Impulse Ventilation Research Articles

Experimental analysis and simulation of a centrifugal jet fan for impulse ventilation systems

Centrifugal jet fans are usually used to stir evenly, remove local airflow blind spots, and improve air quality. They are widely used in HAVC systems of garage buildings recently. However, there are few in-depth studies on its modeling methods, and even the experimental verification of the most basic centrifugal jet fan simulation model has not been fully demonstrated. This paper combines experimental verification with numerical simulation to investigate the appropriate modeling method and jet characteristics of centrifugal jet fans for impulse ventilation systems. Experimental data showed that the air volume of each nozzle of the centrifugal jet fan was different, and that even outlet velocity of a single nozzle was not uniform. Velocity decreased slightly in the jet core area and then decreased gradually until it approached the ambient velocity, while the amount of air entrained by the jet was approximately linear with respect to the jet range. In addition, the design key points and methods of impulse ventilation systems was summarized. CFD was used to simulate the flow field of centrifugal jet fans. Two modeling strategies, involving accurate boundary conditions based on experimental data, and simplified velocity boundary conditions, were used, and displayed differing characteristics. When designers focus on the coverage range of jet fans and the velocity distribution at the far-field, or the operation performance of jet fans in HAVC systems, the simplified velocity boundary conditions can be used. When the aim is to study and optimize nozzle, an accurate model and boundary conditions should be utilized.

Numerical study of modeling methods and evaluation indexes for jet fans

With the rapid development of turbulent jet technology, jet fans have been widely used in building ventilation system, especially for underground buildings. Researchers often use CFD to design the impulse ventilation system, but the study of modeling methods for jet fans have not been studied comprehensively. Because of the characteristic of jet fan, different kind of inlet boundary condition types coupled with different turbulence models lead to different flow fields. In order to find the most suitable modeling method, this paper studied the effect of the combination of 8 turbulence models and 3 flow boundary conditions on modeling accuracy of jet fans. In addition to comparing velocity and turbulence intensity, the research adopted jet core area length and diffusion angle to evaluate the pros and cons of the simulation results. Results showed that the Fan Boundary Method (FBM) integrated with the k-w SST or RSM (Stress-BSL) turbulence model; the Velocity Boundary Method (VBM) integrated with the k-w SST turbulence model; the Momentum Source Method (MSM) integrated with the standard k-ε turbulence model can represent most jet fans' performance with free jet. When the main task is to verify jet fan nozzles performance or optimize nozzles design, the RSM (Stress-BSL) and k-w SST turbulence models are recommended. When the main focus is on the fan range or the performance of the impulse ventilation system, the standard k-ε turbulence model is recommended. The choice of the final model depends on the available data and the application scenario.

Performance of impulse ventilation system in an underground car park fire: Case study

In this paper, a detailed sensitively analysis for significant parameters was conducted to assess the ability of impulse ventilation system (IVS) to guarantee safe evacuation of occupants, public and fire fighters due to fire in an existing underground car park. The significant parameters include parked cars, extract rate, jet fan number and fire location. Analysis is performed using a general-purpose CFD code to simulate 9 different scenarios in a 10,021 m2 car park with a fire source having an experimental transient heat release rate simulating two car fires. The influence of significant parameters on IVS performance for smoke clearance was illustrated to provide insight into performance-based design of IVS in an underground car park.

Optimum Design of Impulse Ventilation System in Underground Car Parking Basement by Using CFD Simulation

The most significant development in car park ventilation design has been the introduction of Impulse Ventilation. It is an innovative alternative to traditional systems and provides a number of significant benefits. The ventilation of car parks is essential for removing vehicle exhausts Fumes and smoke in case of fire containing harmful pollutants. So design of impulse systems is usually proven by use of CFD (Computational Fluid Dynamic) analysis. In this study considered one of the car parking basement which is in Riyadh, Saudi Arabia and study was conducted by using ANSYS-Fluent. The field study was carried to collect the actual data of boundary conditions for CFD simulation. In this study, two Cases of jet fan smoke ventilation systems were considered, one has 8 jet fans according to the customer and another one has 11 jet fans which positions were changed accordingly. Base on the comparison of simulation data, ventilation system with 11 jet fans can help to improve the evacuation of fumes in the car parking area and it is also observed that the concentration of CO minimized within 15 minutes.

Application of Induced Ventilation for Smoke Control in Underground Car Parks

In this paper, the existing methods of ventilation system and smoke control system that used in the underground car parks have been briefly reviewed. Compared to other methods, the impulse ventilation system (IVS) has a lot of advantages, and has great development space in the current. The progresses of research on IVS are summarized, and some key problems (like flow field characteristics, installing parameters of induced fan, influence of space structure to smoke and so on) that have a guiding effect on relevant standard specification are discussed. Some basic principles that followed in the process of layout of IVS are analyzed.

Convective Heat Transfer Coefficients of the Human Body under Forced Convection from Ceiling

The average convective heat transfer coefficient for a seated human body exposed to downward flow from above was determined. Thermal manikin with complex body shape and size of an average Scandinavian female was used. The surface temperature distribution of the manikin’s body was as the skin temperature distribution of an average person. The measurements were performed in a room with controlled thermal environment. Air temperature was set at 26oC for cooling and at 20oC for heating. The radiant temperature asymmetry in horizontal and vertical direction was close to zero, i.e. mean radiant temperature was equal to the air temperature. The air velocity of the isothermal downward flow from the ceiling at height of 1.5 m above the floor (above the top of the head) was set in a range between still air and 0.73 m/s. Based on the analyses of the results relationships for determination of the convective heat transfer coefficient of the whole body (hc [W/(m2•K)]) was proposed: hc=4.088+6.592V1.715 for a seated naked body at 20oC and hc=2.874+7.427V1.345 for a seated naked body at 26oC. Differences in the convective heat transfer coefficient of the whole body in low air velocity range, V<0.3 m/s, due to the natural convection were found. The results may be useful during design of air distribution in rooms, e.g. low impulse ventilation, diffuse ventilation, etc.

Numerical Study on Impulse Ventilation for Smoke Control in an Underground Car Park

This study examines smoke control capacity of impulse ventilation system (IVS) in an underground car park. An analysis is made in relation to important parameters including jet fan number, jet fan velocity, extract rate and system robustness on fire position. The comparison with ductwork system is also performed to determine the different effect of smoke control between two systems. Fire Dynamic Simulator version 5.30 is applied to simulate 10 scenarios in a 80 m long, 40 m wide and 3.2 m height domain witha fire source simulating a car fire with an peak heat release rate of 4 MW. Results show that impulse ventilation system not noly prohibit fire smoke spreading but also maintain a good visibility providing clear access for fighters. However it may cause temperature rise on the downwind zone of fire source with a maximum value between 80-100 and fire plume e tilt. Smoke control capacity of impulse ventilation system is sensitive to jet fan numbers. Too high jet fan velocity may cause severe smoke recirculation. Increment in extract rate is conductive to relay jet flows. An impulse ventilation system can effectively control smoke movement and induce smoke to extract points under two typical different fire locations, which is of great practical importance. Impulse ventilation system seems superior to ductwork system in maintaining high visibility.

Numerical Simulations on Sprinkler System and Impulse Ventilation in an Underground Car Park

As more and more underground car parks are built in the city, it is important to design an good fire protection system. Nowadays, many car parks use the impulse ventilation system to control smoke when fire takes place. In order to study the smoke control of impulses ventilation during car park fires when sprinkler system is installed, FDS is used to simulate the smoke temperature, concentration and activated sprinkler number during the fire. It is found that with the impulse ventilation, there would be much less smoke upstream the fire, which is favorable for firefighters to put out the fire. Besides there would be much less sprinklers activated with impulse ventilation system, which will help to stable the water pressure of the sprinkler system.

The use of impulse ventilation for smoke control in underground car parks

Impulse ventilation systems (IVS) are used to provide ventilation for covered car parks and to control the smoke in the event of fire. In this paper the interaction between the fire ceiling jet and the flow driven by jet fans is studied using CFD simulations. A sensitivity analysis considering important parameters as position and intensity of fire source, transversal distance between jet fans, restriction of exhaust flow rate and dimension of car park exhaust opening is carried out and rules for the design of 50 N thrust jet fans are deduced. An analytical model for the flow field near the ceiling is developed and compared with CFD simulations. This model is intended to support a first approach of the design of IVS.

The Use of Impulse Ventilation to Control Pollution in Underground Car Parks

The ventilation of underground car parks is important to avoid health problems associated with the inhalation of combustion products released by car engines, in particular carbon monoxide CO (which is commonly used as the indicator of car park indoor air quality). In recent years, a new mechanical ventilation system has appeared, based on the use of axial ventilators (jet fans) suspended under the car park ceiling. In this paper the flow generated by jet fans and their effects on pollutants are studied. It is concluded that jet fans may have a pumping effect, entraining the surrounding contaminated air into the jet. In this way jet fans are able to restrict the dispersion of contaminants, provided that the exhaust flow rate from the car park is not lower than the jet flow rate. Impulse ventilation may also provide fast dilution of the local pollution peaks, but in this case the removal efficiency will be low. This paper also suggests criteria to define the distance between jet fans.