نشریه مهندسی مکانیک تبدیل انرژی
سال دهم شماره 4 (پیاپی 38، زمستان 1402)

Impingement jet is a fluid flow that hits a surface perpendicularly or at a specific angle for the purpose of cooling or heating. The rate of transfer processes in turbulent impingement flows is affected by the formation of coherent structures, the interaction between them and transfer of It's energy.By oscillating the incoming flow in the impinging jets, the formation of coherent structures can be affected, and as a result, the amount of heat removal is affected. In this study, the effect of pulsed impinging jet using step and sinusoidal functions The flow and temperature field of a dimpled surface has been investigated by numerical method. The key parameters in this study include the shape of the input function, the frequency and the amplitude of the oscillating jet. The results of this study have been validated using previous researches and then The effect of key parameters on the  formation of coherent structures and the amount of heat extraction have been discussed and analyzed. The results show that bypulsating the inlet flow, it is possible to change the recirculation zones and the vorticity field in the flow and overally The heat increases on the dimpled surface. Such results show that the flow patterns and Nusselt number are highly dependent on the parameters of the input function such as frequency and amplitude.

The increase in air pollution and the production of greenhouse gases and the reduction of fossil fuel sources and the increase in costs and the need to reduce energy consumption, cause the use of new materials and insulation and the invention of new methods and specific implementation details (double-layer facades and curtains, etc.) in different sectors. The building has become a facade of buildings. Most of these technologies and innovations and insulating materials are used in the facade of buildings. Investigations showed that many of these materials and innovations have the potential of igniting and spreading fire and releasing smoke and toxic gases, such that a significant part of the many human and financial damages that are caused to people and buildings in fires on a daily basis are affected by These are the materials, innovations, and implementation technologies. The current research intends to reduce the knowledge gap and the lack of theoretical and experimental studies in this field, and to reduce the weakness of life and financial damages with the help of architectural principles and components, solutions to control and limit fire and the emission of smoke and toxic gases and protect people. and provide property. The research method has been exploratory up to the stage of building the tool in order to extract the factors affecting the vulnerability of the facade of the building in fire. The research method was a combination of quantitative and qualitative methods. Part of the research has also been done with the Delphi method. The statistical population in the Delphi department was engineers of the engineering system organization from all over the country. The results have been analyzed with the help of the R factor, and the most effective factors on reducing fire damage in the facade of the building have been extracted. According to the results of the research, the most important factors influencing the reduction of vulnerability are: materials, accessibility (rescue and extinguishing), suitable and blocked facades against the spread of fire, evacuation and reduction of casualties, suitable geometrical structure and form to prevent the spread of fire, arena Suitable body with no fire propagation, isolated, blocked and non-propagating in fire, location and proper location of the building.

In this research, the hydrodynamic effects of the flow around a submerged rectangular surface near the bed and the free surface of water has been investigated. This analysis was done using FLUENT and the multiphase method of volume of fluid (VOF) and the standard k-ɛ model was used to simulate turbulence. After checking the mesh and computational space independency, first the effects of changing the depth of the geometry immersed in water from the free surface and also changing the velocity of the fluid flow on the waveform of the free surface and hydrodynamic coefficients were investigated and then the effects of close This geometry has been evaluated on the floor. The results of the present research show that as the submerged rectangular plate moves away from the free surface (increasing the depth) at a specific water velocity, the drag coefficient and negative effect increase, and on the contrary, with the increase of the fluid velocity at a specific depth from the surface, the performance The hydrodynamics of the system increases. Also, as the geometry approaches the water bed (floor), the hydrodynamic performance is improved, while there is no significant change in the drag coefficient. In addition, at a certain depth from the floor, the hydrodynamic performance increases significantly with the increase in fluid velocity.

In this paper, using computational fluid dynamics, the air flow pattern and temperature distribution for a high-density data center is presented. The Air-pack software is employed to evaluate the performance of the cooling system within the data center. A high-density data center with a total power density of 227.2 kW is considered. The arrangement considered for the data center is a cold/hot aisle layout and also two computer room air conditioning (CRAC) units are employed to produce cold air flow. A three-dimensional analysis of cold/hot air flow within the data center is provided and high temperature and hot air re-circulation areas are predicted. The results of this research show that in the entrance of the higher thermal density rack servers, there are areas with a temperature of 32.7℃ , which exceeds the permissible limit determined by the ASHRAE standard. But the temperature distribution of lower thermal density rack servers is completely consistent with the ASHRAE temperature range. Also, the hot exhaust air is recirculating into cold aisles and mixing with the supplied cold air.  This model could be used to evaluate the air flow and thermal mapping in order to design a new data centers or to optimize existing data centers in terms of reducing the problems in data center cooling, including hot air return and cold air bypass.

Cryogenic rocket technology is of great importance in space science. The use of this technology has improved the design of rockets that make space exploration easier. In addition, the development of this technology has increased the success of complex space missions. Cryogenic technology is a process that uses propellants at cryogenic temperatures in rockets. Cryogenic temperature is set from - 150 degrees Celsius to absolute zero. In this research, the cryogenic rocket engine has been investigated. The cryogenic rocket engine is a type of rocket engine that uses cryogenic fuel and oxidizer, that is, both the fuel and the oxidizer are gases that are liquefied and stored at a very low temperature. In other words, they are kept cold to stay liquid. Liquid propellants play a significant role in the development of this technology. According to the investigations, this technology does not produce any harmful products and does not cause pollution to the environment. Also, cryogenic propellants in the liquid rocket engine have a very high specific impact, which are suitable for use in the upper stage of the rocket and booster stages. From analyzing the results, it is understood that the cryogenic rocket engine with LH2/LOX propellant combination is very suitable for the design of the upper stage of the rocket.