Radiative Heat Transfer Characteristics Research Articles

FRACTAL FRACTIONAL MODEL OF RADIATIVE HEAT AND MASS TRANSFER CHARACTERISTICS OF TIME DEPENDENT FLOW WITH VARIABLE VISCOSITY, INDUCED MAGNETIC FIELD, DUFOUR AND SORET EFFECTS: AN ENTROPY GENERATION

: In this article, the Caputo Fabrizio fractal fractional order derivatives operator with an exponential kernel was employed to examine the radiative heat and mass transfer characteristics of time dependent flow with variable fluid viscosity, induced magnetic field, Soret and Dufour effects. The local mathematical model for the flow problem is formulated by take into account the impacts of thermal radiation, heat source, and viscous dissipation. The governing equations in-terms of fractal fractional model with an exponential kernel were solved numerically using finite difference method. The influence of flow variables such as induced magnetic field, concentration field, entropy rate, thermal field, and velocity field profiles against the pertinent parameters are discussed through graphs. Increase the values of magnetic Prandtl number results to rises of induced magnetic field. Higher Dufour number significantly grows the thermal field. The fractal fractional parameters enhance the velocity field, thermal field, Bejan number, entropy rate, concentration field and induced magnetic field profiles. The velocity field profiles recede with higher values of fluid variable viscosity parameter whereas the thermal field and induced magnetic field has an opposite effect. Larger Soret number amplifies the concentration field. Increase of Brinkman number, thermal radiation parameter, and magnetic Prandtl number intensifies the entropy generation rate. Increases of Brinkman number, magnetic Prandtl number, Soret number and Dufour number leads to a decrease of Bejan number whereas Bejan number rises with an increase of thermal radiation parameter and heat source

Radiative MHD Boundary Layer Flow and Heat Transfer Characteristics of Fe-Casson Base Nanofluid over Stretching/Shrinking Surface

In this paper, there is considered MHD boundary layer flow and heat transfer characteristics of Fe-Casson base nanofluid over an exponentially stretching/shrinking surface along the heat source/sink and Newtonian heating effects. In this regard, to develop the system of the governing equations, the one phase model named as Tiwari and Das model is considered with iron nanoparticles. The non-linear governing PDEs are first changed into the system of ODEs using suitable similarity transformations. Later on, the equations are solved numerically by using bvp4c in Matlab software. Effects of certain physical parameters on skin friction coefficient and the local Nusselt number are illustrated graphically. Moreover, the velocity and temperature profiles are examined to observe the influence of various physical parameters such as, Casson, magnetic, suction, radiation, Newtonian heating, heat source/sink and the nanoparticles volume fractions. It is seen that an increase in Casson, magnetic, suction and the nanoparticle volume fractions decrease the velocity profiles for both shrinking and shrinking cases of surface. The temperature profile recedes due to augmentation of Prandlt number and the suction parameter for both stretching/shrinking case while increases with increase in Magnetic, radiation and nanoparticles volume fractions.

Topological phase-dependent thermalization dynamics in radiative heat transfer: insights from a one-dimensional Su-Schrieffer-Heeger model.

Various unusual behavior of artificial materials is governed by their topological properties, among these, the edge state in classical and quantum wave systems has captured significant attention due to its widespread relevance and applications across various fields of study. Observation of such topological features has led researchers to extend the idea of band theory to diffusive systems. Inspired by the well-known Su-Schriefer-Heegar (SSH) model we employed the concept of band topology to explore the topological characteristics of radiative heat transfer in a one-dimensional chain consisting of an odd number of nanoparticles. We demonstrate the topological phase transition, and topological modes with edge as well as bulk states in an array of nanoparticles exchanging heat via radiation. The demonstrated topological features of radiative systems can find important applications in the future studies of heat transfer at the nanoscale.

A novel approach based on equivalent sky radiative temperature for quick computation of radiative cooling in building energy simulation

Passive radiative cooling materials (RCM) can cool surfaces by radiating heat to outer space via long-wave radiation. In simulation application, co-simulation of the thermal process between RCMs and building structures is generally required; however, the high computing time cost and low integration level have hindered the integrated whole-building simulation in architectural design. Traditional building energy simulations utilize the effective sky temperature to numerically approximate the effect of sky radiation. However, given the limitations of effective sky temperature concept, it is more suitable to evaluate diffusive gray surfaces while not fully capturing the characteristics of radiative heat transfer for spectrum-selective surfaces. In this study, an innovative equivalent-sky-radiative temperature was introduced as a new equivalent parameter to accurately simulate the thermal performance of RCMs in buildings. Embedding this new parameter into whole-building energy simulation tools such as EnergyPlus and DeST is expected to significantly improve the calculation accuracy and reduce the computational cost. Case studies in this work have shown an average error of 5.47 W/m2. The generation of the new parameter for 50 cities worldwide also demonstrated the technical feasibility of applying the equivalent-sky-radiative temperatures to evaluate the thermal performance and energy savings of real-world RCMs in buildings.

New coefficients of the weighted-sum-of-gray-gases model for gas radiation characteristics of hydrogen/natural gas blends combustion

To achieve carbon neutrality, hydrogen/natural gas blends are gaining momentum as a clean low-carbon fuel for the future. In order to accurately carry out the CFD numerical simulation of hydrogen/natural gas blends combustion, it is imperative to establish a precise model for gas radiation characteristics. The existing weighted-sum-of-gray-gases model (WSGGM) is not suitable for high hydrogen content fuels, such as hydrogen/natural gas blends. Hence, new coefficients of WSGGM is formulated specifically for the combustion of hydrogen/natural gas blends, drawing upon the groundwork established by the statistical narrow-band model (SNB model). This model is specifically designed to be applicable within the ambient pressures, encompassing the temperature regime of 400–2500 K, a path-length range of 0.001–60 m, and a hydrogen blending ratio of 20%–70%. The radiative heat transfer characteristics of the sum of the molar fraction of H2O and CO2 at 0.9, 0.6, and 0.3 were studied according to application conditions. The WSGGM is implemented to compute the radiative heat transfer in non-isothermal and non-homogeneous gas mixtures. When compared to the benchmark model, the deviation of the wall heat flux does not surpass 5.20%. The results demonstrate the excellent adaptability of the WSGG coefficients in simulating the radiative heat transfer during hydrogen/natural gas blends combustion.

A Review of Radiative Heat Transfer in Fixed-Bed Particle Solar Receivers

A highly efficient receiver is required because re-radiation loss increases dramatically with increased working temperature. Among a large number of receivers, the fixed-bed Particle Solar Receiver (PSR) represents a new pathway to high temperature with maximum overall thermal efficiency. The incoming solar radiation can penetrate deeper into the fixed-bed PSR filled with semi-transparent quartz and ceramic particles (spheres or Raschig rings), resulting in an increased volumetric effect. Reports show that an optimized PSR can realize overall receiver efficiency of around 92% at outlet temperatures above 1000 K, and achieve the annual temperature above 1000 K over 65% annual operating hours integrated with a concentrated solar power (CSP) system. To fully understand radiative heat transfer characteristics and provide deep insight into thermal efficiency, radiation energy is classified as incident solar radiation and radiative heat exchange in two parts. The transfer mechanism, the solution method and the progress of the investigation for each section are summarized and discussed in detail. Then, challenges and future directions, including an innovative design method, an improved experimental approach and an effective simulation method are proposed to put forward this receiver to be a preferred substitute in advanced, high-temperature power cycles.

Numerical study of the geometrical dimensions for glass curtain wall with an enclosed rectangular cavity

ABSTRACT To gain further insight into the thermal performance of a glass curtain wall with an enclosed rectangular cavity, a 2D mathematical model was established to analyze the characteristics of radiation and convective heat transfer in the glass curtain wall with an enclosed rectangular cavity, as well as to evaluate the effect of the glass curtain wall structure on thermal performance. The results showed that the total heat flux of the glass curtain wall with an enclosed rectangular cavity decreased at a decreasing rate with the increase in emissivity of glass. The total heat flux of the glass curtain wall with an enclosed rectangular cavity decreased with the increasing height of the enclosed rectangular cavity. At 15 mm thickness of the glass curtain wall, the total heat flux reached its minimum value and then increased with further thickeness of the enclosed rectangular cavity. In addition, the least square method was used to obtain the Nu correlation of argon with a relative deviation of less than 12% for better predicting the flow and heat transfer characteristics of argon in the glass curtain wall.

Epsilon-near-zero characteristics of near-field radiative heat transfer between α-MoO3 slabs.

Epsilon-near-zero (ENZ) materials, which manifest a wealth of exotic optical characteristics, have attracted significant research interest in recent years. However, these characteristics have rarely been considered in the study of near-field radiative heat transfer (NFRHT). In this work, we investigated the ENZ characteristics of the NFRHT between two symmetric biaxial α-MoO3 slabs. The numerical results show that the NFRHT is greatly enhanced around the ENZ frequency of 1.604 × 1014 rad s-1. Notably, near the other two ENZ frequencies (1.832 × 1014 rad s-1 and 1.891 × 1014 rad s-1), only the NFRHT between α-MoO3 slabs of certain thicknesses is enhanced. The reasons can be explained by the fact that the VHPs can be excited in almost all azimuthal angles at angular frequencies of 1.604 × 1014 rad s-1 and 1.891 × 1014 rad s-1. For the ENZ frequency of 1.832 × 1014 rad s-1, the VHPs can be excited at the top and bottom, while the SHPs excited at the left and right sides. It is worth noting that both the hyperbolic and ENZ characteristics affect the NFRHT between α-MoO3 slabs. Moreover, the excitation is strongly dependent on the thickness of the slab. Our findings contribute to understanding the physical mechanisms underlying the characteristics of the NFRHT at ENZ frequencies.

Natural Convection and Radiative Heat Transfer From Constant Surface Area Vertical Helical Coils: Effect of Pitch and Height

Abstract In this work, numerical simulations are carried out to delineate the natural convection and surface radiation heat transfer characteristics of vertically oriented isothermal helical coils having a constant surface area. Numerical computations using the finite-volume method are carried out in the laminar regime for the following non-dimensional parameter ranges: Rayleigh number (104 ≤ Ra ≤ 108), surface emissivity of the coil (0 ≤ ɛ ≤ 1), pitch to the rod-diameter of the coil (3 ≤ p/d ≤ 7.5), and coil-height to the rod-diameter (40 ≤ H/d ≤ 60). Temperature-dependent fluid properties have been implemented to obtain accurate results. The impact of Ra and ɛ on both convective and radiative heat losses is discussed in detail. At a high Ra of 108, when H/d varies from 40 to 60, the mass flowrate inducted through the coil reduces from 40.6% at p/d = 3 to 11.4% at p/d = 7.5. As a result, the relative strength of convection heat loss declines with a rise in H/d. For a higher emissivity of the coil surface of 0.9 and a lower Ra of 104, heat transfer by convection contributes only 12.66% of the total heat transfer. In contrast, the contribution of radiative heat transfer is only 7.46% for a lower emissivity of the coil surface of 0.1 and a higher Ra of 108.

Numerical investigation on radiative and evaporative characteristics of a liquid droplet radiator through Monte-Carlo method

The liquid droplet radiator (LDR), a frameless heat dissipation device, is regarded as a preferred heat control solution for megawatt-scale space power systems. Accurate calculation of evaporation loss in the droplet layer is important for LDR systems since it determines the operating life of the LDR. In the present work, a novel model based on the Monte-Carlo Method (MCM) was developed to calculate the evaporation loss of the droplet layer. Compared to previous work in the literature, this model considers the evaporation loss of the droplet layer in the thickness and length directions. The radiative heat transfer characteristics of the droplet layer are also studied. The effects of optical thickness, operation temperature, and flight time on the droplet layer's heat transfer and evaporation processes were obtained and analyzed. The calculation results show that the temperature difference between the center and the edge of the droplet layer is larger than 65 K when the optical thickness is greater than 5. The heat dissipation power no longer varies significantly when the optical thickness of the droplet layer is greater than 6. The region with a negative specific evaporation loss rate accounts for 55.2 %, 58.2 %, and 0 for the whole droplet layer with optical thicknesses of 10, 5, and 0.2, respectively. The main evaporative loss comes from the beginning 5 m of the droplet layer. This paper may provide favorable reference to the design and optimization of the LDR systems.

Numerical simulation of the thermal radiation and convective heat transfer characteristics of the second superheater in a coal-fired thermal power plant boiler

Superheaters are critical components in a coal-fired power plant because they sustain the highest tube wall (metal) temperature point in the boiler. The pressurized steam flowing in superheater tubes is mainly heated via the thermal radiation and convection from the combustion gas in the radiant zone. To prevent the bursting of superheater tubes caused by the high-temperature creep, corrosion, and thermal fatigue for proper plant operation and maintenance, accurately predicting complex heat transfer characteristics, estimating the local temperature, and assessing the heat flux of the superheater are essential. In this study, a computational fluid dynamics model of the boiler and the superheater in a coal-fired power plant was developed using radiation and turbulence models. The local metal temperature and heat flux of the superheater were evaluated by calculating the heat exchange between the combustion gas and pressurized steam flows in the tubes. The calculated values of the steam outlet temperature accurately matched the values measured using the equipment at the plant, and thermal radiation was confirmed to be dominant in the boiler. The metal temperature and heat flux of the superheater at the outermost heat transfer tubes, which receive the maximum thermal radiation, were larger than those of the superheater at the inner tubes. Therefore, the outermost tubes were determined to be under the most severe thermal conditions despite having a higher mass flow rate of steam. Additionally, the heat fluxes on the center lines of superheater tube panels were higher due to the large gap between the adjacent heat transfer tubes at the bent part.

Errata: Numerical simulation of the thermal radiation and convective heat transfer characteristics of the second superheater in a coal-fired thermal power plant boiler [Mechanical Engineering Journal, Vol. 9, No. 4 (2022), 22-00040

Errata: Numerical simulation of the thermal radiation and convective heat transfer characteristics of the second superheater in a coal-fired thermal power plant boiler [Mechanical Engineering Journal, Vol. 9, No. 4 (2022), 22-00040

Experimental and Theoretical Research on the Radiative Heat Transfer Characteristics of Transformer Oil Jet Flame

ABSTRACT In this paper, a series of transformer oil jet fire experiments with different tanks of inner diameters (0.05 m/0.08 m/0.1 m), different filling rate (80%/100%) and different pool diameters (0.3 m/0.4 m) were carried out to study the radiation characteristics of transformer oil jet fire. The flame combustion characteristics such as the fire plume temperature, mass loss and radiant heat flux were measured and analyzed. The experimental results showed that: The shape of the transformer oil jet fire was approximately cylindrical. The radiant heat flux increased exponentially with the increased of flame height. And radiant heat flux decreased exponentially as the horizontal distance increased. The multi-point source model and the line source model performed well in the prediction of the fire radiant heat flux of the transformer oil jet. As the Froude number increased, the radiation fraction change could be divided into two stages. In the first stage, the radiation fraction maintained almost constant. In the second stage, the radiation fraction dropped significantly. The research results provided valuable data support for the fire protection design of substation equipment. In addition, it could effectively improve the fire prevention and control ability of substation personnel.

Theoretical and numerical investigation of heat transfer characteristics of an integrated cookstove under different atmospheric pressures based on theoretical models of solid flame and impingement heat transfer

At present, the problems of the efficient use of energy and heat transfer characteristics of the stoves on plateaus have attracted much attention. In this work, a three-dimensional numerical calculation and theoretical analysis model of impact flame heat transfer was established for the integrated cookstoves widely used in China and verified with the experimental thermal efficiency value. It was found that, with decreased atmospheric pressure, the combustion intensity in the furnace decreases, the flame combustion temperature significantly decreases, the heat transfer rate of the stove decreases, and the total thermal efficiency decreases by 7.5% under pressure of 0.05 MPa compared with normal pressure. By using jet impinged and solid flame models, a heat transfer mathematical model suitable for the inner wok and water jacket of the integrated stove was established. The heat transfer error between theoretical calculation and three-dimensional numerical calculation was no more than 6%. In addition, some methods are proposed to improve the thermal efficiency of integrated stoves under a high-altitude and low-pressure environment. This study not only theoretically reveals the change law of heat transfer characteristics of convective shock and flame radiation heat transfer under low pressure but also has constructive theoretical guiding significance for the improvement of thermal efficiency of highland stoves.

Non-Gray Radiative Heat Transfer in Two-Dimensional Cylindrical System

Radiative heat transfer in a concentric cylinder system with a participating medium is demonstrated to be inherently two-dimensional, even for the consideration of heat transfer to the total inner or outer surface with uniform boundary conditions. For the evaluation of two-dimensional nongray radiative heat transfer, the zonal exchange factor, together with the concept of point mean beam length, is shown to be an effective solution approach. Optimal point mean beam length for radiative heat transfer between a differential area and a finite area with different geometrical configurations within the concentric cylindrical enclosure is generated. Numerical data for an example calculation is presented to illustrate the characteristics of nongray two-dimensional radiative heat transfer.

Study on Spectral Radiative Heat Transfer Characteristics of a Windowed Receiver with Particle Curtain

In this paper, a windowed receiver with a particle curtain is numerically simulated under full-spectrum conditions. The discrete phase model (DPM) is used to model the particle flow and interactions between the particle phase and the air phase. The scattering, absorption of the particle curtain and quartz glass window are considered in detail. The spectral characteristics of glass have an important influence on the heat transfer characteristics and the receiver efficiency. The results show that the quartz window can reduce the convective heat loss and the cavity re-radiation heat loss. Under the same conditions, the receiver efficiency of a windowed receiver with a particle curtain is increased by 11.9% compared with an aerowindow receiver with a particle curtain. Under the same mass flow, the particle curtain thickness and particle size have a non-negligible influence on the flow pattern and temperature distribution of the particle curtain. When the particle curtain thickness is low, the flow stability of the particle curtain is high; as the particle curtain thickness increases, the volume fraction of the particle curtain decreases, and the flow stability of the particle curtain decreases, which affects the shape of the curtain. The scattering and absorption characteristics of the particles are different, resulting in different net fluxes of incident radiation under the reflection of the particle curtain and the back wall. As the particle curtain thickness increases, the particle average exit temperature and the receiver efficiency show a trend of first increasing and then decreasing. When d = 30 mm, the incident radiation (G) at the position of the particle curtain is larger, the particle average exit temperature reaches 1156.72 K, and the receiver efficiency reaches 74.4%. Therefore, different particle sizes also have a significant impact on the flow pattern of the particle curtain and the radiation distribution inside it. In the range of 250–750 μm particle size, the particles average exit temperature reaches above 1150 K, and the receiver efficiency is above 72.6%. As the particle size increases, the particle average exit temperature, and the receiver efficiency show a trend of first decreasing and then increasing. When the particle size is 500 mm, the particle average exit temperature reaches 1175.8 K, and the receiver efficiency reaches 79.4%.

Operation performance analysis of a liquid metal droplet radiator for space nuclear reactor

Liquid droplet radiator (LDR) is the frameless space radiator designed for heat dissipation of large-power space nuclear reactors. This paper analyzes the radiative heat transfer and evaporative characteristics of liquid metals adopted in LDR including lithium, aluminum and tin. Firstly, the cooling process of different working fluids is simulated and the temperature distribution at the droplet collector is obtained. The radiant energy of per unit mass fluid with different optical thicknesses and temperatures is calculated. Secondly, the evaporative characteristics of the working fluid are studied. Finally, the system operation performances are evaluated including the system life and radiant energy with different optical thicknesses and temperatures. Results show that liquid lithium is appropriate for heat dissipation system working under 600 K, while liquid aluminum and tin are more appropriate for working under 1200 K and 1500 K, respectively. This work provides the theoretical support for liquid droplet radiator thermal design.

Study on heat transfer characteristics of liquid droplet radiator: With VS without inter-droplets coupling

Liquid droplet radiator (LDR) is a promising cooling system for the high-power spacecraft. The study of the droplet radiation heat transfer mechanism is vitally important for the optimal design of the whole LDR system. Firstly, the radiation heat transfer characteristics of the isolated droplet are analyzed. Then, the Monte Carlo method is used to calculate the angel factor for multiple droplets interacting with each other. Finally, the radiation heat transfer characteristics of the LDR are numerically simulated by the angular coefficient matrix. For two identical droplets, when the ratio of the distance to the radius is greater than 3, the temperature changes of the interacting droplets are the same as the isolated droplets. In addition, the results reveals that tin is the most suitable working fluid for the LDR. These conclusions can lay basis for the optimal design of the LDR and provide guidance for the subsequent research about LDR.

Parametric investigation of radiation heat transfer and evaporation characteristics of a liquid droplet radiator

The liquid droplet radiator (LDR) as a frameless heat removal system is considered as a promising solution for the waste heat dissipation of megawatt aerospace applications. The radiation heat transfer and evaporation characteristics of the LDR working fluid are tightly coupled with the operational performance of the liquid droplet generator. In this paper, the effects of operational parameters of droplet generator on the radiative heat transfer and evaporation loss rate are clarified, including the pressure disturbance frequency, pressure difference between the inside and outside of the droplet generator. It is observed that higher coolant mass flow rate does not assure higher heat transfer power for the LDR. For cases with higher pressure difference, where the coolant flow rate is higher consequently, the evaporation loss rate increases continually with pressure difference while the heat transfer power does not increase any more. The disturbance frequency has inconspicuous impact on the evaporation characteristics. Besides, cases with higher pressure differences have wider suitable frequency ranges according to the droplet formation restriction. Generally, a relatively higher pressure difference coupled with a higher disturbance frequency (such as 0.3 MPa and 12 kHz) is suggested to achieve a higher heat transfer power and low evaporation loss rate. This paper may provide favorable reference for determining the operational parameters of the droplet generator in consideration of radiation heat transfer and evaporation characteristics.

Numerical Study of Convective and Radiation Heat Transfer Characteristics in an Upward-Facing Cylindrical Cavity under Back-Side Windy Condition

Under the back-side windy condition, the convection and radiation heat transfer characteristics in an iso-flux upward-facing cylindrical cavity were studied by three-dimensional numerical simulation. The impacts of cavity tilt angle, wind incident angle and wind speed on convection and radiation heat transfer Nusselt number Nuc and Nur were analyzed, and the possible explanations for their impacts were presented. Results show that due to the disturbance of wind, the influence of cavity tilt angle becomes more complicated and is related to wind incident angle and wind speed. The variation of Nuc or Nur with wind incident angle is different for different cavity tilt angles. Despite of the changes of cavity tilt angle or wind incident angle, the Nuc increases with the wind speed while the Nur presents a declination with the increasing of wind speed. Hence, compared with cavity tilt angle and wind incident angle, wind speed may be the dominant factor affecting or controlling the convective and radiation heat transfer of cavity.