Outlet Of Cavity Research Articles

Analysis of Entropy Generation and Potential Inhibition in an Aeroengine System Environment

From a system perspective, the entropy generation of an aeroengine is directly related to the thermal efficiency when the Brayton cycle pressure ratio and maximum temperature remain constant. The lower the entropy generation of the engine is, the higher the thermal efficiency. However, the secondary air system of the engine generates a large quantity of entropy compared to the components of the main flow channel, because the irreversible losses of the internal flow and heat exchange between the air system components generate considerable entropy within the system. In this study, the theoretical method is used to build entropy generation model for different characteristics of air system components during the aerothermal process. In this basis, an integrated model of the whole engine is introduced to identify the key components for entropy generation in the system environment. The results show that the labyrinth at outlet of unloading cavity is recognized as the one that generates the most entropy in the entire aeroengine system, and the total entropy generation of the system is highly related to this component. Besides, in the system environment, entropy generation is the sum of the local entropy generated by the components and the total entropy generated by mixing of airflows in each component. High local entropy generated by components does not necessarily result in a high system entropy production, and vice versa. Therefore, when the minimum system entropy generation is the design goal, the most critical operations for entropy generation should be identified according to the corresponding sensitivity and parameter variation range, and the design should be improved accordingly.

Modelling of thermal energy individualities in novel enclosure with uniformly heated circular obstacle and multi-shaped heated ribs

The thermal flow field of Newtonian fluid in novel cavity is investigated numerically. The three different shaped heated ribs namely triangular, rectangular and circular are installed case-wise at lower wall of cavity. The uniformly heated circular cylinder is taken fixed in center of cavity for each case. The no-slip condition is imposed on both the top wall and exterior surface obstacle. The fluid enters from the inlet of a cavity with a specific velocity profile. At outlet, a Neumann condition is taken. The upper wall, inlet and outlet of cavity are taken cold. Thermal flow field individualities are explored by using the energy, momentum and continuity equations. The finite element approach is used to solve these equations. The contour plots, line graphs and tabular data are used to report the ultimate observations on velocity, pressure, temperature and hydrodynamic forces. Particularly, the lift and drag coefficient values are obtained via line integration. The variations pattern in Nusselt for triangular, rectangular and circular ribs at lower wall are shared. It is noticed that the coefficients values towards heated obstacle are higher in magnitude for the case of heated rectangular rib as compared to heated triangular and circular ribs.

Impact of rotation of wheels and bogie cavity shapes on snow accumulating on the bogies of high-speed trains

The snow accumulation on the bogies of a high-speed train was studied using the unsteady Reynolds-Averaged Navier-Stokes simulations (URANS) coupled with the Discrete Phase Model (DPM). The effects of the rotation of wheels, shape of bogie fairings and length of bogie cavities on the flow characteristics and snow accumulation around bogie regions are discussed. The results show that the rotation of wheels significantly affects the flow characteristic and snow distribution around rear plates and the snow accumulation on the top surface of bogies. The shape of bogie fairings has been found to have large influence on the velocity profiles at the inlet and the outlet of bogie cavity, and thereby on the snow accumulation. The bogies without fairing have been found to be less influenced by the snow in the flows without crosswinds. The length of the bogie's cavity was found to have dominant role on the distribution of particle concentration and snow accumulation on the bogie surface. The total mass of snow accumulation on the bogie surface was shown to decrease with the shorter bogie cavity. Finally, the shorter bogie cavity is recommended for the design of the high-speed trains running under the circumstances permitted by the vehicle gauge.

Surgical treatment of sciatic nerve entrapment syndrome in the outlet of pelvic cavity

Objective To investigate the etiology and clinical diagnostic criteria of sciatic nerve entrapment syndrome in the outlet of pelvic cavity, and establish the indications and methods for surgical treatment. Methods From July 2013 to September 2016, 14 cases of sciatic nerve entrapment syndrome in the outlet of pelvic cavity were analyzed. There were 6 cases of pain and sensory disturbance, 8 cases of combined movement disorder, 14 cases being positive results in limb elevation test, 7 cases being positive results in piriformis muscle tension test. The MRI examination of the pelvic outlet of the sciatic nerve in the unilateral lower extremities was performed in 11 cases, and the positive results were 10 cases, all of which were confirmed by intraoperative surgery. All the 14 cases underwent surgical treatment. Intraoperative exploration confirmed that there were 4 cases of simple piriformis hypertrophy entrapment, 3 cases of muscle hypertrophy combined with nameless band compression, 3 cases of abnormal sciatic nerve branches, 3 cases of transverse action vein compression, 1 case of sacroiliac joint osteophyte hyperplasia, 1 case of piriformis absence combined with gluteal maximus degeneration. All of them were relieved and the piriformis and obturator muscles were cut off. 10 cases were treated with neurolysis. Results The postoperative follow-up ranged from 6 to 48 months with an average of 16 months. There were 7 cases whose symptoms were completely disappeared and being competent for the original job, 6 cases whose symptoms were obviously improved and 1 case whose symptom was partially relieved. Conclusion The sciatic nerve entrapment syndrome in the outlet of pelvic cavity is a common syndrome of lower limb extremity neuralgia with variable etiology. Preoperative sciatic nerve pelvic outlet MRI examination and preoperative diagnostic closure should be the main diagnostic criteria. Attention should be paid to the double compression of the high nerve root and sciatic nerve. Surgical release is the most direct and effective method for treatment. Key words: Sciatic nerve; Piriformis muscle syndrome; Diagnosis

An empirical model to predict the performance of typical solar chimneys considering both room and cavity configurations

The solar chimney is a reliable passive ventilation system that can largely reduce the energy requirements with both low costs and maintenance for buildings to overcome the current energy crisis. To optimize its design, an empirical model is developed to predict the performance of typical solar chimneys considering both room and chimney cavity configurations using easily acquired inputs. Fire Dynamics Simulator (FDS) as an excellent and open-source tool to solve heating, ventilation and air conditioning problems is selected for this study. The numerical modelling of FDS was first validated by previous experimental data, and then used to develop the empirical model. In this model, a coefficient describing room and chimney configuration (e.g., room opening, inlet and outlet of cavity) is proposed. It is shown that room size (length, width and height) and opening location have limited influence on performance. Also the radiation from hot walls can be ignored when compared to convection heat transfer between the hot walls and the air inside the cavity. This study provides key knowledge to optimize the design of solar chimneys in energy saving for buildings.