continued up to θ = 16.67° (curvature degree) for air. This limitation helps us to find an optimum angle for the rate of heat transfer.