Vapor formation and heat transfer in liquid helium cooling channels under transient and steady state conditions

The recovery of a normal zone produced in a superconducting magnet following a mechanical disturbance depends on the heat transfer rate to the liquid helium cooling channels. One of the factors which affects the heat transfer to the channel is the amount of vapor accumulated in the channel during and following a disturbance. The present work is undertaken to determine the void fraction in a liquid helium channel and to study the effect of the amount of vapor in the channel on the heat transfer characteristics. Heat pulses of 30 to 300 ms duration are introduced into the simulated conductor, and observations are made of the resulting temperature response and of the vapor fraction in the channel. The vapor fraction is determined by means of a capacitance bridge which responds to the small difference in dielectric constant between liquid and vapor helium. For completeness steady state measurements of temperature and vapor fraction are also reported.     

The conditions of existence of autooscillations in a dropwise liquid flow through a vertical capillary

A model describing the dropwise liquid flow through a vertical capillary, taking into account the mutual influence of the drops, is developed, and the conditions of existence of an autooscillatory regime in this system are established. The period and amplitude of the autooscillations are described as functions of the system parameters.     

Free convection heat transfer to steady radiating non-Newtonian MHD flow past a vertical porous plate

Non-Newtonian fluid motion generated by a vertical porous hot plate in the presence of a transverse magnetic field is studied when viscous and ohmic dissipations are significant. When the temperature of the plate is very large, a general differential approximation for the radiative flux enables the asymptotic flow, valid far away from the tips of the plate, to reduce to a set of nonlinear and coupled ordinary differential equations. The solutions of these differential equations are studied for both small and large values of the absorption coefficient. The temperature, velocity and magnetic field distributions are discussed quantitatively. A primary conclusion of the analysis is that the distributions of temperature, velocity and magnetic field are much larger for a fluid with a large absorption coefficient than for a fluid with a small absorption coefficient.     

A study of the downward flow of a liquid film along a vertical surface with attendant heat transfer

This report deals with a theoretical and experimental study concerning the measurement of local values of mean film thickness throughout the film length and with theoretical relations derived for determining the film thickness in the laminar-wave as well as in the turbulent region. The experimental studies have also covered local characteristics of wave motion on the film surface as well as the velocity field in the continuous layer, the local heat-transfer coefficients along the height of a vertical channel, and a critical relation for determining them has been derived.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 4, pp. 674–682, April, 1971.     

Hydrodynamics and heat transfer in turbulent pipe flow of liquid under conditions of monotonic time variation of the flow rate

The available experimental and theoretical studies of hydrodynamics and heat transfer in turbulent pipe flow of liquid under conditions of monotonic increase or decrease of the flow rate are reviewed and analyzed. The reason is found why the effect of hydrodynamic nonstationarity on heat transfer and skin friction coefficient turns out to be different from that in the case of laminar flow. The differences in this effect on heat transfer and drag are treated. The experimentally observed effects are reproduced most accurately when simulated on the basis of equations for turbulent stresses and heat fluxes.__________Translated from Teplofizika Vysokikh Temperatur, Vol. 43, No. 2, 2005, pp. 212–222.Original Russian Text Copyright © 2005 by E. P. Valueva.     

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.     

Radiative heat transfer to a laminar liquid flow

A calculation is presented of the temperature distribution in a laminar liquid flow moving in a circular tube. The heat exchange on the outer surface of the channel is determined by the Stefan — Boltzmann law.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 3, pp. 487–491, March, 1970.     

Mixed convection under conditions of weak external flow in a vertical channel with a finite-size heat source

Mixed convection is investigated in a vertical plane-parallel channel from a finite-size heat source located on one of the walls. Numerical calculations are performed for the Prandtl number value of 0.7, in the ranges of values of Grashof number from zero to 10⁵ and Reynolds number from zero to 10. Two-dimensional unsteady-state Navier-Stokes equations in the Boussinesq approximation are used as model. The model is formulated in the “speed eddy-stream function-temperature” variables and solved by the finite element method.     

Hydromagnetic flow and heat transfer on a continuously moving vertical surface

Summary A theoretical solution for hydromagnetic convection over a continuously moving vertical surface with uniform suction is obtained. A flow of this types represents a new class of boundary-layer flow at a surface of finite length. The solutions for the velocity and temperature profiles are obtained. It is observed that the velocity decreases considerably in the presence of a magnetic field, as compared to its absence.     

Measurements of heat transfer to supercritical helium in vertical tubes under forced and mixed convection conditions

New experimental data on convective heat transfer to downflow and upflow of supercritical helium in vertical heated tubes are presented.     

层流状态下纳米流体的对流传热特性

通过数值模拟的方法研究了层流状态下雷诺数、体积分数、颗粒和基液种类以及颗粒粒径对纳米流体对流传热特性的影响。研究结果表明,纳米流体的对流传热系数明显高于基液,并且与基液和颗粒的性质、颗粒的体积分数及颗粒粒径密切相关。纳米流体的对流传热系数随着颗粒和基液热导率的增加、颗粒体积分数的增加以及颗粒粒径的减小而增大。研究发现,对于一定体积分数的Cu-水纳米流体,在层流状态下对流传热系数的提高程度基本保持一致,与雷诺数大小无关。     

Experimental study of laminar natural convection heat transfer from a vertical cylinder to slush nitrogen under constant heat flux conditions

Natural convection heat transfer from a vertical cylinder immersed in slush and subcooled liquid nitrogen and subjected to constant heat fluxes was investigated in order to determine the relative merits of slush nitrogen (SlN₂) for immersion cooling. A glass dewar was used as a test vessel in which a cylindrical heater was mounted vertically, and heat transfer measurements were carried out for SlN₂ and subcooled liquid nitrogen (LN₂) in the laminar flow range. The results revealed advantages of SlN₂ over subcooled LN₂ in natural convection cooling. The local temperatures of the heated surface surrounded by solid nitrogen particles are measured to increase at much slower rates than in subcooled LN₂, which is due to the latent heat of fusion of solid nitrogen. Even after the solid nitrogen particles surrounding the heater are apparently depleted, the average heat transfer coefficients for SlN₂ are still found to be greater than those for LN₂ with the improvement in heat transfer being larger for lower Grashof number regime. Our analysis also indicates that solid nitrogen particles in close proximity to heated surface do not discourage local convection due to the porous nature of SlN₂, making the heat transfer in SlN₂ more effective than in the case of solid–liquid phase change of nitrogen involving melting and conduction processes.     

Conjugate heat transfer and thermostressed state of the wall in steady flow in a triangular pipe

Consideration is given to the problem of joint analysis for the parameters of conjugate heat transfer and the thermostressed state of the wall in steady laminar flow in a thick-walled triangular pipe. The solution is obtained by successive use of a finite-element method (FEM) and a finite-difference method (FDM). Analysis is given of the results of calculations at different values of similarity criteria.Dnepropetrovsk State University. Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 64, No. 1, pp. 107–112, January, 1993.     

Semianalytic method for heat transfer calculation in the liquid film under conditions of a constant heat flux on the wall

For calculating the heat transfer in the free-falling liquid film, a semianalytic method is offered in which the temperature field in the liquid is presented as a series of basis functions which satisfies boundary conditions. The proposed method is demonstrated by the example of the problem regarding the film heating under conditions of the constant heat flux on the wall taking into account the heat transfer on the interfacial surface. The analytical solution is derived for the thermal initial section, on which the liquid heating occurs in a thin layer near the wall. Calculations using the proposed method are well agreed with the numerical solution obtained by the finite-difference method and with experimental data.     

Integral methods of calculation of heat transfer and drag under conditions of turbulent pipe flow of liquid of variable properties: Pulsating high-frequency flow

An integral method is suggested for approximate calculation of oscillation-period average heat transfer and drag under conditions of pulsating high-frequency flow of gas in a pipe with constant density of heat flux to the wall. It is found that the flow rate oscillation superimposed on the flow has little effect on the period average Nusselt number and coefficient of friction drag; these quantities may be calculated by the method developed for a steady-state flow of liquid of variable properties. The oscillation affects significantly the period average coefficient of hydraulic drag whose values increase with the amplitude of superimposed oscillation.     

The calculation of heat transfer and resistance under conditions of stabilized turbulent pipe flow of electrically conducting liquid in longitudinal magnetic field

The model of turbulence, developed previously for a flow in the field of mass forces (buoyancy, Coriolis) and for an unsteady flow, is applied to the case of liquid flow in magnetic field. The model describes the suppression of turbulence by the magnetic field and the laminarization of turbulent (at the pipe inlet) flow. The calculation results agree well with the experimental data on heat transfer and resistance obtained in the region of stabilized flow and heat transfer.     

Mixed convective flow and heat transfer in a vertical helicoidal pipe with finite pitch

Fully developed laminar mixed convective flow and heat transfer in a vertical helicoidal pipe with finite pitch is studied numerically in this paper. The centrifugal, buoyancy, and torsion forces created by the pitch of the helix are considered. The thermal boundary conditions are uniform heat flux axially and uniform wall temperature peripherally. The velocity, the temperature profiles, the friction factor, and the Nusselt number are obtained. The results indicate that torsion can significantly change the axial and secondary flow patterns and temperature distributions in the helicoidal pipe with a fixed pressure gradient. Torsion can also remarkably affect the flow rate, the friction factor, and the Nusselt number. However, at a fixed Dean number, there is only slight difference in the Nusselt numbers of the upward and downward flow.The results presented in this paper were obtained in the course of research sponsored by the National Science Foundation (NSF) under Grant No. CTS-9017732     

Combined heat and mass transfer in natural convection flow from a vertical wavy surface

Summary In the present paper, effects of combined buoyancy forces from mass and thermal diffusion by natural convection flow from a vertical wavy surface have been investigated using the implicit finite difference method. Here we have focused our attention on the evolution of the surface shear stress,f(0), rate of heat transfer,g(0), and surface concentration gradient,h(0) with effect of different values of the governing parameters, such as the Schmidt number Sc ranging from 7 to 1500 which are appropriate for different species concentration in water (Pr=7.0), the amplitude of the waviness of the surface ranging from 0.0 to 0.4 and the buoyancy parameter,w, ranging from 0.0 to 1.Notation C species concentration in the boundary layer - C species concentration of the ambient fluid - C _w species concentration at the surface - D chemical molecular diffusivity - f dimensionless stream function - g acceleration due to gravity - Gr _x local modified Grashof number - N ratio of the buoyancy forces due to the temperature difference and the concentration difference - p pressure of the fluid - T temperature of the fluid in the boundary layer - T temperature of the ambient fluid - T _w temperature at the surface - u, v thex- andy-components of the velocity field - x, y axis in the direction along and normal to the plate Greek symbols thermal diffusivity - _T volumetric coefficient of thermal expansion - _C volumetric coefficient of expansion with concentration - stream function - nondimensional similarity variable - x/L - density of the ambient fluid - v kinematic coefficient of viscosity - stream function - dimensionless skin friction - fluid viscosity     

Influence of ultrasound on heat transfer under the conditions of forced flow of a high-temperature melt

The influence of elastic oscillations at a frequency of 20 kHz on the heat transfer associated with the forced flow of a high-temperature melt in a tube is investigated experimentally. It is shown that the heat-transfer coefficient can be as much as doubled.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 2, pp. 322–325, February, 1985.