Spray Flash Research Articles

Comprehensive Performance Evaluation and Advanced Exergy Analysis of the Low-Temperature Proton Exchange Membrane Fuel Cell and Spray Flash Desalination Coupled System

This study introduces an innovative integrated system comprising steam methanol-reforming, low-temperature proton exchange membrane fuel cell, and spray flash desalination. Through thorough performance and advanced exergy analyses of the system, crucial areas for enhancing components were identified. The findings demonstrate that raising the reforming temperature or increasing hydrogen utilization rates can notably enhance system efficiency. Furthermore, the LCOE increased by only 0.152＄/kWh, while CO2 emissions remained unchanged. Conventional exergy analysis reveals that exergy destruction attributed to fuel cell amount to 27.6% (13.26 kW) of total exergy destruction. Advanced exergy analyses indicate that fuel cell contribute significantly (10.23 kW) to endogenous exergy destruction, primarily due to internal factors. Furthermore, the order of contribution to the total exergy destruction within the system is identified as follows: LT-PEMFC, Combustor, and Reformer. These findings suggest that prioritizing the LT-PEMFC in efforts to enhance system efficiency is essential, followed by the burner and subsequently the reformer. These results highlighted the potential of the integrated system and suggested approaches for improving system efficiency and boosting component performance. Furthermore, the findings provided novel insights for advanced research on integrated systems that combined low-temperature proton exchange membrane fuel cell.

Investigation on flash boiling of superheated acetone spray under low vacuum conditions

Spray Flash Evaporation has recently demonstrated promising results in various fields of application and has more recently shown potential in the elaboration of nanoenergetic materials. This technique offers advantages in terms of morphology, size, and reactivity of the produced materials. However, specific thermodynamic conditions are required to produce these materials using acetone as a solvent: high injection temperature (typically between 80 and 160 °C) and low pressure (generally between 10 and 100 mbar) in the chamber are needed, i.e., superheat level. The study on the formation of acetone droplets in the far-field and under such conditions is lacking. Consequently, we propose here to further understand the relationship between injection temperature and back pressure in the chamber with nucleation and droplets characteristics (velocity, average size, size distribution, and concentration) in order to find optimal conditions for generating theoretically smaller particles through droplet evaporation. The tests were conducted in an unusual range of injection temperatures and pressures for flash boiling but commonly used for the production of energetic particles, from 80 to 200 °C and from 12 to 300 mbar, respectively. By using such conditions, it has been found that increasing the injection temperature and decreasing the back pressure are beneficial for generating a large concentration (up to 27.0 x 106droplets.cm−3) of smaller droplets with a narrow size distribution (down to 2.13 ± 0.13 µm) and high velocity (up to 204.2 m·s−1). It was also shown that there is an injection temperature threshold above 160 °C, beyond which the size distribution widens again by 12 % at 200 °C, and the number of droplets decreases by 64 %. This phenomenon can be observed only if we use a very high superheat level. This study demonstrates that these conditions are likely to promote and ultimately lead to the production of particles that are as fine and uniform in size as possible. Nevertheless, operating at very high injection temperatures (>160 °C) could hinder the nucleation and the formation of uniform droplets due to the high competition between the superheat level (Rp > 1188) and the surface tension of the liquid approaching near-zero values. By introducing the use of criteria related to mechanic and thermodynamics, along with droplet size and velocity, it was also observed that the droplet size is primarily influenced by the nucleation rate, while droplet velocity is influenced by both driving forces (mechanical and thermodynamic). The temperature and pressure in the chamber must therefore be carefully chosen to improve droplet formation and potentially produce smaller, homogeneous particles in size as they evaporate.

Orifice section velocity fitting method and its application in flash spray research

Although spray technology is widely used, research on spray flow is limited by the complexity of its flow field. To simplify the spray simulation, this work proposed an orifice section velocity fitting method, which can simplify the calculation of the flow field inside the nozzle by using a set of special velocity fitting equations as boundary conditions. For the application and verification of the method, the characteristics of methyl nonafluorobutyl ether (HFE7100) flash spray under temperature influence were experimentally studied in this paper using phase Doppler particle analyzer equipment and compared the results of simulation and experiment. The comparison results show that the simulation and experimental results of the spray axial velocity distribution have good consistency at different temperatures. The simulation results show that the swirling flow in the orifice is stronger when the temperature is lower than the boiling point and the spray velocity isosurface is conical. The swirling flow in the nozzle is attenuated by flash evaporation when the temperature increases above the boiling point, while the spray velocity isosurface changes to a bell shape. The experimental results show that the spray velocity increases with increasing evaporation caused by increasing temperature and that the spray axial velocity distribution also changes from a saddle shape to a single peak shape. The spray droplet size increased significantly under the influence of flash evaporation, but the spatial distribution maintained a saddle shape. This study can provide a reference for spray simulation analysis and the study of flash spray characteristics.

Impact of flash boiling spray on soot generation of a rich fuel–air mixture under various ambient pressures

Particulate emission is one of the critical challenges for the modern gasoine direct injection (GDI) engines. Especially under cold start conditions, the global equivalence ratio inside the cylinder is often set quite rich, leading to the generation of a large amount of soot. The fuel distribution state, such as homogeneous mixing and heterogeneous mixing with local rich pockets prior to the combustion is the key factor affecting soot generation under cold start conditions in GDI engines. Flash boiling injection, as a method to promote fuel air mixing, could be a potential solution to sooting problems of rich mixture combustion under cold start conditions. However, the unclear influences of flash boiling spray to fuel–air mixing state and subsequent soot generation pose a challenge to soot reduction in GDI engines. This work aims to study the effect of various flash boiling degrees on fuel–air mixture formation and subsequent soot generation utilizing a customized constant volume combustion chamber (CVCC) incorporated with the gasoline direct injection scheme under moderately cold start ambient temperature of 30 °C. A global high equivalence ratio of 1.7 representing extremely rich combustions under cold start conditions is selected for strong sooting propensity. By setting different fuel temperatures (Tf= 30 °C and 120 °C) and various ambient pressures (Pa= 40 kPa, 100 kPa and 160 kPa), various spray flash boiling states (subcooled, transitional flash boiling and flare flash boiling sprays) are achieved, and finally various fuel distribution states of rich mixtures prior to combustion are obtained. High speed color camera and soot sampling TEM grids were used to capture and evaluate the characteristics of spray atomization, combustion and soot aggregate structures. Based on this investigation, the effect of flash boiling degree on fuel–air mixing and subsequent soot generation is analyzed. The results show that flash boiling spray enhances fuel atomization and produces much more homogeneous rich mixture with smaller local rich pockets and richer global premixed gaseous portion. Over-rich global premixed mixture combustion is prone to nuclei inception and agglomeration, producing soot aggregates with small primary particles. While the local rich pocket combustion is prone to surface growth, producing larger primary particles. Flash boiling spray could reduce the size of soot particles under cold start conditions by generating smaller local rich pockets.

Achieving high thermal conductivity in CNTs@GF/Al laminates via a rapid and simple strategy

The present work developed a rapid and simple fabrication strategy to achieve the high thermal conductivity (TC) in graphite film (GF)/Al laminates. CNTs@GF prepared by spray flash technique was selected as reinforcement in Al matrix, then consolidated with Al foils by vaccum hot-pressing sintering. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectroscopy were used to evaluate the GF and interface structure. The results revealed that no interfacial reaction products were generated in the highly dense composites. Specially, due to the heat conduction channel and interlocking effects of CNTs on GF/Al interface, the laminated composite containing 56.5 vol% CNTs@GF showed an in-plane TC of 897 W (m k)−1 without bending strength sacrifice. The present work paves an efficient new way to design and fabricate GF/Al laminates for potential thermal management application.

Experiment and simulation study on the characteristics of pressure swirl nozzle flash spray under the influence of superheat

The good atomization performance of the pressure swirl nozzle makes it widely used in the fuel injection device of the internal combustion engine. Flash spray caused by fuel inlet superheat can affect spray and combustion characteristics. In this paper, a spray parameter measurement system is set up, combined with phase Doppler particle analysis (PDPA) technology to research the effect of superheat on spray velocity and droplet diameter distribution. To improve the safety of the experiment, Methyl Nonafluorobutyl Ether (HFE7100) with a boiling point of 61°C was used as the spray fluid. The cavitation model and VOF model are used to simulate the pressure swirl nozzle flash spray. The results show that when the temperature changes from 40°C to 60°C, the velocity of spray droplets increases and the particle size decreases under the action of weak evaporation; When the temperature changes from 60°C to 70°C, the evaporation mode is dominated by flash, making the droplet velocity at the spray center greatly increase and the velocity distribution change from saddle-shaped distribution to unimodal distribution. The droplet diameter increases, which may be due to the expansion of the droplet caused by the formation of bubbles inside the droplet under the action of flash.

Thermodynamic modeling and optimization of a novel hybrid system consisting of high-temperature PEMFC and spray flash desalination

The current study proposes a novel hybrid system consisting of the high-temperature proton exchange membrane fuel cell (HTPEMFC) and spray flash desalination (SFD) system to harvest the waste heat from HTPEMFC. The output power density and energy efficiency are analyzed to evaluate the system performance. Comparing the hybrid system with the stand-alone HTPEMFC system reveals that the maximum power density and energy efficiency of the proposed system are 69% and 40% higher than those of the stand-alone HTPEMFC system. Moreover, many parametric studies are conducted to determine how the performance of the hybrid system depends on its design and operating conditions. The cell working temperature exhibits contrary effects on the HTPEMFC and SFD system. The doping level should be less than 30 considering the stability of the membrane and the improvement of thermodynamic performance. A lower flow rate of feed water or a higher flow rate of cooling water is conducive to the proposed system. Finally, the multi-objective optimization is performed based on the genetic algorithm.

A proposed method of solar-driven spray flash evaporation assisted by MPCM applied to solution regeneration with experimental analysis

Solution regeneration belongs to a separation and purification technology for multi-component liquid systems, which is involved in many fields such as liquid desiccant air-conditioning, desalination, and sewage treatment. Solar-driven evaporation technology has enormous energy-saving potential in solution regeneration, but it has the disadvantages of instability and slow regeneration rate. In this work, the method of solar-driven spray flash evaporation assisted by microencapsulated phase change material (MPCM) is proposed for solution regeneration. The spray flash evaporation experimental platform working with NaCl-MPCM suspension is constructed, and the spray characteristics and heat and mass transfer characteristics of NaCl-MPCM suspension are examined under different operating parameters. The results show that the addition of MPCM to the solution can significantly improve its equivalent specific heat capacity, which mitigates dispersed and discontinuous defects of solar energy. Furthermore, it can effectively reduce the severe temperature drop of the solution during the flash evaporation process, which ensures a high driving potential difference between the solution and flash evaporation environment. It is worth mentioning that under the same operating conditions, the regeneration amount per unit mass flow rate of the NaCl-MPCM suspension (wMPCM = 10 wt%) is 24.8 g/kg, which is about 19 % higher than that of the NaCl solution. Additionally, the flash performance of the NaCl-MPCM suspension can be further improved by reducing the initial fluid velocity at the nozzle or the flash evaporation pressure. This study aims to provide guidance for the efficient utilization of solar-driven flash evaporation assisted by MPCM.

Design and Simulation of a Low‐Temperature Thermal Desalination System

AbstractThe prototype of a low‐temperature thermal desalination system treating 2500 L day−1 of saline water was designed thermally and geometrically, to be integrated with a vacuum spray flash drum and spray nozzles, a plate heat exchanger‐type condenser, and a thermosyphon solar water heater to produce potable water for a small community. The design bases were the feed flow rate, the feed temperature from 45 to 65 °C, the salinity of 0.035 kg kg−1, and the vacuum drum pressure from 2 to 6 kPa absolute. The estimated yield of potable water based on the simulated droplet dynamics was in the range of 68.91–75.80 %. The plate heat exchanger and the thermosyphon solar water heater were designed for effective condensation and passive heating, respectively.

Analysis of a spray flash desalination system driven by low-grade waste heat with different intermittencies

Analysis of a spray flash desalination system driven by low-grade waste heat with different intermittencies

Cover Picture: Synthesis of submicron‐sized silver azide by multi‐nozzle spray flash synthesis (Prop., Explos., Pyrotech. 7/2023)

Cover Picture: Synthesis of submicron‐sized silver azide by multi‐nozzle spray flash synthesis (Prop., Explos., Pyrotech. 7/2023)

Integrated system model of spray flash vacuum distillation with internal heat recovery

This study proposed an integrated system model for an original spray flash vacuum distillation system that enhances and leverages the thermal non-equilibrium of the flash process via active vapor extraction to realize an internal heat recovery feature, in which partial heat from hotter vapor is recovered to cooler spray residue within the same stage of feed circulation. This system contains four interlinked sub-systems: (1) an evaporation chamber in which a vacuum-promoted spray flash vaporization occurs, with an active vapor extraction and an outflow of evaporation-cooled brine, (2) a recirculation loop of feed-brine mixture, with the circulation pump, feed heater, and spray nozzle, (3) a hybrid dual-condenser combination, with the internal heat recovery from condensing vapor to the recirculating feed and a secondary cooling by an external coolant, and (4) a vacuum source that maintains vacuum conditions to the entire system as well as discharges the non-condensable gases. The pressure of vapor phase, as the major interlinked operation parameter, is in order of sequential decrease from the evaporation chamber, through condensers, to the vacuum source while the depressurization level in each sub-system is strongly coupled with other transport characteristics such as flash vapor generation in the evaporation chamber or condensing vapor flow in condensers. Thus, the integrated system model is composed of four sub-models to describe the key processes in such four sub-systems. For the modeling validation, a lab-scale experimental system is developed to provide relevant measurements. Comparisons between model predictions against measurements show a good match. Major process characteristics (such as spray flash rate, yield rate, and operating temperatures and pressures) and operational thermodynamic characteristics (such as thermal consumption and heat recovery efficiency) are investigated parametrically. The system's multivariate impacts concerning distillate yield rate and heat recovery effectiveness are also studied with varied operating parameters. Results indicate the pronounced thermal non-equilibrium feature arising from the spray flash process can be effectively utilized via the internal heat recovery design of our system to recover up to more than half of the heat from the yield vapor. Meanwhile, the developed system model can effectively analyze various operational and parametric effects, proving valuable for system design and optimized operation.

Synthesis of submicron‐sized silver azide by multi‐nozzle spray flash synthesis**

AbstractSubmicron‐sized powders of silver azide (AgN3) were prepared by Curtius’ reaction between silver nitrate (AgNO3) and sodium azide (NaN3) in aqueous solutions by a new process: the Spray Flash Synthesis (SFS). The SFS process consists in spraying the two precursor solutions in a heated atomization chamber (130–190 °C), maintained under low vacuum (15–30 kPa). The reaction occurs in the droplets which have collided; the final size of particles is limited by the fast evaporation of water and the small amount of matter available in each droplet which can be considered as an individual micro‐reactor. The mean particle sizes of silver azide synthesized by the SFS process range from 220 nm to 390 nm, which means that these particles are three times smaller than those obtained by the conventional precipitation method. Submicron‐sized AgN3 powders can be initiated by a photographic flash.

Optimization of a novel spray flash desalination system integrated with concentrated solar power utilizing response surface methodology

In the present study, the performance of a novel spray flash desalination system integrated with concentrated solar power is experimentally investigated and optimized. The effect of four factors, namely, flow rate (0.2–0.4 LPM), feed water temperature (30–50 °C), salinity (15,000–35,000 PPM), and vacuum pressure (0.1–0.5 bar), was examined on three responses (i.e., condenser exit temperature, boiler exit temperature, and distillate production). Mathematical models are developed for each response, and optimization is performed with Design Expert software using response surface methodology. The results revealed that the feed water temperature and vacuum pressure positively impacted condenser and boiler exit temperatures and vice versa for salinity and flow rate. However, the flow rate, feed water temperature, and vacuum pressure were found to impact the distillate production positively. The optimum factor settings are 0.4 LPM flow rate, 50 °C feed temperature, 15,000 PPM salinity, and 0.5 bar vacuum pressure for optimal condenser exit temperature of 55 °C, boiler exit temperature of 58.8 °C, and distillate 7010 mLPH. The energy and exergy analyses were conducted, and the mean efficiencies were found to be 55.6 % and 2.2 %, respectively.

Numerical study on the phase change and spray characteristics of liquid ammonia flash spray

Ammonia is regarded as one of the carbon-free alternative fuels for energy systems. The direct utilization of liquid ammonia in gas turbines can reduce the complexity and start-up time of the system. Liquid ammonia is susceptible to flash boiling because of its low boiling point, especially under standard conditions. The boiling point is 239.7 K under 1 atm, which is different from those of traditional hydrocarbon fuels and brings challenges for liquid ammonia spray and combustion simulation. However, the validity of phase-change models for liquid ammonia remains unclear and needs further exploration. Therefore, the present work aims to numerically evaluate the existing evaporation and boiling models for liquid ammonia flash spray. Large eddy simulations were conducted in the Euler-Lagrangian framework, considering droplet kinetics, evaporation, boiling, radiation, and gas-particle interactions. Specifically, five phase-change models were evaluated by comparing the simulation results with recently published experimental data for the vaporization of the ammonia flash spray in terms of the penetration length, spray morphology, and temperature-diameter distribution law. The results indicated that the combined model (the Zuo model combined with the Langmuir-Knudsen model) was more suitable under superheated conditions and agreed reasonably with the experimental results obtained under various temperature and pressure conditions. The evaporation rate tended to increase with decreasing pressure, leading to a significant reduction in the droplets and gas field temperatures. The interaction between the droplet and gas phases was significantly affected by pressure. The ammonia vapor mass fraction first decreased and then increased with an increase in temperature under low pressure, whereby it exhibited only a positive correlation at high ambient pressure. Finally, the effect of the particle diameter distribution was explored and discussed.

Enhancement of heat transfer on micro- and macro- structural surfaces in close-loop R410A flashing spray cooling system for heat dissipation of high-power electronics

High effective spray cooling system is urgently required for the thermal management of high-power electronics in small areas. These electronic devices need to be cooled at functional operating temperature, and it is particularly lacking in current spray cooling studies. For this purpose, a hybrid structural surface that integrates micro- roughness and macro- structure is investigated in close-loop R410A flash spray cooling system. The heat transfer performance is tremendously enhanced as the increase of roughness on flat surface until it reaches the value of 3.5 μm. Meanwhile, a novel tetrahedral fin surface is proposed and compared with modified surfaces including flat, wavy, square, and pyramid fins. It performs high heat flux of 411.2 W cm−2, a 101.5 % enhancement over the flat surface. What’s more, the hybrid structure with 3.5 μm roughness can further improve the maximum critical heat flux and heat transfer coefficient by up to 424 W cm−2 and 814 kW K−1 m−2, respectively, while keeping the surface temperature below 50 °C. Besides, correlations and energy efficiency are studied to explore the performance of structural surfaces. These findings in a wider range of roughness and macrostructure will provide insights to guide the surface modification in flash spray cooling.

Parametric investigation on the close-loop R410A flash spray system for high power electronics cooling under low temperature

For high power density electronics, flash spray cooling is one of the most effective ways of dissipating heat at safe working temperature. Spray parameters exert significant influences on the heat transfer capacity. This paper conducted an experimental investigation to explore the influences of spray chamber pressure, mass flow rate and subcooling degree on the cooling capacity on a flat heated surface in a spray cooling cycle using R410A as the working fluid. The results indicated that the initial increases in spray chamber pressure, mass flow rate and subcooling degree all improved the heat transfer performance. The best cooling performance was achieved once these parameters reached their optimal values; those were 0.57 MPa, 4.9 g/s and 5 °C respectively. The subsequent increase of them deteriorated spray cooling heat transfer, decreasing critical heat flux and heat transfer coefficient while increasing surface temperature. The main reasons responsible for the heat transfer were related to the atomization performance of flash spray affected by the spray parameters. The critical heat flux and maximum heat transfer coefficient yielded on a simple flat copper surface achieved 300 W/cm2 and 550 kW/(K m2) while surface temperature was maintained below 30 °C under the optimal spray parameters.

Spatially dependent salinity effect in actively vacuumed spray flash desalination

Spray flash desalination is one of the most promised distillation methods, which is realized by spraying the superheated droplets into a depressurized chamber to generate flash evaporation. This intensive evaporation leads to a strongly temperature-salinity coupled polarization near the surface region within droplets, which in turn reduces the evaporation rate. In a spray flash desalination chamber with active vacuuming of vapor extraction, such internal polarizations also weaken the thermal non-equilibrium between the extracted hot vapor and the discharged cooler feed residue during the process. This paper aims to establish an integrated modeling-experiment-CFD methodology for quantifying the spatially dependent salinity effect within droplets to the overall processing characteristics in an actively vacuumed spray flash desalination, such as the evaporation rate and efficiency, the coupled internal heat conduction and salt diffusion within droplets, the thermal non-equilibrium between vapor and spray, as well as the non-uniformed vapor flow from vacuum extraction. Specifically: the heat conduction and salt diffusion coupled droplet flash model is proposed; a further simplified point-based droplet flash model is established for CFD simulations; an experimental system of spray flash desalination with active vacuuming is developed for model validations. The evaporation rate and the thermal non-equilibrium are found to be positively related to the initial superheat levels of the spray but negatively impacted by the initial salinity. Modeling predictions indicate that ignoring the spatial dependence of salinity can over-estimate the flash rate by up to 30% in high salinity cases of salty-water distillation. The thermal non-equilibrium between vapor and feed can be effectively generated under active vacuum, even with a low initial superheat level and high salinity. Increasing feed salinity from 0% to 10% in different cases will narrow the temperature gap between outlet vapor and feed residue by about 10% on average. For typical industrial flash desalination (with salinity up to 10%), with or without considering the spatial dependence of salinity will cause relatively minor differences (less than 5%) on the prediction of evaporation rate.

Study on cooling performance of rapid cooling system based on vacuum spray flash evaporation

• Vacuum spray flash cooling (VSFC) system was used for the first time with rapid cooling. • VSFC could cool almost six times fast than the freezer. • The cooling process of beverages could be divided into two stages. • The relevant operational parameters that could optimize VSFC cooling performance were studied. • The optimal discharge coefficient of nozzle was found in VSFC. The present study proposes a rapid cooling method based on vacuum spray flash evaporation, and establishes an experimental system to study the cooling performance of this method by taking beverages as an example. The feasibility and superiority of vacuum spray flash cooling (VSFC) are demonstrated by making the comparisons with the existing rapid cooling methods. A cooling performance evaluation is presented concentrating on the influence of the discharge coefficients of nozzle, multi-nozzle array, and vacuum degree of flash chamber. Meanwhile, the relevant operational parameters of VSFC are optimized. Experiments have shown that the VSFC cools almost six times faster than a freezer. Combined with the simulation, it is found that the cooling process of beverages could be divided into the initiating enhancement stage and the gradual decline stage, in accordance with the characteristics of the internal flow of the beverage during rapid cooling. Parametric analysis indicates that there is an optimal discharge coefficient of nozzles in order to achieve maximum cooling rate for VSFC.

Numerical Study on the Phase Change and Spray Characteristics of Liquid Ammonia Flash Spray

Numerical Study on the Phase Change and Spray Characteristics of Liquid Ammonia Flash Spray