Creation of a computer model of the deflector operation

The stages of the problem solution using computational hydrodynamics are the following:

1. Creating a geometric model.

2. Creation of a mathematical model and description of boundary conditions.

3. Obtaining the results.

In our research we used the Autodesk software, namely, for a geometric model, Autodesk Inventor and Autodesk CAD as a computational hydrodynamics package were used. These programs have a simple user interface, which allows starting work without delving into the processes of their functioning.

Computations were made for different wind speeds. The air temperature, both internal and external, was excluded from the calculation to assess the deflector's efficiency influenced only by the wind. The k-ε model was chosen as the model of air turbulence.

As a result, an exact geometric copy of the existing deflector was created. All fasteners were excluded from the geometric model. The results of the simulation are shown in Figure 2.

Figure 2 Results obtained using the CFD package

Results

To determine the accuracy of the created model, the obtained values were compared with the tabular ones obtained from the wind tunnel experiment. The curves of dependencies are shown in Figure 3. It is clear that the results of mathematical modeling are close to the outcomes of the full-scale experiment. The average difference between the values does not exceed 5%, which makes it possible to apply this calculation method to other more complex types of deflectors without making an expensive full-scale experiment in a wind tunnel. Based on the graphical results, it is possible to evaluate the processes occurring in the deflector and improve its geometric parameters for the achievement of a greater effect.

Figure 3 Comparison of experimental results

Conclusion

1. Simulation using computational hydrodynamics allows reducing the expenses of conducting experiments in a wind tunnel at the initial stage of the development of the deflectors geometric shape.

2. Due to modeling, it is easy to see and understand the design mistakes of the created or existing geometry of deflectors.

Despite the fact that the effect of using deflectors in the natural ventilation system has been proven for a long time, the model range of deflectors is improved every day. The application of computational hydrodynamic techniques is preferable when it is necessary to identify the most efficient models. Based on the data obtained from the calculations, it is possible to speak with confidence about the effectiveness of a particular model in the process of air removal from the room.

Reference list

1. Modeling technique used in building HVAC control systems : A review / Z. Afroz, G. M. Shafiullah, T. Urmee, G. Higgins. – Text : electronic. – DOI 10.1016/j.rser.2017.10.044 // ResearchGate : [site]. – URL: https://www.researchgate.net/publication/321767380_Modeling_techniques_used_in_building_HVAC_control_systems_A_review (date accessed: 01.03.2021).

2. Pichurov, G. HVAC control based on CFD analysis of room airflow / G. Pichurov, P. Stankov, D. Markov. – Text : electronic. – DOI 10.3182/20061002-4-BG-4905.00036 // ResearchGate : [site]. – URL: https://www.researchgate.net/publication/289822903_HVAC_control_based_on_CFD_analysis_of_room_airflow (date accessed: 30.03.2021).

3. Абрамкина, Д. В. Особенности применения систем вентиляции с тепловым побуждением / Д. В. Абрамкина // Вестник Сибирского государственного автомобильно-дорожного университета. 2017. № 6 (58). С. 78–84.

4. Пудикова, С. В. Обзор технологий, обеспечивающих стабильность работы систем естественной вентиляции / С. В. Пудикова // Инновации. Наука. Образование. 2020. № 23. С. 535–540.

 

Anton Yakovlev	Антон Яковлев
Perm National Research Polytechnic University	Пермский Национальный Исследовательский Политехнический Университет
Some problem solution results of gas diffusion in polyethylene	Некоторые проблемные решения, полученные в результате газовой диффузии в полиэтилене
Abstract: The way of accelerating the irradiation polyethylene crosslinking process by preliminary isolation of polyethylene samples in ethylene atmosphere is observed. The problem statement of gas diffusion in polyethylene is given. The time needed to preliminary deoxygenation and the time required for ethylene absorption by polyethylene samples are calculated.	Аннотация: Изучается способ ускорения процесса облучения полиэтиленового скрещивания за счет предварительной изоляции полиэтиленовых проб в атмосфере этилена. Приведена проблемная характеристика газодиффузии в полиэтилене. Рассчитывается время, необходимое для предварительной деоксигенации, и время, необходимое для абсорбции этилена образцами полиэтилена.

       Keywords: crosslinked polyethylene, gas diffusion in polyethylene

Introduction

Products made from crosslinked polyethylene (PEX) are widely used in different areas, namely, in manufacturing heat-shrink tubes and corrosion protection tapes, high-tension and low-tension electricity cable insulation, pipes for water supply and heating, prosthetic devices and implants. The main PEX advantages are improved physical and mechanical properties, increased temperature and chemical resilience, insulation resistance and a shape memory effect [1, 2].

There are three most frequently used ways of making PEX [2]:

1. Irradiation crosslinking method. Beta or gamma radiation causes polymer chains to bond with each other.

2. Peroxide crosslinking method. Organic peroxide is an initiator of polymer chain chemical bonds.

3. Silane-induced crosslinking method. Formation of polymer chain bonds happens by means of organic silanes with a small amount (0.1-0.2%) of peroxide.

The irradiation crosslinking method will be given much attention to in this paper due to the fact that PEX products do not have any chemical contaminants, which makes it possible to use them in such fields as pipe production for drinking water transportation [3], or making prosthetic devices. In addition, the irradiation crosslinking method has some more advantages in comparison with other methods [2]:

1. less power consumption; 

2. less floor space;

3. possibility to control the crosslinking degree by means of adjusting the total radiation dose.

However, the main disadvantage of the crosslinking method is long-time duration of the irradiation process, i.e. the time that is needed to reach a required total dose might equal tens or hundreds of hours. Therefore, technological enhancement of the crosslinking method is required. It is a well-known fact that the polyethylene crosslinking in the atmosphere of hydrocarbon gases significantly increases the speed of crosslinking process [4, 5] since the hydrocarbon gas penetrates into polyethylene and takes part in chemical reactions induced by radiation. Therefore, it is also possible to accelerate crosslinking by placing the samples in hydrocarbon gases before the crosslinking process.

During the irradiation process, polyethylene film rolls are located in the rotating airtight containers. In this case, the rotating axis is parallel to the line along which gamma radiation sources are positioned. The time required for placing the polyethylene film rolls in hydrocarbon gas atmosphere can be determined by mathematical modelling. The purpose of the research given is to calculate the time required for ethylene absorption by polyethylene samples until they reach limit concentration in given conditions.