Discrete Transfer Radiation Model Research Articles

Simulation study of a box type solar cooker for different locations

Solar cooker which relies on solar energy can be a viable alternative for the reduction of pollution during the combustion of biomass during the cooking process. The emission from biomass contains hydrocarbons as its major source. This simulation study of box type solar cooker performed using ANSYS Fluent version R1 2022 helps in optimizing the design of solar cooker to predict solar heat flux values for different locations such as Chennai, Vellore, Karur and Rameswaram for a particular day and particular time intervals such as 9 am, 12 pm, 2 pm, 5 pm. The proposed work further highlights the region where the solar cooker can be efficiently used by utilizing non-conventional energy sources for cooking process. In the simulation process, Discrete Transfer Radiation Model (DTRM) was used for tracking the solar radiation and solar calculator to predict the direct and diffuse solar irradiation for a particular day, by considering the latitude, longitude and Greenwich Mean Time (GMT) for specified locations. The specified geographical regions are plotted in a spatial map with solar radiation data obtained from Indian Meteorological Department (IMD) through ArcGIS geospatial techniques. The maximum solar heat flux values obtained at 12 pm, in the simulation results are 718 W/m2, 698 W/m2, 726 W/m2 and 720 W/m2, it is identified that among the four regions karur recorded the highest solar heat flux value of 726 W/m2. The minimum solar heat flux values at 5 pm are 215 W/m2, 202 W/m2, 265 W/m2 and 230 W/m2. Vellore was observed to have the minimum solar heat flux value of 202 W/m2. Solar radiation data obtained from the solar calculator and IMD radiation data were in good agreement with each other with a maximum error percentage of 2.36% because of the variation in the sunshine factor.

Model evaluation and experimental validation of thermal jet drilling for geothermal energy

Thermal jet drilling is a technology, which has the potential to be suitable for the exploitation of geothermal energy in relatively deep formations with low costs. Several investigations on this drilling method have been carried out for the depths of less than 1 km or deeper than 2 km. To the best of our knowledge, there is almost no specific study on simulation for thermal jet drilling at the depths between 1 km and 2 km. This paper focuses on investigating applications of different reaction (i.e., laminar, non-premixed, eddy dissipation concept, eddy dissipation model and finite rate), turbulence (i.e., standard k-epsilon, realizable k-epsilon, renormalization group k-epsilon and scale-adaptive simulation) and radiation (i.e., P1, discrete ordinate, discrete transfer radiation model and surface-to-surface) models to downhole reaction of thermal jet drilling. The objective is to identify the pros and cons of each model and determine a set of models that are the most appropriate for the reaction. Experiments are also carried out and data are collected as the benchmark for comparison. Relative errors and iteration for convergence are analyzed for each simulation model. Results show that the modified simulation temperature by considering the environmental temperature becomes more accurate compared with the experimental data. The laminar model over-predicts the temperature and yields unreasonable results. Finite rate and eddy dissipation model are the candidates with highest accuracy and acceptable computational time within selected model settings and boundary conditions. In addition, compared with renormalization group, realizable and scale-adaptive simulation turbulence models, the standard k-epsilon model is the most appropriate model under the conditions selected for this investigation. The discrete ordinate model can be applicable for the simulation if the error tolerance is 10%. The P1 model is the most suitable radiation model. Results in this paper can provide implications for the reaction simulation of thermal jet drilling.

Transient 3D

This article describes the limitations and the environmental effects of fossil fuels have provided the drive to create replacement strategies, such as the utilization of renewable energy resources. Solar energy and related technologies are also among fast-growing renewable resources and technologies. Despite different research on solar technologies, an extensive research on the effects of different parts of the collector, such as an absorber, glass cover, and the air gap has not conducted in the warm climate in the Middle East. This article focuses on an unsteady and three-dimensional simulation of a flat plate solar collector considering Discrete Transfer Radiation Model (DTRM). The parameters effecting on efficiency of collector such as the absorber material, tilt angle of the collector and effect of double glazing are analyzed. The result of the numerical analysis shows parameters effecting on collector efficiency, and double-glazed glass.

Implementation of a simple and reliable human model to evaluate thermal cabin comfort using CFD methods

The optimization of thermal comfort in buildings and passenger cabins has become one of the major aspects during the conception phase of HVAC systems. The static PMV model is among the most recognized thermal comfort models and depends besides the dry air temperature, radiant temperature, humidity and air velocity also on the activity level and the clothing of the human. The aim of this investigation is the application of a simple and reliable model of human metabolism based on Olesen combined with CFD simulations to attain a sufficiently accurate reflection of the human heat exchange to evaluate the PMV index and predict thermal comfort in a fast and cost-effective way by CFD simulations. Basis of the CFD model developed in the current investigations are measurement results obtained during experimental investigations inside a cabin mock-up model placed in a controlled climatic chamber under various pre-defined steady-state environmental conditions. The cabin mock-up model is equipped with a radial-flow fan for influencing convective flow inside the cabin and a temperature control system for adjusting the ceiling surface temperature to obtain mainly the impact of radiant temperature on the thermal comfort. Depending on the activity level, the local clothing and ambient conditions such as the flow structure inside the cabin, the local human heat flux due to convection and radiation is examined within a steady-state, two-way-coupled CFD simulation coupling human and environment with one continuous fluid phase (dry air) and the usage of the discrete transfer radiation model.

Impact of Radiation Models in Coupled Simulations of Steam Cracking Furnaces and Reactors

As large floor-fired furnaces have many applications in refinery and (petro-) chemical units and about 80% of heat transfer in these furnaces is by radiation, the accurate description of radiative heat transfer is of the most importance for accurate design and optimization. However, the impact of using different radiation models in coupled furnace/reactor simulations has never been evaluated before. Therefore, coupled furnace/reactor simulations of an industrial naphtha cracking furnace with a 130 kt/a capacity have been conducted. Computational fluid dynamics simulations were performed for the furnace side, while the one-dimensional reactor model COILSIM1D was used for the reactor simulations. The Adiabatic, P-1, discrete ordinates model (DOM), and discrete transfer radiation model (DTRM) were evaluated for modeling the radiative heat transfer. The results with DOM and DTRM are very similar both on the furnace and the reactor sides. The flue gas temperature using DOM is higher than when using the P-1 radiation model, resulting in higher incident radiation. Comparing the simulated results of all radiation models to the industrial product yields and run lengths shows that DOM and DTRM outperform the others. As DOM has a broader application range than DTRM, and because the current implementation of DTRM in FLUENT/14.0 cannot be run in parallel yet, DOM is the recommended radiation model for run length simulations of steam cracking furnaces.

Investigation of radiation models in entrained-flow coal gasification simulation

Adequate modeling of radiation heat transfer is important in CFD simulation of coal gasification process. In an entrained-flow gasifer, the non-participating effect of coal particles, soot, ashes, and reactive gases could significantly affect the temperature distribution in the gasifier and hence affects the local reaction rate and life expectancy of wall materials. For slagging type gasifiers, radiation further affects the forming process of corrosive slag on the wall which can expedite degradation of the refractory lining in the gasifier. For these reasons, this paper focuses on investigating applications of five different radiation models to coal gasification process, including Discrete Transfer Radiation Model (DTRM), P-1 Radiation Model, Rosseland Radiation Model, Surface-to-Surface (S2S) Radiation Model, and Discrete Ordinates (DO) Radiation Model. The objective is to identify the pros and cons of each model’s applicability to the gasification process and determine which radiation model is most appropriate for simulating the process in entrained-flow gasifiers.The Eulerian–Lagrangian approach is applied to solve the Navier–Stokes equations, nine species transport equations, and seven global reactions consisting of three heterogeneous reactions and four homogeneous reactions. The coal particles are tracked with the Lagrangian method. Six cases are studied—one without the radiation model and the other five with different radiation models. The result reveals that the various radiation models yield uncomfortably large uncertainties in predicting syngas composition, syngas temperature, and wall temperature. The Rosseland model does not yield reasonable and realistic results for gasification process. The DTRM model predicts very high syngas and wall temperatures in the dry coal feed case. In the one-stage coal slurry case, DTRM result is close to the S2S result. The P1 method seems to behave stably and is robust in predicting the syngas temperature and composition; it yields the result most close to the mean, but it seems to underpredict the gasifier’s inner wall temperature.

Numerical investigations of buoyancy-driven natural ventilation in a simple three-storey atrium building and thermal comfort evaluation

The numerical investigations of buoyancy-driven natural ventilation and thermal comfort evaluation in a simple three-storey atrium building as a part of the passive ventilation strategy was undertaken using a validated Computational Fluid Dynamic (CFD) model. The Reynolds Averaged Navier–Stokes (RANS) modeling approach with the SST-k–ω turbulence model and the discrete transfer radiation model (DTRM) was used for the numerical investigations. The steady-state governing equations were solved using a commercial solver FLUENT©. Various flow situations of the buoyancy-driven natural ventilation in the building during day and night time were examined. The numerical results obtained for the airflow rates, airflow patterns and temperature distributions inside the building are presented in this paper.Using the numerical results, the well-known thermal comfort indices PMV (predicted mean vote) and PPD (predicted percentage of dissatisfied) were calculated for the evaluation of the thermal comfort conditions in the occupied regions of the building. It was noticed that thermal conditions prevailing in the occupied areas of the building as a result of using the buoyancy-driven ventilation were mostly in comfort zone. From the study of the night time ventilation, it was found that hot water (80 °C) circulation (heated by solar collectors during daytime) along the chimney walls during night time and heat sources present in the building can be useful in inducing night ventilation airflows in the building as a part of the passive ventilation strategy.

Numerical study of buoyancy-driven natural ventilation in a simple three-storey atrium building

Abstract A simple three-storey atrium building was modeled to investigate the development of buoyancy-driven natural ventilation airflows induced by solar radiation and by the heat sources present on each floor of the building using a validated Computational Fluid Dynamics (CFD) model. The Reynolds Averaged Navier–Stokes (RANS) modeling approach with the SST-k-ω turbulence model and the Discrete Transfer Radiation Model (DTRM) was used for the numerical solution. The steady-state governing equations were solved using a commercial CFD solver FLUENT©. The air flow patterns, temperature distributions and the ventilation flow rates as predicted by the CFD model for this case study are presented in this paper. The ventilation flow rates were compared in non-dimensional form with the analytical design curves found in literature developed through the use of an analytical approach for a simple geometry atrium building. It was found that the CFD predictions agreed with the general trends described by the analytical model. The effect of solar intensity on the buoyancy-driven ventilation flow rates and the temperature distributions during the day-light hours and at different geographical locations was also investigated.

Numerical investigations of buoyancy-driven natural ventilation in a simple atrium building and its effect on the thermal comfort conditions

Abstract In the present study use of solar-assisted buoyancy-driven natural ventilation in a simple atrium building is explored numerically with particular emphasis on the thermal comfort conditions in the building. Initially various geometric configurations of the atrium space were considered in order to investigate airflows and temperature distributions in the building using a validated computational fluid dynamics (CFD) model. The Reynolds Averaged Navier–Stokes (RANS) modelling approach with the SST-k–ω turbulence model and the Discrete Transfer Radiation Model (DTRM) was used for the investigations. The steady-state governing equations were solved using a commercial CFD solver FLUENT©. From the numerical results obtained, it was noted that an atrium space integrated with a solar chimney would be a relatively better option to be used in an atrium building. In the geometry selected, the performance of the building in response to various changes in design parameters was investigated. The produced airflows and temperature distributions were then used to evaluate indoor thermal comfort conditions in terms of the thermal comfort indices, i.e. the well-known predicted mean vote (PMV) index, its modifications especially for natural ventilation, predicted percent dissatisfied (PPD) index and Percent dissatisfied (PD) factor due to draft. It was found that the thermal conditions in the occupied areas of the building developed as a result of the use of solar-assisted buoyancy-driven ventilation for the particular values of the design parameters selected are mostly in the comfortable zone. Finally, it is demonstrated that the proposed methodology leads to reliable thermal comfort predictions, while the effect of various design variables on the performance of the building is easily recognized.

Evaluation of various turbulence models for the prediction of the airflow and temperature distributions in atria

In this paper the performance of various turbulence models potentially suitable for the prediction of indoor air flow and temperature distributions in an atrium space was evaluated in a systematic way. The investigation tested these models for various thermal conditions in atria of different geometrical configuration in two existing buildings using the Reynolds Averaged Navier–Stokes (RANS) modeling approach. The RANS turbulence models that were tested include the one-equation model (the Spallart–Allamaras) and two-equation models (the standard k-ɛ, RNG k-ɛ, realizable k-ɛ, standard k-ω and SST k-ω models). The radiation exchange between the surfaces of the atrium space was considered using the Discrete Transfer Radiation Model (DTRM). The resultant steady state governing equations were solved using a commercial CFD solver FLUENT. The numerical results obtained for a particular time of the day were compared with the experimental data available. Relatively good agreement between the experimental and CFD predictions was obtained for each model. However, from the results obtained, it was found that the performance of two-equation turbulence models is better than one-equation model and among the two-equation models, the SST k-ω model showed relatively better prediction capability of the indoor environment in an atrium space than k-ɛ-models.

Validation of numerical modeling of conditions in an atrium space with a hybrid ventilation system

Quite extensive measurements undertaken in a three-story atrium space (floors 14th–16th) with a hybrid solar-assisted natural ventilation system in the Engineering building of the Concordia University, Montreal, Canada have recently become available. The thermal conditions of the atrium space have been studied numerically using the Reynolds Averaged Navier-Stokes (RANS) modeling approach. The RANS turbulence models that were tested include the standard k-ε, RNG k-ε, ‘realizable’ k-ε, and SST k-ω turbulence models. The radiation exchange between the surfaces of the atrium space was considered using the Discrete Transfer Radiation Model (DTRM). The resultant steady state governing equations were solved using a commercial CFD solver FLUENT. Numerical results were obtained for the conditions existing when measurements were taken in the Concordia atrium on typical clear days with the blinds fully open or fully closed and with the natural ventilation system (NV) ON or OFF. The CFD model predictions were validated by the comparison against the experimental measurements available and it was found that the numerical predictions implying CFD model agree well with the measurements.

Flow processes in a radiant tube burner: Combusting flow

This paper describes a study of the combustion process in an industrial radiant tube burner (RTB), used in heat treating furnaces, as part of an attempt to improve burner performance. A detailed three-dimensional Computational Fluid Dynamics model has been used, validated with experimental test furnace temperature and flue gas composition measurements. Simulations using the Eddy Dissipation combustion model with peak temperature limitation and the Discrete Transfer radiation model showed good agreement with temperature measurements in the inner and outer walls of the burner, as well as with flue gas composition measured at the exhaust (including NO). Other combustion and radiation models were also tested but gave inferior results in various aspects. The effects of certain RTB design features are analysed, and an analysis of the heat transfer processes within the burner is presented.

Investigation of Radiative Heat Transfer and Three Thermal Radiation Models in a Turbulent Non-Premixed Methane/Air Flame

A numerical simulation of a turbulent non-premixed flame as a two-dimensional problem is carried out to assess the performance of three thermal radiation models, namely, discrete transfer radiation model (DTRM), P-1 radiation model, and discrete ordinates method (DOM). A finite volume staggered grid approach is employed to solve the governing equations. The SIMPLEC algorithm is used to handle the velocity and pressure coupling. The eddy dissipation/finite rate model is employed to predict the heat release and the realizable κ − ε model is applied to simulate the flow behavior. Computational results with and without thermal radiation effects are compared with the available experimental data and the three radiation models are evaluated in terms of the computational efficiency and prediction accuracy. With the consideration of thermal radiation using all the presented models, the predicted radial temperatures of flame at different locations along the combustor are noticeably closer to the existing experimental data. The use of DTRM involves a relatively high computational cost from the time consumption viewpoint. The P-1 radiation model overpredicts the wall heat flux strongly. However, the DOM is a relatively useful and accurate model with acceptable time consumption.

Effects of radiation heat transfer space non-uniformity of combustion chamber components on in-cylinder soot emission formation in diesel engine

Combustion chamber components (cylinder head-cylinder liner-piston assembly-fuel film) were treated as a coupled body. Based on the three-dimensional numerical simulation of heat transfer of the coupled body, the multi-dimensional simulation computation coupling flow and solid on working process and combustion chamber components of internal combustion engine was performed using Discrete Transfer Radiation Model (DTRM) radiation heat transfer model, zoning solution method and boundary coupling method. The simulation was applied to the influence investigation of the space non-uniformity in radiation heat transfer among combustion chamber components on the generation of in-cylinder soot emissions. The results show that the space non-uniformity in heat transfer among the combustion chamber components has great influence on the generation of in-cylinder NOx emissions. The difference value of total soot in cylinder when exhaust valves are opened is 1.3% (no radiation), 0.8% (radiation). So the effect of radiation heat transfer space non-uniformity of combustion chamber components on total soot production can be ignored. While in local area radiation heat transfer space non-uniformity has certain effect on soot production inside whole combustion chamber space, and has less effect on soot production in the area near the wall of combustion chamber components.

Computational fluid dynamics (CFD) modeling of an electrical heating oven for bread-baking process

Radiation is the most dominant heat transfer mode in an electrical heating oven. A 3D CFD model for an electric heating baking oven was developed. Three different radiation models namely, discrete transfer radiation model (DTRM), surface to surface (S2S) and discrete ordinates (DO) were employed for the simulation of the electrical baking oven. All models predicted almost similar results, which tallied well with the experimental measurements. During the full heating cycle, the oven set-point temperature was reached after 360 s. Lower temperature zones occurred near oven wall due to lower air flow. Based on preliminary evaluation of applicability, the DO radiation model was selected for bread baking simulation and validated with the experimental measurement of bread temperature. Bread simulation was carried out to study the profiles of temperature and starch gelatinization of crust and crumb of the product. This study indicated the baking process to be complete at 1500 s when the temperature of bread-center reached 100 °C.

Numerical investigation of full scale coal combustion model of tangentially fired boiler with the effect of mill ducting

In this paper a full scale combustion model incorporating upstream mill ducting of a large tangentially fired boiler with flue gas recirculation was examined numerically. Lagrangian particle tracking was used to determine the coal particle paths and the Eddy Dissipation Model for the analysis of the gas phase combustion. Moreover volatiles and gaseous char products, given off by the coal particles were modelled by Arrhenius single phase reactions and a transport equation was solved for each material given off by the particles. Thermal, prompt, fuel and reburn NOx models with presumed probability density functions were used to model NOx production and the discrete transfer radiation model was used to model radiation heat transfer. Generally, the findings indicated reasonable agreement with observed qualitative and quantitative data of incident heat flux on the walls. The model developed here could be used for a range of applications in furnace design and optimisation of gas emissions of coal fired boiler plants.

非構造メッシュを用いたラージ・エディ・シミュレーションに適した並列ふく射伝熱計算法(熱工学,内燃機関,動力など)

A parallel calculation method for radiative heat transfer that is suitable for LES (Large Eddy Simulation) on unstructured mesh is proposed. It is based on a discrete transfer radiation model coupled with a coarse mesh generation technique. Each coarse cell is automatically generated by grouping of a certain number of cells used for fluid dynamics calculation. The number of cells in a group is called agglomeration ratio. Two thermal radiative heat transfer problems are solved for validation. One validation case is a three-dimensional L-shaped geometry problem. The results of heat flux obtained by the proposed radiation method agree well with the result of Sakami et al. Simulation speed of radiation is improved by a factor of 7.4 when the agglomeration ratio is 8. The other validation case is a high temperature (1420[K]) turbulent jet, which is solved by a LES code coupled with the proposed radiation method. Calculated temterature distributions agree well with experimental data if radiative heat transfer is taken account. The simulation speed is improved by a factor of 8 when the agglomeration ratio is 16. The temperature error caused by the cell grouping is less than 23[K].

A new approach to construct dynamic models for NOx control in a FGR furnace

This paper presents a new approach to construct dynamic models for NOx control of an industrial furnace with flue gas recirculation (FGR). In this paper, the full‐scale computational fluid dynamics (CFD) simulations are carried out for the FGR furnace and the CFD results are used to construct the transfer functions to represent the linearized dynamic models of the furnace. The controllers are then designed based on these models. Finally, the results obtained from full‐scale CFD simulation are used to validate the dynamic models. It is indicated that the dynamic models obtained by the new approach are capable of capturing the dynamic characteristics of the combustion system. The numerical simulation of the turbulent non‐premixed combustion process in the furnace is conducted using a moment closure method with the assumed – probability density function (PDF) for the mixture fraction. The combustion model is derived based on the assumption of instantaneous full chemical equilibrium. The discrete transfer radiation model is chosen as the radiation heat transfer model, and the weighted‐sum‐of‐gray‐gases model is used to calculate the absorption coefficient.

The Response of Framed Steel Structures to Fire

A combined computational fluid dynamics and structural stress investigation was conducted to study the response of steel structures to fire. The structure was a two-story building with six rooms. The fire was confined to one room on the first floor. The free convection of air and thermal radiation were both included in the analysis. The governing differential equations of flow and energy were solved by FLUENT. The air turbulence was modeled by the standard k-ϵ model, and the radiation was simulated by the Discrete Transfer Radiation Model. The temperature of the beams and columns were subsequently used in the thermal stress analysis to obtain the deflection and total strain using ANSYS. The result of FLUENT analysis indicates that the air velocity was high in the middle of the room above the fire and adjacent to the ceiling. The temperatures of the beams and columns generally decreased away from the center, with a more rapid decrease toward the ends. It was also observed that radiation played an important role in fire modeling (i.e., 20–40% of the heat transfer took place by radiation). The ANSYS analysis indicated a maximum deflection of 28.66 mm at a beam-column joint in the room with fire at the first level of the structure. The corresponding steel column design load capacity is exhausted after 34 minutes of standard ISO 834 fire due to a combined temperature and gravity loads. The maximum strain was observed at the center of the longitudinal beam, and the minimum was on the steel members of the second floor.

Evaluation of CFD Modeling Methods for Fire-induced Airflow in a Room

Methods for exploiting the technique of computational fluid dynamics (CFD) to model fires and the associated fundamental processes of combustion and radiation are appraised by applying the CFD model JASMINE to simulate the fire-induced airflow in a room-sized compartment. For a systematic evaluation of these methods describing the fundamental processes and the associated mathematical formulation, a two-stage-verification and validation procedure is adopted here. In the verification stage, a number of important model parameters, e.g., the choice of fire source model (e.g., combustion model vs. volumetric heat source (VHS) model), radiation transport model (e.g., six-flux vs. discrete transfer radiation model), gas property model (e.g., constant absorption coefficient vs. grey gas model), design and resolution of the numerical grid, etc. are assessed by comparing the predicted results against a specific fire scenario selected from the data of Steckler, K.D., Quintiere, J.G. and Rinkinen, W.J. (1982). Flow Induced by Fire in a Compartment, NBSIR B2-2520, National Bureau of Standards, Pittsburgh [2]. The validation stage has then focused on the detailed comparison of the CFD fire model against the comprehensive data set of Steckler et al. [2] for a wide range of fire scenarios covering a range of fire strengths (i.e., heat release rates), fire source locations, the sizes and shapes of the ventilation opening (i.e., door or window). Such a systematic study has demonstrated the predictive capability of the CFD methodology in reproducing detailed thermal and flow field behavior of the enclosure fires, and has also shown that the predictive accuracy of the CFD methodology can be significantly improved by careful selection of the fire models and model parameters. Some guidance on the use of CFD methodology has been provided for performing the fire modeling properly and effectively for performance-based fire safety design.