Gwon Hyun Ko

An Experimental Study on the Effect of Slope on the Critical Velocity in Tunnel Fires

The present article deals with the experimental study to investigate the effects of tunnel slope on the critical velocity in the tunnel fires. The 1/20 reduced-scale model tunnel is adopted on the basis of Froude scaling law. The methanol, acetone, and n-heptane pool fires are used as fire sources with the heat release rate ranging from 1.11 to 1.85 kW, 3.13 to 5.21 kW, and 9.16 to 15.6 kW, respectively. The angle of tunnel slope is varied as five different degrees 0, 2, 4, 6, and 88. A load cell is used to measure the mass loss rate of the burning fuel. The location of smoke layer is determined on the basis of temperature variation measured at the tunnel ceiling by K-type thermocouples. The present experiments observe the effects of the tunnel slope, fire size, and ventilation velocity on the back-layering distance. The results showed that critical velocity increases with tunnel slope due to the stack effect. The correlation between the critical velocity and the angle of tunnel slope was obtained for the pool fires whose heat release rate was varied with the ventilation velocity.The present article deals with the experimental study to investigate the effects of tunnel slope on the critical velocity in the tunnel fires. The 1/20 reduced-scale model tunnel is adopted on the basis of Froude scaling law. The methanol, acetone, and n-heptane pool fires are used as fire sources with the heat release rate ranging from 1.11 to 1.85 kW, 3.13 to 5.21 kW, and 9.16 to 15.6 kW, respectively. The angle of tunnel slope is varied as five different degrees 0, 2, 4, 6, and 8°. A load cell is used to measure the mass loss rate of the burning fuel. The location of smoke layer is determined on the basis of temperature variation measured at the tunnel ceiling by K-type thermocouples. The present experiments observe the effects of the tunnel slope, fire size, and ventilation velocity on the back-layering distance. The results showed that critical velocity increases with tunnel slope due to the stack effect. The correlation between the critical velocity and the angle of tunnel slope was obtained for the pool fires whose heat release rate was varied with the ventilation velocity.

Development and Application of a New Spray Impingement Model Considering Film Formation in a Diesel Engine

The present article presents an extension to the computational model for spray/ wall interaction and liquid film processes that has been dealt with in the earlier studies (Lee and Ryou, 2000a). The extensions incorporate film spread due to impingement forces and dynamic motion induced by film inertia to predict the dynamic characteristics of wall films effectively. The film model includes the impingement pressure of droplets, tangential momentum transfer due to the impinging droplets on the film surface and the gas shear force at the film surface. Validation of the spray/ wall interaction model and the film model was carried out for non-evaporative diesel sprays against several sources of experimental data. The computational model for spray/wall interactions was in good agreement with experimental data for both spray radius and height. The film model in the present work was better than the previous static film model, indicating that the dynamic effects of film motion should be considered for wall films. On the overall the present film model was acceptable for prediction of the film radius and thickness.

A Numerical Study on the Spray-to-Spray Impingement System

The present article aims to perform numerical calculations for inter-spray impingement of two diesel sprays under a high injection pressure and to propose a new hybrid model for droplet collision on the basis of literature findings. The hybrid model is compared with the original 0’ Rourke’s model, which has been widely used for spray calculations. The main difference between the hybrid model and the O’Rourke’s model is mainly in determination of the collision threshold condition, in which the preferred directional effect of droplets and a critical collision radius are included. The Wave model involving the cavitation effect inside a nozzle is used for predictions of atomization processes. Numerical results are reported for different impingement angles of 60° and 90° in order to show the influence of the impinging angle on spray characteristics and also compared with experimental data. It is found that the hybrid model shows slightly better agreement with experimental data than the O’Rourke’s model.

Numerical Study on Bouncing and Separation Collision Between Two Droplets Considering the Collision-Induced Breakup

The main purpose of the present study is to perform numerical study on bouncing and separation collision between two droplets considering the collision-induced breakup. In this study, the collision model proposed in our previous study is used for simulation of collision-induced breakup, and we modify this model to consider the effect of liquid property on the behavior of droplet-droplet collision. This collision model is based on the conservation laws for mass, momentum, and energy between before and after collision and provides several formulae for post-collision characteristics of colliding droplets and satellite droplets. Improving the accuracy of the model, in this study, appreciate criterion for bouncing collision is added and dissipation energy during collision process is newly modeled. To validate the new model, numerical calculations are performed and their results are compared with experimental data published earlier for binary collisions of water, propanol, and tetradecane droplets. It is found from the results that the new model shows good agreement with experimental data for the number of satellite droplets. It can be also shown that the predicted mean diameter by the new model decrease with increasing the Weber number because of the collisioninduced breakup, whereas the O’Rourke model fails to predict the size reduction via the binary droplet collision.

An Analysis on the Major Parameter and the Relations of Pressure Difference Effect of Leakage Area in the Smoke-Control Zone

This study is experimentally analyzed to extract the major parameters affecting the performance of the smoke-control system and the relations of pressure difference between vestibule and supply air pressure zone effect of supply mass flow rate and leakage area in the smoke-control zone. To obtain this, the mock-up building of three-story scale with a total of 10 compartments was constructed, and several apparatus were also installed for in-situ measurement of the ventilation flow rate, pressure difference between compartments, smoke defensive air velocity, the opening-closing force of door, etc. This article show that pressure difference in the smoke-control zone is significantly related with leakage area of vestibule in low pressure region, leakage area of supply air pressure in over pressure region and both of them in pressure control region when the pressure control range of damper is 45 Pa~55 Pa.