Previous studies indicate photovoltaic (PV) module efficiency decreases with rising operating temperature. Inspired by tree leaf vein nutrient transport, this paper proposes a novel PV-F-PCM system featuring a bionic dendritic fractal fin structure and studies its thermal management. Comparative experiments under 600-1000 W/m2 irradiance show the PV-F-PCM system reduces panel temperature by 3.6-4.5 degrees C, increases average maximum power by 7.9 %-9.4 %, and exhibits higher cooling efficiency with increased irradiance. A significant negative correlation exists between system tilt angle and panel temperature. When the tilt angle of the system is reduced from 60 degrees to 30 degrees, the average temperature of the front panel decreases by 3.95 degrees C, and the efficiency factor increases by 0.62 %. At 1000 W/m2 and an optimized 30 degrees tilt, the PV-F-PCM system's front plate temperature is reduced by 45.35 degrees C and 12.61 degrees C compared to PV-PCM and conventional PV systems, respectively. Peak power increased by 29.09 % and 13.07 %, while average power rose by 18.76 % and 9.43 %, respectively. The bionic fin structure significantly enhances PCM heat transfer, improving overall thermal management. The optimal condition is Crosswise fin arrangement at 1000 W/m2 and 30 degrees. This study provides a theoretical basis for developing high-efficiency PV cooling technologies.

A voltage-regulated electrodeposition strategy is reported for fabricating superhydrophobic polytetrafluoroethylene (PTFE) coatings with hierarchical micro/nanostructures on aluminum alloys. By tuning the deposition voltage from 40 to 100 V, the coupled processes of hydrogen evolution and PTFE nanoparticle adsorption were precisely controlled, leading to distinct surface morphologies. Increasing voltage raised the current density from 13.0 to 32.6 mA/cm2 and promoted hydrogen bubble generation, which acted as dynamic templates to form micro/nanoscale cavities. The coating prepared at 70 V exhibited an optimized hierarchical structure, achieving an ultralow surface free energy of 1.90 mJ/m2, a water contact angle of 166.9°, and a 52% reduction in effective solid–liquid contact area compared with the 40 V coating. As a result, ice adhesion strength was reduced to 23.5% of that on bare aluminum, and ice accumulation was limited to 19.2% under dynamic icing conditions. Freezing experiments under atmospheric and near-vacuum environments further revealed that the coating suppressed droplet nucleation and mitigated frost-assisted freezing, reducing freezing temperatures by up to 5.6 °C. These findings clarify the role of voltage-controlled bubble dynamics in tailoring PTFE coatings and provide guidance for designing energy-efficient icephobic surfaces.

This paper takes two typical CO2-fixing microalgae-Chlorella sp. and Chlamydomonas reinhardtii-as the research subjects, aiming to comprehensively analyze the radiative characteristics of mixed-species aggregates. The models of mixed-species microalgae aggregates considering internal microstructures were constructed. The absorption cross section (Cabs), scattering cross section (Csca), and scattering phase function of aggregates in the wavelength range of 400-750 nm were calculated using the multi-sphere T-matrix method. The theoretical calculations of the T-matrix and the experimental measurement results are highly consistent, confirming the accuracy of the theoretical method. The effects of the number of cell aggregates (N = 2-8) and species mixing ratio were systematically examined. The results show that the absorption and scattering cross-sections of the mixed-species aggregates increase with increasing N, but the shielding effect causes the rate of increase to slow down. In the N = 8 fixed co-culture system, increasing the proportion of Chlamydomonas reinhardtii enhanced light absorption, while a higher proportion of Chlorella increased light scattering. The scattering phase function is primarily determined by the optical structure of the cells themselves and is less influenced by the aggregation state. Comprehensive evaluation showed that a mixture of 75% Chlorella sp. and 25% Chlamydomonas reinhardtii was optimal, achieving synergistic optimization of high light absorption and low scattering loss across the entire visible spectrum.

The issue of heat exchanger fouling caused by calcium carbonate (CaCO3) has become increasingly severe. To investigate the scale inhibition performance of chitosan derivatives on crystal scaling, N,O-carboxyethyl chitosan (CEC) was synthesized by substitution of chitosan (CS) with 3-chloropropionic acid. The carboxyl substitution degree of CEC was characterized by Fourier transform infrared (FT-IR) spectroscopy and elemental analysis. Using calcium carbonate (CaCO3) scaling as the target, the effects of various factors such as CEC concentration, substitution degree, temperature, heat flux density, and mass flow rate on the scale inhibition performance of CEC were studied through techniques including the plate weighing method, pH shift method, electrochemical impedance spectroscopy, and flow experiments. The results showed that an increase in CEC concentration led to a decrease in the free calcium ion concentration in the solution, indicating a better chelation effect of CEC with calcium ions, thereby enhancing its scale inhibition performance on CaCO3 crystal scaling. As the substitution degree of CEC increased, the amount of deposited scaling on the plate surface decreased. The best scale inhibition effect was achieved with CEC-3 at a concentration of 100 mg/L, which had the highest substitution degree. The influence of temperature on the scale inhibition effect of CEC was not monotonic, with the optimal inhibition effect observed at 50 degrees C. During the growth of CaCO3 crystals, CEC interferes with the normal crystal growth by occupying the active growth sites on the CaCO3 crystal surface, thereby reducing the binding strength between the crystal and the stainless-steel surface. Additionally, CEC formed stable chelates with Ca2+ in water, decreasing the collision probability between Ca2+ and CO32-. As a chain-like polymer, the carboxyl groups on CEC could adsorb multiple Ca2+, weakening the binding between Ca2+ and CO32-. Furthermore, as a polysaccharide molecule, CEC exhibited physical adsorption and dispersion effects on CaCO3 particles, inhibiting their continuous growth. This study provides a comprehensive understanding of the mechanisms underlying the scale inhibition performance of CEC, highlighting its potential as an effective antifouling agent in industrial applications.

The influence patterns of wind speed, dust particle size, and PV module tilt angle on accumulation behavior and power generation performance are thoroughly examined in this study using both theoretical analysis and actual observations. The silicate-dominated multiscale morphological features are made clear by physicochemical characterization of actual accumulated dust. A framework for deposition dynamics based on fluid drag force, gravitational force, and collision force is established using force analysis. According to the experimental findings, there is a critical value for the impact of wind speed on dust deposition: if the wind speed is too high, particle detachment results; if it is too low, particle transport is inadequate. As particle size and tilt angle increase, dust accumulation density typically decreases; nevertheless, non-monotonic changes arise because of changes in the prevailing forces. Because it directly influences the effective irradiance received by the surface, performance studies further demonstrate that the PV module tilt angle is the most important factor limiting output performance. Additionally, using Box-Behnken design and response surface methodology analysis, the study develops a second-order prediction model for dust accumulation density and its affecting elements. Variance analysis shows that dust particle size has the biggest impact when there is a steady dust source and low wind speed. The study's findings can serve as a theoretical foundation for developing dust removal techniques based on the fluid drag mechanism, including blow-cleaning, and for improving the installation tilt angle of PV power plants.

Based on a hybrid-structured thermal energy storage (TES) system (high-temperature phase change material H-PCM, quartzite, low-temperature phase change material L-PCM), this study breaks through the limitation of the narrow operating temperature range of single-material systems through the synergistic effect of multi-level PCMs, achieving a higher thermal storage density. Specifically, the ternary carbonate Li2CO3-Na2CO3-K2CO3, quartzite, and NaNO3 serve as H-PCM, sensible heat material, and L-PCM, respectively. The heat transfer fluid (HTF) employed in the TES system is NaNO3-KNO3. Six types of hybrid structure packed beds are designed by adjusting the volume fractions of the PCMs. A continuous solid-phase model is adopted for numerical simulation, and the dynamic performance differences among the six hybrid-structured packed bed TES systems are comparatively analyzed under steady cyclic conditions. Furthermore, the effects of the operating parameter (cutoff temperature threshold Delta T) and structural parameter (phase change material capsule diameter d) of the hybrid-structured thermocline packed bed on the thermal storage performance of the TES system are investigated in detail. The results indicate that the hybrid-structured TES system exhibits optimal thermal storage performance when the total volume fraction of PCMs is 12 %. Additionally, within the scope of this study, the optimal thermal storage performance of the hybrid-structured TES system is achieved when the cutoff temperature threshold Delta T is 30 degrees C and the PCM capsule diameter d is 16.53 mm. This work provides a reference for the practical engineering application of hybrid-structured packed bed TES systems in concentrated solar power (CSP) plants.

Fouling is a prevalent issue in heat exchangers, significantly impairing their thermal performance. To address particle fouling in heat exchanger channels, this study selected a rectangular channel with dimensions: length 1000 mm, width 40 mm, and height 20 mm. The anti-fouling performance of various perforated vortex generator structures in pulsating channel at Re 6334 is optimized through experimental and simulation studies. We experimentally characterize particulate fouling and flow resistance in pulsating channel, a pulsating rectangular wing channel, and a pulsating perforated rectangular wing channel, and validate the numerical model. Additionally, numerical simulations analyze how different perforation sizes and perforation positions (longitudinal and transverse) affect flow resistance and particulate fouling. The results indicate that, compared with the pulsating channel and the pulsating non-perforated rectangular wing channel, the pulsating perforated wing channel achieves superior anti-fouling effect with lower flow loss. For perforation sizes variations, the optimal condition occurs at r/a is 0.6, where flow loss is minimized and the anti-fouling effect reaches 42.2%. At longitudinal position h/b is 0.2, flow loss remains low and the anti-fouling effect peaks at 44.1%. At lateral position d/a is 0.3, flow loss is low and the anti-fouling effect reaches 44.6%. Moreover, within the scope of this study, longitudinal perforation position exerts a greater influence on anti-fouling effect than lateral positioning.

In order to study the deposition of fly ash particles on the heat exchanger tube wall, a model was developed by combining the direct simulation Monte Carlo (DSMC) method with the random function method (RFM). The model incorporates the collision (including rebound and coagulation), deposition, and erosion processes of fly ash particles. Dynamic mesh technology was employed to accurately track the dynamic evolution of particle deposition morphology on heat exchanger tube surface. The model findings are consistent with the experimental data, and the obtained deposition morphology is also similar to that observed in the experiments. In addition, the effects of different incident velocities and mass flow rates on the deposition of fly ash particles are investigated, both in the presence and absence of collisions. This study found that under identical working conditions, the deposition mass on the tube is greater when particle collisions are considered than when they are not considered.

As an important and effective means of enhancing boiling heat transfer, surface modification has garnered extensive attention and application. The flow boiling heat transfer characteristics of rectangular microchannels with three different surface types: Smooth copper surfaces (Smooth), front-end superhydrophobic surfaces (Front), and spaced superhydrophobic surfaces (Spaced) were experimentally investigated, using deionized water as the working fluid. The mass flux varied from 52.06 to 259.38 kg/(m2 & sdot;s), the heat flux ranged from 10 to 300 kW/m2, and the inlet subcooling of the working fluid was Delta Tc=5 degrees C-15 degrees C. A comprehensive experimental investigation was conducted to examine two-phase flow characteristics, including flow patterns, boiling curves, local heat transfer coefficients, pressure drop, and instability phenomena under varying operational parameters such as heat flux and mass flow rate. Flow pattern observations showed that the spaced hydrophilic/hydrophobic surface not only promoted efficient bubble nucleation but also significantly inhibited bubble coalescence, thereby maintaining a stable annular flow pattern. This surface delayed dryout and outperformed smooth copper and front-end superhydrophobic surfaces in flow boiling heat transfer. The spaced superhydrophobic structure, leveraging its alternating hydrophilic/hydrophobic pattern, significantly reduced the onset of nucleate boiling (ONB) wall temperature (with a wall superheat of merely 0.595 degrees C) and enhanced the heat transfer coefficient by 66 % compared to the smooth copper surface. The two-phase pressure drops of the front-end and spaced superhydrophobic surfaces are similar, yet both are higher than that of the smooth copper surface. Time-domain analysis of wall temperature and pressure drop shows that the fixed contact line formed by spaced superhydrophobic surface effectively restricts upstream bubble expansion, significantly reducing boiling instability. Additionally, the mass flux and inlet subcooling exert significant effects on the boiling heat transfer performance of the modified surfaces.

With the rapid advancement of modern industry, heat exchangers often operate with fluids containing fine particulate impurities that easily deposit within heat exchange channels, forming particulate fouling. To address this issue, this study combines pulsating flow with wing vortex generators. First, particulate fouling and pulsating flow models were developed, and their accuracy was validated through experimental testing. Numerical simulations were then conducted to compare the anti-fouling performance of three types of wing vortex generators under pulsating flow conditions. Finally, a detailed analysis was carried out on the effects of the relative height and length of rectangular wing vortex generators on particulate deposition. The results indicate that, compared to smooth channels, the use of pulsating flow offers a certain degree of anti-fouling performance, and combining pulsating flow with wing vortex generators further enhances this effect. Among the three types of wing vortex generators, the rectangular wing vortex generator exhibited the most effective anti-fouling performance under pulsating flow conditions. As the relative length and height of the rectangular wing vortex generator increased, fouling resistance first decreased and then increased. The minimum fouling resistance occurred when the relative length and height were 0.1 and 0.45, respectively, resulting in an anti-fouling performance improvement of up to 42.1 %.

At present, heat exchangers are widely used in industrial production processes, but fouling will lead to an increase in their energy consumption, and the application of ultrasonic can effectively reduce fouling. This study presents a crystallization fouling model under the action of ultrasonic, aimed at investigating the inhibitory effect of dual-frequency ultrasonic on CaCO3 fouling in heat exchanger tubes. Based on the constructed model, this study primarily compares the effects of single-frequency and dual-frequency ultrasonic, with a detailed analysis of the impact of pressure amplitude and frequency of the dual-frequency ultrasonic. The results indicate that dual-frequency ultrasonic at 20 + 40 kHz exhibits the fouling inhibition rate 19.9 % and 36.2 % higher than single-frequency ultrasonic at 20 kHz and 40 kHz, respectively. The fouling layer thickness under ultrasonic action increases progressively with tube length, while the wall shear force varies periodically over time. The average of wall shear force under dual-frequency ultrasonic action is higher than that under single-frequency. In the research range of dual-frequency ultrasonic, increasing pressure amplitude enhances its fouling inhibition effect. As pressure amplitude increases from 100 kPa to 250 kPa, the fouling inhibition rate rises by 21 %. An increase in frequency weakens the fouling inhibition effect. When the co-frequency increases from 30 + 30 kHz to 60 + 60 kHz, the fouling inhibition rate decreases by 19.9 %. When the different-frequency increased from 20 + 40 kHz to 50 + 70 kHz, the fouling inhibition rate decreased by 24.1 %. Additionally, the fouling inhibition rate at different-frequency ultrasonic is consistently higher than that at the co-frequency, indicating that different-frequency ultrasonic provides better inhibition. Furthermore, the fouling layer thickness decreases with increasing pressure amplitude and increases with frequency.

To reduce the impact of renewable energy generation on power grid stability, preheating combustion technology is introduced to maintain coal-fired boiler efficiency at low loads. A 330 MW coal-fired boiler is retrofitted with preheating combustion devices to improve combustion performance and lower NOx emissions. The device is installed in the reduction zone between the furnace burnout zone and the burner zone. The combustion characteristics of the boiler with and without these devices are examined at 50% rated load. Numerical simulations are conducted to analyze the effects of preheating coal input and burner arrangement on temperature and species distribution within the boiler. Results show that increasing preheating coal input from 0 to 30 t/h enhances NOx reduction due to a higher flow rate of preheated products. At a preheating coal input of 20 t/h, the combustion efficiency reaches 96.9%. The NOx concentration at the furnace exit rises from 122.4 to 171.3 mg/Nm3 as the height of the burner arrangement increases. The middle three-layer burner arrangement achieves a uniform temperature distribution and a peak combustion efficiency of 97.6%. The bottom and middle three-layer burner arrangements are recommended for efficient and clean combustion. Compared to the original boiler, the retrofitted boiler’s combustion efficiency increases from 96.3% to a maximum of 97.6%, while the NOx concentration at the furnace outlet drops from 168.1 to 93.2 mg/Nm3, showing that installing preheating combustion devices promotes efficient and clean combustion.

This paper proposed a particle deposition model that took into account inter-particle collisions. The deposition characteristics of particles in a two-dimensional flow channel were studied by numerical simulation. To account for the influence of particle collisions on their movement and deposition, the direct simulation Monte Carlo method (DSMC) was introduced to calculate inter-particle collisions. The random function method was used to model the deposition of particles. The proposed model was used to calculate the dimensionless deposition velocities of particles with five different particle diameters (1 mu m, 3 mu m, 5 mu m, 9 mu m, and 16 mu m) at inlet velocities of 2.2 m/s, 5.3 m/s, and 9 m/s, and compared to the experimental data. The simulation results were mostly consistent with the experimental results, demonstrating that the proposed model is accurate and effective. At the same time, compared to the results of particle deposition without considering collision, the results considering particle collision were closer to the experimental data. This indicated that collision must be considered in the calculation of particle deposition.

With the advancement of modern industry, water is commonly used as a working fluid for heat energy applications. However, this frequently leads to the accumulation of deposits and suspended particulates at specific locations on heat exchange surfaces, forming particulate fouling. This study introduces a local particulate fouling model for the liquid side within a channel, utilizing dynamic mesh technology to investigate the characteristics of localized particulate fouling. The validity of the model was established by comparing simulation results with experimental data. Additionally, a comparative study was performed to assess local particulate fouling characteristics with and without the application of dynamic mesh technology. Detailed analysis was conducted on the effects of various operating parameters on local fouling characteristics using the dynamic mesh approach. Results indicate that the local fouling model with dynamic mesh technology aligns more closely with experimental observations. Evaluation of local fouling resistance along the channel showed that resistance values obtained with dynamic mesh technology are higher than those without it. Measurement of fouling layer thickness within the dynamic mesh channel revealed a rapid increase in thickness, which stabilized after approximately 15 h. The increasing fluctuation range of the thickness curve suggests a rise in inhomogeneity over time. Furthermore, the morphology of the final fouling layer on the deposition wall closely matched experimental findings, both exhibiting an uneven distribution. Comparison across different operating conditions showed that average local fouling resistance decreases with increasing flow velocity, while higher wall temperatures and particulate concentrations result in increased fouling resistance. Specifically, in the numerical range of this paper, when the flow rate is 0.2 m/s, the wall temperature is 333 K, and the particle concentration is 400 mg/L, the thickness and unevenness of the fouling layer reach the maximum.

A preheating combustion device was designed and implemented in a 330 MW tangentially fired boiler to enhance combustion efficiency and reduce emissions. The device was placed between the primary combustion and burnout zones of the furnace. It pre-treated the fuel (bituminous coal) to generate high-temperature combustible gas and char under the excess air ratio range of 0.35-0.7, effectively lowering the nitrogen oxide (NOx) emissions in the primary combustion zone. Experimental investigations were carried out to analyze the composition of the preheated combustion products under varying pulverized coal concentrations and coal feed rates. The main combustible gases produced were CO, CH4, and H2. Additionally, numerical simulations were performed to evaluate the combustion characteristics and NOx emissions of the boiler with and without the preheating combustion device. The composition, temperature, and mass flow rate of gas and char measured from the experimental tests were used as input for the numerical simulations in the reduction zone. The study focused on the impact of pulverized coal concentration and coal feed rates on boiler performance. The results showed that retrofitting the boiler with the preheating combustion device led to a significant reduction in NOx emissions and improved combustion efficiency. As the pulverized coal concentration increased, the retrofitted boiler efficiency improved with minimal variation in NOx emissions. Moreover, increasing the preheating coal feed rate from 10 t/h to 40 t/h resulted in a rise in combustion efficiency, while the NOx emissions decreased from 167.6 mg/Nm3 to 121.1 mg/Nm3 (at 6% O2), promoting cleaner and more efficient boiler combustion.

The extensive accumulation of magnesium slag (MS), a metallurgical byproduct, has raised critical environmental concerns. This study pioneers the application of wet carbonation technology to convert MS into recycled artificial aggregates, offering a potential solution for sustainable solid waste management. By adjusting the carbonation temperature (20 degrees C, 40 degrees C, and 60 degrees C) and carbonation solution medium (the water and Ca(OH)2 solution), the changes of individual particle strength, water absorption, apparent density and CO2 sequestration of aggregates were systematically evaluated. It was found that wet carbonation significantly enhanced the strength (from 4.6 MPa to 11.0 MPa) and reduced the water absorption to 7.9 %. Aggregates carbonated in Ca (OH)2 solution showed better strength, pore structure and CO2 sequestration effect. This is due to the addition of Ca(OH)2 to improve the reaction rate and environment of carbonation reaction and hydration reaction. The microstructure analysis shows that the internal structure of the aggregate is composed of a dense outer CaCO3 shell, an intermediate CaCO3-CSH gel interlaced layer, and an internal un-hydrated MS particles. Compared with high temperature carbonation, normal temperature carbonation contributes to deeper carbonation reaction, while avoiding internal stratification and structural damage caused by rapid carbonation. Through calculation, the carbon emission of concrete prepared by using the aggregate developed in this study is reduced by about 36 %. This study provides theoretical support and technical path for the development of high-efficiency and low-carbon materials.

This study develops an innovative branched-tandem symmetric pulsating heat pipe (BT-PHP) for thermal management of proton exchange membrane fuel cells (PEMFCs), addressing critical challenges in heat transfer efficiency, thermal response, and temperature uniformity. The experimental and numerical simulations were conducted to investigate the thermal-hydraulic performance under three representative orientations (x, y, and z-axis). The results show that the secondary bubble pumping effect generated by the auxiliary branch significantly enhances the working fluid flow capability, and successful start-up of three typical orientations can be achieved at 80 W heat input power; Layouts using z and x-axis orientations readily induce localized high-pressure zones (due to synergistic effects of branch channels and gravity), while y-axis orientation exhibit a 66 % reduction in pressure differential, optimal flow uniformity, and effective prevention of local dry-out. Under steady-state operation at 140 W, the bubble pump effect reduces thermal resistance by 20 % in y-axis orientation relative to z-axis orientation, while gravity-assisted x-axis orientation enhances the mitigation to 32 %. y and x-axis orientations exhibit periodic high-low pressure oscillations that sustain fluid pulsation characteristics, whereas z-axis orientation requires greater thermal accumulation to overcome localized high-pressure constraints. This study provides an efficient thermal management solution for PEMFC systems.

The corrosion of the heat exchanger in the actual operation process will make the heat exchange wall rough, and the rough heat exchange wall will cause local fouling deposition in the channel. Based on the constructed local crystallization fouling model, this study compares the local fouling deposition of smooth channel and triangular roughness element channel, and analyzes the relative spacing of triangular roughness elements and the effect of different working condition parameters in detail. Results indicate that compared to smooth channels, triangular roughness elements significantly influence fouling deposition, appearing an extreme value in local fouling resistance. As the relative spacing decreases, the average value of the local fouling resistance initially decreases, reaching its minimum at a spacing of 0.125, before slightly increasing and stabilizing. For the average value of fouling resistance, the increase of inlet velocity or the decrease of calcium carbonate concentration will reduce it; an increase in wall temperature will increase it. Additionally, the thickness of the fouling layer decreases with increasing inlet velocity, decreases with lower concentration of calcium carbonate, and increases with rising wall temperature, both in the smooth zone outside the roughness element and in the roughness element affected zone.