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16 pages, 5874 KiB

Open AccessArticle

Comparative Numerical and Experimental Analyses of Conical Solar Collector and Spot Fresnel Concentrator

by Haedr Abdalha Mahmood Alsalame, Kang Kyeong Sik and Gwi Hyun Lee

Energies 2024, 17(21), 5437; https://doi.org/10.3390/en17215437 - 31 Oct 2024

Viewed by 464

Abstract

This paper aims to compare the thermal performances of the conical solar collector (CSC) system and the spot Fresnel lens system (SFL) using water and CuO nanofluid as the working fluids. The studied CFD models for both systems were validated using experimental data. [...] Read more.

This paper aims to compare the thermal performances of the conical solar collector (CSC) system and the spot Fresnel lens system (SFL) using water and CuO nanofluid as the working fluids. The studied CFD models for both systems were validated using experimental data. At an optimal flow rate of 6 L/min, the SFL system showed higher optical and thermal performance in comparison with that of the CSC system. In the case of the SFL system, the availability of a greater amount of solar energy per unit collector area caused an increase in thermal energy. Moreover, in the case of the CSC system, the non-uniform distribution of solar flux on the absorber’s outer surface leads to an increase in temperature gradient and heat losses. As a heating medium, the CuO nanofluid outperformed the water in terms of higher thermal conductivity and heat capacity. The average thermal efficiencies of 64.7% and 61.2% were achieved using SFL with and without CuO nanofluid, respectively, which were 2.4% and 0.5% higher than those of the CSC with and without nanofluid. CFD simulations show a 2.80% deviation for SFL and 2.92% for CSC, indicating acceptable accuracy compared to experimental data. Full article

(This article belongs to the Special Issue Thermal Energy Storage Systems Modeling and Experimentation)

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19 pages, 6318 KiB

Open AccessFeature PaperArticle

Assessment of Thermal Management Using a Phase-Change Material Heat Sink under Cyclic Thermal Loads

by Fangping Ye, Yufan Dong, Michael Opolot, Luoguang Zhao and Chunrong Zhao

Energies 2024, 17(19), 4888; https://doi.org/10.3390/en17194888 - 29 Sep 2024

Viewed by 745

Abstract

Phase-change materials (PCMs) are widely used in the thermal management of electronic devices by effectively lowering the hot end temperature and increasing the energy conversion efficiency. In this article, numerical studies were performed to understand how temperature instability during the periodic utilization of [...] Read more.

Phase-change materials (PCMs) are widely used in the thermal management of electronic devices by effectively lowering the hot end temperature and increasing the energy conversion efficiency. In this article, numerical studies were performed to understand how temperature instability during the periodic utilization of electronic devices affects the heat-dissipation effectiveness of a phase-change material heat sink embedded in an electronic device. Firstly, three amplitudes of 10 °C, 15 °C, and 20 °C for fixed periods of time, namely, 10 min, 20 min, and 40 min, respectively, were performed to investigate the specific effect of amplitude on the PCM melting rate. Next, the amplitude was fixed, and the impact of the period on heat sink performance was evaluated. The results indicate that under the 40 min time period, the averaged melting rate of PCMs with amplitudes of 20 °C, 15 °C, and 10 °C reaches the highest at 19 min, which saves 14 min, 10 min, and 8 min, respectively, compared with the constant input of the same melting rate. At a fixed amplitude of 20 °C, the PCM with a period of 40 min, 20 min, and 10 min has the highest averaged melting rate at 6 min, 11 min, and 19 min, saving the heat dissipation time of 3 min, 8 min, and 14 min, respectively. Overall, it was observed that under identical amplitude conditions, the peak melting rate remains consistent, with longer periods resulting in a longer promotion of melting. On the other hand, under similar conditions, larger amplitude values result in faster melting rates. This is attributed to the fact that the period increases the heat flux output by extending the temperature rise, while the amplitude affects the heat flux by adjusting the temperature. Full article

(This article belongs to the Special Issue Thermal Energy Storage Systems Modeling and Experimentation)

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17 pages, 6043 KiB

Open AccessArticle

Experimental Study on Heat Recovery in a CaO/Ca(OH)₂-Based Mechanical Fluidized Bed Thermochemical Energy Storage Reactor

by Viktor Kühl, Marc Linder and Matthias Schmidt

Energies 2024, 17(19), 4770; https://doi.org/10.3390/en17194770 - 24 Sep 2024

Viewed by 603

Abstract

Long-term storage of seasonally available solar energy and its provision to balance heating energy demand can contribute significantly to the sustainable use of energy resources. Thermochemical energy storage is a suitable process for this purpose, offering the possibility of loss-free long-term energy storing [...] Read more.

Long-term storage of seasonally available solar energy and its provision to balance heating energy demand can contribute significantly to the sustainable use of energy resources. Thermochemical energy storage is a suitable process for this purpose, offering the possibility of loss-free long-term energy storing and heat supply. In order to develop suitable technical solutions for the use of this technology, novel reactor concepts and scientific questions regarding material and technology development are being investigated. In this publication, the energy storage process of a long-term energy storage system based on a ploughshare reactor is experimentally investigated under various technically relevant operating conditions. One specific aspect of this technology is related to the release of water vapour during the charging process. Therefore, this work focusses, in particular, on the possibility of technically utilizing the latent heat of the released water vapour in the range of 45 °C to 80 °C, which covers the operating requirements of common heating systems in households. The experiments have shown that the dehydration process enables the separation of two heat fluxes: the chemically bound energy for long-term storage and the physically (sensible and latent) stored energy for short-term applications. However, the limitation of gas transport was also identified as the most important influencing parameter for optimising the performance of the process. Full article

(This article belongs to the Special Issue Thermal Energy Storage Systems Modeling and Experimentation)

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19 pages, 6022 KiB

Open AccessArticle

Analysis of Characteristics on a Compressed Air Power System Generating Supercavitation Drag Reduction for Underwater Vehicles

by Yijian He and Han Zhang

Energies 2024, 17(7), 1735; https://doi.org/10.3390/en17071735 - 4 Apr 2024

Cited by 3 | Viewed by 967

Abstract

An unmanned underwater vehicle (UUV) powered by a compressed air power system is proposed to address challenges for battery/motor-powered vehicles under high-speed navigation, long endurance, and high mobility. These vehicles actively utilize supercavitation drag reduction by the exhausted gas from the compressed air [...] Read more.

An unmanned underwater vehicle (UUV) powered by a compressed air power system is proposed to address challenges for battery/motor-powered vehicles under high-speed navigation, long endurance, and high mobility. These vehicles actively utilize supercavitation drag reduction by the exhausted gas from the compressed air power system. MATLAB/Simulink and FLUENT are used to establish theoretical models of the compressed air power system and ventilation supercavitation. The relationship between system power and navigation resistance is examined with different air flows, along with a comparison of endurance of different power vehicles at various speeds. The issue of the endurance-enhancing effect of supercavitation at high speed is investigated. The results demonstrate that increasing the air flow leads to higher power and reduced navigation resistance, and there is a balance between them. Furthermore, compared to the battery-powered vehicles with equal energy storage capacity, the compressed air power system shows 210.08% to 458.20% longer endurance times at speeds of 30 kn to 60 kn. Similarly, considering equal energy storage mass, it achieves 42.02% to 148.96% longer endurance times at high speeds (30 kn to 60 kn). The integration of supercavitation and air-powered systems can greatly enhance the endurance and maneuverability of the vehicle at high speeds while ensuring a compact system structure. The investigations could offer valuable ideas for the development and application of compressed air power systems for UUV at 30 kn to 60 kn or higher maneuvering. Full article

(This article belongs to the Special Issue Thermal Energy Storage Systems Modeling and Experimentation)

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27 pages, 20428 KiB

Open AccessArticle

Study on Multivariable Dynamic Matrix Control for a Novel Solar Hybrid STIGT System

by Shupeng Zheng, Zecheng Luo, Jiwu Wu, Lunyuan Zhang and Yijian He

Energies 2024, 17(6), 1425; https://doi.org/10.3390/en17061425 - 15 Mar 2024

Viewed by 824

Abstract

To construct a clean and efficient energy system, advanced solar thermal power generation technology is developed, i.e., a solar hybrid STIGT (Steam Injected Gas Turbine) system with near zero water supply. Such a system is conducive to the efficient use of solar energy [...] Read more.

To construct a clean and efficient energy system, advanced solar thermal power generation technology is developed, i.e., a solar hybrid STIGT (Steam Injected Gas Turbine) system with near zero water supply. Such a system is conducive to the efficient use of solar energy and water resources, and to improvement of the performance of the overall system. Given that the strong correlation between multiple-input and multiple-output of the new system, the MDMC (Multivariable Dynamic Matrix Control) method is proposed as an alternative to a PID (Proportional-Integral-Derivative) controller to meet requirements in achieving better control characteristics for a complex power system. First, based on MATLAB/Simulink, a dynamic model of the novel system is established. Then it is validated by both experimental and literature data, yielding an error no more than 5%. Subsequently, simulation results demonstrate that the overshoot of output power on MDMC is 1.2%, lower than the 3.4% observed with the PID controller. This improvement in stability, along with a reduction in settling time and peak time by over 50%, highlights the excellent potential of the MDMC in controlling overshoot and settling time in the novel system, while providing enhanced stability, rapidity, and accuracy in the regulation and control of distribution networks. Full article

(This article belongs to the Special Issue Thermal Energy Storage Systems Modeling and Experimentation)

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11 pages, 1999 KiB

Open AccessArticle

Exploratory Testing of Energy-Saving Characteristics of Large-Scale Freeze-Drying Equipment

by Yiqiang Liu, Yanhua Tian and Yijian He

Energies 2024, 17(4), 884; https://doi.org/10.3390/en17040884 - 14 Feb 2024

Viewed by 1041

Abstract

The advantages of continuous freeze-drying are increasingly being emphasized, including energy saving, high production efficiency, and superior quality. In this context, an innovative continuous production process and cold trap structure for large-scale freeze-drying equipment is proposed. Built-in alternating cold traps are adopted instead [...] Read more.

The advantages of continuous freeze-drying are increasingly being emphasized, including energy saving, high production efficiency, and superior quality. In this context, an innovative continuous production process and cold trap structure for large-scale freeze-drying equipment is proposed. Built-in alternating cold traps are adopted instead of the stationary type to reduce the defrosting downtime, significantly improving the energy efficiency of the refrigeration and heat pump heating units. In the freeze-drying production of shiitake, comparisons between the built-in alternating cold traps and the stationary type indicate a reduction in energy consumption of approximately 24% for the full production process when the alternating cold traps with tube coils are used, that is, from 1937 kW·h for the stationary type to 1471 kW·h. In addition, the energy consumption for the built-in alternating cold traps with finned tube coils could be further reduced by about 8%. Finally, through the implementation of the new continuous production process and built-in alternating cold traps in industrial large-scale freeze-drying equipment, the systematic energy consumption per unit of food dehydration (kg) is reduced by approximately 40%, i.e., from 1.31 kW·h in the intermittent production process to 0.79 kW·h in the new continuous production process. Full article

(This article belongs to the Special Issue Thermal Energy Storage Systems Modeling and Experimentation)

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Review

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51 pages, 6514 KiB

Open AccessEditor’s ChoiceReview

Review on Absorption Refrigeration Technology and Its Potential in Energy-Saving and Carbon Emission Reduction in Natural Gas and Hydrogen Liquefaction

by Lisong Wang, Lijuan He and Yijian He

Energies 2024, 17(14), 3427; https://doi.org/10.3390/en17143427 - 11 Jul 2024

Cited by 1 | Viewed by 1966

Abstract

With the requirement of energy decarbonization, natural gas (NG) and hydrogen (H₂) become increasingly important in the world’s energy landscape. The liquefaction of NG and H₂ significantly increases energy density, facilitating large-scale storage and long-distance transport. However, conventional liquefaction processes [...] Read more.

With the requirement of energy decarbonization, natural gas (NG) and hydrogen (H₂) become increasingly important in the world’s energy landscape. The liquefaction of NG and H₂ significantly increases energy density, facilitating large-scale storage and long-distance transport. However, conventional liquefaction processes mainly adopt electricity-driven compression refrigeration technology, which generally results in high energy consumption and carbon dioxide emissions. Absorption refrigeration technology (ART) presents a promising avenue for enhancing energy efficiency and reducing emissions in both NG and H₂ liquefaction processes. Its ability to utilize industrial waste heat and renewable thermal energy sources over a large temperature range makes it particularly attractive for sustainable energy practices. This review comprehensively analyzes the progress of ART in terms of working pairs, cycle configurations, and heat and mass transfer in main components. To operate under different driven heat sources and refrigeration temperatures, working pairs exhibit a diversified development trend. The environment-friendly and high-efficiency working pairs, in which ionic liquids and deep eutectic solvents are new absorbents, exhibit promising development potential. Through the coupling of heat and mass transfer within the cycle or the addition of sub-components, cycle configurations with higher energy efficiency and a wider range of operational conditions are greatly focused. Additives, ultrasonic oscillations, and mechanical treatment of heat exchanger surfaces efficiently enhance heat and mass transfer in the absorbers and generators of ART. Notably, nanoparticle additives and ultrasonic oscillations demonstrate a synergistic enhancement effect, which could significantly improve the energy efficiency of ART. For the conventional NG and H₂ liquefaction processes, the energy-saving and carbon emission reduction potential of ART is analyzed from the perspectives of specific power consumption (SPC) and carbon dioxide emissions (CEs). The results show that ART integrated into the liquefaction processes could reduce the SPC and CE by 10~38% and 10~36% for NG liquefaction processes, and 2~24% and 5~24% for H₂ liquefaction processes. ART, which can achieve lower precooling temperatures and higher energy efficiency, shows more attractive perspectives in low carbon emissions of NG and H₂ liquefaction. Full article

(This article belongs to the Special Issue Thermal Energy Storage Systems Modeling and Experimentation)

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20 pages, 605 KiB

Open AccessReview

A Review on the Heat-Source Tower Heat Pump Systems in China

by Xiangyu Yao, Rong Feng and Xiuzhen Li

Energies 2024, 17(10), 2389; https://doi.org/10.3390/en17102389 - 16 May 2024

Viewed by 808

Abstract

Based on air-, water-, and ground-source heat pump systems, a novel type of heat pump system, named the heat-source tower heat pump system (HSTHPS), has recently been developed in the southern area of China. The HSTHPS overcomes the evaporator frosting problems of the [...] Read more.

Based on air-, water-, and ground-source heat pump systems, a novel type of heat pump system, named the heat-source tower heat pump system (HSTHPS), has recently been developed in the southern area of China. The HSTHPS overcomes the evaporator frosting problems of the air-source heat pump system (ASHPS) when the ambient temperature is lower, and it avoids the geological condition constraints of the water- and ground-source heat pump systems. However, studies on the HSTHPS are insufficient, thereby limiting its development and applications. Thus, the present review provides a detailed literature review on the advancements of HSTHPSs in China, including the HSTHPS operation principle, heat-source tower (HST) structure, heat and mass transfer characteristics, HSTHPS performance, antifreeze solution use, and antifreeze solution regeneration. Studies on the heat and mass transfer characteristics of HSTs are sufficient for guiding the application. Regarding open systems, the solution drifting to the air needs to resolved, and future studies need to focus on structure optimization for heat exchangers in closed systems. Moreover, advanced defrosting technology should be applied to closed-type HSTs, and a suitable operation strategy for HSTHPSs should be developed. Future priorities should involve integrating HSTHPSs with additional renewable energy in order to achieve continuous, stable, and efficient heating in winter based on the characteristics of local climate and renewable energy. Full article

(This article belongs to the Special Issue Thermal Energy Storage Systems Modeling and Experimentation)

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