Smoke Damage >> Smoke Damage Restoration Tips

Gandhi [98,99] performed some simple modeling of three types of gas collections systems that could be used in corrosion tests, the CNET test, the cone corrosimeter, and a third system that utilized a piston cylinder chamber. He used the mass fraction of an arbitrary corrosive component of the fire effluent, a, as an indicator of how each capture system works and Smoke Damage Restoration Tips developed design parameters for each test. 

However, the important quantity for determining corrosivity is the concentration. The non dimensionalized concentration measures for the three tests are also developed in Appendix C. For the CNET test, Smoke Damage Restoration Tips the concentration is much easier than the mass fraction and is simply(7)where Ca*is the non dimensionalized concentration, is the non dimensionlized time, ya is the production rate of product a in units of kg of product a produced per kg of fuel burned and f*is a non dimensionlized mass loss rate. 

Thus, at the end of the burning phase of the CNET test, the concentration of product a is dependent on the amount of product a produced by the material being tested. With one caveat, Smoke Damage Restoration Tips there is a very straightforward relationship between the test material and the concentration of a particular corrosive product. 

The caveat is that there is concern about the mass loss rate being limited by the available oxygen.To show how serious the concern about oxygen limited combustion is, Smoke Damage Restoration Tips assume that the oxygen lower limit is 15.5 %, then the maximum sample size that can undergo complete combustion given the stoichiometric oxygen to fuel ratio is calculable as shown in Figure 13. 

Note that the non dimensionalized mass of a test material in ISO 11907-2 is 1.0. A number of common materials Smoke Damage Restoration Tips could experience oxygen limited burning in the CNET test so some care must be taken with interpreting the results of the test. Modeling the cone corrisometer Gandhi makes two significant simplifications. 

The first is to assume that the test uses mass flow control instead of volume flow control and Smoke Damage Restoration Tips that the control is sufficiently good to maintain constant mass in the exposure chamber. The second is not so much a simplification as a potential for misunderstanding. Gandhi assumes that the amount of mass entering and leaving is related to the mass loss rate (MLR) by a fraction f. 

While there is no requirement for f to be a constant it is easy to make that mistake. To make the analysis easier, it is desirable to consider a constant mass flow (see details in Appendix C). Since the volume is constant and the assumption is the mass is also constant, Smoke Damage Restoration Tips then the mass fraction of product a.

Ya, is also the non dimensionalized concentration and is given by (8)where fin*is the non dimensionalized mass flowing into and out of the exposure chamber, Ya is the fraction of the mass in the exposure chamber that is product a and Smoke Damage Restoration Tips is the rate of the mass of air entrained by the fire to the MLR. 

The term represents the fraction of the total flow of mass, both effluent and entrained air, Smoke Damage Restoration Tips generated by the test sample in the cone. This term will overestimate the fraction of the mass flowing into the exposure chamber at points where the total mass flow from the product is less than the forced flow of the pump, but should not be a significant error.

The fifth paper by the PFPC compared the results of the four standards and performed extensive analysis [79]. They reviewed the entire project and Smoke Damage Restoration Tips then did an overall analysis of the results.They looked at three factors in the comparison and analysis:1. Precision – Is the test repeatable? Does the test differentiate corrosive potentials? 

2. Accuracy – Does the test differentiate corrosive potential consistent with known chemistry? Are the test results consistent with existing standards?3. Cost, availability and convenience – Is the test equipment accessible, easy to operate and mechanically sound? To assess repeatability, Smoke Damage Restoration Tips they looked at the average coefficient of variation (the standard deviation divided by the mean expressed as a percentage), as well as the standard deviation of the coefficient of variation. 

Their results are given in Table 8. Clearly the indirect tests were the most repeatable of all the tests. None of the direct tests had a particularly low average coefficient of variation. The question becomes Smoke Damage Restoration Tips are they sufficiently repeatable. To answer this question they used two statistical tests to see how many statistically differentiated groups each test could break the 24 products into. 

CNET differentiated product 20 into one group, product 19 into a second group and the rest into a final group. Overall, Smoke Damage Restoration Tips they found that none of the four test methods satisfied all the criteria for a useful corrosion test. Since the tests did not give the same rankings they were not interchangeable. They recommended that both the cone corrosimeter and the radiant panel needed to have their repeatability improved and that development on the CNET test should stop. 

Use of Smoke and Species Yields as Model Inputs While there are detailed combustion models available that fully address gas-phase chemistry, Smoke Damage Restoration Tips they are not practical for the large domains encountered in typical fire scenarios. As such,modeling of chemistry in most current computer fire models is not considered in detail beyond a one-step effective reaction and is largely a bookkeeping exercise based on a simple reaction of fuel and oxygen such as shown below [100].

For complete combustion of the simplest hydrocarbon fuel, methane reacts with oxygen to form carbon dioxide and water. The only input required is the pyrolysis rate and Smoke Damage Restoration Tips the heat of combustion. For fuels that contain oxygen, nitrogen, or chlorine, the reaction becomes more complex. 

In this case, the user specifies model inputs for the composition of the fuel and a nynon-ideal combustion yields (such as the production of soot or Smoke Damage Restoration Tips carbon monoxide) to allow the model to calculate the mass of species produced during combustion. 

Most typically, these are specified as molar yields (i.e., the number of moles of a given species produced per mole of fuel consumed in the combustion reaction), Smoke Damage Restoration Tips though other normalized values are also used 5. For example, for soot, the effective molar yield, νS, is related to the soot yield, yS, via the relation where Wf and WS are the effective molar mass of the fuel and soot, respectively. In most cases these are idealized estimates for actual complex fuels.

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