Radiation Heat Sink Research Articles

Performance analysis and structure optimization for concentrated photovoltaic-phase change material-thermoelectric system in space conditions

High-efficient thermal management is urgently needed for concentrated photovoltaic-thermoelectric hybrid system due to the high heat flux. In present paper, a three-dimensional model for the hybrid system in outer space conditions was established by coupling phase change temperature control and radiation heat sink technologies to find the propriate thermal management scheme. Firstly, the three shortcomings in the typical hybrid system were proposed and their adverse effects on efficiency were elucidated. Then, a heat transfer pillar for temperature control unit and a newly designed circular fins for heat sink were designed. The effects of structure parameters on power generation performance were investigated, and the interaction between temperature control unit and heat sink were discussed. The results show that the hybrid systems with the newly designed heat transfer pillar and circular fins have higher efficiency. After that, a united structure optimization by artificial neural network-multi-objective genetic algorithm was performed to solve the interaction and to balance the electrical efficiency and power density of hybrid system. The comprehensive power generation performance of hybrid system can be further improved after the optimization. The system with PCM thickness dPCM = 6.33 mm, heat transfer pillar width a = 18.19 mm, fin length L = 49.99 mm and fin radius R = 50 mm, has the maximum average total efficiency (31.83%, 2.98% higher than the typical system); the system with dPCM = 3.02 mm, a = 10.05 mm, L = 47.03 mm and R = 25.86 mm, has the maximum average power density (36.97 W/kg, 15.78% higher than the typical system).

Effect of diffusion‐thermo on a mixed convective heat and mass transfer magnetohydrodynamic flow through a vertical porous plate including radiation absorption

AbstractThe effect of Dufour on a magnetohydrodynamics (MHD) mixed convection in the presence of radiation absorption and heat sink is performed in this work. The dimensional governing equations involved here are transferred to non‐dimensional form and then solved using perturbation technique. The changes due to the effect of several relevant parameters on the velocity field temperature field and concentration field are graphically displayed. The rates of momentum transfer, heat transfer and mass transfer are also analyzed and their influence due to the related parameters are visualized graphically. Rise in Dufour parameter enhances the fluid velocity and fluid temperature. Also, the heat sink parameter lowers the fluid velocity and temperature. The chemical reactions cause a fall in the fluid's velocity, temperature and concentration.

Effect of Non-Linear Radiation and Non-Uniform Heat Source/Sink on Flow over a Linear Stretching Sheet with Fluid Particle Suspension

In this paper, the flow and heat transfer of dusty flow over a linear stretchable sheet has been analyzed. The effects of non-linear radiation and non-uniform heat source or sink have been studied. Considering the mentioned terms and conditions, the problem has been formulated. The formulation consists of systems of nonlinear PDEs which has been converted to a system of ODEs by taking suitable similarity transformations. Then the systems of ODEs have been solved by using Rungakutta method of 4th order. The computations work has been carried out by using BVP4C tool of MATLAB. The impact of flow parameters like radiation parameter, prandtl number, eckret number, fluid Particle interaction parameter β and diffusivity parameter on flow and heat transfer are investigated. The results are presented through graphs and tables. From the graphs, it is concluded that the presence of particles in fluid has some impact of different parameters in flow and heat transfer. The parameters like Eckert number, Fluid- particle interaction parameter, diffusivity parameter have remarkable effects of presence of particles

Non-uniform heat generation and Stefan blowing on nonlinear radiative Casson-nanofluid flow through microorganisms through leading-edge accretion or ablation

The effect of Stefan blowing on bioconvection of microorganisms mixed on non-Newtonian fluid with water-based nanofluids to an accretion/ablation of the leading edge was investigated in this current analysis. The effects of convective heat boundary conditions are one more important physical parameter in the flow investigation and have been studied for that analysis. Furthermore, the influence of nonlinear thermal radiation and irregular heat source or sink was more integrated. Even systems of conservative governing PDEs were transformed within the dimensionless structure of equations by utilising the appropriate conversion. The recent systems of equations including comparable transformed boundary conditions were again defined numerically for the use of the finite element method. It is notable about the accuracy and validity of the current numerical solution was an attractive understanding of the actual definite results in the literature. It is observed that velocity decreases by increasing Casson fluid parameter.

High power density of radiative-cooled compact thermoelectric generator based on body heat harvesting

Advancements in flexible and wearable electronics have led to the development of self-powered, wearable systems. Thermoelectric generators (TEGs) offer promising solutions toward self-powered energy harvesting from body heat. However, previously developed TEGs are large-sized owing to their heat sinks. Hence, high-quality heat sinks are required for flexible TEGs with a small size and high power for wearable devices. Herein, a TEG integrated with a flexible, micron-thin poly(vinylidene fluoride-co-hexafluoropropylene) radiative-cooled heat sink, with an emissivity of 97.47%, is proposed. The TEG with the radiative heat sink (TEG_rad) generates power by depositing heat into a cold space (temperature of 3 K) through passive radiative cooling. Thus, TEG_rad achieved a power density of 12.48 µW/cm 2 with a temperature difference (Δ T ) of 1.9 °C, higher than those of flexible TEGs that were previously reported, based on body heat harvesting under natural convection. Further, TEG_rad is not only more than two times compact, but also delivers high power output compared with a TEG with a bulky finned heat sink. Moreover, a flexible lithium–sulfur (Li-S) battery was coupled with TEG_rad to store the generated power for uninterrupted power supply to a self-powered wearable system. Integrated wearable radiative-cooled compact thermoelectric generator and Li-S battery system to offer high power density based on body heat harvesting. • Novel design of wearable thermoelectric generator with high emissivity of P(VdF-HFP) micron thin radiative heat sink. • Power output of TEG_rad outperformed TEG_fin during daytime and nighttime. • TEG_rad achieves highest power density of 12.48 µW/cm 2 based on body heat harvesting under natural convection condition. • Integration of flexible thermoelectric-Li-S system.

Modeling and analysis of peristalsis of hybrid nanofluid with entropy generation

This investigation intends to explore the peristaltic transport of rotating fluid in a channel. The channel is considered symmetric with flexible walls, and porous medium fills the saturated space. In this analysis, hybrid nanofluid consisting of titanium oxides and copper particles is taken. Water is used as the base fluid. MHD and Hall effects are employed in this problem. Formulation of energy equation is based on radiation and non-uniform heat source or sink parameter. Convection conditions are utilized for the boundary. Thermodynamics second relation is employed for entropy generation. Maxwell–Garnetts model of thermal conductivity is employed. Numerical analysis is carried out using NDSolve of Mathematica. The effect of nanoparticle volume fraction, Taylor number, Hartman number, porosity and Hall parameters is analyzed for axial and secondary velocities, temperature, entropy generation and heat transfer rate. This study divulges that an enhancement in rotation parameter caused an increase in secondary velocity. Moreover, as volume fraction of nanoparticles enhances from 0.01 to 0.04, decay is noticed in fluid’s axial and secondary velocities. In this case, entropy also decreases. This study further disclosed that heat transfer rate gradually increases as we exceed the volume fraction of nanoparticles from 0.02 to 0.08. More pores also lead to an enhancement in fluid velocity, temperature and entropy.

Group theoretical analysis for magnetohydrodynamic generalized Stokes’ flow and radiative heat transfer model of a non-Newtonian nanofluid with heat generation/absorption

The fully developed boundary layer flow and heat transfer model of an unsteady, incompressible, electrically conducting, optically thick and thermodynamically compatible third-grade nanofluid are investigated from the viewpoint of Lie symmetry approach. We have studied the Stokes’ model in which flow is generated due to motion of the bounding surface with an impulsive time-dependent velocity. The mathematical model also includes the effect of thermal radiation and internal heat source or sink in the flow regime. Lie symmetry approach is employed to obtain the symmetry algebra of the governing nonlinear partial differential equations for both flow and heat transfer models. The governing nonlinear partial differential equations describing the flow and heat transfer model are reduced to different classes of nonlinear ordinary differential equations under the implication of symmetry generators. The reduced ordinary differential equations are investigated using the compatibility and generalized group theoretical method. The exact closed-form solutions for nanofluid motion and temperature distribution within the boundary layer are obtained. The effect of various thermophysical parameters on the characteristics of flow and heat transfer for Cu-water nanofluid model is explored from a physical point of view.

Numerical Study of Performance of Porous Fin Heat Sink of Functionally Graded Material for Improved Thermal Management of Consumer Electronics

The ever-increasing demand for high-performance electronic and computer systems has unequivocally called for increased microprocessor performance. However, increasing microprocessor performance requires increasing the power and on-chip power density of the microprocessor, both of which are associated with increased heat dissipation. In recent times, thermal management of electronic systems has gained intense research attention due to increased miniaturization trend in the electronics industry. In this paper, we present a numerical study on the performance of a convective–radiative porous heat sink with functionally graded material (FGM) for improved cooling of various consumer electronics. For the theoretical investigation, the thermal property of the FGM is assumed as a linear and power-law function. We solved the developed thermal models using the Chebyshev spectral collocation method (CSCM). The effects of inhomogeneity index of FGM and convective and radiative parameters on the thermal behavior of the porous heat sink are investigated. This paper shows that increase in the inhomogeneity index of FGM and convective and radiative parameters improves the thermal efficiency of the porous fin heat sink. Moreover, for all values of Nc and Rd, the temperature gradient along the fin of FGM is negligible compared to HM fin in both linear and power-law functions. For comparison, the thermal predictions made in this paper using CSCM agree excellently with the established results of Runge–Kutta with shooting and homotopy analytical method.

Impacts of Radiation and Upper-Tropospheric Temperatures on Tropical Cyclone Structure and Intensity

Abstract Potential intensity theory predicts that the upper-tropospheric temperature acts as an important constraint on tropical cyclone (TC) intensity. The physical mechanisms through which the upper troposphere impacts TC intensity and structure have not been fully explored, however, due in part to limited observations and the complex interactions between clouds, radiation, and TC dynamics. In this study, idealized Weather Research and Forecasting Model ensembles initialized with a combination of three different tropopause temperatures and with no radiation, longwave radiation only, and full diurnal radiation are used to examine the physical mechanisms in the TC–upper-tropospheric temperature relationship on weather time scales. Simulated TC intensity and structure are strongly sensitive to colder tropopause temperatures using only longwave radiation, but are less sensitive using full radiation and no radiation. Colder tropopause temperatures result in deeper convection and increased ice mass aloft in all cases, but are more intense only when radiation was included. Deeper convection leads to increased local longwave cooling rates but reduced top-of-the-atmosphere outgoing longwave radiation, such that the total radiative heat sink is reduced from a Carnot engine perspective in stronger storms. We hypothesize that a balanced response in the secondary circulation described by the Eliassen equation arises from upper-troposphere radiative cooling anomalies that lead to stronger tangential winds. The results of this study further suggest that radiation and cloud–radiative feedbacks have important impacts on weather time scales.

Mathematical modelling of frequency and force impacts on averaged metal flows in alternating magnetic field

The averaged quasi-steady flow patterns of metal melt situated in alternating magnetic field are studied numerically. It is taken into account the buoyancy due to non-uniform heating, the intensive radiation heatsink from the melt surface and the Lorentz forces arising in conductor in the alternating magnetic field. The governing equations of the suggested mathematical model are given and the model validations are described. The flow regime maps are plotted based on analysis of melt velocity dependence on the Hartmann number and the parameter of magnetic field diffusion. Flow patterns corresponding each parameter area at the map are given and interpreted. The way of acceleration of melt motion computation is suggested.

A transient model for optimizing a hybrid nocturnal sky radiation cooling system

Abstract Nocturnal sky radiation cooling (NSRC) is a passive, sustainable, cooling method that utilizes the sky as a radiation heat sink. Here, a reliable, hybrid NSRC system including a heat pump is presented and analyzed for the cooling of remote, off-grid data centers. An analytical system model that incorporates thermal and life cycle cost analyses including system control logic has been developed. The thermal analysis was validated by a detailed numerical analysis. In addition, a model for the radiator was developed and a performance curve of an ideal radiator is introduced. The strength of the here developed analytical, transient model lies in its ability to simulate a wide variety of possible system configurations using local, site dependent meteorological conditions over multiple years. The analysis determines the optimal system design based on minimum life cycle costs. The here presented concepts can be used for similar systems encompassing different components.

CFRP radiator concept for space applications

The paper presents the work conducted by HPS GmbH on manufacturing, analysis and testing of an innovative CFRP radiator for spacecraft applications, having the same thermal performances and a mass reduction of more than 30 % compared to standard aluminum radiators (in addition see Schlitt et al. in 40th international conference on environmental systems, 2010). The developed configuration can be used as condenser or radiation heat sink on the East/West panels of the spacecraft for either two-phase or single-phase heat transportation systems.

The thermosphere general circulation modeling with the parametrization of radiative processes

The paper presents a new version of the global three-dimensional general circulation model of the Earth’s thermosphere (90-500 km) with high spatial resolution (2 × 2.5 × 80), including consistent calculation of radiative processes. Based on a detailed analysis of the reproduction of the various components of radiation transfer a good agreement of radiation balance with empirical data is shown in the new model. Analytical estimations and model results proved that the thermosphere global state formation is essentially determined by the ratio between the radiation heating and heat sink due to molecular parameters, as well as by the lower boundary conditions. On the base of the preliminary model identification with empirical data a satisfactory reproduction of the thermal balance and the thermospheric general circulation features is shown.

Heat and Mass Transfer on MHD Flow of a Viscoelastic Fluid through Porous Media over a Shrinking Sheet.

An attempt has been made to study the heat and mass transfer effect in a boundary layer flow through porous medium of an electrically conducting viscoelastic fluid over a shrinking sheet subject to transverse magnetic field in the presence of heat source. Effects of radiation, viscous dissipation, and uniform heat sink on the heat transfer have been considered. The method of solution involves similarity transformation. The coupled nonlinear partial differential equations representing momentum, concentration, and nonhomogenous heat equation are reduced into a set of nonlinear ordinary differential equations. The transformed equations are solved by applying Kummer's function. The exact solution of temperature field is obtained for power-law surface temperature (PST) as well as power-law heat flux (PHF) boundary condition. The interaction of magnetic field is proved to be counterproductive in enhancing velocity and concentration distribution, whereas presence of porous matrix reduces the temperature field at all points.

Hall Current And Dufour Effects On Mhd Flow Of A Micropolar Fluid Past A Vertical Plate In The Presence Of Radiation Absorption And Chemical Reaction

Heat and mass transfer effects on an unsteady MHD flow of a chemically reacting micropolar fluid over an infinite vertical porous plate through a porous medium with Hall effects and thermal radiation in the presence of radiation absorption and heat sink are studied. The governing system of partial differential equations is transformed to dimensionless equations using dimensionless variables. The dimensionless equations are then solved analytically using the perturbation technique to obtain the expressions for velocity, microrotation, temperature and concentration. With the help of graphs, the effects of the various important parameters entering into the problem on the velocity, microrotation, temperature and concentration fields within the boundary layer are discussed. Also the effects of the pertinent parameters on the skin friction coefficient and rates of heat and mass transfer in terms of the Nusselt number and Sherwood number are

Design and Validation of a High-Temperature Comparative Thermal-Conductivity Measurement System

A measurement system has been designed and built for the specific application of measuring the effective thermal conductivity of a composite, nuclear-fuel compact (small cylinder) over a temperature range of 100 °C to 800 °C. Because of the composite nature of the sample as well as the need to measure samples pre- and post-irradiation, measurement must be performed on the whole compact non-destructively. No existing measurement system is capable of obtaining its thermal conductivity in a non-destructive manner. The designed apparatus is an adaptation of the guarded-comparative-longitudinal heat flow technique. The system uniquely demonstrates the use of a radiative heat sink to provide cooling which greatly simplifies the design and setup of such high-temperature systems. The design was aimed to measure thermal-conductivity values covering the expected range of effective thermal conductivity of the composite nuclear fuel from 10 W . m−1 . K−1 to 70 W . m−1 . K−1. Several materials having thermal conductivities covering this expected range have been measured for system validation, and results are presented. A comparison of the results has been made to data from existing literature. Additionally, an uncertainty analysis is presented finding an overall uncertainty in sample thermal conductivity to be 6 %, matching well with the results of the validation samples.

DEVELOPMENT OF A CFRP RADIATOR WITH INTEGRATED LOOP HEAT PIPE TUBING

§The paper presents work conducted on manufacturing, analysis and test of an innovative all CFRP thermal radiator for spacecraft application. The developed configuration can be used as condenser or radiation heat sink for either two-phase or single-phase heat transportation systems. For this purpose high-conductivity carbon fiber has been employed in the radiating face sheet. Thermal test results for a demonstration panel showed good agreement with analytical prediction. The new radiator configuration exhibits a weight saving of about 33% compared to a currently used all-aluminum radiator panel. The technology is intended for use in future communication satellites.

Errors Associated With Light-Pipe Radiation Thermometer Temperature Measurements

Accurate measurement of surface temperature distribution is of concern in the semiconductor industries, particularly in rapid thermal processing. The International Technology Roadmap for Semiconductors 2004 has established requirements of uncertainties of plusmn1.5 degC at a temperature of 1000 degC, with temperature calibration traceable to ITS-90 (International Temperature Scale-1990). Light-pipe radiation thermometers (LPRTs) are becoming increasingly important as an industrial tool for temperature measurement, especially in the semiconductor industry. However, achieving improved accuracy will be difficult without fully understanding several issues associated with LPRTs. In this paper, the "drawdown effect," the "shadow effect," and the "environmental effect" are investigated. The drawdown effect is caused by the physical mass of the light-pipe probe acting as a radiation heat sink for the measured object. The shadow effect is caused by distortion of the wafer radiosity distribution due to the presence of the light-pipe probe. The environmental effect is caused by nonspecular reflection due to surface imperfection or impurity of the light-pipe material. Monte Carlo simulation was conducted to better understand the underlying physics, and the simulation results are compared to the experiment results. The latter two effects were found to be very important in the present study

The effect of temperature on the power drop in crystalline silicon solar cells

The influence of temperature and wavelength on electrical parameters of crystalline silicon solar cell and a solar module are presented. At the experimental stand a thick copper plate protected the solar cell from overheating, the plate working as a radiation heat sink, or also as the cell temperature stabilizer during heating it up to 80°C. A decrease of the output power (−0.65%/K), of the fill-factor (−0.2%/K) and of the conversion efficiency (−0.08%/K) of the PV module with the temperature increase has been observed. The spectral characteristic of the open-circuit voltage of the single-crystalline silicon solar cell is also presented. It is shown that the radiation-rate coefficient of the short-circuit current-limit of the solar cell at 28°C is 1.2%/(mW/cm 2).

Vacuum system for a space simulation facility

To study the thermal behaviour of satellite systems, measurements under simulated thermal space environment conditions are performed. These conditions are pressure below 10 −5 mbar, radiative heat sink and solar radiative input. The capabilities of IABG's space simulation and thermal vacuum facility WSA/TVA will be described. The vacuum chamber is a horizontal stainless steel cylinder of 6.8 m diameter and 13 m length resulting in a total chamber volume of approximately 500 m 3. The high vacuum pressure of < 2 × 10 −6 mbar for thermal testing is achieved by 6 helium refrigerator cryopumps of 150,000 I s −1 effective pumping speed. The operational characteristics as pump-down curve, residual gas analysis and repressurization procedure will be presented.