Temperature-time profile

The hydration rate of sodium tripolyphosphate to its stable hexahydrate, Na P O Q 6H20, directly affects detergent processing and product properties. The proportion of STP-I (fast-hydrating form) and STP-II (slow-hydrating form) in commercial sodium tripolyphosphate is controUed by the time—temperature profile during calcination. In most processes, a final product temperature of near 450°C results in a product containing about 30%... 

Henry and Fauske (1975, 1976) have proposed a model to describe the events leading to a large-scale vapor explosion in a free contact mode. Their initial, necessary conditions are that the two liquids, one hot and the other cold, must come into intimate contact, and the interfacial temperature [Eq. (1)] must be greater than the homogeneous nucleation temperature of the colder liquid. Assuming the properties of both liquids are not strong functions of temperature, the interface temperature is then invariant with time. Temperature profiles within the cold liquid may then be computed (Eckert and Drake, 1972) as... 

Fig. 2. Time—temperature profile for kettle calcination. Points A—B represent the fill period B—C, the boil or drag C—D, falling rate or cook-off D, discharge for hemihydrate. Points D—E show firing rate to second boil E—F, second boil F—G, second cook-off G, second-settle discharge.

The cure reactions, the viscosity-time-temperature profile, the processing conditions, the resultant epoxy chemical and physical structure, and the mechanical response of a C-fiber/TGDDM-DDS cured epoxy composite are modified by the presence of a BF3-amine complex catalyst within the prepreg. These factors also will be modified... 

Apply the time-temperature profile necessary to crystallize the sample. 

The sterilization process time is determined from the design F value and the product heat transfer data. The sterilization cycle design must be based on the heating characteristics of the load and of containers located in the slowest heating zone of the load. The variation in the rate of heating of the slowest heating zone must be known, so this variation must be determined under fully loaded conditions. The effect of load-to-load variation on the time-temperature profile must also be determined. Then, the statistically worst-case conditions should be used in the final sterilization process design. 

In estimating the sterilization time for the medium, one must define the contamination, the desired degree of apparent sterility, and the time-temperature profile of the medium that is, T = f(t). For typical bacterial spore contaminants, the constants used in most designs have the following values. 

This allowed the determination of the reduced parameter (T-T ) during cure of the resin under a variety of time-temperature profiles. The dynamic mechanical properties were then estimated as a function of (T-T ). This estimate is compared with the results of torsion impregnated cloth analysis of the curing of the ATS resin. 

Preceramic Polymer Pyrolysis. Chemical options also are available for the pyrolysis step. Certainly, the rate of pyrolysis, that is, the time-temperature profile of pyrolysis, is extremely important. However, the gas stream used in pyrolysis also is of great importance. Inert- or reactive-gas pyrolysis can be carried out. 

Figure 8-21 Numerically Predicted Time-Temperature Profile at the Center of a Canned 3.5% Cornstarch Dispersion Intermittently Rotating at 0 and 146 rpm, and Experimental Heat Penetration Data.

The effect of different flow properties on heat transfer to canned dispersions undergoing intermittent axial rotation was studied by Tattiyakul et al. (2002b). In addition to the 3.5% cornstarch dispersion discussed above, a 5% CWM dispersion whose rheological data are shown in Figure 8-9 and a tomato concentrate that followed a simpler thermo-rheological behavior were studied. Because of the high apparent viscosity over a wide temperature range of the CWM dispersion, it had the slowest time-temperature profile (not shown here). Results on the effect of continuous axial rotation on heat transfer to a canned starch dispersion can be found in Tattiyakul (2001). 

To estimate the lowest temperature maximum which might have been reached soon after the intrusion occurred, some insight into the time-temperature profile is necessary and some assumptions are required concerning the rate at which crystallization and cooling of the sill took place. Daly (29) gives estimates for the crystallization of magma in contact with air of 3 and 300 yr for sill thicknesses of 10 and 100 m. Direct extension of these estimates to a subterranean sill is unwarranted but if applied cautiously they can provide the order of magnitude. 

Fig.3 - Time-temperature profiles at several radial positions for beech wood cylinders exposed to Q=28 and 49kW/m. ... 

Fig.4 - Time-temperature profiles at the sample centerline for chestnut (dashed lines) and beech (solid lines) wood cylinders exposed to several radiation intensities.

---