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Aiming at the high-efficiency OTEC application, a 30 kW radial-inflow turbine using ammonia was constructed via the one-dimensional design. In addition, a 3D CFD simulation was carried out to research the turbine performance. Furthermore, the effects of blade tip clearance on the flow characteristic in turbine were elucidated and the turbine performance under the off-design conditions was examined. It is indicated that the performance of the designed turbine is satisfactory with a theoretical isentropic efficiency of 85.2% under the design condition. The leakage flow encounters the scraping flow after leaving the tip clearance, forming the vortexes in the cross-section of the flow passage, which decreases the turbine efficiency, and the best ratio of blade tip clearance to inlet blade height is suggested to be 0.04–0.06. When the rotational speeds deviated from the design value, the vortexes appear in the flow passage of the turbine, resulting in non-negligible impact loss of blade and the consequent efficiency reduction. At the design rotational speed, the turbine shows a good adaptability to the inlet temperature variations with the inlet temperature varying from T 0 = 296K to T 0 = 304K. When the inlet pressure increases, the rotational speed corresponding to the maximum efficiency is also increased. [ABSTRACT FROM AUTHOR]

Liquid air energy storage (LAES) presents a promising solution to effectively manage intermittent renewable energy and optimize power grid peaking. This paper introduces a LAES system integrating LNG cold energy to flexibly manage power peaking, including intermediate energy storage, power generation using organic Rankine cycle, multi-stage direct expansion, and solar energy for heating. Aiming to maximize the electrical round-trip efficiency, a genetic algorithm is employed to optimize the operational parameters of the proposed LAES system. The results indicate that the combined design of cold energy utilization, multi-stage direct expansion and solar heating for proposed LAES system significantly improve the power performance, achieving an energy capacity of 0.125 kWh/kg LNG and an electrical round-trip efficiency of 376.7 %. The exergy losses of heat exchange equipment are far larger than mechanical equipment in the LAES system, so the optimization design of heat exchange equipment is preferred to improve the exergy performance. The proposed system achieves both high efficiency and flexibility and hence contributes to the development of liquid air energy storage systems. • LNG cold energy is used for air cooling and liquefaction. • Solar energy is used to increase the maximum temperature of direct expansions. • An outstanding electrical round-trip efficiency of 376.7 % is achieved. • Energy capacity reaches 0.125 kWh/kg LNG. • Heat exchanger equipment optimization is priority to improve exergy performance. [ABSTRACT FROM AUTHOR]

• Pumped two-phase loop (PTL) integrated with thermal storage (LHS) is proposed. • Thermal response behaviors of PTL-LHS under step heat load are investigated. • Fast tracking and delay response is sequentially observed as heat load increases. • Thermal response behavior regime diagram is quantitatively recognized. • Variable flow rate optimization strategy is validated by comparative experiments. Pumped two-phase loop integrated with thermal storage is an emerging solution for the short-term high-heat-flux cooling. The transient microchannel boiling heat transfer of pumped two-phase loop (PTL) integrated with latent heat storage (LHS) under step heat load are experimentally investigated, with special focuses on dynamic thermal response of two-phase loop and latent heat storage unit. The transient thermal behaviors of PTL-LHS are determined based on the wide variations of heat load and flow rate. A thermal behavior regime diagram is proposed to quantitatively recognize the transient thermal response of PTL-LHS, depending on the heat load and flow rate. The results indicate that the fast tracking mode and the delay response mode are observed and sequentially experienced for PTL-LHS as the step heat load increases. With respect to delay response mode, thermal storage efficiency is high with short thermal storage duration but cooling performance is insufficient, while the transient thermal performances are contrary under the fast tracking mode. The increase of heat load accelerates the transformation of the heat transfer mechanism in LHS from sensitive-heat-dominated to latent-heat-dominated, while increasing flow rate is conducive for the enhancements of thermal capacity and thermal stability of PTL-LHS. Increasing heat load brings about a larger critical flow rate of the transient thermal behavior regime transition, and hence the range of flow rate tends to be larger for the delay response mode. Particularly, the proposed variable flow rate optimization strategy is validated by comparative experiments, showing better cooling performance (the average evaporator wall temperature decreases by 10 °C) and more remaining load of phase change material. [Display omitted] [ABSTRACT FROM AUTHOR]

The ocean thermal energy conversion (OTEC) is essential to support the development of renewable energy for tropical islands. This paper introduces an efficient OTEC using Kalina cycle that utilizes the ammonia-water mixture as the working fluid. Aiming to develop a reliable control strategy for rapid load-tracking processes, a dynamic model for heat transfer and power generation in an OTEC using Kalina cycle is proposed, and an experiment of 30 kW-level OTEC using Kalina cycle is conducted to validate this model. Moreover, a multi-objective control strategy consisting of power, evaporation, superheat, and liquid-level control loops for rapid load-following is proposed. The results indicate that the proposed control strategy demonstrates high effectiveness in load-tracking control and ensuring the operational stability of superheat degree and separator liquid-level. When the power load is stepped from 34 kW to 40 kW, the load-tracking process is completed within 8.48 min, with a maximum overshoot of 6.58 % and a settling time of 5.27 min. Furthermore, the step responses of power output to the flow rates of working fluid and warm seawater exhibits underdamped second-order behavior with a transient time less than 5 min, while its response under step disturbance in flow rate of cold seawater presents general inertia. [ABSTRACT FROM AUTHOR]

• Thermodynamic model of a novel solar pond-assisted OTEC system is developed. • Extraction temperature's role on the system power generation potential is analyzed. • Comparative studies of OTEC system using KC, RC, and TEG is carried out. • Ideal thermal efficiency of the system is 3.97% with extraction temperature at 86 ℃. • The system using KC outperforms RC and TEG in annual power generation. The low thermal efficiency of ocean thermal energy conversion (OTEC), resulting from narrow temperature difference in ocean thermal energy, can be improved by introducing a solar pond to preheating warm seawater entering the OTEC system. Therefore, a solar pond-assisted OTEC system is proposed and its thermodynamic model is developed in this paper. By this model, the role of extraction temperature and pumping depth of cold seawater on power generation potential of the system are analyzed. Furthermore, a comparative analysis is conducted among solar pond-assisted OTEC systems using Rankine cycle, Kalina cycle, and thermoelectric module from thermodynamic, economic, and environmental aspects. The results indicate that the overall thermal efficiency is only 3.97 % for solar pond-assisted OTEC system using Carnot cycle at an extraction temperature of 86 °C. The solar pond-assisted OTEC system using the Kalina and Rankine cycles produce almost the identical annual power generation, which significantly outperforms the system employing thermoelectric module. The exergy efficiency of the thermoelectric module improves with higher extraction temperatures, while Rankine and Kalina cycles demonstrate optimal extraction temperatures of 80 °C and 75 °C. Moreover, the systems using Rankine cycle, Kalina cycle, and thermoelectric module exhibit minimum levelized CO 2 emission of electricity at 0.961 kg/kWh, 0.98 kg/kWh, and 10.7 kg/kWh, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Natural hematite had excellent photoelectric responsiveness and biocompatibility. • Sunlight-assisted hematite anode significantly enhanced the power output of MFC. • Hematite and P. aeruginosa PAO1 have remarkable electron transfer relationship under irradiation. • Hematite- P. aeruginosa PAO1 anode MFC has great potential for simultaneous reduction of NO 3 – and Cr(Ⅵ). Microbial fuel cells (MFCs) hold currently great potential in energy generation and environmental remediation. The utilization of semiconducting minerals to efficiently harvest solar energy is a crucial approach for enhancing the MFC performance. Along these lines, in this work, a sunlight-assisted two-chambered MFC with hematite modified anode was developed. The hematite anode MFC exhibited maximum voltage output (85.2 ± 4.5 mV) and power density (5.2 W/m2) under light illumination conditions, which were 1.76 times and 1.63 times higher than that in dark conditions, respectively. From the acquired electrochemical results, it was demonstrated that hematite cooperative microorganisms exhibited higher current density (6.8 μA/cm2) and lower polarization resistance (77.2 Ω) under light condition, suggesting that the sunlight-assisted hematite anode facilitates the rapid electron transfer and significantly reduces the polarization loss. Furthermore, the removal percent of NO 3 − and Cr(Ⅵ) in hematite anode MFC were 95.50 % and 66.67 % under irradiation conditions, respectively, which were 1.3 times and 1.5 times higher than that in dark conditions. Our work provides valuable insights for harnessing solar energy through a hematite-modified anode, which holds promise for enhancing MFC performance and wastewater treatment. [ABSTRACT FROM AUTHOR]

Relevant advancements in microbial fuel cells (MFCs) are impeded by the limited oxygen reduction reactions at the cathode. The challenge prompted the development of a jarosite-biochar catalyst using a straightforward biomineralization method. Through X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis, we observed a reduction in the agglomeration phenomenon of nano jarosite and a decrease in particle size. The biochar-jarosite MFC demonstrated a significant increase in voltage (682.5 mV) and a maximum power density of 1211 mW/m2. Electrochemical impedance spectroscopy (EIS) showed that the charge transfer resistance of the cathode decreased from 2580 Ω to 111 Ω, demonstrating excellent oxygen reduction reaction (ORR) performance. The jarosite-biochar significantly enhanced the MFC degradation of Cr (VI), exhibiting a 5.2-fold increase, while demonstrating exceptional stability. The X-ray photoelectron spectroscopy (XPS) of Fe and Cr on the surface of jarosite-biochar further substantiates the role of jarosite as an electron mediator between biochar and Cr (VI) in the MFC. Our study presents a cost-effective and efficient biomineralization strategy for the modification of cathode materials in MFCs, offering significant potential for enhancing the catalytic performance of iron-containing carbonaceous composites in Cr (VI) environments. [Display omitted] • Agglomeration challenge of Jarosite overcome by carbon skeleton successfully. • Jarosite-biochar catalyst prepared by biosynthesis method for the first time. • Jarosite-biochar MFC performed excellent oxidation-reduction reaction. • Efficient biominerals provided new insight for designing bioinspired catalyst. [ABSTRACT FROM AUTHOR]

l A pumped two-phase cooling loop via microchannel boiling is fabricated. l Control structure of two-phase cooling loop is developed and certified. l Active disturbance rejection temperature control is superior for two-phase loop. l The optimal flow rate and subcooling degree are experimentally determined. l The curve of microchannel wall temperature with flow rate is like a character "v". High-heat-flux heat removal is critical for the long-term safety of the high-power electronic device. However, the precise and uniform temperature control of the device is challenging due to various nonlinearities, couplings and disturbances. To this end, active disturbance rejection controller (ADRC), hybrid with an auxiliary feed-forward flow rate controller and an auxiliary subcooling degree controller, is introduced in this paper for the wall temperature control of a microchannel mechanically pumped two-phase cooling loop. First, the optimal flow rate in terms of the heating power is identified to minimize the temperature level and variance. The relative curves between the flow rate and heating power are like character 'v' which are used as a feed-forward law for the flow rate regulation. Second, the reference of the sub-cooling degree is determined based on the closed-loop control of the preheater to get a uniform temperature field with least variance. Finally, ADRC is used in the primary loop to control the average wall temperature. The experimental results indicate the efficiency of thermal control for two-phase cooling loop via combination of primary and auxiliary loop. In addition, ADRC performs better in both temperature tracking and disturbance rejection when compared with the conventional PI controller, with superiority in terms of faster tracking and stronger robustness to disturbances and couplings. [ABSTRACT FROM AUTHOR]

Latent heat thermal storage (LHTS) using phase change materials (PCMs) faces a significant challenge of poor heat transport efficiency. Fortunately, nature has evolved numerous features and functions that can enhance material properties and heat transport efficiency. This paper provides a comprehensive review of bionic studies on LHTS technology, summarizes bionic strategies for improving LHTS performance, and explores in detail the research progress and challenges faced by bioinspired PCMs and LHTS configurations. The review demonstrates that natural morphology, structure, and function can improve heat charge/discharge efficiency. However, current research mainly focuses on simple configurations of morphological and structural bionics, so more attention is needed to develop high-level functional bionics to maximize LHTS performance. The paper also emphasizes the enhancement methods of heat transfer rate in bioinspired LHTS systems, such as synthesizing bionic hierarchical porous and three-dimensional networks, constructing biomimetic shells, extending the heat exchange area, enhancing the convective heat transfer, and optimizing the heat transport path in PCM regions. Importantly, future research should focus on micro/nano-scale bionics to construct bioinspired PCM and LHTS configurations with more advanced performance. Moreover, a complete enhancement mechanism of multiscale phase-change heat transport needs to be investigated for the development of multiscale biomimetic LHTS technology. • Bionic optimization is deemed to be a pathway for highly efficient heat storage. • Bionic strategies include morphology, structure, and functional bionics. • Bioinspired materials and configurations facilitate thermal storage efficiency. • Multiscale bionic on latent heat storage is the most promising development direction. [ABSTRACT FROM AUTHOR]

• Evaporation regimes in an enclosed narrow space is studied by MRT LB simulation. • Evaporation regimes are evaluated in a regime diagram depending on Bo and Ja. • Five typical evaporation regimes are identified by changing local heat flux. • Occurrence of liquid-bridge evaporation arises from the chamber confinement. • Transition boiling and film boiling are more likely to occur under a smaller Bo. A hybrid multiphase lattice Boltzmann method is utilized to investigate the vapor-liquid thermos-hydrodynamic behaviors in a flat two-phase thermosiphon. The evaporation regimes in the enclosed narrow space are quantitatively evaluated in a regime diagram with the Bond number and Jakob number, which are directly related to the heat flux, chamber height and filling ratio. The results indicate that the surface evaporation, nucleate boiling, transition boiling and film boiling are sequentially experienced in a flat two-phase thermosiphon as the local heat flux increases (i.e. Jakob number increases). The surface evaporation regime can be subdivided into the pool-surface evaporation and the liquid-bridge evaporation. Liquid-bridge evaporation is a unique evaporation regime due to the confinement of a narrow space under the combined effects of evaporation and condensation. In addition, for a smaller Bond number (i.e. the enclosed narrow space is more confined), the transition boiling and film boiling are more likely to occur, and the interval of Jakob number is smaller for the nucleate boiling in which the thermal performance is superior. [ABSTRACT FROM AUTHOR]

A model of vapor condensation on a solid surface is developed and numerically analyzed using the free-energy lattice Boltzmann method. Based on the model, the condensation phase change on hydrophobic, hydrophilic and gradient surfaces are simulated with a particular focus on the condensation on a gradient surface. The droplet nucleation, growth, deformation, coalescence and motion during the condensation on a gradient surface are investigated. The present simulation reproduces the self-propelled dropwise condensation on a gradient surface, the film condensation on a hydrophilic surface and the conventional dropwise condensation on a hydrophobic surface. The results indicate that the condensed droplets on a gradient surface can be swept in time to provide a favorable condition for the subsequent condensation. On a smooth gradient surface, owing to the unbalanced wetting force, the vapor condenses into a thin film firstly and then fractures into droplet nucleation as the condensation process goes on. The larger wettability gradient results in a larger amplitude oscillation of condensation rate and a slighter variation of surface coverage. [ABSTRACT FROM AUTHOR]

The condensation flow patterns of ethanol–water mixture in a wide range of ethanol mass concentration inside a hydrophobic microchannel is experimentally studied via a high speed imaging system. The effects of channel surface wettability and ethanol concentration on flow condensation are compared and discussed. The experimental results indicate that the surface hydrophobic modification and ethanol concentration play a significant role in the flow condensation of mixture in a microchannel. The droplet condensation appears almost the whole two-phase flow region when the water steam is the main component, in which the droplet flow, droplet-streak flow, droplet-annular flow, droplet-injection flow and droplet-slug/bubble flow occur sequentially in a hydrophobic microchannel. With increasing ethanol concentration, the droplet-slug/bubble flow after droplet-injection flow disappears and is replaced by the pure slug/bubble flow. When the ethanol vapor is the main component, the droplet condensation almost disappears, and the annular-streak flow, annular flow, injection flow and slug/bubble flow appear sequentially along the flow direction. Both an increase in vapor Reynolds number and a decrease in ethanol concentration cause the injection location move toward the channel outlet. In addition, the surface hydrophobic modification introduces the droplet condensation, which is beneficial for the flow condensation heat transfer. [ABSTRACT FROM AUTHOR]

• LHS is proposed to enhance thermal performance of AGHP under intermittent heating. • Thermal performance of AGHPs with three LHS modes are experimentally investigated. • Introduction of LHS unit into AGHP reduces the temperature of heat source by 27.4%. • The presence of LHS unit greatly enhances the thermostat performance of an AGHP. • Temperature homogenization of AGHP & LHS units becomes worse as heat load increases. Heat pipe coupled with phase change material (PCM) based latent heat storage (LHS) is a significant thermal management system that can efficiently control the intermittent high heat loads of electronic devices. Herein, an axially grooved heat pipe-LHS (AGHP&LHS) system has been proposed. The influence of LHS units and their location on dynamic temperature response of AGHP has been investigated both experimentally and theoretically. The effect of filling rates of phase change materials (PCMs) as well as cooling temperature on thermal response of the AGHP has been compared and analyzed. Results indicate that the LHS effectively stabilizes the heat source temperature under the intermittent heating process, enhances the thermostat performance and brings the temperature uniformity in AGHP. In addition, LHS units arranged at the evaporator section are optimal for AGHP under intermittent heat load conditions, reducing the heat source temperature by 27.4% and prolonging the melting time by 81.5%. As the heat load increases, the melting time of AGHP&LHS system becomes shorter, and the overall temperature uniformity is worsened. In particular, the melting time is prolonged by 34.8% for AGHP&LHS system with PCM filling rate of 89% than that of 44% filling rate. [ABSTRACT FROM AUTHOR]

Methanol-based physical absorption with good capture ability of CO 2 and H 2 S is commercially used in the acid gas removal (AGR) unit. However, the huge energy consumption for cooling methanol and acid gas prevent its massive development. An increasing number of experimental and numerical work has been reported on the benefits of using nanofluid to improve the CO 2 absorption at room temperature to lower the energetic cost. The purpose of this paper is to realign the study with the industrial process by confronting the approach reported in the publications and conclusions with the reality of the overall industrial operations. A brief discussion on the industrial operations of CO 2 removal by methanol solution without nanoparticles is firstly given, with the observations and technical difficulties involved. Then, the available of the Rectisol-based variants for CCS will be reviewed, including the issues of designed models, simulations and the compute of absorption performance. Subsequently, the benefit of nanoparticles to the Rectisol process is studied. Finally, a critical review is performed on the results available in the publications and will propose several suggestions to their evaluation for industrial application. It is suggested that using nanoparticles to enhance absorption and desorption process of CO 2 capture has big room for mature because of the limited data under industrial conditions. • The industrial operations of CO 2 removal by methanol solution without nanoparticles is briefly discussed. • The available of the Rectisol-based variants for CCS is completely reviewed. • The benefit of nanoparticles to the Rectisol process is predicted. • A critical review is performed on the results available in the publications. • Several suggestions to the research for industrial application are proposed. [ABSTRACT FROM AUTHOR]

Basic region/leucine zipper (bZIP) transcription factors function as critical regulators in numerous abiotic stress responses. Massive bZIPs have been systematically identified in plants, but not in sweetpotato. In this study, 87 sweetpotato IbbZIPs unevenly distributed onto 15 chromosomes were identified, and segmental duplications were shown to play dominant roles in the diversity of IbbZIPs. The collinearity between IbbZIPs and the related orthologs from nine plants depicted evolutionary insights into bZIP gene family. Additionally, IbbZIP proteins were clustered into 11 subfamilies while no members were found in the M subfamily, and the regularity of gene structures and conserved motifs was consistent with the subgroup classification. Evidence from transcriptome data and qRT-PCR analysis of 12 selected IbbZIPs revealed that they were significantly and varyingly induced under multiple abiotic stresses (salt, drought, heat and cold) and hormone treatments (ABA, ACC, JA and SA). Consistently, the promoters of IbbZIPs harbored multiple stress- and hormone-related cis-acting elements. Besides, IbbZIP17 and IbbZIP61 exhibited transactivation activity in yeasts, while IbbZIP-14/-69/-84 did not. These findings supply worthy foundations for further functional investigation of IbbZIPs , and multiple members may serve as promising regulators to enhance the abiotic stress tolerance of transgenic plants. [ABSTRACT FROM AUTHOR]

A new, efficient switching median–mean filter is proposed to remove high density impulse noise from digital images. The proposed method consists of detection and filtering stages. The pixels that are labeled noise-free in the detection stage remain unchanged and the noisy-pixels are replaced by the reference image based the proposed filter with 3 × 3 window. The simulation results show that the proposed filter outperforms some existing methods, both in vision and quantitative measurements. Moreover, our method is not only efficient to remove high density impulse noise and preserve the details in the image, but also possess a short processing time. [ABSTRACT FROM AUTHOR]

In this paper, an effective switching morphology-mean filter is proposed to remove impulse noise from digital images. The proposed method consists of two stages. The first stage is to detect the impulse noise in an image. The second stage is to construct adaptive structuring elements and remove the impulse noise. In this stage, the “noise-pixels” are filtered out by using the morphology-mean filter, and the “noise-free pixels” are copied directly to the output image. The proposed filter uses the window of size 3 × 3 pixels. Simulation results show that the proposed method outperforms some existing algorithms for high-density impulse noise, both in vision and quantitative measurements. Moreover, our method can preserve effectively the details in an image, and has less processing time. [ABSTRACT FROM AUTHOR]

The fractal Cantor structure is introduced to characterize the surface topography of solid wall. By this fractal characterization, a molecular dynamics simulation of heat conduction in rough nanochannels is conducted to investigate how surface topography affects the thermal conductance at liquid–solid interfaces. The role of surface roughness on temperature profiles, liquid atom trajectories, interfacial interaction energy and interfacial conductance are all examined and analyzed. The results indicate that, the temperature jump at liquid–solid interfaces is observed irrespective of surface condition, and the existence of surface roughness reduces the interfacial temperature jump. When compared with smooth surface, the presence of surface roughness diminishes the motion capability of liquid atoms in the wall-neighboring region and these atoms could maintain contact with the solid surface for a long time, which intensifies the energy transfer between the liquids and solid surface and hence contribute to large thermal conductance at a liquid–solid interface. Interestingly, it is found that the thermal conductance at a rough liquid–solid interface is affected by more than just statistical roughness height, but also fractal dimension (topographical irregularity). In addition, increases in liquid–solid interaction strength, roughness height and fractal dimension are all beneficial to enhance thermal conduction at liquid–solid interfaces. In particular, a longer trapping time of liquid atoms inside the valley of the fractal surfaces is observed for a larger fractal dimension. [ABSTRACT FROM AUTHOR]

Abstract: A lattice Boltzmann simulation of heat transfer for gas flowing in microchannels incorporating surface roughness as characterized by fractal Cantor structure is conducted to investigate the temperature jump at rough gas–solid interfaces in the slip flow regime. The gas temperature jump at rough interface as quantified by the temperature jump length is evaluated and compared with smooth interface. It is indicated that the temperature jump at a rough gas–solid interface is mainly dependent on Knudsen number, Prandtl number, and surface roughness. The presence of roughness is beneficial to the energy exchange at the gas–solid interface and introduces a smaller temperature jump when compared with a smooth surface. The local gas temperatures in the valley of rough surface are approximately equal to the corresponding surface temperatures while an obvious interfacial temperature jump is detected over the peaks of the rough surface. In addition, increase in Prandtl number, roughness height, surface fractal dimension as well as the decrease in Knudsen number can lead to the reduction of interface temperature jump for gas convection heat transfer in microchannels. Interestingly, in microchannels, the roughness height play a considerable role in the temperature jump at the gas–solid interface, however, the effect of fractal dimension on interfacial temperature jump is not so significant. [Copyright &y& Elsevier]

Abstract: Based on the enthalpy-porosity technique, a model of thermal conduction accompanied with solidification and melting processes is developed and numerically analyzed to investigate the thermal response of the brick wall filled with phase change materials (PCM). The thermal response, which is represented by indoor wall surface temperature response, of brick wall filled with PCM is evaluated and compared with that of solid brick wall. The effects of PCM filling and its filling amount on thermal response of brick wall are investigated and discussed. It is indicated that, compared to the common solid brick wall, the thermal storage of brick wall filled with PCM is elevated by the alternate process of melting and solidification under fluctuating outdoor temperatures. The use of PCM in the brick walls is beneficial for the thermal insulation, temperature hysteresis and thermal comfort for occupancy. In addition, with the increasing filling amount of PCM, the fluctuation of indoor wall surface temperature is significantly smoothed. Correspondingly, the hysteresis in response to the outdoor temperature fluctuation is enhanced. Moreover, the present model is verified by experimental data available in the literature. [Copyright &y& Elsevier]

Abstract: The self-diffusion model of Lennard-Jones fluid confined in a nanoscale space is developed by using equilibrium molecular dynamics simulation. The radial distribution function in free and confined space is evaluated and compared to analyze the fluid microstructure. The effects of the confined scale, strength of the fluid–solid coupling and commensurability of wall and fluid density on the fluid self-diffusion are investigated and discussed. The results indicate that the confined scale, fluid–solid coupling strength and commensurability of wall and fluid density play considerable role in the self-diffusion coefficient for the fluid confined in nanoscale space. Decrease in the confined scale lead to large portion of fluid molecules ‘feel’ the wall interaction, which results in the reduction of self-diffusion coefficient. In addition, the reduction of fluid self-diffusion coefficient in confined space is also demonstrated when the wall and fluid densities are incommensurate and wall–fluid coupling strength is large. [Copyright &y& Elsevier]

Abstract: Flow boiling in constructal tree-shaped minichannel network with an inlet diameter of 4mm is numerically investigated using a one-dimensional model, taking into consideration the minor losses at junctions. The pumping power requirement, pressure drop, temperature uniformity and coefficient of performance of the constructal tree-shaped minichannel network are all evaluated and compared with those of the corresponding traditional serpentine channel, and the fluid stream undergoes a phase change from saturated liquid to saturated vapor. The effects of the length dimension and top view area (i.e. the path length) on saturated gas–liquid two-phase flow boiling heat transfer in tree-shaped minichannel networks are all analyzed and discussed. The results indicated that, the tree-shaped network configured with length dimension of two is able to maximum flow access; the path length plays a significant role in the determination of flow boiling in tree-shaped minichannel networks. In particular, compared to the traditional serpentine channel, flow boiling in constructal tree-shaped minichannnel network possesses less pressure drop, lower pumping power requirement, better temperature uniformity and higher coefficient of performance (COP). [ABSTRACT FROM AUTHOR]

Abstract: A three-dimensional model of heat transfer and fluid flow in noncircular microchannel heat sinks is developed and analyzed numerically. It is found that Nusselt number has a much higher value at the inlet region, but quickly approaches the constant fully developed value. The temperature in both solid and fluid increases along the flow direction. In addition, the comparison of thermal efficiencies is conducted among triangular, rectangular and trapezoidal microchannels. The result indicates that the triangular microchannel has the highest thermal efficiency. [Copyright &y& Elsevier]

Abstract: A theoretical model of fluid flow and heat transfer in a heat pipe with axial “Ω”-shaped grooves has been conducted to study the maximum heat transport capability of these types of heat pipes. The influence of variations in the capillary radius, liquid–vapor interfacial shear stress and the contact angle are all considered and analyzed. The effect of vapor core and wick structure on the fluid flow characteristics and the effect of the heat load on the capillary radius at the evaporator end cap, as well as the effect of the wick structure on the heat transfer performance are all analyzed numerically and discussed. The axial distribution of the capillary radius, fluid pressure and mean velocity are obtained. In addition, the calculated maximum heat transport capability of the heat pipe at different working temperatures is compared with that obtained from a traditional capillary pressure balance model, in which the interfacial shear stress is neglected. The accuracy of the present model is verified by experimental data obtained in this paper. [Copyright &y& Elsevier]

Ocean thermal energy conversion (OTEC) provides a feasible solution for sustainable and stable power supply in remote islands. In this paper, a thermodynamic model of the OTEC system is developed to study the dynamic response of power output and superheating degree to manipulated variables. Afterward, a control strategy of load following for the island OTEC system is proposed. Finally, two controllers, MPC and PI, are designed and compared under fast and slow load changes as well as disturbance rejection test. The results indicate that the power output of OTEC system is sensitive to the speed of working-fluid pump, reaching the adjustment range of 14.7 kW when the nominal speed decreases by 30%. In addition, model predictive control (MPC) shows better performance in both rapid and slow load-change modes. Especially, in the rapid load-change mode, the MPC controller could always keep the evaporator outlet superheating in the range of 2–4.5 °C, while the PI controller may introduce no superheat that may cause liquid impact. Both MPC and PI controller can stabilize the power output at the set point under one day's measured disturbance, while MPC controller makes the superheating degree of evaporator outlet within smaller temperature fluctuations (<0.2 °C). [ABSTRACT FROM AUTHOR]

Renewable ocean energy is regarded as an attractive candidate resource for the development of maritime cold chain systems. To meet the refrigeration requirement of seafood freezing and preservation storage, this study proposes two-type compression-assisted ammonia-water absorption refrigeration cycles using ocean thermal energy. The effects of intermediate pressure on the exergy efficiency and primary energy rate ratio are analyzed and discussed. Moreover, the role of the heat source and sink temperatures on the primary energy rate ratio was examined. The results indicated that the absorption refrigeration system with a compressor in the low-pressure stage has a higher exergy efficiency and a higher primary energy rate ratio than the corresponding compressor in the high-pressure stage. For a warm seawater temperature of 29 °C and cold seawater temperature of 8 °C, the low-pressure compression-assisted refrigeration cycle is the best solution with an exergy efficiency up to 0.284, and the optimal primary energy rate ratio equals 1.392. Furthermore, a higher primary energy rate ratio can be realized by increasing warm seawater temperature or reducing cold seawater temperature. [ABSTRACT FROM AUTHOR]

Airflow patterns around high-rise buildings affect building wind environment (BWE) including infiltration/exfiltration, heating/cooling loads and internal environment. Scaled high-rise building models are usually placed in a wind tunnel to study BWE. However, measuring 3D flow patterns around scaled high-rise buildings in real-time is a challenge. In this study, a 3D real-time Volumetric Particle Tracking Velocimetry (VPTV) system was used to measure the airflows around three different scaled-building setups: single building, double building parallel to the wind, and double building perpendicular to the wind. Trajectories in Lagrangian coordinates system were tracked and then interpolated to generate 3D Eulerian description of the flow field. In this study, the relative errors of velocities measured by VPTV were smaller than 2% for magnitudes range from 0.025 m/s to 2.2 m/s. The local velocity magnitudes measured by hot-wire anemometer and CFD at selected positions were compared with VPTV measurement with relative error 26.2% and 16.3% respectively. Finally, measured streamlines and reattachment lengths were compared with CFD simulation at selected plane. Results show that the VPTV system is capable of capturing detailed and accurate data of airflow around scaled high-rise building models. • 3D real-time flow patterns measurement by Volumetric Particle Tracking Velocimetry (VPTV). • The VPTV measurement system is calibrated versus known velocity with relative errors of less than 2%. • The results of VPTV are compared with that of anemometer measurement and CFD. • The flow patterns measured by VPTV can be used for CFD model development and validation. [ABSTRACT FROM AUTHOR]

• Bionic design of latent heat storage unit is provided using fractal tree. • An energy discharging model is developed and experimentally verified. • Transient temperature distribution and solid-liquid interface evolution are investigated. • Tree fin induces stronger temperature uniformity and hence faster solidification rate. • Length ratio of 1.3 and width index of 1 are beneficial for superior performance. The fractal tree-shaped structure has been demonstrated as a promising optimization method to maximize the point-area heat flow access. Aiming to enhance the energy discharging rate of the latent heat storage (LHS) unit, an innovative fractal-tree-shaped structure is introduced to construct the metal fin of a shell-tube LHS unit. An unsteady model of solidification heat transfer in a LHS unit with tree-shaped fins is developed and numerically analyzed using commercial CFD software, in an effort to demonstrate the improvement of the energy discharging performance for a latent heat storage unit using fractal tree-shaped fins. The transient temperature distribution, solid-liquid interface evolution, and dynamic changes of the liquid fraction and the sensible and latent heat in a tree-fin LHS unit are compared with those of a radial-fin LHS unit. The effects of length ratio and width index on energy discharge performance are examined and analyzed. The results indicate that the tree-shaped fin significantly improves the energy discharge performance of a shell-tube LHS unit. The tree-fin LHS unit possesses a faster solidification rate, higher energy discharge rate, and stronger temperature uniformity. The complete solidification time of the tree-fin LHS unit is decreased by 66.2% and its complete melting time is reduced by 4.4% when compared with the radial-fin LHS unit. For superior thermal energy discharge performance, the length of tree-shaped fins in a shell-tube LHS unit should be shorter inward and longer outward; the optimum length ratio is about 1.3 and an appropriate width index is 1. [ABSTRACT FROM AUTHOR]

• Ice storage process with natural convection is numerically studied and verified. • Natural convection is negatively related to the ice storage performance. • Buoyancy reversal induces the intensification of natural convection. • Optimization of shell-tube ice storage units is performed by Taguchi method. • Fin height is the dominated factor to the overall ice storage performance. The present paper reports on a numerical study of the ice storage process in finned shell-tube ice storage (STIS) units, with a focus on the special solidification behavior using water as the phase-change material (PCM). The proposed model is experimentally verified using an energy-discharging process in an ice storage unit. The effects of natural convection and buoyancy reversal on the solidification behavior are examined and investigated. Moreover, the Taguchi method is utilized to optimize the fin geometry of STIS units. The results indicate that the natural convection and buoyancy reversal are negatively correlated with the ice storage performance. An increase of the superheat factor leads to the enhancement of the buoyancy reversal intensity, which is not conducive to the acceleration of the solidification rate. In addition, the increases in fin height, fin width, and fin number are positively correlated with ice storage performance. It is demonstrated that the fin height is the dominant factor affecting the overall ice storage performance, and it is independent of the superheat factor. From the perspective of trade-off between ice storage rate and ice storage capacity, the optimal fin parameters for the STIS unit are fin height H = 40 mm, fin number N = 10, fin width Δ = 3 mm for engineering applications. [ABSTRACT FROM AUTHOR]

Passive radiative cooling is a vital strategy for mitigating the greenhouse effect. However, the widespread use of synthetic plastics as the primary constituent raises environmental concerns of plastic waste. Addressing these challenges necessitates the development of radiative cooling materials based on natural and renewable resources. Herein, we utilize the abundant but underutilized poplar catkins, which are currently perceived as harmful, to fabricate a poplar catkin-derived (PC) film for radiative cooling. The PC film exhibits exceptional cooling performance, with a maximum cooling power of 75.3 W m−2 under an average sunlight intensity of 819 W m−2. Remarkably, the PC film achieves a sub-ambient temperature reduction of 6.2 °C during 9:00–13:00, within a similar solar radiation intensity. Additionally, the PC film possesses outstanding properties, including UV resistance, mold resistance, and renewability. Even after multiple regeneration cycles, the film experiences only marginal decreases of 0.9 % in sunlight reflectance and 1.4 % in infrared emissivity (8–13 μm). Furthermore, the resulting film demonstrates superior resistance to mildew compared to wood, highlighting its potential for long-term usability. This work not only addresses the environmental concerns associated with synthetic plastics but also harnesses the untapped potential of readily available natural resources to develop sustainable radiative cooling materials. • Poplar catkin-derived (PC) films are developed for sustainable radiative cooling. • Thermal performance, renewability and durability of the PC film are explored. • The PC film can achieve a temperature decrease of 6.2 °C during 9:00–13:00. • The PC film possesses outstanding renewability and long-term usability. [ABSTRACT FROM AUTHOR]

An efficient control method is crucial for the safe and reliable operation of compression-assisted absorption refrigeration using ocean thermal energy. In this study, a dynamic model of 10 kW compression-assisted absorption refrigeration system is developed, and four integrated control strategies containing two cooling-capacity control approaches (Single input control and Cooperation control) and two temperature glide control approaches (Valve-based control and Compressor-based control) are proposed to control thermodynamic process. The proposed control strategies are evaluated in terms of both control and refrigeration performances. The results indicate that the refrigeration system can operate with stability at 50 % cooling load under the proposed control strategies. Moreover, the cooperative control of the flow rates for both warm-seawater and concentrated solution can significantly speed up cooling-capacity regulation. The rotational speed of compressor is a more suitable manipulated variable for regulating the evaporator temperature glide. The equivalent COP for the compressor-based control strategies is greater than 0.12 at 50 % cooling load, while the equivalent COP for the valve-based control strategies is only 0.064. [ABSTRACT FROM AUTHOR]

Ammonia (R717) is widely deemed to be the potential working fluid of the ocean thermal energy conversion (OTEC) system. To further improve the performance of OTEC Rankine cycle, R717-based binary non-azeotropic blends are employed as the working fluids, where R134a and R125 are selected as the additives. The thermodynamic model as well as the cost estimation model of OTEC system is developed to demonstrate the potential of power generation. The energy, net efficiency, and Levelized cost of electricity are evaluated and examined for OTEC system employing different blends, encompassing R717/R134a and R717/R125. The results indicate that the thermodynamic and economic indexes of R717-based blends are superior to pure fluids (i.e., R134a, R125, and R717). To maximize the net power, the mass fractions of R717 are 0.1 and 0.5 for the R717/R134a and R717/R125 blends, respectively, in a 30 kW-scale OTEC system, where the net power are higher than that of the pure R717 by 134% and 87%. In addition, R717-based blends perform better in energy cost than pure fluids, with 0–67% lower Levelized cost of electricity. Especially, a large-scale OTEC power plant is more economically profitable than a small one. [ABSTRACT FROM AUTHOR]

Due to the confinement effect, vapor backflow is ubiquitous in flow boiling process in microscale confined domains. This, in turn, severely deteriorate the flow boiling performances. To solve this dilemma, many microchannel configurations have been exploited to regulate two-phase flows such as inlet orifices and auxiliary channels. However, the inlet orifices would lead to significant increase of flow resistance, scarifying the pumping power. In this study, periodic symmetric saw-tooth structure is designed and fabricated along sidewalls of parallel copper microchannels to effectively suppress the vapor backflow without the cost of pressure drop. The effects of this periodic symmetric saw-tooth structure on suppression of vapor backflow and two-phase flow mixing are studied in both forward and reverse directions. The flow boiling performances of this saw-tooth microchannel configuration was experimentally investigated for total inlet flow rates ranging from 30 to 70 ml/min (mass flux ranging from 183.3 kg/m2·s to 427.7 kg/m2·s). The experimental results and visualization study demonstrate that the successful suppression of vapor backflow in the forward direction and enhancement of two-phase flow mixing in the backward direction can dramatically enhance flow boiling performance. Significant boost on both HTC and CHF is demonstrated. A CHF of 217 W/cm2 is demonstrated at 70 ml/min in the forward direction. Also, significant difference in CHF is observed between the two flow directions as the further increase of flow rates. Compared to conventional plain wall microchannels, the CHF and HTC of this study can be significantly enhanced by ∼77.4 % and ∼250 %, respectively. Note that this improved boiling performance is achieved without sacrificing pressure drops. • A new microchannel configuration with periodic saw-tooth structures was explored to effectively inhibited the unwanted two-phase backflow. • Flow boiling performances (regarding HTC, CHF and pressure drops) of this saw-tooth copper microchannel were experimentally studied on DI water for total inlet flow rates varying from 30 to 70 ml/min. • Suppression of vapor backflow in the forward direction and enhancement of two-phase flow mixing in the backward direction can dramatically enhance flow boiling performance. • Significant boost on both HTC and CHF is demonstrated. A CHF of 217 W/cm2 is demonstrated at 70 ml/min. CHF and overall HTC are increased by ∼77.4 % and ∼250 %, respectively. • These enhancements of thermal performances are achieved without the additional pumping power. [ABSTRACT FROM AUTHOR]

The small temperature difference in ocean thermal energy conversion (OTEC) causes the high sensitivity of thermodynamic process to perturbations such as temperature and power load, which requires an efficient control strategy of thermodynamic process for OTEC. To this aim, an integral dynamic model is established to study the dynamic response of thermodynamic process in an OTEC system. To ensure the system efficiency and operating safety of power cycle, a multi-objective active-disturbance rejection control (ADRC) strategy is proposed and compared with corresponding single-objective ADRC and PI controller. Multi-objective ADRC includes a load-following control loop and two auxiliary control loops (evaporator control loop and condenser control loop). The results indicate that the multi-objective ADRC is most efficient to track the change of power load, in which the overshoot and integration absolute error (IAE) of load-following are reduced by 50% and 16% when compared with the single-objective ADRC. In addition, the multi-objective control strategy can maintain the stability of superheat degree and condensation pressure, and hence improves the system efficiency by 8.64% for the output power of 35 kW. Especially, the feedback-feedforward controller and feedback controller are attractive candidates to maintain the stable superheat degree and condensation pressure. [ABSTRACT FROM AUTHOR]