Development of a Prototype Plant for the Heat Treatment of Workpieces with Preferably Bainitic Properties

In vehicle construction, components with high tensile strengths are used, especially in the chassis area. At the same time, these components must have high toughness and be insensitive to cracking. For this purpose, hardened and tempered but also salt-bainitized components are used. The associated usual process chain after steel production consists of forming processes with subsequent cooling of the forging blanks and subsequent heat treatment with renewed heating to set the required material properties. From an energy point of view, heat treatment from the forging heat is desirable, which in addition to shortening the process chain is also associated with a reduction in CO2 emissions. A prototype system for controlled bainitization has been developed, which implements the heat treatment immediately after hot forming by utilizing the still existing forming temperature. Here, a controlled spray field generates both a quenching and an isothermal holding phase. Various sensors generate input variables to cool the workpieces in a controlled manner. This paper gives an overview of the system technology, realized cooling curves and the resulting hardness.

Powder Impact Temperature Influence on Metallurgical Bonding—An Investigation for Soft Particle Deposition on Hard Substrate

Segregating the convoluted effects of particle size; impact temperature and velocity on deposition behavior and adhesion is of utmost interest to the cold spray field. The current study aims to associate the particle impact behavior and adhesion to its in-flight characteristics by studying and decoupling the influence of particle size; temperature and velocity for single particle impacts and full coatings. Experimental results reveal that in-situ peening processes contribute to the adhesion at low impact temperature while η (V.VC) controls the adhesion/cohesion at increased particle impact temperatures. The benefits of both bonding mechanisms are discussed in terms of measured adhesion/cohesion; bend-to-break fracture surfaces; pseudoplasticity; deposition efficiency and critical velocity. Computational fluid dynamics (CFD) results provide individual particle trajectory; size; temperature and velocity; of successfully deposited particles; which have led to the observed signs of metallurgical bonding.

The Motion of Strawberry Leaves in an Air-Assisted Spray Field and its Influence on Droplet Deposition

HighlightsA visualization method for the motion of strawberry leaves in an air-assisted spray field is proposed.Strawberry leaves showed two motion states in different critical velocity ranges of the sprayer airflow.The airflow instability and the turbulence effect are considered important factors for the leaf vibrations.A strawberry leaf azimuth angle in the range of 90° to 270° can provide good deposition with smaller droplets.Abstract. The reasonable motion of crop plants in an air-assisted spray field can improve droplet deposition. Therefore, this study focuses on the motion of strawberry leaves and the droplet deposition mechanism in an air-assisted spray field. First, this study proposes a descriptive method for strawberry leaf motion in an air-assisted spray field and clarifies the important influence of strawberry leaf motion on droplet deposition. Second, an experiment was performed on the motion and droplet capture of single strawberry leaves in multi-position postures in an air-assisted spray field. The results showed that the leaves had two motion states (i.e., low amplitude with low frequency and high amplitude with high frequency) at different airflow velocities and inclination angles, and the critical airflow velocity corresponding to the two motion states was determined to be 8.7 m s-1. When the azimuth angle of the strawberry leaves is in the range of 90° to 270°, a reasonable inclination angle of the airflow and the high frequency and high amplitude vibration state of the leaves driven by the airflow will provide good deposition and canopy penetration of droplets with smaller diameters. Keywords: Air-assisted spray field, Droplet deposition, Motion, Spray, Strawberry leaves.

Spray Structure and Characteristics of a Pressure-Swirl Dust Suppression Nozzle Using a Phase Doppler Particle Analyze

In order to understand the characteristics of the spray field of a dust suppression nozzle and provide a reference for dust nozzle selection according to dust characteristics, a three-dimensional phase Doppler particle analyzer (PDPA) spray measurement system is used to analyze the droplet size and velocity characteristics in a spray field, particularly the joint particle size–velocity distribution. According to the results, after the ejection of the jet from the nozzle, the droplets initially maintained some velocity; however, the distribution of particles with different sizes was not uniform. As the spray distance increased, the droplet velocity decreased significantly, and the particle size distribution changed very little. As the distance increased further, the large droplets separated into smaller droplets, and their velocity decreased rapidly. The distributions of the particle size and velocity of the droplets then became stable. Based on the particle size-velocity distribution characteristics, the spray structure of pressure-swirl nozzles can be divided into five regions, i.e., the mixing, expansion, stabilization, decay, and rarefied regions. The expansion, stabilization, and decay regions are the effective dust fall areas. In addition, the droplet size in the stabilization region is the most uniform, indicating that this region is the best dust fall region. The conclusions can provide abundant calibration data for spray dust fall nozzles.

Numerical Study of the Effects of Injection Fluctuations on Liquid Nitrogen Spray Cooling

Spray cooling with liquid nitrogen is increasingly utilized as an efficient approach to achieve cryogenic cooling. Effects of injection mass flow rate fluctuations on the evaporation, temperature distribution, and droplet distribution of a spray field were examined by employing a validated Computational Fluid Dynamics (CFD) numerical model. The numerical results indicated that injection fluctuations enhanced the volume-averaging turbulent kinetic energy and promoted the evaporation of the whole spray field. The strengthened mass and heat transfer between the liquid nitrogen droplets and the surrounding vapor created by the fluctuating injection led to a lower temperature of the whole volume. A relatively smaller droplet size and a more inhomogeneous droplet distribution were obtained under the unsteady inlet. The changes of the frequency and the amplitude of the fluctuations had little effects on the overall spray development. The results could enrich the knowledge of the relation between the inevitable fluctuations and the overall spray development and the cooling performance in a practical spray cooling system with cryogenic fluids.

Analysis of internal flow and outlet velocity characteristics associated with dust suppression nozzles and their impact on spray field

In order to understand the relationship between nozzle structure and spray field, the present paper conducts velocity-based parametric study on two types of dust suppression nozzles, focusing on the link among nozzle structure, velocity distribution, and the resulting spray field. The simulation investigation indicates that the increase of flow velocity mainly occurs in the convergence section and the outlet region of a nozzle, with its magnitude dictated by the convergence angle, ratio of inlet to outlet diameter, and the length–diameter ratio of the outlet. Based on the velocity distribution characteristic of axis direction and radial direction near different nozzles’ outlet, one can predict that fluid density is higher in the central axis region and lower in the boundary region in spray field with cylindrical outlet, which can form a “solid cone” shape and stable spray. In the case where the nozzle outlet has “dash” type, one can find that the spray field, which associated with this type of nozzle, is a fan-shaped, with the fluid density fluctuating up and down. The above hypothesis has been corroborated by the spray experiments which have been conducted here. The simulation results concerning the internal flow field in dust suppression nozzles can provide guidance over the nozzle design and the parametric optimization and are of great significance to enhance the atomization quality of spray field.

Experimental Study on Spray Pattern of Pressure-Swirl Nozzle in Reactor Containment

Spraying system plays an important role in the safety of PWR. To ensure homogeneous spraying of the containment, the layout of nozzles on the spray header was taken into consideration in design. In this paper, an experimental study was conducted to obtain spray characteristics data, including spray cone angle and 2-D spray flux distribution for the purpose of achieving optimal design of the spraying system. According to the specialty of the spray field involved, a testing loop with four pressure-swirl nozzles was established for the study. Spray cone angles were obtained by photograph method. The volume flux distribution was measured by collecting the spray droplet along the cross-section diameters. Based on the experimental data, typical spray flux distributions were obtained. The flux distribution results were used to build 3-D coverage models. Then these models were used to calculate the overall spray coverage in the containment. The present work introduces the experimental study of spray behavior of a typical pressure-swirl nozzle in containment and the method to evaluate spray coverage through building 3-D spray flux distribution models. The work is expected to be helpful for the optimization design of spraying systems.