Papers by Keyword: Heat Flux

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Authors: Zhong Lin Hou, Ting Li, Jun Qiao, Sheng Li Li
Abstract: The heat transfer coefficient between the alloys and cooling water is affected by a lot of factors and hard to measure, a new method was investigated with a self-designed system ultilizing SP-15 high-frequency inductive heating unit. Based on measured temperature curves and Fourier heat transfer model, quantitative correlation between heat transfer coefficient and temperature was obtained by inverse algorithm method of iterative simulation and automatic optimization. The results showed that in submerged water-cooling process, the heat transfer coefficient reached to a peak value at the beginning and then decreased with increasing temperature. A decrease of cooling water temperature increased the peak value of the heat transfer coefficient, but did not change temperature range of the peak value from 200°C to 225°C . The heat transfer coefficient was mainly dependent of interfacial temperature between the Al-Cu alloys and the cooling water.The temperatures range from 200°C to 225°C gave the highest heat flux transfer.
Authors: Haifa Sallem, Hédi Hamdi
Abstract: Grinding process is an energy intensive process in the sense that, it requires a larger amount of energy per unit of volume of material removal compared to other metal cutting processes. In this case, effects on the ground workpiece in terms of induced residual stresses and metallurgical changes due to heat generated play an important role on the lifetime of parts in their mechanism. In order to investigate effects on the workpiece during external cylindrical grinding process, a new analytical approach is firstly developed to model the action of the grinding wheel as a heat flux, which moves along the workpiece surface. The value and the shape of the heat flux entering the workpiece are directly identified. Based on the established model, numerical simulations are performed to predict temperature, cooling and its effects on residual stress distribution in the ground near surface.
Authors: Om Shankar Prajapati, A. K. Rajvanshi
Abstract: Anofluids are suspensions of metallic or nonmetallic nanopowders in base liquid and can be employed to increase heat transfer rate in various applications. In this work turbulent flow forced convection heat transfer of Al2O3-water nanofluid inside an annular tube with variable wall temperature was investigated experimentally. The Nusselt number of nanofluid was obtained for various Reynolds numbers and nanoparticle concentrations at atmospheric pressure. The addition of nanoparticles in water enhances heat transfer coefficient and the enhancement increases with increase in the nanoparticle concentration and flow rate. Experimental results emphasize the enhancement of heat transfer due to nanoparticles presence in the fluid.
Authors: Karinate Valentine Okiy
Abstract: This article looks at the effects of considering two-dimensional temperature distributions in analyzing different fin configurations (radial rectangular fins, planar rectangular fins) in contrast to the one-dimensional assumption commonly used in most design methodologies. The investigation of the temperature distributions along the length of the extended surfaces was performed both analytically and by using Computational Fluid Dynamics (CFD) software. The results obtained were then compared and the observed deviations reported. From these investigations, it was discovered that the one-dimensional approach does not always give good results for the heat fluxes and temperature distributions for plain and radial rectangular fins. This calls into question the validity of the one-dimensional assumption utilized in the design methodologies for heat exchange equipment incorporating plain and radial rectangular fins. Keywords: Fins, heat flux, heat transfer coefficient, Temperature distribution, One-dimensional analysis.
Authors: Xian Feng Wang, Feng Xing, Norio Hasebe
Abstract: The thermoelastic problem of a heat flux over a region with a crack near a rigid inclusion is studied. The inclusion is assumed fixed, which implies the translation and the rotation are restrained. The crack faces are assumed free of stress. Both of the inclusion and the crack are under thermal adiabatic condition. In the analysis, the original problem was reduced to a series of displacement boundary value problems by using the principle of superposition. The Green’s function method is used to obtain the solution of the prescribed problem in the forms of integral equations. The basic problems therefore become those for an edge dislocation, and for a heat source couple, as well as the problem of a plane containing the inclusion under a uniform heat flux. These problems are solved using the complex variable method along with the rational mapping function technique. The variations of the stress intensity factors at the crack tips with various crack lengths and heat flux angles are shown. The effects of the inclusion shape and size are also investigated.
Authors: Shahida Begum, A.N. Mustafizul Karim, Mohamed Ansari M. Nainar, Sukhana Sevah
Abstract: Boiler tube failures usually result in frequent forced outages, and ultimately in costly extended outages for major tubing replacement in a plant. There are several failure modes that may occur in a boiler tube, i.e. stress-corrosion cracking, pitting, water-side corrosion, fire-side corrosion, fatigue failure, overheating, dissimilar metal weld fatigue, mechanical fatigue and erosion. In this research the failure modes of boiler and its end cracks due to the dissimilar metal weld is analyzed. Hence data are collected and explored to determine the cause of failure and as a solution ceramic ferrule is suggested. The use of ceramic ferrule in boiler tube can eliminate the crack occurrence or delay the process due to thermal properties. The prevention of crack will reduce frequent maintenance and thus the cost of operation can be minimized.
Authors: Sawsen Youssef, O. Calonne, Eric Feulvarch, P. Gilles, Hédi Hamdi
Abstract: Grinding cup wheel is often used in the case of hand grinding which allows an important material removal rate but with secondary concern of surface integrity. Integrity is strongly affected by the process and consequently influences the surface behaviour in terms of resistivity to stress corrosion and crack initiation. This operation is difficult to master in terms of results on the surface and subsurface due to its manual nature. The paper presents results of an experimental study to investigate the residual stresses induced by this hand grinding process.
Authors: Ivana Turekova, Jozef Harangozo, Zuzana Turnova, Karol Balog
Abstract: Polymers belong to most spread organic flammable materials. They are decisive material – insulator also in cable production. Regarding the safety of buildings it is necessary to know their fire-technical characteristics, which predict their behaviour in case of fire. The article deals with testing cables protected and non-protected with intumescent coating, exposed to heat flux, in dependence on distance. A special equipment was developed for testing the inflammability, allowing objectivisation of critical conditions leading to ignition of tested materials.
Authors: K.M. Pranesh Rao, K. Narayan Prabhu
Abstract: Quench hardening is a process where an alloy is heated to solutionizing temperature and held for a definite period, and then rapidly cooled in a quenching medium. Selection of quenchant that can yield desired properties is essential as it governs heat extraction process during quenching. In the present work, the cooling performance of vegetable oil and mineral-vegetable oil blend quench media was assessed. The vegetable oils used in this work were olive oil, canola oil and rice bran oil. The mineral-vegetable oil blends were prepared by blending 10 and 20 vol. % of rice bran and canola oil in mineral oil. Inconel probe of 12.5mm diameter and 60mm height, instrumented with thermocouples were used to characterize quenchants. The probe was heated to 850°C and quenched in the oil medium. The cooling curves at different locations in the probe were used to study wetting kinematics. Inverse modelling technique was used to estimate spatially dependent metal-quenchant interfacial heat flux. It was found that the vegetable oils exhibited very short vapour blanket stage compared to mineral oil and blends. Faster wetting kinematics obtained with blends resulted in uniform heat transfer compared to that of mineral oil. The temperature distribution in the probe quenched in vegetable oils and blends was more uniform compared to that in mineral oil. It is expected that the parts quenched in vegetable oils and blends would lead to better hardness distribution compared to mineral oils.
Authors: Jozef Harangozó, Karol Balog, Zuzana Szabova, Richard Kuracina, Pavol Cekan
Abstract: The article deals with assessing the impact of the heat flux on the flammability of wood materials with application of fire retardants potassium hydrogen carbonate (KHCO3) and azanium dihydrogen phosphate (NH4H2PO4), which can limit or slow down the combustion of the material. After application of fire retardants on samples time to ignition increased and thus confirmed the retardation effect. Retarding effect was observed depending upon the concentration of the solution applied to the sample.
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