The results of a numerical analysis of unsteady heat transfer in the “metal-mold-environment” system during continuous combined casting and extrusion of an aluminum alloy in an installation with a ...horizontal carousel mold are presented. The heat engineering zones characterized by different intensity of heat transfer between the melt and the surface of the mold have been determined. A quantitative assessment of the influence of the rate of heating of the crystallizer on the temperature-time characteristics during the period of the transient thermal process is given. It is shown that an increase in the productivity of the installation reduces the duration of the transient thermal process when starting the installation from a cold state until it reaches a stationary thermal regime. The dependence of the time at which the installation reaches the stationary thermal regime on the rotation speed of the crystallizer wheel has been obtained.
•To simulate chip formation under transient conditions, a numerical model is proposed.•The chip formation is affected by the non-stationary heat transfer process.•The tribological conditions depend ...strongly on the work material behavior.
The Arbitrary Lagrangian Eulerian approach (ALE) presents a lot of advantages. However, its use is limited to the cutting with a constant uncut chip thickness h. On the one hand, the previous numerical studies were focused on the prediction of the quasi-stationary response for cutting forces and heat transfer along the tool rake face. But on the other hand, in the industrial machining processes, as milling operations, the removal of the material from the workpiece varies with time. The aim of the present work is to extend the use of the ALE approach to the milling processes where the cutting conditions are transient: h varies with time. A new strategy combining the ALE approach and the tool translation is presented. In the present model, the out flow surface of the chip is assimilated to an Eulerian surface with a vertical moving direction of the mesh. This strategy allows to consider the increase of the tool-chip contact length with h as in up milling. The limitations of the conventional use of the ALE were also discussed in this study. The experimental study was focused on dry machining of the aluminum alloy AA2024–T351 at very high speed 51.5 and 66.2 m/s. The predicted cutting forces have been compared with the experimental results. The cutting forces are not proportional to h especially for the feed force. This tendency, reproduced by the model, is directly related to the thermal softening of the work material in the secondary shear zone. At the tool rake face, the variation of the local parameters in function of time is also discussed: tool-chip contact length, sticking zone and temperature.
Display omitted
This paper shows the influence of mortar joints on the thermal resistance of external walls made of autoclaved aerated concrete blocks. Due to the fact that the thermal conductivity of cement ...mortars and adhesives is significantly higher than the thermal conductivity of autoclaved aerated concrete products, their effect must be considered when designing the walling. The article contains a table of thermotechnical uniformity coefficients of aerated concrete walls depending on the thickness and thermal conductivity of mortar joints. The work describes the simulation of heat transfer in stationary and non-stationary conditions. In the case of unsteady heat transfer, the influence of masonry joints on the thermal resistance of the enclosing structure was considered. Thermal resistance was characterized by the range of temperatures and the estimated damping of range of temperatures. There was calculated a correction value for the effect of mortar joints on the complex damping coefficient of estimated range of temperatures.
The purpose of this article is to present and validate a computationally efficient numerical approach for the calculation of the ground-coupled heat transfer in buildings with periodic boundary ...conditions. When the boundary conditions of the heat transfer problem are described by periodic functions, it is possible to consider the transient state problem as a quasi-stationary problem with considerable savings in terms of computational time. The method is presented in detail from a mathematical point of view, together with a validation for two simple cases of slab-on-grade thermal losses, four comparisons with the ISO 13370:2007 procedure, a case with a complex shape and an evaluation of the computational efficiency.
This paper presents the results of a multiobjective optimization of integration of the Trombe wall in a typical residential building in Uzbekistan using a full factorial experiment. The following ...parameters were used as factors of the experiment: orientation of the southern wall of a typical building, thermal resistance of translucent fences, ratio of the surface area of the thrombus wall to the surface area of the building façade, and air flow rate through the Trombe wall. Calculations were made for the building with three levels of thermal protection under climate conditions of the city of Tashkent (Uzbekistan). The study object was a typical one-story three-room residential building. It has been revealed that the relative dominance of the factors within the studied range of factor values during the heating period is in the following order: orientation of the southern wall of the building, 4.56%; thermal resistance of translucent fencing, 58.21%; ratio of the surface area of the Trombe wall to the surface area of the building facade, 20.11%, and air flow rate through the Trombe wall, 17.12%. On average, the optimal combination of factors makes it possible to save from 11.1–23.5 to 68.1–93.7% of the annual specific energy consumption of the building during the heating period. Reductions in CO
2
emissions with the use of coal for building heating range from 2106 to 129 731 kg per year. Depending on the investment, the simplified payback period for the integration of the Trombe wall is 12.279 to 28.445 years. Regression equations are proposed for three levels of thermal protection of the study object, which makes it possible to determine the specific energy consumption for heating.
As a result of research, the conditions for the effective use of the volume of heat accumulator based on solid materials were determined. In the course of research, various schemes of the device of ...tubular heating elements for charging the channel elements of the heat accumulator were considered. Fire clay was used as a heat-accumulating material, capable of operating in a wide temperature range (up to 600 °С). Mathematical modeling of temperature change in the process of discharge over the cross section of the heat-accumulating unit has been carried out. Mathematical modeling was carried out using an application package that allows to obtain the temperature distribution over the cross section of the heat accumulator at key points of its work. The obtained simulation results were tested on an experimental setup consisting of four heat-accumulating units during the charging process and during the discharge of the heat accumulator. According to the research results, the most effective layout of the heating elements was determined, which allows to make the most of the volume of the heat-accumulating material. The dependencies to determine the exponent and the averaging coefficient of the heat flux are also found, which allow a more rational use of the volume of the accumulating nozzle.
The research results can be used to reconstruct decentralized heat supply systems for both residential buildings and public buildings. This will significantly align the schedule of electricity consumption during the day and reduce the consumption of hydrocarbon fuels.
This publication is devoted to creation of energy-efficient systems for cold supply and heat supply using heat energy accumulators. Thermal energy accumulation increases the efficiency of heat power ...systems including cooling and air conditioning systems, reduces peak power consumption and capacities of thermal installations at variable loads. It is shown that substances with phase transition (SPT) are widely used for thermal energy accumulation. They are mainly of the solid body-liquid type providing volume and mass density of heat storing and cold energy that is 5–14 times higher in comparison with accumulating liquids. Requirements to SPT with regard to thermal energy accumulators are formulated. We have given an overview of the SPT recommended for application to which organic compounds belong (paraffins, fatty acids), hydrates of salts, eutectics (may include organic and inorganic compounds in their structure). The advantages and disadvantages of each group of substances are shown. The information on the properties of certain SPT in relation to air conditioning systems is presented. It is shown that SPT having industrial applications are hidden under trademarks. It is noted that the creation of heat energy accumulation systems made in Russia requires carrying out a fundamental and applied research complex. We have presented application examples of thermal energy accumulation using SPT in air conditioning systems. The designs of thermal energy accumulators are described, their advantages and disadvantages are noted. We have carried out the analysis of calculation methods for systems with thermal energy accumulators available in literature including solutions of Stefan problem about non-stationary heat exchange at phase transitions in relation to the thermal energy accumulation. The conclusion is drawn on the numerical method advantages for solution of this problem. The research directions are formulated which implementation will allow for developing Russian systems of heat and cold supply with heat energy storage devices.
This work analyzes the manufacturing process of an electron-beam additive form by heating as a result of remelting the supplied filler wire as a control object. Control actions and output values are ...designated that can be used in constructing a control systems with feedback. A mathematical modeling technique is used to study heat transfer in a nonstationary formulation, taking into account the influence of the latent heat of fusion. The transient processes of temperature changes were studied at points, whose values can be used to estimate the extension of the weld pool and the degree of metal overheating. An analysis of the results of computational experiments is carried out, and the range of variations of control actions are shown. The possibility of an independent temperature control in the range of the beam and the extension of the liquid bath is also justified. Recommendations are given for the technical implementation of the system and the option of implementing local regulators, types of sensors, and their installation.
This paper presents experimental results of investigation of high-intensity cooling of high-temperature metal heater by subcooled ethanol flow. The experiments have proved the presence of ...self-excited pressure pulsations with amplitude of 1.15 MPa, arising in ethanol. Expanding real signals of the sensors by the Hilbert−Huang transform has resulted in the intrinsic mode functions. Analysis of these functions and the high-speed video shooting results allows identifying the basic frequencies and mechanisms of pressure oscillations. Comparison of the results with the data of film cooling and bubble boiling on the cooled heater has shown that maximum values of non-stationary heat-transfer coefficients for the self-excited oscillations and for the bubble boiling are the same.
PDF
