Daytime Radiation Research Articles

Numerical study of mid-infrared broadband perfect absorber based on dielectric/aluminium doped zinc oxide multilayer films

We propose a lithography-free wide-angle polarization-insensitive ultra-broadband absorber by using multilayer films consist of five pairs of aluminium doped zinc oxide (AZO) and a dielectric film which is supposed to be fabricated on glass substrate. The absorption spectrum of the proposed model is calculated by using transfer matrix method. The analytic results show that the absorptivity is larger than 95% with normal incidence light in the wavelength range from 7.5μm to 20μm and having high transmittance at the visible wavelength range from 0.4μm to 0.8μm range. Further, the effect of incident angle and polarization on the absorption spectrum are also investigated. The absorption spectrum of the proposed design is highly tunable on changing the damping constant of the AZO film. The electric field and magnetic distributions at different wavelengths show that the absorption is mainly originated due to the constructive interference of electromagnetic waves in the multilayer films. Such physical mechanism of broadening bandwidth based on increasing the carrier concentration of the highly visible transparent conducting films have pave a new direction for the design of tunable broadband absorber in different frequency band. Meanwhile, this broadband absorber is a good candidate for the potential applications in daytime radiation cooling system in the mid-infrared frequency band and also used as transparent conducting electrode in solar cell applications.

Superhydrophobic polytetrafluoroethylene/polyvinylidene fluoride coating for passive daytime radiative refrigeration

Passive daytime radiation refrigeration (PDRR) is a new type of refrigeration that requires no extra energy consumption and also cools objects by reflecting radiant heat from sunlight and mid-infrared wavelengths. However, the properties of ordinary radiative refrigerative (RR) materials are degraded by surface dust accumulation during use. In this work, superhydrophobic radiative refrigerative (SRR) polytetrafluoroethylene/polyvinylidene fluoride (PTFE/PVDF) coating was prepared by one-step spraying method with PTFE as white pigment, PVDF as binder, and N, N-dimethylacetamide (DMAC) as solvent. The PTFE/PVDF coating (containing 20 wt% of PTFE) exhibits synergistic effect with high water contact angle (CA, 153.7°), low water sliding angle (SA, 7.7°), high solar reflectivity (SR, 93.7%), and high infrared emissivity (IE, 93.3%). Under a clear sky and direct sunlight, the coating achieves a RR temperatures of 5.8 °C (shielding convection heat) and 5.3 °C (without shielding convection heat) respectively under two measurement conditions. In addition, the coating exhibits excellent self-cleaning properties that can automatically remove dust accumulated on the surface with the assistance of rainfall, thus maintaining its RR performance for a long time. More importantly, the mechanical robust self-cleaning function also provides excellent corrosion resistance and anti-UV aging ability. The PTFE/PVDF SRR coating developed in this work is simple to fabricate, can be applied over a large area, and has good durability, which is conducive to promoting the practicalization of RR coatings.

Integrated radiative and evaporative cooling beyond daytime passive cooling power limit

Radiative cooling technologies can passively gain lower temperature than that of ambient surroundings without consuming electricity, which has emerged as potential alternatives to traditional cooling methods. However, the limitations in daytime radiation intensity with a net cooling power of less than 150 W·m⁻² have hindered progress toward commercial practicality. Here, we report an integrated radiative and evaporative chiller (IREC) based on polyacrylamide hydrogels combined with an upper layer of breathable poly(vinylidene fluoride-co-trifluoroethylene) fibers, which achieves a record high practical average daytime cooling power of 710 W·m⁻². The breathable fiber layer has an average emissivity of over 76% in the atmospheric window, while reflecting 90% of visible light. This IREC possesses effective daytime radiative cooling while simultaneously ensuring evaporative cooling capability, enhancing daytime passive cooling effectively. As a result, IREC presents the practicability for both personal cooling managements and industrial auxiliary cooling applications. An IRECbased patch can assist in cooling human body by 13 °C low for a long term and biocompatible use, and IREC can maintain the temperature of industrial storage facilities such as oil tanks at room temperature even under strong sunlight irradiation. This work delivers the highest performance daytime passive cooling by simultaneous infrared radiation and water evaporation, and provides a new perspective for developing highly efficient, scalable, and affordable passive cooling strategy.

Facile "Synergistic Inner-Outer Activation" Strategy for Nano-Engineering of Nature-Skin-Derived Wearable Daytime Radiation Cooling Materials.

Natural skin-derived products, as traditional wearable materials are widely used in people's daily life due to the products' excellent origins. Herein, a versatile daytime-radiation cooling wearable natural skin (RC-skin) consisting of the collagen micro-nano fibers with the on-demand double-layer radiation cooling structure is nano-engineered through the proposed facile "synergistic inner-outer activation" strategy. The bottom layer (inner strategy) of the RC-skin is fabricated by filling the skin with the Mg11 (HPO3 )8 (OH)6 nanoparticles by soaking. The superstratum (outer strategy) is constituted by a composite coating with an irregular microporous structure. The RC-skin harvests the inherent advantages of natural building blocks including sufficient hydrophobicity, excellent mechanical properties, and friction resistance. Owing to the subtle double-layer structure design, the solar reflectance and the average emissivity in the mid-infrared band of RC-skin are ≈92.7% and ≈95%, respectively. Therefore, the RC-skin's temperature in the sub-ambient is reduced by ≈7.5°C. Various outdoor practical application experiments further substantiate that RC-skin has superior radiation cooling performances. Collectively, RC-skin has broad-application prospects for intelligent wearing, low-carbon travel, building materials, and intelligent thermoelectric power generation, and this study also provides novel strategies for developing natural-skin-derived functional materials.

Superhydrophobic poly-4-methyl-1-pentene/polyvinylidene fluoride coating with excellent passive daytime radiation cooling performance

Superhydrophobic poly-4-methyl-1-pentene/polyvinylidene fluoride coating with excellent passive daytime radiation cooling performance

Biomimetic Robust All-Polymer Porous Coatings for Passive Daytime Radiative Cooling.

Passive daytime radiation cooling (PDRC) has gained considerable attention as an emerging and promising cooling technology. Polymer-based porous materials are one of the important candidates for PDRC application due to their easy processing, free of inorganic particle doping, and multifunctionality. However, the mechanical properties of these porous materials, which are critical in outdoor services, have been overlooked in previous studies. Herein, a nonsolvent-induced phase separation (NIPS) method combined with ambient pressure drying to prepare polyethylene-polysilicate all-polymer porous coatings is developed. The coatings possess a Cyphochilus beetle-like skeleton structure with optimal skeleton size, laminated anisotropy, and high volume fraction (64±1%). These structure features ensure a maximum skeleton density without optical crowding, thus enhancing light scattering and stress dispersion, and balancing optical and mechanical properties. The coatings exhibit significant mechanical robustness (only ≈70µm thickness reduction after 1000 Taber abrasion cycles at a 750g load without influencing optical performance), durability, optical properties (a solar reflectance of ≈95% and an average near-normal thermal emittance of ≈96%), and PDRC performance (realizing sub-ambient cooling of ≈3-6°C at midday with different weather conditions). The work provides a new solution to improve the practicability of polymer-based porous coatings in PDRC outdoor services and other fields.

High reflective polyethylene glycol terephthalate package layer for passive daytime radiative cooling in photovoltaic cells

Passive daytime radiative cooling is a promising new field for solving the energy shortage all over the world. Especially for passive radiant cooling technology on photovoltaic field, the radiant cooling film must also have high transmittance, which undoubtedly puts forward higher requirements. At present, monocrystalline silicon photovoltaic cell are the dominant products in the photovoltaic market. Many passive cooling equipment such as temperature plates, fins, and phase change blocks will increase the weight and the complexity of photovoltaic cell, so radiative cooling thin films are attracting more and more attention due to lightweight and easy replacement. In this paper, it is proposed a composite structure of polyethylene glycol terephthalate (PET) film combined with a high-reflective layer in part of the wave band, which has a maximum transmittance of 0.97 in 0.3–1.1 μm and a maximum reflectance of 0.91 in 1.1–4.0 μm. In addition to the transmittance and reflectivity of the corresponding wavelength, the effects of electrical efficiency and cooling power are also studied. It was found that the photoelectric conversion efficiency increased, meanwhile the cooling power 211.34 W·m−2 can be reached, and the working temperature of the photovoltaic cell can be reduced by 11.65℃ under the maximum temperature 75.80℃ in normal operating conditions. Due to its excellent performance, this proposed structure may have potential practical applications in daytime radiation cooling of photovoltaic cells on sale.

High-efficiency oil-water separation and passive radiant cooling performance of nano-ZnO- embedded dust-free paper

Developing a flexible nano-composite material which is not only impermeable to low-polar oil, but also has the ability of daytime radiation cooling, remains a huge challenge for both academia and industry. By modifying the fiber network of the dust-free paper using nano-ZnO particles (ZnO-DF), we strategically designed and demonstrated dual capabilities of superhydrophilicity/superoleophobicity and daytime radiant cooling for the flexible cellulose nano-composite simultaneously. A superior surface with superhydrophilic/superoleophobic (oil contact angle up to 159° and water contact angle down to 0°) was attained by regulation of surface energy components and roughness. Furthermore, the materials revealed outstanding corrosion and mechanical damage resistance, 152,788 L m−2 h−1 high permeation flux and >99.2% continuous and efficient oil-water separation performance. In addition, a cooling effect of about 5.6 °C of ZnO-DF paper could be achieved by cooperative function of both radiative cooling and sweat evaporation. It is expected that the ZnO-DF paper is promising for the thermal management of wearable products integrated with passive radiant cooling, phase change cooling (e.g., sweat evaporation) and large-scale industrial oil-water separation.

Integration of Janus Wettability and Heat Conduction in Hierarchically Designed Textiles for All-Day Personal Radiative Cooling.

Personal cooling textiles are a promising energy-free pathway for confronting serious heat-related public health threats and improving industrial worker productivity. Current cooling strategies mainly focus on passive daytime radiation, and there is a lack of research on all-day cooling methods which utilize synergistic radiative, conductive, and evaporative heat dissipation. Herein, we demonstrate a hierarchical polyurethane/silicon nitride fibrous membrane with Janus wettability fabricated via a scalable electrospinning method followed by single-side hydrophilic plasma treatment. High angular-dependent solar reflectance (91%) and human body infrared emittance (93%) allow for a temperature drop of ∼21.9 °C under direct sunlight and ∼2.8 °C at night compared with traditional cotton. The innovative integration of Janus wettability and heat conduction in hierarchically designed textiles ensures a minimum sweat consumption of 0.5 mL h-1, avoiding harmfully excessive perspiration. The excellent all-day cooling performance of this hierarchical textile presents great advantages for smart textile, energy-saving, and personal cooling applications.

Poriferous PVC materials with high daytime radiation cooling property fabricated by etching SBS as template

In this study, poriferous PVC slices were prepared by etching SBS in PVC/SBS composites. The porosity increases slightly and the average pore size decreases with the increase of SBS mass fraction. With the increase of porosity, the thermal conductivity of sample E40 w% decreases by 46% from that of PVC. Although the small pores lead to relatively low scattering efficiency, the solar radiation reflectance of sample E40 w% is still high of 85.3%. The ultimate temperature of sample E40 w% is 3.3 °C lower than the average ambient temperature in outside cooling effect test. These results show that using polymer matrix poriferous materials is an effective daytime radiation passive cooling strategy.

Single electrode piezoelectric nanogenerator for intelligent passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) can cool down objects by simultaneously reflecting sunlight and radiating heat to the cold external space, which has no energy consumption. Traditional PDRC design usually needs to rely on micro-nano structures, which are easily damaged and lose function. On the one hand, the mechanical strength of PDRC can be enhanced. On the other hand, by integrating self-monitoring character in the same membrane fault part can be easily distinguished for fixing or replacing. Monitoring the damage by using traditional sensors will cause additional energy loss. Therefore, an intelligent PDRC that can monitor the failure itself is urgently needed to be developed. Here we found that the polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) nanofiber membrane obtained by electrospinning technology can effectively scatter sunlight, while emitting infrared rays matching the atmospheric window to achieve effective heat dissipation. In the preparation process, the electrostatic field can effectively polarize the PVDF-HFP to obtain good piezoelectric performance, which can be used to monitoring the integrity of membrane function. Meanwhile, the membrane can be used as a nanogenerator to collect mechanical energy in the environment, such as raindrop energy when used on the roof, thereby not only reducing cooling energy loss, but also collecting energy additionally, achieving a dual energy-saving design. Its excellent self-cleaning and recyclable characteristic bring more benefits to its green and energy-saving features. Therefore, this intelligent PDRC provides ideas for new energy-saving designs. At the same time, a simple preparation method is more conducive to the promotion of this technology. • Nanogenerator realizes good passive daytime radiation cooling for the first time. • The single-electrode piezoelectric nanogenerator gives PDRC the self-monitoring function to accurately monitor the working status of each area. • Efficiently collect raindrops' mechanical energy to achieve dual energy-saving design. • Self-cleaning and recyclable capabilities bring additional benefits to energy-saving design.

Assessment of the intensity and flow of straight solar radiation falling onto the horizontal surface of a room

The paper presents the results of experimental studies of straight solar radiation in the Central Chernozem region of Russia. The intensity and flow of straight solar radiation falling onto a horizontal surface of a room were evaluated. Measurements were made of the flow of straight solar radiation on a horizontal surface through a translucent structure. Experimental data were obtained using a high-class measuring device in the period from July 1 to August 1. The measurement results showed an intense wave-like change in the solar radiation flux over 8 hours. The paper describes a method for estimating the intensity and flow of straight solar radiation falling onto a horizontal surface of a room. This method of evaluating daytime radiation allows one to determine the density of the total and straight radiation flux. Using this estimate to calculate solar installations used in the Central Chernozem region, their efficiency will increase by 10%.

Comparison of different techniques for estimation of incoming longwave radiation

Global warming and climate change have left developing countries fragile in terms of agricultural production, and this vulnerability is expected to increase in the near future. The surface energy budget approach is a different perspective to the investigation of energy change over a landscape. In terms of budget items, the net radiation absorbed by the earth is equal to the difference between the sum of the incoming shortwave and longwave radiation and the sum of the reflected shortwave and emitted longwave radiation. The longwave radiation has important effects on dew deposition and drying on crop leaves in agricultural meteorology. A pyranometer provides routine measurement of the daytime radiation, but the longwave part of this radiation cannot be so readily measured at night time. In this study, multiple linear regression, artificial neural networks, deep learning, adaptive network-based fuzzy inference systems (ANFIS) and empirical models have been applied to model and estimate the mean incoming longwave radiation using atmospheric parameters. The ANFIS model appears to show good agreement between the measured and the estimated values for all days considered than other models.

Laboratory based Experimental Investigation of Photovoltaic (PV) Thermo-control with Water and its Proposed Real-time Implementation

The output of Photovoltaic (PV) panel varies with panel temperature and in order to obtain uniform output from PV panels, water cooling system is recommended by several researchers worldwide. In this study, a laboratory scale experimental setup is developed (irradiance over the PV panel is varied from 87.38 W/m2 to 359.17 W/m2 and back to initial value in a triangular cyclic shape analogous to daytime radiation variation) for intermittent and continuous water cooling, which is tested for different flow rates. A mathematical analysis of temperature over PV panel with and without water cooling system is also done. For intermittent cooling case, three different flow rates of 3 lit/min, 5.3 lit/min, and 6.2 lit/min are used, which give an increase in total energy produced against no cooling operation of about 18% for all the three cases. The test results for continuous cooling (wherein a fixed flow rate of 0.6 lit/min was maintained), the total energy produced increases by approximately 29% against no-cooling operation. The proposed method of cooling the PV panels can be integrated with the water supply system of domestic dwellings. Further, a parametric study is carried out in order to choose the appropriate capacity of pump required for the operation. The proposed approach of integrating cooling of PV panels and water supply minimizes water loss (except evaporation loss) and reuses the cooling water back into the main water supply system of the dwelling. It is observed that the continuous cooling system with a water pump of appropriate capacity improves the performance of PV panels while keeping the consumption of water to minimum.

Space spectrophotometry of the natural environment from manned orbital stations

This paper presents the results of the first spectrophotometric investigations of the atmosphere and natural formations of the earth from manned space ships and orbital stations. Visual observations by cosmonauts are compared with the results of the spectrophotometry of the twilight and daytime horizon of the earth. The evolution of optical phenomena in the earth’s atmosphere during interaction with solar radiation as the space ship moves in orbit is described. A brief description is given of a new optical phenomenon—the vertical-ray structure of the daytime radiation of the earth’s upper atmosphere in the transition region from the nighttime emission layer to the zone of a developed colored aureole. A manual satellite spectrograph is briefly described—the first spectral device ever installed on manned space ships. The results are given of the first experiment on eclipse probing of the earth’s atmosphere in order to investigate the vertical distribution of minor gaseous components. A new scientific specialization is formulated—space spectrophotometry of the natural environment.

Flux Measurement of a New Beam-down Solar Concentrating System in Miyazaki for Demonstration of Thermochemical Water Splitting Reactors

A two-step thermochemical water splitting cycle using nonstoichiometric cerium oxide is a promising solar thermochemical hydrogen production process. One of the present authors has developed new solar reactors using “internally circulating fluidized beds” with cerium oxide particles for the high-temperature cycle. These solar reactors need to be combined with a beam-down solar concentrating system. Niigata University, University of Miyazaki, and Mitaka Kohki Co. Ltd. recently started an R&D joint project to demonstrate the up-scaled fluidized bed reactors with solar. A new type of 100 kWth beam-down solar concentrating system was built in August, 2012 at the campus of University of Miyazaki. This paper describes the first results of solar flux measurements on the new Miyazaki beam-down system for demonstration of thermochemical water splitting reactors. The fluxes of concentrated solar radiation at the focus point were measured by moving an array of thirteen Gardon gauges. The solar power in an area of 130 × 130cm in the focal spot was larger than 90 kWth during three hours of daytime radiation, exceeding 110 kWth around noon on October 12, 2012. A new CPC specific to this new beam-down system was designed and fabricated to concentrate the solar fluxes into a 44cm diameter circle of the solar reactor aperture. The solar demonstration of the reactors will start at the Miyazaki beam-down system from October 2013.

Dynamic Emulations of Surface Radiation Components During Day and Night Under all Sky and Surface Conditions Using Temporal Neural Networks

Modeling of land surface radiation budget and its components is essential to a better understanding of soil-vegetation-atmosphere interactions. Time Delay Neural Network (TDNN) and Time Lag Recurrent Network (TLRN) models were used to emulate all the hourly surface radiation components for a temperate peatland during day and night under all-sky and -surface conditions. Sensitivity analyses of full versus reduced models, daytime versus nighttime periods, and TDNN versus TLRN models were carried out using training-, cross-validation, and testing-derived metrics of root mean squared error (RMSE), mean absolute error (MAE), and coefficient of determination (R2) for each of the components. The full daytime temporal neural network models performed best based on RMSE of 2.3 W m−2 in downwelling longwave radiation to 112.2 W m−2 in upwelling shortwave radiation; R2 of 0.52 in downwelling longwave radiation to 0.88 in net shortwave radiation and net radiation; and MAE of 1.73 W m−2 in downwelling longwave radiation to 90.57 W m−2 in upwelling shortwave radiation. The best nighttime TDNN models led to RMSE values that ranged from 4.4 W m−2 in downwelling longwave radiation to 9.3 W m−2 in upwelling longwave radiation; R2 values that ranged from 0.38 in net longwave radiation to 0.60 in downwelling longwave radiation; and MAE values that ranged from 4.1 W m−2 in downwelling longwave radiation to 8.1 W m−2 in upwelling longwave radiation. Temporal neural networks used in this study appear to be a promising approach to predict nonlinear behaviors of the daytime and nighttime surface radiation components.

Assessing the quality of humidity measurements from global operational radiosonde sensors

The quality of humidity measurements from global operational radiosonde sensors in upper, middle, and lower troposphere for the period 2000–2011 were investigated using satellite observations from three microwave water vapor channels operating at 183.31±1, 183.31±3, and 183.31±7 GHz. The radiosonde data were partitioned based on sensor type into 19 classes. The satellite brightness temperatures (Tb) were simulated using radiosonde profiles and a radiative transfer model, then the radiosonde simulated Tb's were compared with the observed Tb's from the satellites. The surface affected Tb's were excluded from the comparison due to the lack of reliable surface emissivity data at the microwave frequencies. Daytime and nighttime data were examined separately to see the possible effect of daytime radiation bias on the sonde data. The error characteristics among different radiosondes vary significantly, which largely reflects the differences in sensor type. These differences are more evident in the mid‐upper troposphere than in the lower troposphere, mainly because some of the sensors stop responding to tropospheric humidity somewhere in the upper or even in the middle troposphere. In the upper troposphere, most sensors have a dry bias but Russian sensors and a few other sensors including GZZ2, VZB2, and RS80H have a wet bias. In middle troposphere, Russian sensors still have a wet bias but all other sensors have a dry bias. All sensors, including Russian sensors, have a dry bias in lower troposphere. The systematic and random errors generally decrease from upper to lower troposphere. Sensors from China, India, Russia, and the U.S. have a large random error in upper troposphere, which indicates that these sensors are not suitable for upper tropospheric studies as they fail to respond to humidity changes in the upper and even middle troposphere. Overall, Vaisala sensors perform better than other sensors throughout the troposphere exhibiting the smallest systematic and random errors. Because of the large differences between different radiosonde humidity sensors, it is important for long‐term trend studies to only use data measured using a single type of sensor at any given station. If multiple sensor types are used then it is necessary to consider the bias between sensor types and its possible dependence on humidity and temperature.

Evaluating Instrumental Inhomogeneities in Global Radiosonde Upper Tropospheric Humidity Data Using Microwave Satellite Data

In this paper, the overall quality of the water vapor profiles of global operational radiosonde data for the period 2000-2009 is investigated using upper tropospheric humidity (UTH) retrieved from microwave satellite data. Overall, the nighttime radiosonde data showed a dry bias (- 5% to -15%) over Europe, Australia, and New Zealand and systematically moist bias (greater than 30%) over China and the former Soviet Union. The nighttime sonde data from the U.S. and Canada showed a bias between -10% and 20%. Most stations indicated a daytime radiation dry bias, except for a few stations from the U.S. and the former Soviet Union. A sensorwise comparison showed a large nighttime wet bias for the Russian (MRZ-3A and MARS) and Chinese GZZ-2 sensors, a relatively small nighttime wet bias for the U.S. Sippican and VIZ-B2 sensors, and a nighttime dry bias for the Chinese GTS1, Vaisala (RS80-A, RS80-H, RS90, RS92K, and RS92-SGP), and the U.S. VIZ-MKII sensors. All sensors had a daytime radiation dry bias, except for the Russian MRZ-3A sensor that had a daytime radiation wet bias that could be because of the daytime radiation bias correction. Because of the large differences between different radiosonde sensors, it is essential for UTH studies to only use the data measured using a single type of sensor at any given station.

Algorithm for daytime radiation fog detection based on MODIS/TERRA data over land

We present an algorithm for daytime radiation fog detection (ADRFD) to characterize the fog distribution over land areas through two main steps: (1) detection of areas with clouds and radiation fog based on edge pixels and (2) separation of radiation fog from clouds based on object properties. The algorithm is tested in southeast China over an area of 2,640,000 km2 (longitude extent: 105°E to 122°E, latitude extent: 23°N to 40°N), with 1 km resolution moderate resolution imaging spectroradiometer/TERRA images, digital elevation model of China (grid size is 1×1 km2 and accuracy of elevation is 25 m), and the fog detection accuracies are evaluated using the observation results from 3590 ground observation stations. Results show that ADRFD can detect areas with clouds and radiation fog and effectively differentiate radiation fog from clouds based on object properties with a Kappa coefficient of 0.89 and critical success index at 0.87. It is concluded that ADRFD is a promising approach for daytime radiation fog detection over large land surfaces based on the condition that fog objects do not intersect with cloud objects or are not located under cloud objects. Extensions of this current study will be on improving the parameters determination method of ADRFD. ADRFD can be used to detect other types of fog in different regions and different seasons theoretically, but it should be tested further. In addition, more improvements are needed to allow for the detection of smaller areas of fog and fog regions intersecting with or under clouds.