Convection Radiation Research Articles

Modeling of Geophysical Flows through GPUFLOW

We present a new model called GPUFLOW for the modeling and simulation of geophysical flows. GPUFLOW, which is based on the cellular automaton paradigm, features a physical model for the thermal and rheological evolution of lava flows (including temperature-dependent emissivity and cooling by radiation and air convection), support for debris flows without thermal dependency, a parallel implementation on graphic processing units (GPUs), and a simpler and computationally more efficient solution to the grid bias problem. Here, we describe the physical–mathematical model implemented in GPUFLOW and estimate the influence of input data on the flow emplacement through different synthetic test cases. We also perform a validation using two real applications: a debris flow that occurred in July 2006 in the Dolomites (Italy) and the December 2018 lava flow from the Etna volcano. GPUFLOW’s reliability prediction is accomplished by fitting the simulation with the actual flow fields, obtaining average values between ~55% and 75%.

Optimization of heat transfer rate in a moving porous fin under radiation and natural convection by response surface methodology: Sensitivity analysis

The remarkable advancement has been made in area of investigation and extensive demands for permeable fin in recent past. Permeable fins have numerous prospective employments including industrial applications specifically in engineering implementations such as in heat exchangers and super heaters. Additionally, the permeable fin performs a key role in aeronautic engineering. In this study the sensitivity analysis of natural convection and radiation transmission of heat in permeable fin is established. The main objective of the study is to optimize the rate of transmission of heat in a moving permeable fin in natural convection and radiation environment by utilizing Response Surface Methodology (RSM). Also, sensitivity of heat transfer rate is evaluated using RSM. The Darcy model is applied to imitate the impacts of permeable medium and convective heat. Midpoint (midrich) method is utilized to solve the energy equation numerically. The outcomes represents that the temperature of the fin enhance to the neighboring temperature as the value of permeable parameter rises. It is investigated that the heat along the length of fin decline for finite fin as the value of the dimensionless ratio of the surrounding temperature T∞to the difference of the base temperature Tb and surrounding temperature and radiation parameter rises. Also, rate of transmission of heat at the fin tip bring down as the value of Peclet number increased. The outcomes of sensitivity analysis represents that expansion in porosity parameter increases the heat transmission rate and its highest value is observed in level of (-1). Also, heat transfer rate has a non-negative sensitivity towards permeable parameter. However, the decline in dimensionless ratio of the surrounding temperature T∞ to the difference of the base temperature Tb and surrounding temperature and radiation parameter increases the heat transmission rate and its highest value is observed in level of (-1) and (+1). Furthermore, heat transmission rate has a non-positive sensitivity towards dimensionless ratio of surrounding temperature T∞ to the difference of base temperature Tb and surrounding temperature and radiation parameter.

Reversible sweat cooling on mobile electronic devices by metal-organic frameworks-based moisture sorption-desorption process

The continuous improving performance of mobile electronic devices urges a larger heat dissipation capacity, while its improvement is encountering a bottleneck due to the limited cooling area and inherent property of natural convection and radiation. Fortunately, a novel passive cooling technique realized by the moisture sorption-desorption process offers new opportunities for enhancing heat dissipation. This article demonstrates the practical application of sorption-based reversible sweat cooling on a commercial 5G smartphone. In specific, about 1.7 g MIL-101(Cr) is coated on the back cover of the device. Comprehensive benchmarks are employed to evaluate the effectiveness of the moisture sorption-desorption process. Experimental results show that the proposed cooling strategy can bring an extra 0.59 W heat dissipation capacity (about 10% improvement), causing a maximum of 25% performance improvement in graphics-intensive gaming benchmarks. This sorption-based cooling strategy can break the heat dissipation limitation caused by heat radiation and natural convection, providing tremendous potential in the cooling of future electronics.

CFD analysis of environmental impacts on a thermochromic smart window

Thermochromic (TC) glazing is an advanced smart window technology that can help to achieve nearly zero-energy buildings. The glazing temperature that affects TC thermo-optical properties directly impacts its energy-saving performance. However, the impacts of solar radiation and natural convection occurring on this temperature-sensitive material are not yet fully understood. Compared to previous focuses on material properties and energy evaluation, this study aimed to provide a different view from thermo-fluid dynamics on the heat transfer characteristics of a TC window, with impacts of environmental factors addressed. A validated Computational Fluid Dynamics (CFD) model identifies the environmental impacts on the TC glazing temperatures under the coupled radiative and convective heat transfer. Furthermore, a theoretical model was developed with an empirical factor obtained from CFD results. It enables a simple calculation to obtain the TC glazing’s temperature by using solar factors, outdoor temperatures and optical properties. The model suggests that the temperature difference between the TC glazing and the ambient is a function of absorbed solar irradiation (∝q̇total0.75). The predictive model is then tested using typical climate conditions in three cities in China with different solar angles, which demonstrates good agreement with an average absolute error of 5% compared to simulated glazing temperature. This estimation method can further assist in material design, product selection and Building Energy Simulations to achieve a TC window design that is ‘smart’ on seasonal change requirements for different regions.

A comparative study of ionospheric TEC diurnal variations at two stations near cusp latitudes in the Southern Hemisphere

Based on ionospheric total electron content (TEC) data for Zhongshan station (ZHS) and Scott Base station (SBA) in Antarctica, acquired during 2010–2020, high-latitude ionospheric TEC diurnal variations of two near cusp latitude stations were studied. The magnetic latitude and longitude differences between the two stations were approximately 5° and 135°, respectively. It was found that during the 11-year solar activity cycle, the maximum diurnal variation of the ionospheric TEC at ZHS occurred mainly between local noon and magnetic noon. Statistically, the TEC peaks occurred closer to local (magnetic) noon under low (high) solar activity conditions. The maximum diurnal variation of ionospheric TEC at SBA occurred mainly around local noon under low solar activity conditions but before magnetic midnight under high solar activity conditions. The effects of solar radiation, particle precipitation, and polar ionospheric convection pattern on the diurnal variation of TEC were investigated. At both stations, photoionization caused by solar radiation was the main reason for the maximum diurnal variation of ionospheric TEC around local noon. During high solar activity with high concentration plasma in the dayside polar ionosphere, the convection pattern was the dominant influence on the maximum diurnal variation of TEC before magnetic midnight (noon) at SBA (ZHS).

Experimental research on the vapor injected photovoltaic-thermal heat pump for heating, power generation and refrigeration

This paper presents a vapor injected photovoltaic-thermal heat pump system (VI-PVTHP), which can take advantages of the vapor injection (VI) heat pump cycle, significantly increase the heating performance of the system. Not only that, but the VI-PVTHP can also be used for refrigeration by effectively use the PVT modules as condenser of the system. As a result, the system can realize three functions of heating, power generation and refrigeration, and can be used to meet building’s heating, electricity and cooling demands. Then a prototype of the VI-PVTHP was established. Based on the test data of the prototype, the performance and operation characteristics of the VI-PVTHP were analyzed. Results show that the system has good operation reliability and considerable heating, power generation and refrigeration performance during the three working conditions of hot water production, winter space heating and summer night refrigeration. Even on cloudy winter days with ambient air temperatures as low as −8.1 °C, the system can produce domestic hot water of 50 °C with an average COP of 2.59. The VI-PVTHP prototype can continuously and stably produce hot water at the temperature of 40 °C which required for space heating, with an average COP of 2.65. The average EER of the VI-PVTHP prototype was 2.12 during the refrigeration test in summer night. The PVT modules can make good use of night sky radiation and air convection for heat dissipation and is suitable for serving as condenser for heat pump. Radiative heat dissipation to sky is the main way of heat dissipation. During the tests, the heat dissipation flux of the PVT module has reached to ∼650 W/m2.

Magnetic radiative buoyancy-driven convection of MWCNTs -C2H6O2 power-law nanofluids in inclined enclosures with wavy walls

The current numerical investigation focuses on the power-law nanofluids behaviors in slant wavy enclosures in the presence of thermal radiation. The entropy of the system together with the flow and thermal features are examined for several patterns of the side wavy walls, namely, Out-Out, In-In and In-out. The components of the suspension are multi-wall carbon nanotubes and ethylene glycol. The magnetic field is considered in the current study to be inclined and its components are expressed in terms of the enclosure inclination angle. The solution scheme is based on the Characteristic-Based Split (CBS) scheme and the resulting system is discretized using the finite element method (FEM). It is noted that the flow structures, temperature, and entropy features have strong responses for changing the patterns of the side walls. Also, for the non-inclined domain, an augmentation in the non-Newtonian fluid flow up to 44.2% is given as the radiation coefficient is altered from 0 to 5.

Method and experimental investigation of surface heat dissipation measurement using 3D thermography

Abstract. Three-dimensional thermography describes the fusion of geometry- and temperature-related sensor data. In the resulting 3D thermogram, thermal and spatial information of the measured object is available in one single model. Besides the simplified visualization of measurement results, the question arises how the additional data can be used to get further information. In this work, the Supplement information is used to calculate the surface heat dissipation caused by thermal radiation and natural convection. For this purpose, a 3D thermography system is presented, the calculation of the heat dissipation is described, and the first results for simply shaped measurement objects are presented.

Thermal Properties of Zn5al and Zn55al Alloys with II a Group Elements

For the first time, the time dependences of the temperature of aluminum, zinc and zinc-aluminum alloys alloyed with II A group elements under spontaneous cooling mode were obtained; an anomalous course and two characteristic times of the cooling process were found, and their mechanism was explained; the temperature dependence of the thermophysical properties of the investigated metals and alloys was established; the temperature dependence of the coefficients of convective heat transfer and radiation of Al, Zn and Zn55Al and Zn5Al alloys was experimentally determined; the influence of the concentration of II A group elements and temperature on the heat capacity and thermodynamic functions of Zn55Al and Zn5Al alloys was revealed.

Numerical investigation on transient third-grade magnetized nanofluid flow and radiative convection heat transfer from a stationary/moving cylinder: nanomaterial and nanoparticle shape effects

In this study, a mathematical model is developed for analyzing the time-dependent magneto-convective flow and heat transfer characteristics of an electrically conducting (functional) third-grade Reiner-Rivlin non-Newtonian nanofluid from a moving or stationary hot cylinder in the presence of magnetic field and thermal radiation. A well-tested convergent Crank–Nicolson type finite difference algorithm is employed to solve the transformed, nonlinear boundary value problem. The Tiwari-Das nanofluid volume fraction model is adopted for nanoscale effects and the Rosseland algebraic flux model for radiative heat flux effects. It has been shown that the shape of nanoparticles remarkably contributes to the enhancement of heat transfer. Several metallic nanoparticle types such as Al2O3, Cu, and TiO2 are examined. It is found from the investigation that the viscoelastic nanofluid with TiO2 nanoparticles results in more heat transfer than the other nanoparticles. Lower velocity and higher temperature values are computed at transient conditions with a higher third-grade fluid parameter for the flow of nanofluid (Al2O3-SA). The plots of transient friction and heat transfer coefficients are visualized at the surface of a hot cylinder. The tabulated heat transfer coefficient is comparatively more for the moving cylinder than the stationary cylinder. Detailed validation of results of the numerical scheme with previous studies is included. The simulations find applications in coating deposition (enrobing) of magnetic nanomaterial at high temperatures, functional nanomaterial synthesis, etc.

Common envelopes in massive stars: towards the role of radiation pressure and recombination energy in ejecting red supergiant envelopes

ABSTRACT We perform 3D hydrodynamical simulations of a common-envelope event involving a 12$\, \rm {M}_{\odot }$ red supergiant donor. Massive stars are expected to be qualitatively different from low-mass stars as their envelopes have significant support from radiation pressure, which increases both the final separation and amount of mass ejected through the common-envelope interaction. We perform adiabatic simulations that include radiation energy through the equation of state, which results in ejecting 60 per cent more mass (up to two thirds of the total envelope mass becoming unbound, or more) and yield a 10 per cent larger final separation compared to simulations that assume an ideal gas. When also including recombination energy, we find that at least three quarters of the envelope, and possibly the entire envelope, may be unbound. The final separation further increases by almost 20 per cent. The additional amount of ejected material is mainly due to energy injected from helium recombination. Hydrogen recombination plays a comparatively small role, as it mainly occurs in gas that has already become unbound. We conclude that the internal energy of the envelope can be a significant energy source for ejecting the common envelope, but ultimately radiation transport and convection need to be included.

Analysis of Natural Convection–Radiation Interaction Flow in a Porous Cavity with Al2O3–Cu Water Hybrid Nanofluid: Entropy Generation

Analysis of Natural Convection–Radiation Interaction Flow in a Porous Cavity with Al2O3–Cu Water Hybrid Nanofluid: Entropy Generation

Dynamic characteristics of convection heat and radiation heat on building surfaces under cyclic heat flow.

The dynamic heat transfer of building surfaces has thermal conduction, convection and radiation at the same time. It is the basis of building thermal environment simulation, air conditioning load calculation, building energy analysis and air conditioning system conservation operation. Under cyclic heat flow, the convection and radiation separating method was used to calculate the radiation heat and convection heat of building surfaces, and dynamic characteristics of convection heat and radiation heat on building surfaces was provided in this paper. For the dynamic heat transfer of building surfaces under cyclic heat flow, three indexes of peak error, mean error and average relative error were used to analyze dynamic heat transfer. The temperature distribution and dynamic heat transfer of convection heat and radiation heat of building surfaces were studied systematically. The separating cooling load and the room cooling load were basically consistent with each other, the convection and radiation separating method was reliable and available. The peak value of convection heat corresponded to the foot value of the radiation heat, and the relative error of them was 1.9%-2.2%. The dynamic characteristics of radiation heat and convection heat had important reference for the study of dynamic heat transfer of building surfaces under cyclic heat flow.

Transient characteristics of coupled thermal radiation and natural convection in a three-dimensional cylindrical cavity containing a heated plate

In this study, a numerical study of transient combined natural convection and surface radiation in a cylindrical cavity with a heated plate placed inside is carried out using the open-source platform OpenFOAM. The effects of the Rayleigh number (105 ? Ra ? 107), inclination angle (0? ? ? ? 90?), and surface emissivity (0 ? ? ? 1) on the velocity components, temperature field, and Nusselt number are investigated in detail. Results show that the Rayleigh number has a greater effect on the radiative heat transfer than on natural convection. Radiative heat transfer increases monotonously with the increase of surface emissivity, and its contribution could be over 50% of the total heat transfer rate. The inclination angle of the plate affects the flow structure, but the difference in total Nusselt number is less than 10% for various inclination angles. Results in this study provide insights into the transient characteristics of coupled thermal radiation and natural convection in a three-dimensional cavity and will guide the optimal design of related devices.

Optimization of Heat Transfer Rate in a Moving Porous Fin Under Radiation and Natural Convection by Response Surface Methodology: Sensitivity Analysis

Optimization of Heat Transfer Rate in a Moving Porous Fin Under Radiation and Natural Convection by Response Surface Methodology: Sensitivity Analysis

Radiative mixed convective flow induced by hybrid nanofluid over a porous vertical cylinder in a porous media with irregular heat sink/source

PurposeHybrid nanofluids have higher mechanical resistance, thermal conductivity, chemical stability, and physical strength when compared to normal nanofluids. Our approach in the current paper is to present a novel exploration comprising radiative mixed convection flow of hybrid nanofluids with irregular heat source/sink effect through a porous vertical cylinder immersed in a porous media. Both opposing and assisting flows are discussed. MethodologyThe transmuted similarity ODEs are numerically worked out utilizing the assist of the bvp4c package in MATLAB for different values of physical parameters. The hybrid nanofluids contain a couple of nanoparticles namely aluminum and copper particles with water as base fluid. FindingsIt was observed that fundamental similarity equations disclose double solutions (first and second branches) for buoyancy assisting and opposing flows. The drag force is enhanced due to the radiation as well as curvature parameters. In addition, the velocity declines due to heat source/sink and radiation parameter. Originality/valueThe writers agree that all numerical outcomes are novel and have not previously been published for the current problem.

Impacts of thermo-optical properties on the seasonal operation of thermochromic smart window

A type of smart window using thermochromic glazing (TCG) is a promising technology for green buildings owing to the self-regulating feature and low-maintenance need. Its most important feature, thermo-optical properties that regulate the blockage of solar heat, is directly linked to the variation of surface temperatures. However, challenges from the inhomogeneity of thermo-optical properties, the coupled solar radiation and natural convection, and varying outdoor conditions all seriously hinder the understanding of its mechanism. In this paper, a validated Computational Fluid Dynamics (CFD) model achieves the simulation of inhomogeneous tinting of TCG by defining the thermo-optical properties of each finite volume according to the surface temperature. Solar radiation and natural convection at outdoor, indoor and the cavity are solved to reflect glazing temperature more accurately. The case studies compared six different switching temperatures in the range of 20 ∼ 42.5 °C with a transition gradient of 10 °C. Averaged meteorological data for both summer and winter, sunny days and cloudy days are selected to present realistic climate impacts. The result reveals the overall saving in transmitted solar radiation in summer and heating penalties in winter. It suggests the best switching temperatures for each climate condition. With the seasonal operation, the highest saving in solar heat gain is 20.9% when adopting a switching temperature of 25–35 °C, while the lowest saving can be negative, meaning TCG is not suitable for those climate zones. The proposed evaluation criteria help to quantify the applicability of TCG with the input of the summer/winter day ratio and sunny/cloudy ratio. The best region to apply TCG is where summer days are longer and winter solar radiation is significantly lower. The in-depth understanding of this temperature-sensitive process benefits the optimization of TCG in buildings, especially for its seasonal operation needs.

Unsteady flow analysis of Maxwell fluid with temperature dependent variable properties and quadratic thermo-solutal convection influence

The current work analyzed the surface effect on the motion of Maxwell fluid with variable transport properties (viscosity, diffusivity, thermal conductivity, and electrical field) in porous, magnetized, radiative, and nonuniform (quadratic) convection processes. In this study, the flow examination modeled the motion of Maxwell fluid under MHD and variable properties influence. The flow field solutions were obtained numerically via the Spectral Collocation Approach (SCM) and justified with Galerkin Weighted Residual Method (GWRM). It was shown that the flat surface dominates the flow fields, a rise in variable viscosity diminished the fluid momentum, variable thermal conductivity and diffusivity enhance the consumption of more fluid particles, the velocity field is promoted to a hike in nonlinear Boussinesq approximation numbers, while sheet variable thickness number is aimed at downsizing the flow distributions. Moreover, the current analysis is applicable in metal spinning, polymer extrusion, machine design, architecture, aluminum aircraft skin, and structural steel beam where the extrudate materials are stretched into a sheet.

Using Radiative Convective Equilibrium to Explore Clouds and Climate in the Community Atmosphere Model

AbstractCharacteristics of, and fundamental differences between, the radiative‐convective equilibrium (RCE) climate states following the Radiative‐Convective Equilibrium Model Intercomparison Project (RCEMIP) protocols in the Community Atmosphere Model version 5 (CAM5) and version 6 (CAM6) are presented. This paper explores the characteristics of clouds, moisture, precipitation and circulation in the RCE state, as well as the tropical response to surface warming, in CAM5 and CAM6 with different parameterizations. Overall, CAM5 simulates higher precipitation rates that result in larger global average precipitation, despite lower outgoing longwave radiation compared to CAM6. Differences in the structure of clouds, particularly the amount and vertical location of cloud liquid, exist between the CAM versions and can, in part, be related to distinct representations of shallow convection and boundary layer processes. Both CAM5 and CAM6 simulate similar peaks in cloud fraction, relative humidity, and cloud ice, linked to the usage of a similar deep convection parameterization. These anvil clouds rise and decrease in extent in response to surface warming. More generally, extreme precipitation, aggregation of convection, and climate sensitivity increase with warming in both CAM5 and CAM6. This analysis provides a benchmark for future studies that explore clouds, convection, and climate in CAM with the RCEMIP protocols now available in the Community Earth System Model. These results are discussed within the context of realistic climate simulations using CAM5 and CAM6, highlighting the usefulness of a hierarchical modeling approach to understanding model and parameterization sensitivities to inform model development efforts.

Thermal radiative mixed convection flow of MHD Maxwell nanofluid: Implementation of buongiorno's model

A mathematical model for steady MHD Maxwell nanofluid flow over the porous stretching sheet with gyrotactic microorganisms is discussed theoretically and numerically. We use the theory of the microorganism to stabilize the suspended nanoparticles, due to bio convection, induced by the impacts of buoyancy forces. Similarity transformations used to transform the mathematical PDEs of non-linear nature i.e., continuity equation, velocity, concentration, density, and energy of motile micro-organisms into the system of non-linear ordinary differential equations. Mathematica 11used to acquire the solutions for the mathematical model. Boundary conditions together with non-zero value of mass flux is imposed on the given problem. Valuations are performed graphically for several protuberant parameters like Hartman number, bio convection, Peclet number, Deborah number, thermophoresis diffusion, Rayleigh number, Brownian motion, and mixed convection parameters. These different parameters are employed on non-dimension velocity function, temperature function, concentration function and density of the motile microorganisms and studied numerically in detail. It is observed that by increasing the value of bio-convection parameter as well as Peclet number, the microorganism field diminishes. Graphical diagrams are showing the consistency of the latest results.