Photon tunneling effects give rise to surface waves,amplifying radiative heat transfer in the near-field regime.Recent research has highlighted that the introduction of nanopores into materials creates additional path...Photon tunneling effects give rise to surface waves,amplifying radiative heat transfer in the near-field regime.Recent research has highlighted that the introduction of nanopores into materials creates additional pathways for heat transfer,leading to a substantial enhancement of near-field radiative heat transfer(NFRHT).Being a direct bandgap semiconductor,GaN has high thermal conductivity and stable resistance at high temperatures,and holds significant potential for applications in optoelectronic devices.Indeed,study of NFRHT between nanoporous GaN films is currently lacking,hence the physical mechanism for adding nanopores to GaN films remains to be discussed in the field of NFRHT.In this work,we delve into the NFRHT of GaN nanoporous films in terms of gap distance,GaN film thickness and the vacuum filling ratio.The results demonstrate a 27.2%increase in heat flux for a 10 nm gap when the nanoporous filling ratio is 0.5.Moreover,the spectral heat flux exhibits redshift with increase in the vacuum filling ratio.To be more precise,the peak of spectral heat flux moves fromω=1.31×10^(14)rad·s^(-1)toω=1.23×10^(14)rad·s^(-1)when the vacuum filling ratio changes from f=0.1 to f=0.5;this can be attributed to the excitation of surface phonon polaritons.The introduction of graphene into these configurations can highly enhance the NFRHT,and the spectral heat flux exhibits a blueshift with increase in the vacuum filling ratio,which can be explained by the excitation of surface plasmon polaritons.These findings offer theoretical insights that can guide the extensive utilization of porous structures in thermal control,management and thermal modulation.展开更多
Passive daytime radiative cooling(PDRC)is an innovative and sustainable cooling technology that holds immense potential for addressing the energy crisis.Despite the numerous reports on radiative coolers,the design of ...Passive daytime radiative cooling(PDRC)is an innovative and sustainable cooling technology that holds immense potential for addressing the energy crisis.Despite the numerous reports on radiative coolers,the design of a straightforward,efficient,and readily producible system remains a challenge.Herein,we present the development of a hierarchical aligned porous poly(vinylidene fluoride)(HAP-PVDF)film through a freeze-thaw-promoted nonsolvent-induced phase separation strategy.This film features oriented microporous arrays in conjunction with random nanopores,enabling efficient radiative cooling performance under direct sunlight conditions.The incorporation of both micro-and nano-pores in the HAP-PVDF film results in a remarkable solar reflectance of 97%and a sufficiently high infrared thermal emissivity of 96%,facilitating sub-environmental cooling at 18.3℃ on sunny days and 13.1℃ on cloudy days.Additionally,the HAP-PVDF film also exhibits exceptional flexibility and hydrophobicity.Theoretical calculations further confirm a radiative cooling power of 94.8 W·m^(-2)under a solar intensity of 1000W·m^(-2),demonstrating a performance comparable to the majority of reported radiative coolers.展开更多
A transparent radiative cooling(T-RC)film with low transmittance in solar spectra and selectively high emissivity in the atmospheric window(8-13𝜇m)is applied on roof glazing for building energy saving.To evalu...A transparent radiative cooling(T-RC)film with low transmittance in solar spectra and selectively high emissivity in the atmospheric window(8-13𝜇m)is applied on roof glazing for building energy saving.To evaluate the per-formance of the T-RC film,two identical model boxes(1.0 m×0.6 m×1.2 m,L×W×H)were constructed and the inside air temperatures were measured in August in Ningbo,China.Results show that the maximum temperature difference between the two model boxes with and without the T-RC film was 21.6℃during the experiment.A whole building model was built in EnergyPlus for the model box.With a good agreement achieved between the calculation results and the measured temperature data,the experimentally validated EnergyPlus model was then extended to an 815.1 m^(2)exhibition building with roof glazing to analyze the annual air conditioning(AC)energy consumption.The results show that by incorporating both the T-RC film’s cooling benefit in summer and heating penalty in winter,the annual AC energy consumption of the exhibition building can be reduced by 40.9-63.4%,varying with different climate conditions.展开更多
In this paper, an optical radiative cooler with quasi-Cantor structure is theoretically proposed and analyzed. This simple and symmetrically designed optical structure operates upon continuous thermal sources in diurn...In this paper, an optical radiative cooler with quasi-Cantor structure is theoretically proposed and analyzed. This simple and symmetrically designed optical structure operates upon continuous thermal sources in diurnal subtropical conditions, and its efficiency is much higher than natural cooling, for instance, when operating upon a typical 323.15 K continuous thermal source with a wind speed at 3 m·s^-1, it can generate a net cooling power of 363.68 W·m^-2, which is 18.26% higher than that of non-radiative heat exchange （natural cooling） under the same conditions. Additionally, several aspects are considered in its design to ensure a low cost in application, which is of great economical and environmental significance.展开更多
Passive daytime radiative cooling(PDRC) is useful for thermal management because it allows an object to emit terrestrial heat into space without the use of additional energy.To produce sub-ambient temperatures under d...Passive daytime radiative cooling(PDRC) is useful for thermal management because it allows an object to emit terrestrial heat into space without the use of additional energy.To produce sub-ambient temperatures under direct sunlight,PDRC materials are designed to reduce their absorption of solar energy and to enhance their long-wavelength infrared(LWIR) emissivity.In recent years,many photonic structures and polymer composites have been studied to improve the cooling system of buildings.However,in cold weather(i.e. during winter in cold climates),buildings need to be kept warm rather than cooled due to heat loss.To overcome this limitation,temperature-responsive radiative cooling is a promising alternative.In the present study,adaptive radiative cooling(ARC) film fabricated from a polydimethylsiloxane/hollow SiO_(2) microsphere/thermochromic pigment composite was investigated.We found that the ARC film absorbed solar radiation under cold conditions while exhibiting radiative cooling at ambient temperatures above 40℃.Thus,in outdoor experiments,the ARC film achieved sub-ambient temperatures and had a theoretical cooling power of 63.2 W/m~2 in hot weather.We also demonstrated that radiative cooling with an energy harvesting system could be used to improve the energy management of buildings,with the thermoelectric module continuously generating output power using the ARC film.Therefore,we believe that our proposed ARC film can be employed for efficient thermal management of buildings and all-season energy harvesting in the near future.展开更多
Colorful radiative coolers(CRCs)can be widely applied for energy sustainability especially and meet aesthetic purposes simultaneously.Here,we propose a high-efficiency CRC based on thin film stacks and engineered diff...Colorful radiative coolers(CRCs)can be widely applied for energy sustainability especially and meet aesthetic purposes simultaneously.Here,we propose a high-efficiency CRC based on thin film stacks and engineered diffuse reflection unit,which brings out 7.1°C temperature difference compared with ambient under~700 W·m^(−2) solar irradiation.Different from analogous schemes,the proposed CRCs produce vivid colors by diffuse reflection and rest of the incident light is specular-reflected without being absorbed.Adopting the structure of TiO_(2)/SiO_(2) multilayer stack,the nanophotonic radiative cooler shows extra low absorption across the solar radiation waveband.Significant radiative cooling performance can be achieved with the emissivity reaching 95.6%in the atmosphere transparent window(8-13μm).Moreover,such CRC can be fabricated on flexible substrates,facilitating various applications such as the thermal management of cars or wearables.In conclusion,this work demonstrates a new approach for color display with negligible solar radiation absorption and paves the way for prominent radiative cooling.展开更多
The sun and outer space are the ultimate heat and cold sources for the earth,respectively.They have significant potential for renewable energy harvesting.In this paper,a spectrally selective surface structure that has...The sun and outer space are the ultimate heat and cold sources for the earth,respectively.They have significant potential for renewable energy harvesting.In this paper,a spectrally selective surface structure that has a planar polydimethylsiloxane layer covering a solar absorber is conceptually proposed and optically designed for the combination of photothermic conversion(PT)and nighttime radiative sky cooling(RC).An optical simulation is conducted whose result shows that the designed surface structure(i.e.,PT-RC surface structure)has a strong solar absorption coefficient of 0.92 and simultaneously emits as a mid-infrared spectral-selective emitter with an average emissivity of 0.84 within the atmospheric window.A thermal analysis prediction reveals that the designed PTRC surface structure can be heated to 79.1℃higher than the ambient temperature in the daytime and passively cooled below the ambient temperature of approximately 10℃in the nighttime,indicating that the designed PT-RC surface structure has the potential for integrated PT conversion and nighttime RC utilization.展开更多
Spectrally selective glazing system attracts great attention for energy efficient radiator applications. The present work reports the possibility of a specific shield (Stainless steel/Borosilicate glass) to provide pa...Spectrally selective glazing system attracts great attention for energy efficient radiator applications. The present work reports the possibility of a specific shield (Stainless steel/Borosilicate glass) to provide passive cooling for the purpose of reducing the use of classical active method. Radiative cooling devices require a convective shield that blocks all incoming solar radiation, but should selectively reemit radiation in the “atmospheric-window” region. In this study, borosilicate glass substrate coated with a stainless steel thin film was prepared by thermal evaporation and low pressure (6.3 × 10<sup>-3</sup> bar) DC plasma sputtering, in order to achieve the radiative cooling effect. The optical properties of the optimal thickness thin film were measured in the wavelength range of 0.3-20 μm by an OL-750 double-beam spectroradiometer. The thin film has high visible band reflectance with high infrared band emissivity across the full 8-13 μm;which indicates that stainless steel thin film can be used as good radiative cooling material.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No.52106099)the Natural Science Foundation of Shandong Province (Grant No.ZR2022YQ57)the Taishan Scholars Program。
文摘Photon tunneling effects give rise to surface waves,amplifying radiative heat transfer in the near-field regime.Recent research has highlighted that the introduction of nanopores into materials creates additional pathways for heat transfer,leading to a substantial enhancement of near-field radiative heat transfer(NFRHT).Being a direct bandgap semiconductor,GaN has high thermal conductivity and stable resistance at high temperatures,and holds significant potential for applications in optoelectronic devices.Indeed,study of NFRHT between nanoporous GaN films is currently lacking,hence the physical mechanism for adding nanopores to GaN films remains to be discussed in the field of NFRHT.In this work,we delve into the NFRHT of GaN nanoporous films in terms of gap distance,GaN film thickness and the vacuum filling ratio.The results demonstrate a 27.2%increase in heat flux for a 10 nm gap when the nanoporous filling ratio is 0.5.Moreover,the spectral heat flux exhibits redshift with increase in the vacuum filling ratio.To be more precise,the peak of spectral heat flux moves fromω=1.31×10^(14)rad·s^(-1)toω=1.23×10^(14)rad·s^(-1)when the vacuum filling ratio changes from f=0.1 to f=0.5;this can be attributed to the excitation of surface phonon polaritons.The introduction of graphene into these configurations can highly enhance the NFRHT,and the spectral heat flux exhibits a blueshift with increase in the vacuum filling ratio,which can be explained by the excitation of surface plasmon polaritons.These findings offer theoretical insights that can guide the extensive utilization of porous structures in thermal control,management and thermal modulation.
基金financially supported by the National Natural Science Foundation of China(No.52273067)the Fundamental Research Funds for the Central Universities(No.2232023A-03)the Shuguang Program of Shanghai Education Development Foundation and Shanghai Municipal Education Commission(No.23SG29)。
文摘Passive daytime radiative cooling(PDRC)is an innovative and sustainable cooling technology that holds immense potential for addressing the energy crisis.Despite the numerous reports on radiative coolers,the design of a straightforward,efficient,and readily producible system remains a challenge.Herein,we present the development of a hierarchical aligned porous poly(vinylidene fluoride)(HAP-PVDF)film through a freeze-thaw-promoted nonsolvent-induced phase separation strategy.This film features oriented microporous arrays in conjunction with random nanopores,enabling efficient radiative cooling performance under direct sunlight conditions.The incorporation of both micro-and nano-pores in the HAP-PVDF film results in a remarkable solar reflectance of 97%and a sufficiently high infrared thermal emissivity of 96%,facilitating sub-environmental cooling at 18.3℃ on sunny days and 13.1℃ on cloudy days.Additionally,the HAP-PVDF film also exhibits exceptional flexibility and hydrophobicity.Theoretical calculations further confirm a radiative cooling power of 94.8 W·m^(-2)under a solar intensity of 1000W·m^(-2),demonstrating a performance comparable to the majority of reported radiative coolers.
基金D.Z.acknowledges the support from“the Fundamental Re-search Funds for the Central Universities”under award number 2242020R10017.
文摘A transparent radiative cooling(T-RC)film with low transmittance in solar spectra and selectively high emissivity in the atmospheric window(8-13𝜇m)is applied on roof glazing for building energy saving.To evaluate the per-formance of the T-RC film,two identical model boxes(1.0 m×0.6 m×1.2 m,L×W×H)were constructed and the inside air temperatures were measured in August in Ningbo,China.Results show that the maximum temperature difference between the two model boxes with and without the T-RC film was 21.6℃during the experiment.A whole building model was built in EnergyPlus for the model box.With a good agreement achieved between the calculation results and the measured temperature data,the experimentally validated EnergyPlus model was then extended to an 815.1 m^(2)exhibition building with roof glazing to analyze the annual air conditioning(AC)energy consumption.The results show that by incorporating both the T-RC film’s cooling benefit in summer and heating penalty in winter,the annual AC energy consumption of the exhibition building can be reduced by 40.9-63.4%,varying with different climate conditions.
基金supported by the Natural Science Foundation of Guangdong Province,China(Grant No.2016A030313851)the Provincial Undergraduate Training Program for Innovation and Entrepreneurship of Guangdong Province,China(Grant No.201610574149)
文摘In this paper, an optical radiative cooler with quasi-Cantor structure is theoretically proposed and analyzed. This simple and symmetrically designed optical structure operates upon continuous thermal sources in diurnal subtropical conditions, and its efficiency is much higher than natural cooling, for instance, when operating upon a typical 323.15 K continuous thermal source with a wind speed at 3 m·s^-1, it can generate a net cooling power of 363.68 W·m^-2, which is 18.26% higher than that of non-radiative heat exchange （natural cooling） under the same conditions. Additionally, several aspects are considered in its design to ensure a low cost in application, which is of great economical and environmental significance.
基金supported by the Industrial-linked Low-carbon Process Conversion Core Technology Development Program (RS2022-00155175)the Materials/Parts Technology Development Program (20022507) funded by the Ministry of Trade, Industry & Energy (MOTIE, Republic of Korea)the Korea Research Institute of Chemical Technology (KRICT) core project (SS2221-20)。
文摘Passive daytime radiative cooling(PDRC) is useful for thermal management because it allows an object to emit terrestrial heat into space without the use of additional energy.To produce sub-ambient temperatures under direct sunlight,PDRC materials are designed to reduce their absorption of solar energy and to enhance their long-wavelength infrared(LWIR) emissivity.In recent years,many photonic structures and polymer composites have been studied to improve the cooling system of buildings.However,in cold weather(i.e. during winter in cold climates),buildings need to be kept warm rather than cooled due to heat loss.To overcome this limitation,temperature-responsive radiative cooling is a promising alternative.In the present study,adaptive radiative cooling(ARC) film fabricated from a polydimethylsiloxane/hollow SiO_(2) microsphere/thermochromic pigment composite was investigated.We found that the ARC film absorbed solar radiation under cold conditions while exhibiting radiative cooling at ambient temperatures above 40℃.Thus,in outdoor experiments,the ARC film achieved sub-ambient temperatures and had a theoretical cooling power of 63.2 W/m~2 in hot weather.We also demonstrated that radiative cooling with an energy harvesting system could be used to improve the energy management of buildings,with the thermoelectric module continuously generating output power using the ARC film.Therefore,we believe that our proposed ARC film can be employed for efficient thermal management of buildings and all-season energy harvesting in the near future.
文摘Colorful radiative coolers(CRCs)can be widely applied for energy sustainability especially and meet aesthetic purposes simultaneously.Here,we propose a high-efficiency CRC based on thin film stacks and engineered diffuse reflection unit,which brings out 7.1°C temperature difference compared with ambient under~700 W·m^(−2) solar irradiation.Different from analogous schemes,the proposed CRCs produce vivid colors by diffuse reflection and rest of the incident light is specular-reflected without being absorbed.Adopting the structure of TiO_(2)/SiO_(2) multilayer stack,the nanophotonic radiative cooler shows extra low absorption across the solar radiation waveband.Significant radiative cooling performance can be achieved with the emissivity reaching 95.6%in the atmosphere transparent window(8-13μm).Moreover,such CRC can be fabricated on flexible substrates,facilitating various applications such as the thermal management of cars or wearables.In conclusion,this work demonstrates a new approach for color display with negligible solar radiation absorption and paves the way for prominent radiative cooling.
基金the National Natural Science Foundation of China(Grant Nos.51776193,51761145109,and 51906241).
文摘The sun and outer space are the ultimate heat and cold sources for the earth,respectively.They have significant potential for renewable energy harvesting.In this paper,a spectrally selective surface structure that has a planar polydimethylsiloxane layer covering a solar absorber is conceptually proposed and optically designed for the combination of photothermic conversion(PT)and nighttime radiative sky cooling(RC).An optical simulation is conducted whose result shows that the designed surface structure(i.e.,PT-RC surface structure)has a strong solar absorption coefficient of 0.92 and simultaneously emits as a mid-infrared spectral-selective emitter with an average emissivity of 0.84 within the atmospheric window.A thermal analysis prediction reveals that the designed PTRC surface structure can be heated to 79.1℃higher than the ambient temperature in the daytime and passively cooled below the ambient temperature of approximately 10℃in the nighttime,indicating that the designed PT-RC surface structure has the potential for integrated PT conversion and nighttime RC utilization.
文摘Spectrally selective glazing system attracts great attention for energy efficient radiator applications. The present work reports the possibility of a specific shield (Stainless steel/Borosilicate glass) to provide passive cooling for the purpose of reducing the use of classical active method. Radiative cooling devices require a convective shield that blocks all incoming solar radiation, but should selectively reemit radiation in the “atmospheric-window” region. In this study, borosilicate glass substrate coated with a stainless steel thin film was prepared by thermal evaporation and low pressure (6.3 × 10<sup>-3</sup> bar) DC plasma sputtering, in order to achieve the radiative cooling effect. The optical properties of the optimal thickness thin film were measured in the wavelength range of 0.3-20 μm by an OL-750 double-beam spectroradiometer. The thin film has high visible band reflectance with high infrared band emissivity across the full 8-13 μm;which indicates that stainless steel thin film can be used as good radiative cooling material.
