Heat-up rates

The thermal mass of parts and tools and the heating capacity of the autoclave naturally limit the maximum heating rate. Attempting to increase the heat-up rate by overheating the autoclave air can result in overheating of areas of the assembly with low thermal mass. 

T = bulk heat-up rate driven by an external heat source, °C/sec TIME-TO-MAXIMUM RATE... 

T = bulk heat-up rate due to external heating alone, °C/min tj j. = time-to-maximum rate as determined by Equation 12-5 with tempertaure T set equal to min... 

Care necessary in commissioning and in heat-up rates due to viscosity changes in medium. 

Many studies on direct liquefaction of coal have been carried out since the 1910 s, and the effects of kinds of coal, pasting oil and catalyst, moisture, ash, temperature, hydrogen pressure, stirring and heating-up rate of paste on coal conversion, asphaltene and oil yields have been also investigated by many workers. However, few kinetic studies on their effects to reaction rate have been reported. 

Heat-up rate effects have been investigated with respect to microwave synthesis of AlPO phases, however there are few publications concerning the heat-up effects in conventional heating [58]. There has also been at least one study of pH and H2O level on aluminophosphate crystallization [59]. A recent paper attempts to study the unique crystallization process of several aluminophosphate molecular sieve compositions [60]. 

Part heat-up rate during autoclave processing can dramatically influence final part quality. At least three variables can affect the autoclave heat-up rate for composite parts (1) tool material and design, (2) the actual placement of the tool within the autoclave, and (3) the autoclave cure cycle used. Recommendations for the design of an individual tool are fairly obvious and well understood in industry (e.g., thin tools heat faster than thick tools materials with a high thermal conductivity heat faster than those with lower thermal conductivity and tools with well-designed gas flow paths heat-up faster than those with restricted flow paths [e.g., tools... 

The location of tooling within the autoclave can also affect the heat-up rate. Gas flow studies conducted previously [16] showed that for large commercial autoclaves, higher heatup rates are experienced near the door due to the turbulence of the gas flow bouncing off the door and then decreases as it flows toward the rear. This phenomena is dependent on the actual design of the autoclave and its gas flow characteristics. 

Griffith, J.M., Campbell, F.C., Mallow, A.R., Effect of Tool Design on Autoclave Heat-Up Rates, Society of Manufacturing Engineers, Composites in Manufacturing 7 Conference and Exposition,... 

Heat Heat-up Rate 1 to Intermediate Hold Temperature... 

Heat Heat-up Rate 2 to Final Hold Temperature. 

When a PTV instead of a classic injector was utilized in the analysis of penicillin residues, the sensitivity and the precision of the analysis were markedly improved (45). With the cooled PTV injector, some microliters could be injected, and the split-splitless mode allowed solvent venting at low injector temperatures with open slit in a first step, and quantitative transfer of volatile or derivatized drugs by a freely selected linear heat-up rate between 2-12 C/s in the splitless mode in the second step. Sensitivity could be enhanced by multiple injections before heat-up. Nonvolatile components of a sample did not contaminate the chromatographic system, since they accumulated in the glass vaporization tube, which could be changed easily. 

The linear heat up rate is important in temperature-programmed units. Temperature rates from about 0.25 to at least 10°C/min should be available. The temperature steps at the bottom end should be small for capillary columns. Program rates in excess of 10°C/min are rarely useful (33). The penalty of large increases in temperature for small decreases in retention times does not warrant program rates above about 10°C/min. 

However, for "cleaning out" the column, faster "ballistic" heat-up rates are desirable. This puts demands on the oven design (low mass oven) and temperature controller. 

Experimental. The test program to study the effects of temperature, hydrogen pressure, particle size, and heat-up rate on the rate and extent of kerogen removal from the shale was carried out with a thermobalance, as diagramed in Figure 1. The design and operation of the equipment have been described in an earlier publication (2). 

In most of the runs, the shale sample (as pebbles) was contained in a stainless steel, wire screen basket, 1/4-3/8 in. in diameter and 3 in. high. The reactor section was brought to the desired initial temperature with a stabilized gas flow stream at about 10 standard cu ft/hr. The sample was lowered into the reactor, and the power to the heating elements was adjusted to achieve the desired heat-up rate. The heat-up rates used included slow (about 15°F/min), fast (about 35°F/min), and very rapid, in which case the sample was lowered quickly into a preheated... 

Figure 3 shows the residual organic carbon for the range of hydrogen pressures and heat-up rates studied. In all of these runs, the final temperature was 1300°F. Apparently kerogen recovery above 1000° F is extremely pressure sensitive. 

Procedure. One hundred grams of coal liquid was combined with a predetermined amount of presulfided Co-Mo-Al catalyst and charged to the autoclave. Reaction temperature for the runs varied from 360 to 435°C, depending on the run. A stirring setting of 1000 rpm was used, and the initial total pressure was varied from 1500 (10.4 MPa) to 2500 (17.3 MPa) psig. The heat-up rate was about 12 to 20°C/min, thus requiring a total heat-up time of about 20-25 minutes. 

The amount of the applied adhesive and the final bond line thickness must be monitored because they can have a significant effect on joint strength. Curing conditions should be monitored for pressure, heat-up rate, maximum and minimum temperatures during cure, time at the required temperature, and cool-down rate. The primary concerns are to ensure the following ... 

The vehicle used was tetrahydronaphthalene (tetralin). Rapid heat-up rates were obtained by immersing the microautoclave in a preheated fluidized sand bath at 425°C. The microautoclave reached reaction temperature in 1-2 minutes. Slow heat-up rates were obtained by immersing the microautolcave in the fluidized sand bath at room temperature and gradually heating the sand bath to reaction... 

Figure V. Effect of heat-up rate on coal conversion using presulfided catalyst precursors.

Generally, the heat -up rate of an actuating medium in an applied electric field is... 

THF-soluble, pentane-insoluble yields at 15°Clsec heat-up rate ( ) yields of THF-soluble, pentane-insoluble products at rCIsec heat-up rate ( ) yields of carbon converted to THF-soluble, pentane-insoluble product as a percent of the total carbon in the coal (O) yields of pentane-insoluble, benzene-soluble products (D) yields of pentane-soluble products after removal of tetralin and naphthalene and other components boiling below 150°C at 10 torr. 

Thermogravimetric and Differential Thermal Analysis has been performed on Cat D. The TG and DTA profiles in Fig 2 show three different steps. The first one is the evaporation of hydrocarbons up to 200 °C with a moderate endotherm. The second step is the oxidation reaction of metal sulfides to oxides (most of the Mo sulfide, and part of the Co sulfide), starting around 200-250 °C. The third step around 350-450 °C is strongly exothermic, due to carbon burn-off as well as the remaining of sulfides oxidation. The carbon bum-off reaction finishes around 500 °C in this experiment performed on a dynamic mode at the heating-up rate of 5 °C/min. 

HP-TPR The High Pressure Temperature Programmed Reduction (HP-TPR) with Mass Spectrometer (MS) from FISONS Instruments was performed to observe the activation reactions of the presulfided catalyst under H2 at 20 bars and 240 °C/hr heating-up rate. 

An interesting aspect of both of these procedures is that a fast heat-up rate on the final 950°C calcine appears to be crucial to success. A second puzzling aspect of this system is that if one tries to sinter powders at temperatures of 950 to 975°C which have only been calcined to 850°C, poor superconducting materials will result, even though XRD shows the powder to be pure 1-2-3. 

All of the activations represented in Figure 250 were carried out with the same heat-up rate. Space velocity does not take into account the effect of the thermal ramp rate. One might expect that doubling the heat-up rate would also double the rate of water vapor release, and therefore the... 

An example of how the model works is shown in Figure 252, in which a typical commercial activation is represented. 273 kg of Cr/silica was charged to an activator. The catalyst was heated to 800 °C at the standard linear ramp rate of 1.4 °C min 1 and an air velocity of 6.4 cm s Then the temperature was held at 800 °C for 12 h. To obtain a predicted conversion, the activation profile (temperature vs. time) was first plotted (Figure 252) and the concentration of water vapor in the gas stream was calculated from the temperatures shown in the plot and a library of laboratory TGA curves that indicate how much water is evolved at each temperature and heat-up rate. The conversion of the chromium to Cr(VI) was calculated at each temperature from the calculated concentration of water vapor by use of the stability curves shown in Figure 251. The Cr(VI) content was found to be high when the temperature reached 500 °C, but it dropped quickly as the temperature was raised, reaching only 0.37% Cr(VI) at 800 °C (Figure 252). 

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