FIRE RESEARCH Fundamental Studies Smoldering combustion Ignition Flame spread Heat release Thermal properties Applied Fire Research Project management Experimental fires of various sizes Data analysis Test Method Development Design and development of fire test apparatuses and methods Development of measuring techniques Recent Research Project: RESEARCH PAPER ACCEPTED FOR PUBLICATION IN FIRE AND MATERIALS SURFACE TEMPERATURE MEASUREMENTS ON BURNING MATERIALS USING AN INFRARED PYROMETER: ACCOUNTING FOR EMISSIVITY AND REFLECTION OF EXTERNAL RADIATION Joe Urbas ~ William J. Parker ~ Gerald E. Luebbers Abstract This paper demonstrates the successful use of an infrared pyrometer, operating in the 8 to 10 micron wavelength band, to measure the surface temperature of combustible specimens in a heat release calorimeter. The temperature histories of ten different materials were measured in the ICAL (Intermediate Scale Calorimeter). The set of materials comprised of four wood products, gypsum board, polyisocyanurate foam, PVC floor tile, PMMA and two non-combustible boards. A small-diameter bare thermocouple was installed on each specimen in order to determine an accurate temperature for comparison. The spectral emissivity and the spectral flux reflected from the surface were measured simultaneously and used to correct the apparent temperature measured by the pyrometer. The spectral emissivity and reflected spectral flux were both constant prior to ignition for all of the combustible materials. During the burning phase all of the combustible materials had a spectral emissivity very close to unity. The agreement between the temperatures measured with the pyrometer and thermocouple was not affected by the flame. The wood products, the polyisocyanurate foam and the calcium silicate board required no correction for reflected spectral flux over the whole temperature range. Current research project (Two year project sponsored by BFRL, NIST, Grant No.: 70NANB3H1113) TECHNIQUES FOR OBTAINING AND USING THE PROPERTY DATA NEEDED TO CALCULATE THE BOUNDARY CONDITIONS IN THE CFD FIRE MODELS Summary Project Description Primary Objective To develop a heat of gasification based system for predicting the burning rate of charring and non-charring materials that can be tested in the vertical orientation. This would include its measurement, calculation and introduction into the CFD fire models. Problem The heat release rate (HRR) calorimeters measure and report the HRR as a function of time at a well defined external flux. The burning rate of a char forming material is controlled by the net heat flux as a function of the char depth which is proportional to the mass loss. The heat of gasification is not a constant for char forming materials. If the model used the heat of gasification, a new value would be needed at every time step. The current models are not set up for that. Before the model can make use of the heat of gasification, it must calculate the net heat flux which depends on the surface temperature. The model can only calculate the average temperature of the char layer. The ratio of these temperatures (TS/Tave) must be given to the model at each time step. The model can only predict the fire behavior of the object if it has the same thickness and rear surface boundary condition as the specimen tested. To lift this restriction the heat of gasification would need to be calculated. This will require a more complete understanding of the controlling mechanisms. Approach In addition to the infrared pyrometer already in place for continuous measurement of the surface temperature, the ICAL will also be instrumented with several total heat flux gauges so that it will be able to measure the net heat flux throughout the test as well as the external radiant flux. Since the ICAL also measures the mass loss rate throughout the test, the heat of gasification can be calculated as a function of the total mass loss up to each time step. The ICAL instrumented in this way becomes a "heat of gasification calorimeter." It is also well equipped to measure the properties of the material. A catalytic converter along with additional oxygen is put into the sampling stream from the exhaust duct to insure complete oxidation of the volatile pyrolysis products. From the concentrations in the gas analyzers, the overall chemical composition of the volatiles and the carbon deficit going into char formation can be determined. From the accumulated heat and the mass of the char, its average temperature can be obtained. Thus the ratio, TS/Tave can be determined as a function of the mass loss. If the model is given the heat of gasification and the TS/Tave ratio both as a function of integrated mass loss and it keeps track of the total predicted mass loss up to the present time step, it can find the correct heat of gasification and TS/Tave to use at each time step. There is a NIST LES model at PFL which would be modified to accommodate a variable heat of gasification. The first test of this approach would be to predict the HRR of Douglas fir at 30, 45 and 60 kW/m2 in the ICAL. In order to develop a more fundamental understanding of the mechanisms that control the burning rate of materials, some of the specimens will be instrumented with embedded thermocouples to study the temperature profiles and to measure the thermal diffusivity of the char at high temperature.
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