Dynamics of discharging of a heat accumulator in an infinite ground massif

Based on the approaches presented in [Inzh.-Fiz. Zh., 77, No. 4, 10–19 (2004)], the problem on discharging of the heat accumulated earlier by single heat exchangers and their combination in an infinite ground massif has been solved. The inefficiency of the accumulation and discharging by single heat exchangers and the high degree of recovery of the accumulated heat in the case of their clustered arrangement have been established. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 6, pp. 70–77, November–December, 2005.     

Heat exchange processes near the boundary of a film boiling nucleus

Results are presented of an experimental investigation of the change in temperature, heat flux to the liquid, and rate of displacement of the isotherms near a film boiling nucleus propagating over a plane surface. The experiment was carried out in a liquid nitrogen bath at atmospheric pressure on the saturation line. The heater was a sapphire plate 1.2 mm thick having a heat transfer surface area of 77×22 mm². The following facts were established: 1) near the boundary of the film boiling nucleus a new heat exchange mechanism takes place caused by the instability of the liquid microlayer; 2) the maximum heat flux to the liquid is considerably greater than the critical heat flux; 3) the vapor film in the film boiling region grows gradually with increasing distance from the boundary, i.e., there is a smooth transition in terms of heat exchange intensity before the equilibrium film boiling level is reached. Pis’ma Zh. Tekh. Fiz. 25, 39–46 (November 12, 1999)     

Efficiency of cooling of laser diode arrays in contact with a porous permeable wall

It has been suggested that heat transfer from a porous permeable material using a liquid coolant may be used to improve heat exchange in powerful laser-diode emitters [V. V. Apollonov, A. I. Barchukov, A. M. Prokhorov et al., Metal Laser Mirror with a Cooled Optical Surface, FIAN Report 1977; V. V. Apollonov, P. I. Bystrov, and V. F. Goncharov, Sov. J. Quantum Electron. 9, 1499 1979. An analysis of typical values of the thermal loads and their dependence on the parameters of the material and the liquid using a one-dimensional model of stead-ystate heat exchange shows that thermal fluxes in excess of 1 kW/cm² can be removed. Pis’ma Zh. Tekh. Fiz. 25, 87–94 (January 12, 1999)     

Thermionic valve effect and cathode crater rhythm in a low-voltage cold-cathode vacuum arc

A vacuum arc with a cold cathode burns rhythmically. The period of the rhythm is determined by a thermionic valve effect which occurs between the hot crater and the cold cathode as a result of the brief retention of the heat in the crater by the oppositely propagating electron flux. Pis’ma Zh. Tekh. Fiz. 24, 67–72 (July 26, 1998)     

Allowance for the contribution of self-adsorption in estimates of the interphase energy in a solid-metal-own-melt system

An expression is verified to allow for the contribution of self-adsorption in the Young equation for the interface between a polycrystalline metal and its own melt using only two properties, the heat of fusion and the gram-atomic volume. The adequacy of this relation is established for precious and nontransition polyvalent metals. Pis’ma Zh. Tekh. Fiz. 24, 81–83 (March 12, 1998)     

Effect of weld heat input on toughness and structure of HAZ of a new super-high strength steel

Fracture morphology and fine structure in the heat-affected zone (HAZ) of HQ130 super-high strength steel are studied by means of SEM, TEM and electron diffraction technique. Test results indicated that the structure of HAZ of HQ130 steel was mainly lath martensite (ML), in which there were a lot of dislocations in the sub-structure inside ML lath, the dislocation density was about (0.3∼ 0.9) x 10¹²/cm². No obvious twin was observed in the HAZ under the condition of normal weld heat input. By controlling weld heat input (E ≤20 kJ/cm), the impact toughness in the HAZ can be assured.     

g-Jitter mixed convection adjacent to a vertical stretching sheet

This paper studies the effect of periodical gravity modulation, or g-jitter induced mixed convection, on the flow and heat transfer characteristics associated with a stretching vertical surface in a viscous and incompressible fluid. The velocity and temperature of the sheet are assumed to vary linearly withx, wherex is the distance along the sheet. It is assumed that the gravity vector modulation is given byg*(t)=g_o [1+ɛ cos(πωt)]k, and the resulting non-similar boundary layer equations are solved numerically using an implicit finite-difference scheme. The effects of the amplitude of modulation, frequency of the single-harmonic component of oscillation, mixed convection parameter and Prandtl number on the skin friction and Nusselt number are discussed in detail.     

The analogy between a problem of magnetohydrodynamics and the Benard problem in the Boussinesq approximation

It is shown that the equations of motion written in a longitudinal plane of symmetry of a liquid-metal current-carrying conductor of rectangular cross section are identical with the equations that describe heat conduction in a flat layer of liquid heated from below in the Boussinesq approximation. The main parameters that determine the threshold of the convective instability that develops under the action of Lorentz forces in a current-carrying liquid metal are found. Pis’ma Zh. Tekh. Fiz. 25, 1–6 (May 26, 1999)     

Specific heat studies in Ho-Ba-CuO superconductors: Fermionic and bosonic contributions

The specific heats of superconducting HoBa₂Cu₃O_7-δ (T _c≅ 92 K) have been theoretically investigated in the temperature domain 70 ≤T ≤110 K. The bosonic (phonons) contribution to the specific heat is estimated from Debye model in the harmonic approximation for high temperature expansion (T > θ_D/2π) using the moments of the phonon density of states. The fermionic constituent as the electronic specific heat is deduced using a suitable trial function above and belowT _c. As a next step the contribution of specific heat by charge oscillations (plasmons) are obtained. The theoretical results from bosonic and fermionic terms are then compared with the experimental results. We find that the specific heats from electronic as well as plasmon term are only a fraction of lattice specific heat and in particular, plasmons do not influence the thermal conduction significantly. The implications of the above analysis are discussed.     

Conversion of heat into work using thermally inhomogeneous systems (Revised)

An error, made when constructing an example of a quasistatic cyclic process for the complete conversion of heat into work using a nonintegrable thermodynamic system with controllable thermodynamic characteristics, is eliminated. Pis’ma Zh. Tekh. Fiz. 23, 91–95 (March 12, 1997)     

Quantum-dot cw heterojunction injection laser operating at room temperature with an output power of 1 W

This paper describes a new cw laser with tunnel-coupled vertically aligned InGaAs quantum dots in an AlGaAs matrix with a room-temperature output power of ∼ 1 W at both mirrors. The maximum operating temperature of the heat sink is ∼ 75 °C. Pis’ma Zh. Tekh. Fiz. 23, 51–54 (February 26, 1997)     

Extremal character of the change in the reverse current of silicon p +-n structures during the formation of nickel Ohmic contacts

The formation of nickel silicide during the formation of Ohmic contacts in silicon devices is investigated, and the dependence of the process on the heat treatment time is described. Pis’ma Zh. Tekh. Fiz. 24, 1–5 (June 26, 1998)     

Drag and heat exchange of an object in a supersonic flow with a planar source of energy in front of the object

The problem of a steady-state wake behind an energy source in a supersonic gas flow is analyzed and solved. The energy source is a planar gasdynamic discontinuity supplying a given energy to the flow. The parameters behind the source correspond to the weak detonation regime (supersonic combustion). The solution obtained is used to investigate the drag and heat exchange of an object in the wake behind the source. It is shown that the drag and thermal loads of the object may be reduced appreciably when the Mach numbers of the incoming flow are fairly high. An investigation was made of the energy efficiency of this method of reducing the drag and thermal loads of an object. The conditions under which this method is energetically favorable are determined. Pis’ma Zh. Tekh. Fiz. 24, 76–82 (December 26, 1998)     

Possible nonlinear heat-pulse propagation in solids at Debye temperatures

Molecular dynamics techniques are used to show that heat can be transferred ballistically in threedimensional crystalline materials at temperatures on the order of Debye temperatures. Pis’ma Zh. Tekh. Fiz. 25, 55–59 (March 26, 1999)     

Negative turbulent heat conduction and its role in the formation of large-scale structures

A mechanism is proposed for the establishment of negative heat conduction under conditions of advanced turbulent convection, which leads to the formation of large-scale structures. A semi-empirical model of turbulent convection and experimental results are used to give some quantitative estimates. Pis’ma Zh. Tekh. Fiz. 24, 67–75 (April 26, 1998)     

Hydrodynamic characteristics of the propagation of polymerization waves in liquid media

An analysis is made of the hydrodynamic characteristics of the propagation of thermal polymerization waves in liquid media without hardening of the final polymer product. The process is described mathematically using a system of equations for the dynamics and the heat and mass transfer in a reacting liquid medium, written in the Boussinesq approximation and assuming the simplest overall polymerization reaction. Pis’ma Zh. Tekh. Fiz. 23, 56–61 (April 12, 1997)     

Experiments on the Self-Organized Critical State of 4He

When a heat flux Q is applied downward through a sample of ⁴He near the lambda transition, the helium self organizes such that the gradient in temperature matches the gravity-induced gradient in T _λ . All the helium in the sample is then at the same reduced temperature and the helium is said to be in the Self-Organized Critical (SOC) state. We have made the first measurements of the ⁴He SOC state specific heat, C _{∇ T} (T(Q)). There is no measurable difference between C _{∇ T} and the static zero-gravity ⁴He specific heat for temperatures between 650 and 250 nK below T _λ . Closer to T _λ , the specific heat is depressed and reaches a maximum value at 50 nK below T _λ . This depression is similar to that predicted theoretically as reported by R. Haussmann (Phys. Rev. B 60, 12349, 1999). Contrary to the expectations of theory, however, we see another depression far below T _λ . In addition, over the heat flux range of 30 nW/cm² to 13 μW/cm², we have made improved measurements of the speed of a recently discovered propagating thermal mode, which travels only upstream against the nominal heat flux of the SOC state. We are able to accurately predict the speed of this wave by treating the helium of SOC state as a traditional fluid with a temperature dependent thermal conductivity.     

The effect of longitudinal heat conduction on a regenerative heat exchanger

Abstract

This study is to discuss the effect of longitudinal heat conduction on a rotary regenerative heat exchanger. An example in Ref. [5] is computed to compare the effect of longitudinal heat conduction. The solutions presented in this study are obtained from the method of numerical analysis as shown in Ref. [3].     

Non-uniform temperature gradients and thermal stresses produced by a moving heat flux applied on a hollow sphere

This work presents numerical analyses of transient temperature and thermally-induced stress distributions in a hollow steel sphere heated by a moving uniform heat source applied on a certain zenithal segment (the heated zenithal segment, Θ _H ) of its outer surface (the processed surface) under stagnant ambient conditions. Along the process, the moving heat source (MHS) moves angularly from the first zenithal segment to the last zenithal segment on the processed surface with a constant angular speed, ω, and then returns backward to the first zenithal segment with the same speed. It is assumed that the inner surface is heat-isolated and that the outer surface except the heated segment is under stagnant ambient conditions. The numerical calculations are performed individually for a wide range of thermal conductivity, λ, of steel and for the different Θ _H s. The maximum effective thermal stress ratio calculated as per the heat flux intensity (q ₀) can be reduced in considerable amounts. By increasing λ(∼75%) and ω(∼63%) the maximum effective thermal stress ratio calculated can be significantly reduced.