Effect Of Radiative Heat Transfer Research Articles

Impact of non-linear radiation on magneto - Casson fluid suspended hybrid nanomaterials in sodium alginate: Smarter textiles

BackgroundThe combination of sodium alginate (SA) and nanoparticles in Casson nanofluids can have several advantages in textile applications such as to enhance the dye absorption and finishing properties and uniform and controlled coatings on complex shapes of the fabric and garments with intricate designs or three-dimensional textile structures etc. These fascinating properties attracted us to work on this article, a Casson hybrid nanoflow under the influence of magnetic effects past a curved stretching surface. Key terms & problem definitionThis study examines the heat transfer characteristics of Casson nanofluid flow over a stretching sheet with nonlinear thermal radiation and convective boundary conditions. A Casson fluid is a non-Newtonian fluid that exhibits a yield stress, meaning it behaves like a solid below a certain shear stress. Nonlinear thermal radiation accounts for the effects of temperature-dependent radiative heat transfer. Convective boundary conditions simulate the heat exchange between the fluid and a surrounding environment. The nanoflow has its base fluid as Sodium Alginate (SA) and a mixture of Silver (Ag) and Titanium oxide (TiO2) is suspended in the fluid. MethodologyThe nanoflow model is cracked numerically employing Runge-Kutta Fehlberg technique along with shooting method. Results of flow affecting parameters on the flow characteristic quantities and engineering quantities are portrayed and presented through graphs and tables. Key findingsHybrid Nanoflow momentum decreases with an increase in the Casson parameter due to the yield stress which quite helps in the controlled and complex shape printing on the garments. The temperature of the nanofluid increases with an increase in nonlinear radiation parameter. In the presence of Ag and TiO2 nanoparticles, the non-linear radiation parameter becomes essential for managing their intricate impact on heat transfer within the fabric. Practical relevanceImproved heat transfer can significantly reduce drying times, leading to increased productivity. More efficient heat transfer can reduce energy consumption. Reduced viscosity can allow for better penetration of fluids into fabrics, leading to more uniform dyeing and finishing. Casson hybrid nanofluids can accelerate the dyeing process and improve colour uniformity. Casson hybrid nanofluids can be used in finishing processes to enhance wrinkle resistance and improve fabric appearance.

Radiative heat transfer to enhance the performance of liquid metal-based phase change heat sink under natural convection condition

Liquid metal phase change materials have the advantages of high thermal conductivity and high volumetric latent heat, which are expected to address the growing challenges of thermal management of advanced electronics. In previous studies, the effect of radiative heat transfer from fins of a phase change heat sink on thermal management performance has rarely been considered. In this study, radiative coating materials with high emissivity were prepared and coated on the fins of the liquid metal phase change heat sink. The effect of radiative heat transfer on the performance of liquid metal phase change heat sink was investigated. The experimental results of continuous heating under natural convection conditions show that the introduction of the radiative coating with an emissivity of 0.9298 can extend the time for the surface temperature of the heat source to reach 100 °C by 9.4%, while shortening the recovery time of the phase change heat sink by 14.9%. The results of high-power cyclic heating indicate that the high emissivity coating can reduce the peak temperature by 16.6 °C in the tenth working cycle. A simplified numerical model was subsequently developed and validated to determine the specific effects of phase change and radiative heat transfer on the overall thermal control performance. The radiation-enhanced liquid metal phase change heat sink proposed in this study is simple and maintenance-free. It is expected to address the thermal management issues of electronic devices that cannot use active cooling or operate in thin-air environments.

Large eddy simulation investigation of the effect of radiative heat transfer on the ignition progress in a model combustor

Radiation significantly influences turbulent combustion. This paper investigates the impact of radiative heat transfer on the ignition process in a multi-staged model combustor. The ignition process is simulated both without and with consideration of radiation. Large Eddy Simulations based on the Euler-Lagrange description of the liquid spray and the Dynamic Thickened Flame model coupled with a skeletal chemical reaction mechanism are employed. The Weighted Sum of Gray Gases method are employed to solve the spectral properties and the Discrete Ordinates method is employed to solve the radiative transfer equation. The results indicate that radiative heat transfer influences the flame structure during the ignition process. In the flame propagation phase, both the total heat transfer and the exit average temperature are higher, with the radiative heat transfer during ignition being less than 15% of the total heat transfer. During the kernel generation phase, radiative heat transfer leads to a 7.24% increase in the maximum temperature of the flame kernel, a 7.74% expansion of the flame surface area, and outward movement of the position of the maximum heat release rate. Additionally, the ignition delay time extends by 14.91%. In the flame propagation phase, the flame transfers heat to the mixed gas and droplets near the flame surface through radiation, promoting flame spread.

Radiative Transfer in Finite Concentric Cylinders by the Zonal Monte Carlo Method

Solutions to two-dimensional radiative heat transfer in a finite concentric cylinder system with a gray absorbing/emitting medium are generated using the zonal Monte Carlo method. The concept of generic exchange factors is introduced. Based on these factors, solutions for finite concentric cylinders with different geometric configurations and optical thicknesses can be generated accurately and efficiently. Numerical data are presented to demonstrate the two-dimensional effects of radiative heat transfer in finite concentric cylinder systems.

Numerical prediction of the two-phase flow and radiation effects on the thermal environment and ablation of solid rocket nozzle

The effects of two-phase flow and radiative heat transfer have a significant impact on the internal thermal environment and thermochemical ablation process in aluminized solid rocket motor (SRM). However, these two effects were not revealed systematically in previous studies. In this paper, a multiscale methodology combined radiative properties of molten alumina particles at microscale calculated by Mie theory and the two-phase flow and radiative heat transfer at macroscale calculated by Eulerian-Lagrangian method coupling with discrete ordinate method is constructed within aluminized SRM. The convection and radiation are coupled with the chemical kinetics to predict the thermochemical ablation and thermal environment. The influence of two-phase fluid flow and thermal radiation on the internal thermal environment and thermochemical ablation of a SRM nozzle is analyzed quantitatively. Comparisons are made among the methodologies that models the alumina particles as gas species, considers the effect of two-phase flow and considers the effects of two-phase flow and radiative heat transfer. The results show that the erosion rate and total heat flux at the inner wall in the convergent section increase noticeably when considering the effect of two-phase flow. Meanwhile, the erosion rate in the divergent section also increases and the thermal environment is dependent on the particle size and aluminum content. Radiative heat transfer considerably enhances the total heat flux, especially in the convergent section. On the contrary, its impact on the erosion rate is very small except for the inner wall with very low temperature.

Investigation of the influence of the fuel element design parameter on the VVER-1000 reactor axial power peaking factor

The paper presents the results of a numerical study into the efficiency of the fuel element operation in the pressurized water reactor (VVER) core filled with uranium dioxide (UO2) pellets. The investigation results were obtained from a three-dimensional simulation of the fuel element power density. The dependencies of the fuel and fuel cladding temperatures on specific power per cubic meter of fuel are compared. Uranium metal and uranium dioxide have been studied as fuel. Engineering constraints on the safe operation of fuel assemblies have been selected as the determining parameters. The paper analyzes the extent of the radiation heat transfer effects on the fuel element specific power. Equations have been obtained that reflect the dependencies of specific power per cubic meter of fuel on the size of the fuel pellet hole diameter in the maximum heat flux conditions. The COMSOL Multiphysics code, a numerical thermophysical simulation package, was used for the study. Calculations show that an additional uranium-235 enrichment with an increase in the fuel pellet hole diameter at a fixed fuel thermal power leads to a reduced reactor axial temperature field peaking factor.

Investigation of Thermal Radiation, Atomization Air, and Fuel Temperature Effects on Liquid Fuel Combustion

Abstract The purpose of the present study is to investigate the effects of radiative heat transfer, atomization air temperature and mass flowrate, and fuel initial temperature on liquid diesel fuel (C16H34) combustion. Fuel is injected by an airblast atomizer inside a model cylindrical combustion chamber. Geometry of the airblast atomizer is modeled in detail so that its impacts on droplet breakup and flow formation are accurately considered. Evaporating fuel spray is simulated by the discrete phase model based on the Eulerian–Lagrangian approach. Turbulent viscosity is numerically computed by the realizable k–ɛ turbulence model while the discrete ordinates model and the steady flamelet model are applied for modeling the radiative heat transfer and combustion, respectively. NO species concentrations are achieved using post-processing. It turns out that neglecting thermal radiation in well-atomized spray combustion only affects high-temperature zones by increasing the axial temperature values of the mixture by almost 8%. Thermal radiation has an imperative effect on producing NO species. Without considering thermal radiation, axial NO concentration becomes almost doubled. Augmentation in mass flowrate and temperature values of atomization air enhances spray formation and combustion efficiency by increasing the evaporation rate. Changing the fuel temperature from 300 K to 325 K rises the total temperature at the end of the centerline of the model combustion chamber by 9.8%. It is shown that increasing the fuel’s initial temperature is not a suitable choice compared to enhancing the temperature and mass flowrate of the atomization air.

Effect of ternary hybrid nanoparticles (GO-MgO-TiO2) and radiative heat transfer on the solidification process of PCM inside a triplex tube with hollow fins

Nowadays, due to the features such as high latent heat and constant phase transition temperature, the utilization of phase change materials (PCMs) in energy storage and thermal management systems has attracted scholars' attention. However, the low thermal conductivity and solidification process of these materials has always been a challenge for widespread implementation of them in disparate industries. The current research investigates the characteristics of the PCM solidification process within a triplex tube Latent Heat Thermal Energy Storage System (LHTESS) with innovative hollow fins in the presence of ternary hybrid nanoparticles (THNPs) and radiative heat transfer. The governing equations are solved using Galerkin Finite Element Method (GFEM) with various boundary conditions in the outer wall, such as constant temperature, adiabatic, and coolant fluid temperature (triplex), through FlexPDE software. Furthermore, the effect of key parameters, including shape factor and volume fraction of THNPs, and radiative heat transfer on thermal storage performance is scrutinized. Ultimately, the Taguchi method is adopted to determine the optimal point at which the full solidification time (FST) is lowest. Results show that at 400000 s, the triplex case improved total discharging energy by 23% and 4% in comparison to the constant temperature and the adiabatic case, respectively. Additionally, by including THNPs with a volume percentage of 0.1 and a shape factor of 16.1 instead of 3, the required time for FTS reduces by approximately 13.1% and 21.9%, respectively. Also, the overall solidification times of the PCMs decrease to 36% by enhancing the radiation parameter from 0 to 1. These outcomes illustrate THNPs and considered fins are effective for reducing the FST and the shape factor of THNPs and radiation are key parameters that should be considered by designers.

Evaluation of radiative absorption effect to estimate mean radiant temperature in environments with high water vapor concentration such as in a sauna

The importance of modeling the radiative absorption in an environment with a high concentration of water vapor, such as inside a sauna, was studied through numerical analyses and fieldwork. Radiative heat transfer analysis using the discrete ordinate method (DOM) was performed using OpenFOAM software to evaluate the influence of thermal radiation inside a sauna. In a high-temperature environment, such as a sauna, the effect of radiation heat transfer in the surrounding medium gradually increases. Therefore, the effects of the medium cannot be ignored. A full-spectrum k-distribution (FSK) was adopted to model the radiative absorption of the medium, which was composed of carbon dioxide and water vapor. The mean radiant temperature (MRT) was also determined using numerical simulations to compare the results with those measured directly using a globe thermometer. The measured MRT was lower than the air temperature because of radiative cooling by the surroundings. To evaluate the quality of the radiative absorption model, the MRT obtained using the transparent gas and FSK methods were compared. When the distance from the cooling front window was approximately 4 m, the FSK method improved the prediction of MRT by approximately 1 °C when compared with the transparent gas method, which is the conventional method. The FSK method improved the MRT prediction from the conventional method by approximately 27% in terms of the Root Mean Square Error. This result indicates the importance of modeling the MRT by considering radiative absorption in the presence of high water vapor pressure.

Radiation-Induced Thermal Runaway Propagation in a Cylindrical Li-Ion Battery Pack: Non-Monotonicity, Chemical Kinetics, and Geometric Considerations

Li-ion batteries play a key role in energy storage and conversion in engineering systems such as electric vehicles and grid energy storage, with critical impact on electrification and storage of renewable energy. A key unresolved technological challenge in Li-ion batteries pertains to thermal runaway initiation and propagation in a battery pack, which can lead to subsequent fire and explosion. Despite significant past work, there remains a critical need to understand how thermal runaway propagates in a pack. This work presents a comprehensive investigation of the effect of radiative heat transfer on thermal runaway propagation. Radiation can be important when a battery is exposed to adjacent heat and fire sources, as well as in thermal runaway propagation from one hot cell to another. A theoretical radiative heat transfer model based on view factor theory is developed. Calculations based on this model for a simple 2D cylinder-to-cylinder geometry are found to be in very good agreement with analytical expressions. Radiation-induced thermal runaway propagation between two cylindrical 18650 batteries is evaluated. It is shown that radiation may play a key role in thermal runaway propagation, depending strongly on the triggering temperature. It is found that radiative effects in thermal runaway propagation exhibit both nonlinear and non-monotonic characteristics. At high temperatures, thermal runaway is triggered rapidly in the region close to the battery surface, where the chemical reactions are strongly coupled, and radiation plays a dominant role. In contrast, at lower temperatures, thermal runaway is triggered much more slowly and towards the core of the cell, where some chemical reactions may be decoupled, and pre-runaway chemical heat release plays an increasingly important role. The results presented here suggest that radiation can either facilitate or mitigate thermal runaway. The net radiation heat flux has a cross-over instant, beyond which radiation starts to retard thermal runaway. Additionally, the blocking effect in radiative heat transfer between cells arranged in equal-spacing homogenous or orthogonal arrangements in a battery pack is investigated, along with the effect of the hot spot size. Results from this work help understand the role of radiation in thermal runaway propagation and provide useful insights into the thermal runaway control and design of safe Li-ion battery packs.

Von Kármán viscous pump of rotating disk in a magnetized Maxwell fluid with Joule heating

The current investigation is concentrated on the constant MHD flow of an electrically charged Maxwell fluid across a radially elastic spinning disc in the presence of a uniform magnetic field. The problem is a generalization of the prevalent von Kármán viscous pump for configurations with or without a stretchy disc. The plane fluid content is controlled using an isothermal approach of homogeneous-heterogeneous processes. Non-linear thermally radiative heat transfer's effects on heat transference properties are investigated. Viscous dissipation and Joule heating are two other factors to consider in the energy equation. The von Kármár adaptations are used to build non-dimensional Navier-Stokes models, which are then, calculated using the bvp4c method. The torque, wall shear stresses, vertical pressure velocity, and heat transfer proportion are all determined. In addition, a statistical method is used to determine the connection between factors and the flow system's physical characteristics. Increasing the radiation parameter lowers the heat transmission rate at the disk's layer is a key finding. When homogeneous and heterogeneous reactants are reinforced at the same time, a significant observation is made that minimizes species concentration behaviors. Fluid flow caused by spinning discs is used in thermal transfer systems for nuclear propulsion devices.

Impact Assessment of Radiative Heat Transport in ARC-Class Reactor FLiBe Liquid Immersion Blanket

Molten salt systems have become of growing interest in the energy industry due to a wide range of applications (concentrated solar power systems, energy storage, Generation IV fission reactors, and high magnetic field fusion reactors). Because of the high temperature that characterizes such materials, radiative heat transfer (RHT) may become a nonnegligible heat transfer mechanism in molten salt components. In this paper, an investigation of FLiBe RHT has been conducted, with a focus on Affordable, Robust, Compact (ARC)–class fusion reactors, a preconceptual design proposed by Commonwealth Fusion Systems and the Plasma Science and Fusion Center. This class of reactors largely employs FLiBe molten salt due to its thermal and neutronic properties. The reactor is characterized by high temperatures, and its 0.5-m-thick liquid immersion blanket is a component where RHT contribution to the temperature distribution is yet to be evaluated. Therefore, this study is the first work that quantifies the contribution of RHT in ARC-class reactor FLiBe systems. FLiBe optical property spectral-banding assessment is carried out, and the impact of RHT in FLiBe systems is assessed in operational ARC-class scenarios through computational fluid dynamics models by taking advantage of COMSOL® Multiphysics. Heat transfer, thermal-dependent properties, and buoyancy effects are considered in a comparison between scenarios with and without RHT modeling. The flow field in the tank is unaffected by RHT effects, even when considering buoyancy effects. The external layer of the vacuum vessel shows an average decrease in the temperature of 5.4 K and an average decrease in temperature on the surface in contact with the FLiBe tank of 8.1 K. Results indicate that for ARC-class reactors, RHT phenomena are negligible (<1% increase in heat transfer) in operational conditions.

Prediction of carbon capture and sequestration (CCS) technology in a 125 MW tangentially coal-fired subcritical thermal power plant for retrofitting in Bangladesh

The main objective of this study is to assess the use of carbon capturing and sequestration (CCS) technology in the existing plant to reduce the emissions leading to retrofitting. A typical 125 MW tangentially coal-fired Barapukuria Thermal Power Plant (BTPP), Bangladesh has been scrutitinized considering air-firing (existing) and five different oxy-firing (OF) cases have been numerically investigated. For predicting the particle flow, radiative heat transfer and turbulence effects, discrete droplet method (DDM), discrete transfer radiation method (DTRM) and k–ϵ model is considered respectively. For homogeneous reaction for the devolatilization and heterogeneous reactions for the char oxidation process, a two steps reaction mechanism is considered. Model has been validated by comparing the predicted flue gas temperature against the plant data at different positions of the furnace and reasonable agreement have been observed. This study assessed the flow characteristics, thermal behavior and species generations of the selected plant under 80% fuel loading. It is predicted that with the increase of cases from air-firing, level of oxiding elements are increasing in the main combustion zone due to enriched O2 level leading to complete combustion of the particles. It is also found that for OF 31 case, level of CO2 is close to the air-firing case. it has been found that wall temperature is comparatively higher for 100% loading and comparatively lower for 50% loading for almost all similar type of air or oxy-firing conditions. For 100% load, the wall temperature has been reached around 2900 K for OF31 case. It is predicted that air operation equivalent to oxy-firing have been found at < OF 30+ % (Flame temp), at = OF 30+ % (Convec Heat transfer) and at > OF 30+ % (radiative Heat transfer) respectively.

Combined numerical approach for the evaluation of the energy efficiency and economic investment of building external insulation technologies

The objective of this paper is to examine the energy efficiency and economic feasibility of different coating technologies used to improve the thermal insulation of external walls in buildings. The comparison is made between traditional coat insulation and ventilated façade, evaluating their impact on energy consumption to maintain a constant indoor temperature throughout the year by means of a combined numerical approach. . Furthermore, the paper investigates the effect of opening and closing the air gap in ventilated façades on thermal insulation during the winter and summer seasons. Energy efficiency calculations are employed to estimate the economic investment required for implementing the different insulation solutions.The paper proposes an innovative combined approach to determine the performance of the building insulation technologies. Firstly, a computational fluid dynamics (CFD) simulation is carried out on the full three-dimensional geometry of the building during two reference days representing extreme temperature and sun radiation conditions during the summer and winter. This modeling includes the effects of solar radiative heat transfer during the day: for a chosen date, time, and geographical location, the model computes sun altitude and azimuthal angles, along with the corresponding direct and diffuse solar fluxes. In addition, the model uses a multiband thermal radiation approach to capture the different nature of radiative heat exchange according to the light wavelengths. The total heat transfer coefficient of the building walls in each scenario is calculated through the computational fluid dynamic analysis and implemented in an in-house developed library based on the open source Open-Modelica platform to simulate the energy requirement of the building throughout the year. This combined numerical approach provides a comprehensive performance analysis of the studied technologies in terms of electric energy and fuel consumption required for maintaining a constant indoor temperature and internal ambient comfort.The results of the simulations demonstrate that by adopting the two proposed solutions, there was a potential to save approximately 37% of the fuel required for the heating system and more than 51% of electric energy required for the air conditioning systems. Finally, the payback period for each scenario is calculated, and it was found that coat insulation offers the best balance between thermal performance improvement and economic effort, with a payback time close to 20 years.

Multi-physics modeling for laser powder bed fusion process of NiTi shape memory alloy

Due to its excellent shape memory effect and super elasticity, NiTi Shape Memory Alloy (NiTi SMA) has broad application prospects in aerospace, ship, biomedicine and other fields. Laser powder bed fusion (L-PFB) has proven to be a feasible way to fabricate NiTi with a complex and precise structure. In this study, a 3D transient multi-physics model based on the computational fluid dynamics (CFD) model is proposed, which incorporates the effects of convective heat transfer and radiation heat transfer on the forming quality of parts and mechanical models such as thermal buoyancy. The temperature field and stress field distribution during the L-PBF forming process of NiTi alloy were studied by using this multi-physics model. Furthermore, the influence of different process parameters on the shape of the molten pool was analyzed, and a nonlinear regression equation was proposed to predict the size of the molten pool. The proposed model is verified by experimental results with a prediction error of 3 %−8 %. Both numerical and experimental results demonstrate that under the process parameters of P= 125 W and V= 500 mm/s, the shape of the molten pool is stable and the NiTi single track is continuous. This work illustrates the reliability of the established simulation method and provides a timesaving approach to optimize the L-PFB process parameters of nickel-titanium alloy.

Numerical investigation of combined effects of radiation and convection heat transfer from tube banks placed in a participating medium

In the present study, combined convective and radiative heat transfer from in-line tube banks placed in an absorbing, emitting and isotropically scattering participating medium was numerically investigated. The governing flow and radiative transfer equations were solved numerically by utilizing the finite volume methodology and the P1 approximation. The flow is laminar, and the tube walls are black and isothermal. The parameters affecting the heat transfer in such media are the tube pitch, scattering albedo, Reynolds number and conduction-to-radiation parameter. Numerical simulations were carried out for Reynolds numbers between 100 and 300, and the transversal and longitudinal pitches ranging from 1.5D to 3-D, respectively. Also, the medium related parameters such as scattering albedo and conduction-to-radiation parameter were ranged between 0 to 1 and 0.0367 to 0.5080, respectively. The effects of the change in scattering albedo, conduction-to-radiation parameter as well as flow characteristic and tube pitch on temperature distribution and heat transfer were examined. The convective and radiative heat transfer from tubes is analyzed via the surface averaged mean Nusselt number over the whole tube wall. The lowest and the highest total-radiative Nusselt number values were achieved as 3.66-0.091 in the purely scattering medium and as 32.95-25.14 in the non-scattering medium, respectively. Also, a novel correlation (with a coefficient of determination of 0.99804) for tube banks subjected to convection and radiation in a participating media was developed.

Entropy Generation and Regression Analysis of Magnetohydrodynamic Stagnation Point Flow of a Casson Fluid with Radiative and Dissipative Heat Transfer and Hall Effects

The phenomenon of heat transfer is prevalent in industries and has an extensive range of applications. However, mostly the discussion of heat transfer problems is limited to the study of the first law of thermodynamics, which deals with energy conservation. It is just restricted to the quantity of energy, not to its quality; i.e., there is no difference between the work (high‐grade energy) and the heat (low‐grade energy). A measurement of the degree of randomness of energy in a system is known as entropy. It is unavailable for doing useful work because work takes place only from ordered molecular motion. Even though many boundary layer models exist in the literature to investigate the flow and heat transfer of various fluids along a stretching surface, they have not yet been used at their maximum ability. The main motive of the current research is to discuss entropy generation or its minimization during heat transfer. This work presents an entropy generation analysis for the transient three‐dimensional stagnation point flow of a hydromagnetic Casson fluid flowing over a stretching surface in the existence of Hall current, viscous dissipation, and nonlinear radiation. The physical configuration of the present work is described in terms of partial differential equations (PDEs) of nonlinear nature. Furthermore, these PDEs are converted into ordinary differential equations by using some relevant similarity transformations. An efficient numerical method named as the spectral quasilinearization method (SQLM) is used to solve this model. The expression of the Bejan number and volumetric entropy generation rate is also computed. A parametric analysis, including the essential physical parameters, is performed to examine the influences of distinct flow parameters on the velocity profile, temperature profile, Bejan number, entropy generation number, and the coefficients of skin friction and the Nusselt number. In order to further insight into the emerging physical quantities of engineering interest, multiple quadratic regression models are used to estimate the coefficients of skin friction and heat transfer.

CFD investigation of the radiative heat transfer effects on the adoption of an electrical heated catalyst to increase the abatement efficiency

The thermal transient of the after-treatment system (ATS) during the cold start and the typical urban drive low load engine operations is a crucial point for the conversion efficiency. In this context, the adoption of electrical heating is regarded as an effective solution to promote the catalytic activity and the pollutants abatement. This paper focuses on the evaluation of the radiative heat transfer affecting the operation of an electrical heated catalyst employed to increase the abatement efficiency of a standard catalyst. The modeling methodology relies on a CFD framework based on a Conjugate Heat Transfer (CHT) approach in OpenFOAM, so that a detailed characterization of the thermal transient of the different components of the exhaust line can be achieved. The electrical heating device under investigation is based on a metallic support and it is heated by the Joule effect. The distribution of the heat and its subsequent interaction with the gas flow significantly influence the catalyst operations. In this context, the CFD modeling framework has been further developed so that it is possible to accurately evaluate the radiative heat transfer in correspondence of the porous regions. The description of such features is mandatory for an accurate prediction of the maximum electrical heating device temperatures, resulting in a reliable estimation of the gas flow temperature and its subsequent interaction with the catalyst. The simulation methodology has been applied at first excluding the radiative heat transfer. Then, the developed radiation modeling is applied, so that its influence on the ATS performance can be fully evaluated.

Study of combined effect of natural convection and radiation heat transfer from annular finned vertical cylinder

AbstractThe present numerical study reports the combined effect of natural convection and radiation heat from a vertical cylinder with annular fins. The study involves simulation for laminar as well as turbulent regimes. For the present study, Rayleigh's number is varied in the range , emissivity in the range , and the fin spacing ratio (s/d) in the range . The radiation heat transfer has been found to share a considerable amount in the total heat transfer of the system for the laminar regime, but in the turbulent regime, its effect is minimal and can be neglected. When the fin spacing ratio is reduced, the total heat transfer increases for both the turbulent and laminar flow conditions. But the radiation heat increases with a reduction in fin spacing ratio for laminar and in case of turbulent flow radiation heat rate reduces with a reduction in s/d ratio. For the range of Rayleigh numbers considered in the present study, the Nusselt number increases with the increment of the fin spacing ratio. Thus, it can be concluded that there is a remarkable enhancement in the heat transfer rate in laminar cases with the fins. For turbulent cases, the fin efficiency lies between 40% and 50%.

Evaluation of Radiative Heat-Transfer Effect on Paraffin-Wax Regression Rate in Hybrid Rocket

A numerical setup has been developed to rebuild the axial profile and time history of the regression rate of a paraffin-wax-based fuel in a hybrid rocket, with the main target of investigating the effect of the local radiative heat transfer from both the combustion gas molecules and soot particles. The numerical approach is based on a quasi-one-dimensional computational fluid dynamic strategy, which is coupled with chemical equilibrium combustion; the vaporization and entrainment components of the wax-fuel regression rate have been estimated with an established liquefying-fuel model. The increase of the convective heat-transfer blocking due to radiation and the effect of recirculation flow due to oxidizer injection have been introduced. Numerical results are compared with experimental data. When radiative heat transfer, blocking-effect correction, and recirculation flow effect are taken into account, the calculated and measured fuel regression rates agree well in both values and axial profiles.