• Elastomers and Composites
• /
• v.59 no.1
• /
• pp.22-33
• /
• 2024

Passive radiative cooling is a promising technology for cooling objects without energy input. Passive radiative cooling works by radiating heat from the surface, which then passes through the atmosphere and into space. Achieving efficient passive radiative cooling is mainly accomplished by using materials with high emissivity in the atmospheric window (8-13 ㎛). Research has shown that polymers tend to exhibit high emissivity in this spectral range. In addition to elastomers, other materials with potential for passive radiative cooling include metal oxides, carbon-based materials, and polymers. The structure of a passive radiative cooling device can affect its cooling performance. For example, a device with a large surface area will have a greater amount of surface area exposed to the sky, which increases the amount of thermal radiation emitted. Passive radiative cooling has a wide range of potential applications, including building cooling, electronics cooling, healthcare, and transportation. Current research has focused on improving the efficiency of passive radiative cooling materials and devices. With further development, passive radiative cooling can significantly affect a wide range of sectors.

• Elastomers and Composites
• /
• v.57 no.2
• /
• pp.62-72
• /
• 2022

Passive daytime radiative cooling (PDRC) is attracting increasing attention as an eco-friendly technology that can save cooling energy by not requiring an external power supply. An ideal PDRC structure should improve solar reflectance and emissivity within the atmospheric spectral window. Early designs of photonic crystal materials demonstrated the benefits of PDRC. Since then, functional arrangements of polymer-based radiative cooling materials have played an important role and are rapidly expanding. This review summarizes the known inorganic, organic, and hybrid materials for PDRC. The review also provides a complete understanding of PDRC and highlights its practical applications.

• Journal of the Korean Society of Safety
• /
• v.19 no.3 s.67
• /
• pp.14-19
• /
• 2004

The objective of the present work is to examine evaporation cooling of droplet due to surface roughness under radiative heat input condition. The surface temperatures varied from $80\~160^{\circ}C$ on aluminum alloy (AL 2024) and surface roughness was $0.18{\mu}m,\;1.36{\mu}m$. The results are as follows; Regardless of surface roughness under radiative heat input condition, as droplet diameter is larger, the in-depth temperature of solid decreases and evaporation time increases. In the case of $0.18{\mu}m\;and\;1.36{\mu}m$ of surface roughness, the larger the surface roughness is, the less the evaporation time is and the larger the temperature within the solid is. In the case of $Ra=0.18{\mu}m$ evaporation time and time averaged heat flux for radiative heat input case is shorter than for the conductive case.

• Journal of the Korean Solar Energy Society
• /
• v.29 no.6
• /
• pp.32-38
• /
• 2009

The effects of surface radiative properties on the radiant cooling of opaque surfaces under clear sky condition are studied. Two types of surfaces, one gray and the other selective, are compared. For the nighttime cooling, black surface gives the lowest plate temperature and on the other hand the ideal selective surface gives the highest temperature. The reverse is true when there is an insolation. Equivalent radiative heat transfer coefficient of radiant cooling without convection is about $1{\sim}7\;W/m^2-K$ for the range of values studied. The surface with black within the $6{\sim}13\;{\mu}m$ band else zero emissivity could be regarded as a black surface for the nighttime radiant cooling purposes. However, lower band limit of $4\;{\mu}m$ is preferred to $6\;{\mu}m$ for small insolation situations.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.16 no.5
• /
• pp.37-46
• /
• 2012

The calculation model for heat transfer analysis of rocket engine combustion chamber considering film-cooling has been established. Convective, radiative heat transfers and film-cooling effect in combustion chamber were evaluated using empirical equations especially for rocket engine combustors, and for heat transfer outward from chamber wall general convective and radiative equations were applied. Structural grid has been generated inside chamber wall for FVM calculations, and transient thermal analyses were carried out by time-marching techniques. LOx/kerosene rocket engine with chamber pressure of 50 bar has been analysed, and it is shown that, in that case, the film-cooling less than 4% remarkably contributes to reduce wall temperature, but the effect of the effect of film-cooling more than about 4% is not significantly increased.

• Journal of The Korean Astronomical Society
• /
• v.34 no.4
• /
• pp.333-335
• /
• 2001

We study the properties of supernova (SN) driven interstellar turbulence with a numerical magnetohydrodynamic (MHD) model. Calculations were done using the RIEMANN framework for MHD, which is highly suited for astrophysical flows because it tracks shocks using a Riemann solver and ensures pressure positivity and a divergence-free magnetic field. We start our simulations with a uniform density threaded by a uniform magnetic field. A simplified radiative cooling curve and a constant heating rate are also included. In this radiatively-cooling magnetized medium, we explode SNe one at a time at randomly chosen positions with SN explosion rates equal to and 12 times higher than the Galactic value. The evolution of the system is basically determined by the input energy of SN explosions and the output energy of radiative cooling. We follow the simulations to the point where the total energy of the system, as well as thermal, kinetic, and magnetic energy individually, has reached a quasi-stationary value. From the numerical experiments, we find that: i) both thermal and dynamical processes are important in determining the phases of the interstellar medium, and ii) the power index n of the $B-p^n$ relation is consistent with observed values.

• Publications of The Korean Astronomical Society
• /
• v.11 no.1
• /
• pp.27-47
• /
• 1996

We have performed the high resolution computer simulation with 1D spherical hydrodynamic code in order to study the dynamical evolution of supernova ejecta interacting with a pre-existing fast wind structure. The fast wind structure has been calculated with $M_{in}=3{\times}10^{-6}M_{\odot}yr^{-1}$ and ${\upsilon}_{in}=1000km/sec$, which velocity is higher than the critical velocity relating to the initial radiative cooling. The fast wind becomes initially adiabatic. After a shell formation time of ${\sim}4000yrs$, the wind becomes radiative cooling at the shell zone, forming a thin dense radiative shell and an adiabatic wind bubble afterward. When supernova explodes in the wind center at 20,000yrs after the wind evolves, the supernova ejecta, which has a dense distribution of ${\rho}{\propto}r^{-n}$(here we have n = 9), interacts initially with, the understood wind zone, producing forward and reverse shocks. The reverse shock heats the supernova ejecta and its temperature increases. In this study, as the mass of the supernova ejecta is larger than that of the wind shell ($M_{ej}=5M_{\odot}$, $M_{sw}=2M_{\odot}$), we can conform two shell structures: an outer shell by the supernova ejecta and a secondarily shocked wind shell by it. The secondarily shocked wind shell should accelerates in this case to be R-T unstable, consequently producing the knots.

• Membrane Journal
• /
• v.32 no.2
• /
• pp.133-139
• /
• 2022

As the issue of reducing greenhouse gases is emerging due to global warming and extreme weather, research on materials capable of radiative cooling without energy consumption is being actively conducted. Among them, silk is known as a natural self-cooling material, but in the conventional mixing process using chemically powdered silk, there is a problem that the radiative cooling effect disappears by the collapses of the intrinsic crystal structure of silk fibroin, so it is difficult to manufacture it in the form of a film or coating agent for radiative cooling. In this study, various types of membranes were manufactured using silk powder that went through a physical pulverization process that does not damage the intrinsic structure of silk fibroin, and the study was conducted to examine its applicability as a coating agent. Electrospun membranes and flat sheet membranes were prepared by using silk fibroin powder for this purpose, and it was observed that the viscosity of the solution had a significant effect on the membrane fabrication and its properties.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.28 no.10
• /
• pp.394-401
• /
• 2016

The configuration of an extruded-type cooling structure was optimized for the light-emitting diode (LED) streetlights that have recently replaced convectional metal halide streetlights for energy saving. Natural convection and radiative heat transfer over the cooling structure were simulated using a numerical model with experimental verification. An improved cooling structure type was suggested to overcome the previous performance degeneration, as confirmed by analyzing the thermal flow around the existing cooling structure. A parameter study of the cooling structure geometries was also conducted and, based on the numerical results, the configuration was optimized to reduce the weight of the cooling structure. Consequently, the mass of the cooling structure was reduced by 60%, while the thermal performance was improved by 10%.

• Journal of Environmental Science International
• /
• v.17 no.6
• /
• pp.623-631
• /
• 2008

Many recent studies have concentrated upon the radiative effects of atmospheric aerosols. Though their scattering and absorption of radiation, aerosols can also induce some other important environment effects. In this study, new radiation code and aerosol data within Atmosphere General Circulation Model (AGCM) is used to assess the aerosol radiative forcing and to analyze relative climate effects. The new Kangnung National University AGCM Stratospheric-15 (KNU AGCM ST15) was integrated by using two sets of radiative effect of aerosols: CTRL as not a radiative effect of aerosols and AERO as a radiative effect of aerosols. Two cases show the difference of net shortwave radiation budget at top-of-atmosphere (TOA) is found to be about $-3.4Wm^{-2}$, at the surface (SFC) is about $-5.6Wm^{-2}$. Consequently the mean atmospheric absorption due to aerosol layer in global is about $2.2Wm^{-2}$. This result confirms the existence of a negative forcing due to the direct effect of aerosols at the surface and TOA in global annual mean. In addition, it is found that cooling over at the surface air temperature due to radiative effect of aerosols is about $0.17^{\circ}C$. It is estimated that radiative forcing of the net upward longwave radiation taken as the indirect effect of aerosol is much smaller than that of the direct effect as there is about $0.2Wm^{-2}$ of positive forcing both at TOA and at SFC. From this study, It made an accurate estimation of considering effect of aerosols that is negative effect. This may slow the rate of projected global warming during the $21^{st}$ century.