Critically review zone and field models which are used for compartment fire modelling.

Critically review zone and field models which are used for compartment fire modelling. Include examples and critically analyse the main assumptions, limitations, advantages and disadvantages of these models.

Fire modelling contains two distinct models; zone and field models

Field Models

Field models are intricate as well as more dynamic and hence recent. This is what makes the models more adoptable in the sophisticated environment and up-to-date setups. The field models described as a whole with quite clear pathways of operations with no compartments like the other model; zone. Quite notable about this model is the demarcation of boundaries in its area of operation instead of compartments. The field model is characterized by one major assumption which is that, it is the domains possessing different and notable properties effects which in an ideal situation, is not easy to come about (Makhviladze, N.d). The effects generated the properties are as a result of the temperature, velocity, and concentration that are viewed as too different depending on domains. These models are made up of the PDE also known as the partial differential equation, a factor that explains how different the model is from the rest of the models. Case illustrations of the model include the CFX, SOFIE, Fluent, as well as Jasmine.

Zone Models

Unlike field model, zone model emerges to be very traditional and hence, precise use of empirical data is upheld in this model. Due to its traditional orientation, Zone model is conveyed as a very archaic and old fashioned model because of its traditional aspects. Field models are treated as a whole with boundary demarcations but in zone models, there are subdivisions called the compartments. The compartment contains the chambers where operations take place in the model. There are chambers emerging from the compartmental segment namely a ceiling called the hot layer, outflows, inflows, as well as the thermal plume (Merci & Beji, 2016). The model also operates on an assumption that in the model, property distribution is quite uniform in all the compartments and the chambers.

The advantages by the models are universal such that the one making the zone model also is experienced in the field model. Generally, the models involve formulation and development of formulas within their compartmental subdivisions and the boundary sets. In zone models, equations are restricted within the zone environment and they are composed of the commercial codes. The most common examples of zone models include the CFAST and the Hazard.

The limitations that coil about the models can also be expressed as single entities (Drysdale, 2011). The common limitation is demonstrated by the instability caused by the excessively large time step with raised cost to counter the disintegration of the steps.

N = T_max divided by ∆t or T_max∆t

Different types of errors tend to crop up in these models, for instance, the truncation errors, which appear to sum up. This summation gives rise to faults in the conclusion involving the models. Apart from truncation errors, accuracy faults are encountered from methods such as the explicit Euler method used in analysis.

Critically analyse the effect of ventilation on the composition of smoke using equivalence ratio. Compare over ventilated and under ventilated combustion.

The total yield of smoke from a source of fire will greatly be influenced by the level of ventilation and the design that has been used to ensure that the smoke gets out of the area that it is being influenced. Therefore, the ventilation size of the smoke, is the one that will be used to determine the composition of the smoke due to the different mixtures that will be formed on the process. An example is the cigarette where the filter ventilation will be the determining factor in diluting the smoke produced by giving the microscopic holes around the filter which will lead to reduction of the tar yield and other compounds that are produced. Many experiments that have undertaken regarding to the smoke composition have shown that the difference in composition of smoke will always depend on the ventilation done within the area of production. Area that have low ventilation will tend to have low number of compounds where as those with high ventilation levels, will tend to have many compounds. However, in the lowly concentrated areas the few compounds found tend to be concentrated while in those areas that are highly ventilated the compounds are diluted due to the reactions that take place with the air (Whiteley, 2008).

Considering the cigarettes based on the investigation that were made where there features 0% ventilation which meant it was absent completely, 35% and 70% ventilation. When investigation on the smoking done on the two different puffing areas the results got were somehow different. In the areas that there was no ventilation it was found out that they had different levels of components. Those at the zero mark had very concentrated compounds compare to those that were ventilated. The one of 70% ventilation had got diluted compounds compared to that of 35%. This means that ventilation has a great impact with the composition of smoke that will be produced from a fire source.

Analyse the process of liquid and solid fuel combustion. What is the role of radiative feedback? Compare the mechanisms of liquid and solid fuel combustion.

Consumption of fuel requires both the heterogeneous and homogeneous reaction for both liquid and solid charring fuels. The structural changes that are required in the process of converting fuel into the state that it can be used in different forms requires that a complete and realistic burning model is developed. Therefore, there is need to understand the structure and forms the fuel will have to undergo to the end (Svoboda, Hartman, & Cermák, 2000). If a given fuel is in a particular state then it will require a given quantity of heat for conversion to occur.

The rank of coal that maybe in a liquid or solid state, has different heating rate, reaction conditions and size of particles (temperature, pressure, gas concentrations) determine behavior, devolatilization, structural changes and reactivity of coal (fuel) particles during drying, char combustion and gas phase oxidation of volatiles. Where the combustion takes place at relatively lower temperatures (< 1000 °C) this happens due to the ash catalytic affect, CaO and other solid that increases the combustion rate of volatility which leads to the transformation of the fuel state. The burning or gasification rates of the solid fuel will depend on the content of fixed carbon and volatile. Development of reactivity of a char ash effects and pore structure have an important role in the combustion process, in releasing and reducing the level of gases and other heavy metals to emit the energy required. The mechanism used in the fuel combustion will lead to a relatively contribute and relative importance that come with heterogeneous catalysts and other non-catalyst reactions of gases and other radicals that are in the devolatilization and volatile where combustion can be analyzed (Svoboda, Hartman, & Cermák, 2000). There are further fuel influences, conditions of combustion and technology that is used in measuring the burning reaction rate, emission and the burning particles at the temperature that they can change and assessment of the whole process. All these are based on the measurements that are experimental.

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