Intermittent Spray Research Articles

Heat and mass transfer characteristics during spray drying of Na2Fe0.6Mn0.4PO4F/C cathode material for Na-ion batteries

The paper presents a detailed experimental investigation on heat and mass transfer characteristics during the synthesis of Na2Fe0.6Mn0.4PO4F/C using intermittent spray drying. The drying process is carried out in a custom-made spray dryer. The novelty of the work is the study of the effect of intermittency on the spray drying process heat and mass transfer characteristics using a volumetric approach. The nozzle orifice diameter, spray duration, and spray pressure are operating parameters of the process that are varied between 0.2 and 0.4 mm at 10 and 40 sand 4 and 7 bar. An increase in nozzle orifice diameter and pumping pressure improves the heat transfer significantly; however, an increase in spray time diminishes the heat transfer. Under considered operating conditions, the volumetric heat transfer coefficient varied between 1.5 and 3.5 kW/m3K. The volumetric mass transfer coefficient ranges between 2.5 and 5.0 s−1. Based on the study, correlations for heat and mass transfer coefficients have been developed that relate the thermophysical properties of both the carrier gas and the precursor fluid in terms of Ohnesorge number and Reynolds number.

Significant Stability Improvement of Fullerene Organic Photovoltaics via ZnO Film Modification through the Intermittent Spray Pyrolysis Technique.

Morphological control of the layers within the bulk heterojunction organic photovoltaics (BHJ-OPVs) is a key feature that governs their performance. In the present work, we demonstrate that zinc oxide—ZnO—interlayers sprayed via the intermittent spray pyrolysis technique, employing a low-concentration precursor solution, can yield inverted BHJ-OPVs as efficient as the standard reported ones using the conventional laboratory-scale spin-coating technique. However, we record a pioneer stability behavior of the fabricated inverted fullerene organic photovoltaics (iF-OPVs) with various sprayed ZnO conditions. Thus, after optimizing the sprayed ZnO interfacial layer morphology for the inverted PTB7-Th:PC70BM devices, by carefully inspecting the interdependence between the sprayed ZnO thin film morphology and the figures of merit of the optimized iF-OPVs, we conducted a distinct analysis on the optical and electronic properties of the fresh and degraded devices using external quantum efficiency measurements and impedance spectroscopy. Hence, we showed that the most proper ZnO microstructural morphology was obtained by spraying 25 running cycles (25R). Remarkably, we observed that 25R-ZnO-based iF-OPV devices showed a stunning stability behavior and maintained 85% of their initial power conversion efficiency even after 16.7 months without encapsulation in a dry nitrogen glovebox, demonstrating an excellent shelf stability. Accordingly, this approach might facilitate the scalability of inverted OPVs for industrial production visibility.

On the evolution of n-octane atomization characteristics using an air-assisted intermittent spray method

In this study, droplet size and velocity of an intermittent air-assisted n-octane spray were measured using a Phase Doppler Particle Analyzer, focusing on the effect of operating parameters on time-resolved droplet behavior and local gas flow characteristics. An electro-magnetically actuated air-assisted injector, which features internal gas-liquid premixing upstream and releasing through an annular nozzle, was used to generate intermittent sprays. The sampling time equalization method is employed to examine the time-resolved spray microscopic characteristics with various injection control parameters and spatial sampling positions. The droplet diameter range is found to be generally independent of air injection duration and sampling time while droplet velocity is correlated with these two parameters. A large air injection duration tends to accelerate droplets in the late spray period and leads to an increasing normalized gas flow velocity. Estimation of local gas flow turbulence intensity indicates a prominent radial sampling position dependence due to the rapid attenuation of the gas flow velocity away from the spray axis. A noteworthy finding for this intermittent air-assisted spray is that at 30 mm from the nozzle outlet, the zero point of droplet-gas mean slip velocity shifts toward the nozzle with sampling time. The time bin size employed to divide the sampling time has been proved to exert no influence on the statistical results of transient spray microscopic characteristics.

Experimental study of intermittent spray cooling on suppression for lithium iron phosphate battery fires

Nowadays, fires caused by thermal runaway (TR) of lithium ion battery (LIB) remains a potential risk in its application. An effective method is urgently required to suppress LIB fires. In this work, a novel cooling method combining dodecafluoro-2-methylpentan-3-one (C 6 F 12 O) agent with intermittent spray cooling (ISC) is proposed for suppression of lithium iron phosphate (LFP) battery fires. Besides, the influence of spray frequency and duty cycle (DC) on spray cooling efficiency are discussed. The results indicate that atomized C 6 F 12 O can effectively suppress LFP fires, reduce the production of toxic gases and heat release rate (HRR). However, after C 6 F 12 O runs out, the rapidly elevated temperature and the release of combustible gases mean that the TR battery requires longer and more efficient cooling. Compared with continuous spray cooling (CSC), ISC not only extends low temperature duration but also decreases the temperature rise rate of the battery. As DC increasing, C 6 F 12 O agent first exhibits an enhancement effect and then an inhibition effect on cooling performance. It is suggested that the optimum DC is 55.4% for the suppression of 14 Ah LFP fires. For the LIBs with higher capacity and higher fraction of active materials, the optimum DC is required to be higher. • A novel cooling strategy is firstly developed for lithium ion battery fires. • Key cooling parameters of thermal runaway suppression with C6F12O are analyzed. • Continuous and intermittent spray modes are compared and investigated. • Duty cycle dominates the cooling performance of intermittent spray cooling.

Experimental investigation on intermittent spray cooling and toxic hazards of lithium-ion battery thermal runaway

The fire extinguishing and cooling of lithium-ion battery thermal runaway have attracted significant research attention. In this study, an intermittent spray method for cooling lithium-ion battery during thermal runaway is proposed. The internal temperature and voltage of the battery, as well as the gases generated during thermal runaway are investigated. In addition, the extinguishing and cooling ability of the intermittent spray method at different intermittent periods (cycle consisting of a spray time and an interval time) and duty cycles (the percentage of the pulse duration occupied in a cycle) are compared and discussed. Furthermore, the toxic effects of the generated gases are evaluated. Experimental results reveal that the internal temperature of the battery is significantly higher than the surface temperature during the thermal runaway. Particularly, the internal temperature of the cell with 100% state of charge was as high as approximately 1000 ℃. In addition, the surface temperature of the cell may rebound after cooling owing to the insufficient heat transfer and a large radial temperature gradient of the battery. Furthermore, intermittent spray with more spray pulses of shorter duration performs better cooling effect. Particularly, the cooling effect initially increases, and then decreases with decreasing duty cycle. The major toxic gases produced during thermal runaway are CO and HF, whose yield increases with an increase in the state of charge, and the toxicity of these gases increases after the water spray. The findings of this study indicate that strict safety protection is needed when water spray is used to extinguish LIB fires.

When Copper Oxide meets graphene oxide: A core-shell structure via an intermittent spray coating route for a highly efficient ammonium perchlorate thermal decomposition

Ammonium perchlorate (AP) is the primary oxygen source for solid propellants; its thermal decomposition behavior is determinant for the overall performance of the ensuing propellant. In this perspective, a novel Intermittent, Spray Coating, Draying, and Mixing (ISCDM) method is introduced herein to prepare AP@CuO, PA@GO, and AP@CuO@GO core-shell composites. The as-synthesized materials morphological information, crystalline structure, and elemental composition are probed by powder X-ray diffraction, Raman spectroscopy, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The as-prepared CuO nanospheres were effectively embedded into the AP microparticles surface. AP@CuO microparticles were continuously coated with graphene oxide (GO) nanosheets. Particle size analyzer was used to probe the particle size distribution of core-shell composites. Results show that the application of ISCDM method results in a typical narrow gaussian size distribution with an average diameter of hundred microns ranking from 158.56 µm to 166.22 µm. The thermal decomposition and the catalytic performances were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). AP@CuO@GO core-shell composite exhibits an excellent thermal decomposition behavior: a low thermal decomposition temperature (LTD) of 337 °C, reduced values of the High thermal decomposition temperature HTD to be overlapped with the LTD step, and a significant energy release of 1543 J g−1 are registered.

Performance enhancement of intermittent spray cooling with a self-rewetting fluid for relatively high-temperature applications

Comparing to continuous spray, intermittent spray is able to offer effective cooling by consuming less liquid. Targeting at relatively high-temperature applications, this study explores the influences of pulse duration and duty cycle (DC) in the cooling performance of the intermittent spray of a self-rewetting fluid, the 1.5% wt.% aqueous solution of 1-pentanol. Unlike water, using the self-rewetting fluid in intermittent spray is able to induce the inverse Marangoni convection which helps to replenish the hot spot with cool liquid even though the surface temperature exceeds 145°C. This leads to a further reduction in fluid consumption because comparable cooling rate can be delivered by spraying the self-rewetting fluid at a much lower frequency. Although dryout can still occur in the low DC regime, the inverse Marangoni convection is proven to sustain effective cooling during spray-off period in the high DC regime. As a result, cooling rate is nearly independent of DC in the high DC regime. For the self-rewetting fluid, cooling performance is not benefited from increasing the pulse duration as excess fluid simply drains out without contributing much to heat removal. Hence, a pulse duration of 1.5 s with a DC of 15% is recommended for the intermittent spray cooling of 1-pentanol/water mixtures at high wall superheats. Since the spray cooling efficiency of the self-rewetting fluid is always higher than that of water in this study, it opens up new possibility in spray quenching with more rapid cooling, better thermal uniformity, and further reduction in liquid consumption.

Effect of air pockets in drug delivery via jet injections

Needle-free jet injections are actuated by a pressure impulse that can be delivered by different mechanisms to generate high-speed jets (Vj~O102 m/s). During filling and transportation of disposable cartridges and ampoules, bubbles can form, which can be problematic especially for viscous fluids. Here, we report on the effect of location and size of entrapped air pockets in cartridges used in spring-powered jet injections. As air bubbles pass through the orifice, they undergo depressurization, which results in intermittent atomization and spray formation, temporarily increasing the jet dispersion. Atomization and dispersion of the jet can lead to product loss during an injection. We find that the effect of bubble location on the jet exit speed, delivery efficiency, and the projected area of the blebs formed after the injection was statistically significant (p<0.05). The findings of this study have implications for the development of pre-filled cartridges for jet injection applications.

Stability Enhancement of High-Performance Inverted Polymer Solar Cells Using ZnO Electron Interfacial Layer Deposited by Intermittent Spray Pyrolysis Approach

In this research work, for the first time, stable high-performance inverted polymer solar cells (iPSCs) have been fabricated utilizing facile and low-cost intermittent spray pyrolysis (SP) techniqu...

A new disinfectant technique for Campylobacter jejuni and spoilage bacteria on chicken skin using a high-pressure pulsed jet spray apparatus

Campylobacter jejuni (C. jejuni) is an important cause of human gastroenteritis worldwide and chickens are considered to be a major reservoir of infection. Recently, a novel high-pressure pulsed jet spray (HPPJS) technique has been developed in order to increase the efficiency of surface cleaning using an intermittent spray system. We evaluated the efficacy of this new technique for reducing C. jejuni and spoilage bacteria on chicken skin. Breast and thigh skin samples were inoculated with C. jejuni and then treated with chlorous acid water (CAW) (200 and 400 ppm), sodium hypochlorite (NaOCl) (100 and 200 ppm) or tap water using the HPPJS at 9 MPa for 5 or 15 s. The C. jejuni counts were determined by the most-probable-number (MPN) method. In addition, aerobic plate counts (APCs) and total coliform (TC) levels were measured using Petrifilm™. Treatment with CAW at 400 ppm or NaOCl at 200 ppm for 15 s showed the greatest efficacy, with reductions of 1.26–2.60 log10 MPN/cm2, 0.55–1.51 log10 CFU/cm2, and 0.92–1.78 log10 CFU/cm2 for C. jejuni, APCs, and TCs, respectively. These results suggest that HPPJS with chemicals is a highly effective technique for the reduction of C. jejuni and spoilage bacteria on chicken skin.

Flow-Controlled Spray Cooling Approaches for Dynamic Thermal Management

Abstract Two-phase spray cooling is considered as one of the most promising thermal management techniques characterized by high heat transfer coefficient (HTC) and critical heat flux (CHF), as well as near-uniform temperatures on target surface. Normally, spray cooling systems feature steady flow rate and continuous spray, and are designed to satisfy the maximum expected heat load. However, if the heat load varies due to operating conditions, such as cold starts and pulsing power cycles, a spray cooling system uses excessive coolant most of the time, and causes low cooling efficiencies because of lower utilization of phase-change heat transfer and higher pumping power. This study aimed to investigate variable and intermittent flow spray cooling characteristics for dynamic thermal management. Variable flow spray cooling scheme requires control of pump input voltage (or speed), and intermittent flow spray cooling scheme requires control of solenoid valve duty cycle and frequency. Tests were conducted on a closed-cycle system with HFE-7100 dielectric coolant at varying liquid flow rate and subcooling conditions, and using smooth and enhanced heat transfer surfaces. Results, compared to a baseline performance from steady flow case, indicated that the variable flow spray cooling conditions achieve similar cooling performance at low and moderate heat fluxes, while the intermittent flow spray conditions result in high temperature penalty and much lower CHF.

Research on Simulation of Heat Transfer Characteristics of Intermittent Spray Cooling

Intermittent spray cooling is a new type cooling technology with the energy-saving advantage which can enhance the spray cooling performance and reduce energy was established consumption. In this paper, the three-dimensional simulation model of intermittent spray cooling, and it is the first time using the simulation method to study the heat transfer characteristics of intermittent spray cooling. The simulation results show that intermittent spray cooling effect can be optimized by adjusting spray cycle and duty ratio, and there is the optimal spray cycle and duty ratio at lower flow rate. The simulation results were compared with the experimental results under the same working conditions, and the calculation error was discussed, which is permitted for engineering application.

A hybrid battery thermal management system for electric vehicles under dynamic working conditions

Lithium-ion batteries have been widely used to propel electric vehicles (EVs) owing to their high energy density, long lifespan, and high stability. However, the inevitable battery heat generation, particularly when there is a rapid increase in power under dynamic working conditions, threatens the safety and performance of EVs. In this study, we develop a hybrid battery thermal management system incorporating micro heat pipe arrays, convective air, and intermittent spray water. The heat pipes siphon the heat from the inside of the battery pack to the outside, and convective air dissipates heat during the normal operation of the EVs, while further cooling is achieved via intermittent spray water at high-power operations. For a 75 Ah lithium-ion battery pack under dynamic working conditions, the proposed hybrid system enables the maximum temperature to be reduced to 29.6°C and the temperature non-uniformity to be 1.6°C, which are 21% and 57% lower than those of thermal management systems without water spraying functions, respectively. Additionally, the energy consumption of the hybrid thermal management system is 4.9 Wh, only accounting for 1.8% of the total battery pack power capacity. Given these advantages, it is expected that the proposed thermal management system is a promising tool to address the practical thermal problems of lithium-ion battery packs used in EVs.

Experimental study on active control of refrigerant emergency spray cooling of thermal abnormal power battery

The technology of the electric vehicle battery overheating and its thermal runaway prevention is becoming research hotspots. This paper proposes an active control method of refrigerant spray to inhibit heat and combustion in thermal accidents. The rapid cooling, suppression of oxygen and flame of the battery module are achieved through the collaborative active control of the spray nozzle and the venting port. The research is carried out with the intermittent spray mode of the refrigerant under the conditions of overall overheating and local overheating. The cooling characteristics and combustion blocking ability of the battery in three typical active control modes of the venting port are compared and analyzed. Studies indicate that the active control of the venting port can effectively prevent the dissipation of the cold energy of the gasified refrigerant in both the case of overall overheating and local overheating, which significantly enhances the cooling capacity, uniformity of temperature change and oxygen suppression effect of the emergency spray cooling compared with that without the active control. In all, the proposed method can further improve the safety of electric vehicles, and win more time for passengers to escape in thermal accidents.

Experimental investigation of water spraying in an indirect evaporative cooler from nozzle type and spray strategy perspectives

Indirect evaporative cooling is a refrigerant-free and low-energy-consumed cooling technology. In practical cases, degraded cooling efficiency of indirect evaporative coolers (IEC) can be observed owning to poor wettability of the wet channels. Although many efforts had been made to improve the unevenly distribution of water film inside an IEC, existing research focus on developing novel materials for better diffusion and optimizing the nozzle arrangement. The influences of nozzle types and water spray strategy (continuous or intermittent) on water distribution performance had seldom been discussed. In this study, the IEC is experimentally investigated from the point of water spraying. Firstly, the water distribution performance of five commonly used spray nozzles has been quantitatively investigated by three proposed indicators (coverage ratio, uniformity coefficient and water volume in distribution regions) under different water rate. Secondly, the optimal nozzles are selected to be used in an advanced porous IEC prototype with good water storage and diffusion characters, which can facilitate the intermittent spray strategy. A series of intermittent spray strategies were tested to recommend a combination of spraying period and intermittent period for higher wet-bulb efficiency and less water consumption. The results show that the spiral type nozzle is the optimal for IEC application because of its high coverage ratio, good uniformity and acceptable water volume in the distribution area. The recommended intermittent spray strategy for porous ceramic IEC is a combination of 10 s–12 s spraying period and 1 min intermittent period.

Fabrication of Pt-graded PEFC catalyst layers by intermittent double nozzle spray

Fabrication of Pt-graded PEFC catalyst layers by intermittent double nozzle spray

Effect of Intermittent Spray Pyrolysis on the Characteristics of Fluorine-Doped Tin Oxide Conductive Glass for Dye Sensitized Solar Cell

One of dye sensitized solar cell’s (DSSC) component is conductive glass, a transparent glass substrate covered with semiconductor oxide, usually fluorine-doped tin oxide (FTO). An economic and scalable method used to deposit the FTO film is spray pyrolysis. A research conducted by Fukano et al. (2004) showed that introducing intermittence in spray pyrolysis using batch atomizer improves the glass’ characteristics. This research aims to observe the effect of intermittence on spray pyrolysis method using nebulizer. A compressor nebulizer and hotplate were used, where the glass’ surface temperature reached 300oC. Transmittance, conductance, morphology and composition of the glasses produced were analyzed. Deposition time and intermittence were varied. Variation of time were 5; 7.5; 10; 16; and 39 minutes. Deposition time of 7.5 minutes showed the highest figure of merit (FOM) of 7.83×10-3 Ω-1. Intermittence was performed by turning the nebulizer off during deposition, with varying period and amount of intermittence. Periods of intermittence were varied for 10, 20, and 30 seconds, and amounts of intermittence were varied 1, 2, and 3 times. Variation of 3 intermittences at 20 seconds each resulted in the highest FOM of 19.29×10-3 Ω-1. DSSC’s efficiency built using produced conductive glass are 1.9×10-4 % and 5.5×10-4 %.

Experimental study on transient heat transfer characteristics of intermittent spray cooling

ABSTRACT Experiments were performed to investigate the transient cooling characteristics of intermittent spray cooling (ISC) in single-phase and nucleate-boiling regimes. The consumption of residual liquid in the non-injection period was confirmed via observations of the dynamic behavior through visualization experiments. The time variation of the surface heat transfer is relatively small in the single-phase regime and minimal in the initial nucleate-boiling regime. Further, ISC was considered as a process where the transient mass flow rate was specified by the characteristic time. This idea was successfully evaluated in the prediction of the critical heat flux in cryogen spray cooling. Abbreviations: CHF: critical heat flux; CSC: cryogen spray cooling; DC: duty cycle; ISC: intermittent spray cooling; SFSM: sequential function specification method

Utilizing the inverse Marangoni convection to facilitate extremely-low-flow-rate intermittent spray cooling for large-area systems

An economical approach is required for solving the portability and maintenance problems of a spray cooling system for facilities stationed in remote areas. To reduce liquid consumption and decrease the number of nozzles required for large-area cooling, we propose the use of a self-rewetting fluid coupled with an intermittent spray that induces a surface-tension-driven flow to extend film evaporation. With an extremely low flow rate of 0.325 ml s−1, the working fluid can be effectively pulled toward a hot region through the inverse Marangoni convection, which promotes thermal uniformity and postpones dryout. Consequently, the cooling rate is considerably improved and the temperature fluctuation over time is reduced. Because of the extremely low liquid consumption, strong film evaporation and intensive nucleation, as opposed to impingement momentum, play major roles in cooling. Although multiple-nozzle configurations outperform single-nozzle configurations at high input power, the performance differentiation between double and quadruple nozzles is small, and excellent cooling can be achieved with a nozzle density as low as 0.10 cm−2. By using double or quadruple nozzles in the short-spray mode, the highest heat flux of 7.4 W cm−2 can be achieved with a temperature fluctuation of ±0.5 °C and spatial deviation smaller than 4%.

Surface orientation effects on heat transfer performance of spray cooling

In this study, the heat transfer performances of spray cooling for upward, vertical, and downward surfaces under different nozzle-to-surface distances, inlet pressures, nozzle types, and surface areas were investigated experimentally. Almost no difference in heat transfer performance can be found among the different orientations in single-phase and two-phase regimes. A considerable orientation dependency of the critical heat flux (CHF) can be observed in medium-spray volumetric fluxes: the CHF of the vertical surface is higher than that of the upward and downward surfaces. The orientation dependency of the CHF reduces as the inlet pressure increases, implying that an increase in droplet diameter or decrease in droplet velocity would enhance this dependency. The surface orientation has no significant effect on surface liquid film flow and temperature distribution. In this paper, interaction between the vapour and spray (or surface wall) is proposed and verified to be the main mechanism that affects orientation dependency by intermittent spray cooling. A macrolayer model for the CHF is semi-empirically introduced to account for the orientation effects and provide a quantitative evaluation of these effects. Finally, based upon this model, a general correlation for the CHF is proposed.