Whirlwind Results on Chamber Verve with Hybrid Airing - Assignment Example

Wind effects on compartment fires with cross ventilation Name: Course: Lecturer: Institution: City & State: Date: Introduction A good number of buildings that are of tall heights are majorly found in the Far East as the main area where they are constructed. Thus, fire safety has over time given provisions regarding these buildings as they are of high concern about the increasing fires in the recent years. These buildings have fire scenarios that have overtime been triggered by the increasing wind velocity that increases from the ground level at zero velocity to higher velocities at higher levels. Because of these strong velocities at higher elevation, wind has influence on fire and smoke spread at these heights, for instance, under the wind effects, cross ventilation might experience difficulties in smoke extraction. Therefore, this creates a necessity to understand the fire behavior as it regards safety of the building that needs provision of safety actions for buildings. In addition, there is a need to have wind-engineering clues when designing natural/mechanical ventilation or airflow patterns under wind environment. Thus, understanding the fire phenomena is essential when designing the high-rise buildings since it will provide necessary steps that may help in designing for fire safety in these buildings (Buchanan and Feasey 83-105). This paper is an experimental investigation to determine the wind effects on compartment fire with cross ventilation. This acts as the initial step in understanding the means through which measures necessary for fire safety building under wind should be undertaken. In this experimental set up, fire in set to burn under steady airflow from a wind tunnel. This is a simulation of a fire compartment set to be on a higher/tall building, which is an explanation of the effect of wind on fire under cross ventilation. Recently there have been new findings that suggest that wind acts as the major cause of many fire accidents. In many cases on high-rise buildings, when fire start on one section of the building it propagates to other sections through the ventilation system, which is triggered and further forced by wind. Buildings with cross ventilation have a considerable height of about 3-4m high within the rooms per floor. Therefore, wind speed variation is not a necessary factor to consider in the high-rise buildings. Thus, the major consideration in these buildings is wind attack to the building. Since the building acts as a barrier to wind, it acts as a blockage to the wind. Moreover, it is necessary to consider the effect of steady flow of air in a wind tunnel. However, profile of the wind speed at different levels of the building height is a major determinant of the wind effect on the fire in cross ventilation (Naveen and Kumar 1549). Generally, in an uncontrolled fire in a compartment, which is with or without wind, fire follows a growth phase in the building. Usually, fire will undergo transition after ignition to a fully developed fire leading to fire burning phase. Research has shown that fire under single ventilation hot gases and smoke will pass through the same ventilation as the air from outside is drawn into the compartment though a buoyancy force. In cross ventilation there are more openings, which trigger higher rates on burning especially when the wind is high. Experimental set up Fig 1 is an experimental setup for a fire compartment set to burn under forced airflow from a wind tunnel. The setup is a long wind tunnel of 20m set to provide steady airflow with a varying wind velocity from zero to 15ms-1. The experimental facility is set in a tunnel measuring 1.8m (height) by 1.8m (width) by 6m (length), which makes the major part that will provide a steady flow of the required wind for the experiment. An anemometer that has multisensory will be placed in different sections of the tunnel to determine the wind speeds at these sections for the tunnel. In addition, another anemometer is used at the measure the wind speed at the exit of the tunnel, which is the front of the fire and the floor level. For different positions in the wind tunnel the wind speeds was at carrying speeds. Figure 1: Experimental layout of the farcicality Set-up Analysis There are anemometers placed at the points labeled 3049, 3050, 3051, and 3052. In addition, the compartment of the set up is made of internal dimensions of 60cm by 60cm by 60cm, with the ceiling and the floor made of structure that has two layers. The inner layer is an 8 mm thick fireproof wall that prevents heat loss to the surrounding, while the outer wall made of 2mm thick steel plate, which helps in maintaining the stability of the structure. Moreover, the compartment has three inner walls, with the inner layer made of 25mm thick combustible fireboard, 32 mm thick middle layer of fire resistant board and 2mm thick steel plate for the outer layer. Further, the compartment has two square windows at the rear and front walls of 20 cm by 20cm by size. Alternatively, the sidewall may be replaced using glass that is fireproof and is used for observation. At the center of the floor, tray burner that contains 250 ml of n-heptanes is placed for burning. The mass of the fuel in the n-heptane heat release is given as: Where rate of mass fuel loss  Combustion heat fuel X= combustion efficiency And Q total heat released For successful functioning of the compartment, thermocouples are planted at the outside and the inside walls to measure the temperatures of surrounding. From the inside, 1mm diameter thermocouples were placed and 2mm diameter thermocouples were place from the outside of the compartment (fig 2). As the experiment is carried out repeatedly, in every experiment wind velocity is calibrated first. Then when fuel is in place, a board is used to block the upwind window and ignition is done via the downwind window using a torch. Consequently, when the fuel is lit, the torch and the upward wind window are retreated sequentially. This information was recorded using cameras for the purpose of comparison with fire experiments with free burning that had been conducted in still and open environment. Figure 2: outside thermocouples arrangement Cases Ambient wind velocity m/s Fuel volume (ml) Ambient temp () Case 1 0 250 11 Case 2 1.5 250 11 Case 3 3 250 10 Case a 0 500 11 Case b 1.5 500 11 Table 1: details of the experiments Results and discussion From the experimental observations, different locations of the experimental setup did provide different observations and conclusions for the experiment. Wind velocity From the compartment, wind velocity was measures from the designated four positions and average speed at these points recorded as for each section. Each section in the compartment did record a different wind velocity from the next, which did give varying effects in the tunnel. Rate of Heat release Experimentally, heat release must have a controlled rate, which was determined using the control experiments at normal environmental conditions. As the fuel continue to burn and wind speed increase, different scenarios are brought about by the rate at which the fuel burns. Further, as the amount of heat increase in the compartment, the lasting time for the heat release gets shortened as the rate of ambient wind speed increases. Therefore, this is means that as the ambient wind speeds increase, it increase the rate at which heat is released and the rate at which fuels burn in the trays. Moreover, in these experiments, as volume of fuel is varied with varying wind speeds, also time required to increase the amount of heat necessary for the compartment in relatively corresponding to the fuel-burning rate of the fuel available. Temperature of the hot gas Different thermocouples were planted at different sides of the compartment to determine the gas temperature from the two sides. Therefore, the relativity of the thermocouples to give accurate temperatures as required for the experiment, different panels consequently determine the efficiency and probability of giving the required data. Comparing the gas temperatures at different cases in the compartment, internal sections of the compartment had 100 higher than those of the outside of the compartment. This further indicated that as the fire developed from the inside, the higher the chances that the flashover points would be attained since wind would be the definite fuel to increase the burning. Consequently, as the wind velocity increased, it had a direct impact on the fuel burning process, which was the main determinant for the temperatures of the surrounding. Thermal stratification All the temperatures at the inside of the entire compartment are uniform. This is as indicated from the internally placed thermocouples in the compartment. Measuring temperatures at all, dimensions in the entire compartment would give almost equal temperatures. Only thermocouples closer to the exit and the entrance can give a different temperature level since there is influence from the external environment, which brings in cold air in the compartment. Therefore, this makes the section a special point since its temperature is not stable as compared to the parts in the compartment, which high very different higher temperatures. At temperatures about 150 and low of 50, the compartment temperatures are at pre-flashover levels. Therefore, at these levels the possibility of the flame touching the thermocouple thus causing such a difference in temperature is very high. For instance, at pre-flashover temperatures the gas in the compartment shows obvious characteristics that are created by force air in the compartment. Therefore, depriving off oxygen from the internal part of the compartment is very dangerous since it has combustible walls that can catch fire. Close monitoring and keen observation is essential for the entire process in the fire developing stages. Moreover, as the wind reduces in the compartment so does the rate at which the fire propagates; although as the hot and cold gases mix cause the fire development to fluctuate, which further shows a smaller influence on the fire. In addition, more wind flows into the compartment there is more oxygen flow, which cause more air to mix causing higher combustion rates of the gases. Consequently, the increased combustion rates increase increases the heat rate filling the entire compartment with hot gases. Wall temperature The law of energy conservation must always be a factor to consider when calculating the temperature of the internal section of the entire compartment. Therefore, thermocouples planted in the entire system must provide sidewall temperatures that are used in the calculations, which almost temperatures of the hot gases in the compartment. Further, the temperature of the fire-resistant walls in the inner side of the compartment has temperature close to that of the gases. Entirely all the thermocouples in the inner side of the compartment had temperatures ranging closer to that of the gases inside. This meant that there was uniformity on temperature flow from the internal section of the compartment, which was determined neglecting the heat losses from the walls of the compartment. Outflow gas temperature Hot smoke accumulates the area below the ceiling of the compartment spilling out through any openings found in the compartment. Further, as the flame reaches the post-flashover stage, it spills out from the openings in the compartments. Therefore, temperature of the spill out hot smoke and flames is the temperature of the outflow gas from the compartment. Moreover, as wind speed affects the flame it also determines the duration under which the outflow gas will last. Generally, temperature at different outflow rates are recorded by different thermocouples placed at different strategic positions in the compartment. Further, the direction of the flame in the compartment is also dictated by the strength and direction of the wind. For instance, when there is no horizontal wind flowing, the flame and the hot smoke move vertically upwards. When the wind in flowing horizontally, all flame and hot smoke is blown horizontally, thus creates temperature differences at different levels depending on the flame concentration. Flow direction and wind effect From the experiments, it is clear that strong wind has relatively high effect on the fire compartment. When wind flows in the compartment it, carries with it flesh air, which makes fire more severe. Therefore, wind flow velocity increase has a consequent increase and relative change on pressure that acts on the hot smoke as well the fire in the compartment. Therefore, for all the wind directions, the leeward, the windward direction and inside the compartment, wind flow rate determines the changes and the effects that the fire will have. Thus, fire direction will depend on the speed and direction of the wind from the flow sides. Wind flow on fire changes the density of the fire compared to its surrounding, this changes buoyancy of fire relative to the environment increasing the size of the flame. Critically, flashover temperatures are very high temperatures while an ambient temperature for the experiments was at 10 compared to 600 temperature. Thus, these temperature differences creatures the pressure differences at the leeward side and the windward side to -0.2 and 0.2 respectively. Conclusion As this case involved a series of experiments that were carried out to investigate the wind effect on compartment fire with cross ventilation, all experiments were done and findings of the experiment recorded. 10 experiments were done at varying wind speeds of 0, 1.5 and 3 m/s using different locations of fuel location with either 250 ml or 500ml n-heptane placed at those positions. Further, 6 burning experiments were carried out as the control experiment at normal conditions with normal atmosphere and calm wind. Moreover, different profiles of the experiment were recorded as per the parameters use in each of the experiment. It was clear from the experiments that fire behavior is majorly influenced by the main flow and backflow of the wind. In addition, fire at different positions as different dimensions at which it spreads. Moreover, it is clearly shown that as the wind increases in presence of fire in a cross ventilation, it makes fire more severe. This is caused by increase in oxygen flow as well as causing a contradictory behavior by carrying and removing combustible gases. The experiments also indicate that as the wind velocity increases to 3 m/s the flame increases and occupies the whole compartment unlike when at lower speed where it occupies only a part of the compartment. In more serious note, the experiments indicate that as the fuel increases this creates the chances of fire reaching post-flashover phase, which can make fire uncontrollable at such levels. Thus amount of fuel also dictates the extend at which wind will have its effect on fire in a cross ventilation. References Buchanan, A. and Feasey, R. (2002) Post-flashover fires for structural design, Fire Safety Journal, 37(1): 83-105 Naveen, M. and Kumar, R. (2007) Compartment fires: CALTREE and cross-ventilation, Combustion Science and Technology, 179(8): 1549-1567 Read More

Experimental set up Fig 1 is an experimental setup for a fire compartment set to burn under forced airflow from a wind tunnel. The setup is a long wind tunnel of 20m set to provide steady airflow with a varying wind velocity from zero to 15ms-1. The experimental facility is set in a tunnel measuring 1.8m (height) by 1.8m (width) by 6m (length), which makes the major part that will provide a steady flow of the required wind for the experiment. An anemometer that has multisensory will be placed in different sections of the tunnel to determine the wind speeds at these sections for the tunnel.

In addition, another anemometer is used at the measure the wind speed at the exit of the tunnel, which is the front of the fire and the floor level. For different positions in the wind tunnel the wind speeds was at carrying speeds. Figure 1: Experimental layout of the farcicality Set-up Analysis There are anemometers placed at the points labeled 3049, 3050, 3051, and 3052. In addition, the compartment of the set up is made of internal dimensions of 60cm by 60cm by 60cm, with the ceiling and the floor made of structure that has two layers.

The inner layer is an 8 mm thick fireproof wall that prevents heat loss to the surrounding, while the outer wall made of 2mm thick steel plate, which helps in maintaining the stability of the structure. Moreover, the compartment has three inner walls, with the inner layer made of 25mm thick combustible fireboard, 32 mm thick middle layer of fire resistant board and 2mm thick steel plate for the outer layer. Further, the compartment has two square windows at the rear and front walls of 20 cm by 20cm by size.

Alternatively, the sidewall may be replaced using glass that is fireproof and is used for observation. At the center of the floor, tray burner that contains 250 ml of n-heptanes is placed for burning. The mass of the fuel in the n-heptane heat release is given as: Where rate of mass fuel loss  Combustion heat fuel X= combustion efficiency And Q total heat released For successful functioning of the compartment, thermocouples are planted at the outside and the inside walls to measure the temperatures of surrounding.

From the inside, 1mm diameter thermocouples were placed and 2mm diameter thermocouples were place from the outside of the compartment (fig 2). As the experiment is carried out repeatedly, in every experiment wind velocity is calibrated first. Then when fuel is in place, a board is used to block the upwind window and ignition is done via the downwind window using a torch. Consequently, when the fuel is lit, the torch and the upward wind window are retreated sequentially. This information was recorded using cameras for the purpose of comparison with fire experiments with free burning that had been conducted in still and open environment.

Figure 2: outside thermocouples arrangement Cases Ambient wind velocity m/s Fuel volume (ml) Ambient temp () Case 1 0 250 11 Case 2 1.5 250 11 Case 3 3 250 10 Case a 0 500 11 Case b 1.5 500 11 Table 1: details of the experiments Results and discussion From the experimental observations, different locations of the experimental setup did provide different observations and conclusions for the experiment. Wind velocity From the compartment, wind velocity was measures from the designated four positions and average speed at these points recorded as for each section.

Each section in the compartment did record a different wind velocity from the next, which did give varying effects in the tunnel. Rate of Heat release Experimentally, heat release must have a controlled rate, which was determined using the control experiments at normal environmental conditions. As the fuel continue to burn and wind speed increase, different scenarios are brought about by the rate at which the fuel burns. Further, as the amount of heat increase in the compartment, the lasting time for the heat release gets shortened as the rate of ambient wind speed increases.

Therefore, this is means that as the ambient wind speeds increase, it increase the rate at which heat is released and the rate at which fuels burn in the trays.

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