DIURNAL ENERGY BALANCE STUDIES OVER WHEAT USING BOWEN RATIO ENERGY BALANCE METHOD

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Evaluation of Self-Propelled Rotary Tool in the Machining of Hardened Steel Using Finite Element Models

This paper presents a model for assessing the performance of self-propelled rotary tool during the processing of hardened steel. A finite element (FE) model has been proposed in this analysis to study the hard turning of AISI 51200 hardened steel using a self-propelled rotary cutting tool. The model is developed by utilizing the explicit coupled temperature displacement analysis in the presence of realistic boundary conditions. This model does not take into account any assumptions regarding the heat partitioning and the tool-workpiece contact area. The model can predict the cutting forces, chip flow, induced stresses, and the generated temperature on the cutting tool and the workpiece. The nodal temperatures and heat flux data from the chip formation analysis are used to achieve steady-state temperatures on the cutting tool in the heat transfer analysis. The model outcomes are compared with reported experimental data and a good agreement has been found.

Experimental investigation of specific cutting forces and estimation of the heat partitioning under increasing tool wear in machining nickel-based super alloy IN 718

Presented are an experimental setup and affiliated methodology to measure the specific cutting forces in the milling process with proceeding tool wear at simplified orthogonal milling kinematics. The cutting forces, cutter rotation angle and chip temperature are acquired by a time sensitive measuring system consisting of a synchronized dynamometer, ratio pyrometer and spindle encoder. The approach allows the accurate acquisition of cutting forces under defined engagement conditions and thus constitutes a valuable basis for cutting force modelling and tool wear monitoring approaches. The results show uniformly and linearly increasing forces over the entire range of undeformed chip thickness due to wear. Besides a mechanical view on the cutting process, also the thermal domain was included into the analysis. Therefore, a ratio pyrometer was used as part of the synchronized measurement system tracking the chips backside temperature in order to estimate a virtually continuous heat flow into the chip. This heat flow increased with wear and process power, which indicates that the chip’s temperature can be used as process monitoring variable for tool wear.

Analytical Formulation for Temperature Evolution in Flat Wheel-Rail Sliding Surfaces

Studying the temperature evolution of the thermally affected zone (TAZ) of sliding surfaces is crucial because of its influence on microstructural evolution, wear, and fatigue. Due to the complexity of thermal analysis of sliding bodies, relationships that predict their surface temperature evolution are very helpful because they can be used as time-dependent boundary conditions; this makes the thermal analysis of sliding bodies independent. In this paper, by assuming thermal contact conductance (TCC) at the sliding common surface, the differential equation governing the thermal analysis of the wheel-rail sliding is solved throughout a wheel flat. The temperature evolution of wheel and rail surfaces and the heat partitioning factor are among the main results. Finally, the equations obtained for wheel and rail surface temperatures are applied to a freight wagon and a passenger car as two real cases. The results are discussed and compared to existing data in the literature and a solid agreement is achieved.

CFD investigation of sub-cooled boiling flow using a mechanistic wall heat partitioning approach with Wet-Steam properties

In this paper, the mechanistic wall heat partitioning approach was used to capture the complex heat and mass transfer in sub-cooled boiling flows. In order to accommodate the changes of local variables to be relevant to the physical properties of sub-cooled fluids, the Wet-Steam (IAPWS-IF97) is used as the working fluid. Currently, the approach is evaluated based on the bubble sliding along the wall before lifting-off, which is usually found in the flow boiling situations. In the simulation, the closure mechanistic models, including the fractal analysis, the force balance and the mechanistic frequency, were coupled with the Eulerian–Eulerian two-fluid framework, while the Shear Stress Transport model was used as a turbulent modelling closure. The Multiple Size Group model was introduced to handle the bubble interactions and predict the bubble size distribution. Moreover, the effect of adopting the sub-cooled liquid properties into the modelling was investigated and compared with the experiments over a wide range of flow conditions. Specifically, the predicted void fraction and the sub-cooling temperature near the heated wall were precisely compared with the cases of using the constant-property liquid. Overall, the satisfactory agreements were found between the experiments and the predictions of the liquid temperature, void fraction, interfacial area concentration, Sauter mean diameter and bubble and liquid velocities with the exception of the case of high heat and mass fluxes. To enhance the current prediction accuracy for a situation of having a high superheating temperature, more bubble interactions on the boiling wall, such as merging of the bubbles while sliding, need to be considered. Furthermore, to assess the model capability, this mechanistic approach will be introduced to elucidate the sub-cooled boiling flow in situations of using different fluids in the near future.