Control of Rayleigh-Bénard Convection in a Fluid Layer with Internal Heat Generation

The control of the onset of convection in a horizontal fluid layer with internal heat generation is studied. The horizontal boundaries of the system are cooled isothermally. The stability of the fluid layer is investigated on the basis of the linear stability theory and the resulting eigenvalues problem is solved numerically. Upon using a feedback proportional control, the heating power of the system is modulated in order to counteract any deviations of the temperature of the fluid from its conductive value. As a result, it is possible to postpone (or advance) significantly the onset of motion. The optimal positions of the thermal sensors can be predicted on the basis of the linear stability theory. The linear stability analysis also reveals the possible existence of Hopf’s bifurcations at the onset of motion. This type of bifurcation can be delayed using differential controllers. Two-dimensional numerical simulations of the full governing equations are carried out and found to agree well with the prediction of the linear stability theory.     

Heat‐Source‐Initiated Thermoelastic State of a Semiinfinite Plate with an Edge Crack

A study is made of the influence of the internal heat source on the factors of intensity of the stresses at the tip of an arbitrarily oriented edge cut in a homogeneous halfplane.     

Identification of the Parameters of a Nested Cylindrical Heat Source under Stationary Self‐Heating of a Raw Material Mass of the Same Form

This paper describes a computer method for determining the coordinate of the center, the heatrelease power, and the sizes of a homogeneous internal cylindrical heat source in a stationary axially symmetric temperature field arising under selfheating of a plant raw material.     

Numerical‐Analytical Investigation of Self‐Similar Regimes of Propagation of Nonstationary Convective Jets and Thermals in a Homogeneous Medium over a Point Heat Source

An integral model of a nonstationary vertical convective jet is suggested that involves a universal equation of the propagation of the upper boundary of a convective front depending on the power of the point heat source. A class of selfsimilar solutions is considered; they correspond to the heat sources whose power changes instantly and also according to the power and exponential laws. Analytical and numerical solutions of the selfsimilar equations are constructed. Numerical calculations are compared with the wellknown experimental data on the profiles of the vertical velocity and temperature on the jet axis.     

Effect of Heat Treatment on the Corrosion Characteristics of Al-Li Alloys

Experiments were conducted to study the general room temperature corrosion characteristics of heat-treated and non-heat-treated Al-Li alloys with different Li compositions. Corrosion rate was measured using both the polarisation method and the weight-loss method. It was observed that the samples with higher Li content had lower corrosion resistance than those with lower Li content. Moreover, for all the specimens tested, it was fOund that heat treatment at 180℃ for 2 h (for the purpose of precipitation hardening) severely reduced the corrosion resistance,whereas heat treatment at 180℃ for 6 h significantly increased the corrosion resistance.     

Feedback Control of the Marangoni-Bénard Convection in a Horizontal Fluid Layer with Internal Heat Generation

Feedback control is applied to the steady Marangoni-Bénard convection in a horizontal layer of fluid with internal heat generation heated from below and cooled from above. The analytical technique is used to obtain the close form analytical expression for the onset of Marangoni-Bénard convection when the lower boundary is conducting. The effects of feedback control are studied by examining the critical Marangoni numbers and wave numbers. It is shown that the critical Marangoni number decreases as the value of internal heat generation but the critical Marangoni number can be increased through the use of feedback control.     

Effect of Heat Treatment on Corrosion Performance of Duplex Steel COR 25

The effect of heat treatment on the corrosionperformance of austenitic-ferritic duplex stain-less steel COR 25 in aqueous solution containing60%H_3PO_4+4%H_2SO_4+1500 ppm Cl~- at 95℃ was in-vestigated.When the solution temperature wasincreased from 950℃ to 1230℃,the corrosionresistance increased by two orders of magnitude,as shown by electrochemical measurements,im-mersion tests and direct observation under thescanning electron microscope.The specimensheat treated at solution temperatures of 950℃and 1030℃ were severely corroded along thephase boundaries;specimens treated at 113C℃and 1230℃ tended to selective corrosion causedby the dissimilar chromium contents of the aus-tenite and ferrite phases after heat treatment.     

Heat Capacity of Liquid 4He Confined in a Nanoporous Glass

We report a preliminary study of heat capacities of ⁴He confined in a nanoporous Gelsil glass that has nanopores of 2.5 nm in diameter. The heat capacity has a broad peak at a temperature far above the superfluid transition temperature obtained by torsional oscillator technique. The heat-capacity peak is attributed to formation of localized Bose-Einstein Condensates in the nanopores, in which the long-range superfluid coherence is destroyed by pore size distribution or random potential inherent to the porous glass.      

Equal-Channel Multi-Angle Pressing Effect on the Properties of NbTi Alloy

An improvement of NbTi alloy functional properties by equal-channel multi-angle pressing (ECMAP) combined with hydrostatic extrusion, drawing and thermal treatment is revealed. The ECMAP method allows to increase the billet accumulated deformation with preserving its initial dimensions. The formed highly dispersed and homogeneous nanocrystalline structure with a more uniform distribution of α-phase precipitations as a result of ECMAP treatment improves the functional properties of the alloy. In the field of 5 T, the critical current density in wire samples produced with application of the ECMAP method is enhanced approximately by a factor of 2 in comparison with the values obtained for the samples produced without the ECMAP treatment.     

Magnetic‐Field Effect on Heat Transfer within a Cathode Arc Spot

The authors present results of an experimental study of the heat flux within the arc spot of the copper cathode of an electric‐arc heater with magnetic‐field‐induced displacement of the arc in an air medium — one of the most important parameters determining the erosion and service life of such a cathode. The investigations were carried out at a current strength of 110–?450 A, a magnetic induction of 0.009–0.38 T, and atmospheric pressure.     

Effect of Critical Current Density and Critical Temperature on ac Susceptibility

Based on the flux creep equation, the effect of critical current density and critical temperature on ac susceptibility is investigated numerically in a superconducting slab immersed in an ac magnetic field. The current density dependence of the flux creep activation barrier is employed as the logarithmic law. The fundamental ac susceptibilities of the slab as a function of temperature for the same ac field have been derived in a unified picture. The results show that ac susceptibility in flux creep regime is affected by critical current density and critical temperature.     

Analysis of Heat Stresses of the Parts of the Cylinder–Piston Group with Heat‐Protective Coatings in an Internal‐Combustion Engine

The process of heat exchange in the cylinder of an internalcombustion engine has been investigated and the heat stresses of the working surfaces of the piston and the cylinder head have been analyzed. A method for calculating the heat resistance, the strength, and the thickness of heatprotective coatings has been developed. Results of thermalcycle testing of a piston with heatresistant coatings, the properties of which were calculated by the method proposed, are presented.     

The Average Power of a System under Random Excitation

1IntroductionFOrmanyyears,scientistshaveusedtheenergymethodeffectively(e.g..LaGrange'sequations)tOstUdythevibr'ationofsystemSbysettingupdifferenti31equationsormdengestimationsofnatutalfrequencies.Naturallythesemethods~usedPredominantlyformodellingcom...     

The Effect of Low-Temperature Heat Treatment on the Superelasticity in Ti–50.6 at % Ni Single Crystals

Technical Physics Letters - As a result of low-temperature aging at 573 K for 1.5 h of Ti–50.6 at% Ni [001]-oriented single crystals quenched from 1253 K, a high-strength state is obtained...     

Effect of cooling rate on the morphology of γ′ precipitates in a nickel-base superalloy under directional solidification

The morphological evolution of γ′ precipitates in a nickel-based superalloy K5 was studied by zone melting directional solidification under vacuum conditions. The results show that at the lower cooling rate of 12.42 K s⁻¹, γ′ precipitates remand big cuboids. γ′ particles become smaller at the cooling rate ranges from 12.42 to 38.80 K s⁻¹. For a rather fast cooling rate of 50.16 K s⁻¹, γ′ particles retain a spherical shape. The experiments show that big cuboids will become unstable and split into several small ones at the lower cooling rate of 1.1 K s⁻¹. The mechanism of the evolution of the γ′ morphologies is also analyzed by introducing a new parameter-shape factor which classifies the total energy into several energy levels. Based on this, the effect of the cooling rate on the γ′ morphology is discussed.     

Influence of a Long Stay of the Heat‐Release Surface in Kerosene on the Critical Heat Flux in Boiling in It under Steady‐State and Step Conditions of Heat Release

Results of experimental investigations of the influence of a long stay of the heatrelease surface in kerosene on the first critical density of the heat flux in boiling under the steadystate and step conditions of heat release are given.     

Effect of Heat Treatment on Acoustic Emission in 7075-T651 Aluminum Alloy

The longitudinal(L),long-transverse(T)and short-transverse(S)orientated samplesof precipitation-strengthened 7075-T651 aluminumalloy were examined.The acoustic emission(AE)characteristicsmeasured during tensile deformation in the alloywere related to prior aging treatment and orienta-tions of samples.A rms AE peak occurred in all the samplesat plastic strain greater than one percent.The heights of peaks have been measured as afunction of prior heat treatment.The shiftof the peak location was dependent on heat treat-ment in samples with L- and T-orientation.The pre-yield,burst-type emission(PYBE)wereobserved in S-orientated samples.The behavioursof PYBE were as a function of prior ageing treat-ment too.The stress and plastic strains at whichthe AE peak stress were generated were consistentwith the peaks arising from the fracture anddebonding of inclusions.Waveform frequencyanalysis of AE signals and fractographic observa-tions using SEM as well as data of microhardnessand charpy test were also consistent with be-haviours of AE,that is,high stress requiredfor the rms peak or the initiation of the PYBE,was higher for the heat treatment,at whichthe interface between inclusion and matrix wasweaker.