Search

• A compact jet receiver based on jet heat transfer is proposed. • The heat transfer and thermal stress properties of the jet channel were investigated. • This study examines the impact of channel structural parameters on performance. The compact solar receiver can withstand high temperature and high pressure, which provides promising solutions for direct supercritical CO 2 (S-CO 2) solar receiver applications. However, it still suffers from local high temperature and large thermal stress due to the non-uniform heating boundary condition. The impinging jet method can significantly enhance the local heat transfer coefficient, holding significant potential in reducing the local high temperature of the compact S-CO 2 receiver. Inspired by this, a novel design for a compact S-CO 2 receiver using the impinging jet was proposed in this work. The heat transfer performance and stress behavior of the jet channel within the receiver were numerically investigated. The results showed that the jet channel has a significantly higher heat transfer performance than the rectangular channel, and the shorter flow path of the jet channel also effectively reduces the pressure loss. Meanwhile, the jet pattern significantly enhances the temperature uniformity, thereby reducing the thermal stress. In addition, increasing the channel aspect ratio improves the thermo-hydraulic performance, but increase the stress at the same time. The increase in the number of jet holes and the jet hole diameters not only enhance the thermo-hydraulic performance, but also reduce the stress of the jet channel. [ABSTRACT FROM AUTHOR]

• Non-uniform solar flux distribution leads to more thermal loss and greater stress. • Flow distribution has great influence on the thermal and mechanical performances. • Better consistency between solar flux and flow distribution means better performances. • The proposed matching factor can be used as an indicator for receiver performances. • Ideal flow allocation can be easily determined by the matching factor being set to 1. The tubular receiver is one of the most attractive options for the directly heated supercritical CO 2 (S-CO 2) solar receiver, of which tubular panels are the basic modules. Due to the high working pressure and the non-uniform solar flux distribution, the thermal-fluid-mechanical analysis becomes an important research topic for the S-CO 2 solar receiver. In this paper, the thermal-fluid-mechanical characteristics of the S-CO 2 tubular receiver panel under non-uniform solar flux distribution using S-CO 2 as the heat transfer fluid is numerically studied. The effects of solar flux distribution and flow arrangements on the thermal and mechanical performances are discussed with emphasis. The results indicate that: (1) the non-uniform solar flux of the receiver panel will result in the increase in the thermal loss and the thermal stress; (2) adjusting the flow arrangement to match the solar flux distribution can decrease thermal loss and thermal stress; (3) the proposed matching factor can be used as an indicator for the thermal-mechanical performances, and a larger matching factor means a good performance; (4) although the I-type flow arrangement lead to uneven flow allocation with more fluid in middle tubes, it cannot always yield good performances under Gaussian-shaped solar flux distribution, which is greatly depended on the standard deviation of the Gaussian distribution; (5) an ideal flow allocation can be easily determined by the matching factor being set to 1, which provides guidelines for the design and optimization of the tubular solar receiver panel. [ABSTRACT FROM AUTHOR]

• Cylindrical fins in compact solar receivers are optimized using adjoint method. • 3-D fins have characteristics of varied cross-section along the height direction. • Thermal-hydraulic performance of 3-D fins is improved by 13 % and 20 %. • The highest entropy generation rate of 3-D fins is reduced by 8.5 % and 16.5 %. The compact solar receiver is a promising option for S-CO 2 solar receivers, designed to operate safely and efficiently under high-temperature, high-pressure, and high solar flux conditions. Adding fins with outstanding thermal-hydraulic performance in the mini-channel contributes to maximizing heat transfer performance and minimizing flow resistance for compact solar receivers. However, most of the research on high-performance fins is limited to two-dimensional optimization, ignoring the effect of shape changes in the height direction of the fins. The present study employs a combination of the finite volume method and the adjoint method to optimize single-row cylindrical fin shapes in three-dimensional for compact solar receivers, and the strengthening mechanism of high efficiency and low resistance is further revealed in the view of entropy generation. The results indicate: (1) three-dimensional fins exhibit significant variation in cross-section along the height direction, and each fin is unique; (2) three-dimensional fins exhibit more excellent thermal-hydraulic performance than cylindrical fins, showing an increase of 13 % and 20 % in the performance evaluation criterion (PEC) in case 1 (q w = 160 kW·m−2, v in = 0.487 m·s−1) and in case 2 (q w = 584 kW·m−2, v in = 1.778 m·s−1), respectively; (3) the entropy generation due to heat transfer is reduced by 4.9% and 3.9%; as well as the entropy generation due to pressure drop is decreased by 8.5 % and 16.5 %, in case 1 and case 2, respectively; (4) robustness results show that three-dimensional fins can maintain higher thermal-hydraulic performance than the initial cylindrical fin even under wide working conditions. [ABSTRACT FROM AUTHOR]

A free-falling particle receiver is a promising technology to be used in concentrating solar power plants. In this study, an optical-thermal coupled model is established by combining a Monte Carlo ray-tracing method with a finite volume method to simulate the energy transfer processes in a solar power tower system employing a cavity receiver. Using the developed model, a novel particle release pattern, zigzag mass-flow controlled pattern, is proposed and compared with three other patterns, straight-line, zigzag, and mass-flow controlled patterns. First, the effects of the amplitude of the zigzag particle release slots on the receiver performance are analyzed. Then, the variations of the solar energy entering the receiver at different times on the vernal equinox is studied. Moreover, a new particle release pattern, zigzag mass-flow controlled pattern, is proposed and evaluated. The results demonstrated that the thermal performance of the zigzag mass-flow controlled particle release pattern was found to be superior to the other three patterns, allowing an increase in the thermal efficiency of 2.90 %. This allows for achieving effective thermal performance improvements while employing cost-effective designs in the free-falling particle receiver. [ABSTRACT FROM AUTHOR]

A free-falling particle receiver is a promising technology to be used in concentrating solar power plants. In this study, an optical-thermal coupled model is established by combining a Monte Carlo ray-tracing method with a finite volume method to simulate the energy transfer processes in a solar power tower system employing a cavity receiver. Using the developed model, a novel particle release pattern, zigzag mass-flow controlled pattern, is proposed and compared with three other patterns, straight-line, zigzag, and mass-flow controlled patterns. First, the effects of the amplitude of the zigzag particle release slots on the receiver performance are analyzed. Then, the variations of the solar energy entering the receiver at different times on the vernal equinox is studied. Moreover, a new particle release pattern, zigzag mass-flow controlled pattern, is proposed and evaluated. The results demonstrated that the thermal performance of the zigzag mass-flow controlled particle release pattern was found to be superior to the other three patterns, allowing an increase in the thermal efficiency of 2.90 %. This allows for achieving effective thermal performance improvements while employing cost-effective designs in the free-falling particle receiver. [ABSTRACT FROM AUTHOR]

• The impacts of buoyancy and flow acceleration on S-CO 2 heat transfer are argued. • A threshold value was identified for buoyancy and thermal acceleration. • New empirical formulas for S-CO 2 heat transfer are proposed. The mini-channel in compact solar receiver deliver the high performance in both heat transfer (HT) and pressure resistance. However, the severe variation of thermophysical properties of supercritical CO 2 (S-CO 2) coupling with the complex nonuniform distribution of solar flux leads to the abnormal flow and heat transfer (FHT) performance of S-CO 2 in mini-channels. The present work numerically investigated the detailed FHT of S-CO 2 in the horizontal mini-channel with one-side heating. The impacts of buoyancy and flow acceleration on FHT of S-CO 2 are demonstrated in detail. The results show that the buoyancy effects can lead to the enhancement on circumferentially average heat transfer performance of S-CO 2 while the local deterioration at the top. In contrast, the thermal acceleration effects can worsen the S-CO 2 HT. The buoyancy and thermal acceleration effects can be ignored when Ri ≤ 2.7 × 10−3 and Ac ≤ 7.8 × 10−8, respectively. The empirical formula for S-CO 2 HT in the mini-channel under single-side heating conditions is developed, with a maximum error of 4.5%. [ABSTRACT FROM AUTHOR]