Abstract.The results of mathematical simulation of the heat transfer processes in the closed domain, which corresponds to production accomodation with the gas infrared emitter operation condition are presented. The system of differential Navier-Stokes equations in the approximation of Boussinesq is solved. The comparative analysis of thermal conditions formation in the closed domain is carried out taking into account heat withdrawal through the upper enclosing construction and under the conditions of its heat insulation. The essential transiency of the analyzed heat transfer process and the influence of heat withdrawal from one of the outer boundaries on the mean temperatures values in largedimension industrial premises are established.The distinguishing feature of modern industry becomes the rigid savings of energy consumption, as a rule, for the purpose of reduction in the economic expenditures. Localization of systems and heat supply sources is one of the ways for reduction in total energy expenditures for the heating of large production accomodations (local heating of separate workplaces). As the most acceptable version the system of gas infrared emitters (GIE) [1] can be used. Scale GIE introduction in the production is strongly limited because of the insufficient experimental and theoretical study of convective heat transfer in the largedimension accomodations with the gas infrared emitters operation conditions.For the mathematical simulation of the studied process the process description of free convection in air region and thermal conductivity in enclosing constructions (Fig. 1) is necessary. In the problem statement system conjugate heat transfer equations [2-5] was used as a base. All energy from emitter came to bottom medium interface H H .To analyze the significant factors impact on the thermal modes in the manufacturing conditions of GIE operation two versions of the heat transfer problem statement were considered. The first version: heat insulation conditions are satisfied on all outer boundaries of solution region. The second: on upper boundary of solution region y = H (Fig. 1) heat exchange condition with environment is satisfied. The problem was solved in the dimensionless formulation.The system of equations describing the heat transfer in the system has the form:1 Sh
536.33:536.244 We have carried out computational modeling of nonstationary conductive-convective heat transfer in a closed rectangular domain in a conjugate formulation with a local heat source (a gas infrared radiator). Four variants of possible description of the radiant energy distribution over the inner surfaces of enclosures have been considered. As a result of the computational modeling, differential (temperature fi elds and stream functions) and integral (Nusselt numbers) heat transfer characteristics have been obtained. It has been shown that the radiant fl ux distribution infl uences the heat transfer intensity.Introduction. The steadily increasing energy consumption, the problems with operating NPPs, and the limited capacities of renewable energy sources make the use of energy-saving technologies more and more topical. The traditional convective heating of large-size industrial premises is at present ineffective in many cases. The use of gas infrared radiators (GIR) can make it possible to reduce the energy consumption, according to the authors of [1], by more than 30% due to by local heat supply to the working places.Investigations of radiant heating systems are carried out mainly with the aim of choosing optimal characteristics of the GIR [2-4]. The obtained experimental data [5,6] have shown that a microclimate favorable for personnel is attained in using GIRs at lower expenditures of fuel resources. It is not always possible to perform natural experiments under the conditions of large-size production shops with locally sitting operating equipment. In this case, it is expedient to use methods of mathematical modeling in choosing the basic parameters of GIR-based heating systems and test subsequently the results of the theoretical analysis under production conditions. It has been found [7,8] that mathematical modeling of the processes of conductive-convective heat transfer in a conjugate formulation in solving analogous problems creates conditions for a much more detailed analysis of the temperature regimes of investigated objects of heat supply. Mathematical models based on the thermal balance of a room [9] do not completely take into account the spatial character of the heat transfer typical in practice. The known solutions of heat transfer problems during operation of radiant heating systems [10,11] ignore the convection. The mathematical model of conductiveconvective nonstationary heat transfer under radiant heating of one of the internal boundaries of a closed rectangular domain in a conjugate formulation [12] was formulated under the assumption that the heat fl ux is distributed uniformly only over the horizontal surface of the lower base. It is interesting to analyze the thermal regimes of heated objects under radiant heating with account for the possible distribution of energy released by the GIR over the surfaces of vertical enclosure structures.The aim of the present work is to model computationally the nonstationary process of radiant heating of a rectangular domain in a conjugate formu...
Abstract.Results of mathematical modeling of convective heat transfer in air area surrounded on all sides enclosing structures, in the presence of heat source at the lower boundary of the media are presented. Solved the system of differential equations of unsteady Navier-Stokes equations with the appropriate initial and boundary conditions. The process of convective heat transfer is calculated using the models of turbulence Prandtl and PrandtlReichard. Takes into account the processes of heat exchange region considered with the environment. Is carried out the analysis of the dimensionless heat transfer coefficient at interfaces "air -enclosures". The distributions average along the gas temperature range are obtained.
Results of numerical modeling of the process of free-convective heat transfer in a turbulent convection regime in a rectangular enclosure heated by an infrared gas radiator are presented. A comparative analysis of two alternative locations of the infrared gas radiators in modeling of typical free-convective heat transfer regimes in the region is conducted. The essential nonstationary nature of the heat-transfer process and the infl uence of heat emission from the surface of the upper horizontal fi ller structure on the temperature patterns of zones of local heating of large work zones are established.The specifi c nature of production processes in many branches of industry manifests itself in the uniqueness of a signifi cant portion of the technological processes, which require for their execution large (in terms of area and sometimes in terms of space) compartments [1,2]. The work of service personnel is often concentrated in zones the area of which is significantly less than the area of the zones occupied by the production equipment. It would, therefore, be useful to reduce the total cost of energy expended on heating the production fl oor areas through localization of the heat supply systems and sources. Thus, as an example, a transition from traditional heating systems [3] for large shops and bays to local heating of particular workplaces with the use of infrared gas radiators (IGR) [4] would be economically justifi ed. The reliability of the heat supply systems would thus also be increased.Despite the obvious promise of IGRs for use in local heating of workspaces, the scales at which IGRs are being introduced is low, largely due to insuffi cient experimental and theoretical treatment of problems of heat transfer under the operating conditions of infrared heat radiators.The mechanism under which a region of heated air forms when an infrared heat radiator is functioning is characteristic. An IGR is generally in the form of a rectangular panel heated to high temperatures (Fig. 1).Since under the ordinary conditions of a well-equipped production fl oor area, air is a medium that is transparent to thermal radiation and is also nonabsorbing and nonscattering, the fl ux of radiation enters the lower boundary of the working zone (as a rule, concrete fl oors or ceilings, covered in certain cases with ceramic tile).The energy produced by IGRs is absorbed by a thin near-surface layer of concrete (or ceramic material) with low coeffi cient of thermal conductivity. As a result, the temperature of the surface of the concrete (or the ceramic material) rises to ≈25°C and warms up the layer of air adjacent to the lower boundary of the working zone. Heating of the entire working zone due to natural convection occurs next. Circulation of the warm air compensates to a signifi cant extent cooling of the warm air in the course of downward motion along the vertical fi ller structures, which absorb heat. The mechanism of natural convection may be considered basic in the analysis of processes of heat transfer in this region.
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