Metal Temperature Distribution Research Articles

Heat and mass transfer behavior in CMT plus pulse arc manufacturing

The metal transfer mode, temperature distribution, flow behavior, and microstructure characteristic in the process of cold metal transfer plus pulse (CMT+P) arc manufacturing were investigated by the in-situ observation and numerical simulation. A novel coupling model for droplet-pool interaction under the CMT+P arc was established, along with a new heat source model that considered Marangoni forces on droplets. These innovations provided significant insights into the heat and mass transfer mechanisms in the CMT+P hybrid arc manufacturing process. The results show that the droplets generated by the CMT+P hybrid arc exhibited a mixed transfer mode: short-circuit transfer in the CMT period and projected transfer of one droplet per pulse during the pulse period. The short-circuit transfer was more stable than the projected transfer, attributed to the smooth transfer of droplets to the molten pool through the liquid metal bridge, dominated by surface tension and Marangoni forces. The main energy of the molten pool was provided by droplets, which had a dominant ability to melt the substrate. However, the liquid metal bridge in the CMT period slowed down the heat transfer to the molten pool and had significant oscillating and stirring effects. During the pulse period, the droplet was accelerated and projected transfer by gravity and electromagnetic force. After solidification, the microstructure exhibited an alternating distribution of columnar and equiaxed grains from the bottom-up in the monolayer deposited layer, with a deflected fusion interface towards the scanning direction. At the top of the deposited layer, coarse columnar grains were distributed obliquely or laterally, inhibiting the growth of equiaxed grains and forming a distinct boundary with the equiaxed grains below.

Structure effect of wall cooling channel on liquid metal heat transfer in aero-engines

In this study, a model of the cooling channel and an experimental system for heat transfer involving liquid metal are studied, to investigate the influence of the wall cooling channel structure of combustor on the heat transfer process. The error between the experimental and simulated outcomes fall is within 3 %, suggesting that the accuracy of the simulation is satisfactory. The simulation results found that the temperature non-uniformity coefficient can be reduced by 13 % and 7 % through adjusting the aspect ratio under the heat flux of 3 MW/m2 and 1.5 MW/m2 respectively, and the wall temperature of gas side can be reduced by 89 K and 47 K respectively. A smaller aspect ratio is favorable for homogenizing the liquid metal temperature distribution. Longer widths, however, can lead to horizontal thermal stratification, which can be unfavorable for heat transfer. With an aspect ratio and rib thickness of about 0.5 and 0.4 mm, respectively, the cooling channel outlet has the lowest non-uniformity coefficient of temperature and enthalpy, which is conducive to the improvement of the wall energy recovery rate. The optimal cooling channel effectively improves the thermal stratification in channel, and provides theoretical guidance for the suitable application of liquid metal to the combustor wall cooling channel.

Determination of interfacial heat transfer coefficient at the frozen sand mold casting process of ZL101 alloy

Compared to the resin sand mold casting process, frozen casting is more environmentally friendly, providing a better working environment and enhanced supercooling degree. The interfacial heat transfer coefficient (IHTC) between frozen sand mold and metal is an important parameter that significantly influences the final mechanical properties and microstructure of the castings. This paper solved the inverse heat conduction problem using the finite difference method (FDM). In addition, the conjugate gradient method (CGM) was adopted to calculate the temperature distribution and heat flux in the molten metal. At the same time, the particle swarm optimization algorithm (PSO) was used in temperature distribution determination in frozen sand mold. The interfacial heat transfer coefficient (IHTC) was estimated during the solidification of ZL101. The results showed a good agreement between calculated and experimental data, obtaining accurate casting interface temperature Tm, frozen sand mold interface temperature Ts, heat flux q, and IHTC. The analysis of the IHTC variation revealed a water content value within the range of 4 wt.% to 5 wt.% resulted in IHTC in two types of interpretation, called ‘fluctuation type’ and ‘turning type’.

Numerical Study of Heat Transport in Static Liquid Metal Exposed to Plasma with Magnetic Field

Suitable management of excessive heat in liquid metal is one of key roles to accomplish the proper liquid metal usage as future alternative fusion plasma facing components. In this work, theoretical heat transfer in liquid metal in contact with magnetized plasma was carried out, and a numerical solver for investigating temperature and induced velocity by j×B force has been developed. The study suggests the trends: 1. lower bulk temperature in liquid metal at which magnetic field is presented, compared to no magnetic field, by additional convection from j × B, stronger than natural convection; and 2. asymmetric temperature distribution in liquid metal along j × B.

Mathematical procedure for predicting tube metal temperature in the radiant superheaters of a tangentially and front fired utility boilers

The superheaters can be indicated as one of the most critical components of the utility boilers experiencing highest temperatures. The local overheating of the heat exchangers material is a significant operational issue. The current and future market conditions implicate new unfavourable regimes of boiler operating conditions bringing the need for prediction capability of tube wall temperature in either design or retrofit process. There is a need to obtain a realistic metal temperature distribution based on uneven heat flux absorbed and complex steam flow. The current paper demonstrates a computational methodology of predicting tube metal temperature of radiant superheaters platens. It couples a full scale 3-D boiler simulations based on CFD technique on the combustion side with an in-house 1-D heated pipe flow model of the steam side. The methodology was applied to two different boilers with different firing strategy (front fired and tangentially fired) to demonstrate the model flexibility. The model is capable of identifying the exact location of specific platen in which the metal maximum temperature occurs. A validation study was conducted by utilising the available measurements. The computations are in qualitative and quantitative agreement with measurement. The modelling approach can be easily extended to boilers utilising all types of fuels as well as heat recovery steam generators.

Computational fluid dynamics investigations of flow, heat transfer, and oxidation in heat recovery steam generator

Modern heat recovery steam generators (HRSGs) operate at elevated temperatures, leading to the formation of oxides inside the tubes of heat exchangers (HXs). This oxide growth reduces the heat recovery efficiency. Moreover, after reaching a certain critical thickness, some oxide scales detach from the tube surface (exfoliation), causing erosion damage to the components downstream. Predicting the metal temperature distribution and associated oxide thickness in the HXs of an HRSG can aid in mitigating these problems. A computational fluid dynamics (CFD) model was developed within the commercial code STAR-CCM+ for the prediction of fluid flow, conjugate heat transfer, and associated oxidation in HRSGs. Moreover, a new Porous Media Model (PMM) method was developed to model the fin effect on the heat transfer in HX, which can substantially reduce the prohibitive computational costs of fin meshes. The developed CFD model was used to conduct a high-fidelity simulation of a real-scale HRSG to investigate flow, heat transfer, and oxide growth. The calculated oxide thickness on different tubes can be used to identify HX regions that require oxide-resistant coatings to prevent exfoliation and ensuing damages. Furthermore, this CFD framework can serve as a reference for future studies that intend to model and investigate high-temperature oxidation in HXs used for any applications.

The Effect of Machining Parameters on the Temperature Distribution in Metal Cutting Operation

This study presents numerical solution by using coupling model between computational fluid dynamic (CFD), and finite element method (FEM) to predicted the temperature distribution through cutting tool. In this study ANSYS/Explicit dynamic used to solve finite element equations in cutting zone. Machining simulations were conducted using Aluminum (AL) and High speed steel (HSS) as a workpeice and tool material respectively. Depth of cut varied from 1.5 mm to 2.5 mm and a cutting speed varied from 6m/s to 10m/s have been considered in the simulations. The CFD model solve by using ANSYS/fluent to find the temperature distribution at the tool surface by using finite volume method. The simulation explained the influence of depth of cut, and cutting speed on cutting temperature. For all simulations, the rake angle is fixed (6°). The rise or reduction in temperature as a result of the various cutting parameters was also estimated and discussed. After solving the problem, it was discovered that the temperature at the tip (tool-work piece contact area) was the highest and gradually decreased towards the surface, and that the results showed a major influence of cutting speed on the temperature generated in the machined models and a very small influence of depth of cut on the workpiece temperature.

Finite Element Modeling of Upper Ball Joint in a Two-Step Hot Forging Process

This paper presented an analysis of the two-step of hot forging process are carried out to manufacture Upper Ball joint, which are including roughing and finishing operation. The part was made from SNCM8 alloy steel. The simulation has been done with application of QForm V10.1.6 software. The constitutive model based on Zener-Hollomon parameter was applied. As a result of simulations, metal flow lines, plastic strain, temperature distribution and effective stress for forgings were obtained. Finite element simulation by QForm V10.1.6. software is suggested as a valuable tool for predicting the hot deformation behavior of material during multi-stage of hot forging process which utilized to enhance the manufacturing process. In addition, the forming load and thickness during the forging process were analyzed. It was found that the deviation of forming load between simulation and experiment was raised to 10.71% and the maximum error of flank thickness was 5.137%. within specification. Therefore, the workpieces of the quality required by specification are obtained.

Experimental study on heat transfer characteristics of metal foam/paraffin composite PCMs in large cavities: Effects of material types and heating configurations

This study explores the effects of material types and structural parameters of metal foam, and heating configurations on the evolution of melting front, heat transfer characteristics, and temperature distribution of metal foam/paraffin composite phase change materials (PCMs) in large cavities. Copper and iron foams were used as the heat transfer enhancement medium, while paraffin with a melting point of 45 °C was chosen as the PCM to store heat. This study identified the heat transfer regimes in large cavities during the melting process. The experimental results on different heating configurations indicated that different from small cavities, both conduction and convection regimes played a fundamental role in the melting process. In addition, the heating configuration controlled the evolution of the melting front of the pure PCM and composite PCM. On the basis of these results, a non-dimensional correlation validated against a large dataset of experiments was fitted to model the melting process of the composite PCMs.

Experimental study of cooling air effect on overall cooling of laminated configuration at a turbine vane end-wall

Turbine vane end-wall cooling management is complicated by the sophisticated cascade flow, generating the non-uniform distribution of metal temperature at end-wall surface, a negative factor of component durability. The double-wall laminated cooling has a huge potential to achieve the two-side thermal protection for end-wall, as well as the minimum cooling air amount. However, the design guidance of laminated cooling end-wall is still scarce, since that the reported flat-plate studies ignored the influence of end-wall flow. In present work, the cooling air effect on the metal overall effectiveness was extracted from the infrared thermography measurements under different cooling air flowrates, indicating that there is an utmost of cooling air consumption for the reduction of metal temperature. The two-dimensional contour of effectiveness induced by cooling air was selected as the new design principle. A case study indicated that the modified laminated cooling layout can acquire the uniform distribution of metal temperature over the entire end-wall surface. A comparison of metal overall effectiveness of original and modified end-walls revealed that in leading edge of pressure side, the novel film cooling design is more proper; and the dense layout of impingement-hole with large diameters is effective in the corner of pressure side.

Effects of sand and gating architecture on the performance of foot valve lever casting components used in pump industries

This work addresses manufacture, testing and simulation of foot valve lever (FVL) for monoblock pump industry, using a cost-effective casting design process. The impact of different types of sands, such as air-set, dry and sodium silicate as well as gating designs, namely H-, U- and O-type, were studied with respect to surface roughness and porosity. The mold pattern was produced using additive manufacturing (AM) technology. Both experimental and numerical investigations were performed on the temperature distribution of molten metal at random locations for the different gating configurations or designs, considering mold filling and solidification. It was evident from the experimental investigation that contribution of air-set sand and O-type gating architecture showed limited consistency effects. Importantly, gating architecture was the most influential parameter to determine all specified quality outcomes, independent of sand mold. An order of O < H < U-type was obtained from the gating designs for minimal surface roughness and percentage of porosity. Furthermore, the microstructure analysis depicted only an irregular defect with minimum quantity at both surface and cross-section of O-type at two different locations. Optimum pouring temperatures of 740, 750 and 790 °C were obtained for mold filling of all 24 components of H-, O- and U-type of gating designs, respectively. The varying solidification temperature was observed from real time thermocouple reading, which was in close agreement with the numerical simulation. Evidently, O-type of gating design exhibited best performance for large-scale development of the FVL in terms of surface roughness, porosity and cooling effects.

Heat transfer modelling of semi-suspension biomass fired industrial watertube boiler at full- and part-load using CFD

In the current work, a computational fluid dynamics model is presented of a semi-suspension fired bagasse boiler which pays special attention to resolving the heat transfer to the furnace walls, superheater tubes and evaporator tube bank. The boiler CFD model includes custom-developed sub-models programmed in the C language which captures the fuel particle grate interaction, cylindrical fuel particle drag effects, superheater steam side heat transfer and evaporator heat exchange using a porous media approach. The model is applied to simulate the case study boiler for 100% and 65% load cases. The CFD model results are verified using a steady-state process model which utilizes well-known empirical heat transfer correlations. The CFD model results are also validated using plant measurements. The results of the CFD model show that it can accurately predict the outlet steam temperatures of the superheaters with relative errors of between 0.89 and 1.6% compared to the site data. The model is also capable of accurately predicting the evaporator outlet gas temperatures with a relative error of approximately 1.4%. Once the model is verified and validated it is used to investigate heat flux and metal temperature distributions in the various heat exchangers. The results show that at part load conditions the combustion occurs much closer to the furnace rear wall due to deeper spreading of the fuel particles, which results in the front wall having a relatively low heat absorption rate compared to the side and rear walls.

Numerical and Analytical Investigation of Heat Transfer Mechanisms and Flow Phenomena in an Intermediate Pressure Steam Turbine Blading During Startup

Abstract As a result of an ever-increasing share of volatile renewable energies on the worldwide power generation, conventional thermal power plants face high technical challenges in terms of operational flexibility. Consequently, the number of startups and shutdowns grows, causing high thermal stresses in the thick-walled components and thus reduces lifetime and increases product costs. To fulfill the lifetime requirements, an accurate prediction and determination of the metal temperature distribution inside these components is crucial. Therefore, boundary conditions in terms of local fluid temperatures as well as heat transfer coefficients (HTCs) with sufficient accuracy are required. As modern numerical modeling approaches, like 3D-conjugate-heat-transfer (CHT), provide these thermal conditions with a huge calculation expense for multistage turbines, simplified methods are inevitable. Analytical heat transfer correlations are thus the state-of-the-art approach to capture the heat transport phenomena and to optimize and design high efficient startup curves for flexible power market. The objective of this paper is to understand the predominant basic heat transfer mechanisms such as conduction, convection, and radiation during a startup of an intermediate pressure (IP) steam turbine stage. Convective heat transport is described by means of heat transfer coefficients as a function of the most relevant dimensionless, aero-thermal operating parameters, considering predominant flow structures. Based on steady-state and transient CHT simulations, the heat transfer coefficients are derived during startup procedure and compared to analytical correlations from the literature, which allow the calculation of the heat exchange for a whole multistage in an economic and timesaving way. The simulations point out that the local convective heat transfer coefficient generally increases with increasing axial and circumferential Reynolds' number and is mostly influenced by vortex systems such as passage and horseshoe vortices. The heat transfer coefficients at vane, blade, hub, and labyrinth-sealing surfaces can be modeled with a high accuracy using a linear relation with respect to the total Reynolds' number. The comparison illustrates that the analytical correlations underestimate the convective heat transfer by approximately 40% on average. Results show that special correlation-based approaches from the literature are a particularly suitable and efficient procedure to predict the heat transfer within steam turbines in the thermal design process. Overall, the computational effort can be significantly reduced by applying analytical correlations while maintaining a satisfactory accuracy.

Improved Computational Fluid Dynamics Framework for Reactor Core Baffle Swelling Assessment

Abstract This paper presents an improved estimation of reactor core baffle temperature distribution, during operation, at the nominal power level to address swelling problems of the reactor internals. Swelling is the main limiting factor in the reactor core internals long term operation of VVER-1000 nuclear units. The material irradiation-induced swelling and creep models are very sensitive to temperature distribution in metal; thus, a more detailed analysis of the core baffle metal thermohydraulic cooling characteristics is required. A framework for the computational fluid dynamics (CFD) analysis of VVER-1000 reactor baffle cooling is presented. First, an analytical model was developed to obtain boundary conditions (BCs) and simplify CFD analysis. Second, the CFD analysis was performed using 60 deg symmetry, which included core, baffle, and core barrel, and it is limited by the height of the baffle. Core is simplified as an equivalent coolant domain with considering of spatial volumetric energy release. Core baffle is presented as monolithic body with considering of gamma-ray heat generation. Model includes cooling ribs and simplified geometry of connecting studs, with cooling flow of the coolant through the nuts grooves. Calculated convection coefficient and temperature are in good agreement with analytical model and give a more accurate result comparing to RELAP5/mod3.2. Obtained temperature field was used to estimate baffle swelling process and justify safe long term operation of the reactor internals.

Simulations and experiments of mould filling in lost foam casting

ABSTRACT A new method for mould filling calculation of lost foam casting (LFC) was developed based on the main hypothesis, which assumes that every point on the melt-pattern interface moves in the radial direction. The value of the normal velocity is calculated by an empirical formula, which is the function of the degree of vacuum, pattern density, pouring temperature, metallic static head, etc. At a given time step, every interface point moves to a new position, and all the points form the shape of the melt-pattern interface. Based on the new position of the interface and the given velocity of the interface cell, the fluid flow and the temperature distribution of the molten metal can be calculated during the mould filling process of LFC. The calculated results were validated by experiments.

Thermal Performance of GaN/Si HEMTs Using Near-Bandgap Thermoreflectance Imaging

Superlattice (SL) structures have been used to reduce the stress in the GaN epilayer of high-electron-mobility transistors (HEMTs). This has led to an improvement in their properties such as the breakdown voltage. The increase in thermal resistance associated with these structures, however, causes elevated device temperatures which may outweigh the benefits of this approach. To verify this, the thermal performance of SL structures on HEMTs must, thus, be accurately characterized. Transient thermoreflectance imaging (TTI) is an optical technique that can map the temperature distribution across a surface. For materials, such as gold, TTI shows a high spatial and temporal resolution. Consequently, the technique has been primarily used to monitor the gate metal temperature distribution in HEMTs. The origin of the localized heating in HEMTs, however, is known to be in the active GaN layer and, thus, accurate thermal characterization of the channel is necessary. Using a UV LED excitation source with a wavelength near the bandgap of GaN, TTI of GaN channels in HEMTs is presented and verified by comparing the gate metal temperature. To ensure a strong thermoreflectance signal from the GaN surface, the importance of using an excitation wavelength near the bandgap of the GaN channel is highlighted. The effect of the bandgap on the magnitude and the linearity of the thermoreflectance coefficient is presented and discussed. Overall, the improvements to TTI discussed in this article make the technique an accurate method to measure the temperature distribution in GaN HEMT SL structures.

Thermal matching using Gaussian process regression

Thermal matching is a key stage of the development process for a gas turbine engine where component models are verified to ensure the correct metal temperature distribution has been used in life calculations. The thermal match involves adjusting parameters of a thermal model in order to match an experimental temperature distribution, usually obtained from a thermal paint test. Current methodologies involve manually adjusting parameters, which is both time consuming and leads to variation in the matches achieved. This paper presents a new method to conduct thermal matching, where Gaussian process regression is utilised to obtain a surrogate model from which optimal parameters for matching are obtained. This standardised procedure removes subjectivity from the match and gives faster and more consistent matches. The method is introduced and demonstrated for a number of cases involving a leading edge impingement system that has been isolated from a high pressure turbine blade.

Model Study of the Effect of Metal Filler Particles on Liquid Metal Temperature Distribution During Casting by Gasified Models

A mathematical model is developed for calculating the temperature field established in liquid alloy after filling a lost foam casting mold when filler metal particles are placed in a expanded foam polystyrene model. The effect of a stepwise drop in temperature of the cast alloy caused by thermal destruction of foam polystyrene and heat exchange with filler particles is observed. The dependence of this effect on filler volume fraction in the area of its location and ratio of thermophysical properties of the basic alloy and filler material is established.

Heat convection coefficients of a tilting-pad journal bearing with directed lubrication

Abstract This paper investigates the impact of heat transfer between leading and trailing pad free surfaces and the space between pad regions of high-speed tilting-pad journal bearings. General influence on pad metal temperature distributions as well as magnitudes of resulting heat convection coefficients are theoretically analyzed and validated with test data for sliding speeds up to 94 m/s and specific loads up to 3.0 MPa. Results indicate significant impact of trailing pad free surface heat transfer on maximum pad metal temperatures as well as potential for optimization based on the general flow pattern. Moreover, limitations, extensions, and improvements of the presented study are comprehensively discussed.

Microstructure and Mechanical Property Inhomogeneities of a Modified AZ80 Magnesium Alloy Wide Plate Under Horizontal Flat Die Extrusion

In the present paper, inhomogeneities in the microstructure and mechanical properties of a modified AZ80 plate under industrial production conditions were investigated. The results indicated that the microstructure of the edge and middle region shows more homogeneous and fine recrystallized grains. Additionally, more coarse recrystallized grains existed between the edge and the middle region. The ultimate tensile strength and yield strength of the edge region of the plate are maximal (287 and 162 MPa), and those near the 1/8 W region are minimal (259 and 152 MPa). The grain size increased from 19.5 to 27.2 μm along the center layer to the surface layer. The ultimate tensile stress (yield stress) increases from 258 (121 MPa) to 284 MPa (176 MPa) in the direction from the surface layer to the middle layer. The microhardness decreased from the surface layer (72HV) to the center layer (64HV). The metal strain state and temperature distribution lead to different degrees of dynamic recrystallization, which causes the microstructure and mechanical properties of the plate.