Ensuring flat heat transfer in heat units of food production

Предлагается способ модификации тепловых блоков пищевых производств с точечным источником генерации теплоты, позволяющий обеспечить плоскостной принцип его передачи на стенки варочного сосуда. Способ обеспечивает повышенную износостойкость и жаропрочность стенок варочного сосуда и теплового блока за счет применения газодинамического напыления запатентованного состава специального покрытия, включающего коллоидный графит, оксид меди, каолин, металлические порошки и мелкодисперсную керамику. Раскрыт порядок нанесения покрытия на стенки теплового блока и варочного сосуда, приводятся физико-химические свойства исходных компонентов керамического жаростойкого покрытия, наносимого на внутренние стенки теплового блока. Предложены образцы теплового оборудования для подготовки исходных компонентов изготовления противоизносного жаростойкого защитного покрытия. Обоснованы условия реализации технических и технологических операций по нанесению покрытий. Исследованы зависимости и получены закономерности изменения теплопередачи и теплопотерь в тепловых блоках пищевых производств в зависимости от состава покрытия и его толщины. A method is proposed for modifying the thermal blocks of food production with a point source of heat generation, which allows to ensure the plane principle of its transfer to the walls of the cooking vessel. The method provides increased wear resistance and heat resistance of the walls of the cooking vessel and the heat block due to the use of gas-dynamic spraying of a patented composition of a special coating including colloidal graphite, copper oxide, kaolin, metal powders and fine ceramics. The procedure for coating the walls of the heating block and the cooking vessel is disclosed, and the physicochemical properties of the initial components of the ceramic heat-resistant coating applied to the inner walls of the heating block are presented. Samples of thermal equipment for the preparation of the initial components for the manufacture of antiwear heat-resistant protective coating are proposed. The conditions for the implementation of technical and technological operations for coating are substantiated. The dependences are investigated and the regularities of changes in heat transfer and heat losses in the thermal blocks of food production are obtained depending on the composition of the coating and its thickness.

Analysis for the Joining of Light Alloys by Numerical Experiment

The current paper deals with the application of numerical experiment of joining light alloys. Modelling and numerical simulation and finite element method in the ANSYS program were used to investigate the course of thermal cycles, the joining process of light alloys by welding. Joining process of light alloys by welding is defined as a moving point source of heat, which generates temperature fields of various kinds, depending on the time and thickness of the material being welded. The paper is therefore devoted to: Thermal energy transfer and solution to differential equation of heat conduction, Initial and boundary conditions for temperatures distribution of a moving point source of heat, Generation (definition) of thermal cycle. Another part of the paper deals with the analysis of the heat-affected zone. Of the result of the solution will be expressed as the temperature field generated in the base material during the welding process.

The Definition of the Optimal Energy-Efficient form of the Building

We consider the problem of finding a geometrical form of a body in a thermal radiation field, for which the thermal balance between the body and the surrounding air is minimal. The case of a point source of heat is investigated. To consider an analogous problem for buildings, one must know the value of incoming thermal energy to a unit square in relation to its orientation. We develop an application package in MATLAB that represents this relation in table form and takes into consideration the direct, diffuse, ground-reflected solar radiation and the thermal radiation of atmosphere.

Transient ventilation dynamics following a change in strength of a point source of heat

We investigate the transient ventilation flow within a confined ventilated space, with high- and low-level openings, when the strength of a low-level point source of heat is changed instantaneously. The steady-flow regime in the space involves a turbulent buoyant plume, which rises from the point source to a well-mixed warm upper layer. The steady-state height of the interface between this layer and the lower layer of exterior fluid is independent of the heat flux, but the upper layer becomes progressively warmer with heat flux. New analogue laboratory experiments of the transient adjustment between steady states identify that if the heat flux is increased, the continuing plume propagates to the top of the room forming a new, warmer layer. This layer gradually deepens, and as the turbulent plume entrains fluid from the original warm layer, the original layer is gradually depleted and disappears, and a new steady state is established. In contrast, if the source buoyancy flux is decreased, the continuing plume is cooler than the original plume, so that on reaching the interface it is of intermediate density between the original warm layer and the external fluid. The plume supplies a new intermediate layer, which gradually deepens with the continuing flow. In turn, the original upper layer becomes depleted, both as a result of being vented through the upper opening of the space, but also due to some penetrative entrainment of this layer by the plume, as the plume overshoots the interface before falling back to supply the new intermediate layer. We develop quantitative models which are in good accord with our experimental data, by combining classical plume theory with models of the penetrative entrainment for the case of a decrease in heating. Typically, we find that the effect of penetrative entrainment on the density of the intruding layer is relatively weak, provided the change in source strength is sufficiently large. However, penetrative entrainment measurably increases the rate at which the depth of the draining layer decreases. We conclude with a discussion of the importance of these results for the control of naturally ventilated spaces.

Experimental Measurement of Steady 3-D Thermal Green’s Functions

In many areas of applied mathematics, the Green’s function is the solution to a field problem due to the application of a potential or a gradient of a potential at a point or line in space on the solution domain. In heat transfer, the ‘thermal’ Green’s function (TGF) is the temperature field that would arise as a result of the application of a point source of heat within or on the surface of a medium. We have been exploring the possible use of the thermal Green’s function as a new way of characterizing the convective heat transfer from the surface of a solid that is cooled by a flow. An experiment was designed to explore possible ways in which the thermal Green’s function can be measured in the laboratory. A small heated spot was created on the wall of a flow channel to approximate a point source of heat. The resulting temperature field was measured by the use of thermochromic liquid crystal thermography, and was compared to an analytical solution derived from the 3-D thermal Green’s function. This paper reports progress towards understanding the limitations in creating and digitally photographing the temperature field from a small heat source on the wall of a convective flow.

Generation of collimated jets by a point source of heat and gravity

New solutions of the Boussinesq equations describe the onset of convection as well as the development of collimated bipolar jets near a point source of both heat and gravity. Stability, bifurcation, and asymptotic analyses of these solutions reveal details of jet formation. Convection (with l cells) evolves from the rest state at the Rayleigh number Ra = Racr = (l − 1)l(l + 1)(l + 2). Bipolar (l = 2) flow emerges at Ra = 24 via a transcritical bifurcation: Re = 7(24 − Ra)/(6 + 4Pr), where Re is a convection amplitude (dimensionless velocity on the symmetry axis) and Pr is the Prandtl number. This flow is unstable for small positive values of Re but becomes stable as Re exceeds some threshold value. The high-Re stable flow emerges from the rest state and returns to the rest state via hysteretic transitions with changing Ra. Stable convection attains high speeds for small Pr (typical of electrically conducting media, e.g. in cosmic jets). Convection saturates due to negative ‘feedback’: the flow mixes hot and cold fluids thus decreasing the buoyancy force that drives the flow. This ‘feedback’ weakens with decreasing Pr, resulting in the development of high-speed convection with a collimated jet on the axis. If swirl is imposed on the equatorial plane, the jet velocity decreases. With increasing swirl, the jet becomes annular and then develops flow reversal on the axis. Transforming the stability problem of this strongly non-parallel flow to ordinary differential equations, we find that the jet is stable and derive an amplitude equation governing the hysteretic transitions between steady states. The results obtained are discussed in the context of geophysical and astrophysical flows.