Turbulent mixed convection heat transfer to liquid sodium

The influences of buoyancy on turbulent heat transfer to a liquid metal flowing in a vertical pipe are considered. A theoretical model is presented which provides a criterion for the conditions under which such influences become significant and which predicts the impairment of heat transfer for upward flow and enhancement for downward flow. The variation with Peclet number of the maximum impairment of heat transfer and conditions under which it occurs are established. A generalization of the model leading to an equation for the entire mixed convection region is proposed. From this an equation for turbulent free convection to liquid metals is obtained.     

Variational approach to unsteady flow and heat transfer in a channel

The transient thermal response of a Newtonian fluid to several assumed forms of pressure pulse in a channel is analyzed by the semi-direct variational method of Kantorovich. The temperature distribution in unsteady laminar flow in a channel is investigated when the pressure gradient is an arbitrary function of time. Results are obtained for the linearly varying as well as the suddenly applied pressure gradient. Received on 1 July 1997     

Dimension reduction of homoclinic orbits of buckled beams via the non-linear normal modes technique

The problem of detecting the homoclinic orbits of an initially straight buckled beam is addressed. Two families of boundary conditions are identified and investigated in detail. For the first family, the homoclinic orbits belong to a planar invariant manifold, and are easily computed in closed form. For the second family, the manifold is no longer planar, and is detected via the non-linear normal modes technique by obtaining approximate expressions which are sufficient to highlight the effects of the non-flatness. A hierarchy of reduced order, single degree of freedom, models is determined. These are obtained by taking into account increasing degrees of non-linearity in the potential energy, which allow for a more and more refined computation of the homoclinic solution. The various models are compared with each other and discussed in detail, and the non-planarity of the manifold is illustrated through examples.     

Multi-objective optimization of a plate and frame heat exchanger via genetic algorithm

In the present paper, a plate and frame heat exchanger is considered. Multi-objective optimization using genetic algorithm is developed in order to obtain a set of geometric design parameters, which lead to minimum pressure drop and the maximum overall heat transfer coefficient. Vividly, considered objective functions are conflicting and no single solution can satisfy both objectives simultaneously. Multi-objective optimization procedure yields a set of optimal solutions, called Pareto front, each of which is a trade-off between objectives and can be selected by the user, regarding the application and the project’s limits. The presented work takes care of numerous geometric parameters in the presence of logical constraints. A sensitivity analysis is also carried out to study the effects of different geometric parameters on the considered objective functions. Modeling the system and implementing the multi-objective optimization via genetic algorithm has been performed by MATLAB.     

A new approach to the analysis of turbulent free convection heat transfer

The principle of surface renewal is utilized in the analysis of fully turbulent free convection. The present analysis together with a previous surface renewal ased analysis of combined forced and free convection associated with supercritical fluids demonstrate the potential usefulness of the surface renewal approach in modelling buoyancy influenced turbulent convection processes.     

Multi-objective optimization of a guide vane in the turning region of a rotating U-duct to enhance heat transfer performance

An optimization has been performed for the design of a guide vane in the turning region of a rotating U-duct using the Kriging meta-model and a hybrid multi-objective evolutionary algorithm. Rotation of the U-duct is accompanied by the Coriolis force that causes a discrepancy in heat transfer between the trailing (pressure) and leading (suction) surfaces of the duct. For the optimization, three geometric variables related to the thickness, angle, and location of the guide vanes are selected as the design variables. A Kriging model is constructed to obtain a Pareto-optimal front through a multi-objective evolutionary algorithm. The values of the objective function at the design points are evaluated by Reynolds-averaged Navier–Stokes analysis. The shear stress transport model is used as the turbulence closure model in the analysis. The tradeoff between the two competing objective functions is discussed for Pareto-optimal solutions in the design space. The optimized guide vanes show an increase in heat transfer performance with a decrease in the friction loss in the turning region and downstream straight passage in comparison with the reference design.     

Conjugate mixed convection heat and mass transfer in brick drying

 In this study, a numerical methodology for the solution of conjugate heat and mass transfer problem is presented. Fluid flow, heat and mass transfer over a rectangular brick due to transient laminar mixed convection has been numerically simulated. The coupled non-linear partial differential equations, for both gas phase and solid are solved using finite element procedure. Flow is assumed to be incompressible, two-dimensional, laminar. Analysis has been carried out at a Reynolds number of 200 with Pr = 0.71. The effect of buoyancy on the brick drying has been investigated. Velocity vectors, streamlines in the flow field and temperature and moisture contours and temperature distribution along the solid surface are presented. It is observed that there is considerable effect of buoyancy during drying. The results indicate a non-uniform drying of the brick with the leading edge drying faster than the rest of the brick. Received on 9 December 1998     

A mixed lumped stress–displacement approach to the elastic problem of masonry walls

We present a novel approach to the elastic problem of masonry walls, which generalizes the lumped stress method presented in [Fraternali, 2001], [Fraternali, 2007] and [Fraternali, 2010] and Fraternali et al. (2002). The generalization consists of a mixed lumped stress-displacement approach to the elastic problem of a wall that incorporates no-tension elements. Such an approach depends on the nodal values of the Airy stress function and the displacements of selected (“pivot”) nodes. The latter coincide with inter-element and boundary nodes. The mixed lumped stress-displacement method can be conveniently coupled with standard finite element and boundary element approaches. Numerical applications dealing with recurrent structural elements are given, showing that such a method is able to capture some essential features of the actual response of masonry constructions.     

Sequences of orbits and the boundaries of the basin of attraction for two double heteroclinic orbits

The boundaries of the basin of attraction are usually assumed to be rather elementary for Hamiltonian systems with autonomous perturbations. In the case of one saddle point, the sequences of orbits before capture are unique for each basin. However, we show that for two saddle points each with double heteroclinic orbits, there is an infinite number of different sequences of nearly homoclinic orbits before capture depending on the four heteroclinic parameters. The probabilities of capture are independent of the capture sequence.     

State space approach to thermoelectric fluid with fractional order heat transfer

A new mathematical model for electromagnetic thermofluid equation heat transfer with thermoelectric properties using the methodology of fractional calculus is constructed. The governing coupled equations in the frame 11 of the boundary layer model are applied to variety problems. Laplace transforms and state space techniques (Ezzat Can J Phys Rev 86:1241–1250 in 2008) are used to get the solution of a thermal shock problem, a layer problem and a problem for the semi-infinite space in the presence of heat sources. According to the numerical results and its graphs, a parametric study of time-fractional order 0 < α ≤ 1, on temperature and the thermoelectric figure of merit are conducted.     

舰船平台上一种改进的传递对准方案设计与仿真

为了提高舰船惯性导航系统在动基座下的传递对准的精度和快速性,针对舰船平台的应用特点,采用卡尔曼滤波器对主、子惯导的"速度加角速率"参数的误差量进行滤波估计并进行了算法设计。运用卡尔曼滤波器的平滑算法改善传递对准的精度。针对卡尔曼滤波器平滑算法会降低对准速度的缺点,在只损失一小部分精度的前提下,创新性的采用卡尔曼滤波器的降阶算法提高了对准速度。通过Matlab软件对卡尔曼滤波器算法、卡尔曼滤波器平滑算法和卡尔曼滤波器平滑加降阶算法的速度误差和姿态误差分别进行了仿真。仿真结果表明,"速度加角速率"匹配传递对准改进算法具有稳健的对准精度和快速性,有一定工程应用参考价值。     

An approach to constitutive modelling of elasto-plasticity via ensemble averaging of the dislocation transport

Using an averaging procedure for large ensembles of dislocations, a basic but mathematically non-trivial modelling framework is developed for the transport of dislocation densities in a macroscopically homogeneous and isotropic film of a crystalline solid subjected to uniform shear. It has the form of a system of nonlinear, non-local partial differential equations of the first order with a source-type right-hand side. The solution to this system is studied numerically, and the associated average stress is evaluated as a function of time. The resulting stress-strain relations exhibit a size effect similar to those that previously motivated strain-gradient plasticity theories.     

A new approach to analyze entrance region mass transfer within a falling film

A boundary layer model is developed to analyze diffusion through a laminar falling film for incomplete penetration of the dissolved gas. Regarding the rather intractable nature of the problem, Kantorovich Integral Method is chosen. Accordingly, a mass transfer boundary layer is assumed to keep growing perpendicularly to the falling film until it hits the wall. Such an approach is superior to its preceding artworks based on Higbie’s penetration theory in terms of implementation of more realistic conditions/modeling assumptions. Furthermore, unlike penetration model, this approach gives a criterion whether the diffusion is complete. Comparing the two models, boundary layer model estimates up to 2.3 % larger mass transfer coefficients. Moreover, a sensitivity analysis of liquid velocity distribution upon Sherwood number is conducted. It is found that the local velocity at gas–liquid interface is of highest dominance. Experimental data of SO₂ absorption in water reported in literature is exploited to validate the model. It is shown that boundary layer model better fits the experimental data.