Herein, we present a comprehensive review of the recent research efforts in addressing the challenge of low cooling power of radiative sky cooling (RSC) and offer promising avenues for further ...performance breakthroughs of this technology, mainly from reducing solar absorption, enhancing infrared emission, switchable emission and hybrid strategy.
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•The emerging materials and engineering strategies for performance advance of radiative sky cooling are summarized.•The efforts in reducing solar absorption and enhancing infrared emission are discussed in detail.•The great potential of thermochromic materials for switchable cooling/heating is highlighted.•The promising applications of hybrid strategies with evaporative cooling and electronics are discussed.•The remaining challenges and the insights are presented for the further performance breakthrough.
With the growing global warming and climate change, the demand for clean cooling technologies has witnessed a sharp increase. Radiative sky cooling (RSC) can dissipate heat via the atmospheric window without pollution and energy consumption. Nevertheless, the low cooling power greatly blocks the large-scale application of this technology. Herein, a critical review of the recent efforts in addressing this challenge is presented to offer promising avenues for further performance breakthroughs of RSC technology. Firstly, working principles are presented to reveal the critical factors for efficient radiative cooling performance. Subsequently, systematic discussions on the efforts of reducing solar absorption are delivered and the promising structures for 99% solar reflectivity are highlighted. Particularly, the two promising strategies for enhancing infrared emission are discussed to evaluate their potential in commercial applications. Additionally, the promising designs for switchable solar reflectance and infrared emission are further outlined with a focus on switchable radiative cooling. More strikingly, hybrid strategies are highlighted for their great improvement in radiative cooling power and application scope. The last section outlines the remaining challenges and the corresponding insights for the further advance of RSC technology.
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•Magnetic entropy change of samples was investigated at low temperatures.•These samples show second-order transition phase.•A discord between experimental magnetic entropy change and ...Landau theory.
Magnetic entropy change of Dy0.5(Sr1−xCax)0.5MnO3 nanoparticles (0≤x≤0.3) was analyzed at low temperatures to investigate the magnetic refrigeration as a promising tool for hydrogen liquefaction. These samples depict interesting values of maximum magnetic entropy change and large relative cooling power, especially for x=0.3 sample (about 169J/Kg). It could be a promising candidate for magnetic refrigeration at cryogenic temperatures. Landau theory presents a discord between the experimental magnetic entropy change and the theoretical one. This disagreement is tending to be in accordance as Ca substitution is increasing and also with augmenting the applied magnetic field.
We show by extensive Monte Carlo simulations that we need a multi-spin interaction in addition to pairwise interactions in order to reproduce the temperature dependence of the experimental ...magnetization observed in the perovskite compound Pr0.67Sr0.33MnO3. The multi-spin interaction is introduced in the Hamiltonian as follows: each spin interacts simultaneously with its four nearest-neighbors. It does not have the reversal invariance as in a pairwise interaction where reversing the directions of two spins leaves the interaction energy invariant. As a consequence, it competes with the pairwise interactions between magnetic ions. The multi-spin interaction allows the sample magnetization M to increase, to decrease or to have a plateau with increasing T. In this paper we show that M increases with increasing T before making a vertical fall at the transition temperature TC, in contrast to the usual decrease of M with increasing T in most of magnetic systems. This result is in an excellent agreement with the experimental data observed in Pr0.67Sr0.33MnO3. Furthermore, we show by the energy histogram taken at TC that the transition is clearly of first order. We also calculate the magnetic entropy change |ΔSm| and the Relative Cooling Power (RCP) by using the set of curves of M obtained under an applied magnetic field H varying from 0 to 5 T across the transition temperature region. We obtain a good agreement with experiments on |ΔSm| and the values of RCP. This perovskite compound has a good potential in refrigeration application due to its high RCP.
•Modeling using a multi-spin Interaction for Pr0.67Sr0.33MnO3.•Unusual temperature dependence of the magnetization.•First-order phase transition using Monte Carlo energy histogram technique.•Large magnetic entropy change and high RCP.•Good agreement between modeling and experiments on above-mentioned properties.
Passive Air Cooling
In article number 2303470, Steven Wang and co‐workers demonstrated a camel‐fur‐inspired passive membrane encapsulated sorbent cooler that can periodically absorb moisture from the ...atmosphere and release it for daytime evaporative cooling, leading to effective regulation of building temperature without additional energy input. In the evaporative‐cooling demonstration, the average cooling power of the camel‐fur‐inspired sorbent can reach up to 630 W m−2, which is much higher than the radiative cooling approach.
Adsorption refrigeration technology is being increasingly investigated over the past few decades as a sustainable technology option for meeting the fast-growing cooling needs for refrigeration and ...air-conditioning. What is attractive about adsorption technology is the opportunity to use low grade thermal energy such as solar heat and industrial waste heat. The present study is an attempt to provide readers a comprehensive update on status and challenges of adsorption refrigeration. The effects of working parameters like evaporator temperature, condenser temperature, regeneration temperature, cycle time, and inter-stage pressure on coefficient of performance and specific cooling power are covered with an objective to include experimental as well as theoretical research work reported thus far. Research work consolidated in this study includes the integrated cycles of adsorption cooling, adsorber design with extended surfaces, multi-stage and/or multi-bed scheme, and heat and/or mass recovery scheme either in combination or individually for thermal performance enhancement. Furthermore, work on a state of the art of various commercially available adsorption chillers highlighting their cooling capacity, working temperature range, novelties, and applications are reported in detail. This review also reveals an opportunity for research in optimizing the mechanism, design, orientation of the heat exchangers, functioning, and customizing the vapour adsorption refrigeration system for widespread applications in various sectors like automobiles and agriculture. Authors present this study with an expectation to provide beginners a quick review in the area of adsorption cooling technology.
•Technological advancements in adsorption chillers are presented chronologically.•Novel hybrid and integrated adsorption cooling-desalination cycles are discussed.•Heat and mass recovery schemes on adsorption cooling are thoroughly explored.•Effect of different fin configurations on adsorber performance has been reviewed.•Commercially available advanced adsorption cycles have been summarized.
•The compound Ca3Ti2O7 has been studied;•The DFT and Monte Carlo simulations have been applied;•The Optical, Electric and Electrocaloric properties have been deduced;•The RCT of Ca3Ti2O7 has been ...envisaged.
Using the DFT we investigated the optical, structural and electronic properties of Ca3Ti2O7 with the full-potential linearized augmented plane-wave (FP-LAPW) approach with the code “Wien2k”. The lattice constants of Ca3Ti2O7 have been derived by the GGA-PBE approximation. We obtained an indirect energy band gap value of Eg = 1.774 eV between N and Γ points. The thermodynamic properties have also been calculated and debated. In addition, the absorption coefficient, reflectivity, optical conductivity, dielectric function, refractive index and extinction coefficient are achieved. In some cases, the electro-caloric properties of the Ca3Ti2O7 compound have been examined by Monte Carlo simulations. The polarization with different electric field values is also demonstrated. This polarization shows a phase transition from a ferroelectric to a para-electric state close to the Curie temperature TC equal to 1104.001 K. At last, the electric entropy changes of the temperatures have been inferred. To complete this study, we have calculated the relative cooling power (RCP) parameter for the corresponding Ca3Ti2O7 and the electrical hysteresis loops.
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•(La1-xBix)0.67Ba0.33MnO3 (x = 0-0.3) ceramics are synthesized through solid state reaction method.•Due to decrease in electronic bandwidth induced by Bi substitution, decrease in ...ferromagnetic TC is noticed.•Occurrence of Griffiths phase becomes prominent for higher Bi contents.•Positive slopes in Arrott plots confirm second order magnetic transition from PM to FM state.•Remarkable enhancement in relative cooling power (RCP) is observed which makes them suitable for magnetic refrigeration.
The magnetic and magnetocaloric properties of (La1-xBix)0.67Ba0.33MnO3 (for x = 0 - 0.3) ceramics are reported. Magnetization measurements reveal the onset of a ferromagnetic ordering (TC) in the range 336 K- 229 K which shifts towards low temperatures with increasing x. Magnetocaloric effect (MCE) measurements yield the maximum value of entropy change (-ΔSMmax) around TC that decreases from ∼6.19 J/ Kg/K for x = 0 to ∼4.79 J/ Kg/K for x = 0.3 for a field change of 9 T. Remarkable enhancement in the relative cooling power (RCP) is observed with the value increasing from ∼400.45 J/Kg for x = 0 to ∼472.81 J/Kg for x = 0.3. The substantial increase in the magnetocaloric properties of (La1-xBix)0.67Ba0.33MnO3 compounds compared to other compounds reported in the literature makes them potential candidates to be used for magnetic refrigeration purposes.
•An innovative conch-shaped radiative cooling film car cover is designed to maximize surface area (up to 57.268 m2) within a limited space of 5 m by 2 m.•The design can achieve a high cooling power ...of 5726.8 W to effectively cool the car under strong solar irradiance of 800 W·m−2. The temperature decrease is up to 27 °C.•Car covers with different surface coverages are compared to a commercial plain car cover. The results show that radiative cooling technology can play a key role in cooling cars, and the cooling effect can be maximized by enlarging the surface area.
Due to the capability of cooling objects without energy consumption by emitting thermal radiation into outer space, radiative cooling technologies have found broad applications in different scenarios. Despite the high demand for cooling automobiles under sunlight, there is no specialized design of a radiative cooling cover for automobiles. This paper demonstrates the first specialized radiative cooling cover for automobiles. As the overall cooling power is linearly proportional to the surface area, we designed a conch-shaped foldable radiative cooling film car cover to maximize the surface area within a limited space, resulting in a total cooling power of 5,726.8 W. As a result, the maximum temperature drop can reach 27 °C under strong solar irradiance (800 Wm−2). In addition, we further demonstrate the effects of the surface coverage on the cooling performance by measuring the temperature drop at different surface coverages (100 %, 90 %, 40 %, and 10 %). It is found that the radiative cooling cover can effectively cool the inner temperature of a car even with a small surface coverage. In addition, it confirms that enlarging surface area is an effective way to improve cooling performance. Our results open new possibilities in designing radiative cooling covers that can achieve large cooling power within a limited footprint. The design principle can be extended and generally applied to other radiative cooling devices for various applications.
•The magnetocaloric effect of Cu0.35Zn0.65Fe2O4 (CZF) covers a large range of temperature.•The relative cooling power (RCP) in CZF is better than RCP of the famous refrigerants.•CZF is advantageous ...to be a working substance in refrigeration.
Here, it is reported that magnetocaloric effect of Cu0.35Zn0.65Fe2O4 (CZF) ferrite covers a large range of temperature as an effective material for magnetic refrigerator (MR). In addition, the relative cooling power (RCP) in CZF ferrite is significantly larger than corresponding values of the famous magnetic refrigerants such as Gd, MnAs1−xSbx, Gd5Si2Ge2, (La–Sr)MnO3, (Pr–Sr)MnO3, (La–Sr)MnO3, (La–Ca–Pb)MnO3, and (La–Ca–Sr)MnO3. Therefore, CZF ferrite is useful to be a working substance in MR as a single magnetic refrigerant, including room temperature and very low temperatures.
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