Effect Of Surface Radiation Research Articles

Investigation of transient conduction–radiation heat transfer in a square cavity using combination of LBM and FVM

In this paper, the effect of surface radiation in a square cavity containing an absorbing, emitting and scattering medium with four heated boundaries is investigated, numerically. Lattice Boltzmann method (LBM) is used to solve the energy equation of a transient conduction–radiation heat transfer problem and the radiative heat transfer equation is solved using finite-volume method (FVM). In this work, two different heat flux boundary conditions are considered for the east wall: a uniform and a sinusoidally varying heat flux profile. The results show that as the value of conduction–radiation decreases, the dimensionless temperature in the medium increases. Also, it is clarified that, for an arbitrary value of the conduction–radiation parameter, the temperature decreases with decreasing scattering albedo. It is observed that when the boundaries reflect more, a higher temperature is achieved in the medium and on boundaries.

Influence of the shape, thermal radiation, and variable properties on the turbulent buoyancy-driven airflow inside cavities with Trombe wall geometry

ABSTRACTThe effects of the radiative heat transfer and the influence of air variable properties on the natural convection flows in cavities with Trombe wall geometry are numerically investigated. The influence of considering surface-radiative effects on the differences reached for the Nusselt number and the mass flow rate obtained with several heating intensities is studied. The effects of the shape change consisting of varying slope angle of the heated wall is also analyzed. The influence of the thermal radiation on the appearance of the burnout phenomenon becomes particularly relevant. Important changes in the thermal and dynamic flow patterns are observed for high enough values of the wall slope angle.

Impacts of absorbing aerosol deposition on snowpack and hydrologic cycle in the Rocky Mountain region based on variable-resolution CESM (VR-CESM) simulations

Abstract. The deposition of light-absorbing aerosols (LAAs), such as black carbon (BC) and dust, onto snow cover has been suggested to reduce the snow albedo and modulate the snowpack and consequent hydrologic cycle. In this study we use the variable-resolution Community Earth System Model (VR-CESM) with a regionally refined high-resolution (0.125°) grid to quantify the impacts of LAAs in snow in the Rocky Mountain region during the period 1981–2005. We first evaluate the model simulation of LAA concentrations both near the surface and in snow and then investigate the snowpack and runoff changes induced by LAAs in snow. The model simulates similar magnitudes of near-surface atmospheric dust concentrations as observations in the Rocky Mountain region. Although the model underestimates near-surface atmospheric BC concentrations, the model overestimates BC-in-snow concentrations by 35 % on average. The regional mean surface radiative effect (SRE) due to LAAs in snow reaches up to 0.6–1.7 W m−2 in spring, and dust contributes to about 21–42 % of total SRE. Due to positive snow albedo feedbacks induced by the LAA SRE, snow water equivalent is reduced by 2–50 mm and snow cover fraction by 5–20 % in the two regions around the mountains (eastern Snake River Plain and southwestern Wyoming), corresponding to an increase in surface air temperature by 0.9–1.1 °C. During the snow melting period, LAAs accelerate the hydrologic cycle with monthly runoff increases of 0.15–1.00 mm day−1 in April–May and reductions of 0.04–0.18 mm day−1 in June–July in the mountainous regions. Of all the mountainous regions, the Southern Rockies experience the largest reduction of total runoff by 15 % during the later stage of snowmelt (i.e., June and July). Compared to previous studies based on field observations, our estimation of dust-induced SRE is generally 1 order of magnitude smaller in the Southern Rockies, which is ascribed to the omission of larger dust particles (with the diameter > 10 µm) in the model. This calls for the inclusion of larger dust particles in the model to reduce the discrepancies. Overall these results highlight the potentially important role of LAA interactions with snowpack and the subsequent impacts on the hydrologic cycles across the Rocky Mountains.

Heating intensity and radiative effects on turbulent buoyancy-driven airflow in open square cavities with a heated immersed body

The influence of the radiative heat transfer and the effects of air variable properties on the natural convection flows within a vented square cavity with a heated inner body are numerically investigated. Two-dimensional, unsteady, laminar, transitional and turbulent simulations are obtained, for both uniform wall temperature and uniform heat flux heating conditions. The average Nusselt number and the dimensionless mass-flow rate are obtained for a wide range of the Rayleigh number varying from 104 to 1012. The results obtained for different heating intensities are analyzed and compared. The influence of considering surface radiative effects on the differences reached for the Nusselt number and the mass-flow rate obtained with several heating intensities is studied for the isothermal heating condition. For isoflux heating, the obtained results show that the effects of thermal radiation on the appearance of the burnout phenomenon are particularly relevant under given circumstances. The conditions under which the flow becomes unstable, giving rise to a transient, mainly oscillating solution, are determined. The relevant changes produced in the flow patterns into the cavity, are also explained.

Effect of surface radiation on natural convection in an asymmetrically heated channel-chimney system

In this paper, a more realistic numerical approach that takes into account the effect of surface radiation on the laminar air flow induced by natural convection in a channel-chimney system asymmetrically heated at uniform heat flux is used. The aim is to enrich the results given in Nasri et al. (Int J Therm Sci 90:122–134, 2015) by varying all the geometric parameters of the system and by taking into account the effect of surface radiation on the flows. The numerical results are first validated against experimental and numerical data available in the literature. The computations have allowed the determination of optimal configurations that maximize the mass flow rate and the convective heat transfer and minimize the heated wall temperatures. The analysis of the temperature fields with the streamlines and the pressure fields has helped to explain the effects of surface radiation and of the different thermo-geometrical parameters on the system performances to improve the mass flow rate and the heat transfer with respect to the simple channel. It is shown that the thermal performance of the channel-chimney system in terms of lower heated wall temperatures is little affected by the surface radiation. At the end, simple correlation equations have been proposed for quickly and easily predict the optimal configurations as well as the corresponding enhancement rates of the induced mass flow rate and the convective heat transfer.

Observed surface radiation and temperature impacts from the large-scale deployment of photovoltaics in the barren area of Gonghe, China

Abstract As the installation of large-scale photovoltaic (PV) facilities in the barren area of Gonghe, China, would cover a substantial portion of the Earth's surface with PV panels, concerns exist about the extent to which PV plants induce unfavorable surface radiative effects from the change in land use. In contrast to the theoretical calculations and model simulations of previous studies, parallel observations derived from in situ experiments spanning two contrasting land surfaces in Gonghe, consisting of a natural barren surface and one covered with PV panel, provide new insight into the potential impact of large-scale PV plants on the surface radiation and temperature. The novel results presented here are as follows. (1) The specific variations of the surface shortwave radiation components enable the PV panels to serve as energy sinks throughout the whole year, especially in the warm season. (2) The cooling of the land surface associated with the PV plant is related to the physical shading by the PV panels and the solar energy conversion. (3) The enhanced temperature of the surface of the PV panel heats the adjacent ambient air, which may subsequently drive a PV heat-island effect. Moreover, recommendations for an improved experimental design are presented. Our findings provide a solid basis for the parameterization of a PV plant in numerical models, with the view to delivering a more realistic quantitative and practical guidance for the development of the solar industry in the future.

Convective heat transfer combined with surface radiation in a rotating square cavity with a local heater

ABSTRACTThe effect of surface radiation on laminar natural convection in a rotating cavity with a discrete heater has been analyzed numerically. The enclosure is insulated at the bottom and top, heated by a constant temperature from the discrete heater located on the bottom wall, and cooled by a constant temperature from the side walls. Governing equations with corresponding initial and boundary conditions formulated in dimensionless stream function, vorticity, and temperature have been solved by finite difference method of the second-order accuracy. The effects of surface emissivity, Rayleigh number, and Taylor number on the fluid flow and heat transfer have been studied. Obtained results have revealed that rotation can be a very good control parameter for heat transfer and fluid flow.

West Antarctic Ice Sheet Cloud Cover and Surface Radiation Budget from NASA A-Train Satellites

Clouds are an essential parameter of the surface energy budget influencing the West Antarctic Ice Sheet (WAIS) response to atmospheric warming and net contribution to global sea level rise. A 4-yr record of NASA A-Train cloud observations is combined with surface radiation measurements to quantify the WAIS radiation budget and constrain the three-dimensional occurrence frequency, thermodynamic phase partitioning, and surface radiative effect of clouds over West Antarctica (WA). The skill of satellite-modeled radiative fluxes is confirmed through evaluation against measurements at four Antarctic sites (WAIS Divide ice camp and Neumayer, Syowa, and Concordia stations). Owing to perennial high-albedo snow and ice cover, cloud infrared emission dominates over cloud solar reflection and absorption leading to a positive net all-wave cloud radiative effect (CRE) at the surface, with all monthly means and 99.15% of instantaneous CRE values exceeding zero. The annual-mean CRE at the WAIS surface is 34 W m−2, representing a significant cloud-induced warming of the ice sheet. Low-level liquid-containing clouds, including thin liquid water clouds implicated in radiative contributions to surface melting, are widespread and most frequent in WA during the austral summer. In summer, clouds warm the WAIS by 26 W m−2, on average, despite maximum offsetting shortwave CRE. Glaciated cloud systems are strongly linked to orographic forcing, with maximum incidence on the WAIS continuing downstream along the Transantarctic Mountains.

Radiative and variable thermophysical properties effects on turbulent convective flows in cavities with thermal passive configuration

The influence of the radiative heat transfer and the effects of air variable properties on the natural convection flows established in square cavities with thermal passive device geometry are numerically investigated. Two-dimensional, laminar, transitional and turbulent simulations are obtained, considering both uniform heat flux and uniform wall temperature heating conditions. The average Nusselt number and the dimensionless mass-flow rate have been obtained for a wide range of the Rayleigh number varying from 103 to 1016. The results obtained for different heating intensities are analyzed and compared. In addition, the influence of considering surface radiative effects on the differences reached for the Nusselt number and the mass flow rate obtained with several heating intensities is studied. The obtained results show that the effects of thermal radiation on the appearance of the burnout phenomenon are particularly relevant under given circumstances. The influence of the wall-to-wall spacing of the vertical channel inside the cavity is also analyzed. The changes produced in the flow patterns into the cavity when the radiative heat transfer and the effects of variation of properties are relevant, are also shown.

Combined Effect of Mixed Convection and Surface Radiation Heat Transfer for Thermally Developing Flow in Vertical Channels

ABSTRACTCombined effect of laminar flow mixed convection and surface radiation heat transfer for thermally developing airflow in a vertical channel heated from a side has been experimentally examined with different thermal and geometric parameters. The channel boundary is made of two isothermal walls and two adiabatic walls, the isothermal parallel wall is heated uniformly and the opposite cold wall temperature is maintained equal to the inlet conditions. The heated wall temperature ranged from 55 to 100°C, Reynolds number ranged from 800 to 2900 and the heat flux was varied from 250 to 870 W/m2. To cover the wide range of Reynolds numbers, two aspect ratios of square and rectangular section were used. Surface radiation from the internal walls is considered through two emissivities i.e. 0.05 and 0.85, to represent weak and strong radiation effects, respectively. From the experiments, surface temperature and Nusselt number distributions of convection and radiation heat transfer are obtained for different heat flux values. Flow structure inside the channel is visualized to observe the flow pattern. The results show the combined effect of laminar flow mixed convection and surface radiation on the total heat transfer rate within the channel. The accumulating buoyancy force and airflow moves together vertically in the upward direction to give significant heat transfer enhancement in the vertical orientation of the channel.

Conjugate mixed convection with discrete heat sources in a rectangular channel with surface radiation

Mixed convection is seen in high power devices where natural convection alone is not enough. At high temperatures radiation also contributes considerably. This work is concerned with the effect of surface radiation on mixed convection and conjugate convection in a channel with discrete heat sources. Flow is laminar and the parameters considered for this study are thermal conductivity of PCB (printed circuit board), Reynolds number, position of heat sources and emissivity of surface (emissivity of the inner surfaces of the channel are kept constant while those of the heat sources is varied). Constant fluid properties with Pr = 0.707 with Boussinesq approximation is considered. All numerical simulation has been done using FLUENT. The Reynolds number ranges from 115 to 690 (corresponding to air inlet velocity 0.25 to 1.5m/sec) and emissivity ranges from 0.1 to 0.9. Temperatures of heat sources decrease with increase in velocity, thermal conductivity of PCB and the emissivity.

Influence of radiation effect on turbulent natural convection in cubic cavity at normal temperature atmospheric gas

The turbulence structure, boundary layer, and heat transfer of turbulent natural convection, including radiation effects inside the cubic cavity, were investigated in this study. Large eddy simulation was conducted, and Vreman model was adopted for the dynamic subgrid-scale model. To calculate the radiative heat flux efficiently, a coupled calculation method, using the radiation element method by ray emission model, was constructed. To separate the radiation effects of the gas and surface radiations, four calculation conditions have been analyzed; non-radiation, gas radiation, surface radiation, and combined radiation. Observing the vortices structure using the Q value revealed that the surface radiation effect was more dominant for the flow instability than the gas radiation effect. An evaluation of the boundary layers for both the gas and surface radiation effects showed that the flow circulation inside the cubic cavity was enhanced. The surface radiation was dominant in the generation of the shear stress by the turbulent flow. The total heat transfer, which includes the convective and radiative heat transfers, have been investigated. The surface radiation affected on the radiative heat transfer significantly as compared to the gas radiation. The radiation effects changed the radiative heat transfers, while the convective heat transfers of all the calculation conditions were similar.

Turbulent natural convection heat transfer with thermal radiation in a rectangular enclosure partially filled with porous medium

ABSTRACTIn this paper, the effects of surface radiation on turbulent natural convection and heat transfer in an enclosure partially filled with a porous medium have been studied numerically. The governing equations for the momentum and thermal energy in both free fluid and porous medium were solved by the finite element method. Effects of thermal radiation on natural convection and heat transfer in both free fluid and porous media were analyzed. It was found that with the increase of Rayleigh number, the convective Nusselt number at the interface between the free fluid and the porous medium increases, and the mean temperature at the interface decreases. Surface thermal radiation can significantly change the temperature fields of free flow. With the increase of surface emissivity, the mean convective Nusselt number at the interface decreases slightly, and the radiative and total Nusselt numbers at the interface increase. The thickness of the porous medium also has a significant effect on heat transfer in the region of free flow, and the convective Nusselt number at the interface decreases with the increase of the ratio of thickness between the porous media and free flow until the ratio is 0.25. Comparing the enclosure with the adiabatic upper wall, the mean temperature at the interface is higher, and the convective Nusselt number at the interface is lower when the upper wall is nonadiabatic.

Interaction of surface radiation with natural convection in tall vertical cavities heated by a linear heat flux

Purpose – A detailed numerical study is conducted on the effect of surface radiation on laminar natural convection in a tall vertical cavity filled with air. The cavity is heated and cooled, through its two vertical walls, by a linear or uniform heat flux q(y) and by a constant cold temperature, respectively. The horizontal walls are considered adiabatic. The paper aims to discuss these issues. Design/methodology/approach – The radiosity method is employed to calculate the net radiative heat exchanges between elementary surfaces, while the finite volume method is implemented to resolve the governing equations of the fluid flow. Findings – For each heat flux q(y) (ascending, descending or uniform), the effect of the emissivity ε (0ε1) on the local, average and maximum temperatures of the heated wall is determined as a function of the average Rayleigh number Ram (103Ram 6×104) and the cavity aspect ratio A (10A80). The effect of the coupling on the flow structures, convective and radiative heat transfers is also presented and analyzed. Overall, it is shown that surface radiation significantly reduces the local and average temperatures of the heated wall and therefore reduces the convective heat transfer between the active walls. Practical implications – The studied configuration is of practical interest in several areas where overheating must be avoided. For this purpose, a simple design tool is developed to estimate the mean and the maximum temperatures of the hot wall in different operating conditions (Ram, A et ε). Originality/value – The originality lies in the study of the interaction between surface radiation and natural convection in tall cavities submitted to a non-uniform heat flux and a constant cold temperature on the active walls. Also, the development of an original simplified calculation procedure for the hot wall temperatures.

A case study of the radiative effect of aerosols over Europe: EUCAARI-LONGREX

Abstract. The radiative effect of anthropogenic aerosols over Europe during the 2008 European Integrated Project on Aerosol Cloud Climate and Air Quality Interactions Long Range Experiment (EUCAARI-LONGREX) campaign has been calculated using measurements collected by the Facility for Airborne Atmospheric Measurements (FAAM) BAe-146 aircraft and radiative transfer modelling. The aircraft sampled anthropogenically perturbed air masses across north-western Europe under anticyclonic conditions with aerosol optical depths ranging from 0.047 to 0.357. For one specially designed “radiative closure” flight, simulated irradiances have been compared to radiation measurements for a case of aged European aerosol in order to explore the validity of model assumptions and the degree of radiative closure that can be attained given the spatial and temporal variability of the observations and their measurement uncertainties. Secondly, the diurnally averaged aerosol radiative effect throughout EUCAARI-LONGREX has been calculated. The surface radiative effect ranged between −3.9 and −22.8 W m−2 (mean −11 ± 5 W m−2), whilst top-of-the-atmosphere (TOA) values were between −2.1 and −12.0 W m−2 (mean −5 ± 3 W m−2). We have quantified the uncertainties in our calculations due to the way in which aerosols and other parameters are represented in a radiative transfer model. The largest uncertainty in the aerosol radiative effect at both the surface and the TOA comes from the spectral resolution of the information used in the radiative transfer model (∼ 17 %) and the aerosol description (composition and size distribution) used in the Mie calculations of the aerosol optical properties included in the radiative transfer model (∼ 7 %). The aerosol radiative effect at the TOA is also highly sensitive to the surface albedo (∼ 12 %).

Investigation of mineral aerosols radiative effects over High Mountain Asia in 1990–2009 using a regional climate model

Mineral aerosols scatter and absorb incident solar radiation in the atmosphere, and play an important role in the regional climate of High Mountain Asia (the domain includes the Himalayas, Tibetan Plateau, Pamir, Hindu-kush, Karakorum and Tienshan Mountains). Dust deposition on snow/ice can also change the surface albedo, resulting in perturbations in the surface radiation balance. However, most studies that have made quantitative assessments of the climatic effect of mineral aerosols over the High Mountain Asia region did not consider the impact of dust on snow/ice at the surface. In this study, a regional climate model coupled with an aerosol–snow/ice feedback module was used to investigate the emission, distribution, and deposition of dust and the climatic effects of aerosols over High Mountain Asia. Two sets of simulations driven by a reanalysis boundary condition were performed, i.e., with and without dust–climate feedback. Results indicated that the model captured the spatial and temporal features of the climatology and aerosol optical depth (AOD). High dust emission fluxes were simulated in the interior of the Tibetan Plateau (TP) and the Yarlung Tsangpo Valley in March–April–May (MAM), with a decreasing trend during 1990–2009. Dry deposition was controlled by the topography, and its spatial and seasonal features agreed well with the dust emission fluxes. The maximum wet deposition occurred in the western (southern and central) TP in MAM (JJA). A positive surface radiative forcing was induced by dust, including aerosol–snow/ice feedback, resulting in 2-m temperature increases of 0.1–0.5°C over the western TP and Kunlun Mountains in MAM. Mineral dust also caused a decrease of 5–25mm in the snow water equivalent (SWE) over the western TP, Himalayas, and Pamir Mountains in DJF and MAM. The long-term regional mean radiative forcing via dust deposition on snow showed an rising trend during 1990–2009, which suggested the contribution of aerosols surface radiative effects induced by snow darkening was increased since 1990.

Effect of Surface Emissivity on Conjugate Turbulent Natural Convection in an Air-Filled Cavity with a Heat Source

The interaction of conjugate turbulent natural convection and surface thermal radiation in an air-filled square enclosure having heat-conducting solid walls of finite thickness and a heat source has been numerically studied. The primary focus was on the influence of surface emissivity on complex heat transfer. The mathematical model has been formulated in dimensionless variables such as stream function, vorticity and temperature using k-ε turbulent model. The effect of surface emissivity on the average total Nusselt number has been defined. The distributions of streamlines and temperature fields, describing characteristics of the analyzed fluid flow and heat transfer have been obtained. The results clearly show an essential effect of surface radiation on unsteady turbulent heat transfer.

Effect of surface radiation on transient natural convection in a wavy-walled cavity

ABSTRACTTransient natural convection in a differentially heated square cavity that has one vertical wavy wall has been studied numerically. The domain of interest is bounded by vertical isothermal walls and horizontal adiabatic walls. The governing equations formulated in dimensionless stream function, vorticity, and temperature, within the Boussinesq approximation with corresponding initial and boundary conditions, have been solved using an iterative implicit finite-difference method. The main objective is to investigate the effect of the dimensionless time 0 ≤ τ ≤ 0.4, Rayleigh number 104 ≤Ra ≤ 106, surface emissivity 0 ≤ ε < 1, undulations number 1 ≤ κ ≤ 6, and shape parameter 0.6 ≤ a ≤ 1.4 on fluid flow and heat transfer. Results are presented in the form of streamlines, isotherms, and distribution of average total Nusselt number at the wavy wall.

Radiative effects on turbulent buoyancy-driven airflow in open square cavities

The effects of the radiative effects and the air variable properties (density, viscosity and thermal conductivity) on the buoyancy-driven flows established in open square cavities are investigated. Two-dimensional, laminar, transitional and turbulent simulations are obtained, considering both uniform wall temperature and uniform heat flux heating conditions. In transitional and turbulent cases, the low-Reynolds k−ω turbulence model is employed. The average Nusselt number and the dimensionless mass-flow rate have been obtained for a wide range of the Rayleigh number varying from 103 to 1016. The results obtained taking into account the variable thermophysical properties of air are compared to those calculated assuming constant properties and the Boussinesq approximation. In addition, the influence of considering surface radiative effects on the differences reached for the Nusselt number and the mass flow rate obtained with several intensities of heating is studied; specifically, the effects of thermal radiation on the appearance of the burnout phenomenon is analyzed. The changes produced in the flow patterns into the cavity when the radiative heat transfer and the effects of variation of properties are relevant, are also shown.

Temperature Field and Thermal Stress Analyses of High-Speed Train Brake Disc Under Pad Variations

Transient heat transfer analysis of disc brake has been performed to find out an ideal shape of pad geometry. The analysis has taken frictional heat between brake disc and pads as heat flux onto the friction surface, the disc and the pad's temperature fields then were explored involving thermal conduction, forced convection and surface radiation effects. The disc thermal expansion stress was then acquired by quasi-static analysis using its temperature of aforesaid heat transfer analysis. Five prototypes of pad designs with geometry and volume variations were implemented for analytical comparison. Both pads and disc are required to have lower and uniform temperature field and thermal stress. The results uncover that heat conduction is domination in heat dissipation progress during braking, and big volume pad is cooler. Pad volume has more impact to heat transfer procedure and temperature gradient than pad geometry variation does. The design has 10 triangle pads is considered to be an ideal candidate. Its maximum disc temperature and thermal stress are the least among the five designs.