Thermal soak time

Dynamic Mechanical Spectroscopy (DMS). Rectangular bars (3 x 12 x 45 mm) were cut from the molded plaques and dynamic mechanical spectra (DMS) obtained using a Rheometrics System-4. Values of G. G" and tans at various temperatures were obtained by oscillatory torsion of the bars at 1 Hz and 0.2% shear strain temperatures were varied between -100°C and 120°C at 5°C Intervals in the transition regions and at 10°C intervals elsewhere. Thermal soak times were five minutes in all cases. 

Most coking heaters have several thousand pounds per hour of high-pressure steam injected into the heater tubes. The velocity steam should increase the linear velocity of resid in the lubes, shorten oil residence time, and hence reduce the thermal soaking time to which the resid is exposed. This ought to reduce the formation of coke in the heater tubes. In practice, there seems little correlation between the amount of velocity steam used and the rale at which coke builds up in the lubes. 

The thermal soak time can be different depending on the final pyrolysis temperature [24]. This parameter may be used to fine-tune the transport properties of a ear-bon membrane using a particular final pyrolysis temperature [91], Previous studies showed [41,87, 89, 91,92] that increments in thermal soak time would inerease the selectivity of carbon membranes. It is beheved that only mierostmctural rearrangement occurs during the thermal soak time, thus affeeting the pore size distribution and average porosity of carbon membranes [34]. 

Nitrogen gas pyrolysis system was designed and set up to transform the PAN hollow fiber membrane into PAN-based carbon hollow fiber membrane. The instrument involved in this system is illustrated in Fig. 5.3. Caibolite (Model CTF 12/65/550) wire wound tube furnace with the Eurotherm 2416CC temperature control system is used for the pyrolysis of the PAN hollow fiber membrane. The furnace can be operated at a maximum temperature of 1200°C and has the abihty to control the heating rate and the thermal soak time during the pyrolysis process. 

Thermal soak time at maximum pyrolysis temperature... 

The solid so obtained was introduced in two different sealed refractory crucibles and immersed in a coke bed. One of the crucibles was submitted to the following thermal treatment in an electric furnace 20-1000 "C at 5"C/min. heating rate, followed by 3 h soaking time at this temperature, obtaining a porous solid composite called SC-100. The other crucible was treated in equal conditions but varying the final temperature to 1550 °C, obtaining in this case another porous composite called SC-155. The SC-155 showed a little volumetric expansion respect to the SC-100 material. (The names SC-100 and SC-155 means S= silica C= carbon and the number is the treatment temperature in °C/10). 

Both steps 3 and 4, can be carried out in the same kiln/reactor and no cooling down is necessary between steps. Soaking times at these two temperatures are around 1 hour for each. Compared with carbons produced by thermal activation, the wood-based carbons activated with H3PO4 have a lower density, lower abrasion resistance and a more developed mesoporosity. These properties are related to the hollow fibrous structure of wood, which gives rise to an important macropore volume in the activated carbons. 

In the second heat treatment, the temperature is higher than that required for H3PO4 activation, and similar to the temperatures used in the case of thermal activation. The beatment requires a soaking time of approximately one hour at maximum temperature. After carbonization, the product is washed with water (or HCl and water) to remove any soluble salts and to recover the carbon. The latter step also removes some of the original mineral matter contained in the raw material. 

Soak times may be required when heating up the PCS, especially when large limiting components are involved in the heatup. Soak times are used so that heating can be carefully controlled. In this manner thermal stresses are minimized. An example of a soak time is to heat the reactor coolant to a specified temperature and to stay at that temperature for a specific time period. This allows the metal in a large component, such as the reactor pressure vessel head, to heat more evenly from the hot side to the cold side, thus limiting the thermal stress across the head. Soak time becomes very significant when the PCS is at room temperature or below and very close to its RT dt temperature limitations. 

To compare heating (soak) times and production rates of copper alloys with those of steel, use equations 3.6 and 3.7, both based on the ratio of diffusivities. (See also eq. 3.2a and 3.2b and fig. 3.25.) Thermal diffusivity (see glossary), a = thermal conductivity divided by volume specific heat, k/c(p). 

Thermal Soak. During this step, the solder, board, and components are further heated. The flux from the solder paste flows onto all metal surfaces in which it is in contact, continnes to react away surface oxides, and also acts as a barrier to prevent oxidation. The soak is designed to provide the requisite time and thermal energy for the flux s prolonged chemical reaction with oxides and tarnishes on metal surfaces and the solder. Were the flux to activate fully too early in the process, it could dry out or be spent too soon. If its potency is lost, fluxed metal surfaces will reoxidize in the critical moments before the onset of solder hquidus, and solder wetting (alloying) would be inhibited. 

W. Khongwong, M. hnai, K. Yoshida, T. Yano, Influence of raw powder size, reaction temperature, and soaking time on synthesis of SiC/Si02 coaxial nanowires via thermal evaporation, J. Ceram. Soc. Jpn. 117 (2009) 439-444. 

Test conditions temperature cycling between —54°C and 75°C, soak time of 2 hr in each chamber. Thermal fatigue failure rate (in percent) was determined by detecting a 360° crack around the solder fillet at a magnification of 40 x at the first cycle and every 25 cycles thereafter. 

In general, the thermal profile created for the reflow furnace contains several distinct regions namely the initial ramp, a dwell at elevated temperature, a ramp to the maximum temperature, and a cool down region, as illustrated in Figure 39. The critical reflow profile parameters that must be controlled are the peak reflow temperature, oxygen level, dwell time above liquidus, soak time, ramp rate, cooling rate, conveyor speed, and the temperature difference across an assembly (AT). If the ramp rate is too low, the assembly may not attain the required soak temperature soon... 

On the same machine and with the same flexural jig, the flexural strength (a), up to 1500°C in air or Argon, was measured on chamfered bars 25 x 2.5 x 2 mm Gength X width x thickness, respectively), using a crosshead speed of 0.5 mm/min. For the high-temperature tests, a soaking time of 18 min was set to reach thermal equilibrium. Five specimens were used for each temperature point. 

The cmde phthaUc anhydride is subjected to a thermal pretreatment or heat soak at atmospheric pressure to complete dehydration of traces of phthahc acid and to convert color bodies to higher boiling compounds that can be removed by distillation. The addition of chemicals during the heat soak promotes condensation reactions and shortens the time required for them. Use of potassium hydroxide and sodium nitrate, carbonate, bicarbonate, sulfate, or borate has been patented (30). Purification is by continuous vacuum distillation, as shown by two columns in Figure 1. The most troublesome impurity is phthahde (l(3)-isobenzofuranone), which is stmcturaHy similar to phthahc anhydride. Reactor and recovery conditions must be carefully chosen to minimize phthahde contamination (31). Phthahde [87-41-2] is also reduced by adding potassium hydroxide during the heat soak (30). 

Secondary recovery, infill drilling, various pumping techniques, and workover actions may still leave oil, sometimes the majority of the oil, in the reservoir. There are further applications of technology to extract the oil that can be utilized if the economics justifies them. These more elaborate procedures are called enhanced oil recovery. They fall into three general categories thermal recoveiy, chemical processes, and miscible methods. All involve injections of some substance into the reservoir. Thermal recovery methods inject steam or hot water m order to improve the mobility of the oil. They work best for heavy nils. In one version the production crew maintains steam or hot water injection continuously in order to displace the oil toward the production wells. In another version, called steam soak or huff and puff, the crew injects steam for a time into a production well and then lets it soak while the heat from the steam transfers to the resei voir. After a period of a week or more, the crew reopens the well and produces the heated oil. This sequence can be repeated as long as it is effective. 

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