Effect Of Heat Transfer Conditions Research Articles

Heat Transfer and Phase Formation through EBM 3D-Printing of Ti-6Al-4V Cylindrical Parts

3D-printing or additive manufacturing (AM) is a group of novel intensively developed production processes, through which a "printed" object is fabricated layer-by-layer in a desired intricate geometrical shape with following joining it into a monolithic bulk by means of electron beam (EB) or laser beam (LB) melting. The present study is concentrated on the production of simple-shaped (cylindrical) Ti-6Al-4V alloy samples by Electron Beam Melting (EBM). During the rapid cooling of as-printed material's layer, martensitic structure is formed while suppressing of material's diffusivity. Effect of heat transfer conditions on the microstructure and properties obtained has been investigated. Heat transfer modelling and simulation was done utilizing the ABAQUS software package. The microstructure of the obtained material has been characterized by means of SEM and XRD. Microhardness have been also determined and correlated with the simulation results.

Effect of heat transfer conditions on the critical pressure of metal ignition in oxygen

Experimental data on the critical pressure of ignition of titanium alloy fragments in gaseous oxygen are analyzed. The fragments are obtained after fracture of alloy samples in the dynamic mode (p2*) and under natural convection conditions (p1*). The results are analyzed with allowance for the heat transfer coefficients from material ignition initiators under similar conditions. Based on the shape of the experimental thermograms of plate cooling, the coefficient of heat transfer from microcraters with a juvenile surface formed due to knockout of metal particles from the plate by the high-velocity flow is found: α2 ≈ 11 kW(m2 ·K). The value of α2 is close to the value of this coefficient calculated with the use of the coefficient α1 ≈ 5 kW/(m2 · K) of heat transfer from titanium rod microfragments (with the size of the order of metal grains) formed during titanium rod fracture in oxygen under conditions of natural convection with allowance for the ratio p2*/p1*.

ВЛИЯНИЕ УСЛОВИЙ ТЕПЛООБМЕНА НА КРИТИЧЕСКОЕ ДАВЛЕНИЕ ВОЗГОРАНИЯ МЕТАЛЛОВ В КИСЛОРОДЕ

ВЛИЯНИЕ УСЛОВИЙ ТЕПЛООБМЕНА НА КРИТИЧЕСКОЕ ДАВЛЕНИЕ ВОЗГОРАНИЯ МЕТАЛЛОВ В КИСЛОРОДЕ

Effect of heat transfer conditions on the ignition characteristics of dispersed solid fuel

The results of experimental investigation of the dependence of the ignition delay time of the dispersed solid fuel (coal) on the temperature of the heat source are reported. The characteristics of the ignition of the tested coal under conditions of local heating and heating of a single solid fuel particle by a steel plate are compared. Substantial differences in the limiting conditions of the ignition of the fuel in these two quite typical cases are revealed. An analysis of the possible mechanisms of influence of heat transfer conditions on the ignition characteristics of dispersed solid fuel is performed.

Heat and Mass Transfer During Heating of Coal-Water Fuel Partcales Coated with a Water Film in a Hight Temperature Gas Medium

The problem has been solved numerically of ignition particles of coal-water fuel (CWF), covered with a water film. The effect of water evaporation in the process of preparation and thermal ignition of the fuel has been achieved. It has been shown that heating of the primary fuel takes place even in the near-surface water film conversion. The scale of the effect of heat transfer conditions on the temporal characteristics of the water film evaporation and ignition of coal-water fuel particles has been achieved.

Effect of Heat-Transfer Conditions on the Ignition Characteristics of Liquid Fuel

The combustion of distillate fuel by single steel particles of fixed size and a massive “hot” metal plate are investigated experimentally. It is possible to conclude that significant differences exist between the heat-transfer conditions at ignition of liquid fuels by a massive heat source and a small-size single heated particle on the basis of analysis and codification of results of the experimental investigations conducted. Experimentally determined thermokinetic ignition parameters of the liquid fuels will also differ appreciably. The results obtained from the experimental investigations are the basis for further development of ignition models of hot liquids, particularly detailed accounting of heat-and mass-transfer processes.

Development of a thermoelectric self-powered residential heating system

Self-powered heating equipment has the potential for high overall energy efficiency and can provide an effective means of providing on site power and energy security in residential homes. It is also attractive for remote communities where connection to the grid is not cost effective. Self-powered residential heating systems operate entirely on fuel combustion and do not need externally generated electricity. Excess power can be provided for other electrical loads. To realize this concept, one must develop a reliable and low maintenance means of generating electricity and integrate it into fuel-fired heating equipment. In the present work, a self-powered residential heating system was developed using thermoelectric power generation technology. A thermoelectric module with a power generation capacity of 550 W was integrated into a fuel-fired furnace. The thermoelectric module has a radial configuration that fits well with the heating equipment. The electricity generated is adequate to power all electrical components for a residential central heating system. The performance of the thermoelectric module was examined under various operating conditions. The effects of heat transfer conditions were studied in order to maximize electric power output. A mathematical model was established and used to look into the influence of heat transfer coefficients and other parameters on electric power output and efficiency.

Investigation of Heat Transfer Effect on Ramp-Rate Limitation of Superconducting Cable

Ramp-rate limitation, which is known as a serious obstacle for fast charging of a superconducting magnet, is investigated by an experiment with a two-strand sample conductor and numerical analysis. During the experiment, typical ramp-rate limitation results were observed. The sample showed quench recovery by current redistribution or irreversible 'cable quench' according to the operation conditions. To investigate the recovery or quench criterion, numerical analysis is performed considering both electro-magnetic and thermal interaction. The simulation results show that the status of the low-current strands determines 'recovery' or 'cable quench' when the 'local quench' first occurs at the high-current strand. From the analysis, heat transfer conditions such as boiling heat transfer and contact heat transfer between the strands as well as current nonuniformity are the most governing factors for the stability criterion. Therefore, it is possible to propose a stability criterion for the ramp-rate limitation according to the operation condition of the superconducting magnet. Moreover, the effect of heat transfer conditions to overcome the ramp-rate limitation for the given operation conditions is investigated quantitatively.

CRACK ARREST ANALYSIS UNDER CYCLIC THERMAL SHOCK FOR AN INNER-SURFACE CIRCUMFERENTIAL CRACK IN A FINITE-LENGTH THICK-WALLED CYLINDER

This article presents a crack arrest depth analysis under cyclic thermal shock for an inner-surface circumferential crack in a finite-length thick-walled cylinder with rotation-restrained edges. The inside of the cylinder is cooled from a uniform temperature distribution. The effects of heat transfer conditions on the maximum transient stress intensity factor for the problem were investigated with systematical evaluation methods formerly developed. Then, under an assumption of a tentative threshold stress intensity range j K th together with the Paris law, the crack arrest depth under cyclic thermal stress was evaluated. The results suggested the existence of an upper limit for the normalized crack arrest depth, independent of the cylinder material in an engineering sense. Finally, the validity of applying j K max h j K th as a crack arrest criterion under cyclic thermal shock was confirmed by fatigue tests under mechanical loads equivalent to those induced by cyclic thermal shock.

Analysis of exothermal process of large sized nanocrystalline cores during mass annealing

In mass annealing process of nanocrystalline cores, it is more difficult to control temperature for large sized cores than the small ones owing to the large amount of heat given out during crystallization transition period. This paper aims at seeking the cause for property inhomogeneity of mass annealed Fe 73.5Cu 1Mo 3Si 13.5B 9 and Fe 73.5Cu 1Nb 3Si 13.5B 9 nanocrystalline cores of large sizes. The experimental results shown in the paper proves that the divergent properties of large sized nanocrystalline cores upon annealing are the results of uncertainty of the onset temperature and the amount of heat generated in exothermal process arising from the variation of the ribbon casting conditions. The effects of heat transfer conditions (such as the diameter of the tube furnace, furnace heating speed, core volume, surface area/volume ratio, ambient temperature as well as the type of protective gases) on the temperature rise of the cores were also investigated. This paper provides a basis for making necessary improvement on annealing process so as to raise the rate of qualified cores with excellent properties in mass production.

A simplified model of heat generation during the uniaxial tensile test

The temperature rise in a sheet tensile specimen has been calculated by the finite difference method for a plain-carbon steel at various strain rates and in several environments. Prior to necking, a uniform heat generation function is used with the governing flow equation while during the post-uniform strain, an empirical heat generation function is used. The empirical function is based on a strain distribution equation generated by curve fitting of experimental data. The effect of heat transfer conditions on the temperature increase has been discussed. The maximum temperature rise in air may reach 42 K at the center of an I.F. steel specimen at a strain rate of 10-2/s. The instability strain during tensile testing has been predicted by taking into account strain hardening, strain-rate hardening, and deformationinduced heating. The results show that significant deformation heating can occur during tensile testing in air at “normal” strain rates near 10-2/s, and that the uniform elongation can be affected markedly. Predictions for other alloys based on tabulated data are also presented.

Effects of heat-transfer conditions on the performance of a liquid thermal-diffusion column

Theoretical concepts on the parasitic-correction mechanism [1] in thermal diffusion columns have been confirmed by experiment.