Time-temperature curve

Complicated problems of transient heat flow can be resolved by computer. Typical time-temperature curves for non-steady cooling are shown in Figures 16.1 and 16.2, and the subject is met again in Section 26.2. 

A common interpretation of the runaway stage is when both the first and second derivatives of the average time-temperature curve are positive. However, because we had an external heat source in our tests, we had to account for the external heater temperature "T ". 

Time-temperature curves for fire resistance for different types of materials are available from American Society for Testing and Materials (ASTM) Standard E 119 (Ref. 41). 

Brenden and Chamberlain (6) measured heat release rate from wall assemblies having fire-retardant-treated studs and gypsum board as interior finish in the FPL fire endurance furnace using three methods (a) the substitution method, by which the amount of fuel required to maintain the ASTM E-119 time-temperature curve for a... 

The FPL vertical wall furnace used in our study was described in some detail by Brenden and Chamberlain (6). This furnace is normally used to evaluate the fire endurance of wall assemblies. The basic guidelines for the furnace test method are given in the ASTM E-119 standard (5). The method was designed to evaluate the ability of a structure to withstand a standard fire exposure that simulates a fully developed fire. The furnace is gas fired, and its temperature is controlled to follow a standard time-temperature curve. A load may be applied to the assembly. The failure criterion can be taken as time at burnthrough, structural failure, or a specified temperature rise on the unexposed side of the wall—whichever comes first. The construction of the furnace is not specified in the ASTM E-119 standard. 

Calibration Test. Before the wall tests were carried out, a calibration test was conducted to evaluate burner performance and to check for agreement between fuel gas and heat release calculations. For this test, the furnace was closed with a masonry wall lined with a layer of ceramic blanket material. The ASTM E-119 time-temperature curve was followed for 60 min. 

One critical factor that affects the heat release rate is the availability of air. The furnace has to be designed so that many requirements can be met simultaneously (a) time-temperature curve of ASTM E—119, (b) adequate air supply, and (c) pressure requirement inside the furnace. To incorporate the heat release rate measurement into the ASTM E-119 standard, specifications must be made to address these three criteria. If these criteria can be agreed upon, the heat release rate measurement should be made a part of the existing test standard. 

Time Temperature Curves for Petroleum versus Cellulosic Fires... 

The technique and apparatus used in this work have been described in detail [81]. The reaction vessel was made hydrophobic by exposure to the vapour of trimethylchlorosilane and evacuated for several hours. Then isobutene, dried by sodium, and methylene dichloride, stored over calcium hydride, were distilled into it, the temperature adjusted, and the reaction started by the breaking of a phial containing a solution of titanium tetrachloride in methylene dichloride and one containing water. These could be broken in this, or the reverse, order, or simultaneously. The ensuing reaction was registered as a time-temperature curve by an automatic recorder. The range of conditions studied was [C4H8] = 0.05 -0.6 mole/1, [TiClJ = (0.1-5) x 10 3 mole/1, [H20] = (0.05-5) x 10 4 mole/1, T= 18°- -95°. 

Provided that the time-temperature curve obtained from the calorimetric experiments is wholly of first-order, or comprises a first-order section, usually after the inflection point of sigmoid reaction curves, a conventional analysis yields a first-order rate constant ku which is related to the concentration of monomer, m, and the initial concentration of initiator, c0, by the equations... 

Figure 5-17. Time-Temperature Curve for Fire Tests...

Fire resistance rating—The time period that a specific fireproofing design will protect structural supports for equipment, piping and so forth from collapse, when exposed to a fire of specified intensity. The fire intensity is usually represented by a time-temperature curve. 

Fig. 12 Time-torque curves for master batch preparations with XNBR and organoclay in the internal mixture at 160°C and 50 rpm rotor speed (a). Time-temperature curves for master batch preparations with XNBR and organoclay in the internal mixture at 160°C and 50 rpm rotor speed (b)...

Figure 9.2 Time-temperature curves for the destruction of M. tuberculosis (...), inactivation...

For the third classification, known as slow burning , the exposure is 20 minutes following the standard time-temperature curve (3). No flame from the specimen may reach the angle frame at any point, and all flaming must cease within 5 minutes after the test flame is discontinued. If a material fails to meet these test requirements, it is rated as combustible. For all classifications, there are restrictions as to the amount of material which may fall from the test panel during the exposure period. 

F (816°C), and 1,700°F (927°C), was described by an equation with an Arrhenius temperature-dependent rate constant. When specimens were exposed to the uniformly increasing fire temperatures of ASTM E119 (earlier linear portion of time-temperature curve) (30), the rate of char development was constant, after the more rapidly developed first 1/4 inch of char. Under the standard ASTM fire exposure, temperatures 1/4 inch from the specimen surface reached 1,400°F (760°C) at 15 minutes,... 

Fig. 33.—Time-temperature curves for wheat starch-water systems heated to 85°C by micro-waves (from Ref. 286).

ISO 834 (standard time/ temperature curve) International Cellulosic or wood fire (similar to ASTM E-l 19) [94]... 

Testing codes within the scenario of a fully developed fire are based on intermediate, large, or full-scale testing. Specimens are typically in the dimension of several square meters and often, real components such as building columns are tested, or the whole product in the case of gas bottles. Tests like the small-scale test furnace based on specimens of 500 mm x 500 mm are exceptions. Intensive flame application or the use of furnaces realizing standard time-temperature curves are used to simulate the characteristics of fully developed fires. Thus, in particular the heat impact of convection and the surface temperature are clearly greater than in the tests discussed earlier. The fire properties investigated are often resistance to fire, or the fire or temperature penetration. 

Thermal Drift or Slow Heat Evolution. Evidence for Very Narrow Pores. For the initial increments of curve a for nitrogen on the bare surface of bone mineral at —195° (V/Vm < 0.05), the observed time-temperature curves were normal, exhibiting no evidence for any slow heat evolution, and the same was true for increments at V/Vm > 0.4, as well as for all points represented in curves b and c. However, for increments of curve a in the region V/Vm = 0.05 to 0.4, heat continued to be liberated for some time after the initial rapid thermal process. For different nitrogen increments within this range of coverage the heat produced in this slow process was from 5 to 12% in excess of that instantaneously evolved. The slow process was observed over a period of 20 to 30 minutes. In one extreme case it was still not complete after 45 minutes, which was about the maximum practicable period for observation. 

There is some evidence that the heat of immersion of the well outgassed samples was liberated during a rather long time. Consequently, the heats of immersion of these samples, and also of some of the samples with small amounts of water adsorbed, were determined by integration of the recorded time-temperature curve from the time the samples were wetted until the temperature of the calorimeter had returned to its steady state. Sixteen hours were required in the case of the freshly outgassed samples instead of the 5 to 6 hours normally required. 

Fig. 5. Reconstructed time-temperature curves for the Brent Group in the Oseberg field, and timing of oil emplacement. After Dahl Yiikler (1991) and Walderhaug (1994).

Another method for measuring thermal diffusivity is the flash method developed by Parker et al. [48] and successfully used for the thermal diffusivity measurement of solid materials [49]. A high intensity short duration heat pulse is absorbed in the front surface of a thermally insulated sample of a few millimeters thick. The sample is coated with absorbing black paint if the sample is transparent to the heat pulse. The resulting temperature of the rear surface is measured by a thermocouple or infrared detector, as a function of time and is recorded either by an oscilloscope or a computer having a data acquisition system. The thermal diffusivity is calculated from this time-temperature curve and the thickness of the sample. This method is commercialized now, and there are ready made apparatus with sample holders for fluids. There is only one publication on nanofluids with this method. Shaikh et al. [50] measured thermal conductivity of carbon nanoparticle doped PAO oil. 

The relative amount of hard-burned lime from a particular kiln can be monitored by study of the time-temperature curve produced by the reactivity test (Fig. 26.7). Any increase in the time at which the maximum temperature begins to fall (by 0.2°C) indicates that the amount of slow-slaking calcium oxide has increased. 

FIGURE 6.1 Torque -time (temperature) curves obtained with the oscillating disc rheometer (ODR) and the moving disc rheometer (MDR). 

Figure 4.6-2 Experimental and calculated time-temperature curves for high-carbon run for two points within the particle ( = 0 and = 0.673). Bulk phase temperature 518°C. Initial particle temperature. (from Wang and Wen [17]).

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