Suction Nozzle Research Articles

Experimental analysis of the R290 variable geometry ejector with a spindle

The aim of this work was to experimentally analyze the variable geometry gas ejector with a spindle designed for operation with the natural working fluid propane (R290). The performance of the ejector was evaluated based on the mass entrainment ratio and critical temperature, being the most crucial parameters for optimizing the cooling capacity in ejector refrigeration systems, as well as the ejector efficiency using common literature notation. Additionally, local pressure drop measurements allowed for the determination of pressure profiles inside for different spindle positions used for capacity regulation. The experimentally defined ejector efficiency curves demonstrated the ability to control the ejector capacity by means of the spindle, irrespective of the unfavorable operating conditions. By decreasing the effective throat area using spindle, the ejector mass entertainment ratio increased by 35%. Spindle movement allowed for the decrease of the motive nozzle flow rate by up to 65%, while still maintaining the suction of the secondary flow of the ejector. Moreover, the behavior of a slight increase in suction nozzle flow with a decrease in motive nozzle flow has been observed for the initial movement of the spindle followed by a huge drop for further reduction of the effective throat area, confirming the previous conclusions shown in the literature.

Experimental performance comparison of various expansion devices for small-capacity subcritical R744 vapour-compression refrigeration units

The target of this study is to experimentally compare the performance of three different expansion devices for small-capacity subcritical R744 vapour-compression refrigeration units. The first considered expansion device was the conventional high-pressure expansion valve, which was selected as the baseline. The second assessed expansion device was a two-phase ejector for expansion work recovery whose refrigerant flow was modulated via the pulse-width modulation (PWM) strategy. Finally, the PWM approach was employed for controlling the refrigerant flow of the ejector motive nozzle while the refrigerant was not permitted to be drawn by the ejector suction nozzle. The results showed that the motive nozzle controlled via PWM effect offers similar effectiveness to a conventional high-pressure expansion valve in the subcritical regime. Furthermore, it was observed that the PWM ejector is able to control the high pressure effectively while increasing the coefficient of performance (COP) by up to 5.3 % without and by up to 7.9 % with overfed evaporator compared to the baseline in the transition regime. The results also showed that the installation of the conventional high-pressure expansion valve is not necessary. Finally, the yearly performance of the aforementioned expansion devices was assessed in five different locations, i.e., Athens (Greece), Phoenix (USA), New Delhi (India), Riyadh (Saudi Arabia) and Bangkok (Thailand). The outcomes revealed that the PWM ejector allows for a higher in yearly average COP (COPyearly avg) from 4.9 % (in Athens) to 11.8 % (in Bangkok) over the baseline.

大型贮罐清理机器人吸尘系统的设计与研究

Taking the large storage tank as the cleaning object, a cleaning robot integrating shoveling, crushing, sweeping and dust-absorbing was developed, and its dust-absorbing system was analyzed and optimized. Firstly, Fluent-EDEM gas-solid coupling was utilized to simulate the dust-absorbing system. By analyzing the fluid distribution and particle trajectory, the internal structure of the dust collection box was optimized to reduce the dust particles entering the fan box. Then, by analyzing the structural parameters of the suction nozzle, the influence of the nozzle shoulder angle, nozzle length, and shoulder height on the dust-absorbing effect was explored, and the parameters were determined, so as to reduce the energy loss and increase the flow rate on both sides of the nozzle. Finally, through the dust suction test, different models of nozzles were tested for dust suction, and the wind speed at the nozzle was measured, and the leakage of dust particles on both sides of the nozzle was significantly reduced after optimization, which verified the reliability of the simulation results and provided a theoretical basis for the design of the sweeping robot.

Parametrical design and optimization of a reverse circulation drill bit for dust control

The reverse circulation down-the-hole air hammer drilling (RC-DTH) method is renowned for its efficiency in hard rock formations and exceptional dust control performance. It presents opportunities for cost-saving, efficiency improvement, energy conservation, and environmental protection. Reverse circulation drill bits are critical components of this method. This study focused on the air reverse circulation regime, investigating various geometric parameters of the RC drill bits through computational and experimental methods to enhance its dust control performance. Results indicate that increasing the layers of suction nozzles, enlarging the diameters of the suction and mixing nozzles, and optimizing the input airflow rate can effectively channel airflow toward the central passage of the drill tool. Consequently, this optimization significantly improves the dust control performance of the RC drill bits. Conversely, increases in the flushing nozzle diameter and alterations in the suction nozzle location have detrimental effects on the dust control capability of the RC drill bits. Field tests were conducted at the Yuan Jiacun iron mine, affiliated with Taiyuan Iron and Steel (Group) CO., LTD. The field tests demonstrate that the optimized RC drill bit exhibits excellent dust performance.

Tissue Tension and Strain as Indicators of Suction‐mediated Cutaneous DNA Transfection: A Parametric Study

AbstractCutaneous suction‐based transfection is a recently developed technique that is painless and simple‐to‐use for the delivery of DNA for nucleic‐acid‐based vaccines. The technique promises high efficiency for both antigen expression and immunogenicity as demonstrated in both animal studies and human clinical trials. To realize this promise, a parametric study and systematic evaluation of the efficacy of cutaneous suction as a transfection method is performed. Using Green Fluorescent Protein (GFP) plasmid expression as a transfection reporter in a rat model, the expression level as a function of both suction nozzle size and suction pressure is quantified. A numerical model is employed to compute skin deformation in terms of strain, which is used to correlate with GFP expression. Based on these results, two quantities, integrated total strain and tissue tension, are proposed as indicators of expression level that can be used to guide protocol development and optimization. These indicators are also discussed in relation to possible cellular uptake mechanisms.

Energy and Exergy Analysis of an Ejector Expansion Transcritical Carbon Dioxide Air Conditioning System

A carbon dioxide based transcritical air conditioning system integrated with an ejector is thermodynamically modeled and the system is simulated for different ambient conditions. Throughout the analysis, the isentropic efficiency of motive nozzle, suction nozzle and diffuser is assumed as 85% while the mixing takes place at constant pressure. A step-by-step iterative procedure is adopted to obtain the pressure lift and entrainment ratio. The present thermodynamic model is validated with the experimental results available in the open literature. Results were then compared to a conventional transcritical carbon dioxide system working between the same operating conditions. Results show a significant improvement of about 21% and more in system performance compared to a conventional system working under the same operating conditions. To justify the application of an ejector as an expansion work recovery device and to identify the component level exergy destruction rate, a comprehensive exergy analysis is implemented and the results show 20% reduction in total exergy destruction rate of the system, with an ejector.

Effects of Suction Velocity and Particle Diameter on Pneumatic Conveying Characteristics of ‍Suction Nozzle with Injection Pipe

Effects of Suction Velocity and Particle Diameter on Pneumatic Conveying Characteristics of ‍Suction Nozzle with Injection Pipe

Quasi One-Dimensional characteristic analysis of ejector nozzle for turbofan propulsion system

To investigate the impact of the ejector characteristics of the exhaust system on the overall performance of a turbofan engine, this paper presents a study on the overall performance of the turbofan engine equipped with an ejector nozzle, focusing on its characteristics. Firstly, the design of the ejector exhaust system is presented and its ejector characteristics are analyzed through two-dimensional computational fluid dynamics simulations. Subsequently, a one-dimensional theoretical analysis of the ejector is conducted, and the pump suction and ejector nozzle’s thrust characteristics are determined based on the analysis results. Furthermore, a two-dimensional interpolation method is proposed to calculate the ejector coefficient, which utilizes the ejector's pump suction characteristics. By applying the matching principle of the ejector coefficient, a component-level model of the turbofan engine with an ejector nozzle is established. Based on this model, a method for predicting the backward infrared radiation intensity of the ejector exhaust system is proposed to investigate the influence of the ejector nozzle characteristics on the overall engine performance and infrared signature. The results demonstrate that the installation of the ejector exhaust system leads to a slight decrease in the overall engine performance, in which the average decrease of thrust is about 1.5%, and the average increase in fuel consumption is about 0.5%.but significantly reduces the infrared stealth characteristics, the average reduction is about 20%, which has good infrared stealth effect.

Design and Parameter Optimization of a Negative-Pressure Peanut Fruit-Soil Separating Device

This study proposes a negative-pressure fruit-soil separating device for peanuts cultivated in hilly and mountainous areas after combined harvesting, and the mechanism of the movement of the material in the process of material screening, fruit-soil separating, and pneumatic conveying of the device was analyzed. In addition, a four-factor, three-level Box-Behnken regression design test was used to explore the optimum operating parameters of the peanut fruit-soil separation device. The results showed that the best fruit-soil separation effect was achieved when the wind speed of the blower was 13.58 m/s, the height of the suction nozzle from the screen surface was 27 mm, the length of the suction port was 64 mm, and the feeding rate was 600 kg/h. Validation tests demonstrated that the impurity rate of 0.16% and the peanut pod loss rate of 0.2% exceeded the industry standard, indicating superior performance.

Optimum Design of Large-Diameter Reverse Circulation Drill Bit for Drilling Rescue Wells Using Orthogonal Experimental Method and CFD Simulation

Down-the-hole (DTH) hammer drilling with reverse circulation is a novel, mobile, high-speed drilling system suitable for the specific requirements of mine rescue. This technology can be applied to shorten the rescue time during mine accidents. The performance of reverse circulation (RC) drilling depends on the structural design of the drill bit. An orthogonal experimental design is executed to investigate the effect of the structural design parameters of the large-diameter drill bit for drilling rescue wells on the cutting carrying capacity and reverse circulation performance. This study employs computational fluid dynamics (CFD) software to solve the Navier–Stokes equation for three-dimensional steady flow and calculate the flow field around the drill bit to evaluate the RC efficiency. Six key geometric parameters were proven to have a direct influence on the RC performance, including the diameter of suction nozzles Dn, the length of nozzles L, the quantity of nozzles N, the diameter of the pilot hole Dg, the inclination angle of nozzles θs, and the deflection angle of nozzles θd. The CFD simulation experiments were implemented according to the orthogonal array L18(37) and were analyzed using the range, variance, and regression analysis. A mathematical model was developed for the RC efficiency to understand the effect of the factors. The results show that the diameter of suction nozzles Dn has an essential effect on the RC performance of the drill bit. An ideal combination is Dn = 20 mm, L = 50 mm, N = 3, Dg = 50 mm, and θs = 35°, θd = 10°, which was obtained through variance analysis and validated via CFD simulation for higher efficiency. To verify its real performance, a large-diameter RC drill bit with a diameter of 1.2 m was manufactured and tested in the field. The result demonstrated that the drill bit had excellent cutting transport and reverse circulation performance.

SU JET POMPALARININ PERFORMANSI VE KATI-SIVI KARIŞIM TAŞIMACILIĞINDA UYGULANMASI

This present work is focused firstly on an experimental investigation for the optimum design of water jet pumps to be used in the hydrotransport of solid particles through pipeline systems. Experiments were conducted in a closed test loop using five types of jet pumps with various dimensions of the driving nozzle, suction nozzle, mixing chamber, and diffuser employing water as driving and suction fluid. The efficiency of each water jet pump element was analyzed and interpretations of results related to each water jet pump were made about the parts to be considered in the optimum design of a water jet pump. From the experimental results, the water jet pump having the optimum mixing chamber, suction nozzle, driving nozzle location, and cross-sectional dimensions produced a maximum efficiency of about 33%. In the second part of the study, the solid particle carrying capacity of water jet pumps in a pipeline system was studied under saltation, moving bed, and heterogeneous flow regimes by introducing seven different types of solid particles having various concentrations into the closed test loop. The effect of jet pumps on separating solid particles from flow in a region was investigated. A curved form of a by-pass system called the ‘flow division unit’ was added to the main pipeline system and through the flow division unit, then most of the solid particles in the flow were forced to flow towards the suction pipe of the jet pump. As a result of this, only water with very small particle concentrations passed through the centrifugal pumps, and in this way, the wear risk of the centrifugal pump was reduced considerably.

Simulation on a new reverse circulation fishing tool: Design and evaluation of the salvage capacity and efficiency

AbstractTo solve the insufficient energy for reverse circulation fishing tools in complex structure wells, it is necessary to further optimize the design of the tools to improve the impurity salvage efficiency. In this work, a three‐dimensional (3D) flow field simulation model of reverse circulation fishing tool with venturi negative pressure is employed to identify the vortex zone of circulation channel and to investigate the negative pressure and jet velocity distribution around the spray nozzle based on the ANSYS‐CFX. The effects of the spray angle, diameter of the suction nozzle, and the nonstructural parameters on negative pressure and jet velocity are investigated through sensitivity analysis. As revealed from the results, there may be an optimum value for the spray angle, and the nozzle jet direction can indeed affect the propagation and attenuation of the bottom hole flow field greatly. The combination of the inner diameter of the nozzle outlet and that of the nozzle inlet (Φ + Φ′ = 3 mm + 6 mm) is the best design solution when the negative pressure at the nozzle outlet can be the highest. The negative pressure and jet velocity increase with the increasement of the inlet flow rate. The comparative analysis of different bottom hole impurity mass in the cases of the borehole inner diameter 5′ and 8.5″ on the salvage efficiency are conducted numerically. It is observed that the impurity mass salvaged and salvage time are not directly related to its total amount, but only related to the flow rate of the sucked fluid flow. The impurity salvage efficiency can be as high as 95.4%, which meets the engineering requirements in the field. This work improves the working performance of the reverse circulation fishing tool and provides theoretical guidance for well washing.

One-dimensional mathematical modeling of two-phase ejectors: Extension to mixtures and mapping of the local exergy destruction

The ejector is a process equipment frequently used in refrigeration processes. There is currently a knowledge gap on the efficiency of ejectors operating with mixtures. To address this knowledge gap, we present a one-dimensional ejector model for mixtures, defined by spatially distributed mass-, energy- and momentum-balances for different zones, which together constitute the full ejector geometry. The recently developed delayed homogeneous relaxation model is used to describe the two-phase transition in the motive and suction nozzles. For evaporation of pure CO 2 in the throat of the motive nozzle, the model yields an average error of 2.6% in the critical mass flow rate, which is significantly lower than the homogeneous equilibrium model that has an average error of 8.4%. A comparison to new experimental data shows that both models give excellent predictions of critical mass flow rates where condensation occurs in the throat, with an average error below 0.9%. New experimental data with CO 2 are presented, which are used to regress two parameters in correlations that describe the momentum transfer between the primary and secondary stream in the mixer and diffuser sections. This leads to accurate reproduction of the pressure lift in five different ejector geometries, with a mean error of 2.3%. By using nonequilibrium thermodynamics, we derive formulae for the local exergy destruction in the ejector. The largest exergy destruction is located in the mixer, and originates in transfer of momentum between the primary and secondary streams. The local exergy destruction profiles through the mixer and diffuser are highly non-uniform, and deviate from the established guidelines for energy-efficient design characterized by equipartition of exergy destruction. This reveals a potential to increase the performance of ejectors by suitable adjustments to their geometric design. The mathematical model validated for pure CO 2 is assumed to also be valid for mixtures rich in CO 2 . We show that minute concentrations of a second component can have a significant influence on the ejector performance. When fixing the inlet conditions and ejector geometry, we demonstrate that adding 2% H 2 to a mixture of CO 2 decreases the critical mass flow rate by 20%, while adding 2% SO 2 increases the pressure lift by 1 bar. • A state-of-the-art, one-dimensional ejector model for mixtures is presented. • New experimental data for ejector operation with CO2 improves the model. • Critical mass flow rates and pressure lifts from experiments reproduced within 3%. • Local mapping of exergy destruction with nonequilibrium thermodynamics. • Minute concentrations of a second component alter the ejector performance.

АНАЛИЗ ВОЗМОЖНОСТЕЙ ФИЛЬТРУЮЩЕГО РЫБОЗАЩИТНОГО УСТРОЙСТВА ПРИ ГОРИЗОНТАЛЬНОМ РАЗМЕЩЕНИИ КАССЕТ

Problem statement. In accordance with the code of rules (SP 101.13330.2012), the use of fish protection devices with a filter screen and a flushing system applies to water intake facilities in various placement conditions, in this regard, it is relevant to expand the possibilities of using filter cassettes at shallow water depths in the water source.
 Results. A methodology has been developed to substantiate the filler parameters of a horizontal filter cassette in the form of plastic balls and their distribution along its length, as well as a preliminary assessment of the uniformity of flow rates over the area of the filter cassette.
 Conclusions. To improve the operational characteristics of the filter fish-protective device in conditions of shallow water sampling depths, instead of the basic design with a vertical cassette layout, a filter cassette with a horizontally positioned water intake surface and a self-washing effect is recommended, in which a filler made of plastic balls (with positive buoyancy) is used and there is free space for their vertical movement. On the basis of hydraulic calculation, a method for preliminary estimation of filtration rates in such a cassette has been developed. To ensure a uniform distribution of the filtration rates of the water flow along the length of the cassette, it is recommended to use balls of different diameters. Evaluation of the working conditions of the cassette allowed us to obtain a pattern of changes in the diameter of the balls along its length, so for a specific example, the calculated diameter of the balls varied from 8 mm, in the suction nozzle, to 40 mm at the end of the cassette. The technique can be used to calculate the parameters of horizontal filter cassettes of fish protection devices.

Design and Optimization of a Machine-Vision-Based Complementary Seeding Device for Tray-Type Green Onion Seedling Machines

Green onion (Allium fistulosum L.) is mainly available as factory-produced seedlings. Although factory seedling production is highly automated, miss-seeding during the seeding process considerably affects subsequent transplanting and the final yield. To solve the problem of miss-seeding, the current main method is manual complementary seeding, which is labor-intensive and inefficient work. In this study, an automatic machine-vision-based complementary seeding device was proposed to reduce the miss-seeding rate and as a replacement of manual complementary seeding. The device performs several main functions, including the identification of miss-seeding holes, control of seed case movement, and the seed uptake and release from the seed suction nozzle array. A majority-mechanism-based miss-seeding tray hole rapid-detection method was proposed to enable the real-time identification of miss-seeding tray holes in the tray under high-speed moving conditions. The structural parameters of the vacuum-generated seed suction nozzle were optimized through numerical simulations and orthogonal experiments, and the seed suction nozzle array and seed case were produced using 3D-printing technology. Finally, the complementary seeding device was installed on the tray-type green onion seeding machine and the effectiveness of the complementary seeding was confirmed by experiments. The results revealed that the average values of the precision, recall, and F1 scores for identifying miss-seeding tray holes were 98.48%, 97.00%, and 97.73%, respectively. The results revealed that the rate of miss-seeding tray holes decreased from 5.37% to 0.89% after complementary seeding.

Airflow basin structure numerical optimization analysis and suction nozzle characteristics experimental study of vacuum-vibration tray precision seeder

The stable and uniformly distributed airflow field can effectively improve the seed suction effect and seed-carrying stability of the pneumatic seeder. With this end in view, this paper was optimized the airflow basin structure of vacuum-vibration tray precision seeder based on the computational fluid dynamics (CFD) simulation technology. The results show that the airflow field is relatively stable and well-distributed when the chamber height is 50 mm and the outlet tube diameter is 65 mm. In addition, the thickness of the base plate with suction holes should be less than 5 mm, and the needle suction nozzle guide should be greater than 15 mm according to the numerical analysis results. On the basis of the above study, the seeding characteristics of the needle type suction nozzle and the plate type suction nozzle were further explored to determine the type of nozzle more suitable for rectangular sucker. Through various experimental designs, the significant influencing factors of the two suction nozzles and their appropriate working ranges as well as the optimal combination of working parameters were determined in turn. The needle suction nozzle requires lower suction height and less grains dispersion according to the experimental results, while the plate suction nozzle is just the opposite, it allows a certain suction height to be maintained with the seeds, and requires high dispersion of grain. In general, the plate suction nozzle can obtain better seeding performance, is a more favorable nozzle for the vacuum-vibration tray precision seeder.

Aerodynamics of two-phase gas-solid flow in a flat suction nozzle during vacuum pneumatic transport

The paper reports the results of research on the effect of the design of a suction nozzle with a rectangular section under horizontal and vertical pneumatic conveying conditions in a pipe with a diameter of D = 30 mm. Five unmanned truncated pyramid-shaped suction nozzles were tested, which differed in height and cone opening angle 25°-120° while maintaining a constant ratio of the inlet to the outlet surface area of 8.5. The working media in the research were air and ten types of bulk materials commonly used in the industry with a variable equivalent particle diameter of ds = 0.2–2.4 mm and the specific density ρs = 495–6730 kg/m3. The materials used in the research were characteristic of bulk materials of type A, B and D defined according to Geldart's classification. The study was carried out at the superficial velocities of air ug = 2.8–46 m/s and solids us = 0.002–2 m/s. This ensured obtaining the mass concentration of the solid in relation to the mass flow of air in the range of μs = 0.6–290. As a result of the analysis of experimental data obtained by means of a high-speed camera and a computer system for archiving experimental data and image analysis, seven flow structures were identified and described. Also an original two-phase gas-solid flow map was developed. A new method has been proposed to calculate pressure drop ΔP2P during two-phase gas-solid flow for different geometries of rectangular suction nozzles with the accuracy mean relative error MRE = −0.83% and mean absolute error MAE = 29.5%. It is the first model of this type described in the literature.

Substantiation of installation design for pneumatic peat harvester suction nozzle

The efficiency of suction of milling chips by pneumatic peat harvesters is largely governed by the height and angle of installation of the suction nozzle relative to the underlying surface. Since there are very few data and recommendations on this topic, in laboratory conditions, using a specially designed and created installation, a series of experimental work was carried out to identify rational values of the height and angle of the nozzle. The criteria were the most pronounced turbulence of the air flow (to create a lifting force) and the maximum length of the axis of the active zone of the suction plume (for a longer time of exposure of the air flow to the milling chips). The results showed that for the two examined types of peat – high-moor peat with a degree of decomposition of 5–10 % and a transitional degree of decomposition of 35–40 % for the maximum allowable fraction of 25 mm, the angle of installation of the suction nozzle of 30–35° is rational, and the height of the nozzle, equal to the size the maximum permissible conditioned fraction of milling chips, is 25 mm. It was with this arrangement of the nozzle th at the length of the axis of the active zone of the suction plume was maximum, and the air flow was with the most pronounced turbulence. To increase the efficiency of the pneumatic harvester, it is proposed to equip the suction nozzles with mouthpieces. The study proves that the maximum efficiency, according to the criterion of the length of the axis of the active zone of the suction flare, has a nozzle installed at an angle of 30–35°, equipped with a mouthpiece with an activation angle of 50–55°. The comparison of the efficiency of the nozzle without a mouthpiece and with a mouthpiece shows that the proposed mouthpiece is able to more than double the length of the axis of the active zone of the suction plume, and, consequently, to increase the efficiency of the machine.

Effect of turbulence models and cavitation intensity on the motive and suction nozzle mass flow rate prediction during a non-equilibrium expansion process in the CO2 ejector

A variety of ejector constructional concepts can be effectively examined by advanced numerical tools. The development of the modelling techniques of the two-phase meta-stable expansion process in the CO2 ejector motive nozzle provides the detailed flow data of the primary stream. However, the complexity of the entrainment processes in the mixing section still requires attention for the accurate prediction of the suction nozzle flow. Hence, in this paper, an analysis of four turbulence models and cavitation phenomena (four intensity levels) in the CO2 ejector was performed on the basis of the calibrated non-equilibrium expansion model of the ejector motive nozzle. Twenty-three motive nozzle points from the subcritical range (from 50 bar to 70 bar and 8 °C to 23 °C) were coupled with the evaporation temperature of -6 °C and two pressure lift levels (3 bar and 6 bar). Simulations of 460 cases were validated using data from the CO2 ejector refrigeration unit with a 50-kW cooling capacity. The vapour quality distribution in the motive nozzle with cavitating evaporation was described in terms of the primary pressures and the considered turbulence models. An influence of the turbulence formulation on the secondary stream behaviour in the mixing zone was also investigated regarding the suction nozzle mass flow rate. Finally, the proposed model of the CO2 ejector was characterised by the mass flow rate prediction discrepancy at an average level of 4.6% and 12.3% for the motive and suction nozzle, respectively.

Heavy metals in private car dusts collected from Universiti Malaysia Pahang, Gambang Campus: Contamination and human health risks

A pilot study was conducted to investigate the concentrations of seven heavy metals (Zn, Cu, Cr, Cd, Fe, Ni and Pb) in private car dusts collected from Universiti Malaysia Pahang (UMP), Gambang campus. Ten private cars were selected among UMP staffs and students, and the dust samples were obtained by using a conventional vacuum cleaner with a clean nylon sampling sock pre-inserted into the suction nozzle. All samples were acid-digested with aqua regia solution and analysed for metal concentration using Atomic Absorption Spectrometry (AAS). The highest mean concentrations were recorded for Fe (650± 480 mg/kg), followed by Zn (160 ± 110 mg/kg), Cu (76.2 ± 18.5 mg/kg), Pb (39.2 ± 99.1 mg/kg), Ni (6.39 ± 8.30 mg/kg), Cr (3.42 ± 5.90 mg/kg) and Cd (0.55 ± 1.40 mg/kg). Hazard quotient (HQ) and hazard index (HI) values lower than 1 indicated no potential non-carcinogenic risks to the adult drivers.