Simulation Of Heat Transfer Processes Research Articles

Влияние заполнения прослоек малотеплопроводными газами на тепловую защиту оконных блоков с экранами

ISPU scientists have developed energy-saving constructions of window units with heat-reflecting screens, have tested them in a climate chamber, and have carried out simulation modeling of the heat transfer process through these constructions. Despite a large number of scientific papers that consider experimental laboratory studies and numerical simulation of heat transfer processes through translucent constructions, there is no data on the effect of the application of low thermal conductivity gases in the gaps formed by glass and metal elements on increasing the thermal protection of window units with screens. The correct calculation of the reduced heat transfer resistance of window units with screens and low-thermal conductivity gases affects the correctness of the heat balance for premises and, consequently, the quality of the design of energy systems to ensure the indoor microclimate. Thus, the development of models of heat transfer process through a window unit with screens is an urgent task to ensure the indoor microclimate. Simulation numerical modeling is carried out using the finite element method based on the fundamental laws of heat transfer. The authors have developed a two-dimensional simulation model of heat transfer through a window unit with heat-reflecting screens, in which the gaps between the glass and aluminum foil are filled with argon and krypton. The distribution of resistance to heat transfer along the height of a translucent enclosing structure has been studied. The adequacy of the proposed simulation model is confirmed by comparison with data of other scientists and regulatory documentation. Filling the gaps between glass and metal foil with argon makes it possible to increase the zonal heat transfer resistance of a window unit with screens in relation to the base-case scenario (air) by 6–23 %, krypton by 8–58 % (depending on the measurement location and the number of screens). The application of the developed simulation model will make it possible to more accurately determine the potential to use heat-reflecting screens in windows for intermittent heating systems of buildings.

Разработка и верификация имитационной модели процесса теплопередачи через оконный блок с теплоотражающими экранами

Window units account for the largest specific heat losses. The use of movable heat-reflecting screens and photovoltaic solar panels is of particular interest among the existing technologies to improve the thermal protection of windows. Despite the large number of scientific papers on this issue, which consider experimental laboratory studies and numerical simulation of heat transfer processes through window units, there is no data on the influence of the edge zones of a double-glazed window, as well as the areas of interface of the window profile and the light opening on the thermal processes that occur in these energy-saving units with screens. Vertical replacing of specific heat fluxes and temperature on the inner surface of the window unit strongly influences the correctness of determining the value of the minimum allowable temperature of the indoor air. Thus, the development and verification of models of the heat transfer process through a window unit with screens is an urgent task in the context of an indoor microclimate creation. Simulation numerical modeling is performed using the finite element method based on the fundamental laws of heat transfer. The authors have used the results of experimental studies of windows with heat-reflecting screens carried out in a certified climatic chamber. The authors have developed a two-dimensional simulation model of heat transfer through a window unit with heat-reflecting screens located in the partition wall of the climate chamber. The distribution of temperatures, air flow velocities, and reduced total thermal resistance along the height of a translucent structures has been studied. The adequacy of the proposed simulation model is confirmed by comparison with the results of the experiment in a certified laboratory, as well as data obtained by other authors and regulatory documentation. The use of heat-reflecting screens in the window unit increases the resistance to heat transfer by 1,6–3,7 times depending on their number. A significant decrease in temperature in the edge zones of the double-glazed window is revealed. The use of the developed simulation model makes it possible to determine the application of heat-reflecting screens in windows for intermittent heating systems including the case of using pre-drying air technology for humid, wet, or normal operation modes of industrial premises.

Development and validation of a computationally efficient hybrid model for temporal high‐resolution simulations of geothermal bore fields

AbstractThis paper presents a hybrid simulation approach for 1U‐, 2U‐ and coaxial single, and field of, borehole heat exchangers. We implement a novel combination of existing solutions for the simulation of heat transfer processes within the borehole and the surrounding ground. The heat transfer in the ground is modelled with a combination of analytically determined g‐functions, the borehole models utilize thermal resistance capacity models and the finite volume method. Critically, we improve the computational efficiency of long‐term simulations by sub‐dividing the time scale into multiple periods, where the influence of past periods on future periods is calculated using the fast Fourier transform (FFT). The accuracy and efficiency of the proposed method is validated against single borehole numerical models and a 40 bore field case study. The method achieves computational times reductions of over 90% in some cases, with greater improvement as the simulation time increases.

Free Convection and Heat Transfer in Porous Ground Massif during Ground Heat Exchanger Operation.

Heat pumps are the ideal solution for powering new passive and low-energy buildings, as geothermal resources provide buildings with heat and electricity almost continuously throughout the year. Among geothermal technologies, heat pump systems with vertical well heat exchangers have been recognized as one of the most energy-efficient solutions for space heating and cooling in residential and commercial buildings. A large number of scientific studies have been devoted to the study of heat transfer in and around the ground heat exchanger. The vast majority of them were performed by numerical simulation of heat transfer processes in the soil massif–heat pump system. To analyze the efficiency of a ground heat exchanger, it is fundamentally important to take into account the main factors that can affect heat transfer processes in the soil and the external environment of vertical ground heat exchangers. In this work, numerical simulation methods were used to describe a mathematical model of heat transfer processes in a porous soil massif and a U-shaped vertical heat exchanger. The purpose of these studies is to determine the influence of the filtration properties of the soil as a porous medium on the performance characteristics of soil heat exchangers. To study these problems, numerical modeling of hydrodynamic processes and heat transfer in a soil massif was performed under the condition that the pores were filled only with liquid. The influence of the filtration properties of the soil as a porous medium on the characteristics of the operation of a soil heat exchanger was studied. The dependence of the energy characteristics of the operation of a soil heat exchanger and a heat pump on a medium with which the pores are filled, as well as on the porosity of the soil and the size of its particles, was determined.

Modeling and CFD simulation of heat transfer process coupled with Unmixed Combustion for the application of generating superheated steam

• Unmixed combustion (UMC) process is investigated for generating supherheated steam. • A design of steam superheater integrated with UMC based reactor system is proposed. • A model of the proposed system is developed and CFD simulations are performed. • Superheated steam of desired temperature (1 atm) is obtained with sustained UMC operation. • Generation of LP and MP superheated steam using UMC was also found to be feasible. Superheated steam is produced in a super-heater using the energy of hot flue gases generated in the premixed combustion and it requires a larger surface area. Recently, unmixed combustion (UMC), an environmentally better process to premixed combustion, a variant of chemical looping combustion (CLC), has been investigated successfully for transferring heat to air, with a relatively compact system. Hence to address the limitations of the size of a super-heater and environmental aspects, it is decided to investigate the application of UMC for generating superheated steam. With this objective, the existing design of UMC based heat transfer system was modified for heating saturated steam to a desired temperature on a continuous basis. The modified system with Cu-based Oxygen Storage and Release Material (OSRM) was investigated using modeling and simulation study. A 2-D computational fluid dynamics (CFD) model was developed and simulated using COMSOL TM . Oxidation and reduction cycles of UMC were studied separately and the study was restricted to laminar steam flow conditions. Results of the representative cases showed that the superheated steam of desired bulk temperature of 650 – 720 K at atmospheric pressure and heat flux of 13,000 – 15000 W/m 2 at the interface can be obtained with sustained combustion (the bed temperatures between 723 and 873 K) in both the cycles. The effect of four important operating parameters viz. inlet steam velocity, inlet reactive gas velocity and concentration, metal loading, was also investigated and optimum ranges were suggested to achieve the maximum possible heat transfer without affecting the bed operation. The simulation study was then extended to generate low and medium pressure superheated steams and obtained results have indicated that it is still possible to generate superheated steam at desired temperatures using UMC.

Numerical investigation of convection heat transfer characteristics in sloshing corium pools

The convection flow and heat transfer actuated by internal decay heat and the sloshing of vessels are the primary problems in the study of thermal behaviors in volumetrically heated reactor corium pools under ocean conditions. The wall-modeled large eddy simulation (WMLES) method, volume of fluid model, and phase-change model combined with dynamic mesh technology, were used to develop a three-dimensional flow and heat transfer process simulation model of the sloshing corium pool. In addition, the heat conduction behavior in the crust and vessel wall, as well as the pressure-vessel-wall integrity evaluation was considered. The predicted internal heat transfer characteristics (the temperature distribution, the wall heat flux, and the shell thickness) in the corium pool and the evolution feature of the free surface height near the wall were in good agreement with the LIVE-L4 test results and sloshing experimental data, respectively. Furthermore, the coupled heat transfer phenomenon of the melt and vessel was simulated. The simulation results indicated that the time required to reach stable heat transfer was shortened, the structure of thermal stratification was transformed, and the heat flux along the inner surface of the vessel wall of the shell was improved at the resonance state. The comparisons of local Nusselt (Nu) number at the near-wall between static and sloshing corium pool conditions showed that heat transfer characteristics were significantly influenced by sloshing (T = 2.5 s, A = 0.07 rad) motion, and the Nu number of forced convection fraction had a strong correlation with the local Reynolds number in sloshing corium pools. Conclusively, the transient heat flux distribution of the sloshing melting pool differed from that of the static corium pool, increasing the molten range, and molten peak depth of the pressure-vessel-wall.

Характеристики охлаждения ракетного топлива жидким азотом в емкостях наземных комплексов с теплообменной рубашкой

The authors developed dedicated computational techniques and combined those with numerical simulation of heat transfer processes in ground complex tanks equipped with heat exchange jackets to discover the specifics of how rocket fuel may be cooled with liquid nitrogen used to sparge antifreeze in the cavities of the heat exchange jackets. The paper provides estimation data for rocket fuel cooling efficiency as a function of mass flow rate of liquid nitrogen for various options of setting up fuel mixing in the storage tank during cooling.

Flow analysis in seamless hot-extruded pipes with helical inner ribbing surface

The article is devoted to numerical simulation of heat transfer processes occurring during the flow of a coolant in seamless hot-extrusion pipes with a spiral inner fin surface (TMK-IRS). A description of the numerical modeling technique is given along with the interface of the program used to create different types of internal fins. Thermohydraulic analysis of finned pipes for transient, turbulent and laminar flow regimes has been carried out. An estimate of the critical Reynolds number characterizing the transition to a turbulent regime, the nature of the transient flow regime in comparison with other classical cases is given.

Simulation of heat transfer processes during the growth of crystals of the NiFeGaCo alloy

Long crystals of NiFeGaCo alloy with shape memory effect, including magnetically controlled ones, were obtained by the methods of Czochralski and Stepanov. A strong influence on the properties of crystals of dendritic formations, especially noticeable in the initial part of the crystal, has been revealed. In order to optimize the growth experiments, the heat transfer process in the thermal growth zone was simulated. It is shown that the formation of dendrites is due to a change in heat transfer during growth, which leads to an increase in the axial temperature gradient near the crystallization front as the crystal grows. This fits into the framework of the classical concepts of the transition from dendritic growth to normal growth.

Обоснование технологических параметров при производстве композитной ленты на основе полифениленсульфида

The purpose of the study was to select technological parameters of the production line of unidirectional thermoplastic polyphenylene sulfide-based tapes. The selection was made relying on the variation of the tape speed, the temperature of the sub-melting furnace, and the calendering module in the simulation of heat transfer processes. Modeling of heat transfer was based on the results of tests to determine the temperatures of phase transitions of a thermoplastic polymer in the composition of composite material and the dependence of the heat capacity of the composite on temperature. The indicated properties of the material were determined by analyzing the dependences obtained during differential scanning calorimetry and thermogravimetric analysis. As a result, the allowable range of distances between the polymer binder melting furnace and the calendering module was determined, which provides the necessary tape temperatures at the stages under consideration and the manufacturability of production. The permissible range of distances between the calendering module and the coiling module was also determined.

Multiple-Criteria Fuzzy Optimization of the Heat Treatment Processes for Two Steel Rolled Products

This paper presents a developed method for fuzzy multiple-criteria optimization of the rolled-steel heat treatment processes in the modern metallurgical plant. At the first stage of the study, by means of passive industrial experiments or a mathematical simulation of heat transfer processes, and using statistical methods, the regression dependencies of the output parameters of process quality on the input variables that are technological parameters are established. Then, based on the quality parameters, membership functions are formed that represent local criteria of the process quality, and their ranks are calculated using the matrix of pairwise comparisons. The practically useful methodology of the fuzzy multiple-criteria optimization of technological processes is proposed. To illustrate this methodology’s practical efficiency, the solutions of two optimization problems are found by maximizing the global criterion that aggregates local criteria using their ranks. It is shown that the efficiency of the obtained optimal heat treatment modes significantly exceeds the efficiency of the technology used earlier in the plant.

Computer simulation of heat transfer processes in aircraft landing gear braking mechanisms

Landing gear brakes – multi-disc brakes, as the responsible mechanism of the aircraft, must have the lowest possible weight and dimensions, high performance, increased service life and reduced life cycle cost. Solving these problems will reduce the design and development cycle of multi-disc chassis brakes. To perform the calculations, a computer mathematical model based on the use of the finite element method is proposed, replacing the classical version of the calculation based on currently used mathematical models, taking into account the heating of the aircraft landing gear braking mechanism, which will increase the speed, accuracy of calculations and reduce their labor intensity. We have developed a computer mathematical model of heat transfer processes occurring in the friction elements of multi-disc landing gear braking systems at the second stage of landing using the COMSOL Multiphysics program. Based on the calculations performed using this model, it is possible to take into account the influence of various system parameters such as the number of friction disks, their diameter and thickness, the medium in the interstitial space, the size of the solver grid on the maximum heating temperature of the brake mechanism, the cooling rate, the calculation time and the calculation error. On the basis of the obtained experimental data, we can conclude about the preferable construction of the brake mechanism. For example, it is possible to produce friction plates, steel with application to the surface of the composite friction material, allowing it to maintain the necessary friction and thus reduce the dimensions and maximum temperature, wet-disc brakes. The results of this work can be applied not only in the aviation industry, but can also be used to calculate the mechanisms of multi-disc oil-loaded brakes, which are used in agricultural, forestry, construction, quarry and other special equipment. In future work, the developed model will allow carrying out calculations taking into account the changes of material properties depending on temperature, refining the geometry of the brake mechanism, taking into account periods of reverse thrust engines and aerodynamic brakes.

Simulation of heat transfer processes in a diesel engine equipped with pistons coated by using Galvanic-plasma Method

The methodology for analyzing the thermodynamics and heat transfer of the combustion chambers of a diesel engine is presented. The work is devoted to the modified quasi-steady method (MQM) for the analysis of a diesel engine piston coated with an aluminum alloy. The oxide-coated piston using a galvanic-plasma modification (GPM) depending on the thickness of the coating, including comparison with the results for uncoated piston temperature, to achieve higher characteristics of the Cummins KTA-50 diesel engine. In thermodynamic modeling of a diesel engine, instantaneous gas temperatures and convective heat exchanges are first predicted. The time-dependent boundary conditions are then applied to the gas-blown surfaces of two-dimensional, transitional finite element models of the components of the combustion chamber. Further, the predictions on the finite elements of the instantaneous heat flux passing through each surface of the component are used to determine when the engine goes into quasi-stationary operation. The results show that our path in methodology can identify the complex transition paths of the heat process in the engine combustion chamber and significantly improve heat conduction and convection heat models when modeling a diesel engine.

Simulation of heat transfer process in shell-and-tube heat exchanger

Simulation of heat transfer process in shell-and-tube heat exchanger

МОДЕЛИРОВАНИЕ ТЕПЛОВОГО СОСТОЯНИЯ СОПРИКАСАЮЩИХСЯ ТВЕРДЫХ ТЕЛ С УЧЕТОМ ЭНЕРГОВЫДЕЛЕНИЯ В ЗОНЕ КОНТАКТА

The paper describes a numerical model simulating thermal conditions of contacting solids considering heat release in the contact region. The finite-volume model is implemented in the Logos Heat digital product within the Logos software package. Logos Heat serves for numerical simulations of heat transfer processes in solids and in air gaps without convective heat transfer. Its methods and algorithms enable thermal simulations of three-dimensional and two-dimensional (including axisymmetric) structures under steady and unsteady conditions using nonconformal mesh models considering contact energy release. We selected and considered the most common ways to determine the heat partition coefficient for the energy released by two solids being at rest or in sliding contact. The methods and algorithms incorporated in the numerical scheme of the Logos Heat product to consider the contact energy release were assessed using a case with a known exact solution and numerical data reported in. The analysis of the calculated data shows that the maximum error does not exceed 0.1% for the resting model and 8% for the sliding-contact model, which indicates that the methods and algorithms are appropriate for such simulations. However, it should be noted that, within the Logos Heat numerical scheme, the solution calculated by Charron's formula introduces an error, which is one order higher than the error associated with the temperature conduction method, and creates a temperature discontinuity at the contact.

RETRACTED: Simulation of heat transfer process of thermal protective clothing based on FPGA and sensor processing system

Abstract Low radiation exposure to the heat transfer of the heat flux protective clothing. Field Programmable Gate Arrays (FPGA) simulation software and the sensor are used to model the heat transfer through a particular multilayer textile structure. The transfer model is verified by comparison with experimental data. In the previous method, is Initial results with the corresponding experimental results are very consistent. The first of a series of tasks to optimize thermal performance for protective clothing in thermal comfort. It protects the skin from exposure to low-intensity aspects of thermal damage caused by heat radiation has the best performance. Exposed to heat and flame, the clothes will burn. However, these burns' nature depends mostly on the fabric, the fabric structure, garment moisture, and the heart of the finishing agent used. The proposed method improves combustion speed will not change wool than other natural fibers (e.g., cotton, linen, and silk) faster. Gas weaved or loosely woven fabric relatively intact motion of light, tight and more massive than the fabric structure to promote faster flame propagation of these materials.

Experimental Investigation of the Regimes of Thermal Action on a Layer of Soil Exposed to Inert Heating

A typical porous material enriched with organic matter, soil, is considered. Investigation of the thermal regimes of such materials exposed to a high-temperature action is important for solving ecological and environmental protection problems, and also those of agriculture. Many authors have established that thermal action on the near-surface soil can have a negative effect on both the soil itself, and further development of grass and forest stands. There is a need for the development of a system of geomonitoring accounting for thermophysical processes in the soil at the level of mathematical models. Verification of such models requires the conduct of experiments. In this investigation, we propose an experimental setup for physical simulation of heat transfer processes in a layer of typical soil exposed to high temperature whose source is an inert heater. A set of thermocouples is set up in the soil layer at different depths. Typical curves are presented demonstrating time dependences at different depths of the layer, as are the results of the analysis of temperature dependences.

Numerical simulation of the heat transfer process in the antiicing heating system for Arctic marine applications

In the Arctic, there is a serious problem of icing of structures, which can cause a catastrophic disruption of the functioning of the equipment necessary to maintain the life support of sea vessels and ground structures. For marine vessels, this problem is especially relevant in view of the limitations on heating systems and the mass of permissible heating equipment. The article is a continuation of work on the research and development of an electrical heating system for the air intake grilles of marine vessels. A numerical simulation of the heat transfer conditions for the design of the air intake grille with a built-in electric heating system was carried out. Some variant calculations of the numerical simulation of heat transfer processes in the system are presented — air, a streamlined structure — an air intake grill case — a heating system. A technique has been developed for selecting the optimal parameters of the electric heating system for various operating conditions of air intake grilles.

Effects of non-darcy flow on heat-flow coupling process in complex fractured rock masses

This paper presented a heat-flow coupling model for simulation of heat transfer process in complex fractured rock masses considering non-Darcy flow. Firstly, the Forchheimer equation and the Reynolds equation were coupled to obtain the governing equation to describe the non-Darcy flow behaviors. Then, combined with the heat transfer equation and considered the heat exchange process between fractures and rock matrix, the heat-flow coupling model was established. The model was solved by the finite element method. The calculation results of the non-Darcy flow model were compared with the fluid flow test results of crossed fracture and complex fracture network models and a good agreement was observed. The numerical simulation results of non-Darcy flow and heat transfer model were compared with analytical solution of flow-heat coupling in a single fracture, and the numerical solution and the analytical solution agreed well. Finally, a two-dimensional complex fracture network was generated for numerical experiments, and effects of equivalent hydraulic aperture df and hydraulic gradient J on the flow behaviors and the heat-transfer process in complex fractured rock masses were systematically discussed. Results showed that the proposed model can well describe the non-Darcy flow characteristics as well as the heat-flow coupling process in complex fracture networks. Considering the non-Darcy flow behaviors, the average temperature of the outlet dropped slower under non-Darcy than which under Darcy flow. It was also found that effects of non-Darcy flow on the heat transfer process will be more significant as the hydraulic gradient or the equivalent hydraulic aperture increases.

Simulation of heat transfer process in a multilateral cylindrical shell taking into account the internal heat sources

Simulation of heat transfer process in a multilateral cylindrical shell taking into account the internal heat sources