Pool fire heat transfer

Gritzo, L. A, et al., 1995a, Heat Transfer to the Fuel Surface in Large Pool Fires, Transport Phenomenon in Combustion, S. H. Choa (ed.), Taylor and Francis Publishing, Washington, DC. 

Liquid Pool Flames. Liquid fuel or flammable spills often lead to fires involving a flame at the surface of the liquid. This type of diffusion flame moves across the surface of the liquid driven by evaporation of the fuel through heat transfer ahead of the flame. If the liquid pool or spill is formed at ambient conditions sufficient to vaporize enough fuel to form a flammable air/fuel mixture, then a flame can propagate through the mixture above the spill as a premixed flame. 

For liquids boiling from a pool the boiling rate is limited by the heat transfer from the surroundings to the liquid in the pool. Heat is transferred (1) from the ground by conduction, (2) from the air by conduction and convection, and (3) by radiation from the sun and/or adjacent sources such as a fire. 

Smoke is composed of combustion gases, soot (solid carbon particles), and unburnt fuel. For outdoor fires, the impact of smoke is usually a secondary consideration after the heat transfer. In many circumstances, the immediate thermal threat from the fire plume (jet, pool, or flash fire) overwhelms the smoke threat, particularly for personnel in close proximity to the event. There may be circumstances where personnel are in a downwind smoke plume where there is no immediate thermal threat. As a rule-of-thumb, all people within a smoke plume may be immediately or nearly immediately affected and at risk from a life safety standpoint (be it from lack of visibility or by toxic products). 

The UL 2085 tank construction is intended to limit the heat transferred to the primary tank when the AST is exposed to a 2-h hydrocarbon pool fire of 1093°C (2000°F). The tank must be insulated to withstand the test without leakage and with an average maximum temperature rise on the primary tank not exceeding 2TC (260 F). Temperatures on the inside surface of the primary tank cannot exceed 204°C (400°F). 

SwRI 97-04, Standard for Fire Resistant Tanks, includes tests to evaluate the performance of ASTs under fire and hose stream. This standard is similar to UL 2080 in that the construction is exposed to a 2-h hydrocarbon pool fire of 1093°C (2000°F). However, SwRI 97-04 is concerned only with the integrity of the tank after the 2-h test and not concerned with the temperature inside the tank due to the heat transfer. As a result, UL 142 tanks have been tested to the SwRI standard and passed. Secondary containment with insulation is not necessarily an integral component of the system. 

Jensen, K.A., Ripoll, J.-F., Wray, A.A., Joseph, D., and El Hafi, M. On various modeling approaches to radiative heat transfer in pool fires. Combustion and Flame, 2007. 148(4), 263-279. 

Dembele, S., Zhang, J., and Wen, J.X. Assessments of spectral narrow band and weighted-sum-of-gray-gases models for computational fluid dynamics simulations of pool fires. Numerical Heat Transfer Part B, 2005.48(3), 257-276. 

Matthews, L., Harris, A., and Garcia, G. "Radiative Flux Measurements in a Sooty Pool Fire Using a Multihead Transpiration Radiometer." In Heat Transfer Phenomena in Radiation, Combustion, and Fires, edited by R. K. Shah, 375-80. New York ASME HTD-Vol. 106,1989. 

Yin, J. et al. 2013. Experimental study of n-Heptane pool fire behavior in an altitude chamber. International Journal of Heat and Mass Transfer 62(0) 543-552. 

ABSTRACT The determination of loads from accidental fires with realistic accuracy in the oil gas industry offshore and petrochemical industry onshore is important for the prediction of exposure of persoimel, equipment and structures to the fires. Standards, Codes of Practice and other similar publications refer to thermal loading from jet fires from 100 to 400kW/m and from 50 to 250kW/m for pool fires. The application of inappropriate fire loads may lead to incorrect predictions of fatalities, explosion of pressure vessels and collapse of structures. Further uncertainties are associated with heat transfer from the flame to pressure equipment and strucmres, and their behaviour when affected by accidental fires. The Paper presents results of a review of fire models from various Standards and Codes of Practice, and data obtained from full scale tests. A parametric study of the various methods used in the industry is presented. A simulation-based reliability assessment (SBRA) method has been applied to quantify potential accuracy range and its consequences to fire effects on structures. 

BAINBRIDGE, B.L., KELTNER, N.R., Heat transfer to large objects in large pool fires, J. Hazard. Mater. 20 (1988) 21 0. 

For high volatility liquids, the vaporization rate of the pool is controlled by heat transfer from the groimd (by conduction), the air (both conduction and convection), the sun (radiation), and other surrounding heat sources such as a fire or flare. The cooling of the liquid due to rapid vaporization is also important. 

Once an ignition has occurred, a pool fire results and the dominant mechanism for damage is via thermal effects, primarily via radiative heat transfer from the resulting flame. If the release of flammable material from the process equipment continues, then a jet fire is also likely (see Section 3.7). If the ignition occurs at the very beginning of the release, then inadequate time is available for the liquid to form a pool and only a jet fire will result. 

Equations (3.51) to (3.53) apply to liquid pool fires on land. For pool fires on water, the equations are applicable if the burning liquid has a normal boiling point well above ambient temperature. For liquids with boiling points below ambient, heat transfer between the liquid and the water will result in a burning rate nearly three times the burning rate on land (Mudan and Croce, 1988). 

Pool fires have some of the characteristics of vertical jet fires, but their convective heating is much less. Heat transfer to objects impinged or engulfed by pool fires is both by convection and radiation. Once a pool of liquid is ignited, gas evaporates rapidly from the pool as it is heated by the radiation and convective heat of the flame. This heating mechanism creates a feedback loop whereby more gas is vaporized from the surface of the liquid... 

PHENTX, SUPERPHENIX and PFR are so-called pool reactors, whereas the other three projects are loop reactors. In a pool reactor, the whole primary heat transfer system including main pumps and intermediate heat exchangers is integrated into the reactor vessel (pool), while the loop reactors have parallel primary sodium heat transfer circuits (loops) with the main heat transfer components external to the reactor vessel. The secondary heat transfer system, installed between primary system and water/steam system for safety reasons, is practically identical in both cases. It also consists of three parallel circuits. Live steam conditions and the achievable efficiency are very similar in all plants 500°C, 165 bar, 40%. These are close to the conditions of coal-fired stations. 

The evolution of the fire depends on many parameters linked to the volume of the call and the heat transfer conditions. In reality tye phenomena are more complex due to the fact that the pool is not really at rest and contact between Na and air is modified. The various phenomena have to be modelled in codes (see below). 

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