Calculation Of Heat Transfer Processes Research Articles

Modeling of heat conduction processes in porous absorber of open type of solar tower stations

An analysis of existing methods for calculating heat and mass transfer processes in porous absorbers of receivers of tower solar power plants is carried out. It is shown that the resulting thermophysical properties of the material are influenced not only by the porosity but also by the location of the pores in the material volume. The criterion of the dislocation vector is proposed as a mathematical indicator of various porous structures. The shortcomings of the existing dependences of the effective thermal conductivity of a material on the type of porosity are shown. The most reliable dependences for determining the thermophysical parameters of a porous medium are also determined and independent factors are proposed on which the mathematical model of heat and mass transfer in open-type solar receivers should be based.The current state of research on the effective thermal conductivity of the porous structure of solar receivers is described in detail. A new formula for calculating the effective thermal conductivity of a porous structure with regard to the dislocation vector and a method for calculating the processes of heat transfer in open solar receivers based on the proposed formula are proposed. The proposed equation has been tested. It is determined that for simple channel structures it is sufficient to use the existing equations to calculate the thermal conductivity coefficient, while for more complex porous structures, such as the StepRec absorber, it is better to use the proposed equation.Among the strengths of this study is a new calculation formula that allows us to build an analytical model of heat transfer in a porous medium. The use of the analytical model can significantly reduce the complexity of modern calculations of heat transfer processes in a porous absorber and will help improve the quality of optimization models of solar receivers.

In relation to question of development of controls, test of heatcover materials, for defence of workers of DSNS of Ukraine

Purpose. Development of means of control, testing of heat-protective materials used for the manufacture of personal protective equipment, both existing and at the stage of creating new ones. Method. Heat-protective materials for special clothing must be tested according to the nomenclature of quality indicators. We have considered the most important, which are associated with the effects of high-intensity heat radiation and high temperature. Results. The solution of the approximate value of the area of existence of the test method is offered. The test method is based on two methods. Previous: the test specimen is clamped in the frame and electric welding is performed near its surface. Particles of molten metal fall on the surface of the sample and leave traces in the form of burns, sticky particles. The depth of burn, the degree of adhesion, etc. are investigated. Currently, a more advanced method is used - the method of melting the welding electrode by blowing on the surface of the test material. However, both methods allow to obtain hot drops of different sizes, different weights, different directions relative to the test material and uncontrolled heating temperature of the hot drop, which does not allow to obtain high reliability of the results of the study. We proposed to create a device that allows you to control the size of the drop, the kinetic energy of the impact, the direction of flight and the temperature of the hot particle. All the above determined the direction of work on creating a methodology for studying these parameters and, as follows, the requirement to create an installation that would ensure the stability of parameters such as mass, velocity, temperature and flight trajectory of heated metal particles with the possibility of controlled change of these parameters. All the above determined the direction of work on creating a methodology for studying these parameters and, as follows, the requirement to create an installation that would ensure the stability of parameters such as mass, velocity, temperature and flight trajectory of heated metal particles with the possibility of controlled change of these parameters. To determine the area of existence of the research criteria by the proposed method, it is necessary to solve the problem with the following assumptions: the shape of a drop of metal is taken in the form of an ideal sphere; the droplet size is taken as the average; the drop is suspended on a non-thermally conductive thin thread in the air; air movement is excluded; heat transfer due to thermal conductivity is excluded from the calculation; the calculation does not take into account the process of oxidation of the surface of the hot drop and the formation of scale; the crystallization time of the metal is not taken into account. The process of influence of the hot metal ball on the investigated material is conditionally divided into three stages: heating of the ball to the set temperature and its control; the flight of the ball in the air with its subsequent cooling; the impact of the ball on the surface of the sample with the transfer of kinetic and thermal energy. In addition, it is necessary to control the force and set the direction of impact of the particle relative to the test material. The calculation of heat transfer processes is a complex mathematical problem that involves solving many systems of nonlinear equations. Using certain assumptions, we accept two mechanisms of heat transfer - molecular and convective. Scientific novelty. For the first time, a new method is proposed that allows to supplement the existing and get more reliable results. Practical meaningfulness. The installation of research of heat-protective materials on spark resistance is developed.

Тепло- и массообмен в области с движущимися границами

Various fields of science and technology require calculations of heat transfer processes in regions of different shapes, the boundaries of which move with time. These are such tasks as a Stefan problem of ground freezing and ingot crystallization, which can be solved analytically under certain assumptions. Later appeared works on calculating the temperature field in burning fuel grains, thermal decomposition of solid mixtures, melting and ablation of heat-resistant coatings. Mathematical models of such processes include the heat equation, initial and boundary conditions, as well as the conditions of boundary displacement. At the same time, there are tasks associated with the calculation of heat and mass transfer processes, when liquid and gas flow in the regions, the boundaries of which move with time. Mathematical models of such problems include systems of partial differential equations, which can be solved only by numerical methods. This paper proposes an effective numerical method for solving such problems on the basis of the finite difference method, which allows tracking the position of region boundaries when they considerably move on the adaptive computational mesh.

Modeling of the polymerization process of the insulating layer of cable thermocouples

A mathematical model describing the main physical processes occurring during thermal processing of cable thermocouples (CT) during their production is presented. The polymerization of the insulating layer is taken into account in the conditions of its intense heating. The developed mathematical model allows to carry out calculations of heat transfer processes under the conditions of substantial heterogeneity of cable thermocouple structure. The computational experiments carried out have established significant differences in the characteristics of heat transfer in CT in the presence of thermoelectrodes with differing thermophysical characteristics.

Measurement testing of heat transfer coefficients in the evaporator and condenser of heat pumps

In our earlier studies, it has been stated that the validity and limits of correlations developed for the calculation of heat transfer processes in the evaporator and condenser of heat pumps are not published in general. The values yielded for model structures and process characteristics indicate extreme ranges of standard deviation. While the description and physical and mathematical modeling of phenomena occurring in heat pump components have developed really much and the mathematical accuracy of solutions can be increased at one’s own discretion, descriptions of changes in heat transfer and heat transfer coefficients in the course of refrigerant flow are quite uncertain. At the same time, these factors highly influence the accuracy of the solution. Our study presents the measurements and the new proposed heat transfer correlations, developed on the basis of such measurements, which can be used for calculating heat transfer in heat pump evaporators and condensers with higher accuracy than existing correlations in the literature.

Исследование теплообмена в пучках профилированных труб

Results of research of heat exchange in banks of the profiled pipes with small longitudinal and back pitches are presented. Criteria dependences for calculation of heat transfer processes are verification. Results of comparison of heat transfer efficiency in the profiled and bare-tube banks of pipes are obtained