Additional Preheating Research Articles

Microstructural development of as-cast AM50 during Constrained Friction Processing: Grain refinement and influence of process parameters

Mg and its alloys have a wide range of structural applications despite the limitations regarding the workability and low ductility associated with its hexagonal closed-packed structure. The Constrained Friction Processing (CFP) is a novel processing technique, developed based on the refill friction stir spot welding process, that has been proposed as an interesting alternative that can help to overcome challenges associated with the processing of Mg and its alloys. This technique is shown to be able to produce homogenous fine-grained rods. Correlation between processing conditions and the evolved microstructure, i.e. texture and grain size, were established for AM50 rods. In the center, the produced rods present a strong B-fiber texture. As the distance from the center changes along the radial direction, there is a progressive outward tilt of the 〈0001〉 because of specific flow conditions during the processing. CFP is shown to be able to produce fine-grained rods with grain sizes comparable with other severe plastic deformation techniques, with advantages like no requirement of additional preheating and short processing times.

Use of Terbium Doped Phosphate Glasses for High Dose Radiation Dosimetry—Thermoluminescence Characteristics, Dose Response and Optimization of Readout Method

The phosphate glass samples doped with Tb2O3 oxide (general formula: P2O5-Al2O3-Na2O-Tb2O3) were synthesized and studied for usage in high-dose radiation dosimetry (for example, in high-activity nuclear waste disposals). The influence of terbium concentration on thermoluminescent (TL) signals was analyzed. TL properties of glasses were investigated using various experimental techniques such as direct measurements of TL response vs. radiation dose, Tmax–Tstop and VHR (various heating rate) methods, and glow curve deconvolution analysis. The thermoluminescence dosimetry (TLD) technique was used as the main investigation tool to study detectors’ dose responses. It has been proved that increasing the concentration of terbium oxide in glass matrices significantly increases the thermoluminescence yield of examined material. For the highest dose range (up to 35 kGy), the dependence of the integrated thermoluminescent signals vs. dose can be considered as a saturation-type curve. Additional preheating of samples improves linearity of signal vs. dose dependencies and leads to a decrease of the signal loss over time. All obtained data suggest that investigated material can be used in high-dose radiation dosimetry. Additional advantages of the investigated dosimetric system are its potential ability to re-use the same dosimeters multiple times and the fact that reading dosimeters only requires usage of a basic TL reader without any modifications.

Influence of the Preliminary Heating of А7075 Aluminum Alloy on the Strength of a SiC-Containing Composite Coating

We created composite coatings on the surfaces of A7075 aluminum alloy by the method of laser melting of the substrate and injection of highly dispersed silicon-carbide (SiC) particles with additional preheating of the base metal and without it. The method of digital image correlation is adapted for the evaluation of the elastoplastic deformation of the material in different zones of the coating. The averaged values of local critical strains are obtained for the coated specimens under the conditions of static bending. It is shown that the preliminary heating of the substrate up to 100°C weakly affects the deformability of the heat-affected zone as compared with heating up to 250°C or without it. At the same time, we show that the fracture force and critical deflection of the specimens preheated to 100°C become higher (almost by one-third) than for the specimens without heating. This can be explained by the formation of Al4C3 aluminum carbides on the boundaries of silicon carbide (SiC) particles.

Modeling of heat transfer processes in ventilated enclosing structures in stationary conditions

One of the ways to increase the energy efficiency of the housing and communal enterprise and solve the problem of space heating is the construction of «Passive houses», which contain elements of structures that effectively absorb the energy of solar radiation. The object of the study is the «Passive house», which is a building in which thermal comfort (ISO 7730) is achieved solely by additional preheating (or cooling) of the fresh air mass. This is necessary to maintain high quality air in the rooms, without additional recirculation.The analysis of heat exchange processes in ventilated enclosing structures is carried out and the calculation methods for their design are analyzed. The application of passive solar heating technology in Ukraine's climatic conditions will provide up to 50 % of the heat needs.It is determined that the movement of outdoor air in the ES (open enclosing structures) along the wall of the house leads to heat loss, but air in the ventilated layer will prevent the formation and accumulation of condensate. This will allow in winter to maintain the thermal properties of the outer layer of insulation at home, reduce the cost of heat for heating and prevent the formation and development of fungal mold.The peculiarities of heat exchange processes in building structures with ventilated channels are studied. On the basis of the analysis of calculation methods for ES design, it can be stated that the classical method for evaluating heat exchange processes is based on the equations for the thermal balance of air for an infinitesimal volume dx. But when using this equation, it is impossible to take into account the distribution of radiant and convective heat flows, and also to estimate the effect of energy losses.The paper proposes a mathematical model that will allow to determine changes in air temperature along the ventilated layer of enclosing structures and to quantify the intake or loss of heat to the room during the cold season.

Microstructural and abrasion wear characteristics of laser-clad tool steel coatings

Several different tool steel grades were deposited on mild steel by the laser-cladding process with coaxial powder feeding. With bidirectional scanning pattern, most of the grades were deposited crack-free with hardness up to 1000 HV without additional preheating. In a 3-body abrasion wear study, the laser clad Ralloy® WR6 with significant portion of retained austenite exhibited superior abrasive wear resistance compared with the predominantly martensitic tool steel coatings (M2, M4, H13, HS-23, HS-30) and the reference material, Raex® Ar500 wear resistant steel. The abrasion wear resistance of austenitic–martensitic WR6 tool steel was further enhanced by the external addition of 20% volume percentage of relatively large (45–106 µm) vanadium carbides. In single point scratch tests, predominantly martensitic tool steels outperformed austenitic–martensitic tool steels and wear resistant steel. The differences in wear performances were explained by different wear mechanisms and types of contact between the abrasive and the surface.

Non-intrusive gas-phase thermometry for industrial oxy-fuel burners

The use of oxy-fuel combustion processes is of large interest for several industrial fields applications since it offers the advantages of low NOx emissions in combination with high combustion temperatures even without additional preheating. For optimization of such processеs a detailed understanding based on precise experimental data is necessary. So far there is still a lack of precise experimental data achieved with high spatial and temporal resolution from industrial relevant turbulent oxy-fuel combustion processes. Beside species concentration information the gas phase temperature is of utmost importance for an improved understanding of the basic chemical reactions and the pollutant formation. The coherent anti-Stokes Raman spectroscopy (CARS) technique is a very well suited laser based tool for a non-intrusive investigation of such turbulent high temperature combustion processes. In this work we analysed an industrial 400 kW oxy-fuel burner with the help of O2 based vibrational CARS system which is integrated in an industrial relevant test furnace. The burner is fed with pure oxygen and natural gas at an equivalence ratio of =0.9. At one downstream position temporal and spatial resolved temperatures were measured along a 600 mm line. Additional air sucked in from the environment seems to influence the gas phase temperature significantly.

Measure of the volumetric efficiency and evaporator device performance for a liquefied petroleum gas spark ignition engine

The use of Liquefied Petroleum Gas (LPG) as fuel for spark ignition engines originally designed to be gasoline fuelled is common practice in many countries. Despite this, some questions remain still open. The present paper deals with the two main problems related to LPG port-fuel SI engines: the volumetric efficiency drop and the LPG evaporator device performance. A passengers car SI engine equipped with a “third generation” kit for the dual-fuel operation was tested using a dynamometer test rig. A single-stage pressure reducer was selected as LPG evaporator, to take advantage of an additional pre-heating of the liquid LPG that allows higher power output than a two-stage device of the same size.Engine performance, volumetric efficiency and change of LPG thermodynamic states in the evaporator were measured both in steady-state and transient operation of the engine. Steady-state measurements show the advantage of LPG in terms of engine efficiency, and quantify the drop in steady-state brake torque due to the volume swept by gaseous fuel in the fresh charge admission process. On the other hand, transient measurements show that a single-stage evaporator device is capable to match overall simplicity and satisfactory performance during strong changes in engine load.

DEVELOPMENT OF A THERMALLY HOMOGENEOUS GASIFIER SYSTEM USING HIGH-TEMPERATURE AGENTS

DEVELOPMENT OF A THERMALLY HOMOGENEOUS GASIFIER SYSTEM USING HIGH-TEMPERATURE AGENTS

Influence of subsurface gaseous combustion on the burning of confined porous energetic materials

The combustion of porous energetic materials under confinement is generally characterized by a relatively rapid increase in the flame-propagation speed as the pressure difference, or overpressure, between the burned gases in the product region and the unburned gases deep within the pores of the unburned solid increases. The structure of the deflagration wave during this transition from "conductive" to "convective" burning is likely to correspond to a previously identified intrusive regime associated with higher overpressures. In this intrusive limit, the distributed gas-phase reactions proceed in the vicinity of the solid/gas interface, where surface reactions representing sublimation and pyrolysis occur. In this merged-flame regime, gaseous combustion can then either be confined to the purely gas-phase region beyond the solid surface or, depending on a number of factors, can penetrate inside the unburned porous material. A large-activation-energy analysis of the latter scenario is presented in this work to investigate the effects of gas-phase reaction permeation on the structure and propagation speed of quasi-steady deflagrations in confined porous propellants. The results of the current study are compared to the corresponding results that are obtained when, in the same intrusive regime, the gas flame is assumed not to penetrate into the subsurface region. It is demonstrated that the burning rate derived in the current scenario exhibits a higher sensitivity to increasing overpressure, because the heat release from gas-phase reactions within the porous solid permits additional preheating of the material.

A Model of Solar Energy Utilisation in the Anaerobic Digestion of Cattle Manure

The anaerobic digestion of cow manure has a higher destruction of pathogens and weed seeds under thermophilic conditions compared to mesophilic conditions. To maintain such conditions, solar energy can be used. In this research, the consequences of the use of solar energy under Egyptian conditions are evaluated. In this study, experiments are combined with modelling. In the experimental part, anaerobic digestion on laboratory scale is studied in two continuously stirred tank reactors at 50 and 60 oC. Daily temperature fluctuations in the tank caused a decrease in methane production rate of only 12 and 20% at 50 and 60 oC, respectively. The results are used in a model for the thermal energy demand. In the model the net thermal energy production as a function of reactor volumes, thermal insulation and additional pre-heating of the influent is evaluated. The model results show that for continuously stirred tank reactors, additional pre-heater is not advised since it decreases the efficiency. The results also show that a maximum overall heat transfer coefficient of 1 W m −2 K −1 is needed for reaching at least 50% of energy efficiency. Furthermore, adding a solar energy system improves the efficiency for large reactors only slightly, while for small reactors a large improvement is achieved. An energy efficiency of 90% can be reached.

A Comparison of Dry Sweet Cream Buttermilk and Non-Fat Dry Milk Solids in Breadmaking , ,

Summary Roller or spray-dried sweet cream buttermilk powder, when used in bread-making at the rate of 6g. per 100g. of flour, gave consistently greater loaf volume than like samples of non-fat dry milk solids. Non-fat dry milk solids containing 0.17 per cent added soybean lecithin (Arlec) produced loaves having the same volume as those made with sweet cream buttermilk. The baking quality of milk powders may deteriorate in storage, the rate of deterioration increasing with increase in moisture content of the powder and in storage temperature. The serum turbidity test, when applied to dry sweet cream buttermilk and non-fat dry milk solids, does not detect loss of baking quality due to storage deterioration. Additional preheating treatment of buttermilk secured from cream pasteurized at 74° C. for 30min. did not affect the quality of the powder for use in breadmaking. Neutralization of ripened buttermilk to an amount equivalent to 0.10 per cent acidity with either caustic soda or lime did not significantly change the quality of the powder for use in breadmaking.