Temperature and Moisture Distributions Inside a Layer of Moist Material Placed on a Hot Isothermal Surface

The problem of contact drying of a layer of moist material placed on a hot isothermal surface is considered. A system of heat and mass transfer equations and equations for the initial and boundary conditions are proposed. Luikov's theoretical approach is utilized, but all relevant thermophysical coefficients are considered to be fully dependent on the temperature and moisture content inside the material during the process. The model is solved numerically. Results for temperature and moisture distributions inside the layer of the material obtained using this model are compared to results obtained by solving a model with constant thermophysical coefficients in the governing equations, formed by using the same type of heat and mass transfer equations and equations for the initial and boundary conditions. The process is also examined experimentally, which provided results that enable verification of the proposed models.     

Analytical Solution of Two‐Dimensional Contact Problems of Unsteady Heat Conduction in the Presence of Mixed Boundary Conditions in the Contact Plane

A method for solution of systems of parabolic differential equations of heat conduction on the model of thermal contact between two bodies with different thermophysical characteristics in the presence of mixed boundary conditions in the plane of their contact has been suggested for the first time. The case of contact of two semibounded bodies has been considered. In this case, a heat source of low heat capacity acts in a circular region of finite radius on the contact surface, and beyond this region the initial temperature is maintained during the whole period of heat transfer.     

Method of nondestructive control of the thermophysical properties of rocks on borehole cores

The problem of the temperature field of a semi-infinite cylinder with a heat source of constant power in the form of a round contact spot acting on its end-face surface has been solved. A method of nondestructive control of the thermophysical properties of rocks on borehole cores is suggested. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 2, pp. 389–393, March–April, 2008.     

Transient thermal contact problem for axial crack in a hollow circular cylinder

The transient behavior of an axial-cracked hollow circular cylinder subjected to a sudden heating is investigated. It is shown that surface heating may induce compressive thermal stress near the inner surface of the cylinder which in turn may force the cracked surfaces to close together. Assuming that the existence of the crack does not alter the temperature distribution, this problem can be divided into two parts and solved by the principle of superposition. First, the temperature and transient thermal stress distributions along the axisymmetric surface of the imaginary cylinder without a crack are obtained by finite element/implicit time integration method. The calculated temperature and thermal stress distributions are in good agreement with the values predicted by the analytical method. Secondly, the opposite senses of the stress distributions along the cracked surfaces, which are obtained previously, are treated as the traction boundary conditions, and the contact length and contact pressure of the real cracked cylinder are obtained by a modified elimination finite element scheme. In this scheme, the concepts of contact-node-pairs' penetration, contact-double-forces and compliance matrix are introduced. The calculated results indicate that the contact length ratio becomes smaller when the crack length ratio increases, and becomes larger as the radius ratio increases. Finally, the normalized stress intensity factor for the crack tip of the cylinder is obtained. It is shown that the larger the crack length ratio the higher the stress intensity factor.     

Heat conduction with variable heat transmission coefficients

An analytical method is shown for determining the temperature field of a body whose variable thermophysical properties are functions of the space coordinates. The problem is solved for a plate and for a cylinder where the thermal conductivity is an exponential function of one space coordinate.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 2, pp. 353–362, August, 1973.     

Crack length measurements with a potential drop method: A finite element simulation

A potential drop method, as used for estimations of crack lengths during three-point-beind experiments, is studied. The mechanical state is calculated using a finite element method. The deformed body obtained is used for a subsequent calculation of the electrostatic state. Calculations are performed for both two- and three-dimensional models. The material is assumed to be elastic, linearly hardening plastic and electrostatically linear. Large deformations are considered. Further, the non-linearity caused by the load, depending on the contact area between the cylinder on which the load is applied and the specimen, is considered. The increased contact area did not influence the mechanical state very much but had a direct impact on the electrostatic state. The changes in the potential drop recordings due to deformation and electrical current passing through the load cylinder were shown to be considerable. The study explains, at least partly, the experimental observations. A more reliable registration of crack growth initiation is the main outcome of the analysis.     

An experimental investigation of the characteristics of explosive boiling of subcooled water on a hot surface under conditions of change of boiling modes

A procedure of estimating the area of contact between cold water and a hot hemispherical surface is developed and described. Synchronous measurements of pressure pulses in liquid, the temperature of a body, and characteristics of contact between a heated body and a coolant are performed under conditions of abrupt change of boiling modes (from film to nucleate boiling). Characteristic features of the investigated processes are determined, which are largely defined by the temperature of the hemisphere, by its thermophysical properties, and by the presence of surface oxide films. It is found that the maximal value of the amplitude of pressure pulses, which may be as high as ∼1 MPa in the experiments, is observed in the region of temperatures of the hot body which are close to the temperature of limiting superheat of water. The dependences are obtained of the rate of spreading of liquid and of the time of delay of its explosive boiling from the instant of boiling on the temperature of the hemisphere.     

Numerical simulation of laminar flow of oil and heat transfer near a circular cylinder with arched guide plates

We have investigated the intensification of the heat transfer from a cylinder in an oil medium due to the setting of arched guide plates on the basis of the numerical solution of the Navier-Stokes and energy equations with the help of multiblock computer-aided technologies realized in the VP2/3 package. Calculations have been made for the laminar nonstationary cross flow around a heated cylinder in a viscous medium with a strong temperature dependence of its thermophysical characteristics. Comparison has been made between the numerical forecasts of the drag, local heat transfer, thermohydraulic efficiency, and total Nusselt number for a cylinder with plates and for a single cylinder. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 705–711, July–August, 2008.     

Dispersion of Axisymmetric Longtudinal Waves in a Pre-Strained Imperfectly Bonded Bi-Layered Hollow Cylinder

This paper studies the dispersion of the axisymmetric longitudinal wave propagation in the pre-strained hollow cylinder consisting of two-layers under the shear-spring type imperfectness of the contact conditions between these layers. The investigations are made within the framework of the piecewise homogeneous body model by utilizing the 3D linearized theory of elastic waves in elastic bodies with initial stresses. It is assumed that the layers of the cylinder are made from compressible hyper-elastic materials and their elasticity relations are given through the harmonic potential. The degree of the mentioned imperfectness is estimated by the shear-spring parameter. Numerical results on the influence of this parameter on the behavior of the dispersion curves related to the fundamental mode are presented and discussed. It is established that the considered type imperfectness of the contact conditions causes two branches of the dispersion curve related to the fundamental mode to appear: the first disappears, but the second approaches the dispersion curve obtained for the perfect interface case by decreasing the shear-spring parameter.     

初始椭圆度对螺旋缠绕结构拉伸刚度的影响

为考虑初始椭圆度对螺旋缠绕结构拉伸刚度的影响,建立了一种新的基于椭圆柱面和螺旋带的分析模型,该模型在两者之间建立了一个新的几何关系,并考虑了在椭圆柱面上螺旋带的轴向应变和曲率变化以及柱面和螺旋层之间的接触压力。通过ABAQUS建立一个3D有限元模型验证了理论模型的合理性。在理论模型中,对初始椭圆度进行参数分析得到不同初始椭圆度对椭圆层拉伸刚度的影响,随着管道初始椭圆度的增加,螺旋层拉伸刚度有下降的趋势,但降幅很小。      

Frictionless elastic contact problem for a curved rigid punch of arbitrary shape

Summary A new method is proposed for the analysis of elastic contact problems for a curved punch of non-elliptic planform under the action of a normal force. The punch base is assumed to be a quadratic surface. The method is based on an integral representation for the reciprocal distance between two points obtained by the author earlier. Some general relationships are established between the applied force and the punch settlement. Specific formulae are derived for a punch whose planform has a shape of a polygon, a rectangle, a rhombus and a cross. An example of a finite rigid cylinder lying on its generator and pressed against an elastic half-space is considered in detail. The method allows to have singular stresses at the cylinder edges and zero stresses at the rest of the boundary of the contact domain. The last condition serves for defining the width of the domain of contact. All the formulae are checked against the solutions known in the literature, and a good accuracy is confirmed in a sufficiently wide range of the aspect ratio.With 3 Figures     

Steady-state temperature field of a finite cylinder in a housing

An analytic solution has been obtained for the steady-state temperature field of two coaxial finite cylinders, the inner of which is a rotor. Two cases corresponding to different conditions of cooling of the outer cylinder, or housing, are considered.     

Computation of heat conduction in materials with random variable thermophysical properties

A method for the direct computation of mean values and variances of the temperature in conduction-heated objects with random variable thermophysical properties is presented. This method is based on a Taylor expansion of the finite element formulation of the heat conduction equation and offers a powerful alternative to the computationally expensive Monte Carlo method. Both steady-state and transient problems are considered. Some example problems are solved and the results discussed. The simulations indicate that the variability of the thermophysical properties may cause a considerable variability of the temperature within the heated object. This may have important consequences on the design of heating operations in food process engineering.     

Coupled transient thermoelastic contact problems for axial cracks in hollow cylinders

A coupled transient thermoelastic behaviour of an axial-cracked hollow circular cylinder subjected to a sudden heating is investigated in this study. It is shown that surface heating may induce the compressive thermal stress near the inner surface of the cylinder which in turn may force the cracked surfaces to close together. Assuming that the existence of the crack does not alter the temperature distribution, we can divide this problem into two parts and solve it by the principle of superposition. First, the temperature and transient thermal stress distributions along the axisymmetric surface of the imaginary cylinder without crack are obtained by finite element implicit time integration method Secondly, the opposite sense of the stress distributions along the cracked surfaces, which is obtained previously, is treated as the traction boundary conditions; the contact length and contact pressure of the real cracked cylinder are obtained by modified elimination finite element scheme. Finally, we also obtained the normalized stress intensity factor for the crack tip of the cylinder. It is concluded that the effect due to thermoelastic coupling term on stress intensity factor becomes more important for higher coupling coefficient, and this coupling term also results in a small time lag in temperature, thermal stress and stress intensity factor.     

Use of the schlieren method to investigate temperature fields in a solid

The use of the Schlieren method to measure the temperature field and temperature gradients in a solid is considered. The results obtained are compared with a theoretical calculation of the temperature field in a finite cylinder for boundary conditions of the second and third kind.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 3, pp. 510–514, March, 1971.     

Modeling of Heat Outflows to a Probe in Thermophysical Testing

The nondestructive method developed by the author with the use of a linear pulsed heat source makes it possible to determine the thermophysical characteristics of solid materials on the basis of the portions of thermograms that correspond to the regularization of the thermal regime in the region of the heater and temperature detectors. Consideration has been given to the influence of the outflows of heat to a probe on the error in determining the thermophysical characteristics of materials in the case where two semiinfinite bodies are in ideal contact. A mathematical expression upon the fulfillment of which one may disregard the heat loss to the material of the probe substrate has been obtained. In the work, consideration has also been given to the problem of heat loss to the probe material in the case where it occurs only in the region of the heater. It has been shown that the temperatures of the first and second bodies in the contact area will become closer with time. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 4, pp. 108–116, July–August, 2005.     

Mathematical simulation of temperature field in a hollow rotating cylinder with nonlinear boundary conditions

An analytical solution is obtained of the nonlinear problem on heat conduction in a hollow infinite cylinder in view of the temperature dependence of its thermophysical characteristics. Results are given of calculations of temperature field for the roll of machine for continuous casting of slabs.     

Analysis of Transient Heat Conduction in a Hollow Cylinder Using Duhamel Theorem

The objective of this paper is to derive the mathematical model of two-dimensional heat conduction at the inner and outer surfaces of a hollow cylinder which are subjected to a time-dependent periodic boundary condition. The substance is assumed to be homogenous and isotropic with time-independent thermal properties. Duhamel’s theorem is used to solve the problem for the periodic boundary condition which is decomposed by Fourier series. In this paper, the effects of the temperature oscillation frequency on the boundaries, the variation of the hollow cylinder thickness, the length of the cylinder, the thermophysical properties at ambient conditions, and the cylinder involved in some dimensionless numbers are studied. The obtained temperature distribution has two main characteristics: the dimensionless amplitude ( $A$ ) and the dimensionless phase difference ( $\varphi $ ). These results are shown with respect to Biot and Fourier and some other important dimensionless numbers.     

Sloshing effects on supersonic flutter characteristics of a circular cylindrical shell partially filled with liquid

This paper aims to revisit the effect of sloshing on the flutter characteristics of a partially liquid-filled cylinder. A computational fluid-structure interaction model within the framework of the finite element method is developed to capture fluid-structure interactions arising from the sloshing of the internal fluid and the flexibility of its containing structure exposed to an external supersonic airflow. The internal liquid sloshing is represented by a more sophisticated model, referred to as the liquid sloshing model, and the shell structure is modeled by Sanders' shell theory. The aerodynamic pressure loading is approximated by the first-order piston theory. The initial geometric stiffness due to prestresses in the initial configuration stemming from the fluid hydrostatic pressure, internal pressure, and axial compression load is also considered. The obtained results reveal that the sloshing of the internal fluid has little influence on the supersonic flutter boundary of a cylinder partially filled with liquid, at least for the case considered here. It is also shown that the critical freestream static pressure predicted by the sloshing model is negligibly larger than that calculated by the hydroelastic model of the internal fluid, which means that the sloshing of the internal fluid slightly overestimates the flutter boundary.     

On the influence of the reinforcement structure of fibrous shells of revolution on the heat conduction in them

The initial boundary-value problem on the heat conduction in shells reinforced with fibers of constant cross section has been considered. It has been established that the specific, anisotropic, inhomogeneous properties of such a shell are determined by its heat conductivity dependent on the thermophysical properties of the phases of the composite material of the shell, the parameters of its reinforcement, and the geometry of this shell. The ways of reducing the three-dimensional problem on heat conduction to the two-dimensional one and the possibilities of reducing the dimension of this problem for thin shells of revolution reinforced symmetrically relative to their axis by two units have been determined. The stationary temperature fields of concrete thin shells of revolution with different Gaussian curvatures and different reinforcement structures have been compared. It is shown that the reinforcement structure and the geometry of a shell of revolution substantially influence the temperature distribution in this shell, which opens up a wide range of ways selecting designs of such shells with improved thermophysical parameters. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 2, pp. 145–155, March–April, 2006.