Investigation of heat transfer by means of pool film boiling on vertical cylinders in gravity

In this study, the heat transfer by means of pool film boiling on immersed vertical cylindrical rods was investigated. For this purpose, the rods with various dimensions, which have been heated up to 600°C, were immersed in a pure water pool in the different temperatures. The centre temperature and water temperature versus operation time were measured by K type thermocouples at the atmospheric pressure. After experimental studies, the surface temperatures of rods and heat transfer coefficients were calculated by means of Lumped method from the measured temperatures. Consequently, an empirical equation was developed between the Nusselt, Grashof, Prandtl and Jakob numbers. The experimental results showed that the specimens having the same characteristic lengths exhibited the same heat transfers performance although the specimen’s diameters and lengths differed considerably.     

Two-dimensional transient dynamic response of orthotropic layered media

In this study, two-dimensional transient dynamic response of orthotropic plane layered media is investigated. The plane multilayered media consist of N different generally orthotropic, homogeneous and linearly elastic layers with different ply angles. In the generally orthotropic layer, representing a ply reinforced by unidirectional fibers with an arbitrary orientation angle, the principal material directions do not coincide with body coordinate axes. The solution is obtained by employing a numerical technique which combines the use of Fourier transform with the method of characteristics. The numerical results are displayed in curves denoting the variations of stress and displacement components with time at different locations. These curves clearly reveal, in wave profiles, the scattering effects caused by the reflections and refractions of waves at the boundaries and at the interfaces of the layers, and also the effects of anisotropy caused by fiber orientation angle. The curves properly predict the sharp variations in the response at the neighborhood of the wave fronts, which shows the power of the numerical technique employed in the study. By suitably adjusting the elastic constants, the results for multilayered media with transversely isotropic layers, or layers with cubic symmetry, or isotropic layers can easily be obtained from the general formulation. Furthermore, solutions for some special cases, including Lamb’s problem for an elastic half-space, are obtained and compared with the available solutions in the literature and very good agreement is found. Preliminary version presented at the Second International Congress on Mechatronics (MECH2K3), Graz, Austria, July 14-17, 2003.     

An in-service primary teacher’s implementation of mathematical tasks: the case of length measurement and perimeter instruction

The purpose of this paper is to examine the cognitive demand levels of tasks used by an in-service primary teacher during length measurement and perimeter instruction and to examine a possible link between these tasks and the teacher’s mathematical knowledge in teaching. For this purpose, a case study approach was used and the data was drawn from classroom observations, semi-structured interviews, and field notes. Specific tasks from length measurement and perimeter instruction were presented and analyzed according to the Mathematical Tasks Framework. Then, how these tasks gave information about the teacher’s mathematical knowledge in teaching in the length measurement and perimeter topics was examined according to the Knowledge Quartet model. According to the findings of the study, the tasks used during length measurement and perimeter instruction were mostly categorized as low-level tasks. In addition, teacher’s mathematical knowledge in teaching affected the implementation of the tasks.     

Positive solutions of nonlinear multi-point boundary value problems

This paper deals with the existence of positive solutions of nonlinear differential equation

$$\begin{aligned} u^{\prime \prime }(t)+ a(t) f(u(t) )=0,\quad 0<t <1, \end{aligned}$$

subject to the boundary conditions

$$\begin{aligned} u(0)=\sum _{i=1}^{m-2} a_i u (\xi _i) ,\quad u^{\prime } (1) = \sum _{i=1}^{m-2} b_i u^{\prime } (\xi _i), \end{aligned}$$

where \( \xi _i \in (0,1) \) with \( 0< \xi _1<\xi _2< \cdots<\xi _{m-2} < 1,\) and \(a_i,b_i \) satisfy   \(a_i,b_i\in [0,\infty ),~~ 0< \sum _{i=1}^{m-2} a_i <1,\) and \( \sum _{i=1}^{m-2} b_i <1. \) By using Schauder’s fixed point theorem, we show that it has at least one positive solution if f is nonnegative and continuous. Positive solutions of the above boundary value problem satisfy the Harnack inequality

$$\begin{aligned} \displaystyle \inf _{0 \le t \le 1} u(t) \ge \gamma \Vert u\Vert _\infty . \end{aligned}$$

     

Crystallographic Analysis of FCC ? BCT Martensitic Transformation in the Alloy Fe-22% Ni-0.8% C

The infinitesimal deformation (ID) approach is applied to analyse the crystallography involved in the fcc to bct martensitic transformation for the case of (101)_γ[<formula><overline>1</overline>01</formula>]_γ twinning shear as LIS (lattice invariant shear) system in the alloy Fe-22% Ni-0.8% C. Analytical solutions are derived for habit plane orientation, orientation relationships between austenite and martensite phases, and the magnitude of the total shape deformation, etc. In order to compare numerical solutions with the ID approach and phenomenological crystallographic theory, the corresponding crystallographic parameters are calculated by using the Ledbetter and Dunn (L-D) theory. The numeric values obtained are compared with the predictions of the phenomenological crystallographic theories, and with experimental results.     

Molar Volume Calculation of Molten Ag–Au–Cu and Cu–Ag–In Alloy Systems Using General Solution Model

Russian Journal of Physical Chemistry A - However, up to the present, there was few reports on the density of the molten Ag–Au–Cu and Cu–Ag–In alloy systems. In this work,...     

Thermodynamic description of the viscosity of liquid solder alloys with minor Co impurities

Because of the increasing complexity and cost of experiments carried out, the data for the multi-component alloy systems have frequently been obtained by numerical modelling. It is clear that the related calculations require reliable data dealing with the pure components and binary alloy systems. Selecting the reliable data concerning the pure components from the literature, the viscosities for the SAC and (SAC)_1?x Co_x solder alloys have been calculated using different viscosity models (geometric and physical). The viscosity decreases as the amount of tin content increases in the SAC387 alloy while the addition of the cobalt to SAC387 solder results in the increasing of the viscosity. Moreover, by computing the root mean square values between theoretical and experimental viscosities, it can be concluded that the lowest value among all models is that of obtained by Kaptay equation.