Single Spray Nozzle Research Articles

Simulation study on the effect of liquid ammonia spray on the heat transfer performance of multiple heat exchange tubes

Abstract In this paper, aiming at the problems of low heat transfer efficiency and uneven heat transfer of heat exchange tubes in refrigeration and air conditioning chillers, a liquid ammonia spray cooling method is proposed, and a flow and heat transfer model is established. The distribution of refrigerant droplets in the fluid domain and the heat transfer on the surface of the heat exchange tube are simulated under different spray speeds, spray directions, and double nozzle sprays. The results show that with the increase of spray velocity, the heat transfer performance of heat exchange tubes decreases first and then increases. The effect of spray velocity on the heat transfer performance of each row of heat exchange tubes is not consistent. The farther away it is from the nozzle, the greater the speed corresponding to the peak value of the heat transfer performance improvement of the heat exchange tube will be; the spray direction (gravity) has little influence on the heat transfer performance of the heat exchange tube, which is within 5.1%. Compared with single-nozzle spray, double-nozzle spray greatly improves the heat transfer performance of multi-row heat exchange tubes.

Parametric study of water spray cooling on enhanced relatively large surfaces

Spray cooling as an effective cooling technique is widely used in practice. Compared to small heating surfaces, the significantly increase of surface would pose a great challenge to the significant enhancement of spray cooling. Specially, single nozzle spray cooling suffers from non-uniform liquid thin film on a relatively large heating surface, severely inhibiting the formation of efficient thin film evaporation. In this study, two enhanced surfaces such as straight fin surface and cubic fin surface with a relatively large heating surface of 4 cm2 were designed for single nozzle spray cooling. A parametric study was conducted with aims to evaluate the effects of flow rate, spray distance and enhanced surfaces on the formation of thin liquid film and then the performance of spray cooling. Visualization was presented to observe the development of liquid film to elucidate the enhanced mechanism of spray cooling. In this work, spraying height is varying from 20 to 40 mm. Coolant flow rate is ranging from 70 to 100 ml/min. The experimental results show the distribution of liquid film plays an important role in spray cooling, especiallyin the single-phase regime. In two-phase regime, nucleate boiling is significantly boosted on the engineered surfaced. For instance, the cubic fin surface leads to an enhancement of HTC of nearly 24 % compared to that of flat surface.

Visualization and characterization of agricultural sprays using machine learning based digital inline holography

Accurate characterization of agricultural sprays is crucial to predict in-field performance of liquid applied crop protection products. In this paper, we introduce a robust and efficient machine learning (ML) based Digital In-line Holography (DIH) algorithm to accurately characterize the droplet field for a wide range of commonly used agricultural spray nozzles. Compared to non-ML based DIH processing, the ML-based algorithm enhances accuracy, generalizability, and processing speed. The ML-based approach employs two neural networks: a modified U-Net to obtain the 3D droplet field from the numerically reconstructed optical field, followed by a VGG16 classifier to reduce false positives from the U-Net prediction. The modified U-Net is trained using holograms generated using a single spray nozzle (XR11003) at three different spray locations; center, half-span, and the spray edge to create training data with different number densities and droplet size ranges. VGG16 is trained using the minimum intensity projection of the droplet 3D point spread function (PSF). Data augmentation is used to increase the efficiency of classification and make the algorithm generalizable for different measurement settings. The model is validated using National Institute of Standards and Technology (NIST) traceable glass beads and six different agricultural spray nozzles representing various spray characteristics. The principal results demonstrate a high accuracy rate, with over 90% droplet extraction and less than 5% false positives, regardless of droplet number density and size. Compared to traditional spray measurement techniques, the new ML-based DIH methodology offers a significant leap forward in spatial resolution and generalizability. We show that the proposed ML-based algorithm can extract the real cumulative volume distribution of the NIST beads, where the LD system measurements are biased towards droplets moving at slower speeds. Additionally, the ML-based DIH approach enables the estimation of mass and momentum flux at different locations and the calculation of relative velocities of droplet pairs, which are difficult to obtain using conventional spray characterization techniques.

Thermal characterization of spray impingement heat transfer over a High-Power LED module

• Thermal management of single nozzle spray for a high-power LED module is explored. • Maximum experimental heat transfer coefficient ∼12 kW/m 2 K is obtained for Re of 12000. • LED substrate temperature is maintained well below safe limits for Re = 8000 and above. • Spatial and temporal thermal fields over the LED module is computationally estimated. • The experimental results are complemented with 3D numerical heat transfer simulations. The cooling demand for a nominal 300 W power LEDs is around 200 W/cm 2 at the chip-scale, and the junction temperature must be maintained below 120 °C for reliable operation. Special thermal management packaging is required to maintain LEDs below this reliability temperature limit. The present study investigates the thermal characteristics of single-nozzle spray cooling over a high-power LED module. The detailed thermal characterization within the LED assembly is explored using both, experimental and numerical approaches. The LED substrate temperature is experimentally obtained for various input power supplies, water flow rate, inlet water temperature, nozzle height, and offset from the LED center. Heat transfer coefficient at two radial locations ( R = 0 mm and 12.5 mm) is estimated to evaluate the heat removal capacity of the spray for these operating conditions. Numerical study is performed to visualize temperature and heat flux distribution within the LED module, and to investigate the appearance of thermally critical locations. Junction temperature is the critical parameter for thermal characterization of the LED module, and is numerically investigated for various operating conditions. The junction temperature is maintained below 95 °C at the nominal electrical input power for a Re ≥ 8,000 using the proposed spray cooling design. The present study establishes the efficacy of spray cooling for high-power LED modules, even when the supply power exceeds 112% of the nominal power range.

PANDA experiments within the OECD/NEA HYMERES-2 project on containment hydrogen distribution, thermal radiation and suppression pool phenomena

In this article, we summarize the experimental results obtained in the large-scale thermal-hydraulics PANDA facility (PSI, Switzerland) within the OECD/NEA HYMERES2 project. The experiments addressing hydrogen distribution allowed characterizing the flow patterns forming from jet flows impacting plates or grating platforms and the following interaction with a postulated hydrogen cloud in the containment dome. The experiments with activation of safety components allowed to compare the effects of multiple spray nozzles with a single spray nozzle or multiple cooler units with unique cooler and to assess the scalability of the related thermal hydraulics phenomena such as pressure histories, power removed, gas mixture distribution. The experiments related to thermal radiation confirmed that the presence of steam in a containment atmosphere even at very low concentration (in the order of 0.1 %) has a significant impact on the evolution of containment mixture temperature.The experiments studying pressure suppression pool phenomena provided insight on the formation and stability of thermocline under a variety of steam release conditions, e.g. from load reduction rings and from multi-hole sparger; moreover allowed to characterize containment pressure histories as function of sparger submergence in the suppression pool.

Deposition, Endo-drift and Exo-drift in the Pulverization in Coffee With Different Equipment

The objective was to evaluate the equipment efficiency in reducing drift and increasing the spray deposition. The experiment was conducted of the conilon coffee plantation, located on the experimental area of the Federal Institute of Espirito Santo, Itapina, Brazil. The experiment was a randomized complete block design with four replications. The treatments consisted: a knapsack sprayer with electrostatic assistance, an electric knapsack sprayer, a knapsack sprayer with a spray shield, and a knapsack sprayer without a spray shield. All sprayers were equipped with a single spray nozzle. Spray deposition was evaluated on wee leaves using a food colourant as a tracer. The knapsack sprayer with electrostatic assistance was the most efficient equipment, providing lower values of drift, and the greatest deposition on the weeds. It is recommended to use the electrostatic sprayer, as it showed greater efficiency in the application of the product on the target, using smaller volume

Experimental characterization of multi-nozzle atomization interference for dust reduction between hydraulic supports at a fully mechanized coal mining face.

To analyze the distribution pattern concerning multi-nozzle interference spray particle granularity between hydraulic supports, the present study conducts atomization interference experimental characterization for three types of nozzles used in coal mines based on a Doppler laser interference spray dust suppression simulation experimental system. The results indicate that for single-nozzle atomization, the impact of spray pressure on spray droplet size is gradually subdued, and a spray pressure of 8MPa yields the best result; compared with single-nozzle spray, the multi-nozzle atomization interference effect can downsize the spray field overlapping zone, leading to an improved uniformity of overall spray particle distribution. As the spray field overlapping coefficient k increases, the particle size of the interference spray field decreases first and then increases. As the spray field overlapping coefficient reaches 0.4, the distribution of spray droplet size is most concentrated, corresponding to the optimal atomized dust suppression effect. Practical testing indicates that the optimal spray field overlapping coefficient measured at a fully mechanized mining face agrees well with the experimental result. Under the optimal parameters, the average total dust and respirable dust suppression rates measured at various measuring points on the downwind side during support relocation reach 78.93% and 80.53%, respectively.

A comprehensive design of rainfall simulator for the assessment of soil erosion in the laboratory

The present paper describes the design of a comprehensive rainfall simulator which is particularly meant for the assessment of soil erosion at plot scale by considering various soil grain types, soil slope angles, and surface exposures under different rainfall conditions. The entire setup is divided into four major parts: (a) water supply system with single spray nozzle, (b) supporting metal frame, (c) hydraulic jack attached container table for slope adjustment, and (d) temperature simulator. It covers an area of 3 m2, out of which 0.5 m2 is the target area or experimental plot and the simulated raindrops fall from a height of 2.3 m. Four types of full-jet spray nozzles are used to simulate rainfall intensities of 65, 93, 112, and 148 mm/h. The experimental plot can attain a maximum slope angle of 40° using a hydraulic jack unit. A temperature simulator is designed to replicate the natural conditions in the laboratory. Physical and numerical simulations are carried out to measure the characteristics of simulated rainfall and compare with those of natural rainfall conditions. The Christiansen coefficient (Cu) of the designed rainfall simulator varies from 81% to 88%. The rain droplet size ranges from roughly 1 mm to 5 mm and their corresponding terminal velocities range from 4.76 m/s to 10.64 m/s, striking velocities are found between 5.56 m/s and 9.63 m/s, and kinetic energies ranging from 0.0081 mJ to 3.0342 mJ. The total kinetic energy of the raindrops striking the soil surface in the entire plot area of 0.5 m2 depends on the rainfall intensity and varies from about 6 J to 12 J. The designed setup is capable of simulating rainfall inside the laboratory with properties very close to those of natural rainfall. We adopt the Taguchi fractional factorial design of experiments to investigate the effects of different factors on soil erosion. Furthermore, statistical analysis of the experimental data is carried out by using signal-to-noise (S/N) ratio and the optimum condition for maximum soil erosion is predicted. The main objectives of this study are to design a comprehensive rainfall simulator setup, evaluate the properties of the simulated rainfall, provide a theoretical model and assess the several factors affecting soil erosion using reduced number of experiments in the laboratory.

Experimental prediction of multi-nozzle spray characteristics for optimal design in a lead frame etching process

The objective of this paper is to provide quantitative information of uniform impact forces on the sprayed surface in order to optimize the multi-nozzle spray etching system. Spray characteristics obtained from optical non-intrusive measurements using particle image velocimetry (PIV) and particle motion analysis system (PMAS) are measured in single- and twin-nozzle sprays, and then the multi-nozzle spray characteristics is simulated based on those of measurement data. The influences of the multi-nozzle arrangement, nozzle pitch, and pipe pitch on the spray characteristics such as droplets’ velocity, diameter, number density, impact force and their uniformity are properly evaluated. The experimental cases E1 and E2 represent single-spray nozzle A and B, respectively. For twin-spray tests, three nozzle combinations, namely E3 (nozzle A-A), E4 (nozzle A-B) and E5 (nozzle B-B) are considered with different nozzle pitches. The multi-spray simulation cases S1 and S6 represent the multi-spray cases with a homo-nozzle arrays which is consisted in all nozzles of nozzle A or B. For cases from case S2 to S5, the multi-spray cases with a hybrid-nozzle arrays which is consisted in all nozzles of nozzle A and B. The results show that the impact force increases approximately twice as much for changing of experimental test cases from E1 to E5 owing to the differences in nozzle characteristics of single-sprays and the overlap region between two adjacent nozzles. For the multi-nozzle spray simulation, the uniformity of impact force (UI) is increased with increasing the number of nozzle B which has larger orifice diameter and a wider spray angle. The optimum multi-nozzle spray arrangement is case S4 with more than 90 % UI, based on the fact that the UI is quite stable with increasing the nozzle pitch ranging from 90 mm to 145 mm.

Automatic Adjustable Spraying Device for Site-Specific Agricultural Application

This paper presents a device for accurate pesticide spraying capable of dealing with amorphous shapes and variable-sized targets. The device includes a single spray nozzle with an automatically adjustable spraying angle, color camera, and distance sensors, all mounted on a pan tilt unit. The site-specific spraying device aims to spray specific targets while reducing the use of pesticides. The spraying diameter is set as the minimum closing circle diameter according to the shape and size of the target. Two preliminary experiments were conducted in order to evaluate the spray nozzle flow rate in relation to the spray diameter and the spray diameter in relation to the nozzle’s angular position. A main outdoor experiment was conducted to evaluate the complete spraying device using artificial targets of varying sizes. The results indicated that the spraying device is capable of reducing the amount of pesticides applied. An economic analysis estimates that up to 45% of pesticide reduction is possible when using the suggested spraying method. Actual savings depend on the spraying durations, target size, and distribution. Note to Practitioners —This paper focuses on the development of a site-specific sprayer solution. The developed device aims to reduce pesticide application by spraying individual targets specifically by setting the diameter of the spraying according to the shape and size of the target. The core of the paper is a detailed description of a spraying device able to change its spraying diameter according to the detected target. A working procedure to calibrate and validate such a device is included. We believe that such a device can be used in modern agriculture and can be combined with a robotic sprayer navigating autonomously along crop fields. Such a device will contribute to reduced pesticide application.

Numerical Simulation of Heat Transfer from Rotary Cylinder by Spray Cooling

A commonly-used method to cool rotating cylinders involves spraying water on the surface to cool its internal particles. This paper conducted a numerical investigation of heat transfer from a rotary cylinder cooled with sprayed water. A 3-D numerical model was generated, and the distributions of the wall temperatures and liquid films were analyzed. Then, the heat transfer characteristics for different parameters were obtained and compared. The results showed that the best location for a single spray nozzle was directly above the cylinder, where it had the most uniform liquid film and highest heat exchange efficiency. With increased rotation speeds, the cylinder wall temperature increased and the distribution of wall temperature and liquid film became more uniform, which improved heat transfer. Because of the influence of gravity, the slope of the cylinder had a negative influence on the distribution of the liquid film. When the cylinder material had lower thermal conductivity, the system needed a much longer period of time before it was stable and had lower heat flux. Furthermore, with the same heat source, the system heat flux could not be determined with only the outer surface temperature, but with the temperature difference between inner surface and outer surface.DOI: http://dx.doi.org/10.5755/j01.ms.23.4.17322

Overall Mass Transfer Coefficient of CO2 Absorption in a Diameter-varying Spray Tower

The application of spray towers for CO2 capture is a development trend in recent years. However, most of the previous jobs were conducted in a cylindrical tower by using a single spray nozzle, whose configuration and performance is not good enough for industrial application. To solve this problem, the present work proposed a diameter-varying spray tower and a new spray mode of dual-nozzle opposed impinging spray to enhance the absorption performance of CO2 spray absorption process. Experiments were conducted to investigate the effects of varies operating parameters on the overall mass transfer coefficient in various operating conditions. Experimental results showed that liquid to gas ratio and mole ratio of MEA to CO2 are key factors which affect the performance of CO2 absorption process and the maximum overall mass transfer coefficient for the diameter-varying dual-nozzle opposed impinging spray tower is 0.4773 kmol·m-3·h-1·kPa-1.

Performance of CO2 absorption in a diameter-varying spray tower

Abstract The application of spray towers for CO 2 capture is a development trend in recent years. However, most of the previous jobs were conducted in a cylindrical tower by using a single spray nozzle, whose configuration and performance is not good enough for industrial application. To solve this problem, the present work proposed a diameter-varying spray tower and a new spray mode of dual-nozzle opposed impinging spray to enhance the heat and mass transfer of CO 2 absorption process. Experiments were performed to investigate the mass transfer performance (in terms of the CO 2 removal rate ( η ) and the overall mass transfer coefficient ( K G a e )) of the improved spray tower under various operating conditions. Experimental results showed that the liquid to gas ratio and mole ratio of MEA to CO 2 are major factors, which affect the absorption performance and the maximums of η and K G a e that are 94.0% and 0.574 kmol·m − 3 ·h − 1 ·kPa − 1 , respectively, under the experimental conditions. Furthermore, new correlations to predict the mass transfer coefficient of the proposed spray tower are developed in various CO 2 concentrations with a Pearson Correlation Coefficient over 90%.

CFD analysis of pre-cooling water spray system in natural draft dry cooling towers

CFD analysis of a wind tunnel with a single spray nozzle was conducted for the water spray system in the natural draft dry cooling tower (NDDCT) built at the University of Queensland. The CFD model was validated with the experiment results. The comparison of pre-cooling performance between the vertical arranged nozzle (VAN) and the horizontal arranged nozzle (HAN) shows that the VAN has better performance than the HAN within the inlet air velocity (va) ranges (0.8–1m/s) of the NDDCT during summer season. The impact of several physical parameters of the continuous phase on the maximum fully evaporated water mass flow (mmaxew) with the VAN was also conducted. The results show that mmaxew witnesses a decrease with the increasing of va from 0.8m/s to 1m/s. The ambient air temperature and the relative humidity have significant impact on mmaxew. The increasing of turbulence intensity could improve mmaxew by enlarging spray coverage area.

Numerical Simulation of Characteristic of Heat Transfer for Jet Impingement with New Single Cone Heat Sink through Single Spray Nozzle

Numerical Simulation of Characteristic of Heat Transfer for Jet Impingement with New Single Cone Heat Sink through Single Spray Nozzle

Numerical simulation of water spray for pre-cooling of inlet air in natural draft dry cooling towers

This paper presents a numerical investigation of inlet air pre-cooling with water sprays to enhance the performance in Natural Draft Dry Cooling Towers (NDDCT). A 3-D numerical model of a test channel was generated and the evaporation from a single spray nozzle was analyzed. The droplet evaporation and the resulting cooling of air were predicted for a range of inlet air conditions and spray characteristics. The results showed that up to 81% evaporation can be achieved for water droplets of 20 μm at a velocity of 1 m/s and that, droplet transport and evaporation strongly depend on droplet size and air velocity.

Experimental study of the SO2 removal efficiency and volumetric mass transfer coefficients in a pilot-scale multi-nozzle spray tower

The spray tower is an industrial device widely employed for liquid–gas contact. In these towers, liquid is sprayed to generate droplets that provide a large interfacial area for heat and mass transfer between the continuous and dispersed phases. The performance of a spray tower is difficult to predict due to the complex hydrodynamics of system. This performance is influenced by several factors, such as droplet size and distribution, droplet velocity, collision and coalescence between droplets, internal recirculation, oscillation and distortion of the droplets, the relationship between different variables, and gas and liquid flow rates. Although spray towers are very common, there are few methodologies for their design, which is typically based on empirical or one-dimensional models. Experimental studies on gas absorption in spray towers have been carried out for years. However, all these studies used a single spray nozzle, whose configuration differs from that used in typical industrial spray towers, thus making the results of these studies difficult to apply in practice. The present work consisted of experimentally determining the volumetric mass transfer coefficient, kga, in a lab-pilot spray tower absorbing SO2, employing different operating conditions and two nozzle configurations, one involving the simultaneous use of a set of five spray nozzles and the other one, a single spray nozzle. New correlations to predict the coefficient kga are proposed, including two new parameters: the diameter of the spray nozzle orifice and the exit velocity of liquid from the orifice, as well as the superficial gas and liquid velocities, which have been used traditionally in other studies.

DROPLET SIZE AND VELOCITY MEASUREMENTS AT THE OUTLET OF A HOLLOW CONE SPRAY NOZZLE

During the course of a severe accident in a nuclear pressurized water reactor (PWR), hydrogen may be produced by reactor core oxidation and distributed into the containment. Spray systems are used in order to limit overpressure, enhance the gas mixing, avoid hydrogen accumulation, and wash out fission products. In order to simulate these phenomena with computational fluid dynamics codes, it is first necessary to know the droplet size and velocity distributions close to the outlet nozzle. Furthermore, since most of the phenomena relative to droplets (condensation, gas entrainment, and collisions) are of particular importance in the region just below the nozzle, accurate input data are needed for real-scale PWR calculations. The objective is, therefore, to determine experimentally these input data under atmospheric conditions. Experimental measurements were performed on a single spray nozzle, which is routinely set up in many PWRs. This nozzle is generally used with water at a relative pressure supply of 3.5 bar, producing a mass flow rate of approximately 1 kg/s. At a distance of 20 cm, in which under ambient conditions atomization is just achieved, it is found that the geometric mean diameter varies from 280 to 340 μm, the Sauter mean diameter varies from 430 to 520 μm, and the mean axial velocity varies from 14 to 20 m/s. The radial velocity is around 7 m/s, whereas the orthoradial velocity is almost equal to zero at this distance of the nozzle. Gas velocity measurements around the spray are also performed.

Study of mist-cooling for semi-enclosed spaces in Osaka, Japan

Evaporative mist cooling systems are increasingly used in Japan to cool urban spaces as a counter to the urban heat island problem. Japan has a humid climate, which reduces evaporation. The balance between cooling and undesirable wetting requires careful control and placement of misting nozzles. Spraying from varying heights in an atrium showed that a single spray nozzle with Sauter mean droplet diameter of 41 microns can provide cooling of 0.7K without wetting. Cooling effects of mists with larger droplet diameters that cause slight wetting cannot be accurately measured due to the wet bulb effect on the sensors. Simulations suggest actual air temperatures are higher than wet sensor readings. Calculations of effective temperature ET* show that increases in humidity do not overcome the increase in thermal comfort due to the temperature reductions from fine mist.

ACELEPRYN AND MERIT FOR THE PREVENTIVE CONTROL OF JAPANESE BEETLE LARVAE IN TURFGRASS, 2008

This study was conducted to compare different formulations of chlorantraniliprole and imidacloprid for the preventive control of JB larvae in turfgrass. Testing was done in a turf plot maintained at the NYS Agricultural Experiment Station (Geneva, NY). The site had been renovated and reseeded to perennial ryegrass in May, and maintained at a mowing ht of 3.5-4 inches. Evaluation units were PVC arenas (diameter 12 inches, depth 4 inches) placed in the ground so that the upper lip was level with the soil surface. Arenas were arranged in a RCB design with eight repetitions of seven treatments. Infestations were made by enclosing 15 male and 15 female JB adults over each ring for 7 days of mating and oviposition. Treatment applications were made 22 Jul 2008 followed by infestations on 29 July 2008. Liquid formulations were applied with a pressurized CO2 sprayer coupled with a single nozzle spray wand and a Teejet 8002VS flat fan tip. Granular formulations were evenly applied using a shaker jar. Conditions at time of application were the following: skies partly sunny; wind negligible; air temp 74.0°F; soil temp at 2-inch depth 75.0°F. Until the study was rated, rainfall was supplemented with 0.25 inches irrigation if 5 consecutive days lapsed with <0.10 inches rain on any of those days. Mean daily precipitation was 0.14 inches; mean daily air temp (min/max) 50.5/70°F; and mean daily soil temp at 2-inch depth (min/max) 54.5/82.5°F. JB larval populations were evaluated on 2 Oct 2008 by destructively searching the soil in each arena. Data were transformed by log(x+0.5) before ANOVA, followed by LSMeans separation using Student’s t.