Security
From Thermal-FluidsPedia
Security involves homeland/defense security, food/water security, and economic security. Efforts to enhance security provide unique opportunities in research and development involving significant transport phenomena components. Topics related to transport phenomena include but are not limited to biological and chemical threat detection, biosensors, aerosol generation and dispersion, distributed power generation, portable power infrastructure, fire protection and particle transport. A few fundamental transport phenomena problems related to security are presented below.
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It is imperative to create a real time capability of emergency response against chemical, biological, or radioactive attacks or accidents so that the resultant fatalities can be reduced to minimum (Pepper, 2007). The long term effects of these events on the environment are also crucial as different substances behave differently. The effects of chemical agents are strongest at its initial release and decay with time. The effects of biological agents initially increase with time until reaching a peak, after which the effects gradually decay. On the contrary, it can take a relative long time to see the effects of radioactive agents by which time it is often too late to undo the damages. Diffusive and convective mass transfer play a significant role on prediction of propagations of these agents under different weather conditions. Wang et al. (2005) developed a 3-dimensional finite element model for using Lagrangian particle transport technique to simulate contaminant transport for emergency response. The real-time simulation will allow instant prediction of trajectory and risk of contamination of the chemical, biological and radioactive agents. Figure on the right shows how containment particles introduced at a corner of a table disperse in an office suite (Pepper, 2007). The door is open and the air inlet velocity at the door is 1 m/s. The containment particles are transported through diffusion and convection from the source in the secretary’s room to the manager’s room.
Another area of security that transport phenomena play a significant role in is fire safety (Atreya, 2007). While both combustion and fire are exothermic chemical reaction processes between fuel and oxidant, combustion is usually a useful process where chemical energy in the fuel is extracted and converted to heat, whereas fires are often results of natural or human disasters. Due to the small scale involved in combustion, detailed numerical modeling of the physical and chemical processes at highly resolved temporal and spatial scales is possible. On the contrary, the large temporal and spatial scales involved in fire simulation do not permit simulation of the onset of fire because the transport phenomena and chemical reactions during onset of fires occurs at temporal and spatial scales below the resolution limits of the most practical calculations (McGrattan et al., 2002).
Another difference between combustion and fire is that combustion takes place in a relatively small scale but fire usually occurs at a very large scale. Fire is not considered as a design load in the prediction and evaluation of structural performance in current design practices. For example, the World Trade Center (WTC) towers could have sustained the impact of the planes during the attack on September 11, 2001, but the resulting fires caused structure failures which lead to total collapse (Usmani et al., 2003). In order to consider fire as a design load, it is imperative to develop a science-based set of verified tools to evaluate the performance of the entire structure under realistic fire conditions. Since the building materials are not intended for use as fuel, the data to characterize the fuel and the fire environment are not available (Baum, 2000); this makes development of reliable simulation tools more challenging. The physical and chemical phenomena that occur during fire that cause structure damage include fire dynamics, thermal response, and structural response; these phenomena cross many temporal and spatial orders of magnitude (Prasad and Baum, 2005). Fire dynamics includes modeling and simulations of combustion, fluid mechanics, convective heat and mass transfer, and most importantly, radiation heat transfer in the gases (air and/or smoke). Thermal analysis involves simulation of heating and cooling of the building materials. Finally, the structural analysis involves modeling displacements, stresses, and loss of load carrying capacity of the structure. Heat and mass transfer play dominant roles in fire dynamics and thermal responses analysis, which subsequently provide the needed data for structure analysis.
References
Atreya, A., 2007, “Transport Phenomena in Fire Security of the Built Infrastructure,” Presentation on National Science Foundation Workshop: Frontiers in Transport Phenomena Research and Education, Storrs, CT.
Baum, H.R., 2000 “Large Eddy Simulations of Fire,” Fire Protection Engineering, Vol. 2, pp. 36-42.
Faghri, A., and Zhang, Y., 2006, Transport Phenomena in Multiphase Systems, Elsevier, Burlington, MA.
Faghri, A., Zhang, Y., and Howell, J. R., 2010, Advanced Heat and Mass Transfer, Global Digital Press, Columbia, MO.
McGrattan, K. B., Baum, H. R., Rehm, R., Forney, G. and Prasad, K., 2002, “The Future of Fire Simulation,” Fire Protection Engineering, Vol. 13, pp. 24-36.
Pepper, D., 2007, “Creating a Real Time Emergency Response Capability,” Presentation on National Science Foundation Workshop: Frontiers in Transport Phenomena Research and Education, Storrs, CT.
Prasher, R., Bhattacharya, P., and Phelan, P.E., 2005, “Thermal Conductivity of Nanoscale Colloidal Solutions (Nanofluids),” Physical Review Letters, Vol. 94, pp. 025901-1–025901-4.
Usmani, A. S., Chung, Y. C., and Torero, J. L., 2003, “How Did the WTC Towers Collapse: a New Theory,” Fire Safety Journal, Vol. 38, pp. 501-533.
Wang, X., Pepper, D. W., Chen, Y., and Hsieh, S., 2005. “A Three Dimensional Finite Element Model for Emergency Response,” 43rd AIAA Aerospace Sciences Meeting and Exhibit, January 10-13, Reno.