MHD flow and heat transfer from continuous surface in uniform free stream of non-Newtonian fluid

An analysis is carried out to study the steady flow and heat transfer characteristics from a continuous flat surface moving in a parallel free stream of an electrically conducting non-Newtonian viscoelastic fluid. The flow is subjected to a transverse uniform magnetic field. The constitutive equation of the fluid is modeled by that for a second grade fluid. Numerical results are obtained for the distribution of velocity and temperature profiles. The effects of various physical parameters like viscoelastic parameter, magnetic parameter and Prandtl number on various momentum and heat transfer characteristics are discussed in detail and shown graphically.

Failure Modes of Lead Free Solder Bumps Formed by Induction Spontaneous Heating Reflow

The shear failure modes and respective failure mechanism of Sn3.5Ag and Sn3.0Ag0.5Cu lead-free solder bumping on Au/Ni/Cu metallization formed by induction spontaneous heating reflow process have been investigated through the shear test after aging at 120℃ for 0, 1, 4, 9 and 16 d. Different typical shear failure behaviors have been found in the loading curves （shear force vs displacement）. From the results of interracial morphology analysis of the fracture surfaces and cross-sections, two main typical failure modes have been identified. The probabilities of the failure modes occurrence are inconsistent when the joints were aged for different times. The evolution of the brittle NiaSn4 and Cu-Ni-Au-Sn layers and the grains coarsening of the solder bulk are the basic reasons for the change of shear failure modes.

Heat transfer of liquid metal alloy on copper plate deposited with film of different surface free energy

Liquid metal alloys(LMAs) are the potential candidates of thermal interface materials(TIMs) for electronics cooling.In the present work, buffer layers of Ag, Ti, Cu, Ni, Mo, and W were deposited on polished Cu plates by DC magnetron sputtering, the contact angles of de-ionized water and diiodomethane on the buffer layers were measured by an easy drop shape analyzer and the surface free energies(SFEs) of the buffer layers were calculated by the Owens–Wendt–Kaelble equation. Samples were prepared by sandwiching the filmed Cu plates and LMAs. The thermal properties of the samples were measured by laser flash analysis method. The SFE of the buffer layer has a strong influence on the interface heat transfer, whereas the measurement temperature has no obvious effect on the thermal properties of the samples. As the SFE of the buffer layer increases, the wettability, thermal diffusivity, and thermal conductivity are enhanced, and the thermal contact resistance is decreased.

Improved kernel gradient free-smoothed particle hydrodynamics and its applications to heat transfer problems

Kernel gradient free-smoothed particle hydrodynamics （KGF-SPH） is a modified smoothed particle hydrodynamics （SPH） method which has higher precision than the conventional SPH. However, the Laplacian in KGF-SPH is approximated by the two-pass model which increases computational cost. A new kind of discretization scheme for the Laplacian is proposed in this paper, then a method with higher precision and better stability, called Improved KGF-SPH, is developed by modifying KGF-SPH with this new Laplacian model. One-dimensional （1D） and two-dimensional （2D） heat conduction problems are used to test the precision and stability of the Improved KGF-SPH. The numerical results demonstrate that the Improved KGF-SPH is more accurate than SPH, and stabler than KGF-SPH. Natural convection in a closed square cavity at different Rayleigh numbers are modeled by the Improved KGF-SPH with shifting particle position, and the Improved KGF-SPH results are presented in comparison with those of SPH and finite volume method （FVM）. The numerical results demonstrate that the Improved KGF-SPH is a more accurate method to study and model the heat transfer problems.

A Finite Element Analysis on MHD Free Convection Flow in Open Square Cavity Containing Heated Circular Cylinder

The problem of Magnetohydrodynamic (MHD) free convection heat transfer in a square open cavity containing a heated circular cylinder at the centre has been investigated in this work. As boundary conditions of the cavity, the left vertical wall is kept at a constant heat flux, bottom and top walls are kept at different high and low temperature respectively. The remaining side wall is open. Finite element analysis based on Galerkin weighted Residual approach is used to visualize the temperature distribution and fluid flow solving two-dimensional governing mass, momentum and energy equations for steady state, natural convection flow in presence of magnetic field in side an open square cavity. A uniformly heated circular cylinder is located at the centre of the cavity. The object of this study is to describe the effects of MHD on the thermal fields and flow in presence of such heated circular cylinder by visualization of graph. The investigations are conducted for different values of Rayleigh number (Ra) and Hartmann number (Ha). The results show that the temperature field and flow pattern are significantly dependent on the above mentioned parameters.

Effect of Hartmann Number on Free Convective Flow of MHD Fluid in a Square Cavity with a Heated Cone of Different Orientation

This paper presents the effect of magnetic field, indicated by Hartmann number (Ha), on the free convective flow of Magneto-hydro-dynamic (MHD) fluid in a square cavity with a heated cone of different orientation. Although similar studies abound, the novelty of this work lies in the presence of the heated cone, whose orientation is varied at different angles. The mathematical model includes the system of governing mass, momentum and energy equations. The system is solved by finite element method. The calculations are performed for Prandtl number Pr = 0.71;the Rayleigh number Ra = 10, 1000, 100,000;and for Hartmann number Ha = 0, 20, 50, 100. The results are illustrated with streamlines, velocity profiles and isotherms. From the results, it is found that for the present configuration, magnetic field (Hartmann number) has no effect on the shape of the streamlines for low Rayleigh numbers. However, for high values of Ra, the effect of Ha becomes quite visible. Magnetic field affects the flow by retarding the fluid movement, and thus affects convective heat transfer. At low Ra, the fluid movement and heat transfer rate are already slowing, thus impressing a magnetic field does not produce much effect. At high Ra, fluid particles move at high velocity and change the stream lines, in absence of any magnetic force. Impressing magnetic field in this situation produced noticeable effect by slowing down the fluid movement and changing the streamlines back to low Ra situations. It is noted that a combination of low Ra with zero or low Ha produces similar effects with the combination of high Ra and high Ha. It can be concluded that with increasing Ha, heat transfer mode in MHD fluid gradually changes toward conduction from convection. It can be surmised that sufficiently large Ha can potentially stop the fluid movement altogether. In that case, heat transfer would be fully by conduction.

Modeling of unsteady MHD free convection flow with radiative heat transfer in a rotating fluid

In this paper, a numerical simulation has been carried out on unsteady hydromagnetic free convection near a moving infinite flat plate in a rotating medium. The temperatures involved are assumed to be very high so that the radiative heat transfer is significant, which renders the problem highly non-linear even with the assumption of a differential approximation for the radiative heat flux. A numerical method based on the Nakamura scheme has been employed to obtain the temperature and velocity distributions which are depicted graphically. The effects of the different parameters entering into the problem have been discussed extensively.

Failure of the free energy relation under a non-Markovian heat bath temperature change

We investigate the free energy relation for a system contacting with a non-Markovian heat bath and find that the validity of the relation sensitively depends on the non-Markovian memory effect, which is especially related go the initial preparation effect. This memory effect drives the statistical distribution of the system out of the initial preparation, even if the system starts from an equilibrium state. This leads to the violation of the free energy relation. A possible way of eliminating this memory effect is proposed.

Effect of Heat Source/Sink on Free Convective Flow of a Polar Fluid between Vertical Concentric Annuli

The purpose of this paper is to find the effect of heat source/sink parameter on free convective flow of a polar fluid in open-ended vertical concentric annuli. Exact solutions of the non-dimensional differential equations describing the flow model have been obtained one by one for two different cases of source and sink. To observe the effect of the physical parameters such as source/sink and vertex viscosity, the numerical results of the velocity and microrotational velocity are finally shown on the graphs.

Radiation Effects on Free Convection MHD Couette Flow Started Exponentially with Variable Wall Temperature in Presence of Heat Generation

Radiation effects on free convection MHD Couette flow started exponentially with variable wall temperature in the presence of heat generation have been studied. The governing equations are solved analytically using the Laplace transform technique. The variations of velocity and fluid temperature are presented graphically. It is observed that the velocity decreases with an increase in either magnetic parameter or radiation parameter or Prandtl number. It is also observed that the velocity increases with an increase in either heat generation parameter or Grashof number or accelerated parameter or time. An increase in either radiation parameter or Prandtl number leads to fall in the fluid temperature. It is seen that the fluid temperature increases with an increase in either heat generation parameter or time. Further, it is seen that the shear stress at the moving plate decreases with an increase in either magnetic parameter or radiation parameter while it increases with an increase in either heat generation parameter or Prandtl number. The rate of heat transfer increases with an increase in either Prandtl number or time whereas it decreases with an increase in heat generation parameter.

Transient free convection flow of a viscoelastic fluid over vertical surface

In this paper, the viscoelsatic boundary layer flow and the heat transfer near a vertical isothermal impermeable surface and in a quiescent fluid are examined. The governing equations are formulated and solved numerically using MackCormak＇s technique. The results show excellent agreement with previously published results by a comparision. Representative results for the velocity and temperature profiles, boundary layer thicknesses, Nusselt numbers, and local skin friction coefficients are shown graphically for different values of viscoelsatic parameters. In general, it is found that the velocities increase inside the hydrodynamic boundary layers and the temperatures decrease inside the thermal boundary layers for the viscoelsatic fluid as compared with the Newtonian fluid due to favorable tensile stresses. Consequently, the coefficients of friction and heat transfer enhance for higher viscoelsatic parameters.

Short-Time Preparation of NaOH-Activated Carbon from Sugar Cane Bagasse Using Microwave Plasma Heating

The microwave induced argon plasma was applied to the preparation of NaOH-activated carbon from sugar cane bagasse. The distinguished feature of the heating technique with this cold plasma is the short operation time. The carbonization and the activation process were finalized in one step within 3 min. The prepared activated carbon with NaOH ratio 3 to bagasse characterized using N2 adsorption of type IV (IUPAC classification) to give specific surface area of 1980 m2/g and mesopore volume of 0.73 ml/g. It also showed a higher specific capacitance of 201 F/g in 1 M H2SO4 solution (with standard three electrodes) than the corresponding one by the conventional heating, previously reported. The other features were the absence of oxygen groups and the presence of carbon centered stable radicals, detected by ESR spectra, on the surface.

A Study of Two Dimensional Unsteady MHD Free Convection Flow over a Vertical Plate

In this paper, unsteady free convection heat transfer flow over a vertical plate in the presence of a magnetic field is discussed in detail. The dimensionless partial differential equations of continuity, momentum along energy are analyzed with suitable transformations. For numerical calculation, an implicit finite difference method is applied to solve a set of nonlinear dimensionless partial differential equations. Dimensionless velocity and temperature profile are also investigated due to the effects of assumed parameters in the concerned problem. An explicit finite difference technique is used to compute velocity and temperature profiles. The stability conditions are also examined.

The Combined Effects of High Temperature and Carbon Monoxide on Heat Stress Response

In this study,we have examined the effects of exposure to high temperature, carbon inonoxideor a combination of both conditions in a model system,the rat and in industrial workers.In the rat liver, HSP70 mRNA and HSP70 synthesis were measured by dot hybridization and western blot. The results showed that after a heat stress HSP70 mRNA and its product, HSP70 increased significantly and there was a synergism in the combined effects of high temperature and carbon monoxide exposure on the induction of HSP70 mRNA and HSP70 synthesis. Heat played a major role in this induction. The presence of antibodies to human HSP27, HSP60, HSP70,HSC73, HSP89 αand β in workers exposed to heat, carbon monoxide was also measured by western blot using purified HSPs as antigens. Plasma free amino acids were measured in the saine group of workers. The incidence of antibodies to HSP27 and HSP70 Was significantly higher in the workers working in an environment with extreme heat, and high carbon monoxide ernission than in a control group. The carbon monoxide exposed group showed the highest incidence of antibodies to HSPs. Although our previous results indicated that workers had an insufficient protein intake,plasma free amino acids tended to increase, especially in methionine and tryptophan two kinds of amino acids which are absent from the main stress protein, HSP70.These results suggest that the major problems that these workers may face are how to facilitate the use of plasma free amino acids and reduce the inhibition of synthesis of normal proteins when they are exposed to occupational harmful factors.These resultsalso add new information on the measurement of HSPs as a potential biomonitor to assess whether organisms are experiencing metabolic stress within their environment.

Influence of Long Chain Free Fatty Acids on the Thermal Resistance Reduction of Bacterial Spores

Aims: The objective of this study was to investigate the effect of free fatty acid length chain and unsaturated bond number on the heat resistance and recovery media of bacterial spores. Methods and results: For 6 species, bacterial spore heat resistances were estimated at different free fatty acid concentrations added to heating media or in recovery media. The addition of free fatty acids to heating media has a slight influence on the heat resistance of bacterial spores whatever the species or type of acid studied. On the contrary, the addition of free fatty acids to the recovery medium after the heat treatment greatly reduces the ability to bacterial spores to recover and form colonies. This effect varies depending on chain length, unsaturated bond number of fatty acid and on the bacterial strain studied. Conclusion: The presence of free acids in the recovery media is an additive stress which decreases the capability of injured spores to germinate and grow thereafter. Significance and impact of this study: The impact of free fatty acids presented in this study can be taken into account to reduce the thermal intensity of food sterilization in relation to their availability in food matrix.

Study on Amino Acid Composition of HSP70 and the Level of Plasma Free Amino Acids of Workers with Long-term Exposure to Harmful factors

In order to know the practical value of heat stress protein 70 (HSP70) and to know the changes of plasma free amino acids of workers with the induction of HSP70 by harmful factors, the amino acid composition of major HSP, HSP70 purified from the heated cultured human leukemia cancer cell line K562, rabbit liver, rat liver and heart, and mouse liver with two-step procedures of DE52-cel-lulose ion exchange chromatography and affinity chromatography on ATP-agarose was examined. The level of plasma free amino acids of workers with long-term exposure to heat, carbon monoxide and the combined effect of both heat and carbon monoxide was also investigated. The results showed that the three richest amino acids in HSP70 of all origins were Gly, Glu and Asp, except that of rat heart which was rich in Gly, Phe and Glu. Additionally, Lys, Val, Leu and Ala were also found very rich in HSP70 of all origins. Compared with controls, the most of plasma free amino acids tended to increase and free methionine and trypto-phan were increased significantly (P<0. 05) after a long-term exposure to heat, carbon monoxide, and both. These findings suggested that further studies need to be done to find the substances or drugs which induce the synthesis of HSP70 and reduce the inhibition of synthesis of normal proteins for the purpose of protecting people with exposure to harmful factors against the damage of the factors.

MHD effects on free convective flow over moving semi-infinite vertical cylinder with temperature oscillation

Numerical solutions of magnetodynamics （MHD） effects on the free convective flow of an incompressible viscous fluid past a moving semi-infinite vertical cylinder with temperature oscillation are presented. The dimensionless, unsteady, non-linear, and coupled governing partial differential equations are solved by using an implicit finite difference method of the Crank-Nicolson type. The velocity, temperature, and concentration profiles are studied for various parameters. The local skin-friction, the average skinfriction, the Nusselt number, and the Sherwood number are also analyzed and presented graphically. The results are compared with available results in literature, and are found to be in good agreement.

硫酸铝对高掺量流化床粉煤灰基泡沫混凝土性能的影响

随着新型循环流化床燃煤技术的发展,循环流化床粉煤灰(CFBFA)的排放量日益增加。结合我国北方地区冬季严寒时保温隔热材料需求量大的现状,采用高掺量CFBFA制备具有保温隔热性能的泡沫混凝土。针对泡沫混凝土存在的凝结时间长以及早期强度低等问题,本工作掺入硫酸铝进行改性,研究并分析了硫酸铝掺量对泡沫混凝土密度、强度和导热系数的影响。利用X射线衍射(XRD)、热重分析(TG)以及扫描电子显微镜(SEM)等研究了硫酸铝作用下CFBFA基泡沫混凝土的水化产物和微观形貌。此外,还利用3D轮廓仪分析了泡沫混凝土的孔隙结构。结果表明,硫酸铝促进了本体系早期AFt的生成,与基准组(硫酸铝掺量为0%(质量分数,下同))相比,15%硫酸铝掺量的CFBFA基泡沫混凝土的初凝时间缩短了470 min,10%硫酸铝掺量的泡沫混凝土3 d强度可达到10.43 MPa,导热系数为0.31 W·m^(-1)·K^(-1)。这种泡沫混凝土具有较快批量化生产的潜力。

Manufacturing of T300 cobalt-free maraging steel and its tensile property

The 18Ni 300 grade cobalt-free maraging steel T300 was successfully manufactured on an industrial scale by application of vacuum induction melting （VIM） and vacuum arc remelting （VAR） process at Baosteel. With the content of O and N less than 15 ppm and 10 ppm respectively （ 1 ppm = 10 -6 ） ,the T300 steel produced by Baosteel obtained a high degree of purity and a good combination of ultra-high strength and fracture toughness. The effects of solution temperature and ageing temperature on tensile property of solution-treated and aged T300 steel were investigated. The results show that the solution temperature slightly influences the strength of the solution-treated steel, indicating that the solution strengthening rather than the grain boundary strengthening is more important to the solution-treated steel. For the solution-treated T300, the elongation and reduction of area don＇t change much with a rising solution temperature, and remain above 17% and 70% respectively at the solution temperature ranging from 800℃ to 1200℃. For the aged T300 steel,the strength and elongation are reduced with an increasing solution temperature, and the solution temperature has a greater effect on the reduction of area than that on the elongation. The reduction of area of the aged steel reaches a high peak when the solution temperature reaches 920℃. The experimental data indicates that precipitation strengthening makes a contribution of l 100 MPa to the tensile strength of the aged steel. The ageing temperature exerts a greater effect on the strength than on the elongation and reduction of area. The steel achieves a better combination of strength and toughness at the peak ageing temperature of 500℃.