Search

An air-based photovoltaic thermal collector (PVTC) is a system that generates both electricity and heat using air flowing over a photovoltaic (PV) module. This system offers the advantage of easy maintenance; however, it suffers from lower thermal efficiency compared to other PVTCs, mostly owing to the low heat capacity of air. Thus, this study introduces a novel PVTC incorporating dual ducts and semicircular turbulators, which were experimentally evaluated under actual weather conditions in the Republic of Korea. The proposed PVTC was compared with two other types of PVTC: one is a single-duct PVTC with semicircular turbulators, and the other is a dual-duct PVTC without turbulators. The results showed that the thermal efficiency of the proposed PVTC increased by approximately 88.7% compared to the single-duct PVTC with a turbulator and by 9.3% compared to the dual-duct PVTC without a turbulator. The electrical efficiency showed a slight decrease of about 7.2% compared to the single-duct PVTC but an increase of 1.4% compared to the dual-duct PVTC without a turbulator. Overall, the total efficiency of the proposed PVTC increased by 54.2% and 7.7% compared to the single-duct PVTC and the dual-duct PVTC without a turbulator, respectively. These experimental results demonstrate that attaching dual ducts and semicircular turbulators to an existing PVTC increases the daily thermal energy output, which ultimately enhances the total daily energy output. [ABSTRACT FROM AUTHOR]

A non-tubular prototype cavity receiver absorber with extended internal surfaces (fins) is proposed to enhance heat transfer in Stirling engine-based Concentrated Solar Power systems. There is limited research on the realization of downsized absorbers in terms of their design and manufacturing. The objective of the absorber solution proposed in this paper is to address the issue of inadequate comprehension regarding the impacts of the geometric and flow parameters on thermohydraulic efficiency. These impacts are numerically investigated in a 100 mm long heat transfer channel with a 10 mm × 10 mm section. The prototype absorber is fabricated using a wire electrode-discharging manufacturing approach, and is experimentally investigated using the enthalpy method. Numerical results indicate that heat transfer to the working fluid in the novel absorber can reach 482 W at the reasonable cost of 0.391% pressure drop per 100 mm (air flow at 0.0015 kg/s and 5 bar). In the experimental investigation, the prototype realizes a 1113.033 W heat transfer rate at 8 bar and 12 kg/h. This implies that a non-tubular design with extended internal surfaces can increase the internal surface area to enhance heat transfer while downsizing the volume to reduce heat loss. [ABSTRACT FROM AUTHOR]

Solar air heater systems are equipment that uses energy captured directly from the sun to heat an existing airflow through the module. The technology to operate these systems is based on clean, renewable and free energy. Solar air heaters absorb thermal energy from the sun using an ab-sorption surface and achieve a transfer of heat from the absorption surface to the air flow supplied by one or two fans. This type of equipment can be used for space heating, drying, or ventilation processes. In addition, the equipment is capable of operating in cogeneration with other systems, e.g., preheating the air used for drying wood, preheating the air used to heat industrial premises, or preheating the water used in different heating systems. This scientific work is meant to reveal the current research context and the future opportunities in the case of cogeneration applications of solar air heaters, which are analyzed in light of their actual evolving dynamics. On this basis, we highlight expectations regarding the main problems that the regenerable energy is currently facing in this specific research and development environment as well as focusing our direction on the eventual solutions that are considered in the present and on their shortcomings in the future with evolved necessities. [ABSTRACT FROM AUTHOR]

In this paper, the effects of simultaneous air and water cooling on the energy performances of a single-pass hybrid PV/T system are experimentally investigated. Both air and water are used as coolants and are tested at four different mass flow rates, ranging from 0.0014 to 0.0026 kg/s. It is found that the overall efficiency of the PV/T system is dependent on the solar intensity and mass flow rate of coolants. Maximum PV/T system efficiency is found to be 62.2% for a simultaneous flow of water and air at a 0.0026 kg/s flow rate, which is 35.5% higher than the efficiency found at 0.0014 kg/s coolant flow rate. Maximum thermal energy outputs are 85.8 and 211.84 W/m2 while using air- and water-based coolants, respectively. Exergy analysis of the developed system indicates that exergy efficiency increased by up to two times by introducing simultaneous air and water cooling in this PV/T system. [ABSTRACT FROM AUTHOR]

A novel roof solar chimney with wind-induced channel was designed herein to augment indoor natural ventilation under combined action of wind and solar energy. Compared with the traditional solar chimney, the new rooftop solar chimney improves the air flow due to the wind-induced channel. The effects of channel width ratio, chimney inclination at different outdoor wind speeds on the natural ventilation performance of the roof solar chimney were studied by numerical simulation. Finite-volume method was used for the numerical calculation. It was found that the trends of ventilation rate are different when the channel widths increase. The mass flow rate of the new structure increases with the increase in the inclination angle. When the inclination angles increase from 30° to 90°, the ventilation rate increases by 212% for U = 1.0 m·s−1, 166% for U = 2.0 m·s−1, and 127% for U = 3.0 m·s−1 under the condition of and the solar radiation I = 600 W·m−2. [ABSTRACT FROM AUTHOR]

This study experimentally investigated the performance of a PVT air collector coupled with a triangular block. The triangular block, newly suggested by the authors, is a triangular-shaped obstacle and was inserted at the bottom of the PVT air collector to enhance the heat transfer performance of the collector. The experiment was carried out in actual climate conditions in Korea with two air mass flow rate conditions: 0.03606 kg/m2 s and 0.06948 kg/m2 s. Results show the average values of electrical efficiency of the collector during the test period to be 16.15% and 16.43% for each air mass flow rate, while thermal efficiencies were 28.83% and 38.36%, respectively. The average values of total energy efficiencies were found to be 44.99% and 54.79%, respectively. The results show that air mass flow rate has a large impact on thermal and total energy efficiency, while it has a small impact on electrical efficiency. Furthermore, it was confirmed that the PVT air collector coupled with a triangular block can enhance the utilization of solar energy since the thermal performance was higher than that of the collector without a triangular block. [ABSTRACT FROM AUTHOR]

The objective of the study was to evaluate the effect of a low-cost solar collector to pre-heat ventilation air in commercial broiler buildings on supplemental heating demand and air quality during the cold season. Six black fabric-based solar collectors of 36 m2 each were installed on the south-facing rooftop of a broiler house. The solar collectors provided fresh warm air into the house during the ON cycle of minimum ventilation and during the OFF cycle of minimum ventilation when the temperature under the collectors met certain criteria. The daily cumulative duration of solar collectors in operation averaged 125 and 133 min during the first two or four weeks of brooding in the fall and winter flocks, respectively. When in operation, the solar collectors were able to raise up to 20 K above the ambient temperature, reducing fuel usage by 7% in the fall and winter flocks. The greatest challenge of solar collector utilization was the collectors providing less than half of ventilation air during daytime due to not enclosing the fresh air inlets. The limited airflow capacity and limited activation of the solar collectors due to the existing minimum ventilation scheme is another reason for low heating fuel savings. [ABSTRACT FROM AUTHOR]

The fluidized particle-in-tube solar receiver concept is promoted as an attractive solution for heating particles at high temperature in the context of the next generation of solar power tower. Similar to most existing central solar receivers, the irradiated part of the system, the absorber, is composed of tubes in which circulate the fluidized particles. In this concept, the bottom tip of the tubes is immersed in a fluidized bed generated in a vessel named the dispenser. A secondary air injection, called aeration, is added at the bottom of the tube to stabilize the flow. Contrary to risers, the particle mass flow rate is controlled by a combination of the overpressure in the dispenser and the aeration air velocity in the tube. This is an originality of the system that justifies a specific study of the fluidization regimes in a wide range of operating parameters. Moreover, due to the high value of the aspect ratio, the particle flow structure varies along the tube. Experiments were conducted with Geldart Group A particles at ambient temperature with a 0.045 m internal diameter and 3 m long tube. Various temporal pressure signal processing methods, applied in the case of classical risers, are applied. Over a short acquisition time, a cross-reference of the results is necessary to identify and characterize the fluidization regimes. Bubbling, slugging, turbulent and fast fluidization regimes are encountered and the two operation modes, without and with particle circulation, are compared. [ABSTRACT FROM AUTHOR]