Zone model compartments

The National Bureau of Standards (NBS, now National Institute for Standards and Technology, NIST) fire and smoke transport model, F.A.S.T., version 18.3, was used to generate the information concerning the temperatures and gas concentrations. This is a zone model which predicts the formation of two layers in each compartment. 

Here T is the uniform temperature in the CV. Equations (3.45) and (3.48) are all equivalent under the three approximations, and either could be useful in problems. The development of governing equations for the zone model in compartment fires is based on these approximations. The properties of the smoke layer in a compartment have been described by selecting a control volume around the smoke. The control volume surface at the bottom of the smoke layer moves with the velocity of the fluid there. This is illustrated in Figure 3.10. 

The above discussion lays out the physics and chemical aspect of the processes in a compartment fire. They are coupled phenomena and do not necessarily lend themselves to exact solutions. They must be linked through an application of the conservation equations as developed in Chapter 3. The ultimate system of equations is commonly referred to as zone modeling for fire applications. There are many computer codes available that represent this type of modeling. They can be effective for predictions if the... 

Generally, compartment fire simulation models predict the fire development in a compartment under varying conditions. These types of simulations are useful for estimating tenability criteria, thermal insult to the compartment, and the likelihood of fire spread from one compartment to another. These types of models can be further subdivided into three categories based on their approach to simulating the fire environment the zone model, the field model, and the post-flashover model. 

Zone models may estimate the upper and lower layer temperature, the interface location between zones, the oxygen concentration, the carbon monoxide concentration, the visibility, and flows in and out of openings in the compartment as a function of time. This information may be useful for evaluating the tenability of a compartment or determining when flashover may occur in a space. A zone model may look at one room with a single opening or multiple rooms with many openings. 

Like zone models, field models require a description of the compartment geometry and the openings within the compartment. Field models are not limited to compartments, however. They may be used to simulate such phenomena as open plumes and unique configurations such as tunnels and shafts. The... 

Of a more complete approach are the zone models [3], which consider two (or more) distinct horizontal layers filling the compartment, each of which is assumed to be spatially uniform in temperature, pressure, and species concentrations, as determined by simplified transient conservation equations for mass, species, and energy. The hot gases tend to form an upper layer and the ambient air stays in the lower layers. A fire in the enclosure is treated as a pump of mass and energy from the lower layer to the upper layer. As energy and mass are pumped into the upper layer, its volume increases, causing the interface between the layers to move toward the floor. Mass transfer between the compartments can also occur by means of vents such as doorways and windows. Heat transfer in the model occurs due to conduction to the various surfaces in the room. In addition, heat transfer can be included by radiative exchange between the upper and lower layers, and between the layers and the surfaces of the room. 

In our present work, we want to find out the suitability of CFAST in fire simulation for fire safety onboard ship, which is a multi compartment zone model, comparing the results with CFX- a general purpose CFD... 

ARGOS, (Denmark) Danish Institute of Fire Technology Multi-compartment zone model [17]... 

POGAR, (Russia) Higher Engineering Fire-Technical School, Moscow Single compartment zone model [19]... 

Export processes are often more complicated than the expression given in Equation 7, for many chemicals can escape across the air/water interface (volatilize) or, in rapidly depositing environments, be buried for indeterminate periods in deep sediment beds. Still, the majority of environmental models are simply variations on the mass-balance theme expressed by Equation 7. Some codes solve Equation 7 directly for relatively large control volumes, that is, they operate on "compartment" or "box" models of the environment. Models of aquatic systems can also be phrased in terms of continuous space, as opposed to the "compartment" approach of discrete spatial zones. In this case, the partial differential equations (which arise, for example, by taking the limit of Equation 7 as the control volume goes to zero) can be solved by finite difference or finite element numerical integration techniques. 

Soil compartment chemical fate modeling has been traditionally performed for three distinct subcompartments the land surface (or watershed) the unsaturated soil (or soil) zone and the saturated (or groundwater) zone of a region. In general, the mathematical simulation is structured around two major cycles the hydrologic cycle and the pollutant cycle, each cycle being associated with a number of physicochemical processes. Watershed models account for a third cycle sedimentation. 

As shown in Fig. 3, CHEMGL considers 10 major well-mixed compartments air boundary layer, free troposphere, stratosphere, surface water, surface soil, vadose soil, sediment, ground water zone, plant foliage and plant route. In each compartment, several phases are included, for example, air, water and solids (organic matter, mineral matter). A volume fraction is used to express the ratio of the phase volume to the bulk compartment volume. Furthermore, each compartment is assumed to be a completely mixed box, which means all environmental properties and the chemical concentrations are uniform in a compartment. In addition, the environmental properties are assumed to not change with time. Other assumptions made in the model include continuous emissions to the compartments, equilibrium between different phases within each compartment and first-order irreversible loss rate within each compartment [38]. 

SimpleBox is a nested multimedia environmental fate model in which the environmental compartments are represented by homogeneous boxes. It consists of five spatial scales a regional scale, a continental scale and a global scale consisting of three parts, reflecting arctic, moderate and tropic geographic zones (Fig. 5)... 

Lipids are transported between membranes. As indicated above, lipids are often biosynthesized in one intracellular membrane and must be transported to other intracellular compartments for membrane biogenesis. Because lipids are insoluble in water, special mechanisms must exist for the inter- and intracellular transport of membrane lipids. Vesicular trafficking, cytoplasmic transfer-exchange proteins and direct transfer across membrane contacts can transport lipids from one membrane to another. The best understood of such mechanisms is vesicular transport, wherein the lipid molecules are sorted into membrane vesicles that bud out from the donor membrane and travel to and then fuse with the recipient membrane. The well characterized transport of plasma cholesterol into cells via receptor-mediated endocytosis is a useful model of this type of lipid transport. [9, 20]. A brain specific transporter for cholesterol has been identified (see Chapter 5). It is believed that transport of cholesterol from the endoplasmic reticulum to other membranes and of glycolipids from the Golgi bodies to the plasma membrane is mediated by similar mechanisms. The transport of phosphoglycerides is less clearly understood. Recent evidence suggests that net phospholipid movement between subcellular membranes may occur via specialized zones of apposition, as characterized for transfer of PtdSer between mitochondria and the endoplasmic reticulum [21]. 

Techniques are available to calculate conditions under which enclosed fires are ventilation- or fuel- controlled. Computer models are available to estimate compartment fire growth and temperature effects. In particular, the zone fire model C-FAST (Jones et al., 2000) is widely used. Additional information on models is contained in Appendix C. 

Azone model calculatesthe fire environment by dividing each compartment in the model into two homogeneous zones. One zone is an upper hot smoke zone that contains the fire products. The other zone is a lower, relatively smoke-free zone that is cooler than the hot zone. The vertical relationship between the zones changes as the fire develops, usually via expansion of the upper zone. The zone approach evolved from observations of such layers in full-scale fire experiments. While these experiments show some variation in conditions within the zones, the variations are most often small compared to the difference between the zones themselves. 

Figure 5.3-11. Scheme of the two-compartment convective-diffusion model and equations for the end zones in BSCR (tested with a liquid tracer) [47],... 

The simulation model depicts the flows of nitrogen between the compartments, and in particular is used to investigate the effect of sedimentation of phytoplankton and zooplankton faeces out of the euphotic zone which is assumed to be 60 m deep however the depth does not affect the conclusions drawn from the results. 

Contaminants in the soil compartment are associated with the soil, water, air, and biota phases present. Transport of the contaminant, therefore, can occur within the water and air phases by advection, diffusion, or dispersion, as previously described. In addition to these processes, chemicals dissolved in soil water are transported by wicking and percolation in the unsaturated zone.26 Chemicals can be transported in soil air by a process known as barometric pumping that is caused by sporadic changes in atmospheric pressure and soil-water displacement. Relevant physical properties of the soil matrix that are useful in modeling transport of a chemical include its hydraulic conductivity and tortuosity. The dif-fusivities of the chemicals in air and water are also used for this purpose. 

Most modem N-cycle models simulate N export using one or the other of these approaches, but details vary and some models combine aspects of expHcit sinking and reminerahzation with Martin curve parameterizations. For example, Chai et al (1996) modeled a 5-component N-based ecosystem including a detrital N compartment with explicit sinking, but did not permit detrital remineralization within the euphotic zone. In contrast, Christian et al (2002a) used a Martin curve to redistribute detrital N vertically, but rather than remineralizing at the specified depth, it is returned to the... 

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