Research

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15 pages, 8882 KiB

Open AccessArticle

A Pore Scale Study on Heat Transfer Characteristics of Integrated Thermal Protection Structures with Phase Change Material

by Ziyuan Huang, Hongming Zhang, Chao Zhang, Wei Tang, Guangming Xiao and Yanxia Du

Energies 2024, 17(2), 465; https://doi.org/10.3390/en17020465 - 18 Jan 2024

Viewed by 598

Abstract

Phase change material (PCM) are characterized by their high latent heat and low density. Combining PCM with building walls, aircraft fuselages, and other structures can significantly enhance the thermal sink capability of these structures. In order to address the issue of low heat [...] Read more.

Phase change material (PCM) are characterized by their high latent heat and low density. Combining PCM with building walls, aircraft fuselages, and other structures can significantly enhance the thermal sink capability of these structures. In order to address the issue of low heat storage efficiency resulting from the low thermal conductivity of PCM, a novel integrated thermal protection structure (ITPS) architecture with a supportive structure based on a porous lattice has been designed. Experimental and numerical methods were employed to investigate the thermal response characteristics of the ITPS with and without PCM, the melting behavior of PCM within the porous lattice, and the effects of lattice configuration and pore size on the PCM melting rate. The current ITPS study includes evaluation of two types of lattice configurations and three different pore sizes. The results indicate that the inclusion of PCM reduces the internal panel temperature of the ITPS by approximately 15%. The melting of PCM occurs primarily at the central region of the porous lattice and gradually spreads towards the periphery until complete melting is achieved. Specifically, the Gibson–Ashby lattice configuration enhances the PCM melting rate by 43.5%, while the tetradecahedron lattice configuration yields a 53.1% improvement. Furthermore, for PCM with different pore sizes, smaller pores exhibit faster melting rates during the early and intermediate stages, whereas larger pores exhibit faster melting rates in the later stages as the proportion of liquid PCM increases. The conclusions of this study provide valuable insights for the application of PCM in the field of thermal management. Full article

(This article belongs to the Special Issue Advances in Solar Thermal Energy Harvesting, Storage and Conversion)

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21 pages, 3961 KiB

Open AccessArticle

Solar-Thermal-Chemical Integrated Design of a Cavity-Type Solar-Driven Methane Dry Reforming Reactor

by Zhou-Qiao Dai, Xu Ma, Xin-Yuan Tang, Ren-Zhong Zhang and Wei-Wei Yang

Energies 2023, 16(6), 2781; https://doi.org/10.3390/en16062781 - 16 Mar 2023

Viewed by 1429

Abstract

In this work, the solar-thermal-chemical integrated design for a methane dry reforming reactor with cavity-type solar absorption was numerically performed. Combined with a multiphysical reactor model, the gradient optimization algorithm was used to find optimal radiation flux distribution with fixed total incident solar [...] Read more.

In this work, the solar-thermal-chemical integrated design for a methane dry reforming reactor with cavity-type solar absorption was numerically performed. Combined with a multiphysical reactor model, the gradient optimization algorithm was used to find optimal radiation flux distribution with fixed total incident solar energy for maximizing overall hydrogen yield, defined as the ratio of molar flow of exported hydrogen to imported methane, which can be applied for guiding the optical property design of solar adsorption surface. The comprehensive performances of the reactor under the conditions of original solar flux and optimal solar flux were analyzed and compared. The results show that for the inlet volume flow rate of 8–14 L·min⁻¹, the hydrogen production rate was increased by up to 5.10%, the energy storage efficiency was increased by up to 5.55%, and the methane conversion rate was increased by up to 6.01%. Finally, the local absorptivities of the solar-absorptive coating on the cavity walls were optimized and determined using a genetic algorithm, which could realize the predicted optimal radiation flux distribution. Full article

(This article belongs to the Special Issue Advances in Solar Thermal Energy Harvesting, Storage and Conversion)

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13 pages, 19287 KiB

Open AccessArticle

A Novel Pressure-Controlled Molecular Dynamics Simulation Method for Nanoscale Boiling Heat Transfer

by Cong Wang, Yalong Kong, Zhigang Liu, Lin Guo and Yawei Yang

Energies 2023, 16(5), 2131; https://doi.org/10.3390/en16052131 - 22 Feb 2023

Cited by 1 | Viewed by 1334

Abstract

Pool boiling, enabling remarkable phase-change heat transfer, has elicited increasing attention due to its ubiquitous applications in solar thermal power stations. An explicit understanding of the effect of system pressure on pool boiling is required to enhance the phase-change heat transfer. Despite its [...] Read more.

Pool boiling, enabling remarkable phase-change heat transfer, has elicited increasing attention due to its ubiquitous applications in solar thermal power stations. An explicit understanding of the effect of system pressure on pool boiling is required to enhance the phase-change heat transfer. Despite its wide application when exploring the potential mechanism of boiling, the molecular dynamics method still needs to be improved when discussing the working mechanism of system pressure. Therefore, in the present study, a novel molecular dynamics simulation method of nanoscale pool boiling was proposed. This method provides a way to change and control pressure during the phase-change process. Furthermore, the bubble nucleation and growth in nanoscale pool boiling are quantitatively investigated through pressure-control molecular dynamics simulations. We expect that this study will improve the present simulation method of pool boiling and provide useful insights to the physics of the process. Full article

(This article belongs to the Special Issue Advances in Solar Thermal Energy Harvesting, Storage and Conversion)

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18 pages, 1483 KiB

Open AccessArticle

A New Two-Foci V-Trough Concentrator for Small-Scale Linear Fresnel Reflectors

by Alberto Pardellas, Pedro Fortuny Ayuso, Luis Bayón and Arsenio Barbón

Energies 2023, 16(4), 1597; https://doi.org/10.3390/en16041597 - 05 Feb 2023

Cited by 1 | Viewed by 1021

Abstract

We present the design of an original secondary cavity for use in Small-Scale Fresnel Reflectors in photovoltaic applications. The cavity is similar to the classical V-trough, but the primary reflector system is configured so that there are two focal points on the aperture. [...] Read more.

We present the design of an original secondary cavity for use in Small-Scale Fresnel Reflectors in photovoltaic applications. The cavity is similar to the classical V-trough, but the primary reflector system is configured so that there are two focal points on the aperture. The rays coming from each side of the primary system reach the opposite side of the cavity, producing a non-symmetrical distribution of the irradiance. This modifies the acceptance half-angle and allows us to break the maximum limit for the concentration ratio of ideal symmetric concentrators. Our study is analytic, and we provide formulas for any number of reflections. Numerical simulations with a ray-tracing program based on MATLAB are included. We provide a comparison of optical concentration ratio, height and cost parameter between our system and two classical designs with a single focal point: the V-trough and the Compound Parabolic concentrators. This way, we verify that our design yields better concentration ratios while keeping the ray acceptance rate at one. Our solution proves to be better than both the classical one-focus V-trough and the Compound Parabolic concentrator. Specifically, the proposed solution is significantly better than the classical one-focus V-trough in optical concentration ratio, with an increase between

15.02

and

35.95

%. As regards the compound parabolic concentrator, the optical concentration ratio is always slightly better (around

4 %

). The height of the cavity, however, is notably less in this design (around

54.33 %

). Full article

(This article belongs to the Special Issue Advances in Solar Thermal Energy Harvesting, Storage and Conversion)

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21 pages, 8529 KiB

Open AccessArticle

Structure Optimization of Longitudinal Rectangular Fins to Improve the Melting Performance of Phase Change Materials through Genetic Algorithm

by Yang Xu, Hang Yin, Chen He, Yong Wei, Ming Cui and Zhang-Jing Zheng

Energies 2022, 15(24), 9610; https://doi.org/10.3390/en15249610 - 18 Dec 2022

Cited by 2 | Viewed by 1449

Abstract

In this paper, the structural parameters of longitudinal rectangular fins used in a horizontal shell-and-tube latent heat storage unit (LHSU) are optimized to increase the melting rate of phase-change materials. The influence of natural convection on the melting process is considered. Due to [...] Read more.

In this paper, the structural parameters of longitudinal rectangular fins used in a horizontal shell-and-tube latent heat storage unit (LHSU) are optimized to increase the melting rate of phase-change materials. The influence of natural convection on the melting process is considered. Due to the extremely nonlinear and expensive computational cost of the phase-change heat-transfer-optimization problem, a new coupling algorithm between genetic algorithm and computational fluid dynamics is developed. The effects of the thermal conductivity of fins; the filling rate of fins; and the number of fins on the optimal structure parameters, including the length, width, and position of each fin, are discussed. The results show that when a single fin is inserted in the half-ring region, the optimal dimensionless fin angle is about 0.2, and the optimal dimensionless fin length is about 0.96. The use of optimal single fin can shorten the dimensionless total melting time by 68% compared with the case of no fin, and 61.3% compared with uniformly arranged single fin. When the number of fins exceeds one, each fin should have a specific length (L), thickness (∆), and position (ψ) instead of uniform distribution. The advantage of the optimized fins decreases as the number of fins increases. When the number of fins is four, the optimized fin distribution is almost uniform, and the dimensionless total melting time is only 15.9% less than that of the absolutely uniform fin. The number of fins is a more sensitive parameter affecting the optimal position and structure of fins than the filling rate and thermal conductivity of fins. Full article

(This article belongs to the Special Issue Advances in Solar Thermal Energy Harvesting, Storage and Conversion)

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19 pages, 4244 KiB

Open AccessArticle

Integration of a Linear Cavity Receiver in an Asymmetric Compound Parabolic Collector

by Dimitrios N. Korres, Evangelos Bellos and Christos Tzivanidis

Energies 2022, 15(22), 8635; https://doi.org/10.3390/en15228635 - 17 Nov 2022

Cited by 8 | Viewed by 983

Abstract

The objective of this work is the integration of a linear cavity receiver in an asymmetric compound parabolic collector. Two different numerical models were developed; one for the conventional geometry and one for the cavity configuration. Both models were examined for inlet temperatures [...] Read more.

The objective of this work is the integration of a linear cavity receiver in an asymmetric compound parabolic collector. Two different numerical models were developed; one for the conventional geometry and one for the cavity configuration. Both models were examined for inlet temperatures from 20 °C up to 80 °C, considering water as the operating fluid with a typical volume flow rate of 15 lt/h. Emphasis was given to the comparison of the thermal and optical performance between the designs, as well as in the temperature levels of the fluids and the receiver. The geometry of the integrated cavity receiver was optimized according to two independent parameters and two possible optimum designs were finally revealed. The optimization took place regarding the optical performance of the collector with the cavity receiver. The simulation results indicated that the cavity design leads to enhancements of up to 4.40% and 4.00% in the optical and thermal efficiency respectively, while the minimum possible enhancement was above 2.20%. The mean enhancements in optical and thermal performance were found to be 2.90% and 2.92% respectively. Moreover, an analytical solution was developed for verifying the numerical results and the maximum deviations were found to be less than 5% in all the compared parameters. Especially, in thermal efficiency verification, the maximum deviation took a value of less than 0.5%. The design and the simulations in the present study were conducted with the SolidWorks Flow Simulation tool. Full article

(This article belongs to the Special Issue Advances in Solar Thermal Energy Harvesting, Storage and Conversion)

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16 pages, 4419 KiB

Open AccessArticle

The Self-Actuating Droplet That Can Turn: A Molecular Dynamics Simulation

by Yalong Kong, Zhigang Liu, Lin Guo and Yu Qiu

Energies 2022, 15(22), 8468; https://doi.org/10.3390/en15228468 - 12 Nov 2022

Viewed by 1281

Abstract

Water collection remains a fundamental challenge to stable and efficient operation of the solar desalination system. Functional surfaces that can realize self-actuation of droplets have shown great potential in improving droplet dynamics without external energy. Therefore, a surface that can make a droplet [...] Read more.

Water collection remains a fundamental challenge to stable and efficient operation of the solar desalination system. Functional surfaces that can realize self-actuation of droplets have shown great potential in improving droplet dynamics without external energy. Therefore, a surface that can make a droplet move spontaneously along a curve was designed for smart droplet manipulation, and the mechanism of the droplet motion was revealed through molecular dynamics simulations. Influences of the wettability difference between the curved track and the background, the width of curved track, and the temperature were evaluated via simulations. The results show that the surface on which the curved track and the background are both hydrophobic enables a faster actuating velocity of the droplet than the hydrophilic-hydrophobic surface and the hydrophilic-hydrophilic surface. The width of the curved track also affects the actuating velocity of the droplet and increasing the TRACK width can increase the actuating velocity of the droplet. However, actuation of the droplet slows down if the width of the curved track is too large. Overall, the mechanism driving the motion of the droplet along the curve was investigated, which opens new opportunities for the application and manufacturing of water collection in solar desalination. Full article

(This article belongs to the Special Issue Advances in Solar Thermal Energy Harvesting, Storage and Conversion)

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Review

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24 pages, 8436 KiB

Open AccessReview

Review of Concentrated Solar Power Technology Applications in Photocatalytic Water Purification and Energy Conversion: Overview, Challenges and Future Directions

by Cheng Zhang, Na Li and Guangqi An

Energies 2024, 17(2), 463; https://doi.org/10.3390/en17020463 - 18 Jan 2024

Cited by 1 | Viewed by 1161

Abstract

Photocatalysis, a promising semiconductor-based technology activated by free and eternal solar energy, has great potential for addressing environmental remediation and energy conversion challenges. Concentrated solar power (CSP) technologies, namely parabolic trough reflectors, solar power towers, parabolic dish reflectors and linear Fresnel reflectors, exhibited [...] Read more.

Photocatalysis, a promising semiconductor-based technology activated by free and eternal solar energy, has great potential for addressing environmental remediation and energy conversion challenges. Concentrated solar power (CSP) technologies, namely parabolic trough reflectors, solar power towers, parabolic dish reflectors and linear Fresnel reflectors, exhibited excellent feasibility for boosting solar-driven photocatalytic processes. Based on the structural characteristics of CSP technologies, the CSP-based photocatalytic reactors could be divided into concentrated types and non/low-concentrated types. This academic review comprehensively investigated the integration of CSP technology in photocatalysis, emphasizing the feasibility of sunlight as an ideal energy source. Additionally, considering the optimal light irradiance and reaction temperature demands for achieving efficient photocatalytic processes, the significance of introducing CSP into solar light-driven photocatalytic reactions was highlighted. Moreover, the current challenges that exist in CSP-based photoreactors were identified, and potential solutions were proposed accordingly. This work hopes to provide some references for the future study of CSP-based photocatalytic reactors under the theme of sustainable development. Full article

(This article belongs to the Special Issue Advances in Solar Thermal Energy Harvesting, Storage and Conversion)

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