Modelling of the Fine-Grained Materials Briquetting Process in a Roller Press with the Discrete Element Method

Problems of operation of positive pressure ventilators on the basis of surveys of Polish officers of the State Fire Service

Positive pressure ventilators (PPV) used by 97.7% of officers of the National Fire Service in Poland, are characterized by work that is not in line with the expectations of the firefighters. In order to improve the technical and operational features of these devices, a survey was conducted among 25,000 eligible firefighters, identifying the application of these devices, problems in use and expected development directions. A total of 682 officers voluntarily completed the survey. Based on their findings, it was determined that ventilators are most often used to smoke out buildings after or during a fire. Mentioned problems when using these devices were mainly noise (78.2%), exhaust emissions (68.5%), and impediments to mobility through the device's relatively heavy weight (40.2%). Other inconveniences were mentioned by less than 20% of firefighters. Polish firefighters expect the development of these devices mainly in terms of the above-mentioned features (noise reduction (81.7%) and reduction of the weight and size of the ventilators (about 50%)). Other expectations relate to the improvement of smoke removal in buildings: increasing the efficiency of smoke removal (46.4%) and efficiency regarding the rate of smoke removal in a building by increasing the size of the incoming airflow from the building's surroundings (33.2%). About 15% of firefighters expect changes in the operation of the ventilator itself, that is, an increase in the effective operating time (electric ventilators) and an increase in the device's uptime. The aim of the article is to identify the issues encountered during the operation and to indicate the expected direction of development for PPV by users. This information can be used by engineers to initiate new development work on these devices.

Modeling of the Efficiency of the Centrifugal Conical Disk Dispenser of Bulk Materials

Centrifugal disk dispensers are widely used in various tasks of dosing bulk, dispersed materials. The design of the disk depends on the physical and mechanical characteristics of the dosing medium. The work discusses the development of an analytical model of the movement of a material particle along a conical centrifugal disk depending on the kinematic characteristics of the dosing process and the characteristics of the dosing material, as well as experimental confirmation of the theoretical model, which is relevant for the calculation and design of working elements of this type. The obtained system of differential equations is solved using the Runge-Kutta numerical method. Experimental studies were carried out using the method of a planned factorial experiment. The experiment was conducted for three factors at three levels. The feedback criterion was the performance of a centrifugal conical disk dispenser for bulk materials. The disk cone angle was set at 10, 20, and 30°. The disk diameter was 130, 150, and 170 mm, the gap between the disk and the edge of the hopper neck was 6, 8, and 10 mm, and the rotational speed of the conical disk was 0.65, 1.02, and 1.39 rad/s. The dispensing rate of the dispenser ranged from 15 to 770 g/s, depending on the values of the experimental factors. For use in the regression equation of the natural values of the factors, a method of transforming the terms of the equation from coded values to natural ones is provided. The obtained experimental correlation dependencies were checked for reproducibility with Cochrane's test, and the adequacy of the model was checked using Fisher's test. The significance of the coefficients in the correlation equation was evaluated using the Student's t-test. The difference between the experimental data and the results of the theoretical modeling does not exceed 5%. The obtained system of differential equations makes it possible to model the radial velocity of the ascent of bulk material from the conical rotating disk depending on the rotation frequency, disk diameter, and the height of the annular gap between the discharge throat of the hopper and the conical disk. The analytical model enables the modeling of the productivity of the conical dispenser for bulk materials for arbitrary parameters of rotation frequency, disk diameter, and the size of the annular gap between the discharge throat of the hopper and the conical disk.

Experimental Study on the Cutting Process of Single Triticale Straws

This paper presents experimental research on cutting a single stalk of triticale straw for the production of biofuel in the process of its compaction using the piston technique. In the first stage of the experimental study of cutting single triticale straws, the variable parameters were the moisture contents of the stem equal to 10% and 40%, the offset between the blade and the counter-blade g, and the linear velocity of the knife blade V. The blade angle and rake angle were equal to α = 0° and β = 0°. In the second stage, the variables, including the blade angle values α = 0°, 15°, 30°, and 45° and the rake angle values β = 5°, 15°, and 30°, were introduced. Taking into account the analysis of the distribution of forces on the knife edge leading to the determination of the force quotients F_c″/F_c and F_w/F_c, and on the basis of the optimization performed and the adopted optimization criteria, the optimal knife edge angle α can be determined (at values g = 0.1 mm and V = 8 mm/s) at α ≅ 0° and the angle of attack β within the range of 5-26°. What the value will be in this range depends on the value of the weight adopted in the optimization. The choice of their values may be decided by the constructor of the cutting device.

Moisture-Dependent Physical-Mechanical Properties of Maize, Rice, and Soybeans as Related to Handling and Processing

Knowledge of physical and mechanical properties of cereal grains is important for designing handling and processing equipment. However, there is still a lack of knowledge on the influence of moisture content on the physical-mechanical properties as related to machine design. The aim of this study was to investigate and describe the changes in select physical-mechanical properties of maize, rice, and soybeans at various moisture content (10%, 14%, 18%, 22%, 26%; wet basis) and their compression behavior at two loading rates of 1.25 mm/min and 125 mm/min. The measured physical and mechanical properties include size, shape, and breakage force of single kernels. It was found that an increase in moisture content increased the kernel size, altered the kernel shape, and decreased the bulk density. The effects of moisture content and loading rate on breakage force, stress, and energy varied depending on the grain type. Our results indicated that an increase in moisture content changed the mechanical behavior of grain kernels from brittle to viscoelastic. To prevent kernel damage during processing and handling, the measured force and stress during compression can be used as the limit value for designing equipment.