Warm-up procedures

These systems have been operated in extremely low quality (and radioactivity contaminated) industrial environments for the past several years without any major equipment or component failures. Utilizing specialized operating/warm-up procedures, they have operated in low grade, out-of-doors, dust ridden, rain-soaked, industrial environments at temperature ranges which greatly exceed the original equipment manufacturers (OEM) specified limits. The systems have been successfully operated at ambient temperatures of minus 10 to plus 103 degrees Fahrenheit without any pre-mature or un-anticipated equipment failures. 

Lithium chloride precipitates during the warm-up procedure. 

Indeed, with mono-metallic studies, we have found that solvent polarity and warm-up procedure can drastically affect resultant crystallite sizes,(29) magnetic properties,(29,31) and ability to form stable colloidal solutions.(32,34) However, a bimetallic such as Au-Sn has not been examined in this way before (although other bimetallics have yielded interesting SMAD catalysts).(40,60,61,62,63)... 

The next series of experiments dealt with solvent variation. Table II summarizes solvent properties, matrix warm-up procedure, and properties of the resultant ultra-fine powder of AuSn obtained. (In these studies gold and tin were... 

Prior to the simulation at finite temperature, the system must be heated up to the target temperature and thermally equilibrated. The temperature should be distributed among all the normal modes in the system. Thermal equilibration usually requires running dynamics for a long period of time (of the order of picoseconds). This time may be shortened if the warm-up procedure does not displace the system far from equilibrium. Thus, the warm-up may be realized by a sequence of kinetic energy pulses, followed by a short relaxation (free dynamics). If these pulses are orthogonal, then different normal mode become excited. It should be emphasized also at this point, that prior to the constrained dynamics simulation, the warm-up and equilibration should be performed with the same constraints that will be used in the sampling simulation. 

It is not only the heat exchanger that has to be carefully monitored conditions upstream of the heat exchanger may promote fouling of the heat transfer surface. For instance long residence times in upstream equipment during "warm up" procedures may generate particulate matter, e.g. from polymerisation reactions, that subsequently deposit in a downstream heat exchanger. 

Schulenberg and Starflinger (2012) reported about a constant pressure start-up and shut-down system for the three-pass core design of the HPLWR, trying to keep the feed-water temperature constant to minimize thermal stresses of the reactor pressure vessel. This concept also includes a warm-up procedure for the deaerator during startup from cold conditions. A battery of cyclone separators is foreseen outside of the containment to produce some steam from depressurized hot coolant of the reactor. 

Where these valves are used, the time available to warm up the pipe work will be known, as it is set on the valve control. In other cases, details of the start-up procedure must be known so that the time may be estimated. Thus boilers started from cold may be fired for a short time, shut off for a period while temperatures equalize, and then fired again. Boilers may be protected from undue stress by these short bursts of firing, which extend the warm-up time and reduce the rate at which the condensate in the mains must be discharged at the traps. 

The placement of the NOx bed ahead of the oxidation bed causes a delay of the warm-up of the oxidation bed from a cold start. Since many of the materials considered for the reduction of NO are also excellent oxidation catalysts, the NOx bed is often used as the oxidation bed by the injection of secondary air during the first two minutes from a cold start. After the oxidation bed is warmed up, the secondary air is diverted from upstream of the first bed to upstream of the second bed. This procedure helps the emission reduction when the catalysts are fresh, but hastens the aging of the NOx catalyst as it is being exposed repeatedly to oxidation and reduction conditions. 

In both cases, the Au nanoparticles behave as molecular crystals in respect that they can be dissolved, precipitated, and redispersed in solvents without change in properties. The first method is based on a reduction process carried out in an inverse micelle system. The second synthetic route involves vaporization of a metal under vacuum and co-deposition of the atoms with the vapors of a solvent on the walls of a reactor cooled to liquid nitrogen temperature (77 K). Nucleation and growth of the nanoparticles take place during the warm-up stage. This procedure is known as the solvated metal atom dispersion (SMAD) method. 

Banks, R. E. et al., J. Chem. Soc., Perkin Trans. 1, 1974, 2535-2536 During an increased-scale preparation of the dioxyl by permanganate oxidation of the hydrolysate of a nitrosotrifluoromethane-tetrafluoroethylene-phosphorus trichloride adduct, an impurity in the dioxyl, trapped out at — 96°C ( — 196°C) and <2.5 mbar, caused a violent explosion to occur when the trap content was allowed to warm up. A procedure to eliminate the hazard is detailed. 

Interaction is violent and may be explosive, even with ice, oxygen being evolved [1]. Part of the water dropped into a flask of the gas was expelled by the violent reaction ensuing [2], An analytical procedure, involving absorption of chlorine trifluoride into 10% sodium hydroxide solution from the open capillary neck of a quartz ampoule to avoid explosion, was described [3], Inadvertent collection of chlorine trifluoride and ice in a cryogenic trap led to a small but violent explosion when the trap began to warm up overnight [4],... 

General procedure for the preparation of 5-alkyl-l-functionalized-5,6-dihydrophenanthridines (26 and 27) A solution of the starting amine 25a or 25b (2 mmol) in THF (15 mL) was treated with 3.5 equiv /BuLi (7 mmol) at -110 °C. The reaction mixture was stirred for 15 min at this temperature. The cooling bath was then removed allowing the reaction to warm up to room temperature. The reaction mixture was then re-cooled to -78°C, the electrophile (3 mmol) was added, and the mixture was stirred for 3 h at room temperature. The mixture was hydrolyzed with water and extracted with ethyl acetate (3 x 20 mL). The combined organic layers were dried over anhydrous Na2S04. After evaporation of the solvent, the residue was purified by flash column chromatography (hexane/ethyl acetate) to afford products 26 - 27. 

The next step involved cooling the reaction mixture to -196°C, removing the H2 at low pressure, and sealing the tube. This sealed tube was then used in the equilibrium measurements. When it warmed up, a fraction of the hydride complex reacted with benzene, yielding H2 and the phenyl complex, according to equilibrium 14.12. Therefore, the total amount of substance of H2 in equation 14.18 is given by the sum of the initial amount of substance of H2 (no) and the amount of substance of Sc(Cp )2Ph in equilibrium. The latter is easily calculated from the relative concentrations of Sc(Cp )2Ph and Sc(Cp )2H determined by H NMR, and the known initial concentration of Sc(Cp )2H (5.4 x 10-5x 1000/0.5 = 0.108 mol dm-3). To evaluate the initial amount of substance of H2, consider the experimental procedure before and after reaction 14.19 takes place. When this reaction occurs (at 25 °C) a certain amount of H2 remains in solution, and it can be calculated by an equation similar to 14.17. This amount will be equal to no, by assuming that (1) there is no further H2 solubilization when the tube is rapidly cooled to — 196 °C, and (2) only the H2 dissolved in the frozen reaction mixture is not removed by the evacuation procedure. 

Preparation of 2-bromo-3-(p-tolyl)propene (typical procedure) A three-necked, 50 mL flask equipped with an argon inleL a rubber septum and an internal thermometer was charged with bis(p-bromophenyl)ditelluride (1.7 g, 3.0 mmol, 1 equiv) and Ni(acac)2 (77 mg, 0.3 mmol, 10 mol%). The reaction mixture was cooled to -40°C and THF (6 mL) was added. It was further cooled to -78°C and Et2Zn (1.5 mL, 15 mmol, 5 equiv) was slowly added via syringe. The reaction was allowed to warm to room temperature and was stirred for 6 h. Meanwhile, a mixture of copper cyanide (2.68 g, 23 mmol) and lithium chloride (2.54 g, 60 mmol) was dried under vacuum (130°C, 2 h) and dissolved in THF (10 mL). This solution was added to the reaction mixture at -60°C, followed by 2,3-dibro-mopropene (6.0 g, 30 mmol, 10 equiv). The reaction mixture was warmed up to room temperature and worked up as usual. The crude oil obtained after evaporation of the solvents was purified by flash chromatography (hexanes), affording the product (1.45 g, 5.2 mmol, 88% yield) as a colourless oil. 

Caution. Considerable pressure builds up in the ampule during this procedure. Do not exceed the recommended heating rate. A protective shield must be placed in front of the furnace during the warm-up and reaction period. The risk of explosion during this step is considerably higher than in any other procedure described here. 

In order to determine the specific activity of the enzyme, the exact concentration of the enzyme must be known. The concentration of the solution of tyrosinase may be determined as a class project by the following procedure. Turn on the spectrophotometer and the UV lamp. Adjust the wavelength to 280 nm. Allow the instrument and lamp to warm up for 15 to 20 minutes. Transfer 1.0 or 3.0 mL of the phosphate buffer to a 1- or 3-mL quartz cuvette. Place it in the sample position of the spectrophotometer and adjust the balance to zero absorbance. Discard the buffer, and clean and dry the cuvette. Transfer 1.0 or 3.0 mL of the tyrosinase solution into the quartz cuvette. Place in the sample position and record the absorbance at 280 nm. Calculate the tyrosinase concentration as described in the Analysis of Results section. 

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