Coupling a two-stage absorption heat transformer with finite heat sources and sinks

The coupling among a two-stage heat transformer (TSHT) and finite heat sources and sinks is considered. A novel configuration is proposed, in which the evaporator of the second stage is fed both by the absorber of the first stage and by the external source. A lumped-parameter mathematical model is used to compute the performance of the proposed TSHT. It has been found that the range of applicability is widened, when compared with the usual configuration. Moreover, the use of a two-stage apparatus allows one to noticeably increase the performance compared with that obtainable with a simpler single-stage transformer. Thus, it is possible to increase the output heat and/or the user temperature, to reduce the discharge temperature, or to use lower quality energy sources. The results also allow one to draw some more general conclusions on the applicability of absorption heat transformers of different configurations, when different heat sources/sinks are considered.     

Determination of heat losses and their influence on the performance characteristics of high-enthalpy hot-shot tubes

An analysis of the losses of heat into the walls of settling chamber in a hypersonic hot-shot tube has been performed. Tests without diaphragm rupture showed that the fall of settling-chamber pressure during the operating flow regime in the tube was the consequence of the transfer of heat from working body to wall; this has allowed us to evaluate the heat-transfer coefficient α and the inner-surface temperature of the wall T _w. An empirical formula relating the coefficient α with the pressure and working-body temperature in the settling chamber in the range of pressures and temperatures 160 to 540 bar and 700 to 3400 K was obtained. Using the gained dependences of α and T _w on pressure and temperature, we have developed a physical model for calculating the working-body characteristics in the tube with allowance for enthalpy losses. We found that by the hundredth millisecond of the operating regime the disregard, in such calculations, of the wall heat flux in the first settling chamber resulted in overestimation of the stagnation temperature in the test section in comparison with similar calculations made without allowance for the heat losses by 6–18 % in terms of the full-scale temperature for aircraft flight in Mach number range 5 to 8. The developed calculation procedure has been tested in experiments without diaphragm rupture.     

The influence of radiation heat exchange on characteristics of liquid fuel ignition by a heated metal particle

A complex of interrelated heat-mass transfer processes at gas-phase ignition of a typical liquid fuel by a hot metal particle immersed partially into a liquid is investigated numerically. The scale of influence of the radiation heat exchange at particle—liquid fuel and particle—gas—vapor mixture interfaces is found. Conditions under which the impact of this factor can be neglected are determined.     

Elaboration and electrochemical characterization of LaZr2Cr4Ni5-based metal hydride alloys

The elaboration of LaZr₂Cr₄Ni₅-based intermetallic compound was performed by mechanical alloying from LaNi₅ and ZrCr₂ precursors and characterized as active materials of negative electrodes in nickel-metal hydride (Ni-MH) batteries. The effect of the milling duration on the phase composition was investigated. The structural properties of the formed phases were determined by X-ray diffraction and quantified from the Rietveld refinement data. The increase of the milling time up to 40 h leads to the highest abundance of the LaZr₂Cr₄Ni₅ phase, estimated at a weight content of 60.6 %, and a complete elimination of the LaNi₅ intermetallic precursor. The chronopotentiometry, cyclic voltammetry, and chronoamperometry techniques were applied to characterize the electrochemical behavior of prepared LaZr₂Cr₄Ni₅-based compounds. The maximum discharge capacity was 152 mAh g⁻¹, and a high electrochemical stability was obtained in the alkaline solution. The value of the hydrogen diffusion coefficient is equal to 2.1 × 10⁻⁸ cm² s⁻¹, reflecting an appropriate electrochemical hydrogenation kinetic in the LaZr₂Cr₄Ni₅-based compounds.

     

The influence of the average electron concentration on the properties of amorphous tin-noble metal alloys and a comparison of the amorphous with the liquid alloys

Measurements of the resistance and Hall coefficient of quench condensed tin-noble-metal films are reported and the results are discussed in comparison with the corresponding liquid alloys. In the amorphous state of these films, which range from about 20 to 70 at % noblemetal content, the absolute value of the band-structure energy discussed in a simple approximation seems to be maximal. This indicates the important role which the conduction electrons play in amorphous films of this kind.     

Photoemission and x-ray studies of metal hydrides and hydride formation at metal/hydride interfaces

Synchrotron radiation photoemission was used to investigate the concentration dependent intensity of hydrogen-induced states for a series of niobium hydrides. These intensities were found to be linearly related to the fraction of β phase hydride present in the sample, as deduced from the bulk phase diagram, and we conclude that fracturing did not produce a self-sustaining surface hydride layer. Photoemission studies of V overlayers on NbH_0.799 showed strong hydrogen outdiffusion and the formation of the interface hydride phase which is more stable than VH prepared in bulk form. X-ray diffraction studies of thick V-H overlayers subsequently showed the absence of long-range order. These results demonstrate that interfacial diffusion of hydrogen from NbH_0.799 into the V overlayer produced a stable hydride with electronic properties analogous to those of crystalline VH but with dominant local interactions.     

Anomalous specific heat and nuclear spin relaxation in Al-transition metal alloys

A mechanism involving dislocation pinning by impurities is proposed to explain the anomalous lattice specific heat and the nuclear spin—lattice relaxation in Al—transition metal alloys.     

波纹参数对板式换热器传热和压降影响研究

建立冷热双流道模型,研究了不同波纹参数对其传热和压降性能的影响,分析了传热机理。结果表明,板式换热器的传热和压降性能主要受流体流动形式和触点密度的影响。波纹倾角β=70°时传热效果最好但压降较大,波纹深度对传热性能的影响效果比波纹倾角和波纹节距大8%和15%左右,波纹倾角对压降性能的影响大于波纹节距。     

Development of high catalytic activity disordered hydrogen-storage alloys for electrochemical application in nickel–metal hydride batterie

Multi-element, multiphase disordered metal hydride alloys have enabled the widespread commercialization of nickel–metal hydride (NiMH) batteries by allowing high capacity and good kinetics while overcoming the crucial barrier of unstable oxidation/corrosion behavior to obtain long cycle life. Alloy-formula optimization and advanced materials processing have been used to promote a high concentration of active hydrogen-storage sites vital for raising NiMH specific energy. New commercial applications demand fundamentally higher specific power and discharge-rate kinetics. Disorder at the metal/electrolyte interface has enabled a surface oxide with less than 70 ? metallic nickel alloy inclusions suspended within the oxide, which provide exceptional catalytic activity to the metal hydride electrode surface. Received: 14 August 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001     

The concentration dependence of the electronic specific heat of nearly and weakly ferromagnetic transition metal alloys

An explanation of the asymmetric peak in the electronic specific heat coefficient at the critical concentration for the onset of ferromagnetism in transition metal alloys is provided in terms of the critical fluctuations of magnetization.     

Theoretical analysis of the influence of external conditions upon the solidification of binary metal alloys

In this paper we present theoretical analysis of the influence of cooling rate, kinetic parameters of solidification and transport coefficients upon the solidification rate, the value of supercooling on the solidification front and upon the change of concentration of the solid and liquid phase during the solidification of binary alloys. This analysis is performed within the framework of the stochastic theory of solidification.     

补偿腔支路对环路热管传热性能影响的实验研究

在环路热管系统工作中,存在因补偿腔温度过高而造成的蒸发器烧干现象。在常规环路热管系统中设计了补偿腔支路,以带走热源向补偿腔传递的径向热量,并对设计的环路热管系统进行实验测试,分析补偿腔支路对环路热管传热特性的影响。实验结果表明:补偿腔支路开启后,在热流密度14 W/cm²时,系统稳定启动所需时间从4 min减少到3 min,表明系统稳定启动所需时间减小,有利于快速启动;在热流密度18 W/cm²下,对应的壁面温度从88.2℃降至85.4℃,系统热阻从0.56 K/W减小到了0.49 K/W,表明系统所能承受的最大热流密度更大,系统热阻也更低,因此系统的传热性能更好。     

Features of the electronic spectrum of alloys with electronic topological transition and their influence on physical properties

Occurrence of a discrete spectrum of electrons of small groups as result of the electronic topological transition in Mo-Re alloys is expected on the basis of the experimental results. Such a spectrum arises against the background of the continuous spectrum of electrons of large groups and corresponds to partial localization of electrons.     

What is required for the commercialization of metal hydride refrigerators and heat pumps: Surface engineering can solve the application problems

Metal hydride devices such as refrigerators, air-conditioners, and steam regenerators have been developing for more than 15 years since the principles of thermal energy conversion were demonstrated by Phillips Research Laboratory, Brookhaven National Laboratories (BNL), and Argonne National Laboratory (ANL). Engineering approaches to improve hydriding properties such as sloped plateau and hysteresis, to control pressure-temperature-composition relations and to improve the effective thermal conductivity have been conducted by many people. As yet we have not yet reached the commecial levels for practical applications.In this paper, the reasons why we could have succeeded in bringing our R&D efforts into commercial levels are pointed out. The aim of this paper is to describe the scientific and technical problems to be solved for realizing metal hydride applications as thermal conversion devices in commercial scales.     

Design and the operational characteristics of a 16 µ CF4 laser

The design and the operational characteristics of a CO₂ laser pumped CF₄ laser developed at BARC are reported. Output energies of up to 20 mJ have been obtained at 615 cm⁻¹ with an absorbed energy conversion efficiency of 10%.     

Stability of a dispersed system in metal alloys

The Gibbs-Thomson relation is obtained for locally ordered alloys and serves as a basis for determining the stability condition for a dispersed system. The form of the distribution function of the precipitate size is found and so are the distinctive features of the time dependence of the characteristic size of the precipitate.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 74–79, April, 1981.     

Thermal expansion coefficients of rare earth metal disilicides and their influence on the growth of disilicide nanowires

The lattice parameters of rare earth metal disilicides at high temperature play a crucial role in the growth of these disilicide nanowires, which takes place at about 873 K. In the present study, the lattice parameters of Sm, Gd, Tb, Dy, Ho, Er, Sc and Er_xGd_1-x disilicides with AlB₂ structure were measured from room temperature to about 873 K by high temperature X-ray diffraction (HTXRD), from which the linear coefficient of thermal expansion (CTE) along each crystallographic axis was determined. The influence of the CTEs on the growth of nanowires will be discussed in terms of anisotropic strain. With these CTEs, the composition of a ternary disilicide, (Er_xGd_1-x)Si_1.67, for example, with optimal lattice parameters at nanowire growth temperature can be engineered to meet the requirement for the growth of high-quality nanowires. PACS 65.40.De; 68.65.La; 68.55.-a     

一种新型R32两级压缩热泵空调器的理论研究

针对R32单级压缩空调器排气温度偏高的问题,提出采用双缸滚动转子式压缩机实现两级压缩制冷循环的方案来降低系统的压缩比和排气温度并提高性能系数(CCOP)。建立相应的理论模型,计算了制冷工况和热泵工况下的性能参数。结果表明:采用两级压缩循环方式在制冷工况和热泵工况下使压缩机的排气温度分别降低了30.1℃和28.5℃,CCOP分别提高了3.02%和8.15%;同时分析了中间温度对压缩比、排气温度和系统的CCOP的影响,给出了最佳中间温度的范围。     

The influence of laser and powder defocusing characteristics on the surface quality in laser direct metal deposition

To investigate the influencing rules of the variations of powder and laser defocusing distance on surface quality and obtain the smooth surface of parts in laser direct metal deposition, the thin-walled metal parts were fabricated under three different powder defocusing distances and three different laser defocusing distances conditions. The experimental results show that a high surface quality can be obtained with the powder focussed below the substrate and laser focussed above the substrate process, and the variation in which the powder focus moves from above to below the melt pool plays a leading role and the variation in which the laser focus moves from above to below the melt pool plays a supplementary role in the influence on the surface quality. To explain the experimental results, a simple model of the track height is established.     

The influence of heat transfer conditions at the hot particle-liquid fuel interface on the ignition characteristics

The problem of ignition in the conditions of nonideal contact between liquid fuel and a single metallic particle heated to high temperatures is numerically solved. A gas-phase ignition model is created with regard to the heat-and-mass transfer processes in the gas region near the ignition source and the layer separating the particle and the fuel. The scale of the impact of the heat source surface roughness upon the ignition characteristics in a hot particle-liquid fuel-oxidant system is determined.